What Are the Menisci and How Are They Injured
The menisci are C-shaped cartilage bushings that sit between the thigh (femur) and shin (tibia) bones in the knee. The ends of the femur and tibia do not match. This allows the knee to act as a complex polyaxial joint rather than a simple hinge. The menisci match the differing shapes together and perform a critical role in protecting the articular cartilage on the end of the bones. Damaging a meniscus therefore increases the risk of arthritis so a repair if possible is always the first option but as you will read below, not all tears are amenable to repair.
Meniscal tears can be classified broadly as either traumatic or degenerate.
1. Traumatic tears occur due to substantial force (usually twisting combined with compression) being applied to an essentially normal meniscus. This produces an unstable, vertical tear that displaces when loaded, causing pain, swelling and sometime locking of the knee. Most meniscal surgery deals with traumatic tears and can be a repair or a partial resection (removal). The best way known to get a traumatic tear is to leave an ACL deficient knee unreconstructed and is one of the primary reasons that ACL ruptures should be reconstruction earlier rather than later (see the ACL Reconstruction page for more information).
2. Degenerate tears are not traumatic and occur due to normal load being applied to an ageing meniscus. Degenerate tears do not heal so repair is not an option. Many degenerate tears do not cause symptoms and are incidental findings on an MRI and should be left alone rather than resected. This is especially the case if the tear is horizontal and / or if knee already has arthritis. There is a large body of quality evidence that says that even if a degenerate tear in an arthritic knee is causing symptoms it is best treated without surgery. The Australian Knee Society has produced a position statement on the subject.
Repair or resect
A meniscal tear can be repaired or removed (resected). Repair restores the function of the meniscus that is to protect the articular cartilage from premature wear (arthritis). Resection removes the unstable torn part of the meniscus and although it can dramatically reduce pain does leave the meniscus partially deficient and so does not protect the knee from arthritis.
The meniscus is largely avascular (no blood supply) and so has limited ability to heal if repaired. Repair is therefore done selectively in circumstances when the tear is close to an available blood supply. The recovery period from a meniscal tear is not insubstantial so there is no point repairing a tear than cannot heal.
A meniscectomy is a day procedure done through keyholes under a general anaesthetic. Weight bearing and movement are not restricted. Forearm crutches are used to control gait (the mechanics of walking) not to take weight and are usually necessary for 1 or 2 days. A couple of quiet days in the house is advisable to keep the knee settled and then activity can be increased gradually provided the knee is not swollen. Physiotherapy is usually not needed after surgery and time off work is usually only 2-14 days depending on how physical work is.
Meniscal repair is most commonly done in concert with an ACL reconstruction but can be an isolated procedure. There are many meniscal repair techniques all of which need to be mastered and available if as many menisci as possible are to be saved. If a blood supply to heal the meniscus is clearly available completing the repair is a case of suturing the meniscus back to its rim and / or bony attachments (roots). If blood supply is compromised an autologous clot (some of your own clotted blood) must be incorporated into the repair.
Meniscal repair is a day or overnight procedure. Weight bearing is totally restricted for 4 weeks and partially restricted for another two weeks. Squatting and running are restricted for at least 2 months after that. The meniscal repair will fail if the restrictions are not adhered to. Physiotherapy is universally necessary and time off work can be substantial for obvious reasons.
Because weight bearing is restricted after meniscal repair there is a definite risk of a DVT (deep venous thrombosis) that must be managed. Being young and healthy is no protection in itself so attention to detail is important.
Bucket Handle Tear Repair
On the left a photo of a bucket handle tear of the Medial Meniscus jammed in the middle of the knee. On the right the meniscus repair with multiple sutures.
Meniscal transplant surgery is reserved for specific circumstance of a young person with almost complete loss of a meniscus causing pain and early arthritis. Meniscal transplant is often combined with other procedures (usually ACL reconstruction and / or osteotomy) as the transplanted meniscus will not tolerate instability or mal-alignment.