Abstract
Introduction:
Although cementless total hip arthroplasty (THA) is well accepted, the optimal femoral component design remains unknown. Among early complications, loosening and periprosthetic fracture persist and are related to implant design. The purpose of this study is to compare the anatomic fit and early subsidence of two different stem designs: a modern, short taper-wedge design and a traditional fit-and-fill design.
Methods:
A retrospective cohort study of 129 consecutive cementless THAs using two different femoral stems was performed. A modern taper-wedge stem was used in 65 hips and a traditional proximal fit-and-fill stem was used in 64 hips. Radiographic analysis was performed at preoperative, immediate postoperative and 1-month postoperative intervals. The radiographic parameters of bone morphology via the canal-flare index, implant subsidence at 1 month, sagittal alignment, and the “anatomic fit” metrics of canal fill and associated gaps were measured and recorded.
Results:
There were no differences between groups in patient demographics (p > 0.4), and in bone morphology via the canal-flare index (p = 0.6) with numbers available. The mean subsidence was less in the taper-wedge design at 0.27 mm compared to 1.1 mm in the fit-and-fill stem (p < 0.0001). Subsidence greater than 2 mm occurred in 26 of 64 fit-and-fill stems (41%) compared to 1 of 65 taper-wedge implants (1.5%). The percentage fill at all levels measured was greater in the taper-wedge design (p < 0.0001). The taper-wedge design was inserted a mean of 2.7° sagittal extension compared to 0.4° in the fit-and-fill design (p < 0.0001).
Conclusion:
Despite being shorter in length, the taper-wedge design demonstrates greater axial stability and less subsidence compared to a traditional fit-and-fill stem. The optimized proximal femoral fit inherent in this anatomic-based taper-wedge design is likely responsible for the minimal subsidence. The clinical implication of greater extension in the sagittal plane is unknown and longer-term clinical follow up is warranted.
