The distribution of brachial plexus lesions after experimental traction: A cadaveric study

Abstract

Objective: The objective of the present study was to determine experimentally the distribution of lesions caused in the cadaveric brachial plexus (BP) by excessive stretching. The authors attempted to delineate the correlation between the direction of stretching and sites of lesions. Methods: Fifteen specimens (each comprised the spinal segment C4-T2 with 2 BPs) were harvested from adult cadavers. Each BP was stretched in a mechanical testing machine at a constant speed of 200 mm/min. Specimens were divided into 3 groups: in group A the BPs were stretched caudally at a 45° angle to the spinal midline; in group B they were stretched perpendicularly to the spinal midline; and in group C the stretching was caudally parallel to the midline. Lesions of each BP were identified and analyzed. A graph of load against dislocation was registered when stretching to delineate the maximal force (Fmax), defined as the maximum load at which BP failure occurs. Results: Based on macroscopic examination, 140 sites of mechanical damage were identified in 30 BPs. Preganglionic injuries (63.6% of lesions), defined as avulsions of the spinal ganglia with their rootlets, were found in 89 spinal nerves. In group B-in which specimens were stretched perpendicularly to the spinal segment-preganglionic injuries were significantly more frequent (41 avulsed spinal nerves) than in groups A and C (21 and 27 avulsed spinal nerves, respectively). Postganglionic lesions equivalent to neurotmesis were found in 51 sites (36.4% of all lesions) along spinal nerves, trunks, divisions, and cords. Postganglionic lesions in group B were much less frequent (8) as compared with groups A and C (24 and 19, respectively). Conclusions: Predominance of preganglionic lesions suggests that attachments of the BP to the spine are more susceptible to traction than postganglionic elements. Preganglionic lesions were mainly produced in C7, C8, and T1 spinal nerves, suggesting their weaker attachment to the spine than in the case of C5 and C6 nerves. Preganglionic lesions were highly correlated with a traction perpendicular to the spine, whereas postganglionic lesions were provoked mainly by traction directed at 45° caudally or by means of caudal traction parallel to the midline. This discrepancy implies a relationship between mechanical resistance of pre- and postganglionic elements of the BP and the vector of force.