Ipsilateral Lower-Limb Alignment after Total Hip Arthroplasty for Dysplastic Hip Osteoarthritis.

Background: Total hip arthroplasty (THA) is an effective treatment for dysplastic hip osteoarthritis (DHOA); however, factors associated with lower limb alignment changes after THA remain unclear. This study investigated factors associated with these changes in patients undergoing THA for DHOA.

Methods: We analyzed 121 patients undergoing THA for unilateral DHOA between 2018 and 2022. Based on the hip-knee-ankle angle (HKAA) changes, patients were divided into neutral (HKAA change <3°), varus (HKAA change ≥3° varus), and valgus (HKAA change ≥3° valgus) change groups. We compared their backgrounds, pelvic and femoral morphology, spinal alignment, and functional outcomes.

Results: The neutral, varus, and valgus groups included 88, 18, and 15 patients, with mean ages of 64 ± 9.9, 60 ± 7.5, and 69 ± 7.6 years, respectively. Patients in the valgus group were significantly older than those in the neutral group (P = 0.018). Preoperative femoral offset was significantly smaller in the varus group (neutral, 29.6 ± 6.3; varus, 23.9 ± 6.1; valgus, 30.7 ± 4.3 mm; P < 0.001). The ΔFemoral length was significantly larger in the valgus group (neutral, 8.1 ± 6.9; varus, 6.3 ± 7.1; valgus, 13.1 ± 6.9 mm; P = 0.014). The ΔFemoral offset was significantly larger in the varus group (neutral, 4.1 ± 5.4; varus, 10.2 ± 5.6; valgus, 1.9 ± 4.0 mm; P < 0.001). Multivariate analysis found that ΔFemoral offset is associated with varus change (odds ratio [OR], 1.25; P = 0.005). Age (OR, 1.10; P = 0.037), ΔFemoral length (OR, 1.15; P = 0.005), and ΔFemoral offset (OR, 0.84; P = 0.043) were associated with valgus change.

Conclusions: In unilateral DHOA, an increase in femoral offset was associated with varus changes in lower limb alignment after THA. Conversely, valgus changes were associated with older age, reduced femoral offset, and increased femoral length.