Correlation between coefficients of impairment at various muscles and active function in the paretic upper limb

Abstract

In hemiparesis, motor function may be hindered to various degrees by soft tissue contracture, spasticity, spastic co-contraction and agonist paresis. This retrospective study explores correlations between neuromuscular impairments at shoulder, elbow, wrist and fingers and overall function in the paretic upper limb. Fifty-one patients with chronic hemiparesis [25 W, 48(±15) years (mean[±SD]), time since lesion, 7.7(±5.5) years] were assessed using the Five Step Assessment, at least three months after any botulinum toxin injection. The first step assessed motor function of the upper limb by the Modified Frenchay scale (MFS; score between 0 and 10). The 2nd, 3rd and 4th steps assessed coefficients of impairment in four key muscles: shoulder extensors, elbow flexors, wrist flexors and fingers flexors. These coefficients were calculated as: coefficient of shortening [C SH = (X N − X V1 )/X N ; X N , normally expected amplitude; X V1 , angle of arrest upon slow stretch], coefficient of spasticity [C SP = (X V1 − X V3 )/X V1 ; X V3 , angle of catch upon fast stretch], coefficient of weakness [C W = (X V1 − X A )/X V1 ; X A , maximal active range of motion]. For each impairment factor, a mean coefficient across the four muscles was calculated (C SHmean , C SPmean , C Wmean ). For each muscle group and for the mean, multivariable correlations were explored between C SH , C SP , C W and MFS. The MFS correlated with C SH-shoulder ( r = −0.28, P = 0.03) and C W-shoulder ( r = −0.46, P = 0.001); C W-elbow ( r = −0.45, P = 0.002); C W-wrist ( r = −0.33, P = 0.003); C W-Fingers ( r = −0.63, P < 0.0001); C Wmean ( r = −0.78, P < 0.0001). The main factors impeding motor function in chronic spastic paresis are the combination of paresis in agonist and spastic co-contraction in antagonist (limiting active motion) for shoulder extensors and for elbow, wrist and finger flexors. Soft tissue contracture for shoulder extensors also contributed to hinder motor function. Spasticity was not correlated with the mean score of MFS, whichever the muscle considered.