Fig. 8: CST and LMN integrity (as assessed by MEP) indicates impairment and recovery after SCI: individuals classified as AIS A and impaired spinal cord function (CST and LMN integrity) display limited motor recovery.

a Cervical SCI (yellow) may damage spinal cord structures and affect the spinal cord functionality below the level of injury with respective weakness of the innervated muscles. Volitional strength and strength recovery are dependent on the residual spinal cord function (red), here quantified by the residual muscle strength and MEP amplitude. b Individuals with absent MEP (MEP⁻) display greater damage to the descending pathway (evidenced by the greater initial impairment) and limited recovery of motor function of the spinal cord (p = 0.492). The presence of an MEP (MEP⁺) indicates variable levels of spinal cord or LMN damage and recovery (p < 0.0001). c Individuals with an MEP⁻ at baseline were predominantly classified as AIS A, and individuals with an MEP⁺ predominantly classified as AIS D. d Strength recovery from baseline (4 weeks) to 48 weeks after SCI is shown as change in the total motor score of the ISNCSCI. For individuals classified as AIS B/C/D (blue circles), recovery is proportional to the available improvement. In AIS D, the regression represents the relationship between available (x) and actual (y) improvement (y = 0·59x, p < 0.0001). No relationship exists between available and actual improvement for sensorimotor complete lesions (AIS A, p = 0.662; red circles). *p < 0.05 simple linear regression (slope is significantly non-zero). Two individuals were excluded from the total MEP sample (203) because of absent AIS classification at baseline in (b). Seven individuals were excluded from the total sample (748) because of absent AIS classification at baseline in (d). SCI = Spinal Cord Injury, CST = Corticospinal Tract, AIS = American Spinal Cord Injury Association Impairment Scale, MEP = Motor Evoked Potential.