Biomechanic changes in passive properties of hemiplegic ankles with spastic hypertonia

Chung SG, van Rey E, Bai Z, Roth EJ, Zhang L-Q. Biomechanic changes in passive properties of hemiplegic ankles with spastic hypertonia. Arch Phys Med Rehabil 2004;85:1638-46. Objective To investigate quantitatively biomechanic changes in the passive properties of hemiplegic spastic ankles. Design Evaluation of spastic hypertonia by moving the ankle joint slowly between dorsiflexion and plantarflexion extreme positions under controlled joint torque and position. Setting Institutional research center. Participants Twenty-four stroke patients with spastic ankles and 32 healthy controls. Interventions Not applicable. Main outcome measures Passive resistance torque at controlled dorsiflexion and plantarflexion positions, dorsiflexion and plantarflexion range of motion (ROM) at controlled torques, and quasistatic stiffness and energy loss in dorsiflexion and plantarflexion. Results Spastic hypertonic ankles showed significant alterations of the passive properties in plantarflexion (P=.041) as well as in dorsiflexion (P=.016) directions. Compared with healthy controls, spastic ankles showed higher resistance torque (9.51±4.79Nm vs 6.21±3.64Nm, P=.016), higher quasistatic stiffness (.54±.19Nm/deg vs .35±.20Nm/deg, P=.001) at 10° of dorsiflexion, larger normalized dorsiflexion energy loss (.068±.04J/deg vs .04±.02J/deg, P=.037), and decreased dorsiflexion ROM at 10Nm of resistance torque (10. 77°±8.69° vs 20.02°±11.67°, P=.014). The resistance torque, ROM, and stiffness of spastic hypertonic ankles in plantarflexion showed similar changes (P<.05) to those in dorsiflexion. The passive ROM, joint stiffness, and resistance torque at controlled positions correlated with each other and also correlated with the Modified Ashworth Scale (P<.01). Conclusions Various biomechanic changes in both plantar- and dorsiflexors are associated with spastic hypertonia of chronic stroke patients, and they can be evaluated quantitatively under well-controlled conditions. With simplifications, the various measures in this study can potentially be used to obtain more comprehensive and quantitative evaluations of spastic hypertonia in a clinical setting.