Foot Progression Angle Walking Test- An Effective Dynamic Test for the Diagnosis of Femoroacetabular Impingement and Hip Instability

OBJECTIVES: Clinical diagnosis of femoroacetabular impingement (FAI) and hip instability is determined by accurate history, physical examination, and imaging assessment. Currently, there is no ideal physical examination maneuver and certainly no dynamic method of testing. In this prospective study, we evaluate the Foot Progression Angle Walking (FPAW) test as a novel diagnostic tool that is sensitive and specific for the detection of FAI and hip instability. METHODS: A prospective cohort of patients who presented with hip pain underwent FPAW testing in addition to the gold standard assessments for impingement and instability, the Flexion Adduction and Internal Rotation (FADIR) test and the Abduction and External Rotation (ABER) test, respectively. Baseline foot progression angles were initially recorded. Patients were then instructed to walk with foot progression angles: 1) internally rotated (-15º) and 2) externally rotated (+15º). A positive FPAW test was defined by an increase in hip pain with either internal or external rotation. Radiographs and/or magnetic resonance imaging were then used to evaluate for abnormal hip morphology and confirm diagnosis. RESULTS: 80 patients (53 Female) with hip pain were evaluated by FPAW testing. Imaging used to assess for hip pathology exhibited FAI (n=48), instability (n=26) and normal anatomic morphology (n=13). Baseline measurements showed a neutral foot progression (64%), out-toeing gait (35%), and in-toeing gait (1%). Analysis of FPAW testing showed a sensitivity of 75% and specificity of 66% for FAI; sensitivity 54% and specificity 61% for instability. A positive predictive value (FAI: 77%; Instability 40%) and negative predictive value (FAI 64%; Instability 73%) were also determined. In comparison, the FADIR test showed a sensitivity and specificity of 96% and 13% for FAI, respectively. Its positive predictive value was 62% while its negative predictive value was 67%. Abduction and external rotation testing showed a sensitivity and specificity of 42% and 96%, respectively for diagnosing instability. Its positive predictive value was 85% and negative predictive value was 78%. CONCLUSION: FPAW testing was found to be more sensitive and specific for detecting FAI than instability. The higher specificity and positive predictive value of FPAW in comparison to the FADIR test makes it a reliable tool to identify patients with impingement. The FPAW test appears to be an effective tool to reproduce hip pathology in FAI patients during weight-bearing activity and could be a useful adjunct to give further clinical prospective in FAI and hip instability.