Background: Chronic ankle instability (CAI) results in hip neuromuscular impairments that can perpetuate dysfunction through reduced lumbopelvic stability and subsequent malpositioning of the lower body during functional movement. Lumbopelvic stability might be further impaired through changes in trunk muscular contractility. However, lumbopelvic stability and trunk muscle morphology have not been compared between individuals with and without CAI.
Purpose: To compare lumbopelvic stability and trunk muscle contractility between individuals with and without chronic ankle instability (CAI) and determine if lumbopelvic stability and trunk muscle contractility are associated with self-reported function.
Study design: Case-control study.
Methods: Ten individuals with CAI, 10 ankle sprain copers (COP), and 10 healthy controls (CON) participated. Diagnostic ultrasound imaging was used to assess transversus abdominis (TrA) and lumbar multifidus (LM) muscle contractility. A percent change in contraction thickness from rested to contracted conditions was calculated for each muscle. Lumbopelvic stability was assessed using unilateral hip bridge, trunk flexion endurance, Biering-Sorensen, and side plank tests. Self-reported function was measured with the Foot and Ankle Ability Measure Activity of Daily Living (FAAM-ADL) and Sport (FAAM-S) subscales. One-way ANOVAs and Cohen's d effect sizes compared scores on clinician and patient-reported outcomes between groups. Pearson product moment correlations analyzed associations between self-reported function and trunk muscle contractility and lumbopelvic stability. Significance was set a priori at P<0.05.
Results: COP had significantly greater TrA contractility than CAI (P<0.01, d=2.65[1.45,3.85]) and CON (P=0.03, d=1.05[0.08,1.94]). Although not statistically significant, a large effect size suggest that CAI had lower TrA contractility than CON (P=0.12, d=0.92[-0.03,1.80]). No differences existed for LM contractility or lumbopelvic stability tests. A moderate direct correlation (r=0.65, P=0.04) existed between CON's TrA contractility and FAAM-ADL scores.
Conclusion: Deficits in TrA contractility are a novel finding among individuals with CAI. While LM contractility and lumbopelvic stability did not differ between groups, future research should continue to examine their relevance to CAI.
Level of evidence: 3b.
Keywords: ankle sprain; core endurance; diagnostic ultrasound; lumbopelvic stability; self-reported function; transversus abdominis.