The morphology of the proximal femur in cementless short-stem total hip arthroplasty: No negative effect on offset reconstruction, leg length difference and implant positioning.

ABSTRACT

BACKGROUND: Correct reconstruction of hip offset (HO) and leg length are important for clinical-functional outcome and patient satisfaction in total hip arthroplasty (THA). The morphology of the proximal femur can pose a risk for increased leg length difference (LLD) in cementless straight-stem THA. We therefore wanted to evaluate, if this is also applicable in THA with a cementless meta-diaphyseal short stem. METHODS: In a retrospective study, 106 patients (index surgery 2014-2019) with unilateral THA and a morphologically healthy hip as a reference (Kellgren-Lawrence ≤ 1) were included. The same cementless short stem with meta-diaphyseal fixation and cementless press-fit cup was implanted. The proximal femur was rated by Dorr's classification, and subgroups were formed afterward. Measurements were carried out on preoperative and 3 months postoperative anterior-posterior radiographs of the pelvis. Kruskal-Wallis test, Fisher's exact test and binary logistic regression were performed to evaluate the influence of the anatomical shape on postoperative leg length difference and offset reconstruction. RESULTS: The Dorr type did not show any significance influence on LLD (p = 0.532), or postoperative difference in femoral offset (p = 0.243), acetabular offset (p = 0.106) and hip offset (p = 0.698). Stem alignment (p = 0.705) and canal fill indices (CFI I p = 0.321; CFI II p = 0.411; CFI III p = 0.478) were also without significant differences. Logistic regression did not show any significant increased risk for a LLD ≥ 5 mm or ≥ 10 mm as well as HO ≥ 5 mm or ≥ 10 mm. CONCLUSION: Reconstruction of hip offset and postoperative leg length difference is not negatively influenced by Dorr type, canal flare index, cortical index and canal-to-calcar ratio in cementless short-stem THA. Implant positioning and canal fill are also not negatively affected by the anatomical shape of the proximal femur. LEVEL OF EVIDENCE Level IV.