Information for Patients

the bearings

5 THE BEARINGS


The bearing refers to the junction between the acetabular component that has been placed into the socket and the ball on the top of the femoral implant. When Sir John Chandley first developed his low friction arthroplasty the acetabular componenet was made of high density polyethylene and the ball was metal and only 22mm in diameter. Sir John was aware of the problems of a bigger ball causing more friction and wear and therefore chose a small ball. The problem with the smaller ball is that that joint is less stable. This leads to an increased risk of dislocation. Therefore in choosing a modern day bearing one has to consider the balance of both wear, to prevent the bearing failing with time, and stability, to prevent the implant dislocating or coming out of joint.

Stability can be improved by increasing the size of the ball within the bearing but this will be at the expense of increasing wear. New sentence Wear debris created from the bearing will influence the longevity of the implant. Therefore there are multiple combinations of bearings that can be used which changed the material or the head size. Although there are always exceptions, my personal aim is to try and achieve a diameter of femoral head of 36. This is considerably smaller than a natural femoral head but its main advantage is that it brings stability. The bearing may be a metal head with a polyethylene liner or a ceramic head against a polyethylene or ceramic liner. I have used in the past a metal head with a metal liner which as a 36 mm diameter head has a good track record. Recently there have been concerns raised about the use of metal on metal bearings in hip replacements and there has been a trend away from the use of metal on metal implants.


The bearings