Isokinetic assessment of the effects of botulinum toxin injection on spasticity and voluntary strength in patients with spastic hemiparesis.

Background: Peak knee flexion during swing phase is frequently reduced following stroke. The main treatment is botulinum toxin injection (BoNT-A) of the Rectus Femoris (RF) muscle. BoNT-A injections have been shown to decrease spasticity (assessed using the modified Ashworth scale) and to improve peak knee flexion during swing phase. Although the effect of BoNT-A has been clearly demonstrated on kinematic parameters during gait, the direct effects on spasticity and strength have been little studied using objective and sensitive outcome measures.

Objective: The aim of this study was to use an isokinetic dynamometer to assess the effects of BoNT-A injection in the RF on stretch reflex-related torque at the knee joint and peak voluntary knee flexor and extensor torque and to evaluate the effect on functional capacity.

Methods: Before-after trial: Assessments were carried out pre and post (four weeks) RF BoNT-A injection. Clinical and isokinetic evaluations were carried out. Methods: Ambulatory care in a hospital setting. Participants. Population-based sample of fourteen chronic spastic hemiparetic patients with stiff knee gait. Methods: Primary outcome measurements were stretch reflex-related torque at the knee joint and peak voluntary knee flexor and extensor torque. Secondary outcomes were knee angle at peak torque, the slope of the torque velocity curve, stiffness and functional outcomes.

Results: Peak knee extensor torque was significantly decreased and peak knee flexor torque was significantly increased during maximal voluntary concentric and isometric contractions following BoNT-A injection of the RF. Stretch reflex-related torque evaluated during passive stretching movements was reduced and the angle of occurrence of the peak was greater. Functional outcomes did not change. CONCLUSIONS AND CLINICAL REHABILITATION IMPACT: The results of this study indicate that BoNT-A injection reduced RF spasticity but also reduced quadriceps strength. In contrast, knee flexor strength increased. These changes did not, however, lead to functional gait changes.