Mechanical and neural changes in plantar-flexor muscles after spinal cord injury in humans

Abstract

Study design: Cross-sectional study. Objectives: To determine the effect of injury duration on plantar-flexor elastic properties in individuals with chronic spinal cord injury (SCI) and spasticity. Setting: National Rehabilitation Center for Persons with Disabilities, Japan. Methods: A total of 16 chronic SCI patients (age, 33 ± 9.3 years; injury localization, C6-T12; injury duration, 11-371 months) participated. Spasticity of the ankle plantar-flexors was assessed using the Modified Ashworth Scale (MAS). The calf circumference and muscle thickness of the medial gastrocnemius (MG), lateral gastrocnemius and soleus were assessed using tape measure and ultrasonography. In addition, the ankle was rotated from 10°plantar-flexion to 20°dorsiflexion at 5 deg s −1 with a dynamometer, and the ankle angle and torque were recorded. After normalizing the data (the initial points of angle and torque were set to zero), we calculated the peak torque and energy. Furthermore, angle-torque data (before and after normalization) were fitted with a second-and fourth-order polynomial, and exponential (Sten-Knudsen) models, and stiffness indices (SI SOP, SI FOP, SI SK ) and Angle SLACK (the angle at which plantar-flexor passive torque equals zero) were calculated. The stretch reflex gain and offset were determined from 0-10°d orsiflexion at 50, 90, 120 and 150 deg s −1 . After logarithmic transformation, Pearson's correlation coefficients were calculated. Results: MAS, calf circumference, MG thickness, peak torque and SI FOP significantly decreased with injury duration (r loglog = − 0.63, − 0.69, − 0.63, − 0.53 and − 0.55, respectively, Po0.05). The peak torque and SI FOP maintained significant relationships even after excluding impacts from muscle morphology. Conclusion: Plantar-flexor elasticity in chronic SCI patients decreased with increased injury duration.

Lower extremity muscle structure in incomplete spinal cord injury: a comparison between ultrasonography and magnetic resonance imaging

“…[1][2][3][4] In rehabilitation research, magnetic resonance imaging (MRI) is often used to quantify reductions in lower limb muscle crosssectional area (CSA) in SCI, 5 but not without excessive and potentially unnecessary costs. Ultrasonography (US) has also been used to study distal skeletal muscle thickness changes in this patient population, 6 providing a potentially more practical and cost-effective alternative to MRI. Although evidence has established a moderate level of reliability for US measures of muscle size (thickness and estimated cross-sectional area, and volume) in healthy human populations, there is limited evidence in clinical populations.…”

Fatigue in complete spinal cord injury and implications on total delay

“…In addition to the changes in the prevalence of the types of muscle fibers in people with SCI, there are significant alterations in the muscle tissue over time, characterized by muscular atrophy, which is caused by the disuse of muscles and tendons . However, the muscle atrophy and decreases in motor unit force seem to affect the EMD velocity more than the increase in type II fiber proportion that may lead to spurious conclusions that the change in proportion could be one of the factors for the Delay TOT value (Figure ) being higher than that observed in the literature with healthy participants. The tendons are responsible for transmitting the force that allows skeletal movement; however, disuse generates adaptations that directly alter the mechanical properties of these structures, thus affecting the transmission of muscle strength and production of tendon tension force.…”