Fatigue fracture in the subchondral bone of the human cadaver femoral head.

Abstract

(1) The strains occurring in the subchondral bone of the cadaver human femoral head were measured when the head was subjected to a load of physiological magnitude and direction. (2) The strains were tensile around the circumference of the femoral head and compressive in the plane of the applied load. (3) In the intact femoral head the magnitude of the strains was such that fatigue fracture of the subchondral bone would not be expected to occur in life. (4) When a cylindrical defect 13 mm in length and 10 mm in diameter was made in the centre of the femoral head, the measured strains in the subchondral bone invariably rose, and in some femoral heads the calculated stresses were high enough to be likely to cause fatigue fracture. (5) It is concluded that cysts developing in the femoral head in osteoarthrosis may usually result in a rise in the stresses in the subchondral bone, with a possible consequent revascularization of the overlying cartilage either via a fatigue crack or by reason of the vascular changes accompanying the healing of an incipient fatigue crack. The probability of either of these events cannot be assessed accurately with the information available, but it appears to be low.