Meniscal Pathology

A meniscus is a crescent of C-shaped fibrocartilaginous structure present in the knee. There are two menisci in your knee the inside or medial meniscus and the outside or lateral meniscus each rests between the femur and tibia. They are shaped concave on the top and flat on the bottom and attach to the tibia by coronary ligaments and by direct insertion into the bone. Towards the center they are unattached and their shape narrows to a thin shelf. The medial meniscus attaches to the deep layer of the medial collateral ligament and the lateral meniscus attaches loosely to the lateral capsule. The menisci have a blood supply at the periphery this lessens and becomes avascular as you move towards the inner or center aspect of the meniscus. This is important because peripheral tears have the potential to heal and conversely central tears do not secondary to the nature of their vascularity.

Function of the meniscus

The menisci have several important functions. They disperse body weight across the surface of the joint by increasing the area of joint contact between the femur and tibia. They also act as important shock absorbers by virtue of their viscoelastic properties (visco – resist shear flow and strain linearly with time when a stress is applied; elastic – materials strain instantaneously when stretched and just as quickly return to their original state once the stress is removed). The medial meniscus provides stability to the knee acting as a secondary restraint to anterior tibial translation (limits the tibia from moving forward). They assist in joint lubrication and articular cartilage nutrition by maintaining a synovial fluid film over the articular surfaces. Lastly they are thought to provide proprioception (sense of relative position of neighboring parts of the body) input by virtue of nerve endings stimulated by motion and deformation.

Mechanism of injury

A combination of rotation and axial loading appears to be the etiology of many meniscal injuries (eg: a football player twists his upper leg with the foot fixed on the ground). Meniscus injury can also be a result of prolonged wear ‘n tear known as a degenerative tear these tears may be exacerbated by rather innocuous activities such as walking or squatting. There are several different classifications of meniscus tears and these are important in determining management of the injury.

Symptoms and signs

Chief complaints are usually knee pain and swelling the pain tends to be worse in a hyperflexed or squatting position. There may be mechanical symptoms of catching and/or locking this may be accompanied by a “clicking” sensation and in some cases individuals may report their knee “gives way”.

Management

In general, management is based on the patient’s symptoms, as well as age and functional expectations. If the individual exhibits concomitant injury such as an ACL tear this may need to be treated. Absolute indications for surgery are tears that are displaced and occur in young patients. The fragment from a displaced tear can cause a locked knee or inability to achieve full extension. Relative indications for surgery include persistent symptoms, such as catching, locking, pain and swelling, and persistent problems after 6 to 12 weeks of conservative treatment.

• Nonoperative Tears

Indications for the conservative treatment of meniscus injuries include absence or improving symptoms, age, functional expectations, and the sight of injury.

Surgical Intervention

• Partial Meniscectomy

This is indicated with tears in the inner or avascular area, during this procedure the torn tissue is removed and the remaining tissue is resected to promote stabilization. This procedure can be completed athroscopically with specialized cutting and motorized shaving instrumentation. Complications although rare exist following meniscectomy including recurrent tearing, injury to the articular surface from rigid instrumentation, and the risk of avascular necrosis to the underlying tibia.

• Meniscal Repair

As discussed previously the periphery of the meniscus is vascular and this enhances its ability to heal and to be a good sight for repair. Techniques for meniscus repair include using arthroscopically placed tacks or suturing the torn edges. Both procedures function by reapproximating the torn edges of the meniscus allowing them to heal in their proper place. Complications exist following meniscus repair and most commonly depend on two factors. First if the meniscus repair is attempted on a tear in the central portion of cartilage (where the blood supply is poor) it is likely to fail. Secondly the patient must be compliant with post operative rehabilitation. One study suggested a 20 to 40% failure rate, if this happens a second surgery may be necessary to remove the re-torn meniscus.

Rehabilitation

Rehabilitation following a Partial Meniscectomy includes immediate gains in ROM and early ambulation. The patient is allowed to walk as tolerated, and full weight bearing is encouraged immediately. It is thought that early ROM and return to weight bearing decrease postoperative pain significantly. The primary goal of rehabilitation is the return of normal bilateral strength of the quadriceps before competition. General guidelines are a return to work in 1 to 2 weeks, resume activity after 2 to 4 weeks, and return to competition in 4 to 6 weeks.

*Please note these are general guidelines and if there is a question a patient should follow there physician’s postoperative protocol.

Rehabilitation following a Meniscus Repair includes immediate control of postoperative effusion as this has been shown to have a profound effect on quadriceps contraction. Weight bearing is allowed immediately as tolerated with crutches and knee braced in full extension. Range of motion exercises are begun immediately with the goal of 0 – 90º. The brace hinge is adjusted at 4 weeks to allow ROM during ambulation with weight bearing out of the brace at 6 weeks. Straight plane running is begun at 3 to 4 months, with return to full athletic participation by 5 months.

*Please note these are general guidelines and if there is a question a patient should follow there physician’s postoperative protocol.