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.