Hip resurfacing concept:

Hip resurfacing has always been an attractive concept and the theoretical advantages of hip resurfacings are:-

Minimal bone resection
Normal femoral loading Avoidance of stress shielding
Maximum proprioceptive feedback
Restores normal anatomy -

·  Offset

·  Leg length

·  Anteversion

Minimal risk of dislocation
Easy revision

Sir John Charnley carried out the first hip resurfacing in the 1950's using Teflon on Teflon bearings but unfortunately these Teflon bearings wore out within two years. This problem of failure of hip resurfacing materials was to plague surgeons and engineers for the following thirty years. The 1970's saw the next significant development of hip resurfacing using materials available for total hip replacement of the day.

Freeman ³⁶ (Fig. 25) and Furuya ³⁷ performed hip resurfacing using polyethylene femoral components and metal acetabular components.

Due to excess wear they and Wagner ³⁸ and Amstutz ³⁹ all converted to metal heads against polyethylene acetabular components with all components fixed with poly- methylmethacrylate cement. (Fig.25)

The Wagner resurfacing arthroplasty was used in Birmingham in both its metal on polyethylene (Fig. 26) and ceramic on polyethylene forms, but the results were very disappointing and show a 34% failure rate at 5-6 years. (Fig. 27)
 

The particular problems with the Wagner were loosening of components and collapse of the femoral head and these extremely disappointing results in the hands of many surgeons encouraged the view that the concept of hip resurfacing arthroplasty was flawed.(Fig.28)

However, closer examination of the failure patterns show that this was a failure of materials rather than a failure of concept.⁴⁰ The ceramic Wagner femoral component shown was resected from a patient whose cup loosened at nine years and the femoral component was solid.(Fig.29)

This was prepared by Professor Archie Malcolm's laboratory in Newcastle upon Tyne. Microradiography of the sliced specimen shows trabeculae streaming down from the cement plugs but worryingly holes are present in the substance of the femoral head. (Fig.30)

Other slices of the femoral head also show marked cavitary defects. (Fig.31)

Histology in the areas of bone loss shows macrophages laden with polyethylene debris. (Fig. 32)