Background: Shortened stems are increasingly used in uncemented total hip arthroplasty (THA) as they represent a compromise between the metaphyseal anchorage of short stems and the facilitated axial alignment of standard stems. The purpose of this study was to compare the metaphyseal canal-fill ratio (CFR) and axial alignment of a shortened double-tapered stem with those of a standard stem. The hypothesis was that the shortened stem would achieve greater metaphyseal fill and comparable axial alignment.
Methods: The authors reviewed routine follow-up anteroposterior radiographs taken 2 months after THA to evaluate metaphyseal fill and axial alignment of a shortened stem (n = 96) and a standard stem (n = 101). The CFR was calculated at the level of the tip and superior margin of the lesser trochanter. Stem alignment was defined as the angle between the stem axis and the proximal anatomic femoral axis. Stems were classified as being in varus or valgus alignment if they deviated by more than 3° from the anatomic axis of the femur.
Results: Hips implanted with shortened and standard stems had comparable demographics and axial alignment (1.1° ± 1.7° vs 0.8° ± 1.2°; p = 0.331). However, varus alignment was observed in 5% of shortened stems compared to only 1% of standard stems, though this difference was not significant (p = 0.111). The femoral CFR was greater using shortened stems than using standard stems, both at the level of the tip of the lesser trochanter (0.91 ± 0.05 vs 0.85 ± 0.08; p < 0.001) and at its superior margin (0.76 ± 0.06 vs 0.72 ± 0.07; p < 0.001).
Conclusions: Compared to the standard stem, the shortened stem had increased metaphyseal filling and equivalent alignment. These findings suggest that shortened stems could provide adequate metaphyseal fixation and correct alignment. Further studies remain necessary to evaluate how shortened stems perform in terms of osseointegration, clinical outcomes and survival.
Keywords: Axial alignment; Canal-fill ratio; Metaphyseal fill; Shortened stems; THA; Total hip arthroplasty.