Dewald - 2001 - Abnormal joint torque patterns in the paretic upper limb of subjects with hemiparesis

Citation

Dewald JP, Beer, RF. Abnormal joint torque patterns in the paretic upper limb of subjects with hemiparesis. Muscle & Nerve. 2001 Jan;24(2):273-83. PUBMED

10 Word Summary

Stroke patients generate compensatory torques from different joints than healthy subjects.

Abstract

This study presents the results of a novel paradigm for characterizing abnormal coordination in subjects with hemiparesis. Subjects generated maximum voluntary torques (MVTs) isometrically in four randomly ordered blocks consisting of elbow flexion/extension, shoulder flexion/extension, shoulder abduction/adduction, and shoulder external/internal rotation. A 6-degree-of-freedom (DOF) load cell was used to measure torques in secondary DOFs at the elbow and shoulder, as well as in the torque direction the subject was attempting to maximize. This allowed characterization of the multijoint torque patterns associated with the generation of MVTs in the eight directions examined. Significant differences were found between the torque patterns exhibited by the paretic limb of the hemiparetic group (n = 8) and those observed for the nonparetic limb and control group (n = 4). Potential neural and biomechanical mechanisms underlying these abnormal torque patterns are discussed along with implications for the functional use of the paretic limb.

Notes

• 8 subjects with hemiparesis (functioning range from 20%-90% post onset) and 4 control subjects
• The wrist was immobilized and forces/moments at the wrist were measured to determine corresponding joint-torques.
• Collected data were the:
  • Residual strength - ratio of paretic to non-paretic maximum voluntary torque
  • Torque patterns
• Maximum strength in the paretic limb was significantly less than in the non-paretic limb.
  • Weakness was not uniform across all joints
• Torque patterns showed possible compensation strategies
  • Elbow flexion/extension
    • Strong coupling of shoulder extension and elbow flexion
  • Shoulder abduction/adduction
    • Significant amount of secondary torque produced for all other motions
• This study shows that abnormal coactivation of elbow flexors with shoulder abductors and elbow extensors with shoulder adductors occurs during the isometric generation of submaximal forces in different directions at the paretic wrist.