Gluteus medius activity during gait is altered in individuals with chronic ankle instability: An ultrasound imaging study

Background: Altered gait mechanics are frequently reported in individuals with chronic ankle instability (CAI), and increasing information suggests proximal muscle adaptations occur in this population. Ultrasound imaging (USI) offers a visual means to evaluate muscle activity during movement, and overcomes limitations of electromyography (EMG) to detect hip muscle activity. Research Question: A descriptive laboratory study was conducted to determine if gluteus maximus (GMAX) and medius (GMED) muscle activity differed throughout gait in patients with CAI compared to healthy counterparts. Methods: Twenty young adults with CAI (21.6 +/- 2.4 years, 10 males) and 20 healthy participants (21.2 +/- 2.8 years, 10 males) walked on a treadmill at 1.35 m/s while researchers obtained 10-second clips of bilateral USI of the GMAX and GMED. USI clips were reduced to 55 frames consisting of 11 points over five full gait cycles. Muscle thickness values during walking were normalized to quiet bipedal standing USI images to obtain functional activity ratios (FARs). FARs with 90% confidence intervals (CI) were plotted as 10% interludes from 0 to 100% of the gait cycle to compare groups and limbs. Mean differences and Cohen's d effect sizes were used to assess the extent of differences. The CAI group had decreased GMED activity bilaterally from 0 to 40% of walking gait compared to healthy counterparts with large effect sizes (d >= 0.60). CAI group FARs were below quiet stance levels (FARs < 1.0) throughout the entire gait cycle. There were no differences noted between groups or limbs for GMAX measures. Significance: Proximal stabilizing musculature was altered bilaterally in CAI individuals compared to healthy counterparts, which may contribute to movement dysfunction. Previous studies using EMG have not detected this extent of bilateral gluteal muscle alterations in CAI groups during gait, however our findings suggest USI was able to detect significant proximal alterations during walking in this population.