HP5: A RANDOMIZED PROSPECTIVE TRIAL TO COMPARE TWO DESIGNS OF HYDROXYAPATITE COATED FEMORAL STEMS FOR TOTAL HIP REPLACEMENT – WHAT SHAPE OF STEM IS BEST?

Abstract

The optimum design for the femoral component for cementless Total Hip Replacement is not known. We conducted an ethically approved, randomized and prospective trial to compare two radically different designs of fully hydroxyapatite (HA) coated femoral stems. We compared the original JRI Furlong stem with the Wright Anca fit stem which is more anatomical in design. The paper discusses the merits and disadvantages of these two stems. The same acetabular component was used in both samples. The only variable was the stem shape.

All patients placed on the senior authors’ waiting list for primary THR were asked if they would enter the trial. There were no restrictions for selection to the sample. Patients were then randomised for one of the two stems. All surgery was performed by or under the direct supervision of the senior author in one center. The surgical approach to the hip, Hardinge antero lateral, was the same in all cases. In all cases the same well-tried JRI CSF acetabular cup and bearings were used. Patients were x-rayed post operatively and reviewed and x-rayed at six weeks and then yearly.

360 patients had been entered into the trial, 219 females and 141 males. 203 patients had the JRI furlong hip implanted (56%) and 157 were in the Anca sample (44%). The periprosthetic and perioperative fracture rates for the two stems were found to be significantly different at three years into the study and the trial was stopped. The number of perioperative fractures in the Furlong group was 17(8.4%)and in the Anca sample 24 (15.3%). This is statistically significant. The possible reasons for this difference are discussed.

Anatomical fit and wedge shaped cementless stems require a more careful technique to avoid fracture during implantation and the shorter stemmed Anca hip proved less stable in the presence of a fracture necessitating further surgical intervention. It is still not certain whether the anatomical shape has long term advantages that may outweigh this initial disadvantage and the cohort of patients continue to be followed up.