Introduction and Aims: Although cortical hypertrophy (CH) in total hip arthroplasty (THA) has been associated with thigh pain and loose femoral stems, its presence has been variable in the literature, and it is an implant-specific phenomenon. The relationship of bony change to clinical outcome has not previously been examined in ceramic THA.

Method: Hardened-bearing surfaces such as ceramics have the potential for altered patterns of force transmission into the femoral stem-bone interface, and as such could lead to altered bone remodelling. We investigate here the incidence and magnitude of CH at the Gruen zones, about the femoral stem of THA utilising ceramic-on-ceramic bearing surfaces without (n=36) or with (n=4) cement, and metal-polyethylene bearing surfaces without (n=40) or with (n=40) cement. Using multifactorial analysis, we examined the relationship of implant alignment, Harris and Oxford hip scores, and bone remodelling parameters.

Results: In this study of 120 patients, the hip scores and x-rays are examined in the first year after total hip arthroplasty (THA), in order to evaluate bone remodelling in relation to clinical outcomes. Ceramics had the highest incidence (25%) and mean size (1.5 mm) of CH, followed by metal-polyethylene (17%, < 1 mm). No cemented implants exhibited CH. There was no significant relationship of bone remodelling to one-year hip scores, although there were significantly reduced pain scores in cases that exhibited endosteal remodelling at one year. CH in ceramic hips appears to be a mechanical phenomenon that is not associated with pain, varus drift, subsidence, or altered clinical outcome. Cement may buffer the stresses seen by the femur, and hence the stimulus for CH appears to be simply mechanical, and is increased with hardened-bearing surfaces.

Conclusion: CH was more common in ceramic THA than metal-polyethylene, but was not associated with increased thigh pain or altered function. CH did not occur when cement was used, and as such we argue for a mechanical origin of the phenomenon, via altered load transmission into the femur through hardened-bearing surfaces.