Abstract
Introduction
Appropriate prosthetic alignment is an important factor in maintaining stability and maximising the performance of the bearing after total hip replacement (THR). With a cementless component, the anteversion of the native femur has been shown to influence the anteversion of the prosthetic stem. However, the extent to which anteversion of a cementless stem can be adjusted from the native anteversion has seldom been reported. The aim of this study was to investigate the difference between native and stem anteversion with two different cementless stem designs.
Method
116 patients had 3-dimensional templating as part of their routine planning for THR (Optimized Ortho, Sydney). 96 patients from 3 surgeons (AS, JB, SM) received a blade stem (TriFit TS, Corin, UK) through a posterior approach. 18 patients received a fully HA-coated stem (MetaFix, Corin, UK) through a posterior approach by a single surgeon (WB). The anteversion of the native femoral neck was measured from a 3D reconstruction of the proximal femur. All patients received a post-operative CT scan which was superimposed onto the pre-op CT scan. The difference between native and achieved stem anteversion was then measured. As surgeons had differing philosophies around target stem anteversion, the differences amongst surgeons were also investigated.
Results
On average, stems were implanted in less anteversion than native. The mean deviation between native and stem anteversion of the blade stems was −3.5° (−34.8° to 13.8°). The mean deviations of the three surgeons using the blade stem were −7.9° (−34.8° to 10.4°), −3.1° (−18.1° to 12.0°) and 2.7° (−8.9° to 13.8°). These were statistically significant, and represented a difference in philosophy around target anteversion amongst surgeons. The mean deviation between native and stem anteversion of the fully HA-coated stems was −6.5° (−24.6° to 9.2°).
Conclusions
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Cementless stem anteversion is not dictated by the native femoral anteversion
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There were differences in target anteversion philosophies amongst surgeons and this was seen in the results.
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Surgical approach, proximal entry point, osteotomy angle, stem design and patient anatomy will all influence the ability to dictate cementless stem anteversion. The effect of these variables are the subject of on-going work.
