The pendulum test for evaluating spasticity of the elbow joint

Abstract

Objective: To develop a modification of the pendulum test to allow evaluation of elbow spasticity.

Design: The main difficulties of directly applying the conventional pendulum test to the elbow were the small inertia of the forearm and the uncomfortable posture. We designed an experimental apparatus similar to a clock pendulum and developed an elbow biomechanic model to measure objectively spasticity of the elbow joint. The model consisted of linear stiffness and damping and gravity contribution.

Setting: A referral medical center in Taiwan.

Participants: Eleven stable stroke patients and 11 able-bodied subjects.

Interventions: A custom-designed accessory apparatus to facilitate the pendulum test in elbow joints.

Main outcome measures: By using an optimization technique, we estimated parameters of the proposed elbow biomechanic model as the candidate indicators of spasticity.

Results: The stiffness constant remained relatively consistent in all groups. Both the damping coefficient and damping ratio increased in the affected side of stroke patients and tended to increase with the severity of spasticity. Damping ratio had marginally better differentiation capability than the damping coefficient.

Conclusions: The damping ratio derived from the proposed model differentiated spasticity from normotonus and increased as spasticity increased.