Load transfer and stress shielding of the hydroxyapatite-ABG hip: a study of stem length and proximal fixation.

We questioned whether the excellent clinical results reported for the hydroxyapatite-coated ABG hip are consistent with results of preclinical computer simulation methods for the prediction of strain-adaptive bone remodeling patterns around implants. We also investigated whether a further improvement of the results can be expected if complete proximal load transfer is enforced by reducing stem length to the metaphyseal area only. Resorption patterns predicted were in good agreement with radiographic clinical findings. Mechanical failure of the bone-implant interface was judged based on a Hoffman interface stress criterion, which was low. Reducing stem length hardly increased interface failure probability, but it did not reduce stress shielding, either. From a mechanical point of view, reducing stem length to the metaphyseal area only is not advantageous.