Unveiling the Correlations between Clinical Assessment of Spasticity and Muscle Strength and Neurophysiological Testing of Muscle Activity in Incomplete Spinal Cord Injury Patients: The Importance of a Comprehensive Evaluation

Abstract

Spasticity and muscle weakness are prevalent symptoms of incomplete spinal cord injury (iSCI) and can significantly impact patients’ quality of life. Clinical spasticity and muscle strength assessments are often used to monitor iSCI patients’ progress and plan rehabilitation interventions. However, these assessment methods are subjective, may have limited accuracy, and may not provide a detailed understanding of the underlying neurophysiological changes that occur following spinal trauma. In this study, we aimed to explore correlations between standard clinical assessments of spasticity and muscle strength and objective, non-invasive neurophysiological measures of muscle activity using surface electromyography (sEMG) in iSCI patients up to 2 months after injury. We evaluated 85 iSCI patients (ASIA C = 24, and D = 61) 1.3 ± 0.3 months after C3-L1 spinal injury and 80 healthy volunteers (for comparison), using standard clinical assessment tools such as the Modified Ashworth Scale (MAS) and the Lovett Scale (Lovett), and neurophysiological tests, including surface electromyography at rest (rsEMG) and during the attempt of maximal contraction (mcsEMG) performed in chosen key muscles for the trunk (rectus abdominis), upper (abductor pollicis brevis), and lower extremities (rectus femoris and extensor digitorum brevis). We analysed pain in Visual Analog Scale (VAS) and also performed electroneurography to evaluate the peripheral motor impulse transmission. We confirmed a similar level of pain and moderate advancement of axonal injury type in all patients, which, therefore, had no significant effect on the differences in the assessment of patients’ muscle activity. Considering evaluation of the iSCI patients in the early post-traumatic stage, depending on the level of the injury, the highest MAS and rsEMG values and the lowest Lovett and mcsEMG scores were found in C3–C5 iSCI patients in most of the key muscles. Patients with Th7–L1 injuries represented moderate MAS and rsEMG results, while the muscle strength and motor units’ activity were the worst in the extensor digitorum brevis muscle. Patients with Th3–Th6 incomplete injuries generally presented a moderate level of muscle pathology compared to the above groups. Considering results in all patients, we found strong positive correlations between MAS and rsEMG (rε = 0.752, p = 0.009), and Lovett and mcsEMG (rs = 0.602, p = 0.008) results, and negative correlations between rsEMG and mcsEMG scores (rs = −0.504, p = 0.008) and MAS and Lovett (rs = −0.502, p = 0.03). The changes in muscle motor units’ properties, recorded in rsEMG and mcsEMG, although they follow a similar pattern, are, however, different depending on the level of injury in an early post-traumatic stage of iSCI patients. The established correlations between clinical evaluations and neurophysiological assessments, as well as electromyography at rest and during the attempt of maximal contraction, depict a fundamental phenomenon that should be considered during the initial stages of formulating rehabilitation strategies in applied medicine. The value of neurophysiological sEMG testing seems to be superior to the standard clinical assessment in evaluating spasticity and muscle strength decrease as pathological symptoms found in iSCI patients. Neurophysiological testing, including sEMG, offers a more comprehensive and precise characterisation of muscle activity, thereby enabling the detection of subclinical changes that may otherwise go unnoticed.