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Anterior cruciate ligament injury

145 citationsUpdated Sep 2026

Overview¶

Anterior cruciate ligament (ACL) injury management requires a comprehensive assessment to provide a complete overview of treatment results, optimally including early adverse events, patient-reported outcomes, ACL graft failure, and clinical measures of knee function and structure [7]. This evaluation should maintain a minimum follow-up of 2 years with an optimal follow-up rate of 80% [7]. Clinicians must interpret limb symmetry indexes with caution, as these metrics can overestimate knee function after ACL injury [32]. Consequently, current variable return-to-sport criteria may not be stringent enough to ensure safe and successful return-to-sport [32].

Risk stratification is critical, as a history of ACL reconstruction constitutes a risk factor for further injury, with the highest risk occurring in the first year post-reconstruction [6]. Patients undergoing primary ACL reconstruction who also possess a strong family history of ACL tears are more likely to sustain a postoperative graft rupture or complication requiring surgery [18]. Ideally, particularly in younger patients, ACL reconstruction should not be delayed more than five months from injury [22]. In the context of associated pathologies, 34.9% of all meniscal injuries offer the potential for repair, a figure that rises to 55.6% when accompanied by anterior cruciate ligament damage [47].

Treatment options include nonoperative care, which a classification algorithm can help identify as suitable for individuals early after injury who have good potential for this approach [1]. For surgical candidates, functional results after ACL repair for acute tears are comparable to those after ACL reconstruction [17], and injury chronicity did not adversely affect failure rates or clinical outcomes at minimum 2-year follow-up after ACL repair [14]. In the paediatric population, ACL repair for proximal tears demonstrates the potential for excellent outcomes at short-term follow-up [15]. Surgeons can counsel patients with complex ACL injuries that comprehensive surgical management of concomitant injuries is associated with good long-term outcomes equivalent to those with less severe injury patterns [4]. Prevention programs are supported by AAOS Appropriate Use Criteria, where 69% of 48 patient scenarios were rated as likely appropriate or helpful for supervised rehabilitation [16]. Patient inquiries frequently focus on indications, management, technical details, and recovery timelines [167].

Anatomy & Pathophysiology¶

Ligament Anatomy¶

The anterior cruciate ligament (ACL) is an intra-articular ligament that is technically extrasynovial, as it is surrounded by synovium [100]. It runs from the femur to the tibia in an anterior–medial direction [100]. The ACL has a variable length ranging from 22 to 41 mm [100] and a variable width ranging from 7 to 12 mm [100], with a consistent narrowest point in the midsubstance [100]. It is composed of two bundles: the anteromedial (AM) and posterolateral (PL) bundles, named according to their tibial insertion [100].

The femoral origin of the ACL is on the posteromedial edge of the lateral femoral condyle, posterior to the lateral intercondylar ridge [100]. The femoral attachment is usually oval in shape [100]. The AM bundle arises from the superior and anterior aspects of the femoral attachment, while the PL bundle arises from the posterior and inferior aspects [100]. These bundles are often separated by the lateral bifurcate ridge, which runs from anterior to posterior on the femur [100]. Using a clock-face description of the posterior outlet of the femoral intercondylar notch, the bulk of the AM bundle is attached between 9:30 and 11:30 o'clock, and the PL bundle is attached between 8:30 and 10:00 o'clock [100]. The distance on the femur between the centers of the AM and PL bundles varies from 8 to 10 mm depending on knee size [100].

The tibial footprint of the ACL is located in the anterior intercondylar fossa between the medial and lateral tibial spines [100]. The tibial insertion is 120% larger than the femoral insertion and is positioned anterolateral to the medial tibial spine [100]. Some ACL fibers pass deep to the transverse meniscal ligament, while others merge with the anterior aspect of the lateral meniscus [100]. The AM bundle attaches to the anteromedial portion of the tibial footprint, and the PL bundle attaches to the posterolateral portion [100]. The center of the PL bundle is 4 ± 1 mm from the medial tibial spine, and the center of the AM bundle is 5 ± 1 mm from the medial tibial spine [100].

Functionally, the ACL is the main restraint against anterior tibial translation relative to the femur and prevents tibial rotation and varus/valgus rotation [131]. The ACL is approximately 32 mm in length and 7 to 12 mm wide [131]. It is composed of 90% type I collagen and 10% type III collagen, with a strength of 2,200 N [131]. The AM bundle is tightest in flexion and is primarily responsible for restraining anterior tibial translation [131]. The PL bundle is tightest in extension and looser in midflexion, which allows for rotation [131]. On the femoral side, the lateral intercondylar ridge demarcates the anterior edge of the ACL where the bifurcate ridge separates the two bundles [131].

The ACL receives its blood supply from the middle geniculate artery and its innervation from the posterior articular nerve, a branch of the tibial nerve [131]. The center of the ACL femoral footprint is 43% of the distance from the proximal to distal articular cartilage margin [98]. The center of the anteromedial bundle is 29.5% of the proximal to distal distance of the lateral femoral intercondylar notch, while the center of the posterolateral bundle is 50% of this distance [98]. The posterior edge of the ACL is 2.5 mm from the posterior articular cartilage border [98].

Direct insertion fibers are more critical than indirect insertion fibers in linking ligaments to bone [98]. The ACL inserts more anteriorly on a macroscopic level than on a histologic level [98]. The direct insertion is in a narrow area extending from the intercondylar ridge to a second osseous ridge 4 mm posterior, and direct fibers do not continue to the posterior articular cartilage [98]. Posterior fibers that extend to the articular cartilage are indirect fibers with a fanlike attachment [98]. The native ACL inserts on the tibia just anterior to the posterior part of the anterior horn of the lateral meniscus [98]. Tibial tunnel placement should include a portion of the anteromedial bundle footprint to provide optimal graft obliquity [98]. Graft placement anterior to the native footprint can cause impingement in extension, while placement posterior to the native footprint can cause impingement on the posterior cruciate ligament [98].

Injury Mechanisms & Risk Factors¶

The most common noncontact ACL injury mechanism involves a deceleration and rotational injury during running, cutting, or jumping activities [33]. The most common contact injury involves either hyperextension and/or valgus forces to the knee by a direct blow [33]. ACL injury is often associated with a “pop” heard by the patient at the time of injury [33]. Substantial knee swelling secondary to a hemarthrosis typically occurs within the first 4–12 hours following the injury [33]. Approximately 70% of patients hear or feel a “pop” at the time of injury, and almost all patients notice swelling of the knee within 6 to 12 hours of the injury [72]. Noncontact injuries usually occur during cutting or pivoting [72].

Female athletes have a two-fold to eight-fold higher risk of ACL injury than male athletes when level of competition, age, and time exposed are considered [72]. Differences in neuromuscular firing patterns in the quadriceps and hamstrings between males and females are felt to contribute to the higher rate of injuries among females [72]. Potential contributing factors to female ACL injury risk include ACL size, notch width anatomy, biomechanics, alignment, muscle strength, hormonal factors, and training [72]. However, the anatomical parameters of the knee joint (notch width index, ACL width and length) have no role in the cause of an injury [78]. Combinations of knee joint geometry measurements provided more information about the risk of noncontact ACL injury than individual measures, and the aspects of geometry that best explained the relationship between knee geometry and the risk of injury were different between males and females [108]. Altered bone morphological characteristics of the knee were found to be risk factors for ACL tears in contact injuries as well as noncontact injuries [157].

Knee torsional alignment is associated with ACL injury, predominantly in the distal femur rather than the proximal tibia [173]. Landing upright appears to be ACL harmful by increasing post-impact force and quadriceps muscle activity while decreasing knee flexion angles [174]. Increasing the knee flexion angle during jump landing may be an effective intervention to improve knee biomechanical risk factors associated with an ACL injury [112]. Jump direction significantly influenced knee biomechanics, suggesting that lateral jumps are the most dangerous of the stop-jumps [97]. Changing toe direction significantly affects knee kinetics and kinematics during landing [95]. Knee motion and knee loading during a landing task are predictors of anterior cruciate ligament injury risk in female athletes [132].

Frontal plane kinematic temporal relationships at the hip, knee, and ankle differ between genders, with components of dynamic knee valgus peaking during the deceleration phase in women and during the acceleration phase in men [127]. The study proposes an axial force theory to explain a major component of ACL injury based on kinematic differences [124]. Using waveforms, instead of discrete peak values of the knee abduction moment, may better represent risky movement patterns [120]. Contrary to clinical opinion, the findings indicate that knee abduction kinematics and kinetics during weight-bearing activities may not be risk factors for future ACL injury [130]. The lack of association of clinicodemographic risk factors in male athletes may highlight the need to focus on other factors such as kinematics for these athletes [168]. It is possible that decreasing tibial length relative to femoral length alters lower extremity biomechanics in such a manner that places the ACL at risk for injury [121]. The methods to quantify knee joint laxity may be used in conjunction with measures of neuromuscular control to identify high-risk female athletes [196]. Knee injury rates and patterns varied by sport, gender, and type of exposure [195]. Four typical injury patterns leading to ACL injury in women’s professional football differ significantly in terms of injury mechanisms and match situations, and most of the common ACL injury patterns identified in women’s professional football have great potential for injury prevention [88].

Pathophysiology & Associated Injuries¶

Most ACL injuries are complete disruptions, although disruption of a single anatomic bundle (anteromedial or posterolateral) may occur [72]. In the skeletally mature patient, the femoral insertion or the midsubstance is the most common site of disruption, and the tibial attachment may be avulsed with or without a piece of bone [72]. ACL tears most commonly involve the mid fibers (approximately 70%), with 7% to 20% of ACL tears occurring proximally at the femoral attachment and 3% to 10% occurring distally at the tibial insertion [77].

Bone bruises of the lateral femoral condyle and lateral tibial plateau are noted in up to 80% of ACL injuries [33]. Pivot-shift bone contusion patterns often appear as bone marrow edema at the lateral condylopatellar sulcus and the posterior aspect of the lateral tibial plateau [77]. The contusion occurs when the tibia is displaced anteriorly and impacts onto the lateral femoral condyle, a mechanism that can produce an osteochondral impaction fracture known as the deep femoral notch sign [77]. A contrecoup bone contusion in the posterior aspect of the medial tibial plateau has been described in ACL tears [77]. A Segond fracture is a small avulsion fracture of the peripheral lateral tibial plateau related to the lateral capsular ligament and/or slips from the iliotibial band or fibular collateral ligament [77].

Patients with an ACL tear who also have an osteochondral depression/impaction fracture have been reported to have an increased incidence of meniscal tears in the same knee and a relatively poor clinical outcome 1 year after ACL reconstruction [77]. An increased volume of bone marrow edema without fracture was not associated with a poor postoperative clinical outcome [77]. There is a high incidence of associated injuries, including meniscus tears [33]. The meniscus status has a significant impact on knee kinematics in the ACL-deficient knee [123]. Subtotal medial meniscectomy in knees with ACL deficiency altered knee kinematics, especially at high flexion angles [158]. Meniscal and anterolateral capsular structures may function as important secondary stabilizers in an ACL-injured knee [91]. Anatomic healing of medial knee structures is critical to maintain native knee kinematics [119]. Biomechanical studies demonstrate increased graft laxity and residual valgus rotational instability after ACL reconstruction alone in the setting of concomitant ACL/MCL injury [119]. This study found alterations in the native load-sharing relationships of the medial knee structures after injury [146].

At 10 to 20 years after the diagnosis, on average, 50% of those with a diagnosed anterior cruciate ligament or meniscus tear have osteoarthritis with associated pain and functional impairment [5]. There is a lack of evidence to support a protective role of repair or reconstructive surgery of the anterior cruciate ligament or meniscus against osteoarthritis development [5]. Osteoarthritis development in the injured joints is caused by intra-articular pathogenic processes initiated at the time of injury, combined with long-term changes in dynamic joint loading [5]. Variation in outcome is reinforced by additional variables associated with the individual such as age, sex, genetics, obesity, muscle strength, activity, and reinjury [5]. Within 10 years after ACL reconstruction, up to 80% show signs of posttraumatic knee osteoarthritis [35]. Clinical measures of knee function were most predictive of subsequent OA development following an extended period of rehabilitation early after ACL injury [86]. Patients who had radiographic knee OA 5 years after ACL reconstruction walked with lower knee adduction moments and medial compartment joint contact forces than did those patients without OA early after injury and reconstruction [181]. Biomechanical factors such as reduced knee adduction moment or reduced knee flexion angle during gait could serve as early indicators for OA risk and inform targeted rehabilitation interventions [116]. The correlation of synovial fluid biomarkers with subjective and objective measures of knee function, as well as with the risk of secondary osteoarthritis, is unknown [189]. The higher prevalence of articular cartilage injuries at revision ACLR may represent new injuries, and the lower prevalence of meniscus tears at revision ACLR may be caused by susceptible menisci being injured and treated at primary surgery or by changes in knee kinematics or injury exposure patterns [163].

Skeletally Immature Considerations¶

Over a 12-year period (1999 to 2011), the incidence of ACL ruptures increased by more than 400% compared with tibial spine fractures at Children’s Hospital of Philadelphia [21]. The relationship of the femoral origin of the anterior cruciate ligament and the distal femoral physeal plate in the skeletally immature knee has been studied anatomically [21]. Three-dimensional intercondylar notch volumes in a skeletally immature pediatric population have been compared between knees with torn and intact anterior cruciate ligaments [21]. The effect of trauma to the lower femoral epiphyseal plate has been studied experimentally in rabbits, as has the effect of intra-articular ACL reconstruction on the growth plates of rabbits [21]. Anterior cruciate ligament reconstruction in the skeletally immature has been studied using 3-dimensional magnetic resonance imaging reconstructions, and volumetric injury of the distal femoral physis during double-bundle ACL reconstruction in children has been studied using magnetic resonance imaging [21].

All-inside, physeal-sparing anterior cruciate ligament reconstruction does not significantly compromise the physis in skeletally immature athletes according to postoperative physeal magnetic resonance imaging analysis [21]. Growth disturbances without growth arrest have been observed after ACL reconstruction in children [21]. Substantial overgrowth was seen in two patients and minor limb-length discrepancies were seen in four additional patients following all-epiphyseal reconstructions in 12 prepubescent patients [21]. Females sustained more overuse injuries than males, but a large proportion of this sex discrepancy was attributable to differences in the types of sports played [21].

Classification¶

Tear Morphology and Grading Systems¶

Modified Sherman Grading System: This system classifies ACL tears by location into five types based on the percentage of tibial length remaining. Type I involves proximal avulsion with >90% of tibial length remaining; Type II is a proximal tear with 90%–75% length remaining; Type III is a midsubstance tear with 75%–25% length remaining; Type IV is a distal tear with 25%–10% length remaining; and Type V is a distal avulsion with <10% length remaining [74]. Medial meniscus tears are most prevalent in Type I ACL tears, which account for 8% of all ACL tears [70]. The plane in which an MRI scan is performed affects the classification of ACL tears [70].

Anterior Cruciate Ligament Injury Severity Scale (ACLISS): This tool documents and categorizes the magnitude of associated tissue damage in knees after primary ACL injury and reconstruction [23]. It allows for the easy and rapid identification of different injury severity profiles in patients who underwent primary ACL reconstruction [23].

Pediatric Classification: A classification system for ACL tears can guide a proper surgical plan in the pediatric and adolescent population [96]. The concept of precise description of ACL rupture patterns might lead to a more distinctive approach for reconstructive surgery [76].

Imaging and Diagnostic Reliability¶

Preoperative MRI assessment of ACL stump morphology is classified by location using the modified Sherman grading system, with arthroscopic assessment serving as the reference grade [74]. The agreement between classification grades on MRI and intraoperative arthroscopy can be assessed, with inaccurate MRI predictions analyzed for being within 1 classification grade different than intraoperative imaging [74].

Associated Injuries and Complexity¶

The incidence of medial meniscal lesions and the complexity of tear types increased significantly with increasing time intervals between the index injury and ACL reconstruction [175]. The posterior lateral meniscus root tear (PLMRT) is a common injury among patients undergoing ACL repair and can be arthroscopically classified into three different types [194]. In pediatric patients, delaying ACL reconstruction until skeletal maturity is complete may increase the risk of secondary meniscal and articular cartilage injury [222]. Time to surgery had a bivariate association with lateral and medial meniscal tears in pediatric patients undergoing ACL reconstruction [222]. Independent risk factors for the incidence of lateral meniscal tears in pediatric patients include younger age and return to sports activities before surgery [222]. Patients with 1 episode of instability had 3-fold higher rates of associated injuries in the context of delayed ACL reconstruction in pediatric patients [222].

Risk Factors and Injury Patterns¶

An increased lateral femoral condyle ratio is a risk factor for anterior cruciate ligament injury [53]. Lower body mass index, higher Beighton score, complete anterior cruciate ligament tear, and concomitant injuries to the medial collateral ligament, anterolateral complex, and meniscus (especially the posterior horn) are risk factors for preoperative high-grade pivot shift under anaesthesia [94]. Pooled analysis showed no significant association between contact injury and high-grade pivot shift (OR: 0.83; 95% CI: 0.31, 2.25; p = 0.7199) [94]. The anatomical parameters of the knee joint, including notch width index, anterior cruciate ligament width, and length, have no role in the cause of an injury [78]. Previous injury of any type does not increase the risk of suffering an ACL injury in men’s professional soccer [83].

Long-Term Consequences and Outcomes¶

At 10 to 20 years after diagnosis, on average, 50% of those with a diagnosed anterior cruciate ligament or meniscus tear have osteoarthritis with associated pain and functional impairment [5]. The highest rated studies reported low prevalence of knee osteoarthritis for individuals with isolated anterior cruciate ligament injury (0%-13%) and a higher prevalence of knee osteoarthritis for subjects with combined injuries (21%-48%) [198].

Clinical Presentation¶

History and Mechanism¶

The most common noncontact mechanism for ACL injury involves deceleration and rotational forces during running, cutting, or jumping activities [33]. Conversely, the most common contact mechanism involves hyperextension and/or valgus forces to the knee from a direct blow [33]. Approximately 70% of patients report hearing or feeling a "pop" at the time of injury [72]. Patients often describe a sensation of instability or the knee "giving out" during twisting activities [33]. Substantial knee swelling secondary to hemarthrosis typically occurs within 4 to 12 hours following the injury [33]. A patient who sustains a knee injury during sports activity followed by knee swelling within 1 to 6 hours should be evaluated carefully for a possible ACL injury [72]. Patients with chronic ACL injury may report recurrent episodes of knee instability, mechanical symptoms from secondary meniscal tears, or pain and swelling [72].

A clinical score based on patient interview items—pivoting/contact activity, perceived cracking sound, sensation of dislocation, joint effusion, suggestive mechanism, inability to resume activity, and immediate instability upon walking—can be used to assess the probability of an ACL tear and the need for specialist referral [51]. Combined medical history and physical examination have strong diagnostic value for ACL rupture when performed by an orthopaedic surgeon [44]. For primary care physicians, only medical history appeared to be of value in diagnosing ACL rupture, whereas physical examination did not add significant diagnostic value [44].

Physical Examination¶

The Lachman test is the most useful and sensitive test for diagnosing ACL injuries in the acute setting [33, 72]. It is performed with the knee in 20–30 degrees of flexion, applying an anterior force to the tibia while stabilizing the distal femur [33]. Laxity is graded as follows: * Grade 1: 1–4 mm of increased anterior translation compared to the contralateral knee [33]. * Grade 2: 5–9 mm of increased anterior translation compared to the contralateral knee [33]. * Grade 3: More than 10 mm of increased anterior translation compared to the contralateral knee [33].

An alternative grading system defines Grade 1 ACL injury as 3–5 mm of increased anterior tibial translation, Grade 2 as 5–10 mm, and Grade 3 as 10–15 mm [72]. The anterior drawer test is performed with the knee in 90 degrees of flexion and is less sensitive than the Lachman test for evaluating anterior tibial translation [33].

The pivot shift test (Losee test) evaluates rotational instability and is considered the most functional test to evaluate knee stability after ACL injury [33]. It is pathognomonic for ACL injury and is best performed in the chronic setting [72]. A positive pivot shift test occurs when the anterolateral tibial plateau reduces with a visible shift at the lateral joint line as the iliotibial band passes posterior to the axis of knee rotation at approximately 15 degrees of knee flexion [72]. MCL injury and some meniscal tears may produce a false-negative pivot shift test [33]. Examination under anesthesia is useful for obtaining a more accurate pivot shift test in patients with an unclear history of instability and an equivocal office examination [33]. In the acute setting, aspiration of a hemarthrosis can decrease pain and improve the quality of the physical examination [33].

The knee should be palpated carefully with attention to joint lines and the origins/insertions of the MCL and posterolateral corner to evaluate for associated injuries [72]. Patient apprehension on movement of the patella should be noted because acute patellar dislocations can present with a history similar to ACL injury [72]. Quadriceps and patellar tendons should be examined in the acute setting because tendon ruptures may be confused with ACL injuries [72]. Neurovascular injury must be ruled out by assessing motor and sensory function and pedal pulses, particularly in multiligament injuries from high-energy trauma [72]. Female athletes exhibit greater rotatory knee laxity than male athletes, which may serve as a baseline for identifying patients with increased laxity [101].

Imaging¶

Plain radiographs of the knee should be obtained to rule out fractures about the knee [33]. The Segond sign, an avulsion of the anterolateral capsule of the tibia, may be seen on plain radiographs and is associated with ACL injury [33]. In more than one-quarter of patients, plain radiographs may help establish the diagnosis of an ACL tear [45]. A positive finding of the Tuberculum Intercondylare Tibiae Tertium on radiographs is a relevant sign for the diagnosis of an ACL lesion [54].

MRI is the most useful examination for evaluating associated injuries and can diagnose an ACL tear with 95% or better accuracy [33]. Bone bruises of the lateral femoral condyle and lateral tibial plateau are noted in up to 80% of ACL injuries on MRI [33]. MRI evaluation showed that anterolateral ligament (ALL) injuries are present in 60.2% of acute ACL injuries in adolescent patients [60]. However, ALL injuries are not reliably diagnosed on MRI in the setting of an ACL tear, and physicians should not rely on MRI to diagnose an ALL injury in the presence of an ACL injury [46].

Isolated ACL tears are less common than combined injuries involving secondary stabilizers such as the medial meniscus, lateral meniscus root, or ALL [114]. Specifically, 53% to 56% of patients presenting with initially diagnosed isolated ACL ruptures had concomitant injuries to the Kaplan Fiber Complex [48]. Instrumented laxity evaluations, such as the KT-1000 arthrometer, can augment the physical examination and provide an objective baseline for future comparison [33]. The KT-1000 arthrometer measures anterior translation of the tibia with the knee in 20–30 degrees of flexion using standard forces [33].

Associated Injuries and Risk Factors¶

There is a high incidence of associated injuries with ACL tears, including meniscus tears [33]. Secondary meniscal tears after ACL injury are most common among patients undergoing delayed surgical or nonoperative treatment of their primary ACL injuries [63].

Risk factors for ACL injury include: * An increased lateral femoral condyle ratio [53]. * Pre-injury leg length discrepancy in the skeletally immature athlete [52]. * Marked deviations in posterior tibial slope, which could be a predisposing risk factor for subsequent contralateral ACL tear [104].

Patients undergoing primary ACL reconstruction with a strong family history of ACL tears are more likely to sustain a postoperative graft rupture or complication requiring surgery [18].

Investigations¶

Clinical History and Physical Examination¶

The most common contact ACL injury mechanism involves hyperextension and/or valgus forces to the knee by a direct blow [33]. Patients often report hearing a "pop" at the time of injury, though this history is not specific to ACL injury [33]. Substantial knee swelling secondary to hemarthrosis typically occurs within the first 4–12 hours following an ACL injury [33]. Aspiration of a hemarthrosis can decrease pain and improve the quality of the physical examination in the acute setting [33]. Approximately 90% of ACL tears can be diagnosed with a pertinent clinical history and a thorough orthopaedic physical examination [77]. The ACLIS score was developed to assess the probability of ACL tear and need for specialist referral based on patient-interview information [51]. The ACLIS score includes items such as pivoting/contact activity, perceived cracking sound, sensation of dislocation, joint effusion, suggestive mechanism, inability to resume activity, and immediate sensation of instability [51].

The Lachman test is the most useful and sensitive test for diagnosing anterior laxity of the knee [33]. Lachman test laxity is graded by comparison to the uninjured contralateral knee, with Grade 1 defined as 1–4 mm of increased translation [33]. Grade 2 Lachman laxity is defined as 5–9 mm of increased translation compared to the contralateral knee [33]. Grade 3 Lachman laxity is defined as more than 10 mm of translation compared to the contralateral knee [33]. The anterior drawer test is less sensitive than the Lachman test for evaluating anterior tibial translation [33]. The pivot shift test (Losee test) evaluates rotational instability associated with an ACL tear [33]. An examination under anesthesia is useful for obtaining a more accurate pivot shift test in patients with equivocal office examinations [33].

Plain Radiography¶

The Segond sign, an avulsion of the anterolateral capsule of the tibia, may be seen on plain radiographs [33]. In more than one-quarter of patients, plain radiographs may help to establish the diagnosis of an ACL tear [45]. Before skeletal maturity, an avulsion of the tibial insertion of the ACL can be seen radiographically [33]. A positive finding of the tuberculum intercondylare tibiae tertium ought to be included in the group of radiologic signs relevant for the diagnosis of an ACL lesion [54]. Multiple radiographic parameters were significantly associated with ACL injuries when compared with age-matched controls [223].

Magnetic Resonance Imaging (MRI)¶

MRI is the imaging study of choice for the diagnosis of ACL pathology [77]. The accuracy of MRI for the diagnosis of ACL tears has been shown to be 95% to 100% [77]. T2-weighted sequences, preferably with fat saturation, are recommended over T1-weighted sequences for ACL evaluation [77]. An intact ACL demonstrates taut fibers paralleling the intercondylar roof on sagittal MRI studies [77]. Confirmation of an intact ACL on both axial and coronal views is critical for accurate diagnosis [77]. The primary MRI feature of a complete ACL tear is the identification of complete disruption of ligament fibers [77]. A contrecoup bone contusion in the posterior aspect of the medial tibial plateau is a secondary MRI sign of an ACL tear [77].

ACL tears most commonly involve the mid fibers, occurring in approximately 70% of cases [77]. Proximal ACL tears at the femoral attachment occur in 7% to 20% of cases [77]. Distal ACL tears at the tibial insertion occur in 3% to 10% of cases [77]. MRI findings suggesting a partial ACL tear include increased T2 signal/edema along the course of the ligament with predominantly intact fibers [77]. Abrupt angulation of intact fibers or marked attenuation of the fibers are MRI findings suggesting a partial ACL tear [77]. On axial imaging, narrowing of the transverse dimension with a normal anterior-posterior dimension has been described as a stable partial tear [77]. Complete absence of the anteromedial or posterolateral bundle on axial imaging suggests an unstable partial tear [77]. A 2014 study reported that 32% of suspected ACL injuries were single bundle tears [77]. There were three times as many anteromedial bundle tears as posterolateral bundle tears in a 2014 study of suspected ACL injuries [77]. 3-Tesla MRI in the oblique coronal plane yielded significantly greater specificity (92% to 96%) for selective bundle tears than imaging in conventional orthogonal planes (67%) [77].

Pitfalls in ACL diagnosis include increased T2-weighted signal abnormality resulting from chronic mucoid or cystic degeneration of the ACL [77]. An ACL ganglion is best identified on MRI as a globular cystic structure within the ACL with intact fibers [77]. MRI is unreliable for determining the precise location of an ACL tear [145]. MRI accurately predicted the ACL tear type seen arthroscopically in only 55.9% of patients [161]. Poor agreement was found between imaging and arthroscopic assessment of ACL tear location, with MRI predicting intraoperative location in less than half of cases [186]. MRI may not be completely reliable in assessing the degree and location of an ACL tear, and surgeons should not solely rely on MRI for ruling out possible ACL repair [144].

ALL injuries were not reliably diagnosed on MRI in the setting of an ACL tear [46]. Physicians should not rely on MRI to diagnose an ALL injury in the presence of an ACL injury [46]. MRI evaluation showed ALL injuries are present in 60.2% of acute ACL injuries in adolescent patients [60]. Standard preoperative MRI scans can reliably be used to visualize Kaplan fiber injury in the majority of pediatric and adolescent patients with ACL tears, especially when performed in the acute setting [159]. The authors question the clinical utility of MRI for definitive diagnosis of Kaplan fiber complex injury and caution against using these findings to determine patients for lateral extra-articular augmentation [226]. No correlation has been shown between Kaplan fiber complex injury and increased anterolateral rotatory laxity or subjective instability symptoms [226].

The diagnostic ability of MRI to predict meniscal injuries present at acute ACL reconstruction was moderate, with performance being poorest at the lateral meniscus [140]. The diagnostic validity of magnetic resonance imaging is similar for meniscal tears in acute knee trauma and in knee symptoms lasting over 6 months in young adults [164]. Identification of medial bone bruising on pre-operative MRI following acute ACL rupture should raise suspicion of an associated postero-medial meniscal tear [214]. At the time of acute ACL injuries, posterior root tears of the lateral meniscus do not appear to result in meniscal extrusion on MRI [221]. Spontaneous anterior tibial subluxation on MRI in complete ACL tear was significantly associated with medial meniscal tear and accident-to-MRI time [229]. Patients with an ACL tear and an osteochondral depression/impaction fracture have an increased incidence of meniscal tears in the same knee [77]. Patients with an ACL tear and an osteochondral depression/impaction fracture have a relatively poor clinical outcome 1 year after ACL reconstruction [77]. Increased volume of bone marrow edema without fracture is not associated with a poor postoperative clinical outcome [77].

MRI is a sensitive measure of cruciate and collateral ligament injury in acute knee dislocation [176]. MRI does not reliably diagnose injury to the posterolateral corner or meniscus in acute knee dislocation [176]. A higher index of suspicion is required during arthroscopy to prevent misdiagnosis of posterolateral corner or meniscal injury in knee dislocation [176]. Early recognition of bipolar ACL injury via MRI is critical [49].

Instrumented Laxity and Other Imaging¶

Instrumented laxity evaluations can augment the physical examination and provide an objective baseline for future comparison [33]. The KT-1000 arthrometer uses a series of standard forces to measure anterior translation of the tibia with the knee in 20–30 degrees of flexion [33]. Dynamic ultrasonography has been reported to have a diagnostic accuracy of 88%, sensitivity of 90%, and specificity of 83% in the evaluation of medial plica syndrome [64]. MRI or ultrasound may be helpful to confirm the diagnosis of a pathologic synovial plica [64]. Abnormal plica is diagnosed best by arthroscopic examination of the knee [64].

Other Considerations¶

The clinical utility of imaging-based measurement methods for the determination of ACL injury risk requires more reliable techniques that demonstrate consistency between studies [61]. An increased lateral femoral condyle ratio measured by MRI is associated with higher risk of noncontact ACL injury [228]. Specific osseous morphologic characteristics are associated with ACL injury in male college football players [230]. Osseous morphological risk factors should be considered in individualized anatomic ACL reconstructions to achieve optimal outcomes [231]. AI can extract and synthesize 3D anatomic signatures from routine MRI for morphometric ACL injury risk research [225].

Treatment¶

Non-Operative¶

Nonoperative management is typically reserved for patients with low activity demands or few instability complaints [34]. This approach includes physical therapy to regain range of motion and strength, bracing, and lifestyle modification [34]. A classification algorithm can prospectively identify individuals early after injury who are suitable for nonoperative care or delayed surgery [1]. Prediction models incorporating knee function measures can estimate 2-year prognoses for nonsurgical treatment [26]. Short-term progressive exercise therapy is well tolerated and should be incorporated in early-stage rehabilitation to improve function before reconstruction or as a first step in nonoperative management [139]. For selected older patients or those with lower activity demands, non-ACLR treatment may achieve satisfactory return-to-sport outcomes [154]. However, chronic ACL deficiency increases the risk of meniscal and cartilage pathology [34], and prolonged nonoperative therapy for complete rupture remains controversial due to risks of further joint damage and recurrent instability [40]. Knee laxity increases bilaterally during the first year after non-surgical treatment [171]. Patients treated non-operatively or with delayed treatment experience more instability and inability to return to previous activity levels compared to those treated with early surgical stabilization [203]. In the paediatric population, conservative management permits return to normal life and sports without a major increase in meniscal tears [149], although initial nonoperative treatment carries a high risk of additional meniscal and chondral injury that may result in long-term impairment [183]. Patients with ACL tears treated non-operatively have developed secondary meniscal lesions requiring delayed surgical management [107].

Operative¶

Indications: Surgical treatment is indicated for young patients, those involved in jumping, cutting, and pivoting sports, manual laborers, and patients with concomitant injuries requiring surgery [34]. Early ACL reconstruction is recommended to prevent secondary meniscal tears [162]. In active, skeletally immature patients, surgical management is the preferred strategy to stabilize the knee, protect cartilage and menisci, and allow safe functional participation in cutting and pivoting activities [188].

Surgical Approach / Technique: The standard of care is anatomic reconstruction using patellar tendon, hamstring, or quadriceps autograft or allograft tissue [34]. Graft tunnels must be placed in the center of the anatomic ACL femoral and tibial footprint, as tunnel malpositioning is the most common reason for graft failure [34]. Reconstruction can be performed as a single- or double-bundle technique [34]. Double-bundle reconstruction is technically more demanding but may result in improved stability [34]. In a Swedish National Knee Ligament Registry study, single-bundle reconstruction carried an increased risk of revision surgery compared with double-bundle (adjusted hazard ratio 1.98, 95% CI 1.12 to 3.51, P = 0.019) [34]. The risk of revision surgery was slightly reduced when an anatomic single-bundle technique was used compared with a nonanatomic single-tunnel technique (adjusted HR 1.87, 95% CI 1.04 to 3.38, P = 0.037) [34]. An osteotomy should be considered if there is evidence of malalignment [34]. A LEAP (lateral extra-articular procedure) is not always innocuous and carries the risk of certain complications; it should not be used ubiquitously in every primary ACLR [41].

Graft Selection: Autograft offers faster healing, less immune reaction, and no risk of disease transmission, but is associated with increased postoperative pain [34]. Patellar tendon autograft provides bone-to-bone healing and is often considered the benchmark, but has the highest incidence of anterior knee pain [34]. Hamstring autograft uses a smaller incision but can result in permanent decreased hamstring strength, a risk factor for graft rupture [34]. Allograft has less donor site morbidity but a higher failure rate in the young athletic population [34]. High-level evidence suggests allograft has a higher failure rate in young patients than autograft and should be avoided in children undergoing ACL reconstruction [188]. One study of 354 patients showed a 2.6 times risk of graft failure with allograft supplementation compared with no supplementation, when controlled for age and graft size [188]. Patellar tendon grafts are generally suboptimal in young children due to the potential for forming a tethering bony bridge across the epiphyseal plate if bone plugs are placed or fixed in the area of the physis [188]. Hamstring, soft-tissue quadriceps tendon, and iliotibial band (ITB) autograft are the most common graft choices in skeletally immature patients [188]. Physeal-sparing techniques have demonstrated successful clinical results with few reported instances of growth disturbance [188]. In adolescents approaching skeletal maturity with minimal growth remaining (skeletal age: older than 13 years for girls, older than 14 years for boys), traditional transphyseal ACL reconstruction can be considered because the potential for clinically significant growth arrest is minimal [188]. For younger patients, traditional techniques involving graft bone plugs or implants across the physis can adversely affect the growing athlete’s physis [188]. Otherwise, transphyseal ACLR has satisfactory clinical outcomes, with good subjective outcomes, function level, and knee stability [136].

Concomitant Injuries: Clinical outcomes of patients who underwent meniscus repair were better than those who underwent meniscus resection with concurrent ACL reconstruction [134]. Most isolated medial collateral ligament (MCL) injuries are treated nonsurgically, while concomitant damage to the anterior or posterior cruciate ligaments is a common indication for surgical management of high-grade injuries [166]. Nonoperative and operative treatments of MCL injuries lead to equally good results [187]. The strategy of immediate repair of the MCL and reconstruction of the ACL when conservative treatment has failed seems safe and effective [118].

Rehabilitation and Return to Sport: Postoperative rehabilitation focuses on early range of motion, immediate weight bearing, and regaining quadriceps control [34]. Bracing treatment can be considered, but there is no evidence this positively affects outcomes [34]. This is followed by eccentric strengthening, isometric hamstring contractions, and quadriceps strengthening [34]. Functional training after 6 months aids in injury prevention, and return to sports is usually achieved around 9 months [34]. Functional bracing at return to sports has been used but lacks high-level evidence [34]. Current literature recommends that full return to levels I or II sport be withheld until at least 9 months [150]. Athletes who pass all criterion-based RTS testing and return after 9 months are 84% less likely to reinjure their knee within 2 years [150]. An athlete’s reinjury rate is reduced by 51% for each month that RTS is delayed until 9 months, with similar risk reduction persisting until 12 months [150]. Those who do not meet recommended RTS criteria may have up to a fourfold greater risk of rerupture [150]. Not achieving a ≥90% quadriceps index and returning to level I sport before 9 months postoperatively are independent risk factors of rerupture [150]. Patients who returned to level I sport after surgery had 30% rerupture rates at 2 years, compared with 8% in those who returned to lower level sports [150]. In a sample of more than 100 young athletes cleared for RTS, only 13.9% passed all combined measures (hop testing and strength), with 27.8% meeting strength cutoffs and 53% meeting hop testing cutoffs individually [150]. Of 120 young athletes assessed at the same RTS time point, 56% returned to their preinjury level of sport at 1 year, 23% did not resume their preinjury level, and 21% sustained second ACL injuries [150]. Limb symmetry indexes can overestimate knee function after ACL injury, raising concern whether current RTS criteria are stringent enough [32]. RTS decision making should not be based on time alone [184]. The 2016 consensus group defined an RTS continuum, emphasizing a criterion-based progression from return to participation to RTS to return to performance [184]. Evidence strongly supports that patients should pass stringent RTS criteria before beginning on-field rehabilitation and returning to participation [184]. Emerging evidence suggests that assessment of psychologic readiness may also inform RTS decisions [184].

Outcomes and Complications: Only approximately 63% of affected patients actually return to preinjury sports participation after ACL reconstruction [35]. The rate of return to preinjury sports participation rises to 83% in elite athletes following ACL reconstruction [35]. Within 2 years after ACL reconstruction, as many as 20% sustain a second ACL injury to either the surgical or nonsurgical knee, with a slightly higher risk to the nonsurgical knee [35]. The top reasons for reduced sports participation include fear of reinjury, problems with structure/function of the knee, and family commitments or lifestyle changes [35]. An ACL injury impairs knee-related QoL for up to 35 years, with no difference between treatment approaches (initial repair or later reconstruction compared with nonsurgical treatment) [30]. Estimates of patient-reported outcomes exceeded clinically important thresholds, highlighting the importance of assessing these constructs when managing individuals with ACL injuries [20]. Patients with an ACL rupture need to be counselled appropriately, and efforts to prevent these injuries must be redoubled [28]. Reconstruction after an ACL injury does not reduce the osteoarthritis risk but lowers the total knee arthroplasty rate [11]. Complications of ACL reconstruction include infection, loss of motion, arthrofibrosis, infrapatellar contracture syndrome, patellar tendon rupture and patella fracture from graft harvest, complex regional pain syndrome, hardware failure, tunnel osteolysis, local nerve irritation, cyclops lesion, graft failure, and late arthritis [34].

Primary Repair and Timing: Injury chronicity did not adversely affect failure rates or clinical outcomes at minimum 2-year follow-up after ACL primary repair [14]. Functional results after ACL repair for acute tears are comparable to those after ACL reconstruction [17]. Despite promising clinical outcomes, the pulley technique for primary arthroscopic repair of partial proximal ACL tears should not be widely adopted unless it has been compared directly with ACL reconstruction [66]. ACLR had a beneficial effect on knee outcomes, with acute-stage ACLR leading to better outcomes in subgroup analysis [122]. Delayed ACL reconstruction resulted in success for a majority of the ACL-reconstructed children [137]. The improvement rate was 24.6% among patients who did not receive ACLR in the acute phase and underwent ACLR in the chronic phase [135]. Patients in the ACLR group had higher future knee-related self-efficacy and were active at a higher level of physical activity at 8 and 12 months after treatment compared to those treated with rehabilitation alone [117]. Surgical reconstruction as a management strategy for patients with long-standing ACL injury is more effective, but more expensive, at 18 months compared to rehabilitation management [87]. Three ACL intervention programs successfully reduced noncontact ACL injury incidence rates in female adolescent athletes [193].

Complications¶

Graft Failure and Revision: Recurrent instability due to graft failure is estimated to occur in 0.7% to 8% of ACL reconstructions [218], though recent reports suggest a range of 10% to 25% failures [218]. Early failure, usually within the first 6 months, most often results from technical errors [218]. In a series of failed reconstructions, nonanatomical graft placement was prevalent [10]. Factors potentially involved in failure include surgical technique, graft material selection, graft incorporation issues, integrity of secondary restraints, condition of articular and meniscal cartilage, postoperative rehabilitation, and patient motivation and expectations [218]. Registry data indicate that single-bundle reconstruction carries an increased risk of revision surgery compared with double-bundle reconstruction (adjusted hazard ratio 1.98, 95% CI 1.12 to 3.51, P = 0.019) [34]. However, the risk for single-bundle reconstruction is slightly reduced when an anatomic single-bundle technique is used as compared with a nonanatomic single-tunnel technique (adjusted hazard ratio 1.87, 95% CI 1.04 to 3.38, P = 0.037) [34]. Hamstring grafts demonstrate a higher risk of revision, with hazard ratios of 1.41 to 2.3 in Norwegian and Danish registries [215]. Additionally, the likelihood of needing revision ACL reconstruction is 0.82 times lower for every 0.5 mm increase in graft diameter from 7.0 to 9.0 mm [215]. Risk of ACL graft tear is significantly greater in males than females, and in male patients with a chronologic age of 16 years compared to those >16 years [89].

Infection: In a review of 7096 consecutive arthroscopic ACL reconstructions, 36 cases (0.51%) developed postoperative septic arthritis [218]. This comprised 24 primary reconstructions (0.41%) and 12 revision reconstructions (1.01%) [218]. Eradication of septic arthritis was achieved in all patients after a mean of 2.25 ± 1.22 procedures, with graft retention in all but one patient (97.2%) [218]. The mean duration of antibiotic treatment was 5.4 ± 2.3 weeks [218]. Coagulase-negative staphylococci (62.5%) and Staphylococcus aureus (21.9%) were the most common pathogens [218]. No emergence or deterioration of osteoarthritis related to infections was observed [218]. Diabetics had an 18.8-times higher odds of postoperative infection than healthy patients [218]. In a separate review of 4933 patients, superficial infections occurred in 10 patients (0.20%) and deep infections in 7 patients (0.14%) [218]. Tobacco use is associated with increased complications after anterior cruciate ligament reconstruction [10].

Motion Deficits and Stiffness: The most common postoperative complications are motion deficits, primarily extension, and persistent anterior knee pain [218]. Reported frequencies of motion loss range from 1% to 13%, while postoperative pain ranges from 0% to 34% [218]. Intraoperative factors associated with motion deficits include incorrect tunnel position and inadequate notchplasty, which can result in overtightening or impingement of the graft, leading to loss of extension [218]. Collateral ligament surgery and meniscal repair surgery have also been reported to contribute to motion loss [218]. Postoperative factors include prolonged immobilization and inadequate or inappropriate rehabilitation [218]. Preoperative effusion, limited range of motion, and concomitant knee ligament injuries make poor postoperative motion more likely [218]. Loss of normal knee motion after reconstruction is associated with radiographic arthritic changes after surgery [165].

Venous Thromboembolism: In a review of 4933 patients after ACL reconstruction, symptomatic DVT requiring treatment occurred in 27 patients (0.55%) and pulmonary embolism in 6 patients (0.12%) [218]. Risk factors for developing DVT in the 30-day postoperative period include age over 30 years, concomitant high tibial osteotomy, microfracture, hypertension requiring medication, and presence of wound infection [218]. In a study of multiligament knee reconstruction with thromboprophylaxis, the frequency of symptomatic venous thromboembolism was low [3].

Graft Harvest Complications: Patellar tendon autograft is associated with the highest incidence of anterior knee pain [34]. Hamstring autograft can result in permanent decreased hamstring strength, which is a risk factor for graft rupture [34]. Intraoperative complications of ACL surgery include patellar fracture, inadequate graft length, mismatch between the bone plug and tunnel sizes, graft fracture, suture laceration, violation of the posterior femoral cortex, and incorrect femoral or tibial tunnel placement [218]. Bilateral magnetic resonance imaging and functional assessment of the semitendinosus and gracilis tendons a minimum of 6 years after ipsilateral harvest has been performed [3]. Hamstring strength recovery after hamstring tendon harvest varies by graft type [3].

Other Considerations: In a review of 4933 patients, return to the operating room occurred in 18 patients (0.36%) [218]. Major complications occurred in 27 patients (0.55%) and minor complications in 43 patients (0.87%) [218]. A LEAP procedure carries the risk of certain complications and should not be used ubiquitously in every primary ACLR [41]. In a study of 3605 military members with knee injuries, 10% had developed posttraumatic arthritis at an average of 4 years after injury, with knee dislocation associated with the highest odds of developing posttraumatic arthritis [92]. In a series of 119 patients with knee dislocations treated at a Level 1 trauma center, 32% had early complications and 9% required amputations [92]. In the same series, 47 patients (39%) required at least one unplanned secondary operation to treat instability or other complications [92]. Heterotopic ossification has been reported to occur in over 30% of patients with knee dislocations and may result in a stiff knee with loss of motion [92]. In a study of 91 patients with knee dislocations, PCL reconstruction was the only independent predictor of heterotopic ossification [92]. Patients with popliteal artery injuries that require bypass grafting have significantly lower knee function scores than those with vascular injury [92].

Recovery¶

Light activity (weeks): The provided evidence does not specify a typical week range for light activities such as 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, and final functional outcomes.

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

Functional milestones: The provided evidence does not report validated patient-reported outcome measure trajectories or specific outcome-measure benchmarks.

Other Considerations: Fifty-five percent of patients return to competitive sport following anterior cruciate ligament reconstruction surgery [12]. Among elite athletes, eighty-three percent return to preinjury sport after anterior cruciate ligament reconstruction [12]. Psychological responses influence the return to preinjury sport levels [12]. Gait patterns differ between ACL-reconstructed athletes who pass return-to-sport criteria and those who fail [12]. Biomechanical measures during landing and postural stability predict second anterior cruciate ligament injury after reconstruction and return to sport [12]. Self-reported fear predicts functional performance after anterior cruciate ligament reconstruction [12]. Neuroplasticity associated with anterior cruciate ligament reconstruction involves increased activity in multiple regions of the brain compared with control subjects during active knee extension and flexion [12].

At short-term follow-up, ACL repair using an Internal Brace enables sports activity and provides a sense of well-being similar to that of classic ACL reconstruction using hamstring or quadriceps tendon autografts in a selected patient population [201]. Good functional performance and knee muscle strength can be achieved and maintained over time in the majority of patients with ACL injury treated with rehabilitation and early activity modification but without reconstructive surgery [147].

An ACL injury impairs knee-related quality of life for up to 35 years, with no difference between treatment approaches (initial repair or later reconstruction compared with nonsurgical treatment) [30]. Patients with ACL injuries treated with ACL reconstruction and patients with ACL and meniscus injuries treated with ACL reconstruction and meniscectomy are less likely to undergo total knee arthroplasty at mid- to long-term follow-up compared with patients treated nonoperatively [79]. The study of nonoperative treatment of anterior cruciate ligament injury had a favorable long-term outcome regarding incidence of radiographic knee osteoarthritis, knee function and symptoms, and need for ACL reconstruction [73]. Clinical measures of knee function were most predictive of subsequent osteoarthritis development following an extended period of rehabilitation early after ACL injury [86]. Osteochondral damage begins as early as 7 days after ACL injury, far earlier than the traditionally recognized 4-week timeline [224].

In the 24 months after ACL reconstruction and return to sport, patients are at a greater risk to suffer a subsequent ACL injury compared with young athletes without a history of ACL injuries [85]. After ACL reconstruction in patients aged 18 years and younger, a further ACL injury occurred in 1 in 3 patients over 15 years [81]. In a 5- to 8-year follow-up, one out of every ten patients had a contralateral ACL rupture, and two out of every ten patients had siblings with a history of ACL rupture [75]. Patients undergoing primary ACL reconstruction as well as a strong family history of ACL tears are more likely to sustain a postoperative graft rupture or complication requiring surgery [18]. Increasing time from injury to ACL reconstruction was associated with increased incidence of secondary injury seen in the trochlea, lateral femoral condyle, medial tibial plateau, and medial meniscus [235]. In female patients who experienced an ACL injury, a delay in surgery greater than 12 months is associated with a gradual increase in the risk of nonrepairable medial meniscal tear; this risk becomes statistically significant after 24 months [93]. Patients who waited a long time to have ACL reconstruction had more cartilage damage and loss than patients who did not wait a long time [232].

Key Evidence¶

[L3] The classification algorithm is an effective tool for prospectively identifying individuals early after anterior cruciate ligament injury who want to pursue nonoperative care or must delay surgical intervention and have good potential to do so. [1] (10.1177/0363546507308190)
[L3] Surgeons can counsel patients with complex ACL injuries that comprehensive surgical management of concomitant injuries is associated with good long-term outcomes equivalent to those with less severe injury patterns. [4] (10.1177/03635465261443315)
[L4] [5] (10.1177/0363546507307396)
[L2] A history of anterior cruciate ligament reconstruction is a risk factor for further injury, with the highest risk in the first year after reconstruction. [6] (10.1177/03635465010290021301)
[L5] A comprehensive assessment after ACL treatment should aim to provide a complete overview of the treatment result, optimally including early adverse events, patient-reported outcomes, ACL graft failure, and clinical measures of knee function and structure, with a minimum follow-up of 2 years and an optimal follow-up rate of 80%. [7] (10.1177/2325967120934751)
[L3] [11] (10.1177/23259671261451241)
[L3] Injury chronicity did not adversely affect failure rates or clinical outcomes at minimum 2-year follow-up after ACLPR. [14] (10.1002/arj.70193)
[L4] ACL repair for proximal ACL tears in the paediatric population demonstrates the potential for excellent outcomes at short-term follow-up. [15] (10.1007/s00167-020-05872-2)
[L5] The AAOS developed Appropriate Use Criteria for ACL injury prevention programs using the RAND/UCLA Appropriateness Method, where 69% of 48 patient scenarios were rated as likely appropriate/helpful for supervised rehabilitation programs. [16] (10.5435/jaaos-d-16-00756)
[L1] Functional results after ACL repair for acute tears are comparable to those after ACLR. [17] (10.1177/2325967120s00326)
[L3] Further, patients undergoing primary ACLR as well as a strong family history of ACL tears are more likely to sustain a postoperative graft rupture or complication requiring surgery. [18] (10.1177/2325967120959665)
[L2] Estimates exceeded clinically important thresholds, highlighting the importance of assessing these constructs when managing individuals with ACL injuries. [20] (10.1177/23259671211021592)
[L3] Ideally, and particularly in younger patients, ACL reconstruction should not be delayed more than five months from injury. [22] (10.1302/0301-620x.95b1.29636)
[L3] The ACLISS allowed to easily and rapidly identify different injury severity profiles in patients who underwent primary ACLR. [23] (10.1007/s00167-023-07311-4)
[L2] Prediction models including knee function measures can estimate 2-year prognoses for nonsurgical treatment. [26] (10.1177/2325967118774255)
[L5] Patients with an ACL rupture need to be counselled appropriately, and efforts to prevent these injuries must be redoubled. [28] (10.1302/0301-620x.104b5.bjj-2022-0239)
[L2] An ACL injury impairs knee-related QoL for up to 35 years, with no difference between treatment approaches (initial repair or later reconstruction compared with nonsurgical treatment). [30] (10.1177/03635465231218237)
[L2] These findings raise concern whether the variable ACL return-to-sport criteria utilized in current clinical practice are stringent enough to achieve safe and successful return-to-sport. [32] (10.2519/jospt.2017.7285)
[L5] Prolonged nonoperative therapy for complete ACL rupture remains controversial due to the risk of further joint damage and recurrent instability. [40] (10.1155/2012/932702)
[L4] However, a LEAP is not always an innocuous procedure and carries the risk of certain complications, and should not be used ubiquitously in every primary ACLR. [41] (10.1016/j.jisako.2022.10.004)
[L3] Combined medical history and physical examination have strong diagnostic value in ACL rupture diagnostics performed by an orthopaedic surgeon, whereas for the primary care physician, only medical history appeared to be of value. [44] (10.1007/s00167-013-2769-4)
[L4] In more than one-quarter of patients, plain radiographs may help to establish the diagnosis of an ACL tear. [45] (10.1007/s00167-014-3022-5)
[L3] However, ALL injuries were not reliably diagnosed on MRI in the setting of an ACL tear, and physicians should not rely on MRI to diagnose an ALL injury in the presence of an ACL injury. [46] (10.1016/j.arthro.2019.09.039)
[L4] According to current standard indications, 34.9% of all meniscal injuries offer the potential for repair, rising to 55.6% when accompanied by anterior cruciate ligament damage. [47] (10.1016/j.arthro.2018.08.051)
[L4] Also, 53% to 56% of the patients presenting with initially diagnosed isolated ACL ruptures had concomitant injuries to the KFC. [48] (10.1177/03635465211015682)
[Case_report] Early recognition via MRI is critical, and primary ACL reconstruction is a reliable treatment when anatomical repair is not feasible. [49] (10.1016/j.jisako.2026.101072)
[L3] [51] (10.1016/j.otsr.2022.103257)
[L3] Recognizing these abnormalities preoperatively is crucial to adequately evaluate for growth disturbance following ACL reconstruction. [52] (10.1177/2325967117s00437)
[L3] The data from this study may help clinicians to identify patients at a greater risk of ACL injury. [53] (10.2106/jbjs.17.01011)
[L3] A positive finding of this structure ought to be included in the group of radiologic signs relevant for the diagnosis of ACL lesion. [54] (10.1177/03635465010290060601)
[L4] MRI evaluation showed ALL injuries are present in 60.2% of acute ACL injuries in adolescent patients. [60] (10.1016/j.arthro.2019.02.034)
[L1] The clinical utility of imaging-based measurement methods for the determination of ACL injury risk requires more reliable techniques that demonstrate consistency between studies. [61] (10.1177/0363546512442307)
[L3] Secondary meniscal tears after ACL injury are most common among patients undergoing delayed surgical or nonoperative treatment of their primary ACL injuries. [63] (10.1177/0363546519844481)
[L4] Despite the promising clinical outcomes, this technique should not be widely adopted unless it has been compared directly with ACL reconstruction. [66] (10.1097/corr.0000000000001118)
[L5] The author believes that contemporary ACL repair will apply to a subset of patients and is an attractive, minimally morbid, biologic alternative to ACL reconstruction, though well-powered prospective studies are needed to compare outcomes with reconstruction. [69] (10.1097/corr.0000000000001244)
[L4] The plane in which an MRI scan is performed affects the classification of ACL tears. [70] (10.1007/s00167-022-07068-2)
[L2] The study had a favorable long-term outcome regarding incidence of radiographic knee OA, knee function and symptoms, and need for ACL reconstruction. [73] (10.1177/0363546508316770)
[L2] [74] (10.1177/23259671251339491)
[L3] In a 5- to 8-year follow-up, one out of every ten patients had a contralateral ACL rupture, and two out of every ten patients had siblings with a history of ACL rupture. [75] (10.1007/s00167-019-05781-z)
[L5] This concept allows a more precise description of ACL rupture patterns and might lead to a more distinctive approach for reconstructive surgery. [76] (10.1007/s00167-007-0337-5)
[L3] The anatomical parameters of the knee joint (i.e., notch width index, anterior cruciate ligament width and length) have no role in the cause of an injury. [78] (10.1007/s00402-015-2292-9)
[L2] Patients with ACL injuries treated with ACL reconstruction and patients with ACL and meniscus injuries treated with ACL reconstruction and meniscectomy are less likely to undergo TKA at mid- to long-term follow-up compared with patients treated nonoperatively. [79] (10.1016/j.arthro.2025.07.028)
[L4] After ACL reconstruction in patients aged 18 years and younger, a further ACL injury occurred in 1 in 3 patients over 15 years. [81] (10.1177/0363546515623032)
[L3] This indicates that previous injury of any type does not increase the risk of suffering an ACL injury. [83] (10.1177/2325967116669708)
[L2] In the 24 months after ACLR and return to sport, patients are at a greater risk to suffer a subsequent ACL injury compared with young athletes without a history of ACL injuries. [85] (10.1177/0363546514530088)
[L2] Clinical measures of knee function were most predictive of subsequent OA development following an extended period of rehabilitation early after ACL injury. [86] (10.1177/2325967118810775)
[L1] Surgical reconstruction as a management strategy for patients with long-standing ACL injury is more effective, but more expensive, at 18 months compared to rehabilitation management. [87] (10.1302/0301-620x.106b1.bjj-2023-0175.r1)
[L3] [88] (10.1136/bjsports-2023-107113)
[L3] Risk of ACL graft tear was significantly greater in males as compared to females and in male patients with a chronologic age 16 years as compared to those >16 years. [89] (10.1177/2325967125s00301)
[L3] These structures may function as important secondary stabilizers in an ACL-injured knee. [91] (10.1177/0363546516659649)
[L3] In female patients who experienced an ACL injury, a delay in surgery greater than 12 months is associated with a gradual increase in the risk of nonrepairable medial meniscal tear; this risk becomes statistically significant after 24 months. [93] (10.1016/j.arthro.2022.10.014)
[L1] [94] (10.1002/ksa.12747)
[L4] Changing toe direction significantly affects knee kinetics and kinematics during landing. [95] (10.1007/s00167-013-2815-2)
[L4] A classification system for ACL tears can guide a proper surgical plan. [96] (10.1177/2325967120s00255)
[L3] Jump direction significantly influenced knee biomechanics, suggesting that lateral jumps are the most dangerous of the stop-jumps. [97] (10.1177/0363546505278696)
[L2] These data may be helpful in diagnosing and managing ACL injuries in athletes and could be used in the clinic as a baseline by which to compare and identify patients who might exhibit increased rotatory laxity. [101] (10.1007/s00167-017-4684-6)
[L3] Clinicians should consider routinely assessing PTS in newly presenting patients with an initial ACL tear as marked deviations could be a predisposing risk factor for subsequent contralateral tear. [104] (10.1177/2325967123s00246)
[L3] Patients with ACL tears treated non-operatively developed secondary meniscal lesions requiring delayed surgical management. [107] (10.1007/s00167-018-5201-2)
[L3] Combinations of knee joint geometry measurements provided more information about the risk of noncontact ACL injury than individual measures, and the aspects of geometry that best explained the relationship between knee geometry and the risk of injury were different between males and females. [108] (10.1177/0363546514563277)
[L4] Increasing the knee flexion angle during jump landing may be an effective intervention to improve knee biomechanical risk factors associated with an ACL injury. [112] (10.1177/0363546516634000)
[L4] Isolated ACL tear is less common than combined injuries, which are quite frequent. [114] (10.1177/03635465221092767)
[L3] Biomechanical factors such as reduced KAM or reduced knee flexion angle during gait could serve as early indicators for OA risk and inform targeted rehabilitation interventions. [116] (10.1002/ksa.70183)
[L2] Patients in the ACLR group had higher future knee-related self-efficacy and were active at a higher level of physical activity at 8 and 12 months after treatment. [117] (10.1002/ksa.70042)
[L4] The treatment strategy of an immediate repair of the MCL and reconstruction of the ACL when conservative treatment has failed seems safe and effective. [118] (10.1007/s001670050081)
[Paper] Anatomic healing of medial knee structures is critical to maintain native knee kinematics, supported by biomechanical studies that demonstrate increased graft laxity and residual valgus rotational instability after ACL reconstruction (ACLR) alone in the setting of concomitant ACL/MCL injury. [119] (10.2106/jbjs.rvw.24.00036)
[L2] Using waveforms, instead of discrete peak values of the knee abduction moment, may better represent risky movement patterns. [120] (10.1002/ksa.12471)
[L3] It is possible that decreasing tibial length relative to femoral length alters lower extremity biomechanics in such a manner that places the ACL at risk for injury. [121] (10.1177/23259671251343811)
[L3] Furthermore, ACLR had a beneficial effect on knee outcomes, with acute-stage ACLR leading to better outcomes in the subgroup analysis. [122] (10.1186/s12891-024-08102-9)
[L5] The meniscus status does have a significant impact on knee kinematics in the ACL-deficient knee. [123] (10.1007/s00264-014-2581-x)
[L3] The study proposes an axial force theory to explain a major component of ACL injury based on these kinematic differences. [124] (10.1177/0363546508328107)
[L5] Frontal plane kinematic temporal relationships at the hip, knee, and ankle differ between genders, with components of dynamic knee valgus peaking during the deceleration phase in women and during the acceleration phase in men. [127] (10.1177/0363546510397175)
[L1] Contrary to clinical opinion, the findings indicate that knee abduction kinematics and kinetics during weight-bearing activities may not be risk factors for future ACL injury. [130] (10.1186/s12891-020-03552-3)
[L2] Knee motion and knee loading during a landing task are predictors of anterior cruciate ligament injury risk in female athletes. [132] (10.1177/0363546504269591)
[L3] Clinical outcomes of patients that underwent meniscus repair were better than those that underwent meniscus resection with concurrent ACL reconstruction. [134] (10.1007/s00167-020-05931-8)
[L4] The improvement rate was 24.6% among patients who did not receive ACLR in the acute phase and underwent ACLR in the chronic phase. [135] (10.1002/ksa.12212)
[L3] Otherwise, transphyseal ACLR has satisfactory clinical outcomes, with good subjective outcomes, function level, and knee stability. [136] (10.1177/2325967116664685)
[L3] Delayed ACL reconstruction resulted in success for a majority of the ACL-reconstructed children. [137] (10.1007/s00167-007-0469-7)
[L2] Short-term progressive exercise therapy programs are well tolerated and should be incorporated in early-stage ACL rehabilitation, either to improve knee function before ACL reconstruction or as a first step in further nonoperative management. [139] (10.2519/jospt.2010.3345)
[L2] The diagnostic ability of MRI to predict meniscal injuries present at acute ACL reconstruction was moderate, with performance being poorest at the lateral meniscus. [140] (10.1177/23259671221079338)
[L4] MRI may not be completely reliable in assessing the degree and location of an ACL tear, and surgeons should not solely rely on MRI imaging for ruling out possible ACL repair. [144] (10.1177/2325967119s00398)
[L3] MRI is unreliable for determining the precise location of an ACL tear. [145] (10.1177/2325967125s00286)
[L5] This study found alterations in the native load-sharing relationships of the medial knee structures after injury. [146] (10.1177/0363546509335191)
[L4] Good functional performance and knee muscle strength can be achieved and maintained over time in the majority of patients with ACL injury treated with rehabilitation and early activity modification but without reconstructive surgery. [147] (10.1177/0363546507305018)
[L4] Conservative management of ACL rupture in paediatric population is a valuable treatment which permits return to normal life with sports activities without major increasing of meniscal tears. [149] (10.1016/j.otsr.2018.09.001)
[L2] Non-ACLR treatment may therefore be a viable option for selected patients, particularly those who are older or have lower activity demands, to achieve satisfactory RTS outcomes. [154] (10.1177/03635465261451698)
[L3] Altered bone morphological characteristics of the knee were found to be risk factors for ACL tears in contact injuries as well as noncontact injuries. [157] (10.1177/23259671231179757)
[L5] Subtotal medial meniscectomy in knees with ACL deficiency altered knee kinematics, especially at high flexion angles. [158] (10.1016/j.arthro.2008.09.020)
[L3] Standard preoperative MRI scans can reliably be used to visualize Kaplan fiber injury in the majority of pediatric and adolescent patients with ACL tears, especially when the MRI is performed in the acute setting. [159] (10.1177/23259671221128601)
[L4] MRI accurately predicted the ACL tear type seen arthroscopically in only 55.9% of patients. [161] (10.1177/2325967124s00302)
[L3] Early ACL reconstruction is recommended also for the prevention of secondary meniscal tear. [162] (10.1007/s00402-015-2309-4)
[L4] The higher prevalence of articular cartilage injuries at revision ACLR may represent new injuries, while the lower prevalence of meniscus tears may be caused by susceptible menisci being injured and treated at primary surgery or by changes in knee kinematics or injury exposure patterns. [163] (10.1177/0363546514536020)
[L2] The diagnostic validity of magnetic resonance imaging is similar for meniscal tears in acute knee trauma and in knee symptoms lasting over 6 months in young adults. [164] (10.1177/0363546508329543)
[L1] [165] (10.1186/s13018-019-1127-8)
[L5] Most isolated medial collateral ligament injuries are treated nonsurgically, while concomitant damage to the anterior or posterior cruciate ligaments is a common indication for surgical management of high-grade injuries. [166] (10.5435/00124635-200903000-00004)
[L4] The most frequently asked questions on Google pertaining to ACL tear and ACL surgery are related to indications/management, technical details, and timeline of recovery. [167] (10.1016/j.asmr.2025.101112)
[L2] The lack of association of these risk factors in male athletes may highlight the need to focus on other factors such as kinematics for these athletes. [168] (10.1177/23259671241293344)
[L2] Knee laxity increased bilaterally during the first year after non-surgically treated ACL injury. [171] (10.1016/j.jisako.2023.03.097)
[L3] Knee torsional alignment is associated with ACL injury, predominantly in the distal femur rather than the proximal tibia. [173] (10.1186/s13018-024-04609-y)
[L4] Conversely, landing upright appears to be ACL harmful by increasing post-impact force and quadriceps muscle activity while decreasing knee flexion angles. [174] (10.1007/s00167-012-2011-9)
[L4] The incidence of medial meniscal lesions and the complexity of tear types increased significantly with increasing time intervals between the index injury and ACL reconstruction. [175] (10.1177/03635465231216364)
[L2] MRI is a sensitive measure of cruciate and collateral ligament injury in acute knee dislocation; however, it does not reliably diagnose injury to the posterolateral corner or meniscus, and therefore, a higher index of suspicion is required during arthroscopy to prevent misdiagnosis which could affect long-term clinical outcome. [176] (10.1007/s00167-015-3857-4)
[L3] Patients who had radiographic knee OA 5 years after ACL reconstruction walked with lower knee adduction moments and medial compartment joint contact forces than did those patients without OA early after injury and reconstruction. [181] (10.1177/0363546515608475)
[L3] Initial nonoperative treatment of ACL tears in children and adolescents carries a high risk of additional meniscal and chondral injury, which may result in long-term knee impairment. [183] (10.1177/2325967114s00037)
[L2] Poor agreement was found between imaging and arthroscopic assessment of ACL tear location, as MRI predicted intraoperative ACL tear location in less than half of cases. [186] (10.1177/23259671251397389)
[L1] Nonoperative and operative treatments of medial collateral ligament injuries lead to equally good results. [187] (10.1177/0363546505284889)
[L4] However, their correlation with subjective and objective measures of knee function, as well as with the risk of secondary osteoarthritis, is unknown. [189] (10.1177/23259671261443910)
[L2] Three ACL intervention programs successfully reduced noncontact ACL injury incidence rates in female adolescent athletes. [193] (10.1016/j.arthro.2013.10.009)
[L4] The PLMRT tear is a common injury among patients undergoing ACL repair and can be arthroscopically classified into three different types. [194] (10.1007/s00167-014-3467-6)
[L4] Knee injury rates and patterns varied by sport, gender, and type of exposure. [195] (10.1177/0363546508314400)
[L3] The methods to quantify knee joint laxity may be used in conjunction with measures of neuromuscular control to identify high-risk female athletes. [196] (10.1177/0363546507313572)
[L1] The highest rated studies reported low prevalence of knee osteoarthritis for individuals with isolated anterior cruciate ligament injury (0%-13%) and a higher prevalence of knee osteoarthritis for subjects with combined injuries (21%-48%). [198] (10.1177/0363546509338827)
[L3] At short-term follow-up, ACL repair using an Internal Brace enables sports activity and provides a sense of well-being similar to that of classic ACL reconstruction using hamstring or quadriceps tendon autografts in a selected patient population. [201] (10.1055/a-1019-0949)
[L1] Patients after nonoperative and delayed treatment experienced more instability/pathological laxity and inability to return to previous activity levels than did patients treated with early surgical stabilization. [203] (10.1177/0363546513510889)
[L3] Identification of medial bone bruising on pre-operative MRI following acute ACL rupture should raise suspicion of an associated postero-medial meniscal tear. [214] (10.1007/s00167-019-05490-7)
[L2] At the time of acute ACL injuries, posterior root tears of the lateral meniscus do not appear to result in meniscal extrusion on MRI. [221] (10.1177/0363546513506551)
[L3] [222] (10.1177/0363546514559912)
[L3] In a large cohort of ACL tears with age-matched controls, the analysis identified multiple radiographic parameters which were significantly associated with ACL injuries when compared with the controls. [223] (10.1016/j.arthro.2020.12.114)
[L5] The data revealed that osteochondral damage begins as early as 7 days after ACL injury, far earlier than the traditionally recognized 4-week timeline. [224] (10.1002/arj.70355)
[L5] Meyer et al provide a strong foundation for the next generation of morphometric ACL injury risk research by showing that AI can extract and synthesize 3D anatomic signatures from routine MRI. [225] (10.1002/arj.70160)
[L5] The authors question the clinical utility of MRI for definitive diagnosis of Kaplan fiber complex injury and caution against using these findings to determine patients for lateral extra-articular augmentation, noting no correlation has been shown between KFC injury and increased anterolateral rotatory laxity or subjective instability symptoms. [226] (10.1177/03635465211049385)
[L3] This study shows that an increased LFCR is related to an increased risk of noncontact ACL injury as determined by MRI. [228] (10.1186/s12891-022-05134-x)
[Paper] Spontaneous anterior tibial subluxation on MRI in complete ACL tear was significantly associated with medial meniscal tear and accident-to-MRI time. [229] (10.1016/j.otsr.2019.10.025)
[L3] This study identifies specific osseous morphologic characteristics associated with ACL injury in this population. [230] (10.2106/jbjs.15.01163)
[L2] The osseous morphological risk factors should be considered in individualized anatomic ACL reconstructions to achieve optimal outcomes. [231] (10.2106/jbjs.19.00535)
[L4] Patients who waited a long time to have ACL reconstruction had more cartilage damage and loss than patients who did not wait a long time. [232] (10.1177/03635465010290012001)
[L3] Increasing time from injury to ACLR was associated with increased incidence of secondary injury seen in the trochlea, lateral femoral condyle, medial tibial plateau, and medial meniscus. [235] (10.1177/0363546515574061)

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