Biomechanical assessment of locomotion in two rodent models of nervous system injury

Abstract

The adaptation of inverse dynamics was performed to quantitatively examine the subtle locomotor changes, previously undetectable, in rodent locomotion following nervous system injury. The first experiment performed an injury with known effects, a unilateral lesion of the medial and lateral branches of the left tibial nerve of Long-Evans rats, and measured the resulting data via inverse dynamics. Special effort was made to account for skin movement artefacts using a global optimization method for marker digitization. The second experiment attempted to apply this technique to Long-Evans rats with spinal hemisections at spinal level T-10. After the peripheral nerve injury to the tibial nerve branches, the main findings were that ankle joint still produces an extensor moment and positive power without the active contraction of the gastrocnemius m. It is possible that this phenomenon is due to passive contractile elements of the muscle and tendon. In addition, the knee and hip of the lesion leg ‘stiffen,’ resulting in substantial reductions in moment generation and nearly total losses of both negative and positive power production. There were also compensations made by the opposite hindlimb and contralateral forelimb. The spinal cord hemisection produced subtle, complicated intra and interlimb changes in both joint moment and joint power analysis that could not be seen by looking at joint angles alone.