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Functional Contribution of T1 to the Brachial Plexus in Infants
Adel Fattah, PhD, FRCS(plast); Christine G. Curtis, BSc, PT; Anne MR Agur, BSc(OT), PhD; Howard M. Clarke, MD, PhD, FRCS(C)
Hospital for Sick Children, Toronto, Canada
Classical accounts of the function of the T1 nerve root limit its activity to the small muscles of the hand and were based on anatomical dissection, clinical examination of brachial plexus injuries and non-physiological electrical stimulation. However, our observations in the multidisciplinary brachial plexus clinic suggest that the range of movements attributed to this root in infants may be greater than previously reported. To determine the contribution of the T1 root to movements of the upper limb in infancy, 40 patients presenting with obstetrical brachial plexus palsy who underwent resection and reconstruction of all brachial plexus roots with the exception of the T1 root were evaluated 3-6 weeks postoperatively when no other nerve supply to the limb was present. The movements of the limb were assessed using the Hospital for Sick Children active movement scale (AMS) and demonstrated considerable variability.
By determining which movements were present or absent at this stage, we found that some patients were able to abduct (n=6) and flex (n=10) the shoulder. Elbow extension was present in 13 cases and supination in 2. Nine patients were capable of wrist extension and extension of the fingers was possible in 26 individuals; thumb extension was a common finding (n=24). Elbow flexion and external rotation of the arm were not observed in any of the forty patients evaluated. The group was then analysed by stratifying the AMS scores. We noted that movements not usually attributed to T1 tended to have a lower AMS score; for example shoulder abduction, shoulder flexion and supination (Table 1). Elbow extension was more common and a greater number of these cases (n=6) had functionally useful movement. A number of cases lacked movements normally attributed to T1 action and this is hypothesized to be due to a dominant role for C8.
We show a greater than generally recognized contribution of T1 to the function of the upper limb in infants. These findings have implication for infants presenting with the 'classic' posture of an Erb's palsy. This is considered to be a consequence of a loss of activity in the C5, C6 and sometimes C7 roots, inferring that the posture is due to retained function in C8 and T1. However, we demonstrate that this posture can be reproduced by the T1 root alone. Thus the diagnostic specificity of the 'waiter's tip' posture of the limb in infants is less discrete than originally described.
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