Introduction Leg length and offset are important considerations in total hip arthroplasty (THA). Navigation systems are capable of providing intra-operative measurements of leg length and offset, and high accuracy has been shown in experimental studies. This study assesses the accuracy of an imageless navigation system with a pinless femoral array (Hip 5.1, BrainLAB, Feldkirchen, Germany) in measuring leg length and offset changes in vivo. Methods A prospective, consecutive series of 37 patients undergoing navigated THA were included in the study. Intra-operative measurements of leg length and offset were recorded using the navigation system. For each patient, pre- and post-operative digital radiographs were scaled and analyzed to provide radiographic measurements for comparison. Results Measurements of leg length change made by the navigation system showed a strong correlation with the size of change measured radiographically (R = 0.71; p<0.0001). The mean difference between the radiographic and navigational measurement was 2.6mm ± 3.0mm (0.0-16.0mm) (mean, SD, range). The navigation system was accurate to within 1mm of the radiographic measurement in 49% of cases, within 2mm in 66% of cases, and within 5mm in 89% of cases. Measurements of offset change by the navigation system also showed a correlation with radiographic measurements, albeit less pronounced (R = 0.35; p=0.035). The mean difference between navigational and radiographic measurements was 5.5mm ± 4.7mm (0.0-16.0mm) (mean, SD, range). The navigation system was accurate within 1mm of the radiographic measurement in 22% of cases, within 2mm in 35% of cases, and within 5mm in 57% of cases. Conclusions This research demonstrates in vivo that an imageless, non-invasive navigation system is a reliable tool for intra-operative leg length (accurate within 2mm) and to a lesser extent offset measurement (accurate within 5mm) when compared to standard practice of plain film radiographs.
Keywords: computer navigation; hips; orthopaedic navigation; robotic surgical procedures; total hip arthroplasty (tha).
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