Take-Home Message: Although individuals with CAI present with decreased hip muscle strength, these adaptations may not relate to dynamic stability during landing from a jump. Hip strength and dynamic stability should each be considered in CAI rehabilitation programs.
Individuals with chronic ankle instability (CAI) have decreased muscle strength not only at the foot and ankle, but also proximally at the hip. It is also known that people with CAI have decreased postural control, especially during functional activities. However, the influence of hip strength on dynamic stability during landing in unknown. Therefore, the authors conducted a laboratory study on 60 participants to determine the relationship between hip muscle strength and stability during a vertical jump test in people with CAI compared healthy and ankle sprain coper groups. Participants performed a 5-minute warm-up followed by vertical jump testing at full effort to record maximum jump height. To determine dynamic stability outcomes, participants performed 5 jumps to 50% of their maximum height. When they landed on a force plate, they landed and stabilized on their single involved limb (or healthy-matched limb) with their hands on their hips, and held the position for 5 seconds. Stability was defined as time taken to stabilize the limb in the anterior-posterior and medial-lateral direction. Investigators then tested for isometric hip extension, abduction, and external rotation strength through hand-held dynamometry. The researchers found that on average the CAI group had decreased hip extension and external rotation strength compared to the coper and healthy groups; however, there were no differences in hip abduction strength or instability outcomes. Additionally, there was no association between hip strength measures and time to stabilization in CAI or healthy groups, but there was evidence of increased hip extension strength related to shorter time taken to stabilize in the coper group.
In summary, the authors were able to detect decreased hip extension and external rotation strength measures in individuals with CAI; however, these outcomes were unrelated to dynamic stability when landing from a jump. It would be interesting to understand if isokinetic, eccentric, and/or endurance measures of the hip muscles relate to stability performance given the demands of the functional task. Additionally, appreciating muscle activation patterns or joint movement throughout the task would help provide a wholistic picture of proximal adaptations in this population. However, this study reinforces prior work that showed proximal alterations exist in people with repetitive ankle sprain, and that hip strength should be considered when creating a structured ankle rehabilitation program for these patients. However, as hip strength may not directly influence dynamic stability, jump-landing technique and other stabilization exercises should still be included in rehabilitation to improve CAI outcomes. In all, hip muscle strength assessments should be included clinically to guide strengthening programs in conjunction with dynamic stabilization rehabilitation in individuals with CAI.
Questions for Discussion: Do you assess hip muscle strength in your patients with CAI as a part of your structured evaluation? What hip strengthening programs do you implement into CAI or ankle sprain patients? What other dynamic stability tests do you include for individuals with CAI?