Isometric hip strength and dynamic stability of individuals with chronic ankle instability

Context: Compared with individuals who have a history of lateral ankle sprain (LAS) without markers of chronic ankle instability (CAI; LAS copers) and healthy people, those with CAI often exhibit neuromuscular impairments and dynamic-stability deficits at the hip. However, the influence of hip-strength deficits on dynamic stability remains unknown. Objective: To compare isometric hip strength and dynamic stability in individuals with or without CAI and examine the degree of dynamic-stability variance explained by isometric hip strength. Design: Case-control study. Setting: Research laboratory. Patients or Other Participants: Sixty individuals (47 women, 13 men; age = 23.7 6 4.6 years, height = 166.6 6 7.7 cm, mass = 70.8 6 15.7 kg) separated into CAI, LAS coper, and control groups based on previously established criteria. Main Outcome Measure(s): Group differences in resultant vector time to stabilization (RVTTS) and isometric hip-extension, -abduction, and external-rotation strength were determined using 1-way analyses of covariance that controlled for sex and limb (dominant or nondominant) tested and Cohen d effect sizes (95% confidence intervals) Backward linear re ressions and Cohen f ² effect sizes (95% confidence intervals) determined the amount of RVTTS variance explained by isometric hip strength. Significance was set a priori at P, .05. Results: The CAI group had less isometric hip-extension strength than LAS copers (P = .02, d = 0.72 [0.06, 1.34]) and controls (P = .01, d = 1.19 [0.50, 1.84]) and less external-rotation strength than LAS copers (P = .03, d = 0.78 [0.13, 1.41]) and controls (P = .01, d = 1.02 [0.34, 1.65]). No group differences existed for RVTTS (F_2,57 = 1.16, P = .32) or abduction strength (F_2,57 = 2.84, P = .07). Resultant vector time to stabilization was explained by isometric hip strength for LAS copers (R ² = 0.21, f ² = 0.27 [0.22, 0.32], P = .04) but not for the CAI (R ² = 0.12, f ² = 0.14 [0.06, 0.22], P = .22) or control (R ² = 0.10, f ² = 0.11 [0.03, 0.19], P = .18) groups. Conclusions: Participants with CAI had decreased isometric hip strength, but that did not equate to dynamic-stability deficits. Clinicians should include hip-muscle strengthening in rehabilitation protocols for patients with CAI, yet these gains may not enhance dynamic stability when landing from a jump.