Can native offset be restored in total hip arthroplasty? A contralateral-based evaluation from the FP-UCBM Hip Study group

Background: Accurate restoration of coronal-plane biomechanics after total hip arthroplasty (THA) needs assessment of the 2 aspects: global offset (GO) and leg-length discrepancy (LLD). The SGL index (sum of the leg-length discrepancy and the difference in global femoral offset) combines ΔGO and LLD into a single measure, which could provide a more complete evaluation than single-parameter measures. The study evaluates SGL for coronal restoration following THA, followed by GO restoration (±5 mm) and its femoral versus acetabular contribution. Methods: This retrospective analysis included 256 hips that underwent unilateral THA with standardised AP pelvic radiographs. Preoperative and postoperative measurements included femoral (FO), acetabular (AO), and GO, as well as LLD and SGL. The contralateral healthy hip was used as a reference, and accuracy was defined to be within ±5 mm. Results: SGL restoration (⩽5 mm) was achieved in 64.5% of hips; compared with non-restored cases, SGL-restored hips had higher postoperative FO (40.0 ± 5.5 vs. 38.5 ± 6.0 mm; t-test p = 0.050; Mann-Whitney p = 0.062), while AO did not differ. Preoperative offsets were similar. The contralateral (healthy) GO was higher in the non-restored group (71.1±7.7 vs. 68.9 ± 6.8 mm; t-test p = 0.024; Mann-Whitney p = 0.011). Conclusions: SGL is a valid parameter for determining coronal-plane restoration following THA. Among single measures, femoral offset (FO) is the most sensitive indicator of global offset restoration.