1 Neurological changes following acute lateral ankle sprain: an 8-week pilot investigation

Abstract

Background Ankle sprains are associated with detrimental long-term sequelae tied to neuromechanical alterations. Neurological adaptations occurring in the initial weeks after injury may be responsible for long-term adaptations resultant in altered movement patterns; however, few studies have quantified neuromechanical and functional adaptations following acute ankle sprains. Objective This study aims to quantify cortical and reflexive excitability following ankle sprain with concurrent changes in function. Design Pilot cohort study. Setting University laboratory. Participants 6 male subjects (age = 20.8 ± 0.8 years, height = 181.2 ± 3.5 cm, body mass = 84.8 ± 9.0 kg) with history of recent ankle sprain volunteered for this investigation. Interventions Participants were tested at 1, 2, 4, and 8 weeks from injury. During each session clinical measures of ankle volume, balance (Y-balance test), and dorsiflexion range-of-motion (weight-bearing lunge) were assessed. Electromyography sensors were placed on tibialis anterior (TA), peroneus longus (PL), and soleus (SOL) and cortical and reflexive excitability were assessed bilaterally using transcranial magnetic stimulation (TMS), and Hoffmann reflex, respectively. Main outcome measurements Stimulus- response curves from TMS were used to determine active motor threshold (AMT, %output) and maximal response (MEP max , %M max ). Side differences were assessed using descriptive statistics. Results Differences in ankle volume, balance, and dorsiflexion were observed at week 1, and, except dorsiflexion, were no longer present at week 8. Notable side-to-side alterations in cortical excitability were noted for TA AMT and PL and SOL MEPmax. These findings indicated decreased TA excitability, but increased PL and SOL excitability at 1-week (TA INJ = 33.4 ± 15.7%, TA NON = 27.7 ± 4.0%; PL INJ = 70.5 ± 35.1%, PL NON = 45.7 ± 34.1%; SOL INJ = 10.6 ± 11.6%, SOL NON = 12.1 ± 5.1%) but the opposite effect 8-weeks after injury (TA INJ = 38.8 ± 2.8%, TA NON = 35.6 ± 12.0%; PL INJ = 35.6 ± 9.2%, PL NON = 48.7 ± 9.0%; SOL INJ = 10.5 ± 7.2, SOL NON = 8.1 ± 5.9%). Generally, the H-reflex was slightly elevated for all muscles and time-points on the injured side. Conclusions Changes in neurological function were observed among this small cohort of participants that reflect both acute and long-term adaptations due to injury. Further analysis is required to determine how these variables might affect functional measures.