The meniscus works like a shock absorber in the knee, assists with lubrication of the joint and helps to stabilise the knee. Most meniscal injuries are from a twisting type movement of the knee. Unfortunately the meniscus has a poor blood supply and it therefore has a limited potential to heal.
Injury to the meniscus and even partial loss of meniscal function significantly alters force transmission across the knee. This allows arthritis to develop in the knee over a very long time period (the severity and timing of the resulting arthritis depends on your age, activity levels, body weight and degree of meniscal damage). Damaging your lateral meniscus has a much poorer long term prognosis than damage to the medial meniscus.
Most patients with a repairable meniscus are under 45 years of age and up to 80 percent of these are associated with a tear of the anterior cruciate ligament. Isolated tears in young patients can result from a specific high energy twisting incident but older patients may develop symptoms just standing from a sitting position.
The clinical features of a meniscal tear can be variable with all or none of these features being present:
- History of sports related injury
- Pain not allowing further movement or game play
- Pain localized to the anteromedial joint line (front and inside of the knee – medial meniscal tear – the pain that occurs with a lateral or outside tear is far more diffuse)
- Locking or catching of the knee
- Swelling can appear hours after the injury but the knee does not always swell with an isolated meniscal tear
- Initial symptoms are relieved by rest
- Symptoms reappear after trivial twists or strains of the knee
- The knee may be held slightly flexed (bent)
- An effusion (swelling or fluid on the knee) may be present
- Localized tenderness over the medial joint is typical of a medial meniscus tear; tenderness on the lateral side is less well-localized;
- Extension (straightening) is often limited; flexion (bending) is generally not reduced
- The thigh muscle will be wasted in long-standing cases
While there are other possibilities the two common forms of meniscal tears are:
- Bucket handle –This is often a larger tear that is amenable to repair.
- Degenerative – The tear starts at the inner edge and works its way back. This causes a horizontal tear which is not repairable.
- Symptomatic degenerative tears are best treated with a partial menisectomy (removing the broken pieces of tissue) but in younger patients every effort should be made to repair the meniscus where possible.
- When assessing a meniscal tear to decide if it is repairable we look at the location of the tear, the type of tear and its related blood supply. Three zones determine the healing prognosis for meniscal injuries: red-red, red-white, and white-white.
- The red-red zone has an excellent blood supply and therefore has an excellent healing prognosis. The red-white zone is at the border of the bood supply and has a generally good healing prognosis. The white-white zone is relatively bloodless and has a poor prognosis for healing.
- Meniscal repair procedures are divided into 2 major types: open and arthroscopically assisted (keyhole). The location of the tear will determine which technique is used.
Rehabilitation after a meniscal tear can take up to 6 months to complete but is well worth the effort as it protects the knee from arthritis in the long term. The success rate of the surgery is about 85%.
Generally speaking younger patients should be referred early for surgery as the results of repair are better if performed soon after the injury.
Since areas with poor blood supply do not heal well, attempts are being made to enhance healing. These methods include: fibrin clot injection, vascular access channel creation and synovial abrasion.
A fibrin clot can be injected into the meniscal lesion to promote healing through hematoma chemotactic factors.
Vascular Access Channels
Vascular access channels (trephination) are tunnels created from vascular portions of the peripheral meniscus (red zone) to the more central avascular area (white zone).
Abrasion of the synovium with a surgical rasping device activates chemotactic factors that stimulate meniscal healing. Synovial cell migration to the meniscal defect may enhance healing
Lasers can be used for ablation or destruction of damaged meniscal material. They are thought to work via photothermal, photochemical, and photomechanical mechanisms but the exact reason for their effectiveness is not actually known.
A meniscal allograft is donated from a cadaver and transplanted into an injured knee. This is usually only done if the patient has ongoing symptoms with their day to day activities several months after their initial surgery. There are 4 types of meniscal allografts: fresh, deep frozen, cryopreserved and freeze dried. In Australia all grafts are irradiated by law which changes their mechanical properties. Results of this type of surgery have been disappointing but if new methods of sterilization (super critical) are approved in Australia this will become a viable option.
Collagen scaffolds may eventually provide the properties necessary for fibrochondrocyte ingrowth to facilitate meniscal regeneration in humans. Histologic studies have shown variable results and further clinical trials are needed to decide if this is a good or bad idea.
Return to full activities after a menisectomy usually takes about 6 weeks. Patients typically walk out of hospital and do not require crutches or splints.
After a meniscal repair patients are typically placed in a splint and given crutches for balance but are asked to fully weight bear through the operated leg. At four weeks the splint is removed and range of motion exercises are started. Straight line running is achieved at 3 months and return to side stepping sports, squatting and twisting achieved at 6 months.
Patients who undergo combined ACL reconstruction and meniscal repair can safely follow the same accelerated protocol as patients who only undergo ACL reconstruction.
Historically, the lack of understanding of the function of the meniscus resulted in its total removal when it was injured. Unfortunately this led to a generation of patients with medial compartment OA. Increased preservation of meniscal tissue has led to less long term arthritis. We now remove as little tissue as possible and repair the meniscus to preserve its function when we can.
We are working on meniscal replacement tissue but so far none of the materials tried are as good as being able to repair the patients own meniscus.
Rehabilitation after a meniscal tear can take up to 6 months to complete but is well worth the effort as it protects the knee from arthritis in the long term. Generally speaking younger patients should be referred early for surgery as the results of repair are better if performed soon after the injury.