Background The influence of the surgical process on implant loosening and periprosthetic fractures (PPF) as major complications in uncemented total hip arthroplasty (THA) has rarely been studied because of the difficulty in quantification. Meanwhile, registry analyses have clearly shown a decrease in complications with increasing experience. The goal of this study was to determine the extent of variability in THA stem implantation between highly experienced surgeons with respect to implant size, position, press-fit, contact area, primary stability, and the effect of using a powered impaction tool. Methods Primary hip stems were implanted in 16 cadaveric femur pairs by three experienced surgeons using manual and powered impaction. Quantitative CTs were taken before and after each process step, and stem tilt, canal-fill-ratio, press-fit, and contact determined. Eleven femur pairs were additionally tested for primary stability under cyclic loading conditions. Results Manual impactions led to higher variations in press-fit and contact area between the surgeons than powered impactions. Stem tilt and implant sizing varied between surgeons but not between impaction methods. Larger stems exhibited less micromotion than smaller stems. Conclusions Larger implants may increase PPF risk, while smaller implants reduce primary stability. The reduced variation for powered impactions indicates that appropriate measures may promote a more standardized process. The variations between these experienced surgeons may represent an acceptable range for this specific stem design. Variability in the implantation process warrants further investigations since certain deviations, for example, a stem tilt toward varus, might increase bone stresses and PPF risk.

Implant loosening and periprosthetic fracture are two major revision causes for uncemented hip stems. The chosen method of cavity preparation could play a key role for both failure mechanisms. The aim of this study was to determine the dependence of the broach type as well as patient bone mineral density (BMD) on densification and contact conditions at the bone-implant interface. Hip stems were implanted into cadaveric femora using compaction, blunt extraction or sharp extraction broaches with computed tomography scans performed prior to broaching, after broaching and after stem implantation. Proximal periprosthetic bone densification as well as press-fit, contact area and stem seating relative to the last broach were determined. Median bone densification was higher with the compaction and blunt extraction broaches compared to sharp extraction broaches (181% and 177%, respectively, p ¼ 0.002). The bone densification of femora prepared with compaction broaching increased with higher BMD (R 2 ¼ 0.183, p ¼ 0.037), while stem seating decreased with higher BMD for all broach types (R 2 ¼ 0.259, p ¼ 0.001). Incomplete seated prostheses were associated with smaller press-fit and bone-implant contact area (R 2 ¼ 0.249, p ¼ 0.001; R 2 ¼ 0.287, p < 0.001). Clinical Significance: The results suggest that compaction broaching maximizes bone densification in patients with higher bone density.However, there appears to be an increased risk of insufficient stem seating in high-density bone that could limit the benefits for primary stability. For lower quality bone, the broach type appears to play a lesser role, but care must be taken to limit extensive stem seating which might increase periprosthetic fracture risk. ß

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