The inclination of the weight bearing surface in the hip joint. The clinical significance of abnormal force.

The mechanical basis responsible for the development of secondary osteoarthritis in adults and slipped capital femoral epiphysis in adolescents is discussed, with the role of the oblique weight-bearing surface in generating abnormal shearing forces in these two conditions emphasized. The same biomechanical principles have been found to apply to the acetabular component in total hip implants. A vertical cup position will lead to abnormal stress concentration in the outer edge of the bone implant interface with an increase in shearing forces. The form of the subchondral bone sclerosis on the radiograph has been studied and found to correlate well with the distribution of stresses in the bone implant interface.