Crowe severity and femoral stem geometry are associated with lower-limb alignment after total hip arthroplasty for unilateral developmental dysplasia of the hip–related secondary osteoarthritis: valgus alignment trajectories

Abstract

BACKGROUND: Total hip arthroplasty (THA) for secondary osteoarthritis related to developmental dysplasia of the hip (DDH) restores hip mechanics. We aimed to quantify pre-to-postoperative changes in ipsilateral knee and global lower-limb alignment after unilateral THA to determine whether alignment changes differ by Crowe classification and femoral stem geometry. METHODS: This retrospective cohort study included 74 patients who underwent unilateral primary THA for DDH-related secondary osteoarthritis, with a mean follow-up of 45.4 months. The predefined primary radiographic outcome set comprised preoperative-to-postoperative changes and final follow-up values in coronal lower-limb alignment parameters, including mechanical and anatomic lateral distal femoral angles (mLDFA and aLDFA), mechanical medial proximal tibial angle (mMPTA), joint line convergence angle (JLCA), global offset (GO), hip-knee-ankle angle (HKA), knee mechanical axis deviation ratio (KMADR), and femoral mechanical-anatomic axis angle (FMMA). The contralateral reference limb was used for side-to-side radiographic comparison. Patients were stratified by Crowe classification (I-II vs. III-IV), and femoral stem geometry analyses were performed according to conical, wedge, and rectangular stem designs. Clinical outcomes included hip/knee visual analog scale, Harris Hip Score, Knee Society Score, Oxford Knee Score, KOOS, and WOMAC. RESULTS: Analysis of the predefined radiographic outcome set demonstrated divergent alignment profiles according to Crowe severity. In Crowe I-II, several preoperative-to-postoperative changes were nominally observed, but these did not remain statistically significant after FDR adjustment; postoperative side-to-side differences largely converged toward the contralateral reference limb. In Crowe III-IV, a more robust valgus-oriented postoperative profile was observed, with FDR-significant changes in mLDFA, aLDFA, mMPTA, JLCA, GO, HKA, and FMMA, and persistent postoperative asymmetry versus the contralateral reference limb for most parameters except GO. Between Crowe groups, postoperative HKA was significantly higher and FMMA significantly lower in Crowe III-IV after multiplicity adjustment, whereas mMPTA and KMADR showed nominal between-group differences. In exploratory stem-geometry analyses, postoperative between-group differences in mLDFA and FMMA remained significant after FDR adjustment, whereas aLDFA and HKA showed nominal differences only. Clinical outcomes improved substantially in both Crowe strata, and clinical scores were comparable across femoral stem geometry groups. CONCLUSIONS: In unilateral DDH-related osteoarthritis treated with THA, postoperative lower-limb alignment changes were associated with Crowe severity and showed only partial normalization relative to the contralateral reference limb. High-grade DDH demonstrated a more valgus-oriented postoperative radiographic profile, whereas low-grade DDH showed smaller changes with partial convergence toward the contralateral side. Stem geometry was associated with different postoperative radiographic profiles in exploratory analyses; however, because stem selection was not randomized and likely reflected underlying femoral morphology and reconstruction requirements, these findings should be interpreted as associative rather than causal. Radiographic differences were not accompanied by significant differences in mid-term clinical outcomes. LEVEL OF EVIDENCE: A level 3 retrospective cohort study.