Patterns of osteoarthritis of the hip

The division of arthrosis (osteoarthritis) into primary and secondary varieties implies that these are etiologically distinct entities, the former being due to some intrinsic defect of cartilage and the latter resulting from previous articular damage. This traditional concept is questioned and the hypothesis is advanced that arthrosis is always secondary to some underlying abnormality of the joint. A detailed clinical, radiographic and morbid anatomical study of 327 cases of arthrosis of the hip is presented. In all but 27 some predisposing abnormality of the joint was diagnosed: 107 (33%) were associated with major pathology such as Perthes' disease or epiphysiolysis; minor acetabular dysplasia was present in 67 (20%), with a male:female ratio of 1:10; minimal femoral head tilt was demonstrated in 59 (18%), the male:female ratio being 14:1; and in 43 (13%) there were features suggesting an underlying arthritis. On the basis of this study a new classification is proposed and arthrosis of the hip is divided into 3 pathogenetic groups: failure of essentially normal cartilage subjected to abnormal or incongruous loading for long periods; damaged or defective cartilage failing under normal conditions of loading; and break up of articular cartilage due to defective subchondral bone.