Frontal plane ankle proprioceptive thresholds and unipedal balance

Reliable unipedal balance is fundamental to safe ambulation. Accordingly, older persons with peripheral neuropathy (PN), who are at increased risk for falls, demonstrate impaired unipedal balance. To explore the relationship between afferent function and unipedal balance, frontal plane proprioceptive thresholds at the ankle were quantified in 22 subjects (72.5 +/- 6.3 years; 11 with PN and 11 matched controls) while they were standing using a foot cradle system and a staircase series of 100 rotational stimuli. PN subjects, as compared to controls, demonstrated shorter median unipedal balance times (3.4 +/- 2.7 vs. 14.3 +/- 8.9 s; P = 0.0017) and greater (less precise) combined ankle inversion/eversion proprioceptive thresholds (1.17 +/- 0.36 vs. 0.65 +/- 0.37 degrees ; P = 0.0055). Combined ankle inversion/eversion proprioceptive thresholds explained approximately half the variance in unipedal balance time (R2 = 0.5138; P = 0.0004). Given prior work demonstrating a similarly strong relationship between ankle torque generation and unipedal balance, neuropathy-associated impairments in ankle frontal plane afferent and efferent function appear to be equally responsible for the inability of older persons with PN to reliably balance on one foot. They therefore provide distinct targets for intervention.