Short femoral stems have been designed with the aims of reducing proximal bone loss, improving load transfer, and increasing compressive loads at the medial proximal femoral calcar. This study examines bone mineral density (BMD) changes associated with a novel neck sparing short femoral stem design.
The study was a prospective, single-center, multi-investigator consecutive series, which assessed bone-remodeling changes after insertion of the MSA Stem (Global Orthopaedic Technology). Dual-energy X-ray absorptiometry scans were performed preoperatively and postoperatively at 6, 12, and 24 months assessing the BMD at the 7 Gruen zones. The secondary objectives assessed were the Harris Hip Score, 12-Item Short Form Health Survey preoperatively, and perioperative complications.
Thirty-nine total hip arthroplasties were performed on 37 patients, with 27 patients completing the 24-month dual-energy X-ray absorptiometry scan. The overall preoperative baseline BMD was 0.2. At 6 months, the Gruen zone BMD had increased significantly in all zones in comparison to the preoperative mean BMD. Between 6 months and 24 months, there were only slight changes in the Gruen zones, with small gains in zones 1-2 and zones 4-6, with no zone showing a significant decrease. The Harris Hip Score improved from a preoperative mean of 39.7-75.3, whereas the 12-Item Short Form Health Survey score also improved from 32.6 to 49 at 24 months. However, 5 patients had aseptic loosening requiring revision surgery (4 femoral and 1 acetabular component).
Short-stem neck-sparing femoral stem prosthesis has the capacity to address the stress-shielding problem identified in femoral stems. However, the high early revision rate is a significant issue.