1. The case of a girl aged sixteen years who avulsed the iliacus muscle from the ilium during a gymnastic exercise is reported.

2. The lesion was complicated by paralysis of the femoral nerve from pressure by the haematoma. Recovery occurred after decompression.

3. Reports of similar cases from the literature are reviewed.

1. If osteoarthritis of the knee is confined mainly to one tibio-femoral compartment and the range of flexion is 90 degrees or more it can be treated safely and reliably by proximal tibial osteotomy.

2. The operation relieves pain in a large proportion of cases while retaining a useful range of knee flexion.

We are grateful to Miss H. M. Briggs, Research Secretary at Harlow Wood Orthopaedic Hospital, for secretarial assistance.

1. Four cases of congenital lateral dislocation of the patella are described.

2. The significance of the associated flexion contracture is emphasised.

3. Early diagnosis and operative realignment of the extensor mechanism is considered to be important because it should avoid the secondary growth changes which can produce serious disability.

1. Fibrous union of an osteotomy occurred in only 3 per cent of osteotomies done during a four-year period.

2. Delayed union sometimes gives rise to pain on bearing weight while union is in progress, and non-union is usually associated with disabling pain.

3. The most significant factors predisposing to delayed or fibrous union are inefficient fixation and excessive displacement. A high or very oblique osteotomy may also have an adverse effect upon the rate of bony union.

1. This is a small series and patients have been treated in a variety of ways. Some impressions emerge, however, concerning the importance of initial trauma, the importance of the factor of heredity and the results of treatment.

2. More than 40 per cent of the patients in the series had an injury to the knee before symptoms began, which tends to support the traumatic theory. Twenty of the twenty-three patients who gave a past history of trauma had a lesion on the medial condyle, next to the intercondylar notch, and one patient of the three who had lesions on the lateral femoral condyle suffered from recurrent dislocation of the patella.

3. Although numerous examples have been reported in the literature of osteochondritis dissecans occurring in several members of a family, the family history of only one patient in this series suggested a familial tendency, and this was doubtful. It seems that patients showing a familial tendency are not commonly seen compared with the number of patients presenting with osteochondritis dissecans.

4. It is often stated that osteoarthritic changes will follow if part of the articular surface is lost, as in osteochondritis dissecans, and this belief has led to the school of thought which advocates restoration of the articular surface by reposition of the fragment. While there is no doubt that this method should be used if a large proportion of the weight-bearing surface of a femoral condyle is affected, the argument has less force if a small area is affected. It is interesting to find that of the five patients treated by replacement of a separated fragment four developed osteoarthritis, whereas in the first series only six patients out of the twenty-two developed such changes. Although these former had what appeared to be an accurate reposition of the fragment it is possible that a "step up" on the joint surface was produced, which gave rise to a more rapid deterioration of the articular cartilage. Accurate conclusions cannot be drawn from five patients, but it may be that attempts to reconstruct the articular surface of a femoral condyle can, over a long period of time, give worse results than simple removal of the lesion.

5. The group of patients treated conservatively gave encouraging results, and improved radiographic appearances were seen in most cases. There was also a notable absence of osteoarthritic changes and these results support the view that conservative treatment is indicated in adolescents and children.