Accuracy of Leg Length and Offset Measurements During Total Hip Arthroplasty Using an Imageless Navigation System

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. 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.

Changes in leg length and hip offset in navigated imageless vs. conventional total hip arthroplasty

“…The significantly higher variance of anteversion in cTHA is implicates that statistically nTHA is more precise than cTHA. Also, recent research demonstrates in vivo that an imageless, non-invasive navigation system is a reliable tool for intra-operative leg length and offset when compared to standard practice of plain film radiographs 34 .…”

Different per-operative techniques to evaluate limb length discrepancy in hip arthroplasty.

“…5 Numerous techniques have been represented in the international literature to calculate limb length in total hip arthroplasty (THA) procedures. 6 The literature has reported the occurrence of LLD after primary hip arthroplasty to range from 1-27%, with variations in discrepancy from 3-70 mm and mean values ranging between 3-17 mm. [7][8][9] LLD following THA is been associated with a variety of issues such as back pain, sciatica, neuritis, gait disorders, general dissatisfaction, dislocation, and early component loosening.…”