Preliminary experience with isoelastic total hip arthroplasty using impaction bone grafting

Isoelastic THA using an uncemented acetabular cup fixed with pegs and screws along with a femoral stem containing a core of metal inside polyacetyl resin was used in 51 hips with an average follow up of 4 years 10 months. All cases were immobilized in abduction for 6 weeks post operative with deferred full weight bearing for another 6 weeks. One case failed due to deep infection, and one had extra medullary placement of the distal prosthesis. All others had improvement in the pain and function score; 2 patients were unsatisfied with the result. Excessive femoral reaming was avoided as we preferred to leave behind the 'living' cancellous bone to promote ingrowth along the prosthesis. This procedure may be a good alternative in young adults where cemented THA is not the procedure of choice. We attribute the good short term results in this series to the rigid post operative immobilisation (which we have labelled as the 'critical period'), filling up of the medullary canal with our technique of bone graft paste prior to prosthesis insertion, and leaving behind the endosteal cancellous bone inside the medullary cavity which possibly hastens bony incorporation of the femoral stem. A unique point in this study was our attempt to study bone formation around the prosthesis by axial CT scans, the results of which are discussed.