Influence of Coronal and Sagittal Femoral Stem Alignment on Mid-Term Functional Outcomes in Direct Anterior Approach Total Hip Arthroplasty Utilizing a Cementless, Trochanteric-Sparing Short Stem.

Abstract

Neutral femoral-stem alignment is thought to promote durability and function after total hip arthroplasty (THA), but the clinical relevance of modest malalignment, particularly in modern, cementless short stems inserted through a direct anterior approach (DAA), remains uncertain. This study aims to evaluate whether coronal or sagittal femoral stem malalignment affects pain and function after direct anterior approach THA with a cementless short stem. We retrospectively reviewed 348 hips (306 patients) that underwent primary DAA THA. Stem orientation was measured on standardized antero-posterior (AP) and lateral radiographs obtained one year post-operatively. Patient-reported outcome measures (PROMs), including Visual Analog Scale (VAS) pain, Harris Hip Score (HHS), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), were collected at a mean of 4.3 ± 1.2 years. Multivariable linear regression examined factors linked to malalignment and its independent association with PROMs. Coronal malalignment occurred in 25 of 348 hips (7.2%) and sagittal malalignment in 77 of 348 (22.1%). Coronal malalignment did not significantly affect final PROMs (VAS, HHS, WOMAC; P >0.05). Sagittal malalignment was associated with lower HHS (91.9 ± 7.6 versus 93.6 ± 6.8; = 0.010) and higher WOMAC (11.9 ± 10.2 versus 9.7 ± 9.1; P = 0.005). The absolute differences (1.7 HHS points and 2.2 WOMAC points) were below the accepted minimal clinically important differences. Factors associated with sagittal malalignment included younger age, lower BMI, stem undersizing, and higher cup anteversion (all P < 0.05). Sagittal malalignment remained an independent (albeit modest) predictor of worse HHS and WOMAC after adjustment. Coronal stem malalignment does not compromise mid-term pain or function after DAA THA with a cementless short stem. Sagittal malalignment shows statistically, but not clinically meaningful, detriments in functional scores. Neutral stem insertion should be targeted as much as possible, but minor deviations appear tolerable. Future long-term studies with larger sample sizes are warranted to see if sagittal malalignment has an effect on revision rates.