Family doctor

Overview

Osgood-Schlatter Syndrome (OSS) is a disorder of the knee (patello-femoral mechanism) that affects boys usually between the ages of 11 and 15 and girls between the ages of 8 and 13.

It affects boys more than girls (ratio 3:2), though the difference is decreasing as more girls take on contact sports. The left knee is more commonly affected than the right. Both knees are affected in 25% of cases.

It is the commonest of the "apophyseal "(growth plates which are susceptible to traction forces) disorders and the commonest condition causing knee pain in adolescents. It is described as a syndrome because of a noted association with patella alta (high riding patella), patella instability and tibio-femoral rotational laxity in a few cases.

Since the first description in 1903, simultaneously by Osgood and Schlatter, several theories have been expounded for the development of the syndrome but the precise cause remains obscure.

The area on the lower leg (tibial tuberosity) is prone to traction forces from the tendon that runs down from the kneecap.

The first theory envisages a major event such as a violent contraction of the quadriceps mechanism leading to avulsion injury followed by inflammation.

The second theory relies on repetitive micro trauma to the (apophyseal) area causing multiple tiny avulsion fractures. These injuries are again followed by an inflammatory cycle leading to the symptoms of pain.

Muscle tendon imbalance has also been implicated in the aetiology. OSS is a condition of the developing skeleton. During a growth spurt muscle development lags behind bony development. This manifests itself as tight and inflexible muscle groups. In an area that is prone to high traction stresses, the relative inflexibility of the muscle groups increases the forces the apophysis has to withstand leading to micro fractures and again the cycle of inflammation and pain.

Diagnosis

This is based on history, examination and plain x-rays.

Patients present following minor trauma, or following an increase in sporting activity with pain and swelling around the front of the knee. The pain is worse with impact and decelerating activities. Some may report limping.

On examination there is tenderness and swelling over the tibial tubercle (TT) which is enlarged with an overlying soft tissue mass. Tenderness may also be noted over the medial patella retinaculum, inferior pole of patella and the patella tendon. Range of movement of the knee is full, though there may be pain with terminal extension, especially against resistance. Straight leg raise may be normal and pain free. There is generally no joint fluid build up (effusion).

Differential diagnosis includes osteochondritis dissecans (knee effusion, x-ray); fractures around the knee (x-rays); tendinitis and bursitis involving the knee (clinical examination and history); osteomyelitis (general malaise, decreased range of knee movement, +/- sympathetic effusion); and Sindig-Larsen-Johansson syndrome (apophysitis involving lower pole patella, obvious on clinical examination). The other pitfall to avoid is referred pain from the hip. Therefore, the hip must always be examined clinically and possibly radiologically as well to rule out slipped capital femoral epiphyses and Perthes disease particularly.

Radiographs of the knee show enlargement and fragmentation of an irregular tibial tuberosity.

Treatment

The condition is essentially a benign one leading to a full recovery with no residual pain or weakness once skeletal maturity has been reached in the majority of cases.

Treatment is therefore directed at symptomatic relief. Modification of activity during the acute phase, along with rest and ice and a short course of anti-inflammatories may be beneficial. Stretching and strengthening programmes should be started once the acute phase has settled. Knee support may benefit some patients, but others may find this makes symptoms worse. Crutches may be necessary during the painful phase.

There had been a vogue for resting resistant cases in a plaster cast, which did ease the symptoms in the short term, but in the long term, the amount of quadriceps wasting occurring in the plaster cast was counterproductive. In the skeletally immature skeleton there is no place for surgery.

In the rare case where symptoms persist after skeletal maturity, and are troublesome enough, then the surgical removal of separate bony fragments may be of benefit.

Prognosis

As stated above, the natural history of the condition is benign with an excellent prognosis.

In summary OSS, despite its ominous sounding name, is a benign condition with full recovery anticipated on reaching skeletal maturity. Treatment is aimed at symptomatic relief and does not alter the course of the condition.