Primary osteoarthritis of the hip. Interrelationship between intraosseous pressure, X-ray changes, clinical severity and bone density.

The intraosseous pressure of the femoral head and greater trochanter was measured during 146 Charnley hip replacement operations. In 108 hips with primary osteoarthritis the pressure in the femoral head averaged 49.6 and in the greater trochanter 31.6 mmHg. The pressures in the greater trochanter were significantly lower than those in the femoral head. There was no sex difference, and the pressures were independent of age. The intraosseous pressure in the femoral head varied appreciably with a dispersion which did not significantly differ from the normal distribution. There was a faintly positive correlation between the mean blood pressure and the intraosseous pressure. No relationship was found between the pressure in the femoral head and the radiological severity of the osteoarthritis or between the intraosseous pressure and the duration of symptoms, severity of rest pain, walking ability, range of motion or degree of bone density at the site of measurement. The haemodynamic conditions in bone depend upon blood flow and resistance. Variations in these two factors determine the actual intraosseous pressure. As a consequence intraosseous pressure measurement as the only evaluation of the haemodynamic conditions is of limited value. The vascular factor in osteoarthritis needs further clarification.