Investigation into the tribological condition of acetabular tissue after bipolar joint replacement hip surgery

The aim of this research was to investigate the tribological condition of a cetabular tissue before and after bipolar hip surgery. Articular cartilage was taken from the femoral head of patients undergoing primary joint replac ement as a control. Tissue was also taken from the acetabular cups of patie nts undergoing revision hip surgery after primary bipolar surgery and compa red with the control cartilage. The biomechanical characteristics of the two tissue types were tested using friction and compression tests. The friction tests were carried out on a s liding friction rig under nominal contact stresses of 0.5 and 4 MPa. The co mpression tests were carried out under a 0.8 MPa contact stress. The majority of the bipolar patients produced friction coefficients that we re significantly higher than those produced by the control group, and the c ompression tests highlighted that the tissue from the bipolar patients prod uced a much greater rate of increase in displacement compared with the cont rol cartilage. Histology showed major differences between the control carti lage and the bipolar tissue. The control cartilage showed a healthy collage n structure with a good distribution of proteoglycan whereas the majority o f the bipolar tissue had lost tissue architecture and had a sparse fibrous structure. The high friction coefficients with the bipolar tissue imply that the frict ional torque at the outer head of the bipolar prosthesis would be large com pared with the inner bearing frictional torque. It was therefore predicted that the motion of the bipolar prosthesis should occur at the inner bearing .