Abstract
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.
Objective
This in-vivo study assesses the accuracy of an imageless navigation system, with a pin-less femoral array, in measuring offset and leg length changes.
Method
A prospective, consecutive series of 24 patients undergoing navigated total hip arthroplasty 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 analysed to provide radiographic measurements of change in leg length and offset.
Results
Measurements of leg length change made by the navigation system showed a statistically significant correlation with the size of change measured radiographically (R=.77, P < 0.0001). The mean difference between the radiographic and navigational measurement was 0.4 ± 2.8 mm. The navigation system was accurate to within 1 mm of the radiographic measurement in 50% of cases, within 2 mm in 67% of cases, and within 5 mm in 96% of cases.
Measurements of offset change by the navigation system also showed a statistically significant correlation with radiographic measurements, however the correlation was less pronounced (R=.47, P=0.02). The mean difference between navigational and radiographic measurements was 1.4 ± 6.4 mm. The navigation system was accurate to within 1 mm of the radiographic measurement in 8% of cases, within 2 mm in 25% of cases, and within 5 mm in 75% of cases.
Conclusion
This study demonstrates in-vivo that an imageless, non-invasive navigation system is a reliable tool for intra-operative leg length and offset measurement.
