Strategies for the Abnormal Co-Contraction of Internal Rotators of the Shoulder in Children with Obstetrical Brachial Plexus Palsy

Abstract

Obstetrical brachial plexus palsy (OBPP) is caused by traction of the brachial plexus during delivery. The incidence of OBPP was once reported to be 2.9 per 1,000 live births, and the incidence of persisting OBPP was 0.46 per 1,000 [1] . Although most patients with OBPP recover spontaneously in the first 2 months, up to 35% are left with varying degrees of shoulder weakness, contracture, or joint deformity [2] . Even after neuro-reconstructive surgery, children with incomplete recovery often have abnormal motor performance [3] . The upper trunk of the brachial plexus (C5 and C6) is most commonly affected in OBPP [3,4] . Paresis of the deltoid, supraspinatus, infraspinatus, and teres minor, which are innervated by the upper trunk, results in poor performance of the shoulder abduction/external rotation. The relatively unaffected or better recovered internal rotators can lead to adduction/internal rotation contracture of the shoulder due to the muscular imbalance. Besides, the internal rotators are often overactive while the patients flex, abduct, or externally rotate their shoulders. The phenomenon of this overactivation is called abnormal co-contraction, which is something like unilateral synkinesis after facial palsy that can be treated by botulinum neurotoxin [5] . On physical examination, the muscle tightness of the lattisimus dorsi and teres major can often be palpated. Active range of flexion and abduction are limited. The patients perform movements of arm elevation usually with elbow flexion, scapular wing protruding outward, and trunk extension. The complex movements such as handto-mouth and hand-on-neck are hard to accomplish. Co-contractions can be identified by physical examination and further confirmed by the electromyography (EMG) study. Abnormal co-contractions of the internal rotators impair the active range of motion of shoulder abduction/external rotation, impede the rehabilitation of the affected arm, and cause the functional loss of daily life activities such as putting food into the mouth, dressing, high reaching, and caring of hair. ABSTRACTObstetrical brachial plexus palsy (OBPP) is caused by traction of the brachial plexus during delivery. The incidence of OBPP was once reported to be 2.9 per 1000 live births, and the incidence of persisting OBPP was 0.46 per 1000. Although most patients with OBPP recover spontaneously in the first 2 months, up to 35% are left with varying degrees of shoulder weakness, contracture, or joint deformity. Even after neuro-reconstructive surgery, children with incomplete recovery often have abnormal motor performance.