A tool for quantifying hip flexor function during gait.

An index to measure the change in hip flexor function after hip surgery was developed in the Motion Analysis Laboratory at Gillette Children's Specialty Healthcare (GCSH). The hip flexor index (HFI) utilizes principal component analysis applied to five kinematic and kinetic variables collected during normal acquisition of gait data. A single index number is derived that describes accurately the overall hip function. Initial clinical validation was carried out using a data set of 23 normal controls and six patients with a diagnosis of cerebral palsy. The patients were all independent ambulators who had undergone orthopedic hip surgery. The controls were used to establish patterns of interdependency between selected gait parameters and form a basis for the index number. The HFI based surgical outcome was compared to the subjective rating of six clinicians. The clinicians were versed in gait analysis and were blinded to the HFI based outcome. The HFI measure of post-operative change in hip function was found to correspond well with the subjective clinical evaluation. A valid tool such as the HFI can be used to objectify clinical impressions of change in hip function, and can thereby assist researchers with statistical and outcome analysis of interdependent and redundant gait variables.