Hindlimb Stretching Alters Locomotor Function After Spinal Cord Injury in the Adult Rat

Abstract

Background Stretching is a widely accepted standard-of-care therapy following spinal cord injury that has not been systematically studied in animal models. Objective To investigate the influence of a daily stretch-based physical therapy program on locomotor recovery in adult rats with moderate T9 contusive SCI. Methods A randomized treatment and control study of stretching in an animal model of acute spinal cord injury (SCI). Moderate spinal cord injuries were delivered with the NYU Impactor. Daily stretching (30 min./day, 5 days/wk for 8 wks) was provided by a team of animal handlers. Hindlimb function was assessed using the BBB Open Field Locomotor Scale and kinematically. Passive range-of-motion for each joint was determined weekly using a goniometer. Results Declines in hindlimb function during overground stepping were observed for the first 4 weeks. BBB scores improved weeks 5–10 but remained below the control group. Stretched animals had significant deficits in knee passive ROM starting at week 4 and for the duration of the study. Kinematic assessment showed decreased joint excursion during stepping that partially recovered beginning at week 5. Conclusion Stretch-based therapy significantly impaired functional recovery in adult rats with a moderate contusive SCI at T10. The negative impact on function was greatest acutely, but persisted even after the stretching ceased at 8 weeks post-injury.

Stretching adversely modulates locomotor capacity following spinal cord injury via activation of nociceptive afferents.

“…These results extend our previous observations of the stretching phenomenon [165,186] into a more clinically relevant moderately-severe animal model of contusive SCI.…”

“…Consistent with previous observation, stretching beginning acutely after a moderate SCI significantly impaired locomotor recovery of the animals as measured by BBB Open Field Locomotor Scale, kinematics and swimming assessment [171]. These two studies laid the foundation for the stretching projects in our laboratory and raised additional questions which, when answered, will further our understanding about the stretching phenomenon and its clinical relevance.…”

“…Animals were randomly assigned to one of three experimental groups after the first behavioral locomotor assessment on day four post-injury: Acute Stretch (AcS, n=10), Chronic Stretch (ChS, n=9) or injury control for muscle histology (n=3). The stretching protocol was implemented as previously described [186] for the AcS group starting at 4 days post-injury and continuing for 5 weeks and for the ChS group starting at 10 weeks post-injury and continuing for 4…”

“…In addition, hindlimb kinematics and gait were assessed using digital video (sagittal and ventral views) acquired while the animals stepped in 2" (5 cm) of water sufficient to supply approximately 60% body weight support, as described previously [188]. We used a 3-segment, 2-angle model of the hindlimbs for kinematic analysis with Columbiaville, MI) and custom designed Excel macros [185,186].…”

“…Afferents in the base of the tail were stimulated using a 25mm figure-8 magnetic coil attached to a MagStim 200 (MagStim Ltd., Whitland, U.K.); stimuli were delivered at 80% of maximum intensity, sufficient to induce a plateau response but avoid direct muscle/motor axon activation [171]. Gastrocnemius muscle responses (EMGs) were recorded bilaterally using 26-gauge needle electrodes [186,191]. EMGs were analyzed for onset latency and peak-to-peak amplitude.…”