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.
Mensical 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 woman.
- These may or may not be associated with trauma, unlike acute tears.
Epidemiology including risk factors and primary prevention
Knee meniscal injuries are common with an incidence of 61 cases per 100,000 persons and a prevalence of 12% to 14%.7 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 surgical repair of the meniscus.7 Peak incidence of acute meniscal tears occurs in men from 21 to 30 years old and in women from 11 to 19 years old. 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.3
- 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 and lateral menisci attach to their corresponding lateral 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
- Vascular supply: Primarily avascular structure, but the meniscus receive their main supply from the peripheral branches of the popliteal (medial, lateral inferior, and middle geniculate arteries).21 . Vascularization is limited to 10-25% of periphery for the lateral and 10-30% of the medial menisci, respectively.20,21
- Greater healing potential in vascular region (outer one third or “red-red” zone), which has excellent prognosis if a tear occurs 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
Extent of tear-partial or full thickness- This is described by the vertical depth of tear. 20
Zone classification system- This is devised by Cooper et al, 1990 where the meniscus is divided into three radial zones in a anterior to posterior direction and four circumferential zones going from the periphery to the inner meniscus.20
- 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- Are vertical tears that occur and the posterior and middle thirds of the meniscus and tract 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 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 is the most common type of displaced flap tear.
- Complex Degenerative- Display two or more tear configurations. Most common meniscal lesion and seen with other degenerative joint changes. These are not amendable to meniscal repair. Suspect displaced and bucket-handle tears when mechanical symptoms (buckling, catching, popping, or locking) along with limited range of motion are present
- Medial meniscus: Less mobile, firm attachments to deep medial collateral ligaments. Typically, associated with vertical longitudinal tears.20,28,29 (Human Meniscus; Mordecai; Klimkiewicz)
Lateral meniscus: typically associated with radial tears.20,28,29
- Medial meniscus: Less mobile, firm attachments to deep medial collateral ligaments. Typically, associated with vertical longitudinal tears.20,28,29 (Human Meniscus; Mordecai; Klimkiewicz)
Discoid meniscus variant
- Usually found in lateral meniscus, rate in medial meniscus. Incidence is 3.5% to 5%; about 25% bilateral prevalence. Common in pediatric and young adult populations.3,30, 42
- Increased tear tendency: altered capsular attachments/vascular supply.
- Usually asymptomatic.
- History of snapping/popping knees in childhood/adolescence without history of trauma.30
- If the patient is symptomatic, a partial arthroscopic meniscetomy and/or repair will be recommended. 30,42
Specific secondary or associated conditions and complications
Associated ligament injuries: ACL injury. 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
Associated fractures: tibial-plateau or femoral-shaft fractures. Kissing bony contusion of tibial plateau and femoral condyle if the ACL involves the syndrome of the unhappy triad: medially directed force at the knee when the foot planted, causing tears to the ACL, medial collateral ligament, and medial meniscus.
2. ESSENTIALS OF ASSESSMENT
Acute meniscal tears occurith a twisting injury associated with a feeling of grinding with acute swelling. Posterior horn tears often present with pain on the posterior medial aspect of the knee. Recurrent pain occurs when the athlete tries to rotate, plant, and twist during sporting 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 and catching. Such mechanical symptoms associated with recurrent swelling 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 quadriceps muscle for atrophy, palpate knee for effusion, compare side-to-side, and examine mechanical symptoms during squatting.
No single test is sufficient to establish diagnosis. Provocative maneuvers are less reliable in the presence of degenerative tears or ligamentous injury.
Joint line tenderness1,2,6,14
- Positive when palpation of the medial and lateral joint line elicits tenderness.
- Sensitivity: 55%-83%1,14
- Specificity: 58%-98%1,14
- Positive predictive value (PPV): 45%14
- 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%1,14
- Specificity: 57%-78%1,14
- PPV: 57%14
- Negative results should not be overly emphasized because of relatively low sensitivity.
Apley grind test1,2,6,14
- Positive when pain elicited while 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%1,14
- Specificity: 72%-90%1,14
- PPV: 57%14
Thessaly test 14,15
- Patient stand 1-legged, flatfooted, knee flexed at 5°, and hands held by 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: 62%-64%14,15
- Specificity: 53%-55%14,15
- PPV: 97%
Bounce Home Test
- Patient’s leg is fully flexed with the heel placed in examiners 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
- Are recommended following acute injury and if patient meets one of the five Ottawa Knee rules. They include age greater then 55, tenderness on the patella or head of the fibula, inability to flex beyond 90 degrees, inability to bear weight for four steps.44
- Cannot visualize meniscus.
- Rules out the following:
- Distal femur and proximal tibial fractures
- Loose bodies
- Safe, inexpensive and operator dependent method to assess injury.
- Limitations include the ability to properly assess deep structures of knee.8
- In a study by Park et al comparing ultrasonograpahy 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
- False positives noted with tears of the posterior horn of medial meniscus and false negatives with radial tears.
- Cysts 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
Supplemental assessment tools
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
Early predictions of outcomes
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 point because healing potential is vascular-dependent. Peripheral tears with inherently high healing potential should be repaired and nonvascular tears where healing will not 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 policeman, 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 to 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 function history, in order to guide their progression and recovery.
For patients who have undergone post-meniscectomy, activity can resume fairly quickly as long as their rehabilitation is closely monitored and supervised. The postsurgical 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-play must be factored in for the patient who is an athlete. As early as 4 to 6 weeks is a possibility with meniscectomy not involving 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 sports specific exercises.33Meniscus repair is indicated for unstable tears in the vascular zone and/or extension of a tear in the avascular zone. 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
3. REHABILITATION MANAGEMENT AND TREATMENTS
Available or current treatment guidelines
- Consensus of 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.
- Ice applied for fifteen minutes every 4-6 hours and elevation to decrease swelling.
- Patients should begin isometric straight leg raise exercises without weights aiming to strengthen quadriceps to provide further joint support.
- Avoid exercise that requires maximal knee flexion such as stair stepper and rowing machine.
- General goals include the following:
- Decrease pain and swelling.
- Restore range of motion, muscle strength, and endurance.
- Optimize neuromuscular coordination.
- Individualize rehabilitation based on patient goals, concurrent injuries, and nature of the tear.
Factors that indicated successful nonsurgical treatment include minor swelling with symptoms gradually development 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 Mcmurrys.38
Patient & family education
- Encourage performance of home exercises.
- Remind patients that everyone progresses at a different pace.
- Complications/setbacks may develop (eg, 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 the structural pathology of the meniscus identified during arthroscopy had no association with pre-operative pain and function. This finding questions the need of arthroscopic surgery for the treatment of presumed meniscus related pathology and does not lead to decreased pain and symptoms.17 In addition, the Meniscal Tear for Osteoarthritis Research (MeTeOR) trial found no evidence correlating meniscal pain and symptoms with relevant MRI finding of various meniscal tears. This again shows that meniscal pathology does not determine 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 mensicectomy 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 mensicectomy 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 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 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
4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE
Cutting edge concepts and practice
The future of managing meniscal injuries is focused on increasing the body’s own healing potential through biologic agents. Platelet rich plasma (PRP), derived from autologous whole blood, consists of numerous growth factors and cytokines, which basic and clinical studies have are shown to promote healing by stimulating cell migration, cell proliferation, angiogenesis, and matrix synthesis.11 Meniscus injury is one of the most common conditions treated with PRP, but further controlled studies specifically for PRP into damaged meniscus in humans is needed.11 Adipose tissue derived stem cells are also being used in many orthopedic applications because of its regenerative properties on cartilage, bone, and tendons. In 2014, Pal et al. presented a case of injecting adipose derived stem cells in a meniscus tear and showed improvement in VAS score, function, ROM, and meniscus regeneration under MRI within 3 months post-treatment.12 Bone marrow derived mesenchymal stem cells can also be used with studies showing that postoperative (arthroscopic debridement) intra-articular injection decreased pain and promoted meniscal regeneration.13 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 treatment is completed. Currently, these injection treatments have been reserved for patients who do not improve with activity modification, medications, and supervised, structured physical therapy.
5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE
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 biologic agents and their role in non-surgical management.
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Original Version of the Topic
Christopher T. Plastaras, MD and Jerry Fang, MD. Meniscus injuries of the knee. 09/20/2013.
Brian Pekkerman, MD
Nothing to Disclose
Puneet Ralhan, MD
Nothing to Disclose
Richard G. Chang, MD, MPH
2016 Foundation for PM&R; Richard S. Materson ERF New Investigator Grant, Research Grant paid to institution, Principal Investigator