Who tends to get meniscus tears?

Traumatic tears are common in people aged 13 to 40 whose injuries are sport-related, and in athletic populations more than one third occur alongside an ACL tear. Degenerative tears are seen more often after age 40 and frequently affect the posterior horn of the medial meniscus. The incidence in men is roughly 2.5 to 4 times that in women.

Why do menisci tear, and what are the common tear patterns?

Tears usually happen when the knee is flexed and weight-bearing with an added twist, through either contact or non-contact mechanisms. Common patterns include vertical/longitudinal, bucket-handle, oblique/flap, horizontal, complex, and root tears. Horizontal tears are more common in older adults, and a bucket-handle tear can displace and cause the knee to lock.

What increases the risk of a meniscus tear?

Risk factors include being male, playing soccer or rugby, pre-existing ligament injury, degenerative joint disease, a discoid meniscus, poor quadriceps control, and chronic ACL laxity. Of note, in sports such as soccer and basketball, research on female athletes suggests their risk of meniscus injury can be more than twice that of male athletes.

If a meniscus tear is suspected, what symptoms appear and how is it examined?

Patients often feel knee pain after activity, which may come with locking, sudden giving way, swelling, or a sensation of something loose inside the joint. On physical examination, an effusion combined with joint-line tenderness is relatively reliable, and it can be paired with the McMurray, Apley, and Thessaly tests. MRI is the gold standard for diagnosis, but a physician still needs to interpret the findings in context.

From Prevention to Treatment: Understanding Meniscus Tears of the Knee and Your Treatment Options

The knee menisci are two C-shaped cartilage structures (the medial meniscus is oval-shaped and the lateral meniscus is more circular), with the medial averaging about 3-5 mm thick and the lateral about 4-6 mm. Sitting between the bones of the knee joint, they mainly distribute pressure, absorb shock, provide lubrication and nutrition, bear weight, and stabilize the joint, especially during rotation.

The outer 1/3 of the meniscus (the red zone) has a good blood supply, the middle 1/3 (the red-white zone) has a limited blood supply, and the inner 1/3 (the white zone) has little vascular supply. A meniscus tear can change the biomechanics of the knee joint, leading to various symptoms and making the knee more vulnerable to other short- and long-term consequences, such as quadriceps or popliteus inhibition, patellofemoral pain syndrome, gait changes, and osteoarthritis.

Epidemiology

Traumatic tears usually occur in people aged 13 to 40 and are related to sport-related injuries. In athletic populations, more than 1/3 of cases are associated with an ACL tear; 66.7% of acute ACL injuries are accompanied by a lateral meniscus tear, only 4.6% by a medial meniscus tear, and 6.0% by tears of both menisci at once.
Medial tears are more common than lateral ones, but in patients with an ACL tear, lateral tears more often occur together with it.
Degenerative tears are seen more often in patients over age 40, and in older patients the posterior horn of the medial meniscus is the most commonly affected site.
The incidence is higher in men than in women, with a ratio between 2.5:1 and 4:1.
With increasing age, the turnover rate of meniscal collagen decreases, cellular enzymes and inflammatory signaling increase, capillary supply decreases, advanced glycation end products accumulate, and mechanical properties weaken.

Etiology and Pathophysiology

The meniscus can be divided into three layers, from outer to inner: the red zone, the red-white zone, and the white zone.
The lateral meniscus is less stable, but the medial meniscus bears twice the load of the lateral one.
Meniscus tears can occur under twisting, shearing, or compressive forces, causing injury through contact or non-contact mechanisms.
The injury mechanism is usually a twisting motion of the knee added while it is in a flexed, weight-bearing position.
Injury types include:
Vertical/longitudinal: common, associated with ACL tears
Bucket-handle: may displace into the notch
Oblique/flap: may cause locking of the knee
Horizontal: common in older adults, may be associated with a meniscal cyst
Complex
Root: a lateral root tear may be associated with an ACL tear, and a medial root tear may be associated with cartilage damage

Risk Factors

Male sex (although in sports such as soccer, basketball, lacrosse, and softball, female athletes have more than twice the risk of meniscus injury as males)
Playing soccer or rugby
Ligament injury
Degenerative joint disease
Discoid meniscus
Poor quadriceps control
Waiting more than 12 months from ACL tear to reconstruction surgery
Chronic ACL laxity

History

Patients may describe sudden or gradually worsening knee pain, especially after activity.
Traumatic tears in younger athletic populations usually have a clear history of a twisting or shearing injury, whereas degenerative osteoarthritis in older adults lacks a clear history of trauma.
The pain is usually located on the side of the meniscal damage.
It may be accompanied by knee locking, sudden giving way, swelling (especially after activity), or a sensation of a loose body inside the joint.
Symptoms may ease on their own and typically recur as activity increases.

Physical Examination

The examination should look for swelling, local warmth, redness, and tender points around the knee.
An effusion combined with joint-line tenderness is one of the most reliable findings.
Specific tests, such as the McMurray test, the Apley test, and the Thessaly test, can help diagnose meniscal injury.
The examination should include stability testing of the knee to assess the integrity of the cruciate and collateral ligaments.
Pain may intensify when the patient performs a deep squat or a rotational movement.

Differential Diagnosis

Anterior cruciate ligament tear
Posterior cruciate ligament tear
Osteochondral injury of the knee (OCD)
Tibial plateau fracture
Patellofemoral pain syndrome
Bursitis
Chondromalacia patellae
Patellar dislocation/subluxation
Intra-articular loose body

Diagnostic Tools

X-ray: usually normal; can be used to rule out fractures or assess degenerative changes, but cannot directly diagnose a meniscus tear.
MRI: the gold standard for diagnosing meniscus tears, though false positives are possible. It can show the type of meniscal tear as well as other soft-tissue injuries.
Ultrasound: has some role in diagnosing meniscus tears, with 97% sensitivity and 86% specificity for a meniscal cyst, but it is harder to confirm injury in deeper regions.

Conservative Treatment

Early treatment usually includes rest, ice, compression, and elevation (the RICE principle), along with anti-inflammatory medication (NSAIDs) to control pain and reduce inflammation.
Cast immobilization is not recommended unless there is a fracture or a major ligament injury, but a knee brace can provide support, protection, and symptom relief.
Physical therapy may help improve the stability and function of the knee and reduce the risk of injury.
Weight control: an easily overlooked but important point.
Nutritional supplements: studies are small and carry a risk of bias, so it is advisable to consult a healthcare professional before use; these include boswellia resin, turmeric, and others.

Injection Treatment

Corticosteroid injection: usually relieves symptoms and is suitable as an initial treatment for meniscus tears in degenerative osteoarthritis, but the total volume and frequency of injections should be watched carefully to reduce the risk of cartilage toxicity.
Hyaluronic acid injection: an ultrasound-guided approach usually works better, and it may be considered for some patients who need to avoid the burden of corticosteroids.
PRP regenerative injection: a popular injection approach in recent years. Current research suggests that a high dose of PRP at 50-60 ml was associated with better outcomes in studies than a low dose of 10-20 ml (it is also considerably more expensive). Overall, at 12-month follow-up, PRP was associated with better outcomes than corticosteroid and hyaluronic acid in the studies; these are research findings and do not predict any individual’s outcome.

Surgery

In some situations, if conservative treatment does not work, surgery may be needed, particularly in younger, highly active patients (under 35). The following situations warrant referral for a surgical evaluation: a locked knee, a young patient with a vertical longitudinal tear around the periphery of the meniscus, bucket-handle tears, flap tears, an associated cruciate ligament injury, an osteochondral defect, a loose body, or a fracture.
Meniscal repair: for tears with a good peripheral blood supply, especially in younger patients, meniscal repair surgery can be performed to preserve meniscal tissue, for example vertical and longitudinal types; the failure rate increases in patients over 50.
Partial meniscectomy: when a tear cannot be repaired or is located in a poorly vascularized region, a meniscectomy may be performed to remove the damaged part of the meniscus, for example horizontal tears, which are usually related to degeneration and have a lower chance of healing, or types such as complex and radial tears, or when a repair has failed two or more times.
Meniscal transplantation: for patients with pain persisting more than 6 months after meniscectomy, a BMI under 35, and near-total meniscal removal; recovery takes longer.

Follow-up

Follow-up includes regular physical examinations and imaging studies to assess recovery and detect potential complications early.
Rehabilitation and exercise training play a key role in the postoperative course to help achieve the best possible functional recovery.
The long-term prognosis after meniscal repair surgery is usually better, whereas meniscectomy may increase the risk of future degenerative osteoarthritis of the knee, particularly with extensive resection.

References

Curr Rheumatol Rep. 2023 Feb;25(2):35-46.
JAMA. 2023 Oct 24;330(16):1568-1580.
BJSM blog The MSK playbook – Meniscal Knee Injuries