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Unicompartmental knee replacement

156 citationsUpdated Sep 2026

Overview

Unicompartmental knee arthroplasty (UKA) is a definitive treatment option for appropriately selected patients, including octogenarians and very elderly individuals, where it provides excellent survivorship and reduced complications when proper indications and accurate technique are employed [3, 149]. The procedure is a safe and effective alternative to total knee arthroplasty in patients over 80 years old [25] and is a viable option for those with reduced morbidity [149]. Recent reports demonstrate success in expanding classic indications to younger and heavier patients [4], with UKA accounting for 4.5% of unilateral knee replacements among Medicare beneficiaries from 2000 to 2009, a period marked by dramatic increases in use [6]. For patients aged 60 years or younger, UKA is a safe, reliable, and effective treatment option for medial osteoarthritis [12], though implant survivorship remains a limiting factor for cost-effectiveness in those under 65 [31].

Pre-existing patellofemoral disease does not affect 10-year survivorship in fixed bearing UKA [1] nor intermediate-term outcomes [14]; consequently, it should not be considered a contraindication [1, 14]. Expanded indications have been associated with comparable clinical outcomes and great short-term survivorship [2]. UKA is less destructive to native knee structure than total knee arthroplasty for spontaneous osteonecrosis of the knee and can achieve comparable prognosis with strict patient selection [8]. There is no difference in outcomes between mobile and fixed unicompartmental knee replacements [9], and keys to long-term survival for both designs are patient selection, surgical technique, and surgical experience [26]. The Oxford medial UKA can have a low revision rate through the second decade when correct indications are employed [11], and recent series corresponding to modern use criteria show results as reliable as total knee arthroplasty at 10 years' follow-up [47].

Functional recovery after UKA continues beyond 6 months and up to 2 years [7]. Outcomes tend to exceed results of revision of a previous total knee arthroplasty [15]. Single-stage bilateral UKA is not associated with higher complication rates compared to two-stage surgery and results in substantial cost savings [18]. UKA is an economically attractive alternative in patients sixty-five years of age or older [19], and modest improvements in implant survivorship could make it cost-effective in younger patients [19]. While obesity remains a contraindication [17], UKA offers early advantages despite potentially lower survivorship than total knee replacement in young and active patients [20]. The Unicompartmental Indication Score (UIS) is positively correlated with postoperative Knee Society Score and patient satisfaction, with a cutoff of 25 points predicting optimal outcomes in terms of pain relief, function, and satisfaction [61].

Anatomy & Pathophysiology

Bony Anatomy

The knee joint comprises the distal femur, proximal tibia, and patella [39]. The medial femoral condyle is larger and projects farther posteriorly and distally than the lateral condyle [79]. Conversely, the lateral femoral condyle projects farther anteriorly and is wider in the medial-lateral direction than the medial condyle [79]. The tibial articular surface slopes 7° to 10° in the sagittal plane [79], with the posterior slope of the medial tibial plateau averaging 10.7° and the lateral plateau averaging 7.2° [94]. The medial tibial plateau is larger than the lateral plateau and is concave in both frontal and sagittal planes [79]. The lateral tibial plateau is smaller, more circular, concave in the frontal plane, and convex in the sagittal plane [79]. The patella is the largest sesamoid bone in the body with a mean thickness of 2.5 cm [79, 94]. Its articular surface contains a vertical central ridge separating the broader lateral facet from the medial facet, plus a smaller medial odd facet [79, 94].

Ligaments

The anterior cruciate ligament (ACL) prevents anterior translation and rotation of the tibia on the femur [39]. The posterior cruciate ligament (PCL) prevents posterior subluxation of the tibia on the femur [39]. The medial collateral ligament (MCL) stabilizes the knee against valgus stresses [39], while the lateral collateral ligament (LCL) is the main stabilizer against varus stress [39]. The ACL is composed of 90% type I collagen and 10% type III collagen [79, 80, 94]. It has a mean length of 33 mm and a mean midsubstance width of 11 mm [79, 94]. The ACL femoral attachment is a semicircular area on the posteromedial aspect of the lateral femoral condyle [79, 80, 94], and its tibial attachment is a broad, irregular, oval-shaped area between the medial and lateral tibial spinous processes [79, 80]. The ACL consists of anteromedial and posterolateral bundles named according to their tibial insertions [80, 83, 92]. The anteromedial bundle is tight in knee flexion, while the posterolateral bundle is tight in knee extension [80, 83, 94]. The PCL has a mean length of 38 mm and a mean width of 13 mm [94]. Its femoral attachment is broad and crescent-shaped on the anterolateral aspect of the medial femoral condyle [94], and its tibial insertion is located 10 to 15 mm distal to the joint line on the posterior central sulcus [94]. The PCL anterolateral bundle is tight in knee flexion, and the posteromedial bundle is tight in knee extension [94].

The superficial MCL proximal division resists valgus tibial translation, and the distal division resists tibial external rotation in knee extension [80, 81]. The deep MCL resists valgus translation and tibial internal and external rotation [80, 81]. The posterior oblique ligament resists tibial internal rotation, especially in knee extension [80, 81]. The LCL resists varus tibial translation and tibial external rotation, especially at 30 degrees of knee flexion [80, 81]. The popliteus tendon resists tibial external rotation, especially in knee flexion [80, 81]. The popliteofibular ligament resists tibial external rotation and posterior tibial displacement [80, 81]. The oblique popliteal ligament resists knee hyperextension and varus tibial translation [80, 81]. The ACL is subjected to peak loads of 170 N during walking and up to 500 N with running [95, 96]. The ultimate strength of the ACL in young patients is approximately 1750 N [95, 96]. Sectioning the PCL increases contact pressures in the medial compartment and the patellofemoral joint [95, 96].

Menisci

The menisci are C-shaped fibrocartilaginous disks that provide shock absorption, increase joint congruency, enhance stability, and aid in synovial fluid distribution [39]. The medial meniscus is firmly attached to the joint capsule along its entire peripheral edge [39]. The lateral meniscus is attached to the anterior and posterior capsule but has a region posterolaterally where it is not firmly attached [39]. Consequently, 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 [39]. The lateral meniscus is larger than the medial meniscus and carries a greater share of the lateral compartment pressure [39]. The medial meniscus has a semicircular shape covering approximately 50% to 60% of the medial tibial plateau in adulthood [90]. The lateral meniscus has a more circular C-shape with symmetric sizes of the anterior and posterior horns [90]. The mean lateral meniscus excursion from knee extension to flexion is 11.2 mm, compared to a mean medial meniscus excursion of 5.1 mm [90]. The menisci bear one-third to one-half of body weight during load transmission [95, 96]. Removal of the menisci increases contact stresses and load transfer to bone by up to four times [95, 96].

Kinematics & Biomechanics

The knee is a hinge joint that incorporates both gliding and rolling motions essential to its kinematics [80, 81]. The "screw-home" mechanism involves the tibia externally rotating 5 degrees in the final 15 degrees of extension [80, 81]. Knee joint surface loads are three times body weight during level walking and up to four times body weight with stair walking [95, 96]. The patella bears half the body weight with normal walking and seven times the body weight with squatting and jogging [95, 96]. The mechanical axis of the lower extremity normally passes just medial to the medial tibial spine [95, 96]. This axis is in 3 degrees of valgus angulation from the vertical axis [95, 96]. The anatomic axis of the femur is in 6 degrees of valgus angulation from the mechanical axis [95, 96], while the anatomic axis of the tibia is in 2 to 3 degrees of varus angulation from the mechanical axis [95, 96].

UKA-Specific Pathophysiology & Kinematics

UKA is a logical procedure when the lesion is limited to one femorotibial compartment [76]. The success of UKA is influenced by surgical technique and the choice of proper indication [76]. Indications include osteoarthritis or osteonecrosis limited to one femorotibial compartment ranked as Ahlback 4 [76], a deformity that is fully correctible on stress radiographs [76], and a functional anterior cruciate ligament [76]. UKA can be performed through a mini-incision to minimize extensor mechanism disruption and provide quicker recovery [76]. UKA reliably restores normal knee kinematics and function for arthritis limited to one compartment, but survival rates vary based on patient selection, implant design, and surgeon experience [125]. The in vivo kinematics of bicruciate-retaining total knee arthroplasty reproduces those of normal knees to a lower extent than those of UKA knees [117]. The kinematics of the unloaded knee following mobile-bearing UKA closely resemble those of the native knee, although relative medial overstuffing results in a more valgus joint orientation [118]. Kinematic characteristics do not change significantly after kinematic alignment UKA [122]. Altered contact kinematics and reduced range of contact excursion in UKA knees could lead to excessive cumulative articular surface contact stress, which is implicated in the pathogenesis of osteoarthritis [126]. UKA significantly enhances knee joint kinematics, facilitating the transition from basic to advanced functional activities [108].

The functional flexion axis of a living knee cannot be restored to normal after medial UKA, evidenced by significantly lower vertical translation of the clinical epicondylar axis compared to normal knees [63]. Optimal positioning of the tibial component is crucial to restore normal knee kinematics and prevent implant wear and lesions to adjacent compartments [111]. Varus placement of the tibial component reduces intraoperative bearing mediolateral translation during 0–60° of knee flexion and decreases the risk of impingement with the vertical wall compared with neutral placement [140]. The tibia first technique with tensor measurement allows surgeons to predict final soft tissue tension before femoral osteotomies, helping restore natural knee kinematics [141]. Minor medial joint line elevation after medial UKA triggers a novel, angle-dependent biomechanical cascade driven by dynamic alignment changes [138]. There is a correlation between varus orientation of the tibial component and maximum total point motion from radiostereometry in UKA [152]. Valgus correctability and meniscal extrusion are associated with alignment after UKA and can help predict coronal-plane overcorrection [151].

Phenotype analysis using the functional knee phenotype system demonstrated a wide diversity of coronal alignment phenotypes among knees with anteromedial osteoarthritis [123]. Knees with anteromedial osteoarthritis show substantial phenotypic variation prior to and following medial UKA, challenging the assumption of uniform characteristics among knees with identical wear patterns [144]. Pre-arthritic/kinematically aligned knees in fixed-bearing medial UKA had superior outcomes, including higher KOOS Activities of Daily Living and Sport subscales, compared with non-pre-arthritic/kinematically aligned knees at an average of 10 years [130]. Using the kinematic alignment technique for mobile-bearing UKA, knees that achieved pre-arthritic alignment demonstrated superior survivorship and subjective postoperative knee function compared with those that did not [143]. Robotic-assisted, cruciate-sparing bi-UKA maintains the natural anatomy of the knee in the coronal, sagittal, and axial planes better than a mechanically aligned TKA [137]. Preoperative radiographic severe knee varus, mild-to-moderate patellofemoral joint osteoarthritis, and malalignment of the patellofemoral joint do not adversely influence early outcomes after fixed-bearing medial robotic-assisted UKA [65]. Gender does not influence outcomes and complications in medial UKA, with no significant differences in radiographic outcomes, implant positioning, or knee phenotype [64]. Postoperative fixed flexion deformity greater than 10° leads to poorer functional outcome 10 years after UKA [154]. Although native knee biomechanics are preserved in UKA, younger patients do not seem to perceive this benefit as greater health-related quality of life or patient satisfaction compared to TKA [139].

Lateral UKA survival has evolved with improved understanding of knee compartment biomechanics, indications, surgical techniques, and implant designs [110]. Lateral UKA is a favorable alternative to distal femoral osteotomy and total knee arthroplasty for isolated lateral compartment osteoarthritis, provided indications are strictly selected and surgical techniques are tailored to the lateral compartment's unique anatomy and biomechanics [48]. Despite relevant anatomical and biomechanical contrasts between medial and lateral UKAs, recent literature points to comparable survival rates [145]. The medial mechanical axis, linking the medial femoral head border and medial femoral condyle centre, is parallel to the mechanical axis [147]. There is a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral Oxford UKRs [131]. During knee flexion, all mobile bearings moved posteriorly, and mobile bearings whose femoral components were set laterally tended to move posteriorly while in contact with the lateral wall [133]. Patients with lateral osteoarthritis of the knee showed an impaired gait with an increased knee abduction and hip adduction angle after mobile-bearing UKA [153]. Patellofemoral joint degeneration and malalignment may influence patient-reported outcomes after lateral UKA, potentially explained by realignment of the patella and redistribution of loads across the patellofemoral joint [54].

Classification

Indications and Patient Selection

Unicompartmental knee arthroplasty (UKA) provides reliable and durable results in specific patient populations, including octogenarians [3] and older patients who demonstrate good performance at minimum 21-year follow-up [5]. For isolated compartment spontaneous knee osteonecrosis, UKA yields reliable clinical improvement, minimal complications, and 93% survivorship free of revision at ten years [10]. When correct indications are employed, the Oxford medial unicompartmental knee arthroplasty maintains a low revision rate through the second decade after implantation [11]. Medial mobile-bearing unicompartmental arthroplasty is a viable surgical treatment for young patients with anteromedial osteoarthritis [36]. UKA is a reasonable solution for restoring clinical function and radiological lower-limb alignment in spontaneous or secondary osteonecrosis limited to one compartment, offering durable survivorship [176].

Associated patellofemoral osteoarthritis is not a contraindication for UKA [57]. The grade of associated patellofemoral osteoarthritis does not negatively impact clinical and functional outcomes, complication rates, or survival after femorotibial unicompartmental knee arthroplasty [57]. However, a statistically significant association exists between the magnitude of preoperative femorotibial malalignment and the severity of associated patellofemoral osteoarthritis [57]. To extend indications, associated patellofemoral osteoarthritis must be systematically treated in a tailored, stepwise fashion using different techniques based on its severity [57]. Candidacy for medial unicompartmental knee replacement declines with age [67].

Age-Specific Outcomes

UKA in patients under the age of 60 years provides excellent clinical outcomes and 10-year implant survival [12]. At minimum 10-year follow-up, no differences in outcome scores or survivorship exist between patients younger or older than 55 years of age [162].

Alignment and Deformity

UKA may be preferable for medial knee osteoarthritis before the varus angle reaches more than 15º [22].

Implant Design and Fixation

Fixed-bearing implants: May provide a significantly lower risk of revision and dislocation and improved function compared to mobile-bearing implants [55]. Unconstrained designs: Demonstrated significantly better clinical results and lower revision rates compared to constrained designs [27]. Standard cemented implants: Conventional designs for UKA still represent the optimal solution at the present time [44].

Survivorship and Revision Risk

Recent reports indicate 94% survivorship at 10 years and 90% survivorship at 18 years [16]. Improved survivorship is driven by newer techniques, designs, and improved polyethylene quality [16]. Lifetime revision risk for medial UKA is lower than expected [21]. UKA should be considered a definitive knee replacement rather than a Pre-TKR, even in young patients [21]. Although UKA outcomes may not match those of a primary TKA, they tend to exceed results of revision of a previous TKA [15]. The risk for revision is three times higher in UKA when compared to TKA [170].

Epidemiology and Utilization

UKA accounted for only 4.5% of unilateral knee replacements among Medicare beneficiaries, but its use has increased dramatically [6]. The incidence of UKA is increasing per year at a more rapid rate than total knee arthroplasty, growing by approximately 30% per year [23]. Despite this growth, UKA still represents a very small proportion of all knee arthroplasties [23].

Diagnostic and Preoperative Assessment

A novel 2.5-dimensional deep learning model for “bone-on-bone” detection on magnetic resonance imaging may enhance diagnostic accuracy and consistency for UKA candidates [13]. The objective, reproducible output of this model provides a standardized reference for cartilage assessment and supports preoperative clinical decision-making [13].

Clinical Presentation

The success of unicompartmental knee arthroplasty relies on appropriate patient selection [148]. Physical and radiographic evaluation remains the cornerstone of the diagnostic process for knee osteoarthritis and is particularly important to assess whether a knee with unicompartmental osteoarthritis would be indicated for unicompartmental knee arthroplasty [116]. Evaluation of the presence of unicompartmental knee osteoarthritis through medical history, physical examination, and imaging is essential, with all components contributing to precise patient selection [116].

Pre-operative anterior knee pain does not compromise functional outcome or survival and should not be considered a contraindication to mobile-bearing unicompartmental knee arthroplasty [71]. There is no correlation between preoperative pain location and outcome after Oxford unicompartmental knee arthroplasty at 1 and 5 years [53]. Consequently, localised medial pain should not be a prerequisite to unicompartmental knee arthroplasty [53]. Unicompartmental knee arthroplasty may be performed in patients with generalised or anterior knee pain [53].

Specific clinical and radiographic findings influence candidacy and prognosis. Preoperative bone marrow edema negatively impacted clinical outcomes, especially pain, after unicompartmental knee arthroplasty at a mean of 10 years [70]. Advanced varus deformity associated with medial knee osteoarthritis is a potential predictor of anterior cruciate ligament tear and risk for suitable unicompartmental knee arthroplasty [22]. In selected patients with combined medial unicompartmental knee osteoarthritis and ACL deficiency, unicompartmental knee arthroplasty combined with ACL reconstruction can be a valid treatment option [50].

Unicompartmental knee arthroplasty is a durable and efficient option to treat patients with unicompartmental osteonecrosis of the knee [49]. For spontaneous osteonecrosis of the knee, unicompartmental arthroplasty is less destructive to the native knee structure than total knee arthroplasty but can achieve comparable prognosis with strict patient selection [8]. Patients with reduced bone mineral density could safely undergo cementless unicompartmental knee replacement surgery and have similar clinical outcomes to those with normal bone mineral density [35].

Investigations

Plain radiography: Weight-bearing AP and lateral radiographs serve as the appropriate initial imaging studies for assessing knee arthritis, patellofemoral alignment, and surgical implants [98]. A weight-bearing PA (Rosenberg) view in flexion is specifically used to assess cartilage loss from the posterior femur and tibial plateau [98]. Patellofemoral views evaluate patellofemoral alignment, patellar and trochlear morphology, osteochondral injury, and patellofemoral arthritis [98]. Radiographs may identify subchondral sclerosis, joint space narrowing, subchondral cysts, osteophytes, and joint subluxation in osteoarthritis [98]. While radiographs can underestimate isolated chondral lesions, they may still demonstrate joint space narrowing, osteophytes, sclerosis, and cysts [102]. Axial plane imaging of the hip and knee helps assess the rotational alignment of components in cases of patellar maltracking [98].

MRI: MRI is used to evaluate articular cartilage morphology [102]. It may identify the degree of articular cartilage injury, the presence of associated bone marrow edema, and the location of the injury [98]. MRI is useful for confirming MCL injury and identifying the site of injury [85]. It is also useful to detect the presence of meniscal and other injuries to the knee [85]. In the severely injured knee, MRI is often a useful adjunct for diagnosing posterolateral corner and LCL injuries [107]. Assessment of medial cartilage thickness loss using MRI provides additional utility over standard radiographs in preoperative assessments of medial UKA patients [188]. A novel 2.5-dimensional deep learning model for "bone-on-bone" detection on MRI may enhance diagnostic accuracy and consistency for cartilage assessment in unicompartmental knee arthroplasty candidates [13].

CT: Three-dimensional CT with remodeling is used for preoperative planning for reconstruction associated with dysplasia, post-trauma planning, and complex total knee arthroplasty planning [106].

Bone scan: SPECT bone scan provides information regarding the degree of osteoarthritis in knee weight-bearing compartments for pre-operative planning [200].

Other Considerations: The Kellgren-Lawrence rating grades the extent of osteoarthritis based on review of AP knee radiographs [106]. Primary features used for this rating include osteophytes, joint space narrowing, subchondral sclerosis with or without subchondral cysts, and altered shape of periarticular bones [106]. Kellgren-Lawrence Grade 4 is characterized by prominent osteophytes, absent joint space, subchondral bone sclerosis with cysts, and bone deformity with flattening of femoral condyle contours [106]. Knee arthroplasty is recommended when Kellgren-Lawrence Grade 4 findings are present [106]. However, application of isolated radiologic criteria in patients with knee osteoarthritis results in a unicompartmental knee arthroplasty candidacy that is misleadingly high [202, 203]. A machine learning method using standard X-rays provides a high-accuracy method for surgical decision-making between total and unicompartmental knee arthroplasty [213].

Preoperative radiographic severe knee varus, mild-to-moderate patellofemoral joint osteoarthritis, and malalignment of the patellofemoral joint do not adversely influence early outcomes after fixed-bearing medial robotic-assisted unicompartmental knee arthroplasty [65]. Preoperative patellar tilt angle does not significantly influence clinical outcomes or radiographic parameters following unicompartmental knee arthroplasty [215]. The location and severity of preoperative subchondral bone marrow lesions were not associated with inferior postoperative outcomes after medial unicompartmental knee arthroplasty [52]. Consequently, bone marrow lesions should not be considered a contraindication for medial unicompartmental knee arthroplasty [52]. Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs [186]. The results of unicompartmental knee arthroplasty for medial unicompartmental knee osteoarthritis were excellent regardless of preoperative lateral meniscal pathology on MRI if the patients had no symptoms related to the lateral meniscus lesion [199]. Gender does not influence outcomes and complications in medial unicompartmental knee arthroplasty [64]. No significant differences were evident in radiographic outcomes, implant positioning, and knee phenotype between genders in medial unicompartmental knee arthroplasty [64].

Treatment

Non-Operative

The provided evidence does not detail specific conservative management protocols such as weight loss, physical therapy, or pharmacological interventions. However, high tibial osteotomy is noted as a thoughtful alternative to maintain function and relieve pain in selected cases of young and active knee osteoarthritis [20].

Operative

Indications: Unicompartmental knee arthroplasty (UKA) is a logical procedure when the lesion is limited to one femorotibial compartment [76]. For medial knee osteoarthritis, UKA may be preferable before the varus angle reaches more than 15º [22]. In patients with spontaneous osteonecrosis of the knee (SONK), UKA is less destructive to native knee structure than total knee arthroplasty (TKA) and can achieve comparable prognosis with strict patient selection [8]. UKA is a durable and efficient option for unicompartmental osteonecrosis [49]. For mobile-bearing UKA, indications should be based on the pathoanatomy of the disease as proposed by Goodfellow et al [129]; the indications proposed by Kozinn and Scott and others are not supported for this implant type [129]. A Unicompartmental Knee Arthritis Score (UIS) cutoff of 25 points predicts optimal outcomes in terms of pain relief, function, and satisfaction [61]. Preoperative bone marrow lesions should not be considered a contraindication for medial UKA [52]. Localised medial pain is not a prerequisite for UKA, and the procedure may be performed in patients with generalised or anterior knee pain [53]. Pre-operative anterior knee pain does not compromise functional outcome or survival and should not be considered a contraindication for mobile-bearing UKA [71]. Obesity remains a contraindication, and better defining the ideal candidate will make the procedure more predictable and reliable [17]. UKA is a safe and effective alternative to TKA in patients over 80 years old [25]. In patients sixty years of age or younger and active at the time of surgery, UKA is associated with pain relief and excellent function [29]. Lateral UKA is a favorable alternative to distal femoral osteotomy and TKA for isolated lateral compartment osteoarthritis provided indications are strictly selected [48].

Surgical Approach / Technique: The procedure can be performed through a miniincision to provide quicker recovery because extensor mechanism disruption is minimized [76]. Specific instrumentation limited to the replaced compartment, using either an intra- or extramedullary femoral technique, provides femorotibial component alignment [76]. This instrumentation allows slight undercorrection of the deformity [76]. Radiographic assessment demonstrates that precise implantation of components is possible with a mini-incision, and appropriate kinematics can be restored [76]. The functional anterior cruciate ligament is important for the long-term results of UKA [76]. For lateral UKA, surgical techniques must be tailored to the lateral compartment's unique anatomy and biomechanics to mitigate complications [48]. An objective, reproducible deep learning model for “bone-on-bone” detection on MRI may enhance diagnostic accuracy and consistency for cartilage assessment, providing a standardized reference supporting preoperative clinical decision-making [13].

Implant Selection: Fixed-bearing implants may provide a significantly lower risk of revision and dislocation compared to mobile-bearing implants [55]. Fixed-bearing implants may also provide improved function compared to mobile-bearing implants [55]. Unconstrained unicompartmental knee replacements demonstrated significantly better clinical results and lower revision rates compared to constrained designs [27].

Adjuncts: Robotic-assisted surgery allows surgeons to more accurately and reproducibly plan and achieve operative targets during UKA [43]. Robotic-assisted UKA offers technological advancements that enhance surgical precision compared to manual techniques [127]. Robotic-assisted UKA reduces revision rates compared to manual techniques [127]. However, robotic-assisted UKA does not significantly differ in functional outcomes compared to manual techniques [127].

Pain Management: The addition of a single preoperative dose of 125 mg systemic methylprednisolone to a multimodal analgesic regime significantly reduced postsurgical pain after fast-track UKA [196]. This regimen also significantly reduced opioid consumption [196] and decreased knee swelling in the first 24 h after fast-track UKA [196].

Setting of Care: Patients can be safely and effectively discharged on the day of surgery after UKA within the United Kingdom NHS [32]. Day-of-surgery discharge is associated with high levels of satisfaction [32] and allows for safe, efficient care of appropriately selected patients [37]. Ambulatory surgery centers provide a safe, cost-effective alternative to traditional inpatient settings for UKA [205]. Advancements in technology and perioperative management are expanding the eligible patient population for UKA in ambulatory settings [205].

Revision: Conversion of a failed unicondylar knee arthroplasty to a TKA is technically demanding but may be done successfully with careful preoperative planning [24]. This conversion may require revision techniques [24]. Periprosthetic tibial plateau fractures in UKA can range up to 5% in incidence [185]. Extended vertical saw cuts at the dorsal tibia reduce fracture loads and can be regarded as a major risk factor for periprosthetic tibial plateau fractures [185].

Other Considerations: UKA is an excellent treatment option for patients with unicondylar knee degeneration with optimal survivorship rates of up to 20 years [159]. UKA offers reduced postoperative pain, less postoperative complication, and less revision compared to high tibial osteotomy [204]. UKA patients reported lower pain scores than TKA patients in the immediate postsurgical period [189]. UKA patients required 45% lower opioid medication in the immediate postsurgical period than TKA patients [189]. Single-stage bilateral UKA is a relevant procedure in selected patients [18].

Complications

Perioperative Morbidity and Recovery

Unicompartmental knee arthroplasty (UKA) demonstrates a lower overall postoperative complication rate of 4.3% compared to 11.0% for total knee arthroplasty (TKA) [180]. This advantage extends to specific perioperative events, where UKA is associated with significantly lower rates of manipulation (odds ratio 13.0), blood transfusion (odds ratio 8.5), intensive care unit admission (odds ratio 7.4), and discharge to a rehabilitation facility (odds ratio 5.2) relative to TKA [180]. The mean hospital stay is shorter for UKA at 2.0 days compared to 3.3 days for TKA [180]. Early orthostatic intolerance is uncommon after UKA compared to TKA [33]. Day-of-surgery discharge is feasible and allows for safe, efficient care with high satisfaction in appropriately selected patients [37]. In robotic-assisted UKA, overall complications occurred in 4.2% of knees (462/10,894) versus 5.5% (555/10,065) in manual UKA [121]. The cumulative incidence of complications following robotic UKA was 4.4% for medial procedures and 8.3% for lateral procedures [121]. Increased operative time impacts rates of short-term complications after UKA [156].

Infection (PJI)

Conversion from UKA to TKA is associated with higher rates of periprosthetic joint infection (PJI) than revision TKA across all follow-up intervals in a large United States cohort [146]. However, based on current literature, conversion from UKA to TKA is associated with a similar surgical site infection or PJI rate compared to primary TKA [220]. PJI following UKA results in substantial morbidity, necessitating close follow-up for both aseptic causes of failure and infection recurrence [229]. Survivorship free from persistent PJI at 1 year after debridement, antibiotics, and implant retention (DAIR) is 76% [217]. A wide exposure and thorough synovectomy incorporated during DAIR for UKA improves the likelihood of successful eradication of PJI at the 1-year mark [232]. Intra-articular corticosteroid injection in a UKA doubles the risk of PJI compared to patients who did not receive an injection [231]. Knee arthroscopy within two years of UKA is associated with an increased rate of conversion to TKA and a higher rate of failure from aseptic loosening [77]. There was no increased incidence of PJI when UKA was staged greater than three months after arthroscopy [168].

Aseptic Loosening

Aseptic loosening of the tibial component is one of the most common failure modes for UKA, alongside instability and progression of disease to another compartment [158]. In a series of 1000 consecutive medial mobile-bearing UKAs, aseptic loosening was the indication for revision in 15 cases [165]. Preoperative coronal tibiofemoral subluxation ≥ five mm was associated with a higher risk of conversion to TKA due to aseptic loosening after mobile-bearing UKA [218]. Both groups with and without preoperative coronal tibiofemoral subluxation exhibited survivorship higher than 90% at 15 years after mobile-bearing UKA [218]. With a cemented, fixed-bearing design, failure rates were low, there were no cases of failure secondary to wear or loosening, and the survivorship was similar to that reported for TKA [195].

Instability

Instability is a primary failure mode for UKA [158]. In a series of medial mobile-bearing UKAs, tibiofemoral instability was the indication for revision in 1 case, while mobile bearing dislocation occurred in 2 cases [165]. There may be a difference in knee kinematics where the medial mobile bearing knee closer approximates that of the normal knee, accounting for a significantly lower frequency of radiolucent lines in mobile rather than fixed bearing prosthesis [41].

Other Considerations

Registry results show that UKAs are revised three times more often and much earlier than TKAs [158]. The estimated lifetime risk of revision following knee arthroplasty is dependent on patient age and implant type, with unicondylar knee arthroplasty being associated with a higher lifetime revision risk [210]. UKA has higher revision and slightly higher reoperation rates but lower mortality rates than matched total knee replacement [226]. Reported complications were not uncommon, as nearly 40% of patients required a conversion to a TKA in a large United States cohort [222]. In a series of Oxford UKAs, the most common reason for failure was progression of osteoarthritis in the lateral compartment, occurring in 26 (2.3%) cases [120]. In the same series, there were 59 failures requiring revision surgery with a 5.3% cumulative revision rate [120]. More recent reports of UKA have shown 94% survivorship at 10 years and 90% survivorship at 18 years [16]. Lateral and medial UKA led to similar rates of reoperation and infection within two years of operation [38]. The UKA group had earlier, but less frequent, revision to TKA compared to valgus-producing proximal tibial osteotomy [207]. Comparisons between UKA and TKA are open to bias, particularly in registry data, which can be misleading [69]. The outcomes of UKA in dependent and independent clinical studies do not differ significantly and are in line with arthroplasty register datasets [225].

In a series of 1000 consecutive medial mobile-bearing UKAs, 40 revisions were performed at an average of 23.1 months for a survivorship of 95.2% [165]. Indications for revision included aseptic loosening (15), tibial collapse (7), mobile bearing dislocation (2), persistent pain (12), progression of disease (2), infection (1), and tibiofemoral instability (1) [165]. The 2-year failure rate was six times higher for UKA to UKA revision than after conversion to TKA [216]. Revision-free survivorship and arthroplasty-related complications at two years following revision UKA are lower than that for primary TKA, but higher than that for aseptic revision TKA [169]. Re-revision rates of failed UKA are equivalent to revision rates of primary TKA and substantially better than re-revision rates of revision TKA [208]. Although outcomes of UKA may not match those of a primary TKA, they tend to exceed results of revision of a previous TKA [15]. Conversion of a failed unicondylar knee arthroplasty to a TKA is technically demanding, but may be done successfully with careful preoperative planning and possible need for revision techniques [24]. Aseptic revision from UKA to TKA provides excellent midterm implant survivorship, clinical outcomes, and radiographic results, particularly when performed for the progression of osteoarthritis [219]. Data suggest that the implant survival and clinical outcomes of UKA revisions to TKA were inferior to primary TKA [212].

Recovery

Light activity (weeks): Patients can be safely and effectively discharged on the day of surgery after unicompartmental knee arthroplasty within the United Kingdom NHS, with high levels of satisfaction [32]. Early orthostatic intolerance is uncommon after unicompartmental knee arthroplasty compared to total knee arthroplasty, suggesting a procedure-specific component [33]. Minimally invasive unicompartmental knee arthroplasty allows for rapid recovery, minimal blood loss, and excellent functional outcomes including high flexion and the ability to sit cross-legged [209].

Full activity (months): UKA patients return to work significantly sooner than TKA patients, although WORQ, WAI, and satisfaction scores are similar between groups [177]. The majority of patients returned to sports and recreational activity after unicompartmental knee arthroplasty [58]. Most patients can expect to resume physical activity or sports within a short timeframe after knee arthroplasty, particularly to low-impact activities [160]. Participation in high-impact sports is not a risk factor for revision surgery, and timing of return typically ranges from 3 to 6 months [230].

Functional milestones: Both unicompartmental and total knee arthroplasty groups showed an overall improvement in WOMAC and Oxford Knee scores over time [179]. A good restoration of gait was achieved by most unicompartmental knee patients independently of the UKA design, although some abnormalities persisted in muscle activity around the knee [157]. The functional flexion axis of a living knee cannot be restored to normal after medial unicompartmental knee arthroplasty, as evidenced by significantly lower vertical translation of the clinical epicondylar axis compared to normal knees [63].

Other Considerations: This review aims to raise awareness of the question of return to sports for TKA and unicompartmental knee arthroplasty (UKA) patients and identify factors which influence resumption of sports activity to guide patients using a more personalized approach [184]. More recent reports of unicompartmental knee replacement have been more encouraging with 94% survivorship at 10 years and 90% survivorship at 18 years, driven by newer techniques, designs, and improved polyethylene quality [16]. Unicompartmental knee replacements in this relatively older age group of patients performed well at minimum 21-year followup [5]. At an average duration of follow-up of eleven years, unicompartmental knee arthroplasty was associated with pain relief and excellent function in a cohort of patients who had been sixty years of age or younger and active at the time of surgery [29]. Lateral and medial unicompartmental knee arthroplasty led to an equivalent functional improvement in range of motion and patient-reported outcomes with similar rates of reoperation and infection within two years of operation [38]. Two-staged bicompartmental UKA is a viable less-invasive alternative to TKA conversion for patients with disease progression or ON after primary UKA [175]. Revision surgery for failed medial unicompartmental knee arthroplasty with bone loss using a lateral tibial plateau autograft and cemented posterior-stabilized implant resulted in improved Oxford Knee Scores and satisfactory mid-term outcomes [221]. These findings underscore the importance of restoring the joint line to achieve optimal outcomes and survival after UKA for medial compartmental knee osteoarthritis [228].

Key Evidence

• [L3] These patients should not be contraindicated from undergoing unicompartmental knee arthroplasty. [1] (10.1007/s00167-018-5169-y)
• [L3] Expanded indications for unicompartmental knee arthroplasty were associated with comparable clinical outcomes and great short-term, albeit limited, survivorship. [2] (10.1016/j.arth.2025.08.005)
• [L4] The unicompartmental knee arthroplasty can be expected to provide reliable and durable results in certain octogenarians, and should be regarded as a definitive treatment option in appropriately selected patients of this age group. [3] (10.1097/01.blo.0000223983.67325.61)
• [L5] Recent reports have demonstrated success in expanding the classic indications of unicompartmental knee arthroplasty to younger and heavier patients. [4] (10.5435/jaaos-d-24-00380)
• [L4] Unicompartmental knee replacements in this relatively older age group of patients performed well at minimum 21-year followup. [5] (10.1097/01.blo.0000185451.96987.aa)
• [L3] Although unicompartmental knee arthroplasty accounted for only 4.5% of the unilateral knee replacements among Medicare beneficiaries, the use of this procedure has increased dramatically. [6] (10.2106/jbjs.l.00652)
• [L3] Functional recovery after unicompartmental knee replacement continues beyond 6 months and even up to 2 years. [7] (10.1007/s00167-007-0351-7)
• [L4] Unicompartmental arthroplasty for SONK is less destructive to the native knee structure than total knee arthroplasty but can achieve comparable prognosis with strict patient selection. [8] (10.1155/2021/6614122)
• [L3] There is no difference in outcomes between mobile and fixed unicompartmental knee replacements. [9] (10.1016/j.arth.2012.05.017)
• [L3] Unicompartmental knee arthroplasty for isolated compartment spontaneous knee osteonecrosis results in reliable clinical improvement, minimal complications, and durable survivorship free of revision of 93% at ten years. [10] (10.1302/0301-620x.100b4.bjj-2017-1041.r2)
• [L4] Providing correct indications are employed, the Oxford medial unicompartmental knee arthroplasty can have a low revision rate through the second decade after implantation. [11] (10.1007/s11999-010-1506-2)
• [L4] Unicompartmental knee arthroplasty for medial osteoarthritis is a safe, reliable and effective treatment option for patients of 60 years or younger. [12] (10.1007/s00167-022-07029-9)
• [L4] Its objective, reproducible output may enhance diagnostic accuracy and consistency, providing a standardized reference for cartilage assessment and supporting preoperative clinical decision-making for unicompartmental knee arthroplasty. [13] (10.1016/j.arth.2026.05.043)
• [L4] The presence of preoperative patello-femoral osteoarthritis did not affect intermediate-term outcomes in patients undergoing unicompartmental knee arthroplasty, suggesting it should not be considered a contraindication. [14] (10.1016/j.arth.2025.04.070)
• [L5] Although outcomes of unicompartmental knee arthroplasty may not match those of a primary TKA, they tend to exceed results of revision of a previous TKA. [15] (10.5435/jaaos-d-17-00107)
• [L4] More recent reports of unicompartmental knee replacement have been more encouraging with 94% survivorship at 10 years and 90% survivorship at 18 years, driven by newer techniques, designs, and improved polyethylene quality. [16] (10.1097/01.blo.0000151844.03672.0b)
• [L4] Better defining the ideal candidate for unicompartmental knee arthroplasty, with obesity remaining a contraindication, will make this a more predictable and reliable procedure. [17] (10.1097/01.blo.0000187062.65691.e3)
• [L3] Single-stage bilateral unicompartmental knee arthroplasty is a relevant procedure in selected patients, not associated with higher complication rates compared to two-stage surgery, and results in substantial cost savings. [18] (10.1016/j.otsr.2018.01.021)
• [L5] Unicompartmental knee arthroplasty is an economically attractive alternative in patients sixty-five years of age or older, and modest improvements in implant survivorship could make it a cost-effective alternative in younger patients. [19] (10.2106/jbjs.n.00169)
• [L5] High tibial osteotomy is a thoughtful alternative to maintain function and relieve pain in selected cases, while unicompartmental replacement offers early advantages despite potentially lower survivorship than total knee replacement. [20] (10.1007/s00167-006-0195-6)
• [L3] UKR should be considered to be a definitive knee replacement rather than a Pre-TKR even in the young. [21] (10.1007/s00167-020-05863-3)
• [L3] A unicompartmental knee arthroplasty may be preferable for medial knee OA before the varus angle reaches more than 15º. [22] (10.1016/j.arth.2025.01.005)
• [L4] The incidence of unicompartmental knee arthroplasty is increasing per year at a more rapid rate than total knee arthroplasty, growing by approximately 30% per year, but still represents a very small proportion of all knee arthroplasties. [23] (10.1016/j.arth.2007.04.012)
• [L4] Conversion of a failed unicondylar knee arthroplasty to a total knee arthroplasty is technically demanding, but may be done successfully with careful preoperative planning and possible need for revision techniques. [24] (10.1097/01.blo.0000214431.19033.fa)
• [L4] Unicompartmental knee arthroplasty is a safe and effective alternative to TKA in patients over 80 years old. [25] (10.1016/j.arth.2026.06.071)
• [L4] Keys to long-term survival of both fixed and mobile-bearing designs in unicompartmental knee arthroplasty are patient selection, surgical technique, and surgical experience. [26] (10.1016/j.arth.2008.06.025)
• [L4] At an average duration of follow-up of eleven years, unicompartmental knee arthroplasty was associated with pain relief and excellent function in a cohort of patients who had been sixty years of age or younger and active at the time of surgery. [29] (10.2106/00004623-200409001-00004)
• [L1] Implant survivorship is a limiting factor toward achieving cost-effective unicompartmental knee arthroplasty in patients aged less than 65 years. [31] (10.1016/j.arth.2016.08.019)
• [L4] Patients can be safely and effectively discharged on the day of surgery after unicompartmental knee arthroplasty within the United Kingdom NHS, with high levels of satisfaction. [32] (10.1302/0301-620x.99b6.bjj-2016-0540.r2)
• [L3] Early orthostatic intolerance is uncommon after unicompartmental knee arthroplasty compared to total knee arthroplasty, suggesting a procedure-specific component. [33] (10.1186/s13018-024-04639-6)
• [L3] Patients with reduced bone mineral density could safely undergo cementless unicompartmental knee replacement surgery and have similar clinical outcomes to those with normal bone mineral density. [35] (10.1186/s13018-020-1566-2)
• [L4] Medial mobile-bearing unicompartmental arthroplasty should be considered a viable surgical treatment in young patients suffering from anteromedial osteoarthritis of the knee. [36] (10.1016/j.arth.2018.03.069)
• [L3] Day of surgery discharge after unicompartmental knee arthroplasty allows for safe, efficient care of appropriately selected patients with high satisfaction. [37] (10.1016/j.arth.2013.08.021)
• [L3] Lateral and medial unicompartmental knee arthroplasty led to an equivalent functional improvement in range of motion and patient-reported outcomes with similar rates of reoperation and infection within two years of operation. [38] (10.1016/j.arth.2025.07.012)
• [L1] There may be a difference in knee kinematics where the medial mobile bearing knee closer approximates that of the normal knee, accounting for a significantly lower frequency of radiolucent lines in mobile rather than fixed bearing prosthesis. [41] (10.1016/j.otsr.2009.10.006)
• [L4] Robotic-assisted surgery has become increasingly popular in unicompartmental knee arthroplasty, as it allows surgeons to more accurately and reproducibly plan and achieve operative targets during surgery. [43] (10.1016/j.arth.2018.01.050)
• [L4] At the present time, the standard cemented implants and the conventional designs for unicompartmental knee replacement still represent the optimal solution. [44] (10.1007/s00167-014-3444-0)
• [Paper] Recent series whose indications and technique correspond to modern use criteria have shown results that are as reliable as those of total knee arthroplasty at a 10 years' follow-up. [47] (10.1016/j.otsr.2011.08.003)
• [L5] Lateral unicompartmental knee arthroplasty is a favorable alternative to distal femoral osteotomy and total knee arthroplasty for isolated lateral compartment osteoarthritis, provided indications are strictly selected and surgical techniques are tailored to the lateral compartment's unique anatomy and biomechanics to mitigate complications. [48] (10.1016/j.jisako.2024.100342)
• [L4] UKA is a durable and efficient option to treat patients with unicompartmental ON of the knee. [49] (10.1016/j.arth.2018.11.010)
• [L4] Unicompartmental knee arthroplasty combined with ACL reconstruction can be a valid treatment option for selected patients, with combined medial unicompartmental knee osteoarthritis and ACL deficiency. [50] (10.1007/s00167-017-4536-4)
• [L3] Clinically, these results suggest that bone marrow lesions should not be considered a contraindication for medial unicompartmental knee arthroplasty. [52] (10.1016/j.arth.2016.05.009)
• [L2] [53] (10.1007/s00167-012-2211-3)
• [L3] This may be explained by realignment of the patella and redistribution of loads across the patellofemoral joint. [54] (10.1302/0301-620x.102b6.bjj-2019-1429.r1)
• [L1] Fixed-bearing implants may provide a significantly lower risk of revision and dislocation and improved function compared to mobile-bearing implants for unicompartmental knee arthroplasty patients. [55] (10.1016/j.arth.2026.07.011)
• [L4] [57] (10.1016/j.jisako.2024.04.003)
• [L4] The majority of patients returned to sports and recreational activity after unicompartmental knee arthroplasty. [58] (10.1177/0363546507303562)
• [L3] The Unicompartmental Indication Score (UIS) is positively correlated with postoperative Knee Society Score and patient satisfaction, with a cutoff of 25 points predicting optimal outcomes in terms of pain relief, function, and satisfaction. [61] (10.1007/s00402-018-3069-8)
• [L3] The functional flexion axis of a living knee cannot be restored to normal after medial unicompartmental knee arthroplasty, as evidenced by significantly lower vertical translation of the clinical epicondylar axis compared to normal knees. [63] (10.1007/s00167-014-3296-7)
• [L3] Furthermore, no significant differences were evident in radiographic outcomes, implant positioning and knee phenotype. [64] (10.1002/ksa.12195)
• [L3] Preoperative radiographic severe knee varus, mild-to-moderate patellofemoral joint osteoarthritis, and malalignment of the patellofemoral joint do not adversely influence early outcomes after fixed-bearing medial robotic-assisted unicompartmental knee arthroplasty. [65] (10.1186/s13018-025-06181-5)
• [Paper] Candidacy for medial unicompartmental knee replacement declines with age. [67] (10.1016/j.otsr.2019.11.012)
• [L5] Comparisons between unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are open to bias, particularly in registry data, which can be misleading. [69] (10.1302/0301-620x.99b1.bjj-2016-0515.r1)
• [L3] At a mean of 10 years, preoperative bone marrow edema negatively impacted clinical outcomes, especially pain, after unicompartmental knee arthroplasty. [70] (10.1016/j.arth.2022.10.010)
• [L3] Pre-operative anterior knee pain also does not compromise functional outcome or survival and should not be considered a contraindication. [71] (10.1302/0301-620x.99b5.bjj-2016-0695.r2)
• [L3] [73] (10.1016/j.arth.2009.05.011)
• [L5] [76] (10.1097/blo.0b013e3180986da7)
• [L3] Knee arthroscopy within two years of unicompartmental knee arthroplasty is associated with an increased rate of conversion to total knee arthroplasty and a higher rate of failure from aseptic loosening. [77] (10.1016/j.arth.2020.10.060)
• [L3] UKA significantly enhances knee joint kinematics, facilitating the transition from basic to advanced functional activities. [108] (10.1186/s13018-025-05662-x)
• [L3] Lateral UKA survival has evolved with improved understanding of knee compartment biomechanics, indications, surgical techniques and implant designs. [110] (10.1002/ksa.12785)
• [L4] Optimal positioning of the tibial component is crucial to restore normal knee kinematics and prevent implant wear and lesions to adjacent compartments. [111] (10.1016/j.otsr.2013.03.004)
• [L4] [116] (10.1136/jisakos-2016-000102)
• [L3] The in vivo kinematics of BCR-TKA knees reproduces those of normal knees to a lower extent than those of UKA knees. [117] (10.1007/s00167-019-05754-2)
• [L5] The kinematics of the unloaded knee following mobile-bearing unicompartmental knee arthroplasty closely resemble those of the native knee, although relative medial overstuffing results in a more valgus joint orientation. [118] (10.1007/s00402-017-2794-8)
• [L4] [120] (10.1016/j.arth.2018.01.035)
• [L1] [121] (10.1016/j.arth.2026.08.017)
• [L5] However, the kinematic characteristics do not change significantly after KA UKA. [122] (10.1186/s13018-025-05659-6)
• [L3] Phenotype analysis using the functional knee phenotype system demonstrated a wide diversity of coronal alignment phenotypes among knees with anteromedial osteoarthritis. [123] (10.1002/ksa.12043)
• [L4] UKA reliably restores normal knee kinematics and function for arthritis limited to one compartment, but survival rates vary significantly based on patient selection, implant design, and surgeon experience. [125] (10.1055/s-0038-1625961)
• [L4] The altered contact kinematics and reduced range of contact excursion in UKA knees could lead to excessive cumulative articular surface contact stress, which is implicated in the pathogenesis of OA. [126] (10.1177/23259671221150958)
• [L2] Robotic-assisted unicompartmental knee arthroplasty offers technological advancements that enhance surgical precision and reduce revision rates compared to manual techniques, but it does not significantly differ in functional outcomes. [127] (10.1016/j.arth.2024.10.095)
• [L4] This study provides long-term evidence that for mobile-bearing unicompartmental knee arthroplasty the indications should be based on the pathoanatomy of the disease, as proposed by Goodfellow et al and does not support the contraindications proposed by Kozinn and Scott and others. [129] (10.1016/j.arth.2016.12.036)
• [L4] Pre-arthritic/kinematically aligned knees in this cohort had superior outcomes, including higher KOOS Activities of Daily Living and Sport subscales and achievement of the patient acceptable symptom state, compared with non-pre-arthritic/kinematically aligned knees at an average of 10 years. [130] (10.2106/jbjs.21.00801)
• [L2] This demonstrates a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral OUKRs. [131] (10.1002/jor.24339)
• [L4] During knee flexion, all mobile bearings moved posteriorly, and mobile bearings whose femoral components were set laterally tended to move posteriorly while in contact with the lateral wall. [133] (10.1007/s00167-018-5064-6)
• [L1] Robotic-assisted, cruciate-sparing bi-UKA maintains the natural anatomy of the knee in the coronal, sagittal, and axial planes better, and may therefore preserve normal joint kinematics, compared with a mechanically aligned TKA. [137] (10.1302/0301-620x.102b11.bjj-2020-1166.r1)
• [Paper] This study reveals a novel, angle-dependent biomechanical cascade triggered by minor JLE, driven by dynamic alignment changes. [138] (10.1186/s13018-026-06982-2)
• [L3] Although native knee biomechanics are preserved, younger patients do not seem to perceive this oft-cited benefit of UKA, as this did not translate into greater health-related quality of life or patient satisfaction compared to TKA. [139] (10.1016/j.arth.2017.09.022)
• [L4] Varus placement of the tibial component reduces intraoperative bearing mediolateral translation during 0–60° of knee flexion and decreases the risk of impingement with the vertical wall, compared with neutral placement along the mechanical axis. [140] (10.1002/ksa.70295)
• [L4] The tibia first technique with the tensor measurement has the advantage that surgeons can predict final soft tissue tension before femoral osteotomies with the prosthetic design and help restore natural knee kinematics, potentially improving implant survival and functional outcomes. [141] (10.1007/s00264-014-2531-7)
• [L3] Using the kinematic alignment technique for mobile-bearing UKA, knees that achieved pre-arthritic alignment demonstrated superior survivorship and subjective postoperative knee function compared with those that did not. [143] (10.1186/s12891-025-08363-y)
• [L3] This variability challenges the assumption of uniform characteristics among knees with an identical wear pattern associated with anteromedial OA and emphasizes the complexity and variability of this specific form of OA. [144] (10.1007/s00167-023-07603-9)
• [L1] Despite relevant anatomical and biomechanical contrasts between medial and lateral UKAs, recent literature points to comparable survival rates. [145] (10.1016/j.jisako.2024.100329)
• [L3] In a large United States cohort, UKA-TKA was associated with higher rates of PJI than TKA-TKA across all follow-up intervals. [146] (10.1016/j.arth.2026.04.041)
• [L4] The medial mechanical axis, linking the medial femoral head border and medial femoral condyle centre, is parallel to the mechanical axis. [147] (10.1007/s00167-012-2227-8)
• [L5] The success of unicompartmental knee arthroplasty relies on appropriate patient selection, yet considerable challenges persist in predicting patient-specific success due to variations in patient characteristics and healthcare practices. [148] (10.1016/j.jisako.2024.100348)
• [L4] UKA is a viable option for treating unicompartmental knee osteoarthritis in very elderly patients with reduced complications and morbidity, and excellent survivorship when proper indications and accurate technique are used. [149] (10.1007/s00402-015-2323-6)
• [L3] These factors can help predict coronal-plane overcorrection and guide patient selection to avoid progression of lateral knee osteoarthritis. [151] (10.1097/corr.0000000000001260)
• [L2] There is a correlation between varus orientation of the tibial component and maximum total point motion from radiostereometry in unicompartmental knee arthroplasties. [152] (10.1007/s00167-014-3147-6)
• [L2] Patients with lateral osteoarthritis of the knee showed an impaired gait with an increased knee abduction and hip adduction angle. [153] (10.1007/s00167-014-2944-2)
• [L2] The authors recommend that FFD should be fully corrected intra-operatively if possible while preserving knee balance and stable dynamic function. [154] (10.1007/s00167-017-4749-6)
• [L3] [156] (10.1016/j.arth.2020.08.032)
• [L3] A good restoration of gait was achieved by most unicompartmental knee patients independently of the UKA design, although some abnormalities persisted in muscle activity around the knee. [157] (10.1007/s00167-011-1620-z)
• [L4] [158] (10.1302/0301-620x.99b1.bjj-2016-0272)
• [L4] UKA is an excellent treatment option for patients with unicondylar knee degeneration with optimal survivorship rates of up to 20 years. [159] (10.1302/2058-5241.3.170060)
• [L4] Most patients can expect to resume physical activity or sports within a short timeframe after knee arthroplasty, particularly to low-impact activities. [160] (10.1002/ksa.70267)
• [L3] [162] (10.1097/corr.0000000000000737)
• [L4] [165] (10.1016/j.arth.2013.01.005)
• [L3] There was no increased incidence of PJI when UKA was staged greater than three months after arthroscopy. [168] (10.1016/j.arth.2024.10.021)
• [L3] Revision free survivorship and arthroplasty related complications at two years following revision UKA are lower than that for primary TKA, but higher than that for aseptic revision TKA, whereas medical complications are similar to those following primary TKA. [169] (10.1016/j.arth.2024.12.026)
• [L4] [170] (10.1016/j.jisako.2024.100341)
• [L4] Two-staged bicompartmental UKA is a viable less-invasive alternative to TKA conversion for patients with disease progression or ON after primary UKA. [175] (10.1002/ksa.70040)
• [L4] [176] (10.1097/blo.0b013e31812f7821)
• [L3] UKA patients return to work significantly sooner than TKA patients, although WORQ, WAI, and satisfaction scores are similar between groups. [177] (10.1007/s00167-019-05667-0)
• [L3] Both groups showed an overall improvement in WOMAC and Oxford Knee scores over time. [179] (10.1016/j.arth.2013.05.009)
• [L3] [180] (10.1016/j.arth.2012.03.022)
• [L2] This review aims to raise awareness of the question of return to sports for TKA and unicompartmental knee arthroplasty (UKA) patients and identify factors which influence resumption of sports activity to guide patients using a more personalized approach. [184] (10.1302/2058-5241.2.170037)
• [L5] [185] (10.1007/s00167-011-1698-3)
• [L3] ACL deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs. [186] (10.1016/j.arth.2020.08.024)
• [L3] Assessment of medial cartilage thickness loss using MRI provides additional utility over standard radiographs in preoperative assessments of medial UKA patients. [188] (10.1002/ksa.12611)
• [L3] UKA patients reported lower pain scores and required 45% lower opioid medication in the immediate postsurgical period than TKA patients. [189] (10.1016/j.arth.2020.04.072)
• [L4] With this cemented, fixed-bearing design, the failure rates were low, there were no cases of failure secondary to wear or loosening, and the survivorship was similar to that reported for total knee arthroplasty. [195] (10.1007/s11999-012-2517-y)
• [L2] Addition of a single preoperative dose of 125 mg systemic methylprednisolone to a multimodal analgesic regime significantly reduced postsurgical pain and opioid consumption and decreased knee swelling in the first 24 h after fast-track UKA. [196] (10.1007/s00167-014-3501-8)
• [L3] The results of UKA for medial unicompartmental knee osteoarthritis were excellent regardless of preoperative lateral meniscal pathology in the magnetic resonance imaging, if the patients had no symptoms related to the lateral meniscus lesion. [199] (10.1016/j.arth.2021.03.054)
• [Paper] SPECT bone scan provides very useful information regarding the degree of osteoarthritis in knee weight-bearing compartments for pre-operative planning. [200] (10.1007/s00402-007-0399-3)
• [L3] Application of isolated radiologic criteria in patients with knee OA results in a UKA candidacy that is misleadingly high. [202] (10.1007/s00167-021-06632-6)
• [L4] Application of isolated radiologic criteria in patients with knee OA results in a UKA candidacy is misleadingly high. [203] (10.1177/2325967121s00180)
• [L1] UKA offers a safe and efficient alternative to osteoarthritis reduced postoperative pain, less postoperative complication, and revision. [204] (10.1016/j.arth.2017.10.025)
• [L4] Ambulatory surgery centers provide a safe, cost-effective alternative to traditional inpatient settings for unicompartmental knee arthroplasty, with advancements in technology and perioperative management expanding the eligible patient population while optimizing outcomes. [205] (10.1016/j.jisako.2024.100350)
• [L3] The UKA group had earlier, but less frequent, revision to total knee arthroplasty. [207] (10.2106/jbjs.15.01031)
• [L3] Re-revision rates of failed UKA are equivalent to revision rates of primary TKA and substantially better than re-revision rates of revision TKA. [208] (10.1016/j.arth.2018.03.023)
• [L4] Minimally invasive unicompartmental knee arthroplasty allows for rapid recovery, minimal blood loss, and excellent functional outcomes including high flexion and the ability to sit cross-legged. [209] (10.1016/j.arth.2006.12.109)
• [L3] The estimated lifetime risk of revision following knee arthroplasty was dependent on patient age and implant type, with fully constrained and unicondylar knee arthroplasty being associated with a higher lifetime revision risk. [210] (10.1016/j.arth.2024.11.054)
• [L3] Our data suggest that the implant survival and clinical outcomes were inferior to primary TKA. [212] (10.1302/0301-620x.107b12.bjj-2025-0184.r2)
• [L4] This study provides a high-accuracy method for surgical decision-making between TKA and UKA for KOA patients, requiring only standard X-rays and offering potential for clinical application in automated referrals and preoperative planning. [213] (10.1016/j.arth.2025.06.005)
• [L3] Preoperative patellar tilt angle does not significantly influence clinical outcomes or radiographic parameters following unicompartmental knee arthroplasty, as no significant differences were observed between normal and abnormal tilt groups in functional scores or complications. [215] (10.1186/s13018-026-06896-z)
• [L3] The 2-year failure rate was six times higher for UKA-to-UKA revision than after conversion to TKA. [216] (10.1016/j.arth.2025.04.023)
• [L3] Survivorship free from persistent PJI at 1 year is low at 76% but is consistent with similar reports of DAIRs for total knee arthroplasties. [217] (10.1016/j.arth.2020.02.036)
• [L3] Both groups exhibited survivorship higher than 90% at 15 years; however, preoperative coronal tibiofemoral subluxation ≥ five mm was associated with a higher risk of conversion to total knee arthroplasty due to aseptic loosening after mobile-bearing unicompartmental knee arthroplasty. [218] (10.1016/j.arth.2026.01.066)
• [L4] Aseptic revision from UKA to TKA provides excellent midterm implant survivorship, clinical outcomes, and radiographic results, particularly when performed for the progression of osteoarthritis. [219] (10.1002/ksa.70156)
• [L1] Based on current literature, UKA to TKA conversion is associated with a similar surgical site infection/PJI rate compared to primary TKA. [220] (10.1002/ksa.70228)
• [L4] Revision surgery for failed medial unicompartmental knee arthroplasty with bone loss using a lateral tibial plateau autograft and cemented posterior-stabilized implant resulted in improved Oxford Knee Scores and satisfactory mid-term outcomes. [221] (10.1007/s00167-015-3610-z)
• [L3] Reported complications were not uncommon, as nearly 40% of patients required a conversion to a TKA. [222] (10.1016/j.arth.2024.06.048)
• [L2] The outcomes of UKA in dependent and independent clinical studies do not differ significantly and are in line with arthroplasty register datasets. [225] (10.1007/s00402-020-03336-3)
• [L3] UKR has higher revision and slightly higher reoperation rates but lower mortality rates than matched TKR. [226] (10.1016/j.arth.2021.09.018)
• [L3] These findings underscore the importance of restoring the joint line to achieve optimal outcomes and survival after UKA for medial compartmental knee osteoarthritis. [228] (10.1016/j.arth.2026.02.042)
• [L4] UKA PJI results in substantial morbidity, and patients should be followed closely for aseptic causes of failure in addition to infection recurrence. [229] (10.1097/corr.0000000000000372)
• [L4] Participation in high-impact sports is not a risk factor for revision surgery, and timing of return typically ranges from 3 to 6 months. [230] (10.1016/j.jisako.2024.100338)
• [L3] In this study, IACI in a UKA doubled the risk of PJI compared to patients who did not receive an injection. [231] (10.1016/j.arth.2022.12.005)
• [L3] The data suggest that a wide exposure and thorough synovectomy be incorporated during the DAIR UKA to improve the likelihood of successful eradication of PJI at the 1-year mark. [232] (10.1016/j.arth.2024.03.057)

See Also

• Total Knee Replacement
• Anatomy
• Distal femoral osteotomy
• Knee osteoarthritis
• ACL reconstruction
• High tibial osteotomy
• Knee arthroscopy

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