Meniscus & Collateral Ligaments

Meniscal and collateral ligament injuries: management of traumatic vs degenerative tears and the role of repair in preventing joint degeneration.

Overview

For selected patients with persistent chronic tibial collateral ligament strain due to occult medial meniscus derangement, the treatment of choice is anteromedial arthrotomy and medial meniscectomy [4]. Current standard indications suggest that 34.9% of all meniscal injuries offer the potential for repair [10]. This potential rises to 55.6% when injuries are accompanied by anterior cruciate ligament damage [10]. Meniscal repair is a viable alternative to resection in many clinical situations [20].

Surgical intervention for medial meniscal root tears aims to improve known poor outcomes associated with nonoperative management, but it is unclear which patients are suitable candidates [17]. There is not yet clear consensus on indications for surgical intervention of medial meniscal root tears [17]. It is unclear whether meniscectomy is ever an acceptable treatment for medial meniscal root tears [17]. Meniscal allograft shows adequate outcomes for proper indications as a salvage procedure [19]. The International Meniscus Reconstruction Experts Forum (IMREF) 2015 Consensus Statement outlines a standardized approach to indications, surgical technique, and postoperative care for meniscal allograft transplantation [98]. The goal of the IMREF 2015 Consensus Statement is optimizing patient outcomes for meniscal allograft transplantation [98].

Knee partial meniscectomy has limited benefit for nonobstructive meniscal tears [100]. It is necessary to determine if patients with nonobstructive meniscal tears have osteoarthritis to establish indications for surgical versus nonsurgical treatment [100]. Medial meniscus repair in the ACL-deficient knee is not contraindicated [12]. Although the failure rate of meniscus repair may be greater in an unstable knee, meniscal repair is not contraindicated in a knee with a deficient ACL [21]. The menisci should be repaired if at all possible, especially in the setting of anterior cruciate ligament reconstruction, for optimal functional outcome and patient satisfaction [26]. Meniscal repair success rates exceed 80% when performed with anterior cruciate ligament reconstruction [20].

In appropriately selected patients, meniscal repair can deliver improved subjective outcomes with comparable reoperation rates versus meniscectomy [90]. Meniscal repair has the potential for reduced risk of osteoarthritis over time versus meniscectomy in appropriately selected patients [90]. Older age is not a contraindication to meniscal repair [90]. Meniscal repair in ACL reconstructed knees with expanded indications achieved a healing rate (including incomplete healing) of 75% [85].

Anatomy & Pathophysiology

Menisci and Intermeniscal Structures

The anterior intermeniscal ligament plays a critical role in knee biomechanics; its sectioning leads to decreased contact areas, shifts the force center of application more centrally inside the joint, and increases femorotibial contact pressures [32]. In the context of medial meniscectomy, decreased displacement of the medial meniscus explains higher pressure on knee components, indicating a potential biomechanical risk of knee degeneration [37]. Anterior cruciate ligament (ACL) deficiency alters medial meniscus biomechanics by increasing anterior-posterior meniscal motion and rotational instability, which results in reduced physiological extrusion of the medial meniscus during axial load-bearing conditions [42].

Surgical interventions involving the menisci significantly impact joint kinematics. Autologous semitendinosus meniscus grafts significantly improve knee joint kinematics and tibiofemoral contact after complete lateral meniscectomy, with doubled semitendinosus lateral meniscus autograft restoring tibiofemoral contact mechanics almost comparable to the native situation [43]. Arthroscopic centralization for lateral meniscal injuries reduces laxity in the ACL-reconstructed knee but may overconstrain the knee in certain motions [48]. Furthermore, different medial meniscal resections may increase knee laxity and peak tensile stress in the ACL, potentially leading to collagen fiber fatigue tearing and altered mechanobiology under normal joint loadings [49].

Biomechanical assessment of meniscal attachments requires careful consideration of loading conditions. In vitro tests applying uniaxial loads combined with static knee flexion angles or very low flexion-extension speeds appear to underestimate meniscus attachment forces, whereas forces at the anterior meniscus attachments strongly increase under dynamic knee joint loading [44]. Clinically, patients with knee osteoarthritis and a degenerative medial meniscal tear using a biomechanical foot-worn device for a year showed improvement in gait, physical function, and pain [46].

Collateral Ligaments and Complex Instability

The bone attachments of the medial collateral and posterior oblique ligaments are defined anatomically and radiographically [35]. Defining these attachments facilitates repairs and reconstructions that can restore physiological laxity and stability patterns across the arc of knee flexion [35]. The length-change patterns of the superficial MCL, deep MCL, and posterior oblique ligament (POL) across knee flexion and under various loads provide biomechanical data to inform surgical repair or reconstruction strategies [39]. Understanding the anatomy and biomechanics of the MCL is crucial for good outcomes after total knee arthroplasty, as intraoperative injury to the MCL is an uncommon yet serious complication that often goes unrecognized during the procedure [38].

Prosthetic sizing in unicompartmental knee arthroplasty (UKA) directly influences collateral ligament strain. Overstuffing in UKA leads to more valgus alignment, higher medial collateral ligament (MCL) strains, and altered contact forces, whereas understuffing results in biomechanics closest to the native knee [33].

Multiligamentous knee injuries involve a complex biomechanical disruption where total joint instability exceeds the sum of individual ligamentous injuries [40]. Recognition of secondary stabilizers and comprehensive treatment of all contributing factors are necessary to prevent failure in these injuries [40].

Patellofemoral Anatomy and Kinematics

Tibial tuberosity-trochlear groove distance and its components differ in patients with and without episodic patellar dislocation [36]. However, biomechanical and clinical studies are needed to examine how these radiographic measures translate into kinematic and functional outcomes for patients [36]. Radiographic measures of patellar tracking and alignment change with knee motion, being most abnormal at lower flexion angles in knees with patellofemoral instability symptoms [47].

Patellofemoral instability represents a complex pathology with a considerable number of different influencing factors [50]. A detailed understanding of anatomy and kinematics is required to identify underlying pathologies in this condition [50].

General Biomechanics and Surgical Principles

Comparative anatomical studies suggest that understanding shared kinematic principles can improve the design of external bracing systems and total knee replacements [34]. The basis of anatomic reconstruction techniques is a detailed understanding of quantitative knee anatomy [51]. Regarding specific ligamentous behavior, the anterolateral ligament (ALL) shows no isometric behavior during the range of motion of the knee [45].

Classification

Medial Collateral Ligament: The medial collateral ligament complex is the most commonly injured knee ligament [5].

Discoid Lateral Meniscus: Clinical grading of instability clarifies the natural history of discoid lateral meniscus-associated tearing [9]. An arthroscopic classification system for discoid lateral menisci is based on morphology and instability [53].

Medial Meniscal Ramp Tear: A classification system for patients undergoing anterior cruciate ligament reconstruction (ACLR) is based on anatomic and arthroscopic morphologic tear documentation [56]. Recent research has provided terminology, classification systems, and anatomical and biomechanical knowledge to understand the importance of properly diagnosing and treating meniscal ramp lesions [70]. It is crucial to differentiate between subtypes of lateral meniscus tears, specifically identifying 'ramp-like' lateral meniscus tears in patients with concomitant anterior cruciate ligament ruptures and associated instability [72]. There is limited consistency in descriptive classifications used for meniscal ramp lesions [92].

Meniscal Repair Predictability: A scoring system to predict the reparability of meniscus, limited to tears identifiable by MRI after testing the classification of zones and patterns of meniscal tear based on MRI, has limitations regarding MRI sensitivity, statistical details, and demographic data [71].

Multiple Ligament Knee Injury (MLKI): The current MLKI classification system is more than 20 years old [74]. A proposed MLKI classification system includes each specific structure injured, modifiers for fractures, extensor mechanism injuries, nerve injuries, or vascular injuries, specific anatomic location of structures injured (meniscus and articular cartilage), and injury timing (acute, chronic) [74].

Medial Knee Anatomy: A distinct plane exists between the posterior knee capsule and the meniscotibial ligament complex [75]. The distance between the physis and meniscotibial ligament capsular attachments increases with age [75]. The study delineated a consistent three-layered anatomical pattern of the medial knee [93]. Specific nomenclature for the superficial medial ligament and posteromedial capsule is suggested rather than the term 'posterior oblique ligament' [93].

Meniscal Morphology: No subtypes were detected in the medial meniscus in a cadaver study of morphological variations [78].

Meniscal Extrusion: Global perspectives on meniscal extrusion classification support the development of a new classification measured on MRI scans at the mid-tibial plateau that considers laterality, anatomical location, age, BMI, and aetiology [96].

Other Considerations: Several histological scoring systems are available to assess meniscal structure, but few have been validated for specific application in research settings [69]. Surgical decision making is based on patient factors and understanding of the meniscal structure, function, and pathology [102].

Clinical Presentation

Patients with intact menisci and normal articular cartilage demonstrate significantly better outcomes than those who have undergone meniscectomy or possess damaged cartilage [1]. Conversely, long-term prognosis is often poor; at 10 to 20 years post-diagnosis, approximately 50% of patients with a diagnosed anterior cruciate ligament or meniscus tear develop osteoarthritis accompanied by pain and functional impairment [3].

Inspection and Palpation: The medial collateral ligament represents the most commonly injured knee ligament [5]. Persistent chronic tibial collateral ligament strain may indicate an occult medial meniscus derangement [4]. Discoid meniscus cases are uncommon, and their etiology remains unknown [58]. Symptomatic discoid lateral meniscus occurs most frequently in teenagers [15], though patient presentations and treatments for discoid medial menisci mirror those of the lateral variant [61]. A ring meniscus can be misidentified as an incomplete discoid meniscus [13]. Double-layered lateral meniscus is an extremely rare anatomical abnormality [60].

Imaging and Diagnostic Utility: MRI serves as a sensitive measure for cruciate and collateral ligament injury in acute knee dislocation but does not reliably diagnose posterolateral corner or meniscus injury in this setting [11]. The radiographic condylar cut-off sign offers moderate diagnostic utility for complete discoid lateral meniscus in adolescents aged 10–16 [14]. Anterior medial meniscus detachment, which can occur with an anterior cruciate ligament tear, is relatively rare and difficult to diagnose via MRI [18]. A posterior lateral meniscus root tear is a clinically relevant but likely underrecognized concomitant injury in patients with an ACL tear [54]. In patients with ≥3 mm of meniscus extrusion despite an intact meniscus and minimal knee pathology, a meniscotibial ligament abnormality is likely [55].

Clinical Assessment and Red Flags: Isolated knee injuries are rare, necessitating a comprehensive workup for complex knee instability that includes assessment of alignment, menisci, cartilage, and concurrent ligament injuries [16]. Missed concomitant lesions can lead to reconstruction failure [16]. Management of meniscal tears is predicated on symptoms, as many symptomatic tears become asymptomatic over time [59]. There is a relationship between the type of medial meniscal tear and the characteristic clinical symptoms reported by patients with medial knee osteoarthritis [57].

Investigations

Plain radiography: Plain radiographs may help establish the diagnosis of an ACL tear via the lateral femoral notch sign in more than one-quarter of patients [99]. Several plain radiographic findings in symptomatic discoid lateral meniscus in children are significantly different from those in normal controls [81]. Prediction models improve the diagnostic utility of plain radiography for the detection of complete discoid lateral meniscus in children [89].

MRI: MRI is a sensitive measure of cruciate and collateral ligament injury in acute knee dislocation [11]. However, MRI does not reliably diagnose injury to the posterolateral corner in acute knee dislocation [11], nor does it reliably diagnose meniscus injury in this setting [11]. The diagnostic validity of MRI is similar for meniscal tears in acute knee trauma and in knee symptoms lasting over 6 months in young adults [86]. MRI accuracy in diagnosing discoid lateral meniscus is significantly lower in the presence of radial or longitudinal tears [109]. Intravenous or intraarticular contrast-enhanced magnetic resonance arthrography has increased accuracy in detecting recurrent meniscal tears [103]. MRI is only moderately reliable for the prediction of meniscus reparability [107].

Meniscocapsular separation can involve a segment of less than 5 mm in length [29]. This separation can be occult on MRI [29] and can be challenging to visualize on arthroscopy [29]. The anterior medial meniscus detachment and anterior cruciate ligament tear combination is difficult to diagnose via MRI [18].

CT: MRI is slightly more accurate than radiography in preoperative sizing for meniscus allograft transplantation, but neither technique is highly accurate [91]. Direct MRI measurement of the contralateral intact meniscus better predicts actual meniscal size than estimation of size indirectly from measurement of the tibial plateau [108]. There were no differences between right and left meniscal measurements according to MRI in the studied subset of patients [88].

Other Considerations: The condylar cut-off sign has a moderate degree of diagnostic utility for complete discoid lateral meniscus in adolescents aged 10–16 [14]. The meniscal parameters alteration could be an important imaging biomarker to predict the occurrence of radiographic knee osteoarthritis (ROA) [104]. The meniscus should be probed carefully to differentiate between ring meniscus and incomplete discoid meniscus [13].

Treatment

Non-Operative

High-quality data on the natural history of untreated meniscus tears are lacking, with existing studies limited to case series and no comparative trials [8]. Non-operative treatment is the first-line choice for degenerative meniscal lesions, as the benefits of arthroscopic partial meniscectomy in adults with degenerative and nonobstructive symptoms are limited, showing outcomes similar to physical therapy [65, 95]. The orthopaedic community does not oppose this conservative approach [80]. Arthroscopic partial meniscectomy is reserved for failure of conservative management or selected cases where non-surgical treatment is inappropriate [65, 80]. Meniscal tear location and type likely dictate the success of non-operative treatment [76].

Operative

Indications: Meniscal preservation is the first-line choice for traumatic tears [65]. 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 [10]. Medial meniscal tears pose a challenging dilemma where partial meniscectomy must be balanced against long-term degenerative consequences, and many are correctly treated non-operatively [97]. Guidelines support meniscal surgery in patients with clearly defined indications to reduce unnecessary surgery [68]. For medial meniscal root tears, it is unclear which patients are suitable candidates for surgical intervention, and there is no clear consensus on whether meniscectomy is ever an acceptable treatment [17].

Surgical Approach / Technique: Meniscal repair is a viable alternative to resection in many clinical situations, with success rates exceeding 80% when performed with anterior cruciate ligament reconstruction [20]. The menisci should be repaired if at all possible, especially during anterior cruciate ligament reconstruction, for optimal functional outcome and patient satisfaction [26]. Satisfactory clinical outcomes are achievable for radial meniscal tear repair at short-term follow-up [7]. Meniscal repair systems appear safe and effective, providing a high rate of meniscal healing in patients with complex tears and tears located in Cooper radial zone 2 [79]. Several approaches for medial meniscal ramp lesions associated with ACL tears lead to positive clinical outcomes [101]. Arthroscopic repair may result in slower progression of radiological deterioration compared with meniscectomy and nonoperative management for acute meniscus root tears [28].

Implant Selection: Meniscal allograft transplantation can give good and predictable results when strictly following indications [66]. The ultimate success of meniscal allograft reconstruction depends on the allograft healing in an anatomic position to support proper meniscal functioning and preserve hyaline cartilage [73]. For proper indications, meniscal allograft shows adequate outcomes as a salvage procedure [19]. Positive outcomes are most likely in appropriately selected patients, with studies reporting long-term graft survivorship as high as 89% at 10 years and significant improvements in patient-reported outcome measures [24].

Other Considerations: Patients with both menisci present and normal articular cartilage had significantly better outcomes than those with meniscectomies or damaged cartilage [1]. Long-term evaluation of anterior cruciate ligament–reconstructed knees with concurrent successful meniscal repairs demonstrated a low rate of radiographic arthritis [2]. A meniscectomy after meniscal repair is performed infrequently, supporting the notion that repairing a meniscus is a safe and effective procedure in the long term [6]. Clinical outcomes of patients who underwent meniscus repair were better than those who underwent meniscus resection with concurrent ACL reconstruction [77]. Although the failure rate of meniscus repair may be greater in an unstable knee, meniscal repair is not contraindicated in a knee with a deficient ACL [21]. Medial meniscus repair in the ACL-deficient knee is not contraindicated [12]. Complete healing of both menisci was confirmed arthroscopically 3 years postoperatively in a case of radial tears in the roots of the posterior horns of both the medial and lateral menisci combined with anterior cruciate ligament tear [52]. The results showed the long-term efficacy of arthroscopic treatment of a symptomatic discoid lateral meniscus [62]. Meniscectomy remains overused due to non-scientific factors like technical difficulty, cost, and patient preferences [67].

Medial Collateral Ligament (MCL) Injuries: Both operative and nonoperative management of Grade III medial collateral ligament injuries demonstrated clinical improvements between study enrollment and 2-year follow-up when treated concurrently with anterior cruciate ligament reconstruction [84].

Complications

Natural History & Degeneration: Patients with meniscectomies or damaged articular cartilage have significantly worse outcomes than those with both menisci present and normal articular cartilage [1]. On average, 50% of patients with a diagnosed anterior cruciate ligament or meniscus tear develop osteoarthritis with associated pain and functional impairment at 10 to 20 years after diagnosis [3]. Anterior cruciate ligament–reconstructed knees with concurrent successful meniscal repairs demonstrate a low rate of radiographic arthritis in long-term evaluation [2]. High-quality data do not exist on the natural history of untreated meniscus tears nor whether management alters the natural history of knee function and health [8]. All existing studies on the natural history of untreated meniscus tears are at best case series with no comparative studies [8].

Instability & Ligament Strain: The medial collateral ligament complex is the most commonly injured knee ligament [5]. Occult medial meniscus derangement can cause persistent chronic tibial collateral ligament strain [4]. Meniscocapsular separation can involve a segment of less than 5 mm in length [29]. Meniscocapsular separation can be occult on MRI [29]. Meniscocapsular separation can be challenging to visualize on arthroscopy [29]. Meniscocapsular separation can lead to chronic medial-side knee pain [29].

Discoid Lateral Meniscus Complications: Clinical grading of instability has clarified the natural history of discoid lateral meniscus-associated tearing [9]. Symptomatic discoid lateral meniscus occurred most often in teenagers [15]. Long symptomatic duration (≥6 months) is more frequently related to articular cartilage lesions in symptomatic discoid lateral meniscus than other factors [30]. Asymmetrical shape of discoid lateral meniscus is more frequently related to articular cartilage lesions than other factors [30].

Tear Management & Reoperation Risks: Lateral meniscus tears left in situ at the time of ACL reconstruction did not require reoperation at a minimum 6-year follow-up for 97.8% of tears [22]. Medial meniscus tears left in situ at the time of ACL reconstruction did not require reoperation at a minimum 6-year follow-up for 94.4% of tears [22]. Partial meniscectomy for irreparable medial meniscal tears, applied during the same surgery with anterior cruciate ligament reconstruction, negatively affects clinical outcomes in the short-term follow-up [23]. Longitudinal lateral meniscal tears in ACL-deficient knees derive from a primary recent injury rather than secondary meniscal pathology [31]. The recent lateral meniscal lesion in ACL-deficient knees does not evolve in meniscal length and depth [31].

Repair & Transplantation Outcomes: Meniscectomy after meniscal repair is performed infrequently, indicating that meniscal repair is a safe and effective procedure in the long term [6]. Satisfactory clinical outcomes are achievable for radial meniscal tear repair at short-term follow-up [7]. Positive outcomes for meniscal allograft transplantation are most likely to be achieved when performed in appropriately selected patients [24]. Studies report long-term graft survivorship for meniscal allograft transplantation as high as 89% at 10 years [24]. Meniscal allograft transplantation results in significant improvements in multiple patient reported outcome measures [24]. Long-term results after viable meniscus allograft transplantation are encouraging in terms of pain relief and improvement of function [25]. Meniscal allografts provided subjective improvement at 20 years after surgery [27]. The overall graft survivorship for meniscal allografts was 56.2% after 20 years of implantation [27]. Meniscal allografts are not as durable as the native meniscus [27]. Short-term results of meniscal transplantation are encouraging in terms of reducing knee pain and increasing function [82]. Long-term transplant function for meniscal transplantation remains unknown [82]. Any chondroprotective effects of meniscal transplantation remain unknown [82]. Resection of a single inferior leaflet after a horizontal medial meniscal tear preserves much of the original biomechanical function of the meniscus [106].

Recovery

Light activity (weeks): Evidence does not provide specific week ranges for light activity, desk work, or driving.

Full activity (months): Evidence does not provide specific month ranges for manual work, sport, or full ROM/strength return.

Complete recovery / outcome plateau (months): Evidence does not provide specific month ranges for the stabilization of pain, strength, and final functional outcomes.

Rehabilitation protocol: Evidence does not detail PT phasing, immobilisation duration, weight-bearing/ROM progression, or sling/brace removal timing.

Functional milestones: Patients with both menisci present and normal articular cartilage had significantly better outcomes than those with meniscectomies or damaged cartilage [1]. Satisfactory clinical outcomes are achievable for radial meniscal tear repair at short-term follow-up [7]. Long-term results after viable meniscus allograft transplantation are encouraging in terms of pain relief and improvement of function [25]. Meniscal allograft transplantation is a viable and effective surgical option for the painful meniscus-deficient knee, with good survivorship and functional outcomes in the medium to long term [87]. Patients with a preoperative duration of symptomatic medial knee overload/arthritis of two years or greater do not experience inferior PRO or clinical outcomes than patients with a symptom duration of less than 2 years at mid-term follow-up [113].

Other Considerations: Long-term evaluation of anterior cruciate ligament–reconstructed knees with concurrent successful meniscal repairs demonstrated a low rate of radiographic arthritis [2]. 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 [3]. A meniscectomy after meniscal repair is performed infrequently, supporting the notion that repairing a meniscus is a safe and effective procedure in the long term [6]. High-quality data do not exist on the natural history of untreated meniscus tears nor whether management alters the natural history of knee function and health, and all existing studies are at best case series with no comparative studies [8]. Clinical grading of instability has clarified the natural history of discoid lateral meniscus-associated tearing [9]. Lateral and medial meniscus tears left in situ at the time of ACL reconstruction did not require reoperation at a minimum 6-year follow-up for 97.8% and 94.4% of tears, respectively [22]. Partial meniscectomy for irreparable medial meniscal tears, applied during the same surgery with anterior cruciate ligament reconstruction, negatively affects the clinical outcomes in the short-term follow-up [23]. Meniscal allografts were able to provide subjective improvement at 20 years after surgery and while not as durable as the native meniscus, the overall graft survivorship was 56.2% after implantation [27]. Long symptomatic duration (≥6 months) and asymmetrical shape of discoid lateral meniscus were more frequently related to articular cartilage lesions than other factors [30]. Longitudinal lateral meniscal tears in ACL-deficient knees do not involve secondary meniscal pathology but derive from a primary recent injury, and the recent lateral meniscal lesion does not evolve in meniscal length and depth [31]. Orthopaedic opinion favors salvaging and restoring the damaged meniscus where possible to provide symptom relief and restore form and function for long-term knee health [83]. 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 [110]. The short-term results of delayed meniscus transplantation were close to those of meniscectomy [111]. At long-term follow-up (>8 years), shrinkage of transplanted fresh-frozen meniscal allografts progressed at 1 year postoperative, was on average mild, and was more prominent in the mid-body than in the anterior or posterior horn [112]. Early repair of an injured medial ligament can be expected to give the patient an excellent chance of returning to his or her prior athletic pursuits [114].

Key Evidence

• [L3] Patients with both menisci present and normal articular cartilage had significantly better outcomes than those with meniscectomies or damaged cartilage. (10.1177/03635465000280040201)
• [L4] The long-term evaluation of the anterior cruciate ligament–reconstructed knees with concurrent successful meniscal repairs demonstrated a low rate of radiographic arthritis. (10.1177/0363546510392014)
• [L4] 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. (10.1177/0363546507307396)
• [L4] For selected patients with persistent chronic tibial collateral ligament strain due to occult medial meniscus derangement, the treatment of choice is anteromedial arthrotomy and medial meniscectomy. (10.2106/00004623-195436010-00012)
• [L5] The medial collateral ligament complex has been neglected in terms of study and understanding despite being the most commonly injured knee ligament, and the authors argue it demands more interest and research to obtain objective evidence for surgical decision-making. (10.1007/s00167-020-06116-z)
• [L3] A meniscectomy after meniscal repair is performed infrequently, supporting the notion that repairing a meniscus is a safe and effective procedure in the long term. (10.1177/0363546513503444)
• [L3] Satisfactory clinical outcomes are achievable for radial meniscal tear repair at short-term follow-up. (10.1177/0363546518786035)
• [L3] Clinical grading of instability has clarified the natural history of discoid lateral meniscus-associated tearing. (10.1007/s00167-023-07521-w)
• [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. (10.1016/j.arthro.2018.08.051)
• [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. (10.1007/s00167-015-3857-4)
• [L4] Medial meniscus repair in the ACL-deficient knee is not contraindicated. (10.1007/s00167-006-0162-2)
• [Case_report] The meniscus should be probed carefully to differentiate between these conditions. (10.1007/s00167-009-0924-8)
• [L2] The condylar cut-off sign has a moderate degree of diagnostic utility for complete discoid lateral meniscus in adolescents aged 10–16. (10.1007/s00167-016-4361-1)
• [L4] Symptomatic discoid lateral meniscus occurred most often in teenagers. (10.1007/s00167-021-06635-3)
• [L5] The authors state that treating complex knee instability requires a comprehensive workup including assessment of alignment, menisci, cartilage, and concurrent ligament injuries, as isolated injuries are rare and missed concomitant lesions can lead to reconstruction failure. (10.1007/s00167-015-3665-x)
• [L5] Although surgical intervention aims to improve the known poor outcomes associated with nonoperative management of medial meniscal root tears, it is unclear which patients are suitable candidates, and there is not yet clear consensus on indications or whether meniscectomy is ever an acceptable treatment. (10.1016/j.arthro.2024.12.020)
• [L4] This type of meniscus injury is relatively rare and difficult to diagnose via MRI; early ACL reconstruction is recommended to avoid progression of meniscal injury and facilitate repair. (10.1007/s00167-006-0255-y)
• [L5] Meniscal allograft, for proper indications, shows adequate outcomes (for a salvage procedure). (10.1016/j.arthro.2015.02.042)
• [L4] Meniscal repair is a viable alternative to resection in many clinical situations, with success rates exceeding 80% when performed with anterior cruciate ligament reconstruction. (10.5435/00124635-200205000-00004)
• [L3] Although the failure rate of meniscus repair may be greater in an unstable knee, meniscal repair is not contraindicated in a knee with a deficient ACL. (10.1007/s00264-004-0616-4)
• [L3] Lateral and medial meniscus tears left in situ at the time of ACL reconstruction did not require reoperation at a minimum 6-year follow-up for 97.8% and 94.4% of tears, respectively. (10.1177/0363546515604622)
• [L4] Partial meniscectomy for irreparable medial meniscal tears, applied during the same surgery with anterior cruciate ligament reconstruction, negatively affects the clinical outcomes in the short-term follow-up. (10.1007/s00167-014-2960-2)
• [L5] Positive outcomes for meniscal allograft transplantation are most likely to be achieved when performed in appropriately selected patients, with studies reporting long-term graft survivorship as high as 89% at 10 years and significant improvements in multiple patient reported outcome measures. (10.1007/s00167-020-06058-6)
• [L4] Long-term results after viable meniscus allograft transplantation are encouraging in terms of pain relief and improvement of function. (10.1007/s00167-005-0033-2)
• [L3] The menisci should be repaired if at all possible, especially in the setting of anterior cruciate ligament reconstruction, for optimal functional outcome and patient satisfaction. (10.1177/03635465020300061501)
• [L4] Meniscal allografts were able to provide subjective improvement at 20 years after surgery and while not as durable as the native meniscus, the overall graft survivorship was 56.2% after implantation. (10.1016/j.arthro.2020.04.029)
• [L4] The current level 3 and 4 evidence suggests that arthroscopic repair may result in slower progression of radiological deterioration compared with meniscectomy and nonoperative management. (10.1177/03635465211031250)
• [L4] Meniscocapsular separation can involve a segment of less than 5 mm in length, be occult on MRI, be challenging to visualize on arthroscopy, and lead to chronic medial-side knee pain. (10.1016/j.arthro.2011.06.025)
• [L4] Long symptomatic duration (≥6 months) and asymmetrical shape of discoid lateral meniscus were more frequently related to articular cartilage lesions than other factors. (10.1016/j.arthro.2009.06.024)
• [L4] Longitudinal lateral meniscal tears in ACL-deficient knees do not involve secondary meniscal pathology but derive from a primary recent injury, and the recent lateral meniscal lesion does not evolve in meniscal length and depth. (10.1007/s001670050068)
• [L5] The section of the intermeniscal ligament leads to substantial changes in knee biomechanics, increasing femorotibial contact pressures, decreasing contact areas, and finally moving the force center of application, which becomes more central inside the joint. (10.1016/j.arthro.2018.03.007)
• [L5] Overstuffing leads to more valgus, higher medial collateral ligament strains, and altered contact forces, while understuffing results in biomechanics closest to the native knee. (10.1007/s00167-015-3848-5)
• [L5] Comparative anatomical studies suggest that understanding these shared kinematic principles can improve the design of external bracing systems and total knee replacements. (10.2106/00004623-198769070-00004)
• [L5] These data facilitate repairs and reconstructions that can restore physiological laxity and stability patterns across the arc of knee flexion. (10.1007/s00167-020-06139-6)
• [L4] Biomechanical and clinical studies are needed to examine how the results translate into kinematic and functional outcomes for patients. (10.2106/jbjs.21.00656)
• [Paper] The decreased displacement of the medial meniscus may explain the higher pressure on the knee components, indicating potential biomechanical risk of knee degeneration. (10.1186/s12891-021-04187-8)
• [L5] Understanding the anatomy and biomechanics of the medial collateral ligament is crucial for good outcomes after total knee arthroplasty, and intraoperative injury to the MCL is an uncommon yet serious complication that often goes unrecognized. (10.5435/jaaos-d-19-00355)
• [L5] The study defines the length-change patterns of the superficial MCL, deep MCL, and POL across knee flexion and under various loads, providing biomechanical data to inform surgical repair or reconstruction strategies. (10.1007/s00167-020-06050-0)
• [Paper] Multiligamentous knee injuries involve a complex biomechanical disruption where total joint instability exceeds the sum of individual ligamentous injuries, necessitating recognition of secondary stabilizers and comprehensive treatment of all contributing factors to prevent failure. (10.1016/j.csm.2018.11.009)
• [L3] These findings indicate altered medial meniscus biomechanics due to increased anterior-posterior meniscal motion and rotational instability after ACL injury. (10.1002/ksa.12269)
• [L5] The doubled ST lateral meniscus autograft improved the knee joint kinematics significantly and restored the tibiofemoral contact mechanics almost comparable to the native situation. (10.1007/s00167-022-07300-z)
• [L5] In vitro tests applying uniaxial loads combined with static knee flexion angles or very low flexion-extension speeds appear to underestimate meniscus attachment forces. (10.1177/0363546520988039)
• [L5] The ALL shows no isometric behavior during the range of motion of the knee. (10.1177/2325967114562205)
• [L4] Patients with knee OA and a degenerative medial meniscal tear using a biomechanical foot-worn device for a year showed improvement in gait, physical function and pain. (10.1007/s00167-012-2026-2)
• [L3] Radiographic measures of tracking and alignment changed with knee motion and, in knees with instability symptoms, were most abnormal at lower flexion angles. (10.1016/j.arthro.2014.04.036)
• [L5] However, the procedure may overconstrain the knee in certain motions. (10.1177/03635465211041747)
• [L5] Different medial meniscal resections may increase knee laxity and peak tensile stress in the ACL, potentially leading to collagen fiber fatigue tearing and altered mechanobiology under normal joint loadings. (10.1186/s12891-024-07201-x)
• [L5] Patellofemoral instability represents a complex pathology with a considerable number of different influencing factors, requiring a detailed understanding of anatomy and kinematics to identify underlying pathologies. (10.1007/s00167-018-4860-3)
• [L5] The basis of anatomic reconstruction techniques is a detailed understanding of quantitative knee anatomy. (10.1007/s00167-015-3629-1)
• [Case_report] Complete healing of both menisci was confirmed arthroscopically 3 years postoperatively, and the restoration of a stable and functional knee joint testifies to the efficacy of the treatment strategy. (10.1007/s00167-009-0839-4)
• [L4] An arthroscopic classification system for discoid lateral menisci is proposed based on morphology and instability. (10.1016/j.arthro.2006.09.002)
• [L5] A posterior lateral meniscus root tear is a clinical relevant but most likely underrecognized concomitant injury in patients with a tear of the ACL. (10.1007/s00167-014-2904-x)
• [L4] In patients with three or more millimetres of meniscus extrusion, an intact meniscus and minimal knee pathology, meniscotibial ligament abnormality is likely. (10.1007/s00167-019-05612-1)
• [L4] This study shows that it was possible to establish a medial meniscal ramp tear classification system for patients undergoing ACLR based on anatomic and arthroscopic morphologic tear documentation. (10.1016/j.arthro.2025.03.015)
• [L3] This study demonstrates a relationship between the type of medial meniscal tear and characteristic clinical symptoms reported by patients with medial knee osteoarthritis. (10.1007/s00167-014-2939-z)
• [Case_report] Cases of discoid meniscus are uncommon, and their etiology remains unknown. (10.1177/2325967124s00401)
• [L4] This case demonstrates an interesting and extremely rare anatomical abnormality of the lateral meniscus. (10.1007/s00167-011-1536-7)
• [L4] Patient presentations and treatments for those with discoid medial menisci were similar to those reported for patients with discoid lateral menisci. (10.1177/03635465231159671)
• [L4] The results showed the long-term efficacy of arthroscopic treatment of a symptomatic discoid lateral meniscus. (10.1007/s00167-011-1440-1)
• [L5] Meniscal preservation is the first-line choice for traumatic tears, while non-operative treatment should be the first-line choice for degenerative meniscal lesions, with arthroscopic partial meniscectomy reserved for failure of conservative management. (10.1302/2058-5241.2.160056)
• [L4] Strictly following the indications, meniscal transplantation can give good and predictable results. (10.1177/0363546510375399)
• [L5] The paper argues that while evidence supports meniscal repair and conservative treatment, meniscectomy remains overused due to non-scientific factors like technical difficulty, cost, and patient preferences; it calls for a critical analysis of literature to reduce unnecessary resections. (10.1007/s00167-014-3471-x)
• [L5] The guidelines support the use of meniscal surgery in patients with clearly defined indications while reducing exposure to unnecessary surgery. (10.1302/0301-620x.101b6.bjj-2019-0550)
• [L3] Although several histological scoring systems are available to assess meniscal structure, only few of them have been validated for specific application in research settings. (10.1007/s00167-012-2142-z)
• [L5] Recent research has provided the necessary terminology, classification systems, and anatomical and biomechanical knowledge to understand the importance of properly diagnosing and eventually treating meniscal ramp lesions. (10.1007/s00167-022-07184-z)
• [L5] The authors appreciate the attempt to formulate a scoring system to predict the reparability of meniscus, limited to tears identifiable by MRI after testing the classification of zones and patterns of meniscal tear based on MRI, but highlight limitations regarding MRI sensitivity, statistical details, and demographic data. (10.1007/s00167-019-05825-4)
• [L4] It is crucial to differentiate between subtypes of lateral meniscus tears, specifically identifying 'ramp-like' lateral meniscus tears in patients with concomitant anterior cruciate ligament ruptures and associated instability. (10.1016/j.jisako.2024.04.005)
• [L4] The ultimate success of the operation depends on the allograft healing in an anatomic position to support proper meniscal functioning and preserve hyaline cartilage. (10.1007/s001670050207)
• [Paper] The current MLKI classification system is now more than 20 years old and certainly represents an improvement over previous classification systems; however, it is our hope that by creating a classification system that includes each specific structure injured, modifiers for fractures, extensor mechanism injuries, nerve injuries, or vascular injuries, as well as specific anatomic location of structures injured meniscus and articular cartilage injuries, and injury timing (acute, chronic) that we can use this information to guide further research in this field and to ultimately improve patient care. (10.1016/j.csm.2018.11.006)
• [L5] This defines a distinct plane between the posterior knee capsule and the meniscotibial ligament complex, with a distance between the physis and meniscotibial ligament capsular attachments that increases with age. (10.1016/j.asmr.2023.100852)
• [L5] Meniscal tear location in addition to type likely plays a crucial role in dictating the success of non-operative treatment of the menisci. (10.1007/s00167-018-5090-4)
• [L3] Clinical outcomes of patients that underwent meniscus repair were better than those that underwent meniscus resection with concurrent ACL reconstruction. (10.1007/s00167-020-05931-8)
• [L4] No subtypes were detected in the medial meniscus. (10.1007/s00167-013-2612-y)
• [L3] These meniscal repair systems appeared to be safe and effective, providing a high rate of meniscal healing both in patients with complex tears and in patients with tears located in Cooper radial zone 2. (10.1016/j.arthro.2008.03.003)
• [L5] Meniscal preservation is a major issue and non-surgical treatment is the first-line treatment for degenerative meniscal lesions, though APM remains appropriate in selected cases. (10.1007/s00167-020-06411-9)
• [L2] Several plain radiographic findings in symptomatic discoid lateral meniscus in children were significantly different from those in normal controls. (10.1007/s00167-014-2924-6)
• [L3] The short-term results of meniscal transplantation are encouraging in terms of reducing knee pain and increasing function; however, long-term transplant function and any chondroprotective effects remain unknown and require further investigation. (10.2106/jbjs.e.00347)
• [L5] Orthopaedic opinion favors salvaging and restoring the damaged meniscus where possible to provide symptom relief and restore form and function for long-term knee health. (10.1177/0363546513498503)
• [L3] Both operative and nonoperative management of MCL tears demonstrated clinical improvements between study enrollment and 2-year follow-up. (10.1016/j.arthro.2018.10.138)
• [L4] Meniscal repair in ACL reconstructed knees with expanded indications achieved a healing rate (including incomplete healing) of 75%. (10.1016/j.arthro.2019.04.009)
• [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. (10.1177/0363546508329543)
• [L4] MAT is a viable and effective surgical option for the painful meniscus-deficient knee, with good survivorship and functional outcomes in the medium to long term. (10.1016/j.arthro.2018.01.010)
• [L4] There were no differences between right and left meniscal measurements according to MRI in this small subset of patients. (10.1016/j.arthro.2014.05.009)
• [L3] The results of this study provide improved diagnostic utility of plain radiography for the detection of completed discoid lateral meniscus in children. (10.1016/j.arthro.2017.08.252)
• [L5] In appropriately selected patients, meniscal repair can deliver improved subjective outcomes with comparable reoperation rates and the potential for reduced risk of osteoarthritis over time versus meniscectomy. (10.1016/j.arthro.2024.11.058)
• [L4] Magnetic resonance imaging is slightly more accurate than radiography in preoperative sizing for meniscus allograft transplantation, but neither technique is highly accurate. (10.1177/03635465000280041301)
• [L1] Although there has been a recent increase in the recognition and treatment of meniscal ramp lesions, there is limited consistency in descriptive classifications used for this pathology. (10.1002/ksa.12188)
• [L5] The study delineated a consistent three-layered anatomical pattern of the medial knee, suggesting the use of specific nomenclature for the superficial medial ligament and posteromedial capsule rather than the term 'posterior oblique ligament'. (10.2106/00004623-197961010-00011)
• [L1] The benefits of APM in adults with degenerative and nonobstructive meniscal symptoms are limited, with current evidence reporting similarity in outcomes between APM and physical therapy. (10.1007/s00167-022-07040-0)
• [L4] The findings shed light on global perspectives regarding meniscal extrusion classification, supporting the development of a new classification measured on MRI scans at the mid-tibial plateau that considers laterality, anatomical location, age, BMI, and aetiology. (10.1002/ksa.12183)
• [L5] Medial meniscal tears pose a more challenging dilemma where partial meniscectomy must be balanced against long-term degenerative consequences, and many tears are correctly treated non-operatively. (10.1007/s00167-021-06694-6)
• [L5] The consensus statement outlines a standardized approach to indications, surgical technique, and postoperative care for meniscal allograft transplantation with the goal of optimizing patient outcomes. (10.1177/0363546516660064)
• [L4] In more than one-quarter of patients, plain radiographs may help to establish the diagnosis of an ACL tear. (10.1007/s00167-014-3022-5)
• [L5] Knee partial meniscectomy has limited benefit for nonobstructive meniscal tears, but it is necessary to determine if included patients have osteoarthritis to establish indications for surgical versus nonsurgical treatment. (10.1016/j.arthro.2016.07.013)
• [L4] Several approaches used to treat medial meniscal ramp lesions associated with ACL tears lead to positive clinical outcomes. (10.1016/j.arthro.2020.05.041)
• [L5] Surgical decision making is based on patient factors and understanding of the meniscal structure, function, and pathology. (10.5435/00124635-200205000-00003)
• [L2] We demonstrated an increased accuracy of intravenous or intraarticular contrast-enhanced magnetic resonance arthrography in detecting recurrent meniscal tears. (10.1177/03635465030310062301)
• [L3] The meniscal parameters alteration could be an important imaging biomarker to predict the occurrence of ROA. (10.1186/s12891-024-07706-5)
• [L5] Resection of a single inferior leaflet after a horizontal medial meniscal tear preserves much of the original biomechanical function of the meniscus. (10.1177/0363546515623782)
• [L3] The results of this study suggest that magnetic resonance imaging is only moderately reliable for the prediction of meniscus reparability. (10.1177/03635465990270040601)
• [L2] Direct MRI measurement of the contralateral intact meniscus better predicts actual meniscal size than estimation of size indirectly from measurement of the tibial plateau on which it is located. (10.1016/j.arthro.2007.06.018)
• [L3] The accuracy of MRI in diagnosing discoid lateral meniscus is significantly lower in the presence of radial or longitudinal tears. (10.1007/s00167-017-4704-6)
• [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. (10.1016/j.arthro.2022.10.014)
• [L3] The short-term results of delayed meniscus transplantation were close to those of meniscectomy. (10.1177/0363546514541653)
• [L4] At long-term follow-up (>8 years), shrinkage of transplanted fresh-frozen meniscal allografts progressed at 1 year postoperative, was on average mild, and was more prominent in the mid-body than in the anterior or posterior horn. (10.1016/j.arthro.2019.04.031)
• [L4] Patients with a preoperative duration of symptomatic medial knee overload/arthritis of two years or greater do not experience inferior PRO or clinical outcomes than patients with a symptom duration of less than 2 years at mid-term follow-up. (10.1016/j.jisako.2022.03.003)
• [L4] Early repair of an injured medial ligament can be expected to give the patient an excellent chance of returning to his or her prior athletic pursuits. (10.2106/00004623-197860010-00008)

See Also

• Anterior Cruciate Ligament
• Biomechanics
• Anatomy

References

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