Accuracy of Fluoroscopic Navigation for Predicting Leg Length and Offset in Primary Hip Arthroplasty.

BACKGROUND: Fluoroscopic-assisted computer navigation is widely used to guide intraoperative decisions on leg length (LL) and offset in primary total hip arthroplasty (THA), but its accuracy remains under-evaluated. This study assessed the precision of a fluoroscopy-based navigation system by comparing its intraoperative predictions to validated postoperative measurements. METHODS: We retrospectively reviewed 490 consecutive primary THA cases performed by three surgeons at a tertiary academic center. Intraoperative changes in leg length and offset using a fluoroscopic navigation system were recorded. Pre- and postoperative antero-posterior pelvis radiographs were measured using an artificial intelligence (AI)-based algorithm to determine actual changes in LL and offset. Navigated and radiographic values were compared using mean/median differences and by percentage of cases within clinically relevant thresholds: ± three mm, ± five mm, and ± 10 mm. RESULTS: For leg length, postoperative AI-based measurements showed a mean change of 4.1 ± 5.6 mm (median 3.7), while the intraoperative navigation system predicted a mean change of 2.5 ± 3.1 mm (median two, P < 0.0001). Navigation underestimated leg length change on average. Predictions were within ± three mm in 65.8% of cases, ± five mm in 86.0%, and ± 10 mm in 98.5%.For femoral offset, AI-based measurements showed a mean postoperative change of 1.7 ± 5.4 mm (median 1.6), compared with a mean predicted change of 3.4 ± 5.0 mm (median three) from navigation (P < 0.0001). Navigation overestimated offset change on average. Accuracy was within ± three mm in 44.1% of cases, ± five mm in 64.9%, and ± 10 mm in 93.9%. CONCLUSION: Although the fluoroscopy-based navigation system showed statistically significant differences from postoperative radiographic measurements, it achieved clinically acceptable accuracy in most cases. These findings support the system's utility in guiding THA while emphasizing the importance of intraoperative awareness of its limitations.