Abstract
Background:
The lateral meniscus is a unique structure of the knee joint, and its anatomy, function, pathological process, and treatment are distinct from those of the medial meniscus. To date, no consensus on the management of lateral meniscal lesions has been published, and clinical decision-making is challenging. To facilitate this, consensus and practice guidelines for lateral meniscal lesions were developed and endorsed by the Chinese Society of Sports Medicine.
Study Design:
Consensus statement.
Methods:
This project followed the Delphi approach to the consensus process, involving steering, rating, and peer review groups. A total of 61 experts in the fields of sports medicine and arthroscopic surgery were invited to participate in the compilation of a consensus statement on lateral meniscal lesions. (The discoid lateral meniscus was addressed by separate consensus.) To begin, the steering group drafted a set of questions and replies regarding lateral meniscal lesions. An online panel discussion was then held to provide initial agreement and comments on the statements, followed by a round of anonymous voting. Results and feedback were sent to the steering group for a second draft. A second round of voting was then held, and each statement was discussed during a combined meeting of the steering and rating groups. Finally, a consensus draft was evaluated by a review group.
Results:
Fifty-three questions and answers addressing lateral meniscal lesions were drafted, and 20 statements were excluded because of redundant information during the first round of voting. Ultimately, 33 statements were completed, 9 of which were unanimous.
Conclusion:
This expert consensus process focused on the anatomy, function, pathological processes, and treatment of lateral meniscal lesions. Accepted recommendations in these areas can assist doctors and therapists in standardizing the management of related pathology. The consensus statement indicates that certain types of lateral meniscal tears that were previously considered irreparable can be repaired. Preservation of the lateral meniscus should be the first-line treatment whenever possible, because the long-term clinical and radiological outcomes are worse after partial meniscectomy.
The lateral meniscus is a fibrocartilage structure that covers the margins of the lateral tibial joint. It distributes loads, guides movement, reduces contact stress, and protects the articular cartilage during dynamic and static joint loading. Owing to anatomic and structural differences, the mechanical characteristics of the lateral meniscus are distinct from those of the medial meniscus. The range of movement of the lateral meniscus is longer than that of the medial meniscus. This range is generated by several anatomic structures, including the hamstring tendon, meniscofemoral ligament, and joint capsule. 49,164 The posterior horn transmits 85% of loading when the knee bends. 38 In addition, the lateral meniscus has greater mobility than the medial meniscus and contributes to the rotational stability of the knee. Hence, lateral meniscal tears often occur in athletic patients, 106 and after meniscectomy, the load on the articular cartilage in the lateral compartment is likely to increase and cause injury sooner than that in the medial compartment. 148 The discoid lateral meniscus is a relatively common anatomic variation, which is particularly observed in the Asian population. 109 In contrast, a discoid medial meniscus is an extremely rare observation. 124
Lateral meniscal lesions can be classified as degenerative or traumatic, based on tear patterns. Degenerative lesions develop slowly because of aging or repetitive use and typically involve horizontal cleavage, complex tears, or flap tears. 19 Traumatic meniscal tears, such as longitudinal, radial, or root tears, 115 may occur during traumatic incidents. They can occur in isolation but are often observed in conjunction with ligamentous injuries and cartilage lesions. This classification is considered important in clinical decision-making. It is generally accepted that degenerative tears are not good candidates for repair compared with traumatic tears. However, this concept faces challenges because patients develop worsening osteoarthritis after meniscectomy. 139 The intrinsic molecular biology patterns of traumatic and degenerative tears are distinct, 29 and some tear patterns that are believed to be irreparable can eventually become amenable to repair. 115
Current orthopaedic practice aims to preserve meniscal integrity to delay the onset of osteoarthritis. In the best interests of our patients, the benefits of nonoperative treatment versus surgery for degenerative meniscal tears should be addressed first. Next, it is advisable to identify the types of meniscal tears that are suitable for repair and to avoid unnecessary partial meniscal resections so that we can decrease the risk of osteoarthritis with advances in surgical techniques. Furthermore, postoperative rehabilitation is crucial to enhance the possibility of returning to sports, and the balance between functional recovery and optimal healing should be discussed.
For these reasons, the Chinese Society of Sports Medicine (CSSM) organized and invited experts in sports medicine and orthopaedics to develop a panel and provide consensus statements on essential questions in the diagnosis and treatment of lateral meniscal lesions.
Methods
Physicians from the CSSM with extensive experience in sports medicine and orthopaedics participated in this consensus committee from July 31 to December 26, 2021. This consensus focuses on the definition, diagnosis, treatment, and prognosis of lateral meniscal lesions. The discoid lateral meniscus will be discussed in another consensus because of its unique origin, pathology, diagnosis, and treatment.
The Delphi method was used to develop consensus. Three groups composed of 61 experienced doctors (steering group, n = 9; rating group, n = 37; and peer review group, n =15) were included. First, the steering group of 9 expert knee surgeons proposed a series of statements based on a literature review using the PubMed, Embase, and Cochrane Central Register of Controlled Trials databases. Additionally, the references in the identified studies were searched for other relevant studies. Animal and cadaver studies were excluded. The statements were drafted with the aim of addressing areas of current controversy within the treatment of lateral meniscal lesions: (1) the definition, cause, and pathological changes of lateral meniscal lesions; (2) the clinical manifestation, physical examination, diagnosis, and radiologic examination of lateral meniscal lesions; (3) the indications for nonoperative and surgical treatment of lateral meniscal lesions; (4) the diagnosis of and surgical techniques to treat anterior horn, longitudinal, radial, flap, popliteomeniscal fascicle, and posterior root tears, as well as meniscal lesions combined with ligamentous injuries; (5) lateral meniscal transplantation; (6) biological augmentation; (7) postpostoperative rehabilitation; (8) the evaluation of meniscal healing; and (9) prognostic factors. The levels of evidence cited in the references for each issue were classified as shown in Table 1. All question-and-answer sets were discussed within the steering group according to scientific grading before being sent to the rating group.
Classification of Level of Evidence of Included Studies
Each statement was presented before the first rating round. Afterward, each member of the rating group, composed of 37 physicians, was asked to score the question-and-answer sets anonymously according to the scientific evidence and their clinical experience on a Likert scale ranging from 1 (totally inappropriate) to 5 (totally appropriate). The rating group then held discussions. Eighty percent agreement or above was defined a priori as consensus, and the content was modified if a divergent opinion was proposed and supported by 2 additional participants. If the proportion of favorable votes was ≤50%, the issue was not resolved. If the proportion of favorable votes was between 50% and 80%, then the statement, with its feedback, was returned to the steering group for revision, and the revised draft was prepared and resubmitted to the rating group for final scoring.
Afterward, the draft was sent to the review group, which was composed of 15 doctors who perform daily knee arthroscopies and can be considered representatives of the CSSM. The purpose of this unbiased peer review group was to evaluate the questions and answers after grading by the rating group, to determine the feasibility, accessibility, and readability of the proposed recommendations. See Figure 1 for a flowchart of the consensus procedure.
Flowchart of the procedure used to determine the consensus statement for lateral meniscal lesions.
Results
Fifty-three questions and their answers (statements) regarding lateral meniscal lesions were drafted by the steering group. Twenty statements were excluded because of redundant information during the first round of voting. Ultimately, 33 statements were completed, of which 9 were unanimous.
Statement 1. Definition and classification of traumatic lateral meniscal lesions
Lateral meniscal lesions can be traumatic and degenerative. Traumatic injury refers to damage to the structural integrity of the meniscus caused by knee joint trauma or knee flexion, extension, and rotation movements. It causes pain, locking, popping, joint swelling, joint instability, and other symptoms. Traumatic injury types include longitudinal tears or bucket-handle meniscal tears, radial tears, flap tears, and posterior root tears.
Based on origin, Poehling et al 170 proposed that lateral meniscal lesions can be categorized as degenerative or traumatic injuries. Traumatic injuries, including radial tears, tears within 3 mm of the meniscosynovial junction, and combined anterior cruciate injuries, are often observed in active young people. 170 Beaufils and Pujol 20 reported that a certain type of flap tear of the lateral meniscus is derived from a longitudinal tear, which should also be regarded as a traumatic lesion. Horizontal tears are often observed in older people, mainly because of degenerative processes, and are not traumatic meniscal tears. 198,239 (Evidence level: E)
Statement 2. Definition and classification of degenerative lateral meniscal lesions
Degenerative meniscal lesions develop with age or overuse and are commonly observed in middle-aged or older individuals with horizontal, oblique, or complex tears. Degenerative changes are usually detected incidentally during knee magnetic resonance imaging (MRI). The pathogenesis is not fully understood when there is no clear history of acute knee injury.
Degenerative meniscal lesions develop slowly and typically occur in middle-aged or older individuals. 93 They are usually detected during knee MRI without significant knee symptoms or a clear history of acute knee injury. 19 (Evidence level: E)
Statement 3. Definition of stable and unstable lateral meniscal lesions
Unstable meniscal lesions refer to injuries in which the free edge of the torn meniscus may be displaced toward the center of the femoral condyle or extruding, causing joint interlocking and sudden pain. These include radial, longitudinal, bucket-handle, and flap tears. A stable tear refers to a partial or very short meniscal tear that barely moves when probed.
An unstable meniscal tear is a lesion in which the free edge of the torn meniscus has displaced toward the joint space at the center of the femoral condyle, causing joint locking and sudden pain. 218,225 Unstable meniscal tissue may become trapped in the intercondylar space, or it displaces at least 5 mm on probing. 143 A longitudinal tear may evolve into a bucket-handle or a flap tear, which may become trapped between the femoral condyle and the tibial plateau. 69,157,231 A radial tear is defined as an unstable tear. 115 A stable tear refers to a partial or very short meniscal tear that does not move on probing. 56 (Evidence level: E)
Statement 4. Clinical manifestation of lateral meniscal lesions
The major complaints of lateral meniscal lesions are pain, swelling, joint instability, snapping, interlocking, displacement, and catching of the knee.
Lateral joint line tenderness is often caused by pathological changes in the articular joint cartilage or lateral meniscus. This symptom occurs when the knee is twisted in a weightbearing position, or when the knee rotates while walking. Some patients report an immediate sharp pain that lasts for a few seconds, often followed by a dull ache for hours. The pain from movements in bed may prevent the patient from sleeping. Rest pain is not very common. 66 In a prospective cohort study by Konan et al, 114 pain (92%) and discomfort (95%) were the most reported knee symptoms, followed by knee swelling (56%), “clicking” sensation during knee movement (47%), and knee locking (12%). (Evidence level: B2)
Statement 5. Clinical diagnosis of lateral meniscal lesions
The clinical diagnosis of lateral meniscal lesions includes inspection, palpation, and diagnostic tests. The most widely used diagnostic maneuvers to diagnose lateral meniscal injuries are palpation for lateral joint line tenderness and the McMurray and Thessaly tests.
Evaluation for joint swelling, tenderness, range of motion, and locking or popping during knee flexion and extension is fundamental during the physical examination. Palpation for joint line tenderness is used to screen for meniscal injury. Its sensitivity has been reported as 0.92, specificity as 0.97, and diagnostic accuracy as 0.96. 66 Multiple diagnostic tests have been introduced to examine for meniscal tears, such as the McMurray, Thessaly, Apley, Steinmann, Ege, and Bohler tests. The McMurray and Thessaly tests are the most widely used in clinical practice. In a meta-analysis, Smith et al 199 reported that the overall sensitivity of the McMurray test was 0.61, and its specificity was 0.84. Blyth et al 26 reported that the Thessaly test had a sensitivity of 0.66, specificity of 0.39, and diagnostic accuracy of 0.54, using MRI as the standard reference. Therefore, no single test is accurate enough to diagnose lateral meniscal lesions, and a combination of physical examinations is recommended in clinical practice. Patient examinations should be delayed past the acute phase of severe pain and joint swelling, since physical examination will aggravate the patient’s symptoms and produce false-positive results. (Evidence level: A)
Statement 6. Imaging of lateral meniscal lesions includes radiography, ultrasound, MRI, and arthroscopic examinations
Radiography, ultrasound, MRI, and arthroscopy can be used for further diagnosis of lateral meniscal lesions. Among these, MRI is the most widely used in clinical practice, and it is recommended as the first-line choice for the diagnosis of lateral meniscal lesions. Ultrasound cannot replace MRI, but it can be indicated in selected patients with refractory symptoms or who are unable to undergo MRI. Arthroscopy can be used in the diagnosis of rare, unusual cases, but it is not recommended as a first-line modality.
Regarding diagnostic imaging of meniscal lesions, radiographs are used to screen for osteoarthritic changes in the lateral meniscus in patients aged over 35 years with over 1 month of nonlocking painful knee. 19
MRI and clinical examinations are commonly used when patients are suspected to have meniscal lesions. Although previous studies have argued that careful examination by an experienced clinician can generally diagnose meniscal lesions and is better than MRI, 112,142 routine MRI before therapeutic arthroscopy for clinically diagnosed meniscal tears will reduce the number and cost of unnecessary invasive procedures. The ranges of sensitivity and specificity of MRI for the diagnosis of a lateral meniscal tear have been reported to be 0.73 to 0.81 and 0.85 to 0.96, respectively. 108,162,210 This suggests several issues affecting the diagnostic accuracy of MRI. For example, the magic angle phenomenon for fast spin echo sequences has been reported to lead to missed meniscal tears on MRI. 131 Other lesions might also be missed because of large spacing on imaging. Combined anterior cruciate ligament (ACL) injuries can decrease diagnostic accuracy for lateral meniscal injuries, 108 and posterior root tears of the lateral meniscus are more likely to be missed on MRI. 118 Therefore, in cases of high clinical suspicion, doctors should pay more attention to negative MRI findings.
On the other hand, approximately 25% to 40% people older than 50 years are found to have severe degenerative changes or meniscal tears when assessed with standard MRI criteria, despite being asymptomatic. 27,100,227 Moreover, although arthroscopy is considered the gold standard for diagnosing meniscal lesions, the accuracy of arthroscopic diagnosis has been reported as 95%. 191 Arthroscopy should be generally performed for therapeutic and not diagnostic purposes; its invasiveness is a disadvantage. 184 The results of an imaging study should be considered in the context of the broader clinical picture. At that point, a decision can be made to proceed with therapeutic, rather than diagnostic, arthroscopy.
Ultrasonography has several advantages over MRI, because it is cost-effective, readily available, and easily applied in the standing position; thus, images under axial knee compression are readily available. Ultrasound appears to be useful for screening meniscal tears, but detection of the tear morphology seems insufficient. 8,229 Selby et al 190 reported that the ultrasound diagnosis of radial tears was difficult, and Casser et al 34 found that the detection of lesions on the anterior horn was not reliable because of the anatomic delineation of the infrapatellar fat pad. Therefore, ultrasound examination is recommended for the detection of meniscal extrusion or discoid lateral meniscus. 3,4,45 The sensitivity and specificity of ultrasound were 0.70 to 0.88 and 0.85 to 0.96, respectively, for the diagnosis of lateral meniscal lesions. 50,61,149,213 These values were lower than those for diagnosing medial meniscal lesions. 8 This might be attributable to the anatomy of the lateral meniscus, since the popliteus tendon courses through its substance from the lateral femoral condyle in a downward and posterior fashion. 190 Osteophytes, subcutaneous fatty tissues, and synovial hypertrophy hinder reliable ultrasound assessment. 167,212,234 In conclusion, ultrasound may not replace MRI to diagnose lateral meniscal injuries, but it might be indicated in selected patients with refractory symptoms or in those who are unable to undergo MRI. (Evidence level: C)
Statement 7. Indications for nonoperative management of lateral meniscal lesions
Indications for nonoperative treatment of lateral meniscal lesions include (1) patients without significant symptoms, or in whom the symptoms are not related to meniscal lesions, and (2) MRI grade 1 and 2 meniscal lesions with or without symptoms.
The MRI grading system for abnormally high meniscal signal intensity is as follows 48,60,208 : grade 0 refers to an intact meniscus; grade 1 refers to a small focal area of hyperintensity, without extension to the articular surface; grade 2 refers to linear areas of hyperintensity, without extension to the articular surface; and grade 3 refers to abnormal hyperintensity extending to at least 1 joint surface, which suggests a definite meniscal tear (Figure 2).
(A) Grade 0 meniscal signal. Normal lateral meniscus (arrowhead) without degenerative changes or tears shows no intrameniscal signal on T2-weighted MRI. (B) Grade 1 meniscal signal. Irregularly marginated signal intensity (arrowhead) on MRI. Signal does not communicate with superior or inferior articular meniscal surfaces. At arthroscopy, the posterior horn of this lateral meniscus was found to be normal. (C) Grade 2 meniscal signal. Primarily linear line signal intensity (arrowhead) on MRI. (D) Grade 3 meniscal signal. Primarily linear signal intensity within a meniscus (arrowhead). Signal abuts an articular surface.
The meniscus is composed of collagen. Type 1 and 2 collagen fibers are arranged in a complex 3-layer structure that converts the vertical compressive load into circumferential hoop stress. Grade 1 and 2 meniscal tears do not disrupt the circumferential stability of the meniscus. 79 In such cases, nonoperative treatment, including various rehabilitation protocols, nonsteroidal anti-inflammatory drugs, intra-articular injection, and physical therapy, can be used to treat patients with joint symptoms for 3 to 6 months. 19 For those who are not responsive to this treatment, and if a grade 3 meniscal tear is confirmed by MRI, arthroscopic treatment can be an option.
Previous studies have reported that approximately 25% to 40% of severe degenerative changes or meniscal tears are evident on MRI in people older than 50 years, despite a lack of symptoms. 27,100,227 Therefore, regular follow-up, rather than immediate invasive treatment, is recommended. (Evidence level: A)
Statement 8. Lesions of the anterior horn of the lateral meniscus
Injuries to the anterior horn of the lateral meniscus are mostly due to degenerative changes, overuse, or impingement. Attention should be paid to preserve the integrity of the circumferential fibers. The combined meniscal cyst, the malalignment of the lower extremity, and the posterior slope of the tibia should be assessed together with the meniscal lesions.
Anterior or anterolateral knee pain is a common presentation of anterior horn lesions, especially in the active sporting population, and accounts for 27.9% of lateral meniscal tears. The types of injury include macerated, 249 horizontal, and longitudinal tears from overuse or degenerative changes. Khan et al 105 found that reduced posterior downsloping is likely to cause biomechanical alterations to the posterior rollback of the femur, resulting in the impingement of the anterior horn of the lateral meniscus and predisposing the meniscus to tears. In addition, hypermobility of the anterior horn causes anterior knee pain even without MRI evidence of a meniscal tear. 154 Therefore, a comprehensive sports activity history should be taken in combination with physical examination, including Beighton score 154 and MRI, during the clinical workup.
Recent publications have raised awareness that overlooking a root tear may have significant consequences. 42 Treatment of the anterior horn is challenging; however, reports of surgical outcomes are rare. The treatment for lesions is basically organized by tear type, but they are not consistent in different papers. 40,87,176,249 Several techniques treating longitudinal tears along the meniscosynovial junction or the red-red zone of the anterior horn of the lateral meniscus have been published in succession. 39,111,127,140 Raoulis et al 176 reported that repair of the anterior horn of the lateral meniscus can achieve improved outcomes and tissue healing in young and active patients after a 24-month follow-up period. Dai et al 51 found that covering the repair site with an infrapatellar pedicle fat flap may improve meniscal healing and does not increase the complication rate. Meniscectomy has been used to treat horizontal tears of the anterior horn of the lateral meniscus with good results. 37,110,151 Nevertheless, most clinical reports were case series or case reports, with low levels of evidence.
In addition to this, meniscal cysts, malalignment, and tibial slope are combined lesions that should be considered. Parameniscal cysts have a very high association with meniscal tears; however, expect the lateral meniscal tear on the anterior horn. The transverse ligament and ACL can also be the origins. 65 Anterior lateral cysts extended medially either into the root or into the Hoffa fat pad, but in some cases, the type of extension did not correlate with the presence of an underlying meniscal tear. 54 Zheng et al 249 reported that preoperative anterior horn cysts showed worse patient-reported outcomes. If the anterior horn cannot be repaired, nonanatomic reinsertion of the anterior root of the lateral meniscus can be considered as a salvage procedure. 67 However, this technique should be performed with caution, since only rare cases have been reported, and the long-term outcomes have not yet been confirmed. (Evidence level: C)
Statement 9. Lateral meniscal lesions combined with ACL injury
When ACL injury is combined with lateral meniscal injuries, it is recommended to consider suturing the meniscus at the time of ACL reconstruction.
Lateral meniscal tears occur more frequently than medial meniscal tears in acute ACL injury. 43,194 The lateral meniscus is frequently involved in the initial trauma, but generally with either partial, single longitudinal, or flap tears requiring at most a very selective meniscectomy. 43,104 In knees with third-degree medial collateral ligament injury, radial tears of the lateral meniscus are predominant. 194 Injuries to the posterior horn of the lateral meniscus occur approximately twice as often as to the anterior horn. 200
The timing of surgery and episodes of instability affected the incidence of lateral meniscal tears, with 1.45× odds in subacute (6-12 weeks) and 2.82× odds in chronic (>12 weeks) ACL reconstruction. 9 As instability becomes chronic, more double longitudinal splits and flaps are encountered, indicating more complex meniscal lesions. 104 Granan et al 82 reported that the odds of meniscal tears in young adults increased by 1.004 for each month that had elapsed since injury. For meniscal tears lasting >24 months, the outcome of repair is uncertain because of cartilage degeneration. 237 If meniscal repair is not feasible, partial meniscectomy is performed. Total meniscectomy should be avoided in ACL-insufficient knees whenever possible, particularly in young patients.
It is recommended to repair the meniscus and reconstruct the ACL at the same time, since bone marrow mesenchymal stem cells and blood clots from the concomitant ACL reconstruction can enhance lateral meniscal healing. 15,33,46,223 An unstable knee increases the retear rate of the repaired meniscus. 136 A review of meniscal repair in ACL-deficient knees by Bellabarba et al 22 reported an overall 92% rate of successful meniscal healing with concomitant ACL reconstruction, compared with a 63% rate of healing in an unreconstructed ACL-deficient knee. (Evidence level: B2)
Statement 10. Treatments for longitudinal lateral meniscal lesions
The first line of treatment for longitudinal tears of the lateral meniscus, including traumatic bucket-handle and double longitudinal tears, should be repair. In cases of irreparable degenerative changes, meniscectomy can be performed.
Longitudinal tears are considered the most appropriate indication for repair. However, the complete healing rate has not been as high as expected, possibly because of the dynamics and poor vascular supply around the popliteal hiatus. 52 The reoperation rate for meniscal repair is higher than for meniscectomy, 166 whereas meniscectomy has been shown to negatively affect clinical outcomes after ACL reconstruction. 57
Longitudinal lateral meniscal tears are often seen in ACL injuries. 71,103,128,214 Whether these tears should be repaired during primary surgery is controversial. Biomechanical studies have reported that the longitudinal lateral meniscus does not alter contact pressure significantly 81 ; therefore, some studies have reported leaving stable tears in situ. 172 The healing of the meniscus after repair is affected by many factors, including tear location, type, and length, as well as knee stability. Matsushita et al 136 reported that longer tear length, complete tears, and residual instability were associated with higher retear rates after combined ACL reconstruction and meniscal repair. All Chinese experts supported repair of the longitudinal lateral meniscus simultaneously with ACL reconstruction. Whether combined ACL reconstruction improves long-term healing after meniscal repair is another topic of debate. 115 Previous studies have reported that the success rate of meniscal repair with ACL reconstruction was higher than that of isolated meniscal repair, 89,232 while other studies have proven the opposite. 16,156 Tsujii et al 217 found that the clinical and imaging outcomes at 42 months after repair of longitudinal tears of the lateral meniscus combined with anatomic ACL reconstruction were successful and comparable with those after isolated ACL reconstruction without any other injuries, although the lateral and posterior meniscal extrusions were significant. (Evidence level: B2)
Statement 11. Arthroscopic diagnosis and treatment for the popliteal hiatus of lateral meniscal tears
11.1) Direct arthroscopic visualization of popliteomeniscal tear or forward translation of intact meniscus beyond the midpoint of the lateral condyle to the tibia on probing is the standard method to diagnose lateral meniscal lesions around the popliteal hiatus.
The popliteomeniscal fascicles connect the lateral meniscus with the popliteus tendon to provide meniscal stability, bracing the joint during internal tibial rotation and during sudden directional changes. 112 Lesions to the posterolateral part of the lateral meniscus lead to meniscal hypermobility and subluxation, which are characterized by mechanical symptoms such as snapping and locking. 197,221 On the other hand, anteroinferior popliteomeniscal fascicle plays a more important role in stabilizing the lateral meniscus than posterosuperior popliteomeniscal fascicle. 211
The clinical and imaging diagnoses of these lesions are challenging. The preoperative clinical examination is based on the figure-4 test reported by LaPrade et al 121 and Simonetta et al, 196 but its sensitivity and specificity were not analyzed because of the small cohort of patients. It has been reported that the detection rate of popliteomeniscal fascicles on routine knee MRI in the sagittal and coronal planes is approximately 60%. 185
Direct arthroscopic visualization of popliteomeniscal tear or forward translation of the intact meniscus beyond the midpoint of the lateral condyle to the tibia on probing are the standard methods to diagnose lateral meniscal lesions around the popliteal hiatus. 101,221 Zheng et al 248 defined the popliteomeniscal tear of the lateral meniscus within a range area of 1 cm to the front or rear edge of the popliteal hiatus. They offered an arthroscopic classification of the popliteomeniscal fascicle of a lateral meniscal tear into 3 types and further developed the classification into 8 subtypes involving the meniscal tears anterior to the popliteal tendon. 250 (Evidence level: E)
11.2) It is better to preserve mechanical stability by repairing the tears involving the red-red zone and the red-white zone. When repairing posterolateral meniscal tears, it is recommended not to fix the meniscus to the popliteus tendon. The popliteomeniscal fascicle tear can be repaired when possible.
Both arthroscopic and open repair approaches have been used to repair isolated popliteal tears in different case series. 101,121,196,248 All clinical evidence at final follow-up demonstrated complete resolution of preoperative symptoms, including pain and knee locking. Only LaPrade et al 121 recorded a negative figure-4 test result for all patients at the conclusion of the observation period. The reports above should be interpreted with caution since they were all single-arm studies without control patients. Isolated popliteomeniscal tears are rare, and they seem to occur more often in younger patients with high-demand activities. No complications were reported because the operations were performed by skilled, experienced, and senior surgeons, and the follow-up period was short. (Evidence level: C)
Statement 12. Treatment for radial and flap tears of the lateral meniscus
Radial and flap tears on the midbody of the lateral meniscus are often seen in traumatic injuries and are typically unstable tears. Surgical intervention is aimed at maintaining the continuity of circumferential fibers, including meniscal repair or meniscectomy.
Based on the lateral meniscal regional classification by Cooper et al, 46 radial, flap, and transverse tears involving zones 1 and 2 should be repaired as much as possible to restore the hoop stress of the meniscus. Long-term follow-up results after lateral meniscal repair are significantly better than those after partial meniscectomy. 115,166 The 2019 European Society for Sports Traumatology, Knee Surgery and Arthroscopy (ESSKA) consensus statement for traumatic meniscal tears recommends repair of traumatic lateral meniscal tears. 115 Partial meniscectomy may be considered for irreparable tears, recurrent tears after repair, or radial and flap tears involving zone 3. 175,177,183,241 Techniques of arthroscopic meniscal repair for radial, flap, and transverse tears in the lateral meniscus include inside-out, outside-in, and all-inside suturing techniques. There is insufficient evidence to prove that one suturing technique is better than the others. 132,147 Considering the increasing concern for osteoarthritis after meniscectomy, meniscal preservation with radial tear repair results in improved short-term clinical outcomes; however, long-term outcomes remain unknown. (Evidence level: C)
Statement 13. Diagnosis, classification, and treatment of root tears of the lateral meniscus
13.1) Posterior lateral meniscal root tears (PLMRTs) refer to bony root avulsion or radial tears within 9 mm of the meniscal attachment. For clinical use, the classifications proposed by LaPrade et al, 119 Forkel et al, 78 and Ahn et al 7 can be used.
PLMRTs refer to bony root avulsion, defined as radial tears within 9 mm of the meniscal attachment. 6,23 PLMRTs have been found in 8% to 9.8% of patients undergoing ACL reconstruction. 28,53
Three different classifications have been proposed to distinguish tear type and prognosis. Forkel et al 78 described a classification of PLMRTs according to localization and compromise of the meniscofemoral ligaments. Type 1 is avulsion of the root. Type 2 is a radial tear of the posterior horn close to the root, with an intact meniscofemoral ligament. Type 3 is complete detachment of the posterior horn. LaPrade et al 119 classified PLMRTs according to arthroscopic assessment of morphology. Type 1 (7%) is a partial and stable root tear, and type 2 (68%) is a complete radial tear within 9 mm of the root attachment. Type 2 tears can be subclassified as 2a (38%), within 0 to <3 mm; 2b (17%), between 3 and <6 mm; and 2c (12%), between 6 and 9 mm from the root attachment. Type 3 (6%) is a bucket-handle meniscal tear with complete root detachment, type 4 (10%) is a complex oblique or longitudinal tear with complete root detachment, and type 5 is a root bony avulsion. Ahn et al 7 also proposed a classification for PLMRTs based on arthroscopic findings: type 1 is a radial tear with an oblique flap; type 2 is a longitudinal cleavage between the bony and meniscofemoral ligament insertions; type 3 is a T-shaped injury; and type 4 is a chronic inner loss type.
Meniscofemoral ligaments are fibrous tissues that originate from the posterior horn of the lateral meniscus and are attached to the lateral wall of the medial femoral condyle. They are classified as an anterior meniscofemoral ligament or ligament of Humphrey, passing anterior to the posterior cruciate ligament, or a posterior meniscofemoral ligament or ligament of Wrisberg, passing posterior to the posterior cruciate ligament. PLMRTs often have intact meniscofemoral ligaments preventing meniscal extrusion. 174 Their presence is variable, ranging from 81% to 100%. 84,152 Only the Forkel classification involves meniscofemoral ligaments, and no surgery has been reported to repair or reconstruct meniscofemoral ligaments. LaPrade et al 119 suggested that the preferred surgical treatment for each patient varied based on the indications for surgical repair or debridement, including age, degree of osteoarthritis, and other concomitant surgical factors. These classification systems can be used to correlate certain root tear types with a recommended treatment and may facilitate better reporting of patient outcomes after treatment of meniscal root tears, by reporting outcomes separately for each tear type. (Evidence level: C)
13.2) The indications for partial meniscectomy include (1) patients with moderate to severe osteoarthritis with mechanical symptoms caused by meniscal lesions, who are not responsive to nonoperative treatment; or (2) patients with an intact posterior root insertion, an incomplete radial tear close to the posterior root, and an intact posterior meniscofemoral ligament, so that meniscal stability can be retained.
Partial meniscectomy can be an option for patients with significant mechanical symptoms that are caused by meniscal lesions, who are not responsive to nonoperative treatment, with chronic posterior root lesions or with diffuse Outerbridge grade 3 to 4 cartilage lesions. 23,163 An acute partial radial tear that does not extend to the capsule is another indication for arthroscopic partial meniscectomy. 23 Anderson and Anderson 9 believed that if the untorn posterior horn retains a substantial attachment to the ligament of Wrisberg, then repair is not required; however, if the root tear involves the ligament of Wrisberg or if the ligament is absent, the repair needs to be performed. However, there is a lack of high-quality research analyzing long-term follow-up. In patients with severe osteoarthritis, the interlocking symptoms may not be caused by the meniscus, and OA with malalignment requires osteotomy or replacement, and arthroscopy does not provide long-term benefits for patients. (Evidence level: C)
13.3) For radial or oblique tears within 9 mm of the posterior root, an all-inside suture technique can be used to preserve the meniscus when there is no degeneration of the residual and the meniscofemoral ligaments are intact.
There is no consensus on which meniscal repair technique is most suitable for PLMRTs based on the different classifications. All-inside and transosseous pull-out repairs are most often used. 74 All-inside repair can be performed in radial tears with a root remnant of adequate tissue quality, as it repairs the meniscus anatomically without changing its native physiologic properties. 7,10,203
Several studies have reported optimistic outcomes after all-inside PLMRT repair with or without ACL reconstruction. 6,10,203,247,252 Ahn et al 7 reported that after PLMRT repair with ACL reconstruction, the displaced lateral meniscus was reduced on MRI, regardless of tear type, at a mean follow-up of 8.7 months (range, 6-27 months). Anderson et al 10 retrospectively reviewed 24 patients who underwent PLMRT repair with ACL reconstruction and found that all-inside repair led to successful function over a mean follow-up of 58.6 months (range, 26-168 months). Similarly, Zhang ZZ reported that after a mean follow-up of 30.7 months, all patients experienced overall improvement of knee function, and 80.8% of the patients had meniscal healing when a second arthroscopy was performed. 247 It should be noted that the above studies were case series, and a high level of evidence was lacking. (Evidence level: C)
13.4) For a posterior root avulsion injury, with or without meniscofemoral ligament rupture, a transosseous pull-out technique suture is recommended.
Evidence has shown that complete posterolateral meniscal root tears are associated with a high-grade pivot-shift phenomenon in noncontact ACL injuries. 201,202 Thus, it is better to preserve the integrity of the lateral meniscal root to restore knee rotational stability and prevent osteoarthritis. 23,163 The basic principle of this technique is to reattach the meniscus by placing sutures at the meniscal root and pulling them through a transtibial tunnel. 120,158 Multiple meniscal suture configurations have been reported, including 2 simple stitches, horizontal mattress stitches, modified Mason-Allen sutures, and 2 modified loop stiches. 73 Among these, the 2 simple sutures have been reported to produce the least root displacement, increased stiffness, and a failure load equivalent to the modified Mason-Allen suture. 35,73 It should be noted that there was a high risk of convergence between the ACL and posterior meniscal root tunnels when all tunnels were created on the anteromedial tibia, and reorienting the meniscal root tunnels parallel to the ACL tunnels may help reduce this risk. 85 Forkel and Petersen 77 described an arthroscopic technique to reattach the posterior meniscal root in combination with ACL double-bundle reconstruction using the tibial posterolateral tunnel to fix the meniscal suture. This is easy to perform when an avulsion lesion has occurred. Since the posteromedial ACL bundle is 10.8 mm anterior to the posterior root of the lateral meniscus, 253 the posterior root can be anatomically fixed to its tibial origin by applying only gentle suture tension when pulling in the ACL graft. 77,78 (Evidence level: C)
13.5) A suture anchor technique can also be used to treat a posterior root avulsion injury, with or without rupture of the meniscofemoral ligaments.
The use of suture anchors has been reported for posterior root avulsion injury repair. 59,75,169 Fixation of PLMRT with a suture anchor has been proven to be a biomechanically adequate construct for medial meniscal posterior root tears. Extrapolating these results onto the lateral meniscus, we can assume that suture anchor fixation is an adequate option for posterior lateral root repair. 72 However, this technique is challenging and requires a posterior portal adjacent to the neurovascular structures. In most cases, a good insertion angle is difficult to achieve in the figure-4 position, when the patient’s lateral knee joint is too tight. 130 There is also no adequate evidence to prove that it has an equivalent clinical benefit to the transosseous technique. Therefore, the suture anchor approach needs to be carefully planned by a senior surgeon who is familiar with this technique. (Evidence level: E)
Statement 14. Indications, contraindications, graft choice, technique, outcomes, and rehabilitation of lateral meniscal allograft transplantation (MAT)
14.1) The indications for lateral MAT are (1) when there is residual lateral joint space pain after meniscectomy and (2) when there is a potential for instability from a lateral meniscal defect during knee stability reconstruction surgery, lateral MAT can be performed as a primary operation.
MAT was first introduced in the 1980s, 141 and it has become a state-of-the-art treatment for patients with symptoms after subtotal or total meniscectomy, especially in young patients. 76,216 The indication for lateral MAT is symptomatic meniscal deficiency without the presence of advanced degenerative changes. Concomitant instability, localized osteochondral defects, or malalignment should be amenable to surgical correction.
In 2015, the International Meniscus Reconstruction Experts Forum (IMREF) published a consensus statement regarding different aspects of MAT. In their survey on indications, 18% of surgeons replied that they would perform lateral MAT in an asymptomatic patient only as a prophylactic predecure. 80 In the current consensus statement, 100% of Chinese surgeons agreed that it is not indicated in asymptomatic patients after meniscectomy.
In patients with cruciate ligament injury and meniscal deficiency, laxity should be carefully screened according to physical examination findings and patient history. Medial MAT performed with ACL revision reconstruction can be beneficial, and medial meniscal graft is expected to protect the ACL and vice versa. 80,134,219 In a robotic study, the lateral meniscus was identified as a restraint to anterior tibial translation and contributed to rotatory stability. 150 Several studies have shown that lateral MAT combined with ACL reconstruction achieves satisfactory subjective and objective clinical outcomes. 228,240,243,245 However, the clinical outcomes of lateral MAT have not been assessed independently, and very few studies have focused on rotational stability after MAT. Recently, Yoon et al 242 assessed the effect of lateral MAT on rotational stability in meniscus-deficient ACL-reconstructed knees, and they found that while it showed improvements on the anterior drawer and Lachman tests, it did not improve the pivot-shift test or side-to-side difference on Telos stress radiographs. Therefore, whether lateral MAT should be performed as a primary operation together with knee stability reconstruction remains controversial, and 18.9% of surgeons voted disagreement on this consensus.
Considering the most recent publications on this topic, we suggest that the decision for lateral MAT should be made according to a case-by-case basis, especially in young patients. It is important to note that any malalignment or instability should be considered during decision-making. (Evidence level: C)
14.2) Contraindications for lateral MAT are (1) lack of symptoms after lateral meniscectomy and (2) presence of osteoarthritis of Kellgren and Lawrence (KL) grade 3 or 4 and extensive cartilage lesions.
Classical contraindications for lateral MAT are advanced osteoarthritis, obesity, skeletal immaturity, inflammatory arthritis, previous septic arthritis, and synovial disease. The prophylactic effect of lateral MAT to maintain rotational instability is uncertain; therefore, Chinese experts agree that performing lateral MAT in asymptomatic patients is a contraindication. (Evidence level: C)
14.3) The most suitable graft for meniscal transplantation is fresh-frozen allograft. Irradiated meniscal grafts are at risk for reduced meniscal fiber strength.
Of the experts, 94.6% favored using a fresh-frozen meniscus for MAT.
Fresh-frozen grafts can be stored at –280°C for up to 5 years, and at the time of surgical implantation, the meniscal allograft is usually thawed in another antibiotic solution. There is considerable variability in graft sterilization and storage. 135 In China, gamma irradiation (1.5 Mrad) is most often used for sterilization. 245 Doses >2.5 Mrad of gamma irradiation can cause significant changes in the biomechanical properties of the grafts, irradiation-induced tissue deterioration at the anterior horn junction, and surgery failure as a result of the attached bone plug. 245 (Evidence level: B2)
14.4) The Pollard method using plain radiography, MRI, or computed tomography (CT) can be applied to measure and match meniscal grafts.
An oversized graft may result in an increased joint load. In contrast, an undersized graft may cause significant shear forces, leading to MAT tears. 216 The Pollard method using radiography, 171 MRI, or CT can be applied to measure and match meniscal grafts, 91,137 but it is not clear which methods are the most accurate or reliable.
According to the Pollard method, the meniscal width is measured on an anteroposterior radiograph as the distance between the margin of the tibial metaphysis and the lateral tibial eminence. The length is measured on a lateral radiograph as the distance between the anterior surface of the tibia above the tuberosity and the posterior margin of the tibial plateau. The use of CT or MRI can avoid any deviation caused by the slicing angle and obtain additional information, such as the positions of knee joint cartilage and the bone tunnel from the previous operation, which is often applied in the meniscal measurements. However, it should be noted that CT measurements may underestimate meniscal size. 137 MRI can be used to measure the size of the unaffected knee. Because human knees are not completely symmetrical, this may cause errors. Errors ≤5 mm were achieved in 83% of MRI measurements of the lateral meniscus, with 72% on radiograph. 192 McDermott 138 believed that errors <5 mm are acceptable and should not affect surgical outcomes. (Evidence level: C)
14.5) Lower extremity alignment measurements are required before lateral MAT. If there is severe valgus deformity, osteotomy is required.
As patients with preoperative malalignment have poorer results, mechanical axis alignment should be evaluated before lateral MAT is performed. 219 Lateral MAT together with distal femoral osteotomy has been reported in previous studies, but it has been investigated less than medial MAT plus high tibial osteotomy (HTO). 25,31,226 Verdonk et al 226 demonstrated that medial MAT and HTO can optimize outcomes compared with transplants without osteotomy. However, the appropriate cutoff value indication is still under debate. Stone et al 209 found that axial malalignment <7° did not affect MAT survival, while Van Thiel et al 222 observed that a 3° valgus correction of a neutrally aligned knee performed with medial MAT can decrease the peak and total medial compartment contact pressures significantly.
Patients with severe malalignment are prone to developing chondral lesions. Severe cartilage damage at the time of MAT was a significant predictor of failure. 165 It is unclear whether MAT can prevent or slow down cartilage degeneration. 1 In patients undergoing MAT with Outerbridge grade 3 or 4 degenerative changes, Stone et al 209 demonstrated no improvement in MAT survival with the addition of alignment correction or chondral procedures. It seems logical that protecting the transplanted tissue from overloading as well as the indications for MAT with osteotomy remain surgeon dependent. Patients undergoing MAT should be counseled regarding future interventions, and that the risk of these increases with increased chondral damage. Long-term analysis of this study and definitive randomized controlled trials will hopefully help to answer this question in the future. (Evidence level: E)
14.6) The outcomes of lateral MAT should be assessed by subjective symptoms, objective function, and MRI examination. Postoperative MRI is used to evaluate the morphology of the meniscal graft and extrusion.
The success of lateral MAT depends on performing the procedure with proper indications and using appropriate-sized menisci, meticulous technique, and suitable rehabilitation. Three main fixation methods can be used to fix lateral MAT: suture-only fixation, double-plug fixation, and the keyhole technique. 36,204,216,235 Different fixation methods have similar outcomes, 70,113,244 and therefore, despite biomechanical differences, 246 the selection of method should be made on a case-by-case basis.
Both clinical symptoms and radiological findings are used to evaluate the outcomes of lateral MAT. An optimal outcome means that lateral joint tenderness is alleviated and functional scores have improved. 76 In a meta-analysis, Bin et al 24 found that the medium-term survival of lateral MAT was 89.2% versus 85.8% for medial, but it was much lower for long-term survivorship (56.6% for lateral and 52.6% for medial MAT). The prognosis of concomitant procedures in MAT remains controversial. Lee et al 126 reported no significant differences in patient symptoms and visual analog scale pain scores between isolated and combined MAT, while Parkinson et al 165 found that the presence of severe cartilage damage at the time of MAT was significantly predictive of failure.
MRI is routinely used to evaluate postoperative outcomes including graft healing, graft extrusion, and other concomitant lesions. The IMREF suggested that surgeons assess graft healing and position by MRI at 1 and 2 years postoperatively. 80 Extrusion was defined as the distance between the outer edge of the articular cartilage of the tibial plateau and the outer edge of the meniscus, and the relative percentage of extrusion was calculated. The rate of meniscal extrusion was significantly higher with suture versus bone plug fixation. 2 Koh et al 113 found that extrusion was also significantly higher after lateral versus medial MAT. Most meniscal extrusions occur in the anterior horn or midbody. 125 The extruded graft yields less protection of the joint cartilage, but there is continued debate whether extrusion is a prognostic factor of graft failure, since several studies have found no association between graft extrusion and clinical outcomes. 86,99 Thus, the practical implications of meniscal extrusion are poorly understood. (Evidence level: C)
Statement 15. Measures to promote meniscal healing
Rasping, fibrin clot or gel, bone marrow stimulation, platelet-rich plasma (PRP), and cell therapy may promote meniscal healing, but there is no definitive evidence of this.
Different techniques have been introduced to stimulate meniscal healing, including rasping, fibrin clotting, bone marrow stimulation, PRP, and stem cell therapy. Rasping is an easy-to-perform mechanical procedure. 32 According to Henning et al, 92 rasping the perimeniscal synovial tissue can promote healing of injuries in the vascular region of the lateral meniscus, although the effects are limited within the avascular region. 155 However, the effect of rasping has not been independently investigated; theoretically, bleeding after rasping might promote healing.
Biologics promoting meniscal healing have drawn significant attention in recent decades. However, despite promising evidence in basic science and animal models, its unproven regenerative capacity in clinical studies has also generated criticism. 145,153,186,195,254 Ishimura et al 97,98 proposed that fibrin clots had a healing-promoting effect on posterior horn injuries of the meniscus, but the outcomes were biased, because all patients underwent simultaneous ACL reconstruction. Growth factors, blood, and platelets are released during the preparation of ACL bone tunnels and can promote the healing of meniscal injuries. 159 Some doctors have proposed using bone marrow stimulation techniques 5 ; however, the same concerns remain, that long-term clinical observations are lacking. 116
Autologous blood, including PRP, is regarded as the most valuable technique among the abovementioned items and has attracted increasing interest. 58 Although multiple studies have attributed improved outcomes with PRP to its autologous makeup, high concentration of growth factors, and ability to promote angiogenesis and soft tissue healing, 44,96 the efficacy of PRP in the context of meniscal repair remains controversial. Belk et al 21 published a systematic review reporting that patients undergoing meniscal repair with PRP augmentation experienced similar clinical outcomes at medium-term follow-up when compared with conventional meniscal repair. Everhart et al 68 found that PRP had a substantial protective effect regarding isolated meniscal repair failure over 3 years; however, when concomitant ACL reconstruction was performed, PRP did not reduce the risk of failure. Furthermore, the role of leukocytes in PRP is unclear, and the concentration of platelets in the injection is another important factor that varies significantly depending on the production method.
Two studies comprising 24 patients augmented with mesenchymal stem cells reported clinical improvements in functional outcome scores pre- to postoperatively. However, these were a case series and a retrospective cohort study with level 4 evidence. 41,189
In conclusion, given the lack of high-level evidence, the role of biologics in meniscal lesion treatment remains controversial. (Evidence level: C)
Statement 16. Rehabilitation protocol after lateral meniscal repair
16.1) A hinged knee brace is recommended in the early phase after lateral meniscal repair, and rehabilitation should progress based on the recovery of range of motion, muscle strength, and subjective symptoms.
In general, the rehabilitation protocol should be tailored to the tear pattern, because each pattern behaves differently when subjected to physiological loads. During the early phase after surgery, patients experience swelling, decreased range of motion, decreased muscle strength, altered proprioception, and abnormalities in gait; these factors can be targeted by a rehabilitation program. To date, there is no consensus on an optimal rehabilitation program after lateral meniscal repair, and different protocols have yielded similar outcomes regarding failure rates, patient-reported symptoms, and return to sports. 90,161,205
Postoperatively, patients are advised to use a locked hinge brace in full extension with crutches, with range of motion and nonweightbearing for 2 weeks, followed by gradual increases in motion and weightbearing. 133 Any restriction in motion or weightbearing will lead to muscle atrophy and decreased strength, which will prolong the return to sports; thus, muscle strengthening is emphasized during this period. 236 (Evidence level: C)
16.2) The progression of weightbearing is based on the tear type and surgical procedure. The timeline of weightbearing for patients who undergo meniscectomy can be shorter than for those with meniscal repair. For patients undergoing repair of longitudinal tears, early weightbearing can be allowed. In cases of radial or root tears, weightbearing should be delayed according to the type and suturing technique.
For patients who undergo partial meniscectomy, the recommendation is complete range of motion and full weightbearing as tolerated by the patient. 188 Weight-restricted protocols are used mainly after radial tear repairs; motion-restricted protocols are implemented mainly for unstable vertical tears; dual-restricted protocols are used for radial, horizontal, and root tears; and accelerated protocols are used for vertical longitudinal tears. 161 Weight restriction protocols allow for immediate range of motion but limited weightbearing in the early postoperative period. 205 In vertical and bucket-handle meniscal tears, axial loading exerts hoop stresses that compress the repair and contribute to its healing. 178 The same loading on a radial tear repair will displace its reduction and delay healing. 90 The majority of published studies restrict weightbearing for 4 to 6 weeks after surgery for radial and root tears. Passive range of motion exercises can be advanced in knee flexion as tolerated after 2 weeks, while progressive advancement to full weightbearing begins at 6 weeks. 23,163,188 (Evidence level: C)
Statement 17. Postoperative outcomes
17.1) After repair of lateral meniscal injury, both clinical evaluation and MRI examination can be used to evaluate the outcomes. The status of repaired meniscus can be assessed more precisely at second-look arthroscopy of other knee problems.
The clinical outcomes of meniscal operations can be subjectively and objectively assessed. The criteria for meniscal healing include (1) no major symptoms such as locking, effusion, or knee catching; (2) no joint space tenderness and negative McMurray test; and (3) improved International Knee Documentation Committee (IKDC) score, Lysholm knee scoring system, and Tegner activity scale. 18,251,252 The role of postoperative MRI is to assess the stability or recurrence of a tear in the meniscal remnant, detect tears in other areas of the meniscus, and identify other causes of postoperative knee pain. There may be increased signal intensity in the meniscal entity because of preexisting degenerative changes or meniscal healing, which can mimic a tear. The increased signal may persist for up to 1 year after a successful repair. 233 Signs of retear are fluid within the line extending to the meniscal surface, a displaced meniscal fragment, or a definite change in configuration compared with the previous tear. Surgeons should understand that the criteria for abnormal signal and morphology are less accurate for meniscal tears at the site of surgery than with a preoperative knee. 14,224
The failure rate of meniscal repair differed in terms of follow-up, tear zone, tear type, time elapsed from injury to surgery, and age. Multiple systematic reviews and meta-analyses have reported good short- and medium-term results, with rerupture rates between 10% and 19%. 83,102 The failure rate over long-term follow-up increased to between 5% and 48% on arthroscopic second look. 168 In a systematic review, Barber-Westin and Noyes 16 found that the healing rate of meniscal repairs located in the red-white region was 83%. Costa et al 47 reported that the overall failure rate of bucket-handle tears was 14.8%, and that lateral bucket-handle tears are less likely to retear than medial bucket-handle tears. Chronicity is another prognostic factor for successful meniscal healing. DeHaven et al 55 found a 33% retear rate for chronic repairs versus 14% for acute repairs. In addition, high failure rates were identified in young patients aged between 10 and 22 years, ranging from 38% to 42%. 88,160 This could be related to high levels of activity.
Partial meniscectomy can improve subjective outcome scores; however, degenerative changes according to KL grade increased significantly 5 years postoperatively, especially in patients with root tears. 163 When comparing the outcomes of partial meniscectomy and meniscal repair in young patients, symptomatic arthritis, reoperation, and failure rates are similar; however, there is a trend for increased arthritis symptoms in patients treated with meniscectomy, especially total meniscectomy. 63 It should be noted that athletes are a high-risk population for osteoarthritis, 62,188 and among athletes, partial meniscectomy can be a tempting first choice because of the short recovery time. 181 Nevertheless, there is a lack of evidence demonstrating the causality between partial meniscectomy and osteoarthritis, and the outcomes stratified by sport, type of tear, and level of play remain unclear. Future studies are warranted to better elucidate sports-specific outcomes of partial meniscectomy. (Evidence level: C)
17.2) The arthroscopic classification of meniscal healing after repair is (1) complete healing: no obvious defect on the meniscal surface with complete synovial coverage; (2) partial healing: small defects on the meniscal surface with >50% of synovial coverage; and (3) nonunion: a large defect on the surface of the meniscus with <50% of synovial coverage.
MRI and arthroscopy can be used to evaluate meniscal healing; however, both have limitations. MRI assessment remains difficult because signal changes at the repair site cannot be distinguished as scar tissue or remaining tear, 173,215,224 while second-look arthroscopy is rarely possible because of costs and ethical considerations. Academically, second-look arthroscopy is regarded as the gold standard for the evaluation of meniscal repair, 146 but in clinical practice, knee function, MRI, and second-look arthroscopy can all be used. The most widely used criteria for arthroscopy were first described by Horibe et al, 94 who categorized meniscal healing into 3 levels. Excellent signified almost complete healing with no visible unhealed areas. Good restoration of stability to the repaired site was observed despite a visible partial-thickness defect. Poor results were recorded when the repaired meniscus was unstable owing to poor healing.
Optimistic clinical outcomes do not always correlate with excellent arthroscopic findings. Previous studies have found high clinical success rates of arthroscopic meniscal repair (77%-99%), but complete healing, as seen on direct visualization by arthroscopy, is lower (73%-83%). 30,146,180,187 In clinically successful cases, 25% of the repair site was not always completely healed; even when the repair site was completely healed, approximately 22% of patients had newly formed tears in different areas. 94 This suggests that clinical success does not always mean good healing, and there may be future problems in cases of incomplete healing and minor degeneration of the meniscal body. (Evidence level: C)
Statement 18. Prognostic factors of meniscal repair
18.1) Multiple factors can predict the outcomes of arthroscopic meniscal repair, including age, body mass index (BMI), length of tear, chronicity, and sex.
Various factors that may influence meniscal repair success have been discussed, including joint stability, associated ACL reconstruction, age, tear shape, tear size, and methods of stimulating healing. 115,206 Meniscal repair outcomes can be multifactorial.
Some authors have reported less favorable results for repairs in the older population. 64 The majority of meniscal tears among these patients are degenerative in nature. Barber-Westin and Noyes 16 also found that patients aged younger than 50 years with good meniscal tissue integrity were better able to mend. However, recent studies have not correlated age and increased risks for reoperation. 182,207 For example, Barrett et al 18 argued that the meniscal healing rates in people older than 40 years had comparable outcomes to those in younger patient populations. Some studies have even identified high failure rates in patients between 10 and 22 years of age, ranging from 38% to 42%. 88,160 This could be related to high levels of activity. In adults, several studies have reported the beneficial influence of ACL reconstruction on meniscal healing, but there is no high-level evidence directly comparing the healing rates of isolated repair versus repairs combined with ACL reconstruction in children. 193,230
The time to surgery is another variable that is difficult to assess. In a systematic review, Barber-Westin and Noyes 16 reported that the chronicity of injury did not adversely affect results. In contrast, DeHaven et al 55 observed a 33% retear rate in chronic repairs compared with 14% in acute repairs. Van der Wal et al 220 found no significant difference in failure rates with respect to the time interval between trauma and arthroscopic meniscal repair. Ronnblad et al 179 and Laurendon et al 123 shared similar findings that the data are scarce regarding the influence of time interval from the moment of injury to the moment of meniscal repair on repair survival; the time interval between trauma and meniscal repair remains controversial.
BMI >25 kg/m2 has emerged as a predictive factor for the failure of all-inside meniscal repair. 123 Yeh et al 238 evaluated 129 isolated meniscal lesions in professional National Basketball Association athletes and found that a BMI >25 kg/m2 increased the risk of meniscal lesions, especially in the lateral meniscus. By extrapolation, a high BMI is likely to have the same impact on a repaired meniscus.
Tear length also affects the outcome of meniscal repair. After repair, bucket-handle tears have demonstrated worse clinical outcomes than smaller vertical longitudinal tears. 183 Cannon and Vittori 33 found that the postrepair healing rate of tears <2 cm was 94%, versus only 50% for lengths >4 cm. Hupperich et al 95 used the number of stitches as a reference for tear length and found that it correlated significantly with Lysholm and IKDC scores, which was consistent with previous reports. 13 Among patients with repaired bucket-handle meniscal tears, the failure rate in women (31%) was significantly lower than that in men (69%). 11 (Evidence level: C)
18.2) The location of meniscal tear is one of the most important factors affecting the prognosis of repair. The healing rate of a tear located in the red-red zone is significantly higher than that of one located in the red-white or the white-white zones.
Compared with repairs of the medial meniscus, lateral meniscal repairs result in fewer failures. 166,179 Although the medial meniscus has a better blood supply, 12 the lateral meniscus is not as firmly attached to the tibial plateau, allowing greater mobility. It is, therefore, potentially more forgiving to stress.
Previous studies have found that peripheral tears indicated superior healing because of sufficient blood supply, 33,83 while Barber-Westin and Noyes 16 reported a healing rate for repairs located in the red-white region of 83%. Ronnblad et al 179 found that this effect was not significant. Almost one-third (28%) of related studies did not report the vascularization zone in which a tear was located. Therefore, the effects of the vascularity zone should be interpreted carefully. (Evidence level: C)
18.3) Combined severe articular cartilage injury is more likely to predict poor outcomes. Outerbridge grade 3 and 4 cartilage lesions, lesions >2 cm2, osteoarthritis of KL grades 3 and 4, and preoperative valgus alignment >5° are not candidates for lateral meniscal root tear repair.
There is a paucity of information in the literature regarding overall clinical outcomes after lateral meniscal root repair. 74,107,122,129 Chondral lesions, knee malalignment, age, and osteoarthritis have all been correlated with poor outcomes in medial meniscal root tears, 144 while the prognosis for lateral meniscal root repair has been scarcely reported. The demographic characteristics of lateral meniscal root tears are different. This injury occurs more frequently in younger male patients, often with concomitant ligamentous injury, fewer degenerative changes, and lower BMI. 117 However, chondral lesions have been inversely correlated with the postoperative outcomes of root repair in both lateral and medial menisci. 117 To extend the experience of medial meniscal root tears, poor outcomes might occur if lateral meniscal root repair is performed in a knee with malalignment >5°, concomitant chondral lesions, and osteoarthritis. (Evidence level: E)
Discussion
This Chinese expert consensus statement focused on the anatomy, function, pathological process, and treatment of lateral meniscal lesions, and echoed previous consensus statements on traumatic and degenerative meniscal lesions that saving the meniscus is critical to preserving the knee. 20,115
Understanding of the lateral meniscus has grown exponentially over time, and the mindset of orthopaedic surgeons has shifted accordingly. Experience acquired from the medial meniscus cannot simply be applied to the lateral meniscus, because the lateral meniscus is a unique entity in the knee joint. The lateral compartment is convex in a convex configuration. 17 The posterior stabilizer of the lateral meniscus is composed of the meniscal root, the meniscofemoral ligament, and the popliteomeniscal fasciculi; because of this configuration, the lateral meniscus is relatively loosely attached to the tibial plateau, and thus there is less blood supply. 12 Given this, the demographic features, pathology spectrum, concomitant injuries, and prognosis of the lateral meniscus are distinct. For example, there are more traumatic injuries, often appearing in young and active patients, always combined with other ligamentous injuries, with less meniscal extrusion and high healing rates in certain types of lesions. All the above discrepancies of the lateral meniscus require an independent approach and algorithm under a principled framework for clinical decision-making and management, and we believe this consensus statement adds much information and insight toward that goal.
Preservation of the meniscus is of utmost importance, and repair should be the first choice of treatment for lateral meniscal tears; the agreement between the literature and expert opinion makes this evident. According to the consensus, longitudinal tears, including bucket-handle, radial, and root tears, should be repaired whenever possible. Even when combined with ACL reconstruction, which has been proven to promote meniscal healing, primary repair of the lateral meniscus is recommended, particularly for posterior root tears. The mechanical symptoms caused by popliteomeniscal fascicle lesions were reviewed and discussed. Zheng et al 248 proposed an arthroscopic classification for tears of the popliteomeniscal fascicle of the lateral meniscus. This facilitates communication among surgeons. However, there is still uncertainty regarding the outcomes of popliteomeniscal fascicle repair because no high-quality study with long-term follow-up has yet been reported. The concern remains that surgery might alter the nature of mobility in the lateral meniscus; thus, it might cause irreparable damage.
We noticed that Chinese surgeons are more likely to rely on MRI manifestations in the decision-making process for the meniscus. In contrast, the 2019 ESSKA meniscus consensus statement reported that MRI was not systematically necessary in a knee with a suspected traumatic meniscal tear. 115 As mentioned in many studies, meniscal injury can be asymptomatic, and only the mechanical symptoms caused by unstable injuries are an indication for arthroscopy. 19 It is not enough to emphasize history taking and physical examination, especially among young surgeons. This consensus statement identified that lateral joint line tenderness along with the McMurray and Thessaly tests are the most widely used clinical examinations. Patients who are asymptomatic but have positive MRI findings should not be treated surgically.
For the assessment of meniscal healing after surgery, second-look arthroscopy is the gold standard. However, MRI is the most commonly used tool in the clinical setting. Often, increased signal within the meniscal tissue is mistaken for a meniscal retear. Increased signal may persist for up to 1 year after a successful meniscal repair. 233 In addition, MRI is not obligated to assess whether a patient can return to athletic activities; knee function and mind readiness are more critical. Therefore, a consensus on the application of MRI should be obtained from doctors of multiple disciplines, such as orthopaedic surgeons, radiologists, and therapists.
Another fact that has drawn our attention is that Chinese orthopaedic surgeons performed fewer cases of lateral MAT than their counterparts in other countries. The major reason is that the allografts are gamma irradiated for sterilization. 245 This has been proven to drastically diminish the biomechanical properties at the junction of the anterior horn and the attached bone plug of the meniscal allograft; thus, the rate of surgery failure is inevitably increased. 245 This concern is reflected in the relatively low agreement percentage on the statement of the indications for lateral MAT.
Although only a few studies have compared the prognosis of the lateral versus medial meniscus, after reviewing the literature, we found that the prognostic factors for repair failure of the lateral meniscus, such as age, tear length, chronicity, and BMI, differed substantially from those of the medial meniscus. However, we still found that there is a paucity of published information regarding the overall clinical outcomes after lateral meniscal root repairs 74,107,122,129 because high-quality studies are lacking.
Limitations
This consensus statement has some limitations. The literature revealed a limited number of studies with high levels of available evidence, and our expert opinions were based mainly on the understanding of current studies. Therefore, this article should not be considered a final statement or guideline, as deeper insights will continue to emerge in the future.
Conclusion
This expert consensus statement focused on the anatomy, function, pathological process, and treatment of lateral meniscal lesions. Accepted recommendations in these areas can assist doctors and therapists in standardizing the management of related pathology. This consensus statement clearly states that numerous lateral meniscal tears that were previously considered irreparable can indeed be repaired. Preservation of the lateral meniscus should be the first-line treatment whenever possible, because the clinical and radiological long-term outcomes are worse after partial meniscectomy.
Footnotes
Acknowledgment
The authors acknowledge the contributions of the following doctors: Lun Mi, Xin Tang, Baogang Wei, Lin Guo, Bin Li, Zhong Zhang, Guofeng Cai, Jun Wang, Qiang Jiao, Yingzhi Li, Chunbao Li, Jiajun Zhao, Juan Wang, Jie Zhao, Mingyu Zhang, Xupeng Wang, Wei Gong, Chengqing Yi, Yanfeng Wang, Haobo Wu, Guangbin Wang, Chen Zhao, Sihai Liu, Xiaofeng Zheng, Xinyu Liu, Chunyue Duan, Chengsong Yuan, Ming Cheng, Yu Mei, Jun Yao, Zhu Han, Xiaohu Wang, Zhaoxu Xin, Dong Zhen, Qiliang Zhang, Siyue Xu, Xinghuo Wu, Guangyu Wen, Huige Hou, Jianwen Ma, and Yiran Wang.
Final revision submitted August 19, 2022; accepted August 26, 2022.
One or more of the authors has declared the following potential conflict of interest or source of funding: This study was founded by the National Key Research and Development Program of China (2021YFA1201303/2021YFA1201300). AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.