Femoral prosthetic subsidence after low-friction arthroplasty

A quantitative method has been used to measure femoral prosthetic subsidence after insertion. Increased amounts of subsidence are associated with the development of radiologic signs by one year after surgery. The most marked effect occurs with fractures of the cement tip. Follow-up examination up to five years shows that the rate of subsidence usually stabilizes, or stops at about 5 mm. Less commonly, subsidence is progressive, averaging up to 2 cm at five years. Demonstrable subsidence is also associated with prostheses that subsequently go on to break. The implications are that the nonflanged femoral prostheses are end bearing, with eccentric loading of the distal cement column, which leads to radiologic signs around the cement tip, demarcation, and, eventually, fracture of the cement tip. There may also be resorptive changes in the proximal femur, characteristically demonstrated in the medial femoral neck. It is suggested that the recent improvements in cement technique and the addition of the prosthetic dorsal flange may increase the success of low-friction arthroplasty.