There are different types of cartilage found in the body and each is adapted to its specific function. In the knee, two different types of cartilage function side-by-side.
The knee is no different from most other joints in that it is lined by hyaline cartilage. This cartilage serves to provide a smooth gliding surface for joint motion, and is called articular cartilage. Articular cartilage does not have a blood supply and as such, it has poor intrinsic ability for healing and regeneration. Thus, injuries to articular cartilage, especially in the knee, are a significant cause of pain and disability.
The meniscus is a piece of “C” shaped cartilage. It is tough and rubbery and made up of fibrocartilage. There are two menisci in each knee and they have multiple functions. First, they act as shock absorbers to lower the stress transmitted to articular cartilage. They also help to evenly distribute forces acting through the knee joint and help the ligaments with joint stability. Menisci derive their blood supply from blood vessels that enter them from the periphery. The central area of the meniscus is devoid of blood supply and has poor healing potential, unlike the peripheral zone.
Meniscus tears can be a result of injury (traumatic tear) or associated with routine wear and tear and early arthritis (degenerate tear).
Traumatic tears of the meniscus often result from twisting injuries of the knee sustained during sport. It is often seen in association with knee ligament injuries but also can also exist in isolation. With a meniscus tear of this nature, there is a precipitating incident followed by pain and knee swelling. The swelling often subsides, leaving residual knee pain and, depending on the configuration of the meniscus, the knee can also experience locking episodes where there is a block to normal range of motion because the torn fragment of the meniscus is trapped within the joint. Occasionally, a torn meniscus can result in a locked knee from the outset (at the point of injury).
In a degenerative meniscus tear, the precipitating incident can be very minor. The tear results because the meniscus is already degenerated and fragile so does not require a significant force to tear. Due to the relatively low forces involved, concurrent ligament injuries are uncommon. Symptoms are similar to that of a traumatic meniscus tear.
In the assessment of a suspected meniscus tear, your doctor will perform a physical examination after obtaining a history of the injury. A MRI scan may also be performed to visualise the internal structure of the knee and to confirm the meniscus tear as well as to study the tear configuration.
Initial treatment of symptoms is with rest, ice and anti-inflammatory medications. Surgery may be required in some cases. The decision whether surgery is needed largely depends on extent of symptoms, configuration and location of the tear.
In order to understand the rationale behind how meniscus tears are managed, it is important to know how the meniscus is supplied with blood. Blood supply is critical for healing as blood brings with it healing cells and healing factors. Blood vessels enter each meniscus from the periphery and as a consequence, the meniscus has a good blood supply in the peripheral zone (red zone). A tear in this zone has a fairly good chance of healing. More centrally, the meniscus has a progressively poorer healing potential due to diminishing blood supply. As a consequence, a tear in the red-white zone has a fair potential for healing while a tear involving the white zone will not heal.
Based on the different configurations of a meniscus tear and taking into account the blood supply, some tears do well with repairs while others have to have the torn portion trimmed off. An example of a tear which can be repaired is a bucket handle tear through the red zone. Parrot beak tears, radial tears and complex tears are not repairable.
“Whether the meniscus is to be trimmed or repaired, surgery is performed arthroscopically (keyhole surgery).”
Articular Cartilage Injuries
Articular cartilage injuries can be localised or generalised. Localised damage is usually related to injury while generalised cartilage damage is related to arthritis.
A patient with significant damage to articular cartilage would, most commonly, have recurrent knee pain and swelling. Occasionally, cartilage flaps or loose pieces of cartilage can cause locking symptoms.
Similar to meniscus injuries, localised articular cartilage injuries can be confirmed with a MRI scan. More advanced generalised cartilage loss (as seen in arthritis) can be diagnosed with a simple X-ray.
The initial treatment for either localised or generalised cartilage injuries is rest and anti-inflammatory medications.
Failing non-operative treatment for localised cartilage injuries, operative strategies may need to be employed. One option is stimulating cartilage growth by removing damaged cartilage and creating bleeding points from the underlying bone either by drilling or punching holes in the bone (microfracture). Another option is covering the damaged area with cartilage plugs harvested from other parts of the knee (mosaicplasty) or with cartilage cells grown in a lab (autologous chondrocyte implantation). The choice of procedure is determined primarily by the size of the damaged area and associated damage to the underlying bone.
Cartilage injuries of the knee are common. They cause significant pain and disability. Do consult your doctor if your knee pain does not resolve with rest and anti-inflammatory medications. It is usually easier to deal with these injuries earlier rather than later.
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