1. One hundred patients with osteochondritis dissecans of the knee have been reviewed. Sixty-eight were male. Unilateral lesions were found in seventy-four. The average age at onset of symptoms was eighteen years.

2. The outstanding etiological feature was found to be direct injury to the joint surface (46 percent), repeated injuries sustained in first class athletics and field sports, and mechanical abnormalities of the knee.

3. Osteochondral fracture was found in seven cases.

4. The results of various types of treatment are described and a plan of management outlined.

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.

Both osteochondritis dissecans and coxa plana are diseases with identical pathological changes, namely avascular necrosis. Although the etiology is not known in either case, it seems likely that when the etiological factors are fully determined they will prove to be applicable to either condition. The relative importance of each etiological factor in the multiple pathogenesis of these two conditions is almost certainly different in each disease process, and probably in each individual case. Present day concepts suggest that there is an underlying constitutional disturbance, which is associated with other factors (of which trauma is almost universally accepted as being one; perhaps the only one), to predispose the individual to these conditions.

It is hoped that further studies along these lines will not only help to provide a better understanding of the two conditions mentioned above, but will also be of value in the appreciation of the pathogenesis and etiology of a large number of disturbances including such varied conditions as dysplasia epiphysialis multiplex congenita, cretinoid dysgenesis of the capital femoral epiphysis, adolescent coxa vara, transient synovitis of the hip, and the recently discussed (Merle d'Aubigné 1964) idiopathic avascular necrosis of the femoral head in adults.

That there is an etiological relationship between osteochondritis dissecans and coxa plana seems clear, but much more work is required before we will have at hand the patho-physiological evidence that will permit an accurate correlation of these two conditions.

Osteochondritis dissecans occurring bilaterally in either the knees or the elbows is recorded in four members of one family. The suggestion is supported that the underlying pathology may be developmental, resulting in a form of localised osteochondrodystrophy.

1. The pathological anatomy of osteochondritis dissecans of the hip is described, and its causation is discussed.

2. Eight new cases are reported.

3. The problems of treatment are considered.

1. The record is presented of an attempt to treat osteochondritis dissecans on idealistic lines.

2. The operative technique to be adopted in the various circumstances likely to be encountered in the knee joint is described. Two cases affecting the talus are recorded.

3. The radiological appearance has become virtually normal in twenty-seven cases (the remaining four are recent); healing has been observed directly in seven cases in which a second operation to remove the means of internal fixation was necessary; and the patients' complaints have been eliminated, but the long term results of treatment are unknown.

4. Suggestions are made for possible developments in the technique of operation.

1. A family, in which ten members of the second and third generations had osteochondritis dissecans, is described.

2. It is probable that the disease also occurred in the first and fourth generations.

Nine cases of osteochondritis dissecans of the elbow and knee in three generations of the same family are described. There was clear evidence of a dominant inherited factor.

1. Three patients suffering from osteochondritis dissecans in several joints, and all below average height, are described.

2. There was evidence of a constitutional upset in each case.

3. It is suggested that there was an underlying endocrine imbalance at puberty.

1 . Two cases of osteochondritis dissecans after Legg-Calvé-Perthes' disease observed for thirty years are described.

2. Osteochondritis dissecans of the hip can remain in an apparently unchanged state for many years and in these two patients is associated with excellent function, not requiring surgery.

A case of osteochondritis dissecans complicating Legg-Calvé-Perthes' disease is reported. Despite four years of conservative treatment in an ischial-bearing caliper a part of the fragmented femoral head failed to unite with the rest of the epiphysis and has persisted as an intra-articular loose body.

Freehafer (1960) listed the indications for surgical removal of this fragment in such cases: 1) persisting symptoms; 2) dislocation of the loose fragment into the joint with secondary arthritic changes inevitable; 3) a mechanical block to movement of the hip.

Since our patient had a relatively symptomless hip with a full range of movement, surgical removal of the loose body was not advised. The prognosis for this hip is nevertheless guarded, and surgery can be reserved for the above indications or for reconstructive procedures should they be required in the future.

1. A case of osteochondritis dissecans of the hip in a young girl who at the age of one and a half years underwent open reduction of congenital dislocation of the hip, is reported.

2. The possible relationship between this condition and the osteochondritic changes which followed the reduction is discussed.

1. In sixty mature rabbits osteochondral fractures of various types were made in the medial femoral condyle.

2. The fractures or fragments which remained stable united but those in which movement occurred progressed to non-union.

3. An ununited osteochondral fragment resembled osteochondritis dissecans in the human both radiologically and histologically.

4. Experiments in the cadaveric knee show that the patella articulates with the classical site on the intercondylar aspect of the medial femoral condyle in full flexion of the joint and here an osteochondral fracture could be sustained.

5. It is concluded that the fragment in osteochondritis dissecans follows an osteochondral fracture which remains ununited.

1. A case of flake fracture of the talus progressing to osteochondritis dissecans is reported.

2. The relationship between direct injury and the onset of the lesion is noted.

3. The sequence of events was observed radiographically and clinically for two years from the date of the original injury.

Three cases of osteochondritis dissecans of the knee in two brothers and a sister are described. In the brothers both knees were involved. None of the other joints of the skeleton was affected in any of the patients.

1. Two cases of osteochondritis dissecans affecting several joints are described.

2. There is no evidence that injury, congenital anomaly or constitutional disturbance played any part in the etiology of either case.

We treated a patient with extensive osteochondritis dissecans of the elbow by an osteochondral graft from a rib. It had consolidated seven months after operation. When seen at follow-up, after seven years and eight months, the elbow was free from pain with an improvement in the range of movement of 24°.

We attempted to characterise the biological quality and regenerative potential of chondrocytes in osteochondritis dissecans (OCD). Dissected fragments from ten patients with OCD of the knee (mean age 27.8 years (16 to 49)) were harvested at arthroscopy. A sample of cartilage from the intercondylar notch was taken from the same joint and from the notch of ten patients with a traumatic cartilage defect (mean age 31.6 years (19 to 52)). Chondrocytes were extracted and subsequently cultured. Collagen types 1, 2, and 10 mRNA were quantified by polymerase chain reaction. Compared with the notch chondrocytes, cells from the dissecate expressed similar levels of collagen types 1 and 2 mRNA. The level of collagen type 10 message was 50 times lower after cell culture, indicating a loss of hypertrophic cells or genes. The high viability, retained capacity to differentiate and metabolic activity of the extracted cells suggests preservation of the intrinsic repair capability of these dissecates. Molecular analysis indicated a phenotypic modulation of the expanded dissecate chondrocytes towards a normal phenotype. Our findings suggest that cartilage taken from the dissecate can be reasonably used as a cell source for chondrocyte implantation procedures.