Differences in isokinetic hip muscle torque between individuals with femoroacetabular impingement syndrome and pain-free controls: A cross-sectional study.

Reduced hip muscle strength is a common feature of individuals with femoroacetabular impingement (FAI) syndrome. However, there is limited information on the influence of pain during strength assessment. Strength deficits are evaluated by measuring the peak torque at a pre-determined or optimal angle for force production. This method disregards most of the strength waveform data, which are relevant given the dynamic nature of FAI syndrome. 148 individuals with FAI syndrome and 148 matched pain-free controls underwent isokinetic evaluation of hip abductor, adductor, external and internal rotator strength. The second waveform from three maximal efforts was analysed. Between-group comparisons were carried out with Statistical Parametric Mapping (SPM) independent sample t-tests. The FAI syndrome group was divided between individuals who reported and who did not report pain during isokinetic testing and these subgroups were compared with the pain-free controls. Results showed that individuals with FAI syndrome present deficits in hip abductor, adductor, and internal rotator torque across the entire isokinetic range of motion compared to pain-free controls. External rotator torque was impaired from 1 to 77% of the isokinetic range of motion, with no between group difference at the end-range. Pain during the isokinetic testing seems to influence range-specific and the magnitude of deficits in hip muscle torque. These findings indicate that hip muscle strength deficits in FAI syndrome affect the full isokinetic range of motion in most hip muscle groups. Assessing only peak torque underestimates the extent of these deficits, highlighting the importance of considering strength waveform data in this population.