Measuring femoral neck anteversion—Validation of a technique based on 3D freehand ultrasound

Abstract

s / Gait & Posture 39S (2014) S1–S141 S53 Fig. 1. Change in GPS after 2y ML surgery vs baseline GPS. (age 6–24yrs), who could walk independently or with aids, had undergone SEMLS at our hospital, and had a pre-op as well as post-op gait analysis at around two years following surgery (conventional gait model). The Gait Profile Score (GPS) [2] was selected as a primary outcomemeasure. Predictor variables included (1) age at surgery, (2) pre-opGPS, (3) unilateral or bilateral surgery, and (4) soft tissueonlyorother surgery. Regressionanalysiswasperformed with significance set at p<0.05. Predictor variables were compared to both the post op GPS, as well as the change in GPS compared to pre-op. Results: Overall, 75% of patients demonstrated improvement that exceeded theMCID of 1.6◦, while only 2% deteriorated according to the same criteria. The average improvement in GPS was 3.2◦. Pre-op GPS was found to be the strongest predictor of change (b=0.57, p<0.001) (Fig. 1). It was also found to be a significantly associated with absolute GPS post-op (p<0.001). Age at surgery was found to be a significant predictor of change (p=0.02), but not absolute GPS following surgery (p=0.61). Bilateral compared to unilateral surgery was associated with a greater change (p=0.001) but post-op GPS was not significantly correlated (p=0.01). While the soft tissue surgery subjects, when compared to other surgeries,wasnot a significant predictor of change (p=0.60) or outcome (p=0.37). Discussion and conclusions: This study builds on previous work conducted elsewhere [3] which assessed outcomes one year following SEMLS, and confirms that pre-op GPS is the strongest predictor of improvement. The work presented here shows that this is maintained up to two years following surgery. In addition, pre-op GPS was demonstrated here to be a good predictor of absolute GPS post op. Significant correlation of change, but not final GPS, with bilateral/unilateral surgery would suggest this is related to severity of involvement. Interestingly, the same trend was not observed where soft tissue only surgery was performed, however this may be related to the relatively small sample size (around 10% of patients). Encouragingly, the vast majority of subjects improved following SEMLS by an average of 3.2◦, and this trend was maintained over a significant period of time. Based on the findings of this study the expected change in GPS following SEMLS can be approximated by the following equation: GPS Improvement = (0.6×pre-op GPS)− (0.1× age)−2.6. Reference [1] Thomason, et al. JBJS(A) 2014;93:451–60 [in press]. [2] Baker, et al. Gait Posture 2014;30:265–9 [in press]. [3] Rutz, et al. Gait Posture 2014;36:S6 [in press]. http://dx.doi.org/10.1016/j.gaitpost.2014.04.073