What influences contracture formation in lower motor neuron disorders, severity of denervation or residual muscle function? An analysis of the elbow contracture in 100 children with unilateral Brachial Plexus Birth Injury

• Published in: Journal of children's orthopaedics Vol. 12; no. 5; pp. 544 - 549
• Main Authors: van der Sluijs, J. A., van der Sluijs, M. J., van de Bunt, F., van Ouwerkerk, W. J. R.
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01-10-2018; Sage Publications Ltd; The British Editorial Society of Bone & Joint Surgery
• Subjects: Birth injuries; Brachial plexus; Denervation; Force; Hypotheses; Muscle function; Original Clinical; Orthopedics; Paresis; Pediatrics; flexion contracture; denervation; brachial plexus birth injury; obstetric brachial plexus lesion; muscle paresis
• ISSN: 1863-2521; 1863-2548
• DOI: 10.1302/1863-2548.12.180051

Abstract
Purpose
As in other neuromuscular disorders, both denervation and muscle paresis/imbalance are implicated as aetiological factors for contractures in children with a Brachial Plexus Birth Injury (BPBI). Although both factors are related, it is unclear which factor is dominant. The aim of this study is to assess whether contracture formation in children is predominantly related to denervation or to residual muscle function/imbalance. This might be relevant for understanding contracture formation in other neuromuscular disorders.
Methods
A total of 100 children (61 boys; mean age 10.4 years, 4 to 18) with unilateral BPBI were included in this cross-sectional study. Severity of the denervation was classified according to Narakas. Muscle function of flexors and extensors of both elbows was measured (in Newtons) using a hand-held dynamometer and flexion contractures were measured with a goniometer. The relation between denervation, muscle function/muscle balance and flexion contracture was assessed using univariate and multivariate analysis.
Results
Of the children, 57 were Narakas class I, 13 class II and 30 class III. Mean flexion contracture was 25° (90° to −5°). At the affected side the forearm flexion force was 47% and extension force was 67% of the force of the unaffected side. Contractures were more severe in children with higher Narakas classifications (p = 0.001), after neurosurgery (Mann-Whitney U test, p = 0.009) and were related to age (Spearman's Rho = −0.3, p = 0.008) and to paresis of the extensors (Rho = 0.4, p = 0.000). Flexor paresis as a percentage of unaffected side (Rho = 0.06, p = 0.6) and muscle balance had no influence.
Conclusion
In BPBI, elbow contractures are related to the severity of the neurological lesion, not to residual muscle function.
Level of evidence
Level II – prognostic study