Musculo-Tendinous Changes in Spastic Plantar-Flexor Muscles After Spinal Cord Injury.

Area of Science:

• Neurology
• Biomechanics
• Muscle Physiology

Background:

• Spinal cord injury (SCI) frequently leads to spasticity and altered muscle properties.
• Understanding the time course of muscle stiffness changes after SCI is crucial for rehabilitation.

Purpose of the Study:

• To investigate the mechanisms behind the progressive reduction in plantar-flexor muscle stiffness over time in individuals with chronic SCI and spasticity.

Main Methods:

• A cross-sectional study involving 14 participants with SCI and 10 healthy controls.
• Ankle plantar-flexor torque, muscle fascicle length, pennation angle, and muscle-tendon junction (MTJ) excursions were measured using dynamometry and ultrasound.
• Stiffness indices were calculated for the whole plantar-flexor muscles, tendon, MTJ, and muscle fascicles.

Main Results:

• Plantar-flexor muscle stiffness (SI whole PF), MTJ stiffness (SI MTJ), and muscle fascicle length stiffness (SI MFL) showed a negative correlation with injury duration.
• The time constants for these changes suggest significant alterations within the first 3-8 years post-injury.
• After controlling for morphological and demographic factors, SI whole PF and SI MTJ remained significant predictors of stiffness reduction.

Conclusions:

• The reduction in plantar-flexor muscle elasticity in spastic SCI is partly attributed to changes in the proximal MTJ tissues, including aponeurosis and connective tissues.
• These alterations are most pronounced in the early years of the chronic SCI stage.