EXCURSION AND STRAIN OF THE MEDIAN NERVE

Five fresh-frozen transthoracic cadaver specimens (ten upper extremiti es) were dissected in order to measure excursion and strain of the med ian nerve at the wrist and the elbow in association with different pos itions of the shoulder, elbow wrist, and fingers. The relationships be tween motions of the joints and excursion and strain at the wrist and the elbow as well as between excursion and strain were also determined . When the wrist was moved from 60 degrees of extension to 65 degrees of flexion, the median nerve at the wrist underwent a mean total excur sion of 19.6 millimeters (9.2 +/- 1.38 millimeters [mean and standard deviation] in extension and 10.4 +/- 1.50 millimeters in flexion). The change in strain was not measurable secondary to nerve-wrinkling. Mot ion of the fingers from hyperextension to full flexion caused a mean t otal excursion of 9.7 millimeters (6.3 a 1.31 millimeters in hyperexte nsion and 3.4 +/- 1.04 millimeters in flexion) and a change in strain of 19.0 per cent. This change in strain became more pronounced when th e wrist and the fingers moved in synergy. Such strain, if constant, ha s been shown to decrease microvascular perfusion and nerve conduction in rabbits. With motion of the shoulder, the mean total excursion of t he median nerve at the elbow was 9.1 millimeters (4.4 +/- 1.64 millime ters in abduction and 4.7 +/- 1.81 millimeters in adduction) and the c hange in strain was 13.3 per cent. With motion of the elbow, the mean total excursion was 12.3 millimeters (12.3 +/- 4.20 millimeters in fle xion and zero millimeters in the resting position) and the change in s train was not measurable because of the wrinkle effect in flexion. Wit h motion of the wrist, the mean total excursion was 5.6 millimeters (4 .3 +/- 1.95 millimeters in extension and 1.25 +/- 0.81 millimeters in flexion) and the change in strain was 14.8 per cent. With motion of th e fingers, the mean total excursion was 3.4 millimeters (2.6 +/- 1.13 millimeters in hyperextension and 0.80 +/- 0.92 millimeter in flexion) and the change in strain was 10.3 per cent. Motion of the wrist and t he fingers induced profound excursion of the median nerve at the wrist , whereas motion of the shoulder and the elbow induced marked excursio n of the median nerve at the elbow. These excursions were much more pr onounced when a number of joints were moved in a composite manner. Any factor that might limit normal excursion, such as scarring, could ind uce strains that could adversely affect the function of the median ner ve. The finding that the position and movement of the limb had a profo und effect on excursion and strain of the median nerve at the wrist an d the elbow may aid in the understanding of the pathophysiology of med ian-nerve neuropathy.