What is the meniscus?
The menisci are two crescent shaped wedges of specialised cartilage (connective tissue) that acts as shock absorbers and load distributors between the bone surfaces of the end of the femur (thighbone) and the top of the tibia (shinbone). They are made of tough, rubbery connective tissue, they help absorb vibrations and force within the knee. They also assist in joint lubrication by spreading the synovial fluid over the femoral surfaces.
There are two menisci in each knee:
- The medial meniscus is on the inner side of the knee and is more commonly injured than the lateral meniscus because it’s less mobile and is directly attached to the medial collateral ligament and joint capsule.
- The lateral meniscus is on the outer side and takes approximately 70% of the joint load through the lateral compartment of the knee. Therefore, injuries to the lateral meniscus may be more serious as they proportionately take more load than the medial meniscus.
The blood supply to both menisci is in the peripheral third of the meniscus and therefore poor making it unlikely for them to heal once torn.
How is the meniscus injured or damaged?
The menisci may tear with specific trauma to the knee. This may occur when twisting a flexed (bent) knee with body weight or sudden impact activity.
An individual may describe feeling a “pop” or “crack” but unlike an ACL injury may continue to weight bear or continue their activity with swelling occurring several hours or a day later. They may have clicking, and an individual may complain of “locking” (when the meniscus fragment gets trapped between the femur and tibia) with difficulty in straightening the knee. Sometimes they may complain of the knee giving way particularly with an episode of sharp pain, which may be either on the medial (inner) or lateral (outer) side, when twisting. Acute (traumatic) meniscus tears may occur with almost any sport and with certain gym activities including burpees. They may also occur with certain types of Yoga.
In people over the age of 40 years old the menisci slowly begin to degenerate, they become weaker and less elastic so are more fragile. As they become more fragile small tears may occur as a result of repetitive stress “degenerative tears” rather than as a result of a specific traumatic event. The damage may occur with something as innocuous as kneeling or squatting and may present with pain without swelling.
How is a meniscus injury diagnosed?
Diagnosis is made based on a patient’s symptoms, mechanism of injury and a physical examination. An MRI scan would identify the location of the tear and its extent in most cases. Occasionally an X-ray may be performed if there is a suspicion of osteoarthritis.
How is a meniscal tear treated? Surgical vs. Non Surgical management?
Non-operative treatment involves analgesia, reducing the swelling, certain physiotherapy exercises to improve flexibility and strength and avoiding provocative exercises such as squatting. In the presence of osteoarthritis the joint may be injected with cortisone to reduce the pain. Once torn the meniscus tends not to heal due to the poor or lack of blood supply to the cartilage. For relatively low demand patients with modification of activities and lifestyle this may be sufficient.
Operative treatment is usually indicated for high demand active individuals with persistent or recurrent symptoms, failed conservative treatment and with locked knees. This is performed using an arthroscope (keyhole surgery) and may be a partial meniscectomy (trimming the torn portion of the meniscus) or a meniscus repair (stitching the meniscus back together with special sutures).
Most arthroscopic knee surgeons will try to preserve the meniscus as much as possible as it is an essential shock absorber. Complete or subtotal (nearly complete) removal of the meniscus significantly increases the risk of developing osteoarthritis over a period of 15-20 years. Meniscus repair is therefore performed whenever possible depending on the location and type of tear. Ideally patients with acute symptoms should contact an orthopaedic knee surgeon skilled in arthroscopic meniscus repair promptly as chronic tears tend to be less favourable for repair. Often determining whether a tear is repairable can only be made by the surgeon at the time of arthroscopy.
A meniscus injury can be sustained at the same time as an injury to the ACL, particularly in athletes and sporting individuals. It is important to seek the advice of a specialist soft tissue knee surgeon promptly in order to obtain a prompt diagnosis and to discuss all the treatment options available.
What is meniscal replacement or transplant?
In circumstances where a patient continues to suffer with knee pain and swelling or has a recurrence of symptoms following a meniscectomy they may be a candidate for either a partial meniscal replacement where segments of the missing meniscus are replaced with bioabsorbable scaffolds or a meniscus allograft transplant, replacement of the whole meniscus (meniscus allograft transplantation).
Partial meniscal replacement
A collagen meniscal implant can be fixed into the knee to fill a missing defect in a meniscal cartilage. It is stitched into place arthroscopically (keyhole surgery) with special sutures and allows new meniscus tissue to grow into the scaffold. It is appropriate for small meniscus defects where the peripheral rim this is because the meniscus is a relatively avascular structure with a limited peripheral blood supply.
Meniscus allograft transplantation
A meniscus allograft transplant is applicable for larger meniscus defects where most of the meniscus has been trimmed or where there is no meniscus rim left. The meniscus allograft (meniscus taken from a donor) is matched to fit the recipient’s knee and the donor screened for bacteria and viruses. The graft is appropriately sterilised and frozen for storage. As the graft has no living cells and remaining donor cellular material is deep within a dense matrix tissue, unlike with most other organ transplants, it is inaccessible for the recipient’s immune system to mount a response. As a result there is no risk of immune mediated rejection or the need for immunosuppressive therapy. The allograft transplant is passed arthroscopically into the knee and secured with a combination of stitches and special bone tunnels and bone anchors which secure the ends of the graft to the tibia (top of the shinbone).
Following meniscal replacement or transplant, a rehabilitation program with physiotherapy is started to help you to ultimately return to sport and a wider range of activities. This is dictated by patients meeting milestones and under the supervision of the surgeon and specially trained physiotherapist.