Abstract
Introduction
Post op cup anatomical and functional orientation is a key point in THP patients regarding instability and wear. Recently literature has been focused on the consequences of the transition from standing to sitting regarding anteversion, frontal and sagittal inclination. Pelvic incidence (PI) is now considered as a key parameter for the analysis of sagittal balance and sacral slope (SS) orientation. It's influence on THP biomechanics has been suggested. Interestingly, the potential impact of this morphological angle on cup implantation during surgery and the side effects on post op functional orientation have not been studied.
Our study explores this topic from a series of standing and sitting post-op EOS images
Material and methods
310 patients (mean age 63,8, mean BMI 30,2) have been included prospectively in our current post-operative EOS protocol. All patients were operated with the same implants and technique using anterior approach in lateral decubitus.
According to previous literature, 3 groups were defined: low PI less than 45° (57 cases), high PI if more than 60° (63 cases), and standard PI in 190 other cases.
Results
Mean PI was 55,8° (SD 11,5).
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-In High PI, postop SS in standing was significantly higher than in Low and Medium PI. In Medium PI, postop SS in standing was significantly higher than in Low PI.
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-In High PI, postop SS in sitting was significantly higher than in Low and Medium PI.
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-In Low PI, postop Functional anteversion in sitting was significantly higher than in Medium PI, but not different from High PI.
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-In Low PI, Anatomical anteversion was significantly higher than in Medium and High PI
Discussion, Conclusion
This preliminary study points out the potential influence of pelvis morphology expressed by PI on per-operative cup orientation. As surgeons are accustomed to follow bony landmarks during cup implantation, unexpected variations for cup adjustment may be observed if PI is not standard.
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