Cross-innervation (caused by misdirection of regenerated axons), muscular imbalance (caused by muscle paresis or earlier recovery), and growth are the three main causes of shoulder deformity due to obstetric brachial plexus palsy. If perioperative studies demonstrate the existence of muscle recovery by cross-innervation, a new strategy of muscle transposition to minimize the influence of cross-innervation is used. Release of antagonistic muscles (pectoralis major and teres major muscles) and augmentation of paretic muscles (transferring teres major to the infraspinatus muscle, reinserting both ends of the clavicular part of the pectoralis major muscle laterally) are performed for reconstruction. Since 1993, 29 patients having shoulder deformity caused by obstetric brachial plexus palsy underwent reconstruction utilizing this strategy of muscle transposition. The timing for the reconstruction was at an average of 8.5 years (range, 4 to 21 years). The average shoulder abduction following the muscle transposition was 151 degrees (i.e., average gain 104 percent, or 77 degrees) and that of external rotation was 72 degrees (average gain 200 percent, or 48 degrees). Compared with the patients who had no surgery for shoulder deformity caused by obstetric brachial plexus palsy and early nerve surgery for the infant obstetric brachial plexus palsy, the results of the strategy seem to be significantly impressive.

The operative results proved that earlier timing of nerve surgery (within 3 months) is strongly indicated in patients who have total palsy, and only relatively indicated in patients with isolated rupture of the upper plexus.