Experimental Study Of Mechanism For Co-contraction Between Agonists And Antagonists After Obstetric Brachial Plexus Palsy (OBPP)

Experimental Study of Mechanism for Co-contraction between Agonists and Antagonists after Obstetric Brachial Plexus Palsy (OBPP)Ph.D. candidate ZHOU Youqing Tutor Professor CHEN LiangObstetric brachial plexus palsy (OBPP) is a result of rupture or excessive stretching of the brachial plexus during delivery. Either force or their combined action causes stretching of the neck, depression of the shoulder and tilting of the head increasing the angle between shoulder and head. It results in paralysis in the involved extremity, either singly or bilaterally, which seriously decreases the child activity of daily life and put heavy burden on the family and society. Currently, there is no breakthrough in its treatment outcome. One of reason comes from lack of recognition of its pathological essences and of basic research on the process of the spontaneous recovery. Some authors recommended conservative management, others preferred to surgery treatment, including neurolysis and early nerve surgery. Up to date, there is still controversy at the clinical practice over the optimal nerve exploration timing and surgical methods.Narakas (1987) was the first author who described the haphazard reinnervation during the natural history, which produced the "trumpet sign" linking internal rotation, abduction and elbow flexion. Afterwards, the compromise of function recovery after co-contraction as a result of obstetric brachial plexus lesions was recognized gradually. Co-contraction refers to the result of an aberrant nerve re-innervation at the site of lesion. When the agonist is excited, the contraction of antagonist occurs simultaneously, although under the normal state the antagonist should relax. Under this circumstance, although the appearance of the agonist at the injuried upper extremity was satisfactory with a nearly normal strength, no efficient function was obtained so that the result of nerve regeneration is of no effect. Chuang in 1998 described various shoulder deformity at the late stage of OBPP, and proposed that co-contraction resulted from cross-innervation following nerve regeneration was one of the reason for poor shoulder function restoration. Thus, the strategy of muscle transposition to minimize the influence of co-contraction was used, that was, transfer of pectoralis major and teres major to the infraspinatus muscle. Afterwards, on the basis of co-contraction between agonists and antagonists at the elbow joint, he (2000) recommended biceps-to-triceps transfer for restoration of elbow extension with the preservation of an intact brachialis muscle. In clinical practice YD Gu and L Chen(2000)discovered that co-contraction occurred more frequently in OBPP after conservative treatment and neurolysis than that in the adult brachial plexus lesions, which was one of the important factors hindering the function of the involved upper extremity.In the classification of dysfunction of of shoulder abduction, they found out that the commonest pathological essence was co-contraction between shoulder adductors and abductors. They developed a novel electrophysilogy quantitative examination for detection of co-contraction, and proved that no co-contraction occurred in the normal children. According to the results of electrophysiological examination, they carried out the transfer of latissmus dorsi, teres major and trapezius muscles for reconstruction of shoulder abduction and external rotation and achieved satisfactory results. Except the surgical treatment and non-surgical treatment, there is another non-operative management, that is, intramuscular injection of botulinum toxin type A, which resulted in a lasting reduction of imbalance between antagonists and agonists activity. Hierner(2001)pointed out that muscle co-contraction occurred in every patient with a higer degree(Sunderland III-V) nerve lesion. The above-discussed report of co-contraction was restricted in the exploration of clinical presentation and treatment procedure. It did not involve the research of the essence of co-contra...