The menisci (plural of meniscus) are the two "shock-absorbing" cartilages of the knee. They lie between the end of the femur (thigh bone) and the top of the tibia (shin bone) taking up what appears to be a space on plain X-rays. Comprised of flexible fibrous tissue, these C-shaped structures provide a number of important functions including force distribution, stability and lubrication. They unfortunately have limited blood supply in the adult with vessels only extending about 10-25% from their attachment at the periphery. Much like a fingernail, the remaining tissue is bloodless - however, unlike a fingernail the menisci contain living cells nourished by diffusion and nutrients in the knee joint fluid.

As the meniscus ages it loses elasticity. Like an old rubber washer, it dries out and has a tendency to split and crack. This meniscus degeneration is often seen on MRI but does not necessarily mean there is a tear.

The menisci do not show up on X-ray and are poorly visualized on ultrasound. Arthrograms (X-rays with injection of dye into the joint) are rarely used, having been succeeded by the less invasive and more accurate MRI scan. The "gold standard", however, is visualization at arthroscopic surgery. I have found significant meniscal pathology in the absence of positive MRI findings on a number of occasions in patients with classic clinical symptoms.

Meniscal Tears

Meniscal tears occur when the load applied to the tissue exceeds its strength and flexibility. The force required gets less as we age due to the inherent degeneration in the meniscus. Tear patterns also change. The young individual with an acute twisting injury is likely to have a single, clean tear while an older person will likely have numerous splits and flaps on a background of softening cartilage.

25 years ago, the symptoms of a meniscus tear (see below) meant a trip to the orthopaedic surgeon for an open menisectomy. The knee joint was opened through a 4-5cm incision and the entire meniscus was removed. A particularly barbaric implement, the Smillie knife, (invented by an imposing Scottish surgeon), had a sharp, curved blade and a long handle, enabling the meniscus to be stripped from the knee in a few seconds! Fortunately things have progressed somewhat!

Meniscus Tear Symptoms

• Well-localized sharp pain along the inside or outside joint line of the knee
• Associated swelling, particularly with activity
• Clicking or clunking in the area of the pain
• Locking-up of the knee with inability to straighten it

Meniscus Surgery

The vast majority of meniscus surgery is now performed through the arthroscope, a fibre-optic system allowing excellent visualization and access to all areas of the joint. The meniscus can be seen and examined on the big screen in glorious technicolour - you may even get photos to take home!

The majority of meniscus tears are not suitable for repair. The tears are either outside the vascular healing zone, are too old, macerated or complex for repair to be considered worthwhile. In this case, a simple resection of the torn portion is carried out. Usually this only results in loss of 10-30% of the meniscus and is not associated with long-term problems such as arthritis. (We know that taking the whole structure out, as was done in the past, does lead to early degenerative wear). Recovery is swift with immediate weight-bearing and bending with return to sports in 6-8 weeks, sometimes earlier.

A tear in the peripheral part of the meniscus can often be repaired. This is particularly true for longitudinal splits, the most common type in a younger individual. The repair procedure is much more complex and takes a lot longer than resection. It may require an additional incision and there are added risks of infection and nerve damage. In addition, the recovery is more prolonged. I generally keep patients on crutches and avoid bending the knee for 3-4 weeks after the procedure. For patients who expect to be back to full activity soon after surgery, this can be a little upsetting so I normally discuss repair restrictions with the patient pre-operatively.

Success rates for meniscus repair are in the region of 80-90%, with the higher percentages occurring when the repair is done at the same time as an Anterior Cruciate Ligament (ACL) reconstruction. In the event of failure, re-repair is possible.

Future advances will likely involve the use of tissue proteins that promote healing. Success with artificial or transplanted menisci has thus far been limited and is performed experimentally at only a few centers.

Following surgery, participating in an exercise program is important to strengthen the specific muscles groups that support the knee joint. Inactivity due to injury often allows key muscle groups to weaken. A knee injury may also cause an altered gait pattern (walking pattern) which can lead to further muscle imbalances not only in the knee, but also the hip and ankle as well. Physiotherapy can help to identify these muscle imbalances and develop an exercise program to correct them. As well as developing an exercise program, physiotherapy may also include joint mobilizations to help restore normal knee joint range of motion.