Abstract
BACKGROUND: Heterotopic ossification (HO) is a common complication of total hip arthroplasty (THA), which can adversely affect patient satisfaction. Although the direct anterior approach (DAA) has been associated with lower rates of HO, the exact clinical impact of even low-grade ossification following DAA THA remains underreported. We aimed to assess the clinical impact of HO in DAA THA and identify demographics and implant-related risk factors. METHODS: A retrospective single-center cohort study of 348 hips treated via DAA THA with a cementless short stem between January 2011 and December 2021 was performed. HO was graded at ≥12 months using the Brooker classification on standardized anteroposterior radiographs. The Harris Hip Score (HHS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Visual Analogue Scale (VAS) were assessed at a mean of 4.3 years of follow-up. Comparative analyses and multivariable logistic regression were performed to identify independent predictors of HO. RESULTS: HO occurred in 18.1% of hips: Brooker grade I in 12.4%, II in 3.0%, and III in 3.0%; no grade IV lesions developed. At final follow-up, patients without HO had significantly better outcomes compared with those with HO (all p < 0.001). When stratified by severity, even low-grade HO (Brooker I-II) was associated with significantly worse WOMAC (p = 0.023) and HHS (p < 0.001) compared with the non-HO group. Although VAS pain was higher in the low-grade group, the difference did not reach statistical significance (p = 0.084). On multivariable analysis, independent implant-related risk factors included use of the Continuum acetabular cup (odds ratio [OR] 2.10; p = 0.014), each additional millimeter of cup diameter (OR 1.16; p = 0.003), and longer femoral neck length (OR 2.06; p = 0.006). CONCLUSIONS: HO was observed in nearly one-fifth of hips, and even low-grade ossification was associated with significantly worse mid-term functional outcomes. Cup design, size, and neck length were identified as significant, modifiable predictors of HO risk. Careful implant selection may help reduce the incidence of HO and enhance postoperative function. LEVEL OF EVIDENCE: Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.