Soleus arthrogenic muscle inhibition following acute lateral ankle sprain correlates with symptoms and ankle disability but not with postural control

Abstract

Background: Acute lateral ankle sprains (ALAS) are associated with long-term impairments and instability tied to altered neural excitability. Arthrogenic muscle inhibition (AMI) has been observed in this population; however, relationships with injury-related impairments are unclear, potentially due to the resting, prone position in which AMI is typically measured. Assessing AMI during bipedal stance may provide a better understanding of this relationship.

Methods: AMI was assessed in 38 young adults (19 ALAS within 72 h of injury: 10 males, 21.4 ± 2.7 years; 19 healthy controls: 10 males, 21.9 ± 2.2 years; mean ± SD) using the Hoffmann reflex (H-reflex) during bipedal stance. Electrical stimulation was administered to identify the maximal H-reflex (H_max) and maximal motor response (M_max) from the soleus, fibularis longus, and tibialis anterior muscles. The primary outcome measure was the H_max/M_max ratio. Secondary outcomes included acute symptoms (pain and swelling), postural control during bipedal stance, and self-reported function.

Results: No significant group-by-limb interactions were observed for any muscle. However, a significant group main effect was observed in the soleus muscle (F_(1,35) = 6.82, p = 0.013), indicating significantly lower H_max/M_max ratios following ALAS (0.38 ± 0.20) compared to healthy controls (0.53 ± 0.16). Furthermore, lower H_max/M_max ratios in the soleus significantly correlated with acute symptoms and self-reported function but not with postural control.

Conclusion: This study supports previous evidence of AMI in patients with ALAS, providing insight into neurophysiologic impacts of musculoskeletal injury. Our results suggest that assessing AMI in a standing position following acute injury may provide valuable insight into how AMI develops and guide potential therapeutic options to curb and offset the formation of joint instability.

Keywords: Acute injuries; Balance; Hoffmann reflex; Neural excitability; Patient-reported outcomes.

Graphical abstract

Fig. 1

Background EMG activities in the lower leg muscles that were recorded 100 ms prior to a stimulus eliciting maximal Hoffmann reflex. Data are presented as root mean square measures and their SDs, indicating no significant differences between the acute ankle sprain and healthy control groups or between limbs of each group. EMG = electromyography.

Fig. 2

Soleus H_max/M_max ratios in the injured limbs of the acute ankle sprain group significantly correlate with both (A and B) acute symptoms and (C and D) ankle disability. ALAS patients with greater reduction in soleus spinal reflex excitability would report greater pain and ankle swelling and worse perceived ankle disability during ADL and sports. ALAS = acute lateral ankle sprain; ADL = activity of daily living; H_max/M_max = maximal H-reflex/maximal motor response.