Can Ultrasound Accurately Assess Ischiofemoral Space Dimensions? A Validation Study

Background: Ischiofemoral impingement is a potential cause of hip and buttock pain. It is evaluated commonly with magnetic resonance imaging (MRI). To our knowledge, no study previously has evaluated the ability of ultrasound to measure the ischiofemoral space (IFS) dimensions reliably. Objective: To determine whether ultrasound could accurately measure the IFS dimensions when compared with the gold standard imaging modality of MRI. Design: A methods comparison study. Setting: Sports medicine center within a tertiary-care institution. Participants: A total of 5 male and 5 female asymptomatic adult subjects (age mean = 29.2 years, range = 23-35 years; body mass index mean = 23.5, range = 19.5-26.6) were recruited to participate in the study. Methods: Subjects were secured in a prone position on a MRI table with their hips in a neutral position. Their IFS dimensions were then acquired in a randomized order using diagnostic ultrasound and MRI. Main Outcome Measurements: The main outcome measurements were the IFS dimensions acquired with ultrasound and MRI. Results: The mean IFS dimensions measured with ultrasound was 29.5 mm (standard deviation [SD] 4.99 mm, standard error mean 1.12 mm), whereas those obtained with MRI were 28.25 mm (SD 5.91 mm, standard error mean 1.32 mm). The mean difference between the ultrasound and MRI measurements was 1.25 mm, which was not statistically significant (SD 3.71 mm, standard error mean 3.71 mm, 95% confidence interval 0.49 mm to 2.98 mm, t(19) = 1.506, P =.15). The Bland-Altman analysis indicated that the 95% limits of agreement between the 2 measurement was 6.0 to 8.5 mm, indicating that there was no systematic bias between the ultrasound and MRI measurements. Conclusions: Our findings suggest that the IFS measurements obtained with ultrasound are very similar to those obtained with MRI. Therefore, when evaluating individuals with suspected ischiofemoral impingement, one could consider using ultrasound to measure their IFS dimensions.