Clinicians › Knee

Cartilage repair of the knee

127 citationsUpdated Sep 2026

Overview

Knee cartilage repair addresses focal full-thickness articular cartilage loss resulting from degeneration, trauma, congenital defects, or inflammatory conditions [2]. Approximately 11% of knee arthroscopies reveal defects suitable for restoration [5]. Diagnosis requires concomitant physical examination and advanced imaging, as MRI underestimates defect size in approximately 75% of cases [15]. Indications are limited to patients with symptoms localized to focal full-thickness loss [24]. Procedures are contraindicated in multifocal loss, diffuse arthritis, or inflammatory arthropathy [24]. Unaddressed ligamentous instability, malalignment, or meniscal deficiency precludes repair unless concurrently treated [24, 84]. Advanced degenerative joint disease is the primary contraindication for autologous chondrocyte implantation (ACI) [46]. Isolated repair is generally not recommended with complete joint space loss [84].

Treatment selection depends on chronicity, severity, and lesion extent [2]. Key factors include age, lesion size, activity level, alignment, and meniscal integrity [15]. Bone marrow stimulation techniques, such as microfracture, are single-stage procedures suitable for small defects (<2 to 3 cm²), yielding good results in 60% to 80% of patients [15, 24]. Osteochondral autograft transfer (OAT) is effective for lesions 1 to 3 cm², while osteochondral allografts address larger lesions (≥4 cm²) with bone loss [15, 84]. ACI is indicated for medium to large chondral lesions without bony defects [15]. Allograft cell-based therapies offer single-stage options but lack long-term data [24].

Outcomes vary by location, with condylar lesions demonstrating superior results compared to patellofemoral lesions [15]. For smaller lesions, microfracture, OAT, and ACI show similar functional results [15]. ACI provides durable outcomes, with 71% survivorship at 10 years [3]. OAT remains durable with low reoperation rates at 10 years [49]. Combined meniscal allograft transplantation and cartilage repair yield outcomes similar to isolated procedures [48]. Current treatments often result in mechanically inferior tissue, prompting emerging regenerative strategies [21]. Techniques appear safe in pediatric populations [7].

Anatomy & Pathophysiology

Etiology and Prevalence

Articular cartilage injuries in the knee arise from age-related degenerative changes, previous trauma or injury, congenital osteochondral defects, inflammatory conditions, infection, and other causes [2]. The predominant reason for localized articular cartilage damage is earlier trauma, which may involve direct impact or distortion [28]. Osteochondral lesions of the knee are most frequently traumatic in origin [96]. Chondral or osteochondral lesions are present in as high as 61% to 66% of patients undergoing knee arthroscopy [79], while the overall prevalence of focal chondral defects in athletes is estimated at 36% [79]. Determining true incidence and prevalence is difficult because a large percentage of defects are asymptomatic [79]. Cartilage damage is often associated with injuries to other anatomic structures of the knee and seen in conjunction with malalignment [79]. Acute anterior cruciate ligament tears and meniscal derangement have been highly correlated with chondral defects [79], and chondral and osteochondral lesions have been reported in upward of 90% of patients following patellar dislocation [79]. Women exhibit a different knee chondral lesion pattern and more often have unfavorable conditions related to the cause of injury, site, and activity level [27].

Basic Science and Healing Potential

Articular cartilage and subchondral bone should be viewed as a closely related osteochondral unit [45]. Any disturbance of this unit can lead to altered biomechanics and abnormal joint contact pressures, leading to an inflammatory response [45]. Spontaneous healing or regeneration of traumatic cartilage damage in adults is rare due to insufficient proliferation and migration of chondrocytes into the defect [28]. Injury of cartilage together with the adjacent subchondral plate induces a wound clot that may generate fibrous repair tissue [28]. This fibrous repair tissue lacks the biomechanical properties of hyaline cartilage due to a different molecular and textural configuration [28] and predominantly shows early deterioration and failure, at least in larger defects [28]. Partial-thickness articular cartilage defects do not heal but are only rarely associated with significant clinical problems [193], whereas chondral lesions that involve the subchondral bone may fill with fibrocartilage [193]. Biomechanical studies have demonstrated increased stress concentration on the rim of the osteochondral defect [96]. Larger osteochondral lesions of the knee are associated with symptoms appearing approximately one decade earlier than the degenerative cartilage changes associated with idiopathic osteoarthritis [96]. Traumatic injury to the articular cartilage may progress to arthritis [180], and osteoarthritic-like degeneration of the articular cartilage was found in all specimens in an experimental study of patellar trauma [180].

Natural History and Progression

The natural history of articular cartilage defects is not completely understood [79]. Any disruption of the osteochondral unit may result in altered biomechanics and increased joint contact forces to the surrounding chondral surfaces and subchondral bone [79]. Mechanical wear and loose body formation may initiate an inflammatory response with release of cartilage-degrading enzymes, further leading to joint degeneration [79]. If left untreated, chondral defects can lead to osteoarthritis [79]. Surgical intervention may delay or prevent progression of degenerative changes in select symptomatic patients who could be at risk for developing osteoarthritis [79]. Patients treated with cartilage repair demonstrated less progression of degenerative changes on MRI at 6-year follow-up than a control group treated nonsurgically with initial identical osteochondral defects [79]. Osteochondral defects (OCD) in adults are usually symptomatic and lead to arthritis if left untreated [15]. Poor prognostic factors for OCD include larger, more severe lesions; older age; discoid meniscus; and mechanical symptoms [15]. The relationship between knee function and the cartilage defect is unclear, suggesting the prime focus in treatment should be on knee function [63].

Associated Pathology and Risk Factors

Correction of ligamentous instability and limb malalignment is paramount to success of cartilage restoration procedures and meniscal transplantation [16]. It is critical that surgeons address any concomitant knee pathology, such as malalignment or instability, to avoid compromising cartilage restoration [69]. History of ACL injury is a well-recognized cause of posttraumatic osteoarthritis, with several studies showing >40% incidence of posttraumatic osteoarthritis 5 to 15 years after injury [149]. Patients who have a concomitant meniscus tear at the time of ACL injury are at further increased risk for the development of posttraumatic osteoarthritis [149]. Accumulating evidence suggests that the cartilage damage at the time of injury rather than persistent joint instability is the incipient cause of eventual joint degeneration [149]. There is little difference in the development of posttraumatic osteoarthritis in patients who have undergone ACL reconstruction and those treated conservatively [149]. Meniscus injury or dysfunction results in altered joint loading, which is postulated to result in articular cartilage injury and early joint degeneration [149]. Total menisectomy has been calculated to increase the contact stress in the joint by 235% [149], and 48% of patients developed advanced radiographic changes (Kellgren Lawrence ≥ 2) 21 years following total menisectomy [149]. Additionally, 44% of intra-articular fractures of the knee will progress to posttraumatic osteoarthritis 7.5 years after injury [149]. Intra-articular fractures often create articular step-offs or gaps at the articular surface [149]. Preoperative measurement of cartilage defects by MRI underestimates lesion size [47].

Anatomical Structures and Biomechanics

The medial femoral condyle is larger and projects farther posteriorly and distally than the lateral condyle [104], while the lateral femoral condyle projects farther anteriorly and is wider in the medial-lateral direction than the medial femoral condyle [104]. The sulcus terminalis is a small ridge on the lateral femoral condyle just distal to the intercondylar notch that separates the patellofemoral and tibiofemoral articular surfaces [104]. The tibial articular surface slopes 7° to 10° in the sagittal plane [104]. The medial tibial plateau is larger than the lateral plateau and is concave in its frontal and sagittal planes [104], whereas the lateral tibial plateau is smaller and more circular than the medial plateau, concave in the frontal plane and convex in the sagittal plane [104]. The patella has the thickest articular surface in the body, approximately 5 mm in the midportion and 2 mm on the sides [104].

The menisci are C-shaped fibrocartilaginous disks that provide shock absorption, allow for increased congruency between joint surfaces, enhance joint stability, and aid in distribution of synovial fluid [55]. The medial meniscus is firmly attached to the joint capsule along its entire peripheral edge [55], while the lateral meniscus is attached to the anterior and posterior capsule, but there is a region posterolaterally where it is not firmly attached [55]. The medial meniscus has less mobility than the lateral meniscus and is more susceptible to tearing when trapped between the femoral condyle and tibial plateau [55]. The lateral meniscus is larger than the medial meniscus and carries a greater share of the lateral compartment pressure than the medial meniscus carries for the medial compartment [55].

The knee is a hinge joint that also incorporates both gliding and rolling, which are essential to its kinematics [105]. The "screw-home" mechanism involves the tibia externally rotating 5 degrees in the final 15 degrees of extension [105]. The greatest range of motion in the knee occurs in the sagittal plane, approximately 160° [125]. Knee rotation ranges from 45° in external rotation to 30° in internal rotation [125]. In the frontal plane, the range of motion in both abduction and adduction reaches a maximum of 10° [125]. The normal instant center of the knee joint follows a semicircular path, which is related to the tibiofemoral surface and ligaments crossing the joint [125]. Rupture of the cruciate ligaments or disruption of the tibiofemoral surface, including the menisci, causes a major change in the path of the instant center, leading to articular dysfunction [125].

The anterior cruciate ligament is composed of 90% type I collagen and 10% type III collagen [104]. The mean length of the anterior cruciate ligament is 33 mm and the mean midsubstance width is 11 mm [104]. The posterior cruciate ligament has an average length of 38 mm and a mean diameter at the midpoint of 13 mm [119]. The cross-sectional area of the posterior cruciate ligament is approximately 120% to 150% greater than that of the anterior cruciate ligament [119].

The vascular supply of the meniscus is derived from the geniculate arteries, which penetrate into 20% to 30% of the peripheral medial meniscus and 10% to 25% of the peripheral lateral meniscus [110]. The medial meniscus is torn approximately three times more often than the lateral meniscus [25]. Lateral meniscus tears occur more commonly with acute ACL tears [25]. There is an increased rate of osteoarthritis in knees after meniscal tears and meniscectomy, particularly on the lateral side [25]. Meniscal root tears completely disrupt the circumferential fibers of the meniscus and result in a loss of hoop stresses and an increase in contact forces [25]. Meniscal root tears are functionally equivalent to a total meniscectomy [25]. Lateral root tears are associated with ACL tears, while medial root tears are associated with chondral injuries [25]. The vascular supply of the meniscus is a primary determinant of healing potential, with tears in the peripheral third having the highest potential for healing [25]. Partial meniscectomy increases peak stresses in the affected compartment [25].

The articular cartilage on the medial facet of the patella is most commonly injured during reduction of the patella [128]. If patellar cartilage injury is associated with femoral anteversion, genu valgum, and pronated feet, symptoms can be exacerbated, especially in adolescents [128]. Patellar cartilage defects are associated with worse clinical outcomes than defects of the femoral condyles [208]. Clinical outcomes after patellar cartilage repair are deteriorated with time [208]. Increased shearing forces in the femoropatellar compartment after excessive debridement and malalignment of the extensor mechanism that has not been corrected may explain worse outcomes in patellar cartilage repair [208]. Outcomes are generally worse in the patellofemoral compartment than in the tibiofemoral joint [241]. Pediatric knees demonstrate relatively thick cartilage regions in multiple zones of the knee compared with adult specimens [243].

Classification

Articular cartilage injuries within the knee arise from age-related degenerative changes, previous trauma or injury, congenital osteochondral defects, inflammatory conditions, infection, and other causes [2]. Determining the source of symptoms and selecting appropriate surgical intervention after nonsurgical measures fail requires concomitant use of physical examination and radiographic or advanced imaging findings [2]. Nonsurgical measures include activity modification, weight loss, nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroid injections, and physical therapy [2].

Traumatic Etiology: The predominant reason for localised articular cartilage damage is earlier trauma, such as a direct impact or distortion [28]. Osteochondral lesions of the knee are defects of the cartilaginous surface and underlying subchondral bone, most frequently traumatic in origin [96]. Larger osteochondral lesions are associated with immediate significant clinical impairment and symptoms appearing approximately one decade earlier than degenerative cartilage changes associated with idiopathic osteoarthritis [96].

Osteochondritis Dissecans: The reason for other localised cartilage defects, such as osteochondritis dissecans (OD), is still unknown [28]. Posttraumatic changes and subchondral circulatory disorders are currently discussed as causes for osteochondritis dissecans [28].

Healing Biology: Spontaneous healing or regeneration in adults is rare, mainly due to insufficient proliferation and migration of chondrocytes into the defect [28]. Injury of cartilage together with the adjacent subchondral plate induces a wound clot that may generate fibrous repair tissue [28]. Such scar tissue lacks the biomechanical properties of hyaline cartilage due to a different molecular and textural configuration [28]. This scar tissue predominantly shows early deterioration and failure, at least in larger defects [28].

Other Considerations: Lesion size, activity level, and patient age are factors generally taken into account to determine the technique for repairing the cartilage [26]. No relationship has been established between the size of the injury and clinical progress after treatment [26]. The patient’s activity should influence the result, with improvements in function greater in active patients than in sedentary ones [26]. Other factors for consideration include age, time over which the condition has developed, and the site and depth of the injury [26]. Age could be related to the degenerative process [26].

Women have a different knee chondral lesion pattern than men [27]. Women more often have unfavorable conditions related to the cause of injury, site, and activity level [27]. Women have lower raw, not standardized, scores for cartilage surgery outcomes [27]. The presence of high-grade cartilage lesions is significantly increased in an ACL-deficient knee when reconstruction is performed more than 12 months after injury [67].

The vast majority of cartilage repair procedures were applied in degenerative, non-traumatic cartilage defects [90]. Only a small proportion of all cartilage defects are potentially available for regenerative cartilage repair procedures due to defect morphology and overall joint conditions [150]. Late-stage osteoarthritis (OA) is a contraindication for treatment with regenerative cartilage approaches [150]. Between October 2013 and June 2014, the vast majority of patients in the German Cartilage Registry were treated for degenerative lesions and lesions with early osteoarthritis [150]. In a recent published multi-centre trial of more than 400 patients treated with matrix-induced chondrocyte transplantation, almost 40% of the chondral defects were described as degenerative or chronic [150].

Clinical Presentation

Etiology and Prevalence

Cartilage defects arise from idiopathic causes, trauma, repetitive microtrauma, or a combination of these factors [79]. In direct trauma, articular cartilage injury results from rotational forces [15]. Chondral or osteochondral lesions are identified in 61% to 66% of patients undergoing knee arthroscopy [79], with 11% of all knee arthroscopies revealing defects suitable for carticular repair procedures [5]. Osteochondritis dissecans (OCD) in adults is typically symptomatic and progresses to arthritis if left untreated [15].

Symptoms and Physical Examination

Patients with nonfocal cartilage loss typically present with knee swelling, locking, catching, or sudden giving way [83]. Those with isolated cartilage defects exhibit significant deficits in quadriceps muscle strength in the injured leg compared with the uninjured leg [109]. The prime focus in treatment should be on knee function rather than the cartilage defect, as the relationship between the two is unclear [63].

A detailed history for knee pain must include the onset, quality, duration, tempo, and location of symptoms, modifying factors, ability to bear weight, and history of trauma [188]. Inspection reveals skin abnormalities, evidence of trauma, malalignment, and swelling [188]. Palpation focuses on points of tenderness to identify focal pathologies such as joint line tenderness, patellar tendon tenderness, or pes anserine bursa tenderness [188]. Palpation of peripatellar tissue detects effusion and/or synovitis [188].

Determination of overall knee alignment (varus, valgus, or neutral) is an important diagnostic adjunct, as malalignment may point to specific conditions [188]. Alignment must be assessed in both supine and standing positions, as weight-bearing may dynamically change the knee’s alignment [188]. When active and passive ranges of motion differ, the diagnostician must differentiate between pain-related, mechanical, or neuromuscular causes [188]. Hip range of motion should be examined to identify referred pain from intra-articular hip pathology [188]. Basic varus and valgus stability testing is performed at 0° and 30° of flexion [188]. Testing at 30° of flexion best isolates the MCL and LCL, as testing in full extension also engages secondary stabilizers [188].

Imaging

Plain radiographs are appropriate initial imaging studies for most knee conditions, allowing assessment of traumatic injury, arthritis, patellofemoral alignment, osteochondral injury, bone neoplasm, and surgical implants [39]. Specific views include: * Weight-bearing AP (extension): Assesses cartilage loss from the distal femur and tibial plateau [39]. * Weight-bearing PA (Rosenberg; flexion): Assesses cartilage loss from the posterior femur and tibial plateau [39]. * Patellofemoral views: Assess patellofemoral alignment (tilt/subluxation), patellar and trochlear morphology, osteochondral injury, and patellofemoral arthritis [39]. * Notch view: Assesses posterior femoral cartilage, notch width, and osteophytes [39].

Radiography may identify subchondral radiolucency for osteochondral defects, which is most common in the medial femoral condyle [39]. MRI identifies the degree of articular cartilage injury (chondrosis, full-thickness cartilage loss), associated bone marrow edema, and location (medial condyle, lateral condyle, trochlea, patella; anterior, posterior) [39]. No current MRI classification system has been shown to correlate with clinical outcomes after all types of cartilage repair surgery [33], and strong evidence determining whether morphological MRI is reliable in predicting clinical outcome after cartilage repair is lacking [59]. However, increasing preoperative degenerative change, evidenced by a higher WORMS on preoperative MRI, was associated with inferior patient-reported outcomes at a minimum of 2 years after cartilage restoration surgery [72].

Natural History and Prognosis

The clinical outcome in patients with multiple cartilage defects is inferior to that of patients with a single defect [62]. Multifocal chondral defects were noted in 59% of knees, with the most common defect location being the patella (64%) [131].

Investigations

Plain radiography: Supine AP knee radiographs do not adequately estimate joint space width required to determine the degree of osteoarthritis progression [130]. Plain frontal radiographs may fail to accurately display actual joint space due to varying cartilage wear patterns, meniscal integrity, or tibial slope variances [130]. To improve joint space evaluation, a 45° standing flexion view was introduced [130]. The fixed flexion view (FFV) offers improved reproducibility and good joint space evaluation [130]. The Lyon Schuss view (LSV) requires fluoroscopic adjustment of the irradiation angle relative to the medial tibial plateau and is more accurate for measuring actual joint space width than the FFV [130]. PA (Rosenberg; flexion) radiographs assess cartilage loss from the posterior femur and tibial plateau [39]. The notch view assesses posterior femoral cartilage, notch width, and osteophytes [39]. Goniometer readings of long limb alignment or measured on an FFV correlate well with angles measured on long limb radiographs, providing an alternative imaging source if long limb radiographs are unavailable [130].

MRI: Clinical magnetic resonance imaging (MRI) is the method of choice for non-invasive evaluation of articular cartilage defects and follow-up of cartilage repair procedures [88]. MRI is the most useful study for differentiating osteonecrosis from osteochondritis dissecans, transient osteoporosis, bone bruises, or occult fractures [133]. A serpentine lesion within a well-demarcated border is a specific MRI finding for osteonecrosis [133]. Compared with arthroscopy, MRI displays moderate sensitivity for detecting and classifying chondral knee injuries [211]. Quantitative Magnetic Resonance Imaging demonstrates greater sensitivity in diagnosing chondral lesions compared to standard methods [71]. High-resolution MRI with well-defined variables is a reliable, reproducible, and accurate tool for assessing cartilage repair tissue [159]. In arthritic patients, MRI is not indicated if the joint space is significantly narrowed on radiograph; however, it is used when osteonecrosis is suspected [127]. Radiographic evaluations are essential for diagnosing osteochondritis dissecans (OCD), though important aspects of OCD lesions may be better visualized with MRI [74].

CT: Three-dimensional CT with remodeling is used for preoperative planning for reconstruction associated with dysplasia, post-trauma planning, and complex total knee arthroplasty (TKA) planning [127]. Three-dimensional CT reconstructions assist in preoperative planning for complex intra-articular fractures, multiplanar osteotomy for limb malalignment, and reconstitution of bone loss in joint arthroplasty [39].

Other Considerations: Physical examination must be used concomitantly with radiographic or advanced imaging findings to determine the source of symptoms and appropriate surgical intervention when nonsurgical measures have failed [2]. Joint assessment must combine physical examination with radiographic (including full-length alignment views) and MRI findings [16]. The indications for arthroscopic autologous minced cartilage implantation are symptomatic cartilage defects or osteochondral defects of the knee [30]. Clinically significant improvements in IKDC scores associate with a more mature MRI appearance of autologous chondrocyte implantation grafts, indicated by higher MOCART scores [226]. One should remain alert to subclinical cartilage degeneration in asymptomatic patients showing no degenerative changes on plain radiographs or conventional MRI [223]. Persistent subchondral alterations documented at long-term MRI evaluation suggest limits of matrix-assisted chondrocyte transplantation with bone grafting to regenerate the osteochondral unit in patients with knee OCD [196]. Clinical results comparable with MRI T2 mapping and ICRS evaluations suggest that arthroscopic cell-based cartilage repair is efficacious and reproducible at a mean of 36 months of follow-up [217]. Satisfactory clinical outcomes and new cartilage formation observed by MRI are achieved with AMIC at mid-term follow-up for ICRS grade 3–4 in small-to-medium-sized patellar defects in patients under 52 years of age, with improvements maintained for up to 5 years [218]. Patients treated with all-arthroscopic matrix-assisted autologous chondrocyte transplantation show good, long-lasting clinical outcomes and close to native cartilage characteristics on MRI T2-mapping [232].

Treatment

Non-Operative Management

Nonsurgical treatment of arthroscopically verified focal cartilage lesions yields results comparable to most surgical interventions, with a mean KOOS QoL subscore of 58.1 at 19.1 years follow-up [11]. An initial trial of nonsurgical management is usually warranted, consisting of rest, activity modification, anti-inflammatory medications, physical therapy, bracing treatment, or injections [45]. Surgical intervention is indicated for patients who do not respond to conservative measures [45]. In the absence of mechanical symptoms, knee arthroscopy with débridement is not effective in managing osteoarthritis of the knee [154]. Arthroscopic débridement may provide relief from mechanical symptoms in carefully selected osteoarthritis patients, but should not be offered as a first-line treatment in lieu of nonsurgical measures [16].

Operative

Indications: Cartilage repair procedures are generally limited to the younger patient without global osteoarthritis of the knee [84]. It is generally not recommended to perform isolated cartilage repair techniques in patients with complete joint space loss [84]. Patellar dysplasia should not be seen as a contraindication for cell-based cartilage repair procedures [157].

Surgical Approach / Technique: Bone Marrow Stimulation Techniques: These are single-stage arthroscopic surgeries that fill the defect with nonhyaline fibrocartilaginous tissue [24]. Mesenchymal stem cell (MSC) concentration decreases with age, which may render marrow stimulation procedures less efficacious in older patients [24]. Good clinical results in small defects (<2 to 3 cm²) are obtained in 60% to 80% of patients treated with marrow-stimulating techniques [15]. Microfracture is considered by some orthopedic experts as the first-line, gold standard treatment of isolated cartilage defects [167], with approximately 78,000 procedures performed annually in the United States [167]. Current clinical evidence does not allow for unequivocal recommendation of enhanced microfracture to treat symptomatic focal grade III/IV knee cartilage lesions [19]. Both biphasic cartilage repair implant (BiCRI) and microfracture treatments showed significant effectiveness in improving clinical outcomes in patients with small symptomatic articular cartilage defects of the knee [44]. The BiCRI group demonstrated a superior radiological outcome than microfracture over a five-year period [44].

Osteochondral Autograft Transfer (OAT): Primary OAT is an effective and durable cartilage restoration procedure for some patients with symptomatic knee cartilage lesions at mid- to long-term follow-up [8]. OAT can be used to address medium-sized lesions (2–3 cm²) that include subchondral bone loss [15]. Lateral trochlea and medial trochlea are acceptable harvest locations for OAT [15]. OAT is best suited to lesions that are 1 to 2 cm in diameter because donor tissue volume is limited [84]. The primary indication for mosaic osteochondral transplantation is deep, small defects on the medial femoral condyle [156]. Middle-aged patients with focal, chronic non-traumatic osteochondral lesions of the knee also profit from OAT at a short follow-up [215]. Complications of OAT include donor site morbidity [15].

Osteochondral Allograft Transplantation: Osteochondral allograft transplant utilizes cadaveric donor plugs [15]. Osteochondral allografts can be used for larger lesions (≥4 cm²), especially with bone loss [15]. Allograft cell-based therapy allows for single-stage surgery and is technically easy [24]. Main concerns with osteochondral allografts include the small risk of disease transmission and chondrocyte viability [15]. Chondrocyte viability in osteochondral allografts has improved with graft preservation techniques [15]. Allograft cell-based therapy lacks long-term outcome data [24].

Autologous Chondrocyte Implantation (ACI) and Matrix-Assisted Techniques: ACI is an effective treatment for full thickness chondral defects of the knee, providing an improvement of clinical outcomes [134]. ACI allows for creation of type II collagen–rich hyaline-like cartilage, with minimal type I collagen or fibrocartilage present [15]. ACI provided durable outcomes with a survivorship of 71% at 10 years and improved function in 75% of patients with symptomatic cartilage defects of the knee [3]. Long-term results suggest that first- and third-generation ACI methods are equally effective treatments for isolated full-thickness cartilage defects of the knee [220]. Matrix-induced autologous chondrocyte transplantation (MACT) represents a suitable option in the treatment of local cartilage defects in the knee, with significantly improved results on 3 outcome measures after 10 years [41]. MACT is an excellent surgical therapy for full-thickness cartilage defects of the knee, with good long-term results for simple defects [228]. Matrix-induced chondrogenesis is a valid and safe cartilage repair option for small- to medium-sized defects of the knee [61]. The treatment of symptomatic cartilage knee defects ≥3 cm² in size using matrix-induced autologous chondrocyte implantation (MACI) was clinically and statistically significantly better than with microfracture [136]. MACI and microfracture had similar structural repair tissue and safety profiles for defects ≥3 cm² [136]. Collagen-membrane-covered matrix-associated chondrocyte implantation (cMACI) showed superior safety compared with periosteum-covered MACI (pMACI) for large cartilage defects [75]. cMACI and pMACI showed similarly improved outcomes in approximately 75% of patients [75]. Arthroscopic gel-type autologous chondrocyte implantation presents histologic evidence of regenerating hyaline-like cartilage in the knee [29]. Arthroscopic gel-type autologous chondrocyte implantation is an acceptable, minimally invasive, and technically simple option for the restoration of cartilage defects of the knee [29].

Other Cell-Based and Scaffold Techniques: Repair of full-thickness cartilage injury in the knee with a hyaluronic acid-based scaffold embedded with mesenchymal stem cells sourced from bone marrow aspirate concentrate (HA-BMAC) provides good to excellent clinical outcomes at long-term follow-up in the treatment of small to large lesions [13]. Cartilage repair using HA-BMAC leads to successful medium-term outcomes independent of age or lesion size [140]. Implantation of tissue-engineered cartilage-like tissue can be proposed as one option for repairing full-thickness cartilage defect of the knee [10]. A cell-free biomimetic scaffold is a safe and effective treatment for cartilage knee lesions, offering positive clinical results at 2 years with a low failure rate [141]. While approaches using stem cells for cartilage defects are highly promising, there is currently limited evidence of a direct clinical benefit, and further research is required to assess the overall outcome of stem cell therapies for knee cartilage repair [137].

Adjuncts: Concurrent osteotomy significantly increased graft survivorship for ACI (88% with osteotomy versus 66% without) [53].

Other Considerations: Some studies suggest that prior marrow stimulation procedures such as microfracture may have a detrimental effect on outcomes following ACI [53]. In a review of over 300 consecutive patients, 26% of grafts in the prior marrow stimulation group failed compared with 8% in the patients who did not have a prior marrow stimulation procedure [53]. There were significantly more failures associated with ACI after microfracture (7 of 28) than with ACI as a first-line treatment (1 of 28) [53]. Inferior clinical outcome was also associated with ACI after microfracture [53]. Increased patient age and lesion size greater than 4.5 cm² were determined to be risk factors for revision surgery and failure following ACI [53]. Donor-site problems and creation of true articular cartilage at the recipient site are still challenges for cartilage repair procedures [15].

Outcomes and Prognosis: Cartilage repair surgery prevents progression of knee degeneration over 6 years compared to non-operated control subjects with initially identical defects [9]. Treatment of osteochondral defects at any time had a positive effect on healing compared to no treatment [135]. Treatment of articular cartilage defects of the knee with ACI in physically active young individuals can return nearly two-thirds of individuals to daily activity with decreased pain and improved function [17]. Treatment of articular cartilage defects of the knee joint leads to satisfactory results concerning everyday activities [14]. Patients in whom cartilage repair treatment is only partially successful can go on to obtain clinical benefit from other cartilage repair options [43]. Existing articular cartilage repair techniques can return the athlete with articular cartilage injury to high-impact sports, but treatment does not produce normal articular cartilage [139]. This limitation in producing normal articular cartilage limits the success rate and durability of current cartilage repair in athletes [139]. Available cartilage regeneration techniques only produce fibrocartilage or fibrohyaline cartilage with poor integrative capacities and higher friability [221]. Recent advancements in cartilage restoration and arthroplasty techniques, along with appropriate patient selection and meticulous surgical technique, have resulted in promising outcomes in patients with patellofemoral cartilage lesions who undergo surgical treatment [93]. Cartilage repair has become a focus of increased interest due to its potential to provide pain relief and alter the progression of degenerative disease, with the hope of delaying or obviating the need for joint replacement in young patients with early osteoarthritis [70]. The near future of cartilage repair will likely involve refinement of current techniques along with incorporation of scientific advances in cartilage biology, potentially leading to a single-stage surgical technique that replicates normal articular cartilage [89]. No definitive conclusion could be made in respect to the best current surgical technique for articular cartilage and osteochondral lesions in football players [158]. Scientific analysis of articular cartilage repair methods is difficult due to the lack of controlled, randomized studies and the absence of data on long-term durability [54]. The methodologic quality of knee articular cartilage surgery studies was poor overall and also for individual techniques [97].

Complications

General and Arthroscopic

Infection: Infection is the most common complication overall in knee arthroscopy [98]. The incidence of infection associated with anterior cruciate ligament reconstructions is slightly increased when the reconstruction is performed in conjunction with meniscal repair [98].

Nerve palsy: Saphenous and peroneal nerve injuries are reported with arthroscopic repairs, though the frequency has decreased dramatically with all-inside techniques [98].

Stiffness / Arthrofibrosis: The incidence of arthrofibrosis associated with anterior cruciate ligament reconstruction is increased when meniscal repair is performed [98].

Thromboembolism: DVT is a concern with long, complicated procedures, particularly in patients who are overweight, have a history of DVT, are taking birth control pills, or have been inactive as a result of injury [98].

Other Considerations: Overall complication rates for knee arthroscopy are generally cited as less than 1% in recent reports [98]. Complex regional pain syndrome is a poorly understood condition that possibly could be decreased by better patient selection and decreased operating time [98]. Chondral or meniscal injuries fall under the category of surgical limitations for which surgical control is often limited [98].

Bone Marrow Stimulation (Microfracture/Abrasion)

Other Considerations: Mesenchymal stem cell concentration decreases with age, which may render bone marrow stimulation procedures less efficacious in older patients [24]. MRI assessment shows that the repair cartilage over microfracture generally is depressed with respect to native cartilage [174]. Propensity for bony overgrowth is most marked in the microfracture group, with loss of adjacent cartilage evident with progressive followup [174].

Osteochondral Autograft Transfer (OAT/Mosaicplasty)

Donor Site Morbidity: Donor site morbidity is a complication of osteochondral autograft transfer [15]. Donor site morbidity is a listed disadvantage of whole tissue transplantation using autografts [24].

Osteochondral Allograft

Immunological and Infectious Risk: Risk of immunological rejection or disease transmission is a complication of osteochondral allograft transplantation [24]. A high short-term failure rate has been observed with decellularized osteochondral allograft plugs, leading to advice that they be used with caution [82].

Autologous Chondrocyte Implantation (ACI/MACI)

Graft Hypertrophy and Overgrowth: Complications related to ACI include chondrocyte overgrowth and periosteal flap hypertrophy [15]. Graft hypertrophy occurred in 63% of ACI surgeries in MRI assessments [174].

Surgical Morbidity: The morbidity of the second surgical procedure is a complication associated with ACI [15].

Risk Factors for Failure: Increased patient age and lesion size greater than 4.5 cm² are risk factors for revision surgery and failure following ACI [53]. Prior marrow stimulation procedures such as microfracture may have a detrimental effect on outcomes following ACI, with 26% of grafts failing in the prior marrow stimulation group compared with 8% in patients who did not have a prior marrow stimulation procedure [53]. Female patients and individuals with previous surgeries have an increased risk of reoperation and failure to attain clinically relevant improvement following ACI [194]. Women have more often unfavorable conditions related to the cause of injury, site, and activity level, and they have lower raw, not standardized, scores in cartilage surgery [27].

Revision and Failure

Secondary Failure: One of every 4 patients may experience a secondary failure after undergoing a revision cartilage procedure [99].

Histologic Findings: The histologic appearance of the repair tissue of 3 different failed articular cartilage resurfacing procedures was similar and did not resemble normal articular cartilage [51].

Pediatric Population

Other Considerations: No differences in complication rates are reported when comparing articular cartilage repair techniques in children and adolescents to adult patients [7].

Recovery

Light activity (weeks): The provided evidence does not specify a typical week range for the resumption of desk work, driving, or light activities of daily living.

Full activity (months): The provided evidence does not specify a month range for the return to manual work, sport, or full range of motion and strength.

Complete recovery / outcome plateau (months): The provided evidence does not specify a month range for the stabilization of pain, strength, or final functional outcomes.

Rehabilitation protocol: The provided evidence does not detail specific physical therapy phasing, immobilisation duration, weight-bearing or range-of-motion progression schedules, or sling and brace removal timing.

Functional milestones: Validated patient-reported outcome trajectories are reported at long-term follow-up intervals rather than as short-term recovery benchmarks. Nonsurgical treatment of focal cartilage lesions yielded a mean KOOS QoL subscore of 58.1 at 19.1 years follow-up [11]. MACT treatment resulted in significantly improved results on three outcome measures after 10 years [41]. ACI provided durable outcomes with a survivorship of 71% at 10 years [3] and resulted in improved function in 75% of patients with symptomatic cartilage defects at a minimum of 10 years after surgery [3]. A 2014 study confirmed that survivorship was 71% at 10 years for ACI [53] and that 75% of patients reported improved function at 10 years after ACI [53]. The 20-year survival rate was 63% in a study of first-generation ACI [53].

Other Considerations: Long-term survivorship and failure rates vary by lesion type and concomitant procedures. In a 2014 study of ACI, at least one graft failed in 53 of 210 patients (25%) [53]. Concurrent osteotomy significantly increased graft survivorship to 88% with osteotomy versus 66% without [53]. In a study of ACI for chronic chondral and osteochondral defects, 27 patients (26%) experienced graft failure at a mean of 5.7 years [53]. Of the 73 patients with surviving grafts in that study, 88% reported good to excellent results [53]. In a systematic review of 771 patients treated with ACI, successful outcomes were reached in 82% of patients, while the revision surgery rate was 37% [53]. Increased patient age and lesion size greater than 4.5 cm2 were determined to be risk factors for revision surgery and failure in ACI [53].

Failure rates for autologous chondrocyte transplantation (ACT) differ by indication. The failure rate was 11% among patients with isolated femoral condylar lesions [20], 14% among patients with osteochondritis dissecans lesions [20], 18% among patients who had the procedure combined with ACL repair [20], and 24% among patients treated for patellar lesions [20]. Good-to-excellent results were seen in 85% of patients with femoral condyle defects treated with ACT [20]. Histological analysis of second-look arthroscopy specimens after ACT showed that all specimens stained positive for cartilage oligomeric matrix protein and aggrecan [20]. Hyaline-like cartilage in ACT specimens stained positive for type II collagen in the predominant part of the tissue (50%) [20], while fibrous areas stained positive for type I collagen [20].

Prior marrow stimulation negatively impacts ACI outcomes. In a 2009 study, 26% of grafts in the prior marrow stimulation group failed compared with 8% in patients who did not have a prior marrow stimulation procedure [53]. A 2012 study found significantly more failures associated with ACI after microfracture (7 of 28) than with ACI as a first-line treatment (1 of 28) [53], and inferior clinical outcome was associated with ACI after microfracture [53]. However, in patients with discrete articular cartilage lesions and a history of failed microfracture, ACI may render favorable clinical outcomes comparable to primary ACI [18]. The clinical outcome in patients with multiple cartilage defects is inferior to that of patients with a single defect after microfracture [62].

Matrix-assisted cartilage repair (MACR) and other techniques show specific long-term profiles. Treatment failure rates for matrix-assisted cartilage repair increase from short-term to midterm follow-up [23], and 11% of patients undergoing matrix-assisted cartilage repair had undergone further surgery at a minimum of 5 years' follow-up [23]. The combination of microfracture and a cell-free polymer-based implant immersed with autologous serum is safe for the treatment of cartilage defects in the knee [4], with patients showing gradual clinical improvement postoperatively [4]. Repair of full-thickness cartilage injury in the knee with a HA-BMAC provides good to excellent clinical outcomes at long-term follow-up [13] and is effective in the treatment of small to large lesions [13]. ACI is effective in filling full-thickness chondral defects of the knee, with improvements noted in 86% of patients at 6-year follow-up [86]. Mosaicplasty results in a better, clinically relevant outcome than microfracture in articular cartilage defects (2-5 cm2) of the distal femur of the knee in patients aged 18 to 50 years at short, medium, and long term (minimum 15 years) [92]. A 6-mm osteochondral plug placed in a 10-mm defect better preserved the articular surface and contour of the condyle compared to untreated or bone-grafted defects at 6 months and 1 year [85]. Treatment of osteochondral defects in the ankle and knee joint with a biomimetic scaffold resulted in incomplete cartilage repair and poor subchondral bone repair at 1- and 2.5-year follow-up [173]. The value of AMIC relative to other cartilage repair procedures and to the natural course remains undefined [235].

Patient satisfaction and demographic factors influence perceived outcomes. In a 2010 study, 92% of patients were satisfied and would have the ACI procedure again [53]. In a large multicenter study of ACI for patellar defects, 92% of patients stated they would undergo the procedure again [53], and 86% rated their knees as good or excellent at final follow-up [53]. In a study of 30 patients with isolated chondral lesions of the patella treated with ACI, knee function was rated as good to excellent in 25 (83%) at final follow-up [53], fair in 4 (13%) [53], and poor in 1 (3%) [53]. There were three failures that occurred at 6.25 years postoperatively in a study of ACI for patellar lesions [53]; all three failures were in workers compensation patients who were older (average age 42 years) at the time of surgery [53]. Women have lower raw, not standardized, scores after knee chondral surgery [27], although a case-control analysis with normalized data showed that on equal terms women have the same success possibilities as men after surgical treatment for knee cartilage regeneration [100].

Nonsurgical management and long-term joint preservation are relevant considerations. Nonsurgical treatment of arthroscopically verified focal cartilage lesions of the knee had results equal to those of most surgical treatments [11]. The 20-year cumulative risk of knee arthroplasty after a focal cartilage lesion in the knee was 19% [78]. In a 20-year follow-up study of first-generation ACI, 79% of patients maintained their native knee and were satisfied at final evaluation [53]. Cell-based regenerative cartilage therapy of the knee has become the standard of care for large and isolated chondral defects [42]. ACI and MACI procedures for the treatment of knee cartilage lesions associated to OA showed long-term success and allowed delaying arthroplasty [102]. Most studies have failed to show improved clinical outcomes in the short term when adding cartilage restoration procedures to high tibial osteotomy [77]. Injury origin, sex, symptom duration, lesion size, lesion site, age, and previous surgery might determine the final outcome and can be used as a sort of clinical profiling to guide the surgeon in the choice of this procedure and in giving realistic expectations to patients requiring cartilage treatment [103].

Key Evidence

• [L4] ACI provided durable outcomes with a survivorship of 71% at 10 years and improved function in 75% of patients with symptomatic cartilage defects of the knee at a minimum of 10 years after surgery. [3] (10.1007/s11999-013-3146-9)
• [L4] The procedure is safe for the treatment of cartilage defects in the knee, with patients showing gradual clinical improvement postoperatively. [4] (10.1007/s00167-011-1763-y)
• [L4] Eleven percent of all knee arthroscopies show cartilage defects that may be suitable for cartilage repair procedures. [5] (10.1177/0363546503259345)
• [L2] Patients who have moderate to large symptomatic chondral knee lesions, significant functional impairment and pain, and failed prior cartilage repair procedures can expect durable and significant functional improvement and symptom reductions following ACI. [6] (10.1016/j.arthro.2008.04.021)
• [L5] Articular cartilage repair techniques appear to be safe in children and adolescents, with no differences in complication rates reported when compared with adult patients. [7] (10.1177/2325967118760190)
• [L4] Primary OAT is an effective and durable cartilage restoration procedure for some patients with symptomatic knee cartilage lesions at mid- to long-term follow-up, with a majority of patients demonstrating sustained improvements in clinical outcomes and achieving the MCID. [8] (10.1177/23259671251399796)
• [L3] Cartilage repair surgery prevents progression of knee degeneration over 6 years compared to non-operated control subjects with initially identical defects. [9] (10.1007/s00167-018-5321-8)
• [L4] This procedure can be proposed as one option for repairing full-thickness cartilage defect of the knee. [10] (10.1007/s00167-013-2521-0)
• [L4] Nonsurgical treatment of arthroscopically verified focal cartilage lesions of the knee had results equal to those of most surgical treatments, with a mean KOOS QoL subscore of 58.1 at 19.1 years follow-up. [11] (10.2106/jbjs.24.00777)
• [L1] Cartilage repair in adolescent knees using ACI provides success across different clinical outcomes measures. [12] (10.1016/j.arthro.2016.03.007)
• [L4] Repair of full-thickness cartilage injury in the knee with a HA-BMAC provides good to excellent clinical outcomes at long-term follow-up in the treatment of small to large lesions. [13] (10.1177/0363546519845362)
• [L4] Treatment of articular cartilage defects of the knee joint leads to satisfactory results concerning everyday activities. [14] (10.1177/0363546515614578)
• [L4] Treatment of articular cartilage defects of the knee with ACI in physically active young individuals can return nearly two-thirds of individuals to daily activity with decreased pain and improved function. [17] (10.1177/2325967117706057)
• [L3] In patients with discrete articular cartilage lesions of the knee and history of failed microfracture, ACI may render favorable clinical outcomes comparable to primary ACI. [18] (10.1177/2325967116s00125)
• [L1] Current clinical evidence does not allow for unequivocal recommendation of enhanced microfracture to treat symptomatic focal grade III/IV knee cartilage lesions. [19] (10.1007/s00167-019-05832-5)
• [L4] [20] (10.1177/03635465020300011601)
• [L4] Current clinical treatments for articular cartilage defects have limited ability to repair tissue and often result in mechanically inferior cartilage; emerging regenerative approaches and strategies informing future treatment options are discussed to address these limitations. [21] (10.3389/fbioe.2021.770655)
• [L4] Treatment failure rates for matrix-assisted cartilage repair increase from short-term to midterm follow-up, with 11% of patients having undergone further surgery at a minimum of 5 years' follow-up. [23] (10.1016/j.arthro.2015.07.025)
• [L4] [26] (10.1016/j.injury.2011.06.033)
• [L3] Women have a different knee chondral lesion pattern and more often have unfavorable conditions related to the cause of injury, site, and activity level, and they also have lower raw, not standardized, scores. [27] (10.1177/0363546513480780)
• [Paper] [28] (10.1016/j.injury.2008.01.039)
• [L4] Therefore, it is an acceptable, minimally invasive, and technically simple option for the restoration of cartilage defects of the knee. [29] (10.1007/s00167-019-05572-6)
• [L4] [30] (10.1177/23259671241297970)
• [L1] No current MRI classification system has been shown to correlate with clinical outcomes after all types of cartilage repair surgery. [33] (10.1177/0363546513485931)
• [L4] Tissue-engineered cartilage implantation is questionable for this indication as a salvage procedure for young patients affected by knee osteoarthritis. [34] (10.1177/0363546512463675)
• [L1] When selecting a procedure, patient and cartilage defect characteristics should be assessed to determine the best technique for each individual patient. [36] (10.1002/ksa.12525)
• [L4] The significantly improved results on 3 outcome measures after 10 years suggest that MACT represents a suitable option in the treatment of local cartilage defects in the knee. [41] (10.1177/0363546514548160)
• [L4] Overall, cell-based regenerative cartilage therapy of the knee has shown tremendous development over the last years and has become the standard of care for large and isolated chondral defects. [42] (10.1007/s00167-021-06497-9)
• [L3] Patients in whom treatment is only partially successful can go on to obtain clinical benefit from other cartilage repair options. [43] (10.1007/s00167-014-3295-8)
• [L1] Both BiCRI and microfracture treatments showed significant effectiveness in improving clinical outcomes in patients with small symptomatic articular cartilage defects of the knee, with the BiCRI group demonstrating a superior radiological outcome than microfracture, over a five-year period. [44] (10.1186/s13018-024-05392-6)
• [Paper] Based on current evidence, an indication for ACI is given for symptomatic cartilage defects starting from defect sizes of more than 3-4 cm², or 2.5 cm² in young and active sports patients, while advanced degenerative joint disease is the single most important contraindication. [46] (10.1055/s-0032-1328207)
• [L4] Clinical outcomes after combined MAT and cartilage repair/restoration are similar to those after either procedure in isolation. [48] (10.1016/j.arthro.2010.08.007)
• [L3] OATS remains a durable knee preserving cartilage repair operation with low incidence of reoperation 10 years following index procedure. [49] (10.1177/2325967124s00003)
• [L4] The histologic appearance of the repair tissue of 3 different failed articular cartilage resurfacing procedures was similar and did not resemble normal articular cartilage. [51] (10.1177/0363546507308359)
• [L5] Scientific analysis of articular cartilage repair methods is difficult due to the lack of controlled, randomized studies and the absence of data on long-term durability; future research requires careful basic science investigations and controlled, prospective, randomized clinical trials. [54] (10.1177/03635465980260022701)
• [L1] Strong evidence to determine whether morphological MRI is reliable in predicting clinical outcome after cartilage repair is lacking. [59] (10.1177/0363546512473258)
• [L1] Results of RCTs comparing matrix-induced chondrogenesis with other treatment options showed that matrix-induced chondrogenesis is a valid and safe cartilage repair option for small- to medium-sized defects of the knee. [61] (10.1007/s00167-021-06513-y)
• [L3] The clinical outcome in patients with multiple cartilage defects is inferior to that of patients with a single defect. [62] (10.1007/s00167-009-0974-y)
• [L3] The prime focus in treatment should be on knee function rather than the cartilage defect as the relationship between the two is unclear. [63] (10.1007/s00167-014-3472-9)
• [L2] The presence of high-grade cartilage lesions is significantly increased in an ACL-deficient knee when reconstruction is performed more than 12 months after injury. [67] (10.1007/s00167-013-2497-9)
• [L5] It is critical that surgeons address any concomitant knee pathology, such as malalignment or instability, to compromise cartilage restoration. [69] (10.1016/j.arthro.2019.08.021)
• [L4] Cartilage repair has become a focus of increased interest due to its potential to provide pain relief and alter the progression of degenerative disease, with the hope of delaying or obviating the need for joint replacement in young patients with early osteoarthritis. [70] (10.1007/s00167-011-1780-x)
• [L1] [71] (10.1016/j.arthro.2024.01.035)
• [L4] Increasing preoperative degenerative change in the knee, as evidenced by a higher WORMS on preoperative MRI, was associated with inferior patient-reported outcomes at a minimum of 2 years after cartilage restoration surgery. [72] (10.1016/j.asmr.2024.100973)
• [L2] cMACI showed superior safety compared with pMACI for large cartilage defects, with similarly improved outcomes in approximately 75% of patients. [75] (10.1002/ksa.70352)
• [L5] Most studies have failed to show improved clinical outcomes in the short term when adding cartilage restoration procedures to high tibial osteotomy, raising questions about whether longer term studies will show improved efficacy. [77] (10.1016/j.arthro.2023.07.002)
• [L4] The 20-year cumulative risk of knee arthroplasty after a focal cartilage lesion in the knee was 19%. [78] (10.2106/jbjs.22.01174)
• [L4] Based on the high short-term failure rate observed in this study, the authors advise that a decellularized OC allograft plugs implant should be used with caution in the treatment of OC lesions of the knee, as similar outcomes have not been noted with other cartilage restoration techniques. [82] (10.1016/j.arthro.2017.07.018)
• [L5] At 6 months and 1 year, a 6-mm osteochondral plug placed in a 10-mm defect better preserved the articular surface and contour of the condyle compared to untreated or bone-grafted defects. [85] (10.1177/0363546505279914)
• [L4] ACI is effective in filling full-thickness chondral defects of the knee, with improvements noted in 86% of patients at 6-year follow-up, though longer follow-ups are needed to confirm long-term effectiveness. [86] (10.1016/j.otsr.2012.04.019)
• [Paper] Clinical magnetic resonance imaging (MRI) is the method of choice for the non-invasive evaluation of articular cartilage defects and the follow-up of cartilage repair procedures. [88] (10.1016/j.injury.2008.01.043)
• [L5] The near future of cartilage repair will likely involve refinement of current techniques along with incorporation of scientific advances in cartilage biology, potentially leading to a single-stage surgical technique that replicates normal articular cartilage. [89] (10.1016/j.csm.2013.12.003)
• [L4] The vast majority of cartilage repair procedures were applied in degenerative, non-traumatic cartilage defects. [90] (10.1007/s00402-016-2453-5)
• [L1] At short, medium, and long term (minimum 15 years), mosaicplasty results in a better, clinically relevant outcome than microfracture in articular cartilage defects (2-5 cm2) of the distal femur of the knee in patients aged 18 to 50 years. [92] (10.1177/0363546517745281)
• [L5] Recent advancements in cartilage restoration and arthroplasty techniques, along with appropriate patient selection and meticulous surgical technique, have resulted in promising outcomes in patients with patellofemoral cartilage lesions who undergo surgical treatment. [93] (10.5435/jaaos-d-16-00009)
• [L4] [96] (10.2106/jbjs.j.00813)
• [L4] The methodologic quality of knee articular cartilage surgery studies was poor overall and also for individual techniques. [97] (10.1016/j.arthro.2013.02.023)
• [L4] One of every 4 patients may experience a secondary failure after undergoing a revision cartilage procedure. [99] (10.1177/03635465241260271)
• [L3] However, a case-control analysis with normalized data showed that on equal terms women have the same success possibilities as men after surgical treatment for knee cartilage regeneration. [100] (10.1177/2325967113s00034)
• [L4] ACI and MACI procedures for the treatment of knee cartilage lesions associated to OA showed long-term success and allowed delaying arthroplasty. [102] (10.1007/s00167-022-07030-2)
• [L4] Injury origin, sex, symptom duration, lesion size, lesion site, age, and previous surgery might determine the final outcome and can be used as a sort of clinical profiling to guide the surgeon in the choice of this procedure and in giving realistic expectations to patients requiring cartilage treatment. [103] (10.1177/0363546513518552)
• [L3] Patients with isolated cartilage defects of the knee joint have significant deficits in quadriceps muscle strength of the injured leg compared with the uninjured leg. [109] (10.1177/2325967117703726)
• [L4] Multifocal chondral defects were noted in 59% of knees, and the most common defect location was the patella (64%). [131] (10.1002/ars2.70064)
• [L1] ACI is an effective treatment for full thickness chondral defects of the knee, providing an improvement of clinical outcomes. [134] (10.1007/s00167-010-1050-3)
• [L5] Treatment of osteochondral defects at any time had a positive effect on healing compared to no treatment. [135] (10.1007/s00167-008-0675-y)
• [L1] The treatment of symptomatic cartilage knee defects ≥3 cm2 in size using MACI was clinically and statistically significantly better than with MFX, with similar structural repair tissue and safety. [136] (10.1177/0363546514528093)
• [L4] While approaches using stem cells for cartilage defects are highly promising, there is currently limited evidence of a direct clinical benefit, and further research is required to assess the overall outcome of stem cell therapies for knee cartilage repair. [137] (10.1177/0363546513508744)
• [Paper] Existing articular cartilage repair techniques can return the athlete with articular cartilage injury to high-impact sports, but treatment does not produce normal articular cartilage, and this limits the success rate and durability of current cartilage repair in athletes. [139] (10.1136/bjsports-2015-094772)
• [L2] Cartilage repair using HA-BMAC leads to successful medium-term outcomes independent of age or lesion size. [140] (10.1177/0363546516656179)
• [L3] This cell-free biomimetic scaffold is a safe and effective treatment for cartilage knee lesions, offering positive clinical results at 2 years with a low failure rate. [141] (10.1002/ksa.12402)
• [L4] [150] (10.1007/s00167-016-4047-8)
• [L4] The primary indication is deep, small defects on the medial femoral condyle. [156] (10.1016/j.otsr.2011.08.005)
• [L3] Patellar dysplasia should not be seen as a contraindication for cell-based cartilage repair procedures. [157] (10.1177/03635465231220028)
• [L4] No definitive conclusion could be made in respect to the best current surgical technique for articular cartilage and osteochondral lesions. [158] (10.1016/j.arthro.2016.01.055)
• [L4] High resolution MRI and well-defined MRI variables are a reliable, reproducible and accurate tool for assessing cartilage repair tissue. [159] (10.1016/j.ejrad.2005.08.007)
• [L4] Overall, the various cartilage restoration techniques reported improvements in patient reported outcomes with low complication rates, though definitive conclusions on the optimal treatment remain elusive due to a lack of high-quality comparative studies. [164] (10.1007/s00167-018-5139-4)
• [Paper] [167] (10.1055/s-0037-1618592)
• [L3] OCA transplantation for treatment of large multisurface cartilage defects in the knee resulted in a 94.7% initial success rate when grafts with high viable chondrocyte density (≥70%) were used and when patients strictly adhered to prescribed postoperative rehabilitation protocols. [170] (10.1177/23259671221102452)
• [L4] Treatment of osteochondral defects in the ankle and knee joint with a biomimetic scaffold resulted in incomplete cartilage repair and poor subchondral bone repair at 1- and 2.5-year follow-up. [173] (10.1007/s00167-015-3538-3)
• [L3] [174] (10.1097/01.blo.0000129162.36302.4f)
• [L2] In contrast to other cartilage repair techniques, patients 40 years and older do not have an inferior outcome up to 24 months after ACI for isolated cartilage defects when compared with younger patients. [178] (10.1177/0363546510376742)
• [L5] [180] (10.1007/s001670100248)
• [L5] [193] (10.1177/0363546504273510)
• [L3] [194] (10.1007/s00167-023-07615-5)
• [L4] Persistent subchondral alterations were documented at long-term MRI evaluation, suggesting the limits of this approach to regenerate the osteochondral unit in patients affected by knee OCD. [196] (10.1007/s00167-020-06230-y)
• [L4] [208] (10.1007/s00167-011-1546-5)
• [L3] Compared with arthroscopy, MRI displays moderate sensitivity for detecting and classifying chondral knee injuries. [211] (10.1007/s00167-015-3622-8)
• [L4] Middle-aged patients with focal, chronic non-traumatic osteochondral lesions of the knee also profit from OAT at a short follow-up. [215] (10.1016/j.otsr.2016.06.004)
• [L4] Clinical results are comparable with MRI T2 mapping and ICRS evaluations, suggesting that this arthroscopic technique for cell-based cartilage repair is efficacious and reproducible at a mean of 36 months of followup. [217] (10.1016/j.arthro.2014.02.032)
• [L3] Satisfactory clinical outcomes and new cartilage formation, as observed by MRI, are achieved with AMIC at mid‐term follow‐up for ICRS grade 3–4 in small‐to‐medium‐sized patellar defects in patients under 52 years of age, with improvements maintained for up to 5 years. [218] (10.1002/ksa.12518)
• [L2] Our long-term results suggest that first- and third-generation ACI methods are equally effective treatments for isolated full-thickness cartilage defects of the knee. [220] (10.1177/0363546520928337)
• [L4] Current treatment modalities vary from conservative to surgical options, but available cartilage regeneration techniques only produce fibrocartilage or fibrohyaline cartilage with poor integrative capacities and higher friability. [221] (10.1530/eor-2024-0083)
• [L4] One should be alert to the possibility of subclinical cartilage degeneration even in asymptomatic patients who show no degenerative changes on plain radiographs or conventional MRI. [223] (10.1007/s00167-014-3469-4)
• [L4] Clinically significant improvements in IKDC scores are associated with a more mature MRI appearance of the autologous chondrocyte implantation graft on postoperative MRI, as indicated by higher MOCART scores. [226] (10.1016/j.jisako.2024.100311)
• [L4] MACT is an excellent surgical therapy for full-thickness cartilage defects of the knee, with good long-term results for simple defects. [228] (10.1177/0363546514526695)
• [L3] Patients treated with this arthroscopic MACT technique showed good and long-lasting clinical outcomes, as well as close to native cartilage characteristics on MRI T2-mapping. [232] (10.1177/2325967121s00607)
• [L4] The value of AMIC relative to other cartilage repair procedures and to the natural course remains undefined. [235] (10.1007/s00167-011-1840-2)
• [L5] Outcomes are generally worse in the patellofemoral compartment than in the tibiofemoral joint. [241] (10.5435/jaaos-d-15-00447)
• [L4] Pediatric knees demonstrate relatively thick cartilage regions in multiple zones of the knee compared with adult specimens. [243] (10.1177/2325967119s00188)

See Also

• Knee arthroscopy
• ACL reconstruction
• Partial meniscectomy
• Meniscal repair
• High tibial osteotomy

References

[2] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Knee Arthroscopy and Preservation, Knee Reconstruction > Introduction.

[3] The John Insall Award: A Minimum 10-year Outcome Study of Autologous Chondrocyte Implantation. Clinical Orthopaedics & Related Research. 2014. DOI: 10.1007/s11999-013-3146-9

[4] The combination of microfracture and a cell‐free polymer‐based implant immersed with autologous serum for cartilage defect coverage. Knee Surgery, Sports Traumatology, Arthroscopy. 2011. DOI: 10.1007/s00167-011-1763-y

[5] Articular Cartilage Lesions in 993 Consecutive Knee Arthroscopies. The American Journal of Sports Medicine. 2004. DOI: 10.1177/0363546503259345

[6] Improvement in Symptoms and Function After Autologous Chondrocyte Implantation in Patients Who Failed Prior Treatment: Results of the Study of Treatment of Articular Repair (STAR) (SS‐20). Arthroscopy. 2008. DOI: 10.1016/j.arthro.2008.04.021

[7] Articular Cartilage Repair of the Knee in Children and Adolescents. Orthopaedic Journal of Sports Medicine. 2018. DOI: 10.1177/2325967118760190

[8] Midterm Outcomes of Primary Osteochondral Autograft Transfer for Symptomatic Chondral Defects of the Knee. Orthopaedic Journal of Sports Medicine. 2026. DOI: 10.1177/23259671251399796

[9] Cartilage repair surgery prevents progression of knee degeneration. Knee Surgery, Sports Traumatology, Arthroscopy. 2018. DOI: 10.1007/s00167-018-5321-8

[10] Implantation of tissue‐engineered cartilage‐like tissue for the treatment for full‐thickness cartilage defects of the knee. Knee Surgery, Sports Traumatology, Arthroscopy. 2013. DOI: 10.1007/s00167-013-2521-0

[11] What Is the Best Way to Treat Focal Articular Cartilage Lesions of the Knee? Perhaps No Treatment at All. Journal of Bone and Joint Surgery. 2024. DOI: 10.2106/jbjs.24.00777

[12] Clinical Outcomes After Autologous Chondrocyte Implantation in Adolescents' Knees: A Systematic Review. Arthroscopy. 2016. DOI: 10.1016/j.arthro.2016.03.007

[13] Long-term Clinical Outcomes of One-Stage Cartilage Repair in the Knee With Hyaluronic Acid–Based Scaffold Embedded With Mesenchymal Stem Cells Sourced From Bone Marrow Aspirate Concentrate. The American Journal of Sports Medicine. 2019. DOI: 10.1177/0363546519845362

[14] Return to Sports Activity and Work After Autologous Chondrocyte Implantation of the Knee. The American Journal of Sports Medicine. 2015. DOI: 10.1177/0363546515614578

[15] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > OSTEOCHONDRAL LESIONS > 1. Osteochondritis dissecans (OCD).

[16] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Knee Arthroscopy and Preservation, Knee Reconstruction > Summary.

[17] Return to Preoperative Function After Autologous Cartilage Implantation of the Knee in Active Military Servicemembers. Orthopaedic Journal of Sports Medicine. 2017. DOI: 10.1177/2325967117706057

[18] Outcomes of Autologous Chondrocyte Implantation in the Knee following Failed Microfracture. Orthopaedic Journal of Sports Medicine. 2016. DOI: 10.1177/2325967116s00125

[19] Enhanced microfracture using acellular scaffolds improves results after treatment of symptomatic focal grade III/IV knee cartilage lesions but current clinical evidence does not allow unequivocal recommendation. Knee Surgery, Sports Traumatology, Arthroscopy. 2020. DOI: 10.1007/s00167-019-05832-5

[20] Autologous Chondrocyte Transplantation. The American Journal of Sports Medicine. 2002. DOI: 10.1177/03635465020300011601

[21] Strategies for Articular Cartilage Repair and Regeneration. Frontiers in Bioengineering and Biotechnology. 2021. DOI: 10.3389/fbioe.2021.770655

[23] Failures and Reoperations After Matrix‐Assisted Cartilage Repair of the Knee: A Systematic Review. Arthroscopy. 2015. DOI: 10.1016/j.arthro.2015.07.025

[24] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Knee Arthroscopy and Preservation, Knee Reconstruction > Knee Preservation > Cartilage Restoration Procedures.

[25] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > MENISCAL INJURIES.

[26] Knee chondral injuries: Clinical treatment strategies and experimental models. Injury. 2012. DOI: 10.1016/j.injury.2011.06.033

[27] Does Patient Sex Influence Cartilage Surgery Outcome?. The American Journal of Sports Medicine. 2013. DOI: 10.1177/0363546513480780

[28] Articular cartilage defects in the knee—Basics, therapies and results. Injury. 2008. DOI: 10.1016/j.injury.2008.01.039

[29] Arthroscopic gel-type autologous chondrocyte implantation presents histologic evidence of regenerating hyaline-like cartilage in the knee with articular cartilage defect. Knee Surgery, Sports Traumatology, Arthroscopy. 2019. DOI: 10.1007/s00167-019-05572-6

[30] Arthroscopic Autologous Minced Cartilage Implantation of Cartilage Defects in the Knee: A 2-Year Follow-up of 62 Patients. Orthopaedic Journal of Sports Medicine. 2024. DOI: 10.1177/23259671241297970

[33] Correlation Between Magnetic Resonance Imaging and Clinical Outcomes After Cartilage Repair Surgery in the Knee. The American Journal of Sports Medicine. 2013. DOI: 10.1177/0363546513485931

[34] Matrix-Assisted Autologous Chondrocyte Transplantation for Cartilage Regeneration in Osteoarthritic Knees. The American Journal of Sports Medicine. 2012. DOI: 10.1177/0363546512463675

[36] Autologous chondrocyte implantation, matrix‐induced autologous chondrocyte implantation, osteochondral autograft transplantation and osteochondral allograft improve knee function and pain with considerations for patient and cartilage defects characteristics: A systematic review and meta‐analysis. Knee Surgery, Sports Traumatology, Arthroscopy. 2024. DOI: 10.1002/ksa.12525

[39] Aaos Comprehensive Orthopaedic Review 3. Radiographic Evaluation and Surgical Anatomy of the Knee > I. Radiographic Evaluation.

[41] Clinical and Radiological Long-term Outcomes After Matrix-Induced Autologous Chondrocyte Transplantation. The American Journal of Sports Medicine. 2014. DOI: 10.1177/0363546514548160

[42] Cell‐based treatment options facilitate regeneration of cartilage, ligaments and meniscus in demanding conditions of the knee by a whole joint approach. Knee Surgery, Sports Traumatology, Arthroscopy. 2021. DOI: 10.1007/s00167-021-06497-9

[43] Matrix-induced autologous chondrocyte implantation (MACI) in the knee: clinical outcomes and challenges. Knee Surgery, Sports Traumatology, Arthroscopy. 2014. DOI: 10.1007/s00167-014-3295-8

[44] A prospective randomized controlled trial comparing biphasic cartilage repair implant with microfracture in small chondral lesions of knee: findings at five-year-follow-up. Journal of Orthopaedic Surgery and Research. 2025. DOI: 10.1186/s13018-024-05392-6

[45] Orthopaedic Knowledge Update Sports Medicine 6. Articular Cartilage of the Knee > Introduction.

[46] Stellenwert der autologen Chondrozytentransplantation (ACT) in der Behandlung von Knorpelschäden des Kniegelenks - Empfehlungen der AG Klinische Geweberegeneration der DGOU. Zeitschrift für Orthopädie und Unfallchirurgie. 2013. DOI: 10.1055/s-0032-1328207

[47] Orthopaedic Knowledge Update Sports Medicine 6. Articular Cartilage of the Knee > Annotated References.

[48] Biological Knee Reconstruction: A Systematic Review of Combined Meniscal Allograft Transplantation and Cartilage Repair or Restoration. Arthroscopy. 2010. DOI: 10.1016/j.arthro.2010.08.007

[49] Mosaicplasty/Osteochondral Autograft Transfer Remains a Durable Solution for Symptomatic Chondral Defects of the Knee: Two to Ten-Year Follow-up Analysis. Orthopaedic Journal of Sports Medicine. 2024. DOI: 10.1177/2325967124s00003

[51] Histologic and Immunohistochemical Characteristics of Failed Articular Cartilage Resurfacing Procedures for Osteochondritis of the Knee. The American Journal of Sports Medicine. 2007. DOI: 10.1177/0363546507308359

[53] Orthopaedic Knowledge Update Sports Medicine 6. Articular Cartilage of the Knee > Outcomes > Autologous Chondrocyte Implantation.

[54] Articular Cartilage Repair. The American Journal of Sports Medicine. 1998. DOI: 10.1177/03635465980260022701

[55] A Lange Medical Book Current Diagnosis Treatment In Orthopedics Fifth Edition. 3Sports Medicine > Image KNEE INJURIES.

[59] Is Magnetic Resonance Imaging Reliable in Predicting Clinical Outcome After Articular Cartilage Repair of the Knee?. The American Journal of Sports Medicine. 2013. DOI: 10.1177/0363546512473258

[61] Matrix‐induced chondrogenesis is a valid and safe cartilage repair option for small‐ to medium‐sized cartilage defects of the knee: a systematic review. Knee Surgery, Sports Traumatology, Arthroscopy. 2021. DOI: 10.1007/s00167-021-06513-y

[62] Microfracture treatment of single or multiple articular cartilage defects of the knee: a 5‐year median follow‐up of 110 patients. Knee Surgery, Sports Traumatology, Arthroscopy. 2009. DOI: 10.1007/s00167-009-0974-y

[63] Symptoms and function in patients with articular cartilage lesions in 1,000 knee arthroscopies. Knee Surgery, Sports Traumatology, Arthroscopy. 2014. DOI: 10.1007/s00167-014-3472-9

[67] Meniscal and articular cartilage lesions in the anterior cruciate ligament‐deficient knee: correlation between time from injury and knee scores. Knee Surgery, Sports Traumatology, Arthroscopy. 2013. DOI: 10.1007/s00167-013-2497-9

[69] How to Manage Cartilage Injuries?. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2019. DOI: 10.1016/j.arthro.2019.08.021

[70] Surgical treatment for early osteoarthritis. Part I: cartilage repair procedures. Knee Surgery, Sports Traumatology, Arthroscopy. 2011. DOI: 10.1007/s00167-011-1780-x

[71] Quantitative Magnetic Resonance Imaging Had Greater Sensitivity in Diagnosing Chondral Lesions of the Knee: A Systematic Review and Meta‐analysis. Arthroscopy. 2024. DOI: 10.1016/j.arthro.2024.01.035

[72] The Condition of the Meniscus and Cartilage of the Injured Knee on Preoperative Magnetic Resonance Imaging Is a Prognostic Factor Affecting Postoperative Outcomes Following Knee Cartilage Restoration Surgery. Arthroscopy, Sports Medicine, and Rehabilitation. 2024. DOI: 10.1016/j.asmr.2024.100973

[74] Orthopaedic Knowledge Update. Osteochondritis Dissecans of the Knee and Elbow* > Summary.

[75] Collagen‐membrane‐covered matrix‐associated chondrocyte implantation improves safety over periosteum‐covered MACI for large knee cartilage defects: A real‐world data analysis in the registry study. Knee Surgery, Sports Traumatology, Arthroscopy. 2026. DOI: 10.1002/ksa.70352

[77] Editorial Commentary: Knee Cartilage Restoration Does Not Greatly Improve Clinical Outcomes After High Tibial Osteotomy—In the Short Term. Arthroscopy. 2023. DOI: 10.1016/j.arthro.2023.07.002

[78] The Long-Term Risk of Knee Arthroplasty in Patients with Arthroscopically Verified Focal Cartilage Lesions. Journal of Bone and Joint Surgery. 2023. DOI: 10.2106/jbjs.22.01174

[79] Orthopaedic Knowledge Update Sports Medicine 6. Articular Cartilage of the Knee > Epidemiology/Natural History.

[82] High Short‐Term Failure Rate Associated With Decellularized Osteochondral Allograft for Treatment of Knee Cartilage Lesions. Arthroscopy. 2017. DOI: 10.1016/j.arthro.2017.07.018

[83] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Knee Arthroscopy and Preservation, Knee Reconstruction > Knee Arthroscopy.

[84] Aaos Comprehensive Orthopaedic Review 3. Nonarthroplasty Surgical Treatment of the Knee > III. Cartilage Reparative/Restorative Procedures.

[85] The Use of a Single Osteochondral Autograft Plug in the Treatment of a Large Osteochondral Lesion in the Femoral Condyle. The American Journal of Sports Medicine. 2006. DOI: 10.1177/0363546505279914

[86] Autologous chondrocyte implantation for traumatic full-thickness cartilage defects of the knee in 14 patients: 6-year functional outcomes. Orthopaedics & Traumatology: Surgery & Research. 2012. DOI: 10.1016/j.otsr.2012.04.019

[88] Magnetic resonance imaging for diagnosis and assessment of cartilage defect repairs. Injury. 2008. DOI: 10.1016/j.injury.2008.01.043

[89] Future Treatment Strategies for Cartilage Repair. Clinics in Sports Medicine. 2014. DOI: 10.1016/j.csm.2013.12.003

[90] Cartilage repair surgery for full-thickness defects of the knee in Germany: indications and epidemiological data from the German Cartilage Registry (KnorpelRegister DGOU). Archives of Orthopaedic and Trauma Surgery. 2016. DOI: 10.1007/s00402-016-2453-5

[92] Randomized Study of Long-term (15-17 Years) Outcome After Microfracture Versus Mosaicplasty in Knee Articular Cartilage Defects. The American Journal of Sports Medicine. 2017. DOI: 10.1177/0363546517745281

[93] Management of Patellofemoral Arthritis: From Cartilage Restoration to Arthroplasty. Journal of the American Academy of Orthopaedic Surgeons. 2016. DOI: 10.5435/jaaos-d-16-00009

[96] Osteochondral Lesions of the Knee: A New One-Step Repair Technique with Bone-Marrow-Derived Cells. Journal of Bone and Joint Surgery. 2010. DOI: 10.2106/jbjs.j.00813

[97] Methodologic Quality of Knee Articular Cartilage Studies. Arthroscopy. 2013. DOI: 10.1016/j.arthro.2013.02.023

[98] Campbell S Operative Orthopaedics 4 Volume Set. ANTERIOR CRUCIATE AND ANTROLATERAL LIGAMENT RECONSTRUCTION (BOX 51.8) > COMPLICATIONS ASSOCIATED WITH KNEE ARTHROSCOPY.

[99] Outcomes of Revision Cartilage Restoration Surgery for Failed Primary Treatment of Chondral or Osteochondral Defects of the Knee: A Systematic Review. The American Journal of Sports Medicine. 2025. DOI: 10.1177/03635465241260271

[100] Does Sex Matter? Analysis Of Results At 5 Years After Matrix-assisted Autologous Chondrocyte Transplantation In A Large Cohort Of Patients. Orthopaedic Journal of Sports Medicine. 2013. DOI: 10.1177/2325967113s00034

[102] Autologous chondrocyte implantation provides good long‐term clinical results in the treatment of knee osteoarthritis: a systematic review. Knee Surgery, Sports Traumatology, Arthroscopy. 2022. DOI: 10.1007/s00167-022-07030-2

[103] Clinical Profiling in Cartilage Regeneration. The American Journal of Sports Medicine. 2014. DOI: 10.1177/0363546513518552

[104] Aaos Comprehensive Orthopaedic Review 3. Anatomy and Biomechanics of the Knee > I. Anatomy.

[105] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > SECTION 1 KNEE > ANATOMY (FIG. 4.1).

[109] Quadriceps Strength in Patients With Isolated Cartilage Defects of the Knee: Results of Isokinetic Strength Measurements and Their Correlation With Clinical and Functional Results. Orthopaedic Journal of Sports Medicine. 2017. DOI: 10.1177/2325967117703726

[110] Aaos Comprehensive Orthopaedic Review 3. Radiographic Evaluation and Surgical Anatomy of the Knee > II. Surgical Anatomy of the Knee.

[119] Rockwood And Green S Fractures In Adults. 59: Patellar Fractures and Dislocations and Extensor Mechanism Injuries > Posterior Knee Anatomy.

[125] Aaos Comprehensive Orthopaedic Review 3. Biomechanics and Wear in Joint Arthroplasty > III. The Knee Joint.

[127] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > SECTION 11 KNEE ARTHRITIS ASSESSMENT.

[128] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > 2. Trauma > 3. Patellar instability.

[130] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Knee Anatomy > Imaging (Radiograph, MRI, CT Scan, Dynamic Versus Static) > Radiograph.

[131] Over Half of Patients Progress to Cartilage Restoration After Initial Cartilage Biopsy in a Military Population. Arthroscopy, Sports Medicine, and Rehabilitation. 2026. DOI: 10.1002/ars2.70064

[133] Aaos Comprehensive Orthopaedic Review 3. General Evaluation of the Knee Patient > III. Osteonecrosis.

[134] Autologous chondrocyte implantation for the treatment of cartilage lesions of the knee: a systematic review of randomized studies. Knee Surgery, Sports Traumatology, Arthroscopy. 2010. DOI: 10.1007/s00167-010-1050-3

[135] The effects of early or late treatment of osteochondral defects on joint homoeostasis: an experimental study in rabbits. Knee Surgery, Sports Traumatology, Arthroscopy. 2008. DOI: 10.1007/s00167-008-0675-y

[136] Matrix-Applied Characterized Autologous Cultured Chondrocytes Versus Microfracture. The American Journal of Sports Medicine. 2014. DOI: 10.1177/0363546514528093

[137] Stem Cell Therapies for Knee Cartilage Repair. The American Journal of Sports Medicine. 2013. DOI: 10.1177/0363546513508744

[139] Cartilage issues in football—today's problems and tomorrow's solutions. British Journal of Sports Medicine. 2015. DOI: 10.1136/bjsports-2015-094772

[140] One-Stage Cartilage Repair Using a Hyaluronic Acid–Based Scaffold With Activated Bone Marrow–Derived Mesenchymal Stem Cells Compared With Microfracture. The American Journal of Sports Medicine. 2016. DOI: 10.1177/0363546516656179

[141] Cell‐free biomimetic osteochondral scaffold for the treatment of knee articular surface lesions: Clinical outcomes differ based on patient and lesion characteristics. Knee Surgery, Sports Traumatology, Arthroscopy. 2024. DOI: 10.1002/ksa.12402

[149] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Degenerative Conditions of the Knee > Posttraumatic Arthritis > Risk Factors.

[150] Chondral and osteochondral operative treatment in early osteoarthritis. Knee Surgery, Sports Traumatology, Arthroscopy. 2016. DOI: 10.1007/s00167-016-4047-8

[154] Orthopaedic Knowledge Update Sports Medicine 6. Nonarthroplasty Management of Osteoarthritis of the Knee > Summary.

[156] Mosaic osteochondral transplantations in the knee joint, midterm results of the SFA multicenter study. Orthopaedics & Traumatology: Surgery & Research. 2011. DOI: 10.1016/j.otsr.2011.08.005

[157] Impact of Wiberg Patellar Type on Outcomes and Survival Following Cell-Based Cartilage Repair for Patellar Chondral Lesions at Midterm Follow-up. The American Journal of Sports Medicine. 2024. DOI: 10.1177/03635465231220028

[158] Prevalence of Articular Cartilage Lesions and Surgical Clinical Outcomes in Football (Soccer) Players’ Knees: A Systematic Review. Arthroscopy. 2016. DOI: 10.1016/j.arthro.2016.01.055

[159] Magnetic resonance observation of cartilage repair tissue (MOCART) for the evaluation of autologous chondrocyte transplantation: Determination of interobserver variability and correlation to clinical outcome after 2 years. European Journal of Radiology. 2006. DOI: 10.1016/j.ejrad.2005.08.007

[164] Changing trends in the use of cartilage restoration techniques for the patellofemoral joint: a systematic review. Knee Surgery, Sports Traumatology, Arthroscopy. 2018. DOI: 10.1007/s00167-018-5139-4

[167] Cartilage Restoration: Microfracture and Osteochondral Autograft Transplantation. The Journal of Knee Surgery. 2018. DOI: 10.1055/s-0037-1618592

[170] Assessment of Outcomes After Multisurface Osteochondral Allograft Transplantations in the Knee. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/23259671221102452

[173] Poor osteochondral repair by a biomimetic collagen scaffold: 1‐ to 3‐year clinical and radiological follow‐up. Knee Surgery, Sports Traumatology, Arthroscopy. 2015. DOI: 10.1007/s00167-015-3538-3

[174] Magnetic Resonance Imaging Appearance of Cartilage Repair in the Knee. Clinical Orthopaedics and Related Research. 2004. DOI: 10.1097/01.blo.0000129162.36302.4f

[177] Aaos Comprehensive Orthopaedic Review 3. Nonarthroplasty Surgical Treatment of the Knee > II. Osteotomy.

[178] Autologous Chondrocyte Implantation for Treatment of Focal Cartilage Defects in Patients Age 40 Years and Older. The American Journal of Sports Medicine. 2010. DOI: 10.1177/0363546510376742

[180] Articular changes in experimentally induced patellar trauma. Knee Surgery, Sports Traumatology, Arthroscopy. 2001. DOI: 10.1007/s001670100248

[188] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Knee Anatomy > History and Physical Examination.

[193] Cartilage Restoration, Part 1. The American Journal of Sports Medicine. 2005. DOI: 10.1177/0363546504273510

[194] Increased risk of reoperation and failure to attain clinically relevant improvement following autologous chondrocyte implantation of the knee in female patients and individuals with previous surgeries: a time‐to‐event analysis based on the German cartilage registry (KnorpelRegister DGOU). Knee Surgery, Sports Traumatology, Arthroscopy. 2023. DOI: 10.1007/s00167-023-07615-5

[196] Matrix‐assisted chondrocyte transplantation with bone grafting for knee osteochondritis dissecans: stable results at 12 years. Knee Surgery, Sports Traumatology, Arthroscopy. 2020. DOI: 10.1007/s00167-020-06230-y

[208] Patellar chondral defects: a review of a challenging entity. Knee Surgery, Sports Traumatology, Arthroscopy. 2011. DOI: 10.1007/s00167-011-1546-5

[211] Diagnosis and classification of chondral knee injuries: comparison between magnetic resonance imaging and arthroscopy. Knee Surgery, Sports Traumatology, Arthroscopy. 2015. DOI: 10.1007/s00167-015-3622-8

[215] Good short- to medium-term results after osteochondral autograft transplantation (OAT) in middle-aged patients with focal, non-traumatic osteochondral lesions of the knee. Orthopaedics & Traumatology: Surgery & Research. 2016. DOI: 10.1016/j.otsr.2016.06.004

[217] Follow‐up of a New Arthroscopic Technique for Implantation of Matrix‐Encapsulated Autologous Chondrocytes in the Knee. Arthroscopy. 2014. DOI: 10.1016/j.arthro.2014.02.032

[218] AMIC achieves sustained clinical improvement in isolated patellar cartilage defects over 5 years, correlating with MRI. Knee Surgery, Sports Traumatology, Arthroscopy. 2024. DOI: 10.1002/ksa.12518

[220] Prospective Long-term Follow-up of Autologous Chondrocyte Implantation With Periosteum Versus Matrix-Associated Autologous Chondrocyte Implantation: A Randomized Clinical Trial. The American Journal of Sports Medicine. 2020. DOI: 10.1177/0363546520928337

[221] Current trends in the treatment of focal cartilage lesions: a comprehensive review. EFORT Open Reviews. 2025. DOI: 10.1530/eor-2024-0083

[223] Subclinical cartilage degeneration in young athletes with posterior cruciate ligament injuries detected with T1ρ magnetic resonance imaging mapping. Knee Surgery, Sports Traumatology, Arthroscopy. 2014. DOI: 10.1007/s00167-014-3469-4

[226] Management of patellar and trochlear cartilage lesions with matrix-induced autologous chondrocyte implantation in conjunction with patellofemoral realignment procedures improves patient-reported outcomes and magnetic resonance image appearance. Journal of ISAKOS. 2024. DOI: 10.1016/j.jisako.2024.100311

[228] Treatment of Full-Thickness Chondral Defects With Hyalograft C in the Knee. The American Journal of Sports Medicine. 2014. DOI: 10.1177/0363546514526695

[232] Paper 43: Long-term Outcomes of an All-Arthroscopic Matrix-Assisted Autologous Chondrocyte Transplantation Technique. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/2325967121s00607

[235] Treatment of isolated chondral and osteochondral defects in the knee by autologous matrix‐induced chondrogenesis (AMIC). Knee Surgery, Sports Traumatology, Arthroscopy. 2011. DOI: 10.1007/s00167-011-1840-2

[241] Cartilage Restoration Techniques for the Patellofemoral Joint. Journal of the American Academy of Orthopaedic Surgeons. 2017. DOI: 10.5435/jaaos-d-15-00447

[243] ARTICULAR CARTILAGE THICKNESS OF THE PEDIATRIC KNEE: IMPLICATIONS FOR CARTILAGE IMPLANTATIONS. Orthopaedic Journal of Sports Medicine. 2019. DOI: 10.1177/2325967119s00188