Robot-aided assessment of ankle position and motion sense acuity in chronic stroke

Research Objectives: More than half of the people affected by stroke experience deficits in lower limb proprioception which compromises balance and gait. Currently, objective data on the extent of ankle motion sense impairment post-stroke are lacking. Further, the prevalence of common motion and position sense deficits remains unclear. Thus, this study examined ankle position and motion sense acuity in people with chronic stroke and healthy controls.

Design: Using an ankle robotic device and employing a psychophysical two-alternative forced choice paradigm, a participant’s ankle was passively plantarflexed either to two distinct joint positions or at two distinct joint velocities. Subsequently, participants made verbal judgments about which of the position further or velocity faster. Each assessment consisted of 30 trials.

Setting: University of Minnesota

Participants: 12 people with chronic stroke (10 ischemic, 2 hemorrhagic; average age 54 years), 13 age and gender-matched healthy controls participated.

Interventions: Not applicable.

Main Outcome Measures: Based on the stimulus-response data, a just-noticeable-difference (JND) threshold as a measure of proprioceptive bias, and the corresponding interval of uncertainty (IU) as a measure of precision were derived for each participant.

Results: First, as a group, stroke participants exhibited significantly elevated mean JND thresholds for position sense (+77%) and motion sense (+153%) compared to the healthy controls. Median uncertainty for position sense (+148%) and motion sense (+78%) was also significantly higher. Second, 67% of stroke participants showed either impaired position sense or motion sense, and 50% had both deficits. Finally, the JND and IU were strongly positively correlated in both senses (ρ = 0.56 - 0.62).

Conclusions: Our robot-aided assessments provided initial data on the prevalence and magnitude of ankle position and motion sense impairment in stroke survivors. Both proprioceptive bias and precision are affected, indicating not only a systematic shift in perception but also an increased uncertainty in perceiving ankle position and motion. Our data demonstrate that impairments in both position and motion sense are common features of chronic stroke.

Author(s) Disclosures: None.