Guidelines on the Diagnosis and Treatment of Lateral Meniscal Lesions: A Consensus Statement by the Chinese Society of Sports Medicine

Statement 1. Definition and classification of traumatic lateral meniscal lesions

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 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

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

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

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

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

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).

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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

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

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

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

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)

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

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

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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

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

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)

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

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)

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

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)

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)

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)

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.