Abnormal development of the structures that make up the hip joint leads to subsequent joint deformity. ‘Dysplasia’ means abnormal growth. The developmental changes appear first and because they are related to growth, they are termed primary changes. Subsequently these changes may lead to excessive wear and tear. The secondary changes may be referred to as (osteo)arthritis (OA), (osteo)arthrosis or degenerative joint disease (DJD).