There are two C-shaped cartilage menisci present in the human knee. While, even 40 years ago, orthopaedic surgeons did not think twice about removing a torn meniscus completely, this procedure is now frowned upon, based on the fact that we now know that these structures fulfil an essential role in the knee. Their wedge shape in cross section provides congruity to the otherwise incongruous knee joint cartilage, thereby preventing rapid onset of wear and tear arthritis (osteoarthritis). These menisci may be injured through tearing, which is usually caused when the meniscus is trapped between the articular surfaces of the knee joint during a twisting moment, such as a sidestep or a rugby tackle. Patients with this problem usually complain of immediate pain in the knee joint line and difficulty or inability to continue playing their sport. Moderate swelling usually occurs within the next few hours and in extreme cases, where the tear is unstable and displaces, the knee may lock and extension may be impossible. Another type of meniscal injury is the degenerative tear, which occurs in patients over 35 where the water content of the meniscus decreases and the dried up cartilage is more prone to tearing with even minor trauma. These tears rarely cause mechanical symptoms until they become unstable and patients in this group will often complain that they have been suffering from joint line pain during squatting for some time but recently the pain has worsened and there is an associated click or intermittent locking of the knee. With a large tear, a meniscal cyst may develop, which will cause localised swelling around the knee joint line.
Treatment of meniscal injurys differs between age groups and is largely based on functional demands of the various patients. Fresh meniscal tears in young athletes should be repaired if it all possible. This is done with an elegant all-inside arthroscopic technique, using suture anchors. Unfortunately not all meniscal tears can be repaired and in the case of repairable tears, healing is by no means guaranteed. Repairability is usually best assessed at arthroscopy. It depends on location and morphology of the tear, which may be determined preoperatively on an MRI scan. Another advantage of a preoperative MRI scan is the determination of any associated problems such as meniscal cysts and/or bone bruising.
Degenerative tears in older patients (35 years or older) are mostly debrided (cleaned up) and shaved back to a stable edge. This sometimes requires subtotal meniscectomy, however it is in the best interest of the patient to leave at least a stable rim of meniscus intact. In patients with degenerative meniscal tears, there are often associated cartilage changes in the knee which represent the earliest form of osteoarthritis. These cartilage flaps or defects may be addressed at the same arthroscopy.
Children may be born with a so-called discoid meniscus, which is a birth defect where the outside meniscus does not develop into a C and remains in the shape of a pancake. Many people may go through life without ever realising that they have a discoid meniscus in their knees (usually occurs on both sides). This is because these structures rarely give any problems, unless they are torn. If it tear does occur, the patient will present as described above. Treatment for this condition involves saucerisation (fashioning it into a C shaped and decreasing thickness) of the meniscus.
