One of the common causes of sudden knee pain is a meniscus tear.
The meniscus is a crescent shaped piece of fibro-cartilage inside the knee joint. Each knee has 2 menisci – a medial meniscus and a lateral meniscus. The medial meniscus is C-shaped whereas the lateral meniscus is more semicircular shaped. Both are composed of fibrocartilage with bony attachments at the anterior and posterior aspects of the tibial bony surface.
The menisci are 50% as stiff as articular cartilage and thereby function as significant shock absorbers in the knee. Loss of the meniscus leads to a loss of this shock absorbency and increased demands on the cartilage. In other words, the meniscus has a “chondro-protective” effect on the knee cartilage.
Loss of meniscus tissue is associated with development of knee osteoarthritis.
Studies have shown that the medial meniscus absorbs 50% of the medial knee joint load while the lateral meniscus absorbs 70% of the lateral knee joint load.
In addition, the meniscus transmits 50% of the joint load when the knee is extended and 85% to 90% of the joint load when the knee is flexed.
The treatment of meniscus tear is generally through knee arthroscopy.
Surgery can result in one of two outcomes for the meniscus. The torn meniscus is either repaired or the torn portion is removed.
For a meniscus to heal, the tear should occur at the portion of the meniscus where there is blood supply. From the capsule to the innermost portion, we know that the outer 1/3 has good blood supply and hence will heal if repaired in a stable manner. The middle 1/3 has some blood supply but the healing is not so predictable after a repair. For the innermost 1/3 of the meniscus, there is no blood supply and hence any repair here will fail.
Commonly accepted criteria for meniscal repair include a complete, vertical, longitudinal tear greater than 10 mm in length, a tear of the peripheral 30% of the meniscus or within 3 mm of the menisco-capsular junction, a peripheral tear that can be displaced toward the centre of the plateau by probing, the absence of secondary degeneration of the meniscus, and a tear in an active patient or one undergoing concurrent ligament or chondral reconstruction.
Numerous factors affect the success of meniscus repair. It is generally believed that patients younger than 40 years old are thought to have a better chance of healing. Knees with associated ligamentous instability, particularly ACL instability, have poorer rates of meniscus healing because of abnormal meniscus stresses from knee instability. The location of the tear and the time lapsed from injury to treatment are also important.
Some meniscus tears should not be repaired. These include tears of degenerate meniscus which have no potential for healing, complex tears, chronic tears, meniscal tears in patients with knee malalignment as well as in patients with an unstable knee (e.g. torn ACL).
This is a patient with a locked knee (knee jammed and cannot straighten) due to a displaced bucket-handle tear of the medial meniscus.
This meniscus tear was repaired using an inside-out meniscus repair technique as shown:
A 2nd look arthroscopy 3 months later showed a healed medial meniscus repair.
Medical devices have advanced to a stage that meniscus tears can be repaired using just 2 portals during knee arthroscopy. These devices allow the surgeon to repair the meniscus tear using an all-inside technique.