Study Design Case-control.

Objectives Compare tibial nerve cross-sectional area (CSA), plantar cutaneous sensation, isokinetic ankle strength, and single-limb postural control in people with and without chronic ankle instability (CAI).

Background Patients with CAI exhibit a range of neuromotor impairments. These impairments include deficits in postural control and ankle strength which may be related to altered somatosensation following repetitive joint trauma. However, it is unclear if tibial nerve injury or entrapment may be an underlying contributing factor to many of these impairments.

Methods and Measures Twelve people with CAI (age: 21.25±2.80, height: 165.96±8.34 cm, weight: 72.01±14.19 kg) were compared to 12 people without CAI (age: 21.75±1.96, height: 166.47±6.97 cm, weight: 67.84±12.92 kg). Tibial nerve CSA was measured at two sites; 5 cm and 1 cm proximal to the distal pole of medial malleolus, using diagnostic ultrasound. Plantar cutaneous detection thresholds were assessed at the 1^st metatarsal head using monofilaments applied through a staircase algorithm. Static postural control was tested during eyes open and closed single-leg balance on a force plate. Centre of pressure variables included x-range, y-range, velocity, and area 95% eclipse. Normalised peak torque was assessed during a concentric/concentric isokinetic strength protocol for dorsiflexion/plantarflexion at 60°/s. Group differences were assessed through a combination of independent t-tests and Mann-Whitney U tests (p≤0.05).

Results The CAI group demonstrated decreased sensation (CAI: 3.65±0.34, Healthy: 3.21±0.43; p=0.02), greater eyes closed area 95% eclipse (CAI: 24.50±7.80 cm², Healthy: 18.65±4.75 cm²; p=0.04), and lower plantarflexion peak torque (CAI: 55.02±32.60°/s, Healthy: 85.13±29.08°/s; p=0.03). There were no significant group differences for any other measures.

Conclusions Individuals with CAI exhibited deficits in sensory acuity, postural control, and strength, however, no morphological changes were identified in the tibial nerve based on CSA. These findings suggest several of the neuromotor impairments associated with CAI may be related to central nervous system alterations rather than peripheral nerve injury or entrapment.