Modulation of the Fibularis Longus Hoffmann Reflex and Postural Instability Associated With Chronic Ankle Instability

Abstract

Context: Individuals with chronic ankle instability (CAI) present with decreased modulation of the Hoffmann reflex (H-reflex) from a simple to a more challenging task. The neural alteration is associated with impaired postural control, but the relationship has not been investigated in individuals with CAI.

Objective: To determine differences in H-reflex modulation and postural control between individuals with or without CAI and to identify if they are correlated in individuals with CAI.

Design: Descriptive laboratory study.

Setting: Laboratory.

Patients or other participants: A total of 15 volunteers with CAI (9 males, 6 females; age = 22.6 ± 5.8 years, height = 174.7 ± 8.1 cm, mass = 74.9 ± 12.8 kg) and 15 healthy sex-matched volunteers serving as controls (9 males, 6 females; age = 23.8 ± 5.8 years, height = 171.9 ± 9.9 cm, mass = 68.9 ± 15.5 kg) participated.

Intervention(s): Maximum H-reflex (Hmax) and motor wave (Mmax) from the soleus and fibularis longus were recorded while participants lay prone and then stood in unipedal stance. We assessed postural tasks of unipedal stance with participants' eyes closed for 10 seconds using a forceplate.

Main outcome measure(s): We normalized Hmax to Mmax to obtain Hmax : Mmax ratios for the 2 positions. For each muscle, H-reflex modulation was quantified using the percentage change scores in Hmax : Mmax ratios calculated from prone position to unipedal stance. Center-of-pressure data were used to compute 4 time-to-boundary variables. Separate independent-samples t tests were performed to determine group differences. Pearson product moment correlation coefficients were calculated between the modulation and balance measures in the CAI group.

Results: The CAI group presented less H-reflex modulation in the soleus (t26 = -3.77, P = .001) and fibularis longus (t25 = -2.59, P = .02). The mean of the time-to-boundary minima in the anteroposterior direction was lower in the CAI group (t28 = -2.06, P = .048). We observed a correlation (r = 0.578, P = .049) between the fibular longus modulation and mean of time-to-boundary minima in the anteroposterior direction.

Conclusions: The strong relationship indicated that, as H-reflex amplitude in unipedal stance was less down modulated, unipedal postural control was more impaired. Given the deficits in H-reflex modulation and postural control in the CAI group, the relationship may provide insights into the neurophysiologic mechanism of postural instability.

Keywords: ankle muscles; balance; postural-control deficits; soleus muscle; spinal mechanism.

Figures

Figure.

The group with chronic ankle instability showed a strong positive correlation between the fibularis longus Hoffmann-reflex modulation from prone position to unipedal stance when the mean of time-to-boundary minima were measured during unipedal stance with eyes closed for 10 seconds. The larger modulation represents better control in modulating the reflexive muscle response, and the greater time-to-boundary value indicates better postural control.