A meniscus tear is a tear in the fibrocartilage wedge structures that fill the space between the rounded femur and flat tibia on both sides of the knee.
Injury to a meniscus of the knee is a very common condition to occur in the knee joint. The meniscus is often called a knee cartilage although the name cartilage is best used for the slippery surface material of our joints.
Many people have meniscal tears and do not know they have. Most people never need surgery as rehabilitation has been shown to be as effective as operation in many cases.
The large rounded condyles of the femur and the flat upper surface of the tibia make up the knee joint but the joint surfaces don’t fit together well. In between the surfaces are two fibrocartilage wedge structures that look like banked tracks and fill up the gap between the joint surfaces. These are the menisci.
One meniscus lies on each side of the joint. The medial meniscus is on the inside of the joint, attached to the medial ligament and is often injured when the ligament is injured. The lateral meniscus is on the outer side of the joint, is not attached to the lateral ligament and is less commonly injured.
The medial meniscus (on the inner side of the knee) covers around 50-60% of the joint cartilage and takes around half the load.
The lateral meniscus (on the outer side of the knee) covers around 70-80% of the joint cartilage and takes around 70% of the load.
There are several other important functions of the menisci in the knee:
- They distribute the forces through the knee by spreading out the stresses across a wider area. Shock absorption is 20% better compared to a knee with the meniscus removed, where the contact stresses between the bones can be much higher.
- Increased joint stability. The menisci are firmly fixed into the bone by their “roots” in the centre of the knee. This helps prevent the large condyles from sliding too far.
- Increased joint lubrication
How Common Are Meniscal Injuries?
A meniscal tear may be the most common knee injury and is thought to occur at a rate of over 60 cases per 100,000 people per year. Men are two and half times more likely to develop a meniscal injury and suffer this injury most commonly between 30 and 40 years old. Women are more likely to suffer this problem in their teens.
Degenerative meniscal tears are common in people over 65 years old. Operations for meniscal tears of all types are very common.
Types Of Meniscus Injury
Meniscus injuries are classified by the pattern of injury to the meniscus:
- Longitudinal tears lie along the substance of the meniscus. As they are attached at both ends they may be called a bucket handle tear as the flap can detach like a bucket handle.
- Radial tears across the meniscus
- Parrot beak tears which are small tears resulting in a flap like a parrot beak
- Horizontal tears across the substance of the meniscus
- Root tears which involve the areas where the ends of the meniscus are attached to the tibia. These are particularly important to diagnose and repair or the function of the meniscus will be lost.
- Complex tears which can be a combination of the above
How A Torn Meniscus Occurs
Sudden twisting or squatting down can cause an acute meniscus tear but it is also common to get a tear with repetitive movements over time rather than a traumatic event.
Meniscus Tear Symptoms
- Intermittent pain, usually confined to the line of the knee joint. This may be due to the abnormal movement of the meniscus irritating the joint.
- Swelling may occur in around 50% of cases. However it may also often occur repeatedly with degenerative tears
- Mechanical symptoms such as giving way of the knee, clicking, catching and locking.
Meniscus Tear Treatment
Meniscal tears do not usually heal without treatment but small tears may heal or the symptoms may settle. If tears are stable, not displaced, degenerative in nature or only partially through the meniscus, conservative management with physiotherapy is recommended.
A torn meniscus is not usually operated on unless the person cannot cope with their daily life or if a displaced tear jams the knee.
Physiotherapy will initially concentrate on reducing pain and swelling by relative rest, ice, a compression sleeve and quadriceps exercises. This keeps the muscle size and strength that can be very quickly lost and maintains the joint position sense of the knee.
Surgeons attempt at all times to maintain as much of the normal meniscus as possible. Removal of a meniscus is associated with an accelerated process of cartilage damage and arthritic change in the knee joint.
There are three regions of the meniscus, defined by how good the blood supply is:
- The red on red zone. This is the outer third of the meniscus and has a good blood supply that allows healing to take place. So surgical repair may be worthwhile.
- The red on white zone. This has reasonable vascularity and may heal after repair.
- The white on white zone has no blood supply so does not heal, often has complex tears and thinning, worn cartilage. Tears in this area are usually trimmed surgically.
Meniscus repair is preferred if the tear is small and likely to heal with operation. Otherwise a partial removal of the meniscus, known as partial menisectomy, is performed and this is the most common outcome.
Arthroscopic surgery to the knee is the main standard of surgery for these tears that are too large or too complex to be repaired. The surgeon snips away the torn and damaged pieces and fashions the remaining meniscus to a smooth edge.
Degenerative meniscal tears without significant osteoarthritis in the joint have not been shown to benefit from surgery. Sham surgery, where incisions are made in the knee but no operation is performed inside, has been shown to have as good results as the surgery itself.
Physiotherapy for Menisectomy and Meniscal Repairs
Physiotherapy after partial menisectomy follows the same goals as for a meniscus tear:
- Reduce pain and swelling by ice and a compression bandage
- Restore full range of movement in the knee with regular exercises
- Restore full knee muscle strength. Static quads exercises, done properly and often enough, are an excellent rehabilitation exercise. Progression to weight-bearing exercises as soon as possible.
- Return to normal activities by working on functional exercises that the person finds difficult or worrying. This produces the confidence that the knee is resilient and reliable.
Physiotherapy after meniscus repair is more complex, with the surgeon’s preferences guiding progress. The load on the meniscus increases as the knee bends, so restrictions on the amount of flexion involved are likely. Too great stresses applied to the repaired meniscus could undo the repair.
Weight bearing may be limited for some weeks and range of movement of the joint is gradually promoted, with rehabilitation continuing for three months or longer. Individuals vary in their progress and in the goals they wish to achieve. Your physiotherapist will continually assess you to see if you’re ready to move on to the next stage.
Meniscus tear knee injury. Boots WebMD. http://www.webmd.boots.com/pain-management/guide/meniscus-tear
Meniscus Tears. AAOS. http://orthoinfo.aaos.org/topic.cfm?topic=a00358
Sihvonen R et al, Arthroscopic Partial Meniscectomy versus Sham Surgery for a Degenerative Meniscal Tear. New England Journal of Medicine 2013; 369:2515-2524. http://www.nejm.org/doi/full/10.1056/NEJMoa1305189#t=articleDiscussion