Intraoperative Transverse Acetabular Ligament–Guided Radiographic Anteversion: Concordance With Hip–Spine Targets and Combined Anteversion

Background The transverse acetabular ligament (TAL) is used as an intraoperative landmark during total hip arthroplasty (THA); however, it remains unclear whether TAL-guided radiographic anteversion (TAL-RA) aligns with contemporary hip–spine classification and combined anteversion (CA) target ranges. Methods We prospectively enrolled 132 patients (140 hips) undergoing primary posterior-approach THA. The TAL was identifiable in 117 hips (83.6%) and used for TAL-RA measurement only. TAL-RA was measured at a fixed radiographic inclination of 40° using augmented-reality navigation and standardized for pelvic tilt. The primary analysis assessed concordance with the hip–spine 1A target range (20°-25°) and a prespecified ±5° margin; secondary analyses evaluated other hip–spine categories and CA targets (40°-60°). Results In the hip–spine 1A group, 15/70 hips (21.4%) fell within the 20°-25° target, increasing to 46/70 (65.7%) with a ±5° margin. In the 2A group, 16.1% fell within the target range, increasing to 61.3% with ±5°. Exploratory analyses of the small 1B and 2B subgroups showed target attainment of 27.3% and 20.0%, respectively. The mean CA was 49.7° and 56.4% of the hips fell within the 40°-60° target range. Conclusions TAL-RA showed wide interpatient variability, limited concordance with hip–spine target ranges, and moderate concordance with a commonly used CA target range. These findings suggest that the TAL may be better regarded as an adjunctive anatomic landmark rather than a stand-alone determinant of cup anteversion. The clinical implications of this discordance remain uncertain.