Accuracy of intraoperative limb length control using the NaviFast 6D system in total hip arthroplasty

Accurate restoration of leg length and femoral offset is critical in total hip arthroplasty (THA), yet intraoperative verification methods remain limited. This clinical study evaluated the accuracy, safety, and feasibility of a novel miniaturized intraoperative measurement arm, NaviFast 6D, in THA. A prospective two-phase investigation was conducted at four centers. In Phase I, measurements obtained using NaviFast 6D were compared to reference radiographic assessments (via LLDcalc) in 22 cases, and RMS of differences and device measurement error were derived. Phase II (20 analyzable cases, 19 cases from one center) enabled intraoperative adjustment of implant selection based on device data, compared with a control group (n = 30) that was operated using only clinical limb length assessment. In the full study sample, the estimated RMS error for NaviFast 6D in LLD measurement was 1.3 mm. Under the prespecified zero-centred normal model, the ratio of control to NaviFast 6D target-centred mean squared postoperative LLD was 5.14 ( \({F}_{\text{30,20}}\) , one-sided p < 0.001). Mean absolute postoperative LLD was 2.46 ± 1.37 mm with NaviFast 6D and 4.94 ± 4.04 mm in controls, corresponding to a mean difference of − 2.48 mm (95% CI − 4.10 to − 0.87 mm; Welch’s t-test, p = 0.004). Clinical validation of femoral-offset measurements was not achieved because variable postoperative limb and pelvic rotation rendered the radiographic reference measurements insufficiently reliable. Objective analysis of hospital records showed that NaviFast 6D use was associated with an inverse-variance-weighted, centre-adjusted mean prolongation of operative time of 8.6 min (95% CI 3.8–13.5; p < 0.001). NaviFast 6D demonstrated promising accuracy, safety, and intraoperative usability for improving leg length restoration in THA.