Fig. 4: Prediction of strength recovery after cervical SCI: the role of baseline MMS.

Baseline MMS is a good predictor of strength recovery at 1-year post-SCI for individuals with AIS D (high R² values) but is in most cases a poor predictor for those with an AIS A/B/C. a Considering all AIS and muscles, the prediction of strength recovery using baseline MMS is poor (R² = 0.148). b, c Individuals classified as AIS A or B show some degree of proportional recovery of upper limb muscles if the initial impairment is low, but strength recovery is constant or is inversely proportional if the initial impairment is high (especially for distal hand muscles). d In individuals classified as AIS C, proportional strength recovery is apparent for elbow flexors, wrist extensors, elbow extensors, and finger flexors. Proportional recovery is also evident for finger abductors if the initial impairment is low to mild (baseline MMS from 3 to 5) but is constant if the initial impairment is high (baseline MMS from 0 to 1). e Proportional strength recovery is evident for all muscles in individuals classified as AIS D. f Summary of the non-linear regression using random forest regressors indicates good prediction of strength recovery for all muscles of AIS D participants with a prediction error of ≈0.5 points. Although the prediction is fair to good for some of the proximal muscles in individuals with an AIS A/B/C, predicting late strength recovery solely based on the initial motor impairment is poor for distal hand muscles (R² ≈ 0.1). Complex analysis using random forest regressor with 50% of the dataset for training and 50% for testing with 100 trees (estimators) in (a–e). Data are Mean ± SD in (f), bottom panel. In (f) the plotted R² and prediction errors are related to the sample sizes described in (b–e). N = number of biological samples (please note that muscles from the left and right sides of the same individual are pooled in this analysis). SCI = Spinal Cord Injury, AIS = American Spinal Cord Injury Association Impairment Scale, MMS = Muscle Motor Score, ZPP = Zone of Partial Preservation.