Impact of the difference between preoperative planning and intraoperative femoral neck osteotomy level on stem alignment

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Abstract
Background The combined anteversion theory is used for implant placement in total hip arthroplasty (THA). While majority of the research emphasizes the precise placement of the acetabular cup, there’s less focus on stem alignment. This study aimed to investigate the impact of the discrepancy between the preoperatively planned femoral neck osteotomy level and the actual osteotomy level during surgery on stem alignment. Materials and Methods The study involved 232 patients (258 joints) who had a total hip arthroplasty (THA) between April 2018 and December 2022 at our hospital. They were implanted with either the ACTIS stem (Depuy Synthes) or Taperloc Complete XR 123° (Zimmer Biomet)—147 joints with ACTIS stem and 111 with Taperloc stem. Three-dimensional templating software was used to evaluate preoperative planning and postoperative stem placement angles. The difference between the actual and preoperatively planned osteotomy levels was also measured. The impact of this difference in femoral neck osteotomy level on stem alignment was evaluated. Results In the ACTIS stem group, the femoral neck osteotomy level was − 0.3 ± 3.7 mm. The stem alignment had a varus of 1.8 ± 1.9°, extension of 0.1 ± 1.5°, and anteversion of 2.4 ± 5.9°, compared to preoperative plans. A positive correlation was identified between osteotomy level and varus/valgus alignment (r = 0.607, p < 0.01), with a weak correlation for anteversion (r = 0.236, p < 0.01). No correlation existed with flexion/extension. In the Taperloc stem group, osteotomy level was 2.2 ± 3.1 mm. The postoperative stem showed a varus of 1.6 ± 1.5°, extension of 0.5 ± 1.7°, and anteversion of 4.9 ± 6.5°. A correlation was observed between osteotomy level and varus/valgus alignment (r = 0.476, p < 0.01), but not with flexion/extension or anteversion. Conclusions The study examined how differences in planned vs. actual femoral neck osteotomy affect stem alignment in THA using ACTIS stem and Taperloc stem. We found that osteotomy level influenced varus/valgus alignment; mildly affected flexion/extension; and had no effect on anteversion.

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