Bone remodeling around short-stemmed hip prostheses

Abstract

Bone remodeling around short-stemmed hip prostheses Degree project in medicine, Carl Hellman, 2017, Department of Orthopedics, Sahlgrenska University Hospital, Mölndal, Sweden BACKGROUND Total hip arthroplasty generally provides excellent results. During the last decades, prostheses with a shorter stem has emerged as an alternative to conventional prostheses. Short-stemmed prostheses are believed to reduce stress shielding and consequently reduce the loss of bone mineral density (BMD) in the proximal femur. Easier revision surgery and improved functional level are also proposed as benefits. AIM The aim of this study was to evaluate the change of BMD around two designs of shortstemmed hip prostheses with the use of two conventional prostheses as controls. METHODS The first study evaluated the CFP (Collum Femoris Preserving) stem and the second one the Fitmore stem. DXA (Dual-energy X-ray absorptiometry) scans were performed after surgery and at 3, 6, 12 and 24 months. The BMD was measured in regions of interests (ROIs) according to Gruen zones 1-7. Differences in change in BMD compared to baseline was calculated at 2 years as primary outcome. RESULTS At 2 years follow-up, BMD values for the CFP stem was inferior in all ROIs compared to the control. The difference was statistically significant in region 1, 6 and 7. The Fitmore stem was inferior in ROIs 1, 2 and 4 but superior in ROIs 3, 5, 6 and 7. The difference was statistically significant in ROIs 1, 2 and 5. CONCLUSION The CFP stem was found to be inferior in all ROIs with large decrease in BMD in the proximal regions, indicating larger degree of stress shielding compared to the control. The Fitmore stem was observed with larger decrease in BMD in the lateral ROIs, but lesser decrease in the medial ROIs. Moderate differences between the Fitmore stem and the control indicates that the Fitmore stem is not an inferior alternative with respect to stress shielding and especially in younger patients.