Measurement of brachial plexus strain in arthroscopy of the shoulder

The purpose of this study was to measure the strain on the brachial plexus that results from traction loads applied at various arm positions and to correlate this with visibility through the arthroscope. We mounted strain gauges to the upper trunk, lateral cord, median nerve, and radial nerve of five fresh human cadavers. Each cadaver was placed in a lateral decubitus position, with the head fixed in a neutral position, as for shoulder arthroscopy, and the strain on the plexus was measured as a function of arm position and traction load. A final cadaver was used to determine the accessibility and visibility in the arthroscope at each of the arm positions. At a given flexion angle, increasing abduction is associated with decreasing strain. At a given abduction angle, increasing flexion results in decreased strain. The minimum overall strain was noted at 90 degrees of flexion and 0 degree of abduction. Visibility at this position is limited. We conclude that the ideal arthroscopic position is a combination of two positions that would maximize visibility while minimizing strain to the nerves. These two positions are 45 degrees of forward flexion and 90 degrees of abduction in combination with 45 degrees of forward flexion and 0 degree of abduction.