Foot Progression Angle Walking Test: A Dynamic Diagnostic Assessment for Femoroacetabular Impingement and Hip Instability

BACKGROUND: Determining an accurate clinical diagnosis for nonarthritic hip pain may be challenging, as symptoms related to femoroacetabular impingement (FAI) or hip instability can be difficult to elucidate with current testing methods. In addition, commonly utilized physical examination maneuvers are static and do not include a dynamic or weightbearing assessment to reproduce activity-related symptoms. Therefore, implementing a dynamic assessment for FAI and hip instability could help to improve diagnostic accuracy for routine clinical examinations of patients with nonarthritic hip pain. PURPOSE: To assess the efficacy of a novel diagnostic foot progression angle walking (FPAW) test for identifying hip pathology related to FAI or hip instability. STUDY DESIGN: Prospective cohort study; Level of evidence, 3. METHODS: This prospective study included 199 consecutive patients who were evaluated for unilateral hip pain and who underwent FPAW testing along with standard physical examination testing. Demographic data, including age, sex and hip laterality, were collected from each patient. FPAW testing was performed with directed internal and external foot progression angles from their baseline measurements, with a positive test reproducing pain and/or discomfort. Comparisons were then made with flexion adduction internal rotation (FADIR) and flexion abduction external rotation (FABER) tests as the designated diagnostic standard examinations for FAI and hip instability, respectively. Sensitivity and specificity, along with the McNemar chi-square test for group comparison, were used to generate summary statistics. In addition, areas under the combined receiver operating characteristic curves (AUC) of test performance were calculated for both FPAW and the designated standard examination tests (FADIR, FABER). Radiographic imaging was used subsequently to confirm the diagnosis. RESULTS: The average age of the study cohort was 35.4 ± 11.8 years, with 114 patients being female (57%). Positive internal FPAW testing demonstrated 61% sensitivity and 56% specificity for an FAI diagnosis, compared with the 96% sensitivity and 11% specificity seen with FADIR testing. Internal FPAW was less sensitive, yet more specific compared with FADIR (P < .001). Combined testing had improved accuracy (AUC = 0.58; P < .05) compared with FADIR (AUC = 0.52; P = .21) or FPAW (AUC = 0.57; P = .057) alone. Positive external FPAW revealed 67% sensitivity and 70% specificity for hip instability, while FABER testing was 54% sensitive and 90% specific. External FPAW was significantly more specific but had similar sensitivity to FABER. Combined testing had greater accuracy (AUC = 0.77) compared with FABER (AUC = 0.70) or FPAW (AUC = 0.67) alone (P < .001). CONCLUSION: The FPAW examination can be used as an adjunct examination to assist and improve the accuracy of the clinical diagnosis for FAI and hip instability.