Injury to the meniscus occurs when its structural integrity is compromised and the fibrocartilage that makes up the meniscus tears, breaks, cracks, ruptures, or splits.
Meniscal tears are caused by a combination of axial loading and rotational forces that create a shearing force on the meniscus. 20
- Usually secondary to trauma affecting younger active individuals.
- Most commonly are vertical-longitudinal tears with peak incidence being 21-30 years of age
- Secondary to age-related cumulative stress and desiccation/deterioration.
- Constitute 30% of all meniscus tears with peak incidence of 41-50 years of age in men and 61-70 in women.
- These may or may not be secondary to trauma, unlike acute tears.
Knee meniscal injuries are common with an incidence of 61 cases per 100,000 persons and a prevalence of 12% to 14%.7. The ratio of men to women is 2.5:1 to 4:1. Degenerative meniscal tears most often occur in men ages 40 to 60 years old.20
There is an increased incidence of meniscal tears with anterior cruciate ligament (ACL) injury ranging from 22% to 86%.7 In the US, of the estimated 850,000 cases per year, 10% to 20% of orthopedic surgeries involve surgery of the meniscus with over 50,000 meniscectomies and 3,000 meniscal repairs performed each year7, 51
Meniscus Anatomy & Functions
- Crescent shaped pads of fibrocartilage between the femoral condyles and tibial plateaus that help with load distribution, knee stabilization during rotation, and lubrication of the knee joint.
- The medial meniscus shape resembles the letter “C,” whereas the lateral meniscus shape resembles the letter “O.”
- Discoid lateral meniscus are normal. Ovoid variants occur where the posterior attachment is absent. Such variants may increase the risk for injury.
- The medial and lateral menisci attach to their corresponding collateral ligaments with the medial meniscus attached more rigidly than the lateral.
- Composed of mainly water (72%) and collagen (22%), with glycosaminoglycans (17%), DNA (2%), adhesion glycoproteins (<15%), and elastin (<1%), which endows shock absorption and joint lubrication properties.21 This composition will vary with age and history of concurrent injury. Meniscectomized knees have about 20% reduced shock absorption due to loss of viscoelastic benefits. 22
- The menisci receive their main supply from the peripheral branches of the popliteal (medial, lateral inferior, and middle geniculate arteries), but are primarily avascular structures21. Vascularization is limited to 10-25% of periphery for the lateral and 10-30% of the medial menisci, respectively.20,21
- There is greater healing potential in the vascular region (outer one third or “red-red” zone), which carries an excellent prognosis if the location of a tear is here. An intermediate zone (“red-white” zone) at the border of the above vascular supply has a good prognosis, whereas the inner central two-thirds (“white-white” zone), is avascular and has poor prognosis for recovery and healing. 23,24,25,26,27
- In younger patients, meniscal tears are often associated with sports injuries and excessive force. In older individuals the meniscus is typically degenerated making it susceptible to injury. Typically, the injury occurs with a twisting or shearing motion with added valgus or varus force onto a flexed knee. It often does not involve contact with another player, can be associated with cutting or deceleration, and can be described as taking a wrong step.20
In general, there is no universally agreed upon system to classify meniscal tears. They are usually classified by tear patterns seen during arthroscopic surgery and/or etiology of the injury, which can further be described as full or partial thickness.20 The extent of the tear – whether it is partial or full thickness – is determined by the vertical depth of tear.20
The Zone Classification System was devised by Cooper et al in 1990 in which the meniscus is divided into three radial zones in an anterior to posterior direction and four circumferential zones going from the periphery to the inner meniscus.20
Morphology of Meniscal Tears20
- Vertical Longitudinal: these tears occur parallel to the long axis of the meniscus between the circumferential collagen fibers. They tend to occur medially in isolated meniscus tears and laterally with ACL tears. May be asymptomatic and able to be repaired with suture fixation.20
- Radial: These are vertical tears that occur at the posterior and middle-thirds of the meniscus and track from the inner margin to the periphery. Are usually traumatic with a large proportion occurring at the posterior horn of the meniscus.
- Horizontal: These tears are parallel to the tibial plateau and cause a division of the meniscus into superior and inferior portions. Most commonly, they occur in the posterior aspect of the medial meniscus.
- Oblique/Bucket Handle: This is a vertical or oblique tear with extension of the tear towards the anterior horn of the meniscus. The inner fragment is often displaced toward the intercondylar notch. These tears usually involve the entire meniscus and are the most common type of displaced flap tear.
- Complex Degenerative: This is the most common type of meniscal lesion and typically involves two or more tear configurations and is seen with other degenerative joint changes. These are not amenable to meniscal repair. Suspect displaced and bucket-handle tears when mechanical symptoms (buckling, catching, popping, or locking) are present along with limited range of motion.
- Medial Meniscus: Less mobile, firm attachments to deep medial collateral ligaments. Typically, associated with vertical longitudinal tears.20,28,29
- Lateral meniscus: typically associated with radial tears.20,28,29
- Root Tear: This is a tear of the posterior attachment of the medial meniscus. Less common than meniscal body tears and frequently unrecognized. These tears often lead to medial meniscal extrusion, a risk factor for rapid joint degeneration. Treatment of root tears with meniscus repair has been found to be the most effective approach. 52 48
Discoid Meniscus Variant
- It is a congenital variant that is typically seen in the lateral meniscus and rarely in the medial meniscus. Incidence ranges between 3.5% to 5% with a bilateral prevalence of about 25%. Common in pediatric and young adult populations.3,30, 42
- While patients with this variant are typically asymptomatic, they are at increased risk for tears given their altered capsular attachments/vascular supply.
- Typically, patients present with a history of snapping/popping knees in childhood/adolescence without a history of trauma.30
- If the patient is symptomatic, a partial arthroscopic meniscectomy and/or repair will be recommended. 30,42
Associated ligament injuries
- ACL: Lateral meniscus tears are often associated with an acute ACL tear, whereas chronic ACL deficient and stable knees are associated with medial meniscal tears.20
- May be associated with syndrome of the unhappy triad, where a medially directed force at the knee when the foot is planted causes tears to the ACL, medial collateral ligament, and medial meniscus.
- Tibial-Plateau fractures; Femoral-Shaft fractures; and bony contusions of both surfaces of the knee, i.e., the femur and tibia (also known as a kissing contusion).
Essentials of Assessment
Acute meniscal tears occur with a twisting injury associated with a feeling of grinding and the presence of acute-onset swelling. Posterior horn tears often present with pain on the posterior medial aspect of the knee. Recurrent pain occurs when the patient tries to rotate, plant, and twist during activity. The pain at the onset of injury is variable and patients with small tears may continue to ambulate. With larger tears, there is often instability and mechanical symptoms, including locking, buckling, and catching. The presence of these symptoms are often associated with recurrent swelling and are indications for earlier surgical consultation.
Degenerative tears typically occur without an inciting event but become symptomatic after a slip/twist injury or fall. These tears are also associated with swelling, sometimes developing the day after the offending activity.
On physical examination: check for antalgic gait, inspect the quadriceps muscle for atrophy, palpate knee for an effusion, compare each knee side-to-side, and observe for mechanical symptoms during squatting.
No single test is sufficient to definitively establish a diagnosis, and provocative maneuvers are less reliable in the presence of degenerative tears or ligamentous injury.
Joint Line Tenderness 1,2,6
- Positive when palpation of the medial and lateral joint line elicits tenderness.
- Sensitivity: 55%-83%1
- Specificity: 58%-98%1
- Positive when there is a palpable or audible clunk and the patient experiences the same sensation as when the knee was initially injured when the knee is put through full range of flexion and extension while the leg is alternatively placed at full internal and external rotation.
- Sensitivity 16%-63%1
- Specificity: 57%-78%1
- Negative results should not be overly emphasized because of relatively low sensitivity.
Apley Grind Test1,2,6
- Positive when pain is elicited while the knee is flexed to 90° and the leg is internally and externally rotated while in neutral position, distraction, or compression.
- Compressional pain suggests meniscal injury.
- Sensitivity: 13%-43%1
- Specificity: 72%-90%1
Thessaly Test 14,15
- Patient stands 1-legged, flatfooted, knee flexed at 5°, and with their hands held by the examiner for balance. The patient then internally and externally rotates the knee and body 3 times. This is repeated at 20° flexion. Test is positive if there is medial or lateral joint line discomfort or mechanical symptoms.
- Sensitivity: 89%14
- Specificity: 97%14
- Accuracy 94% and 96%15 (for medical and lateral meniscal injury respectively)
Bounce Home Test
- Patient’s leg is fully flexed with the heel placed in the examiner’s hand and allowed to passively extend and bounce home. The knee should extend completely, and if the extension is not complete or has a rubber end feel, it is considered positive.1
- Recommended following acute injury and if the patient meets one of the five (5) Ottawa Knee Rules. They include: (1) age greater than 55, (2-3) tenderness on the patella or head of the fibula, (4) inability to flex beyond 90 degrees, or an (5) inability to bear weight for four steps.44
- Radiographs cannot visualize the meniscus, but are an effective way to rule out the following:
- Distal femur and proximal tibial fractures
- Loose bodies
- Degenerative Joint Disease Ultrasound
- Safe, inexpensive and operator dependent method to assess injury.
- Limitations include the inability to properly assess deep structures of knee.8
- In a study by Park et al comparing ultrasonography and MRI for detection of meniscal tears showed a sensitivity and specificity of 86.2% and 84.9% respectively. 31
- Based on meta-analysis by Dai. et al there is a 88% sensitivity and 90% specificity of detecting meniscal injury.8
Magnetic resonance imaging (MRI)
- A study by Yan et al showed sensitivity and specificity of identifying medial meniscal tear on MRI to be 95.7% and 75.8% respectfully.16
- Medial meniscus tears: sensitivity 91.4%-93% specificity 81.1%-88%.5,32
- Lateral meniscus tears: sensitivity 76%-79% specificity 93.3%-86%.5,32
- Root tears: 93.3% sensitivity, 100% specificity and 100% positive predictive value, in a study by Choi et al.53
- False positives noted with tears of the posterior horn of medial meniscus and false negatives with radial tears.
- Cysts are highly correlated with degenerative tears.
Arthrogram (fluoroscopic, computed tomography [CT], or magnetic resonance [MR]) 4
- Fluoroscopy or CT used in patients with metal implants, severe claustrophobia, and obesity.
- MR arthrogram preferred over MRI for assessing recurrent tears in patient’s status post-meniscal repair or with >25% meniscus resection.4
Bone scans are not conventionally used for diagnosis of medial meniscus tear. However, 96% of acute tears have abnormal osseous homeostasis at the region of the tear.4
Decision to rehabilitate, repair, or excise is initially based on the patient’s age and type of tear (degenerative or acute) and mechanical symptoms of locking leading to limited range of motion. Unless there is a mechanical block, the primary treatment will always consist of conservative measures. Tear location based on imaging/arthroscopy is an important decision-making tool because healing potential is vascular-dependent. Peripheral tears with inherently high healing potential should be repaired whereas nonvascular tears, where healing is unlikely to occur, should be excised.
Challenges lie before patients with knee meniscus tears who have occupations that require deep knee bending, twisting, jumping, and kneeling, such as policemen, firefighters, plumbers, construction workers, and roofers. Patients should be rehabilitated past the point of knee pain resolution and ensure that any swelling and locking/catching is resolved. Progressing back to work-specific functional tasks is critical.
Return-to-work/play must be individualized based on the patient’s diagnosis, any associated injuries, past medical and functional history, in order to guide their progress and recovery.
For patients who have undergone post-meniscectomy, activity can resume if their rehabilitation is closely monitored and supervised. The post-surgical rehabilitation program includes moving patients to progressive passive and active range of motion exercises, open kinetic chain (OKC) exercises, and closed kinetic chain (CKC) exercises.
Return-to-sport must be factored in for the patient who is an athlete. A return as early as 4 -6 weeks is possible with meniscectomies without any associated ligamentous repair, but at the risk of increased future articular surface degeneration. An athlete will only be cleared to return to their sport once they possess equal core, hamstring, and quadriceps strength, endurance, and range of motion in their sport-specific exercises.33
Rehabilitation Management and Treatments
- Consensus of the rehabilitation algorithm is not established.
- Initial management includes rest and avoidance of specific maneuvers that place extreme pressure on the knee including squatting, kneeling, and twisting.
- Apply ice for 15 minutes every 4-6 hours and elevate the affected knee to decrease swelling.
- Patients should begin isometric straight leg raise exercises without weights to strengthen the quadriceps to provide further joint support.
- Avoid exercise that requires maximal knee flexion such as stair steppers and rowing machines.
- General goals include the following:
- Decreasing pain and swelling.
- Restoring range of motion, muscle strength, and endurance.
- Optimizing neuromuscular coordination.
- Individualizing rehabilitation based on patient goals, concurrent injuries, and the nature of the tear.
Factors that indicated successful nonsurgical treatment include minor swelling with symptoms gradually developing over one to two days, capable of bearing weight on lower extremity with full range of motion with pain only at end range of flexion. History could involve inability to identify time of injury and recovery for a previous similar injury with physical exam eliciting pain on flexion when performing the McMurray Test.38
Meniscus repair is indicated for unstable tears in the vascular zone, and/or extension of a tear in the avascular zone, and meniscus root tears.48 The goal of repair is to preserve as much meniscal tissue as possible with the “inside-out” technique the gold standard.33 A longer rehabilitation period is the disadvantage with this treatment due to traditional rehab programs limiting postoperative weight bearing and knee flexion less than 90 degrees in the initial period.33,34 However, recent studies seem to show that early weight bearing and range of motion is possible without negatively affecting their repair.35,36,37
Patient & family education
- Encourage performance of home exercises.
- Remind patients that everyone progresses at a different pace.
- Complications/setbacks may develop (e.g., patellofemoral pain secondary to changes in patellar tracking in the setting of altered biomechanics).
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
Management of meniscal injury is determined on the type of tear, age of patient, and previous level of function/goals after surgery. Small intrasubstance and vertical tears that cause minimal symptoms can be managed conservatively. Large complex tears, large tears in contact with articular cartilage, and locked knee should be considered for surgical referral. Recent studies have shown that specific meniscal pathology found during mensical surgery were not associated with pre-operative self-reported pain and function in patients with mensical tears, ultimately questioning the role of arthroscopic surgery to address meniscal structural pathology to improve patient reported outcomes.17 In addition, the Meniscal Tear for Osteoarthritis Research (MeTeOR) trial found no association between type of meniscal damage and frequency of mechanical meniscal symptoms; highlighting the difficulty in predicting symptoms and clinical presentation 39
An intra-articular steroid injection can control pain and inflammation in patients with a degenerative tear and concomitant osteoarthritis, albeit temporarily and should not be used frequently as there is recent evidence of further articular cartilage degeneration and osteoarthritis with repeat corticosteroid exposure.43 Off-loader bracing may decrease activity-related pain in patients with medial and lateral compartment narrowing or chronic tears.38
Surgical options consist of partial/total meniscectomy and meniscus repair. Surgical repair is less successful in older patients with severe osteoarthritis and degenerative meniscal tear. The current literature suggests that nonoperative treatment consisting of physical therapy be first line for degenerative tears in older individuals.
Patients with chronic tears may require longer recovery time and rehabilitation after surgery.9 For patients with chronic degenerative meniscal tears, multiple studies have shown no improvement in pain or function of arthroscopic surgery over physical therapy.10 As per the American Academy of Orthopaedic Surgery (AAOS) guidelines, arthroscopic knee surgery for osteoarthritis is not recommended. However, the guidelines were not able to recommend for or against arthroscopic partial meniscectomy in patients with osteoarthritis.18 In a recent multicenter randomized participant and outcome assessor blinded placebo controlled study evaluating patients with degenerative meniscus tears without osteoarthritis undergoing arthroscopic partial meniscectomy versus placebo surgery showed no difference in outcome between the two groups.19 Therefore, in this study, arthroscopic partial meniscectomy for patients with degenerative meniscus tears is not recommended, even if they have failed conservative therapy.19 In 2020 Sihvonen et.al published the FIDELITY study, a multi-center blinded randomized controlled trial comparing APM vs placebo surgery in degenerative meniscal tears with a 5 year follow up, which revealed an increased risk of progression of knee osteoarthritis with APM and no benefit in patient relevant outcomes.45 In addition, another multicenter RCT by Katz et al showed no significant functional improvement in surgery with physical therapy versus physical therapy alone in patients with mild to moderate OA with meniscal tears.40 In one prospective longitudinal study in the Netherlands of 3,337 patients at high risk and/or with symptomatic knee osteoarthritis confirmed on radiography followed from 2004 to 2016, Rongen et al, found that there was a 3 fold increase in patients undergoing total knee arthroplasty if they had a history of arthroscopic meniscetomy.41 Studies show a 2 year 80% success rate following meniscal repair, especially in younger patients with peripheral horizontal or vertical tears.9
Meniscal root tears can be managed both non-operatively and operatively. Operative options include either partial meniscectomy or meniscal root repair. In patients who are elderly, have multiple comorbidities, or have advanced degenerative joint disease, non-operative management remains the treatment of choice. Partial meniscectomy is indicated in patient with significant pre-existing degenerative joint disease and chronic symptomatic tears while meniscal root repair is indicated in acute traumatic tears who have yet to develop degenerative joint disease, or in patients with chronic symptomatic root tears without significant degenerative joint disease.52 Similar to the management of other meniscal tears, favorable surgical outcomes are more likely in the young and those without significant degenerative joint disease.
In general, the prognosis depends on the age of the patient, type of tear, and underlying condition of the knee, with overall good outcomes in tears amenable to nonsurgical treatment.9,10
Cutting Edge/ Emerging and Unique Concepts and Practice
The future of managing meniscal injuries is focused on increasing and promoting the body’s healing potential through orthobiologic cellular injections and scaffold implants.
Platelet rich plasma (PRP), derived from autologous whole blood, consists of numerous growth factors and cytokines, which basic and clinical studies have shown to promote healing by stimulating cell migration, cell proliferation, angiogenesis, and matrix synthesis.11
Recently there have been multiple studies seeking to explore the relationship between PRP and meniscus tear management. In Pujol et al, injection of PRP in open meniscus tear surgery revealed significant improvement in pain and function. Similarly, in 2018, a RCT by Kiminisky et al, revealed significant improvement in pain, function, and radiological evidence of healing with PRP supplementation in arthroscopic meniscal tear surgery as compared to control (arthroscopic saline injection).46
Mesenchymal Cellular treatments have also garnered much attention.47
Bone marrow (BM) derived mesenchymal stem cells can also be used with studies showing that post-operative (arthroscopic debridement) intra-articular injection decreased pain and possibly promoted post-operative meniscal regeneration.1
Adipose tissue derived stem cells are also being used in many orthopedic applications because of its potential regenerative properties on cartilage, bone, and tendons. Furthermore, it has been found to yield possibly a greater concentration of stem cells compared to BM derived sources. In general, it is more easily accessible tissue because it may be obtained from subcutaneous tissue from the abdomen, thigh, and arm.47 In 2014, Pak et al. presented a case of injecting adipose derived stem cells in a meniscus tear and showed improvement in VAS score, function, ROM within 3 months post-treatment.12 Pak et al conducted a safety cohort report, of which, 32 patients with meniscal tears received an intra-articular mixture ASCs, PRP, and hyaluronic and with significant improvements in pain and function.47
Finally, a systematic review by Korpershoek et al found evidence suggesting that repair and regeneration of meniscal tissue may occur when cellular mesenchymal stem cells are injected intra-articularly (but no definitive data showing full healing of meniscal architecture).48
Although all these recent studies have been promising, at this time, these treatments cannot be formally recommended as first line treatments until further investigative trials comparing these therapies to current nonsurgical and surgical standard of care treatments are completed. Currently, these injection treatments have been reserved for patients who do not improve with activity modification, medications, and supervised, structured physical therapy. Meniscal scaffolding, which uses collagen or polyurethane implants, has also emerged as promising alternative conjunctive therapy in partial meniscectomy. There are currently two commercial scaffold implants available, the Collagen Meniscal Implant along with the polyurethane based Actifit. They both allow for meniscal tissue to grow in the implant. Long-term prospective cohort studies have shown significant improvement in both pain and function when used in partial meniscectomy as compared to partial meniscectomy alone.49 A systematic review of 19 studies in 2018 by Houck et al reinforced these findings.50 Despite the promise of the scaffold implantation seen in many prospective studies, high quality comparative studies with long term follow up are still needed to accurately assess and compare outcomes.49
Gaps in the Evidence-Based Knowledge
Post-repair rehabilitation is undergoing scrutiny. Accelerated protocol successes question the traditional value of protection of the repair above all else. Traditionally, decreased mobility and weight bearing was recommended for 4 to 6 weeks, with progressive removal of activity limitations at periodic follow-ups.33 Accelerated rehabilitation has shown no short-term harm with immediate weight bearing, full range of motion without bracing, unlimited exercise, and early return-to-sports.33-37 Also, future studies with level 1 evidence are needed to further assess the benefits and adverse effects of the various orthobiologic agents and their role in non-surgical management.
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- Pak J, Lee J, Park K, Park M, Kang L, Lee S. Current use of autologous adipose tissue- derived stromal vascular fraction cells for orthopedic applications. Journal of Biomedical Science. 2017 24:9
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- Choi, SH, Bae S, Ji SK, et al. The MRI findings of meniscal root tear of the medial meniscus: emphasis on coronal, sagittal and axial images. Knee Surg Sports Traumatol Arthrosc. 2012;20:2098–2103.
Christopher T. Plastaras, MD and Jerry Fang, MD. Meniscus injuries of the knee. 9/20/2013.
Previous Revision(s) of the Topic
Brian Pekkerman, MD; Puneet Ralhan, MD; and Richard G. Chang, MD, MPH. Meniscus injuries of the knee. 8/7/2017
German Valdez, MD
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Abid Haque, MD
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Richard G. Chang, MD, MPH
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