Longitudinal motion of the median nerve
ART Literature Review:
by Everett Johnson, DC, ART
Longitudinal motion of the median nerve.
Longitudinal motion of nerves is an important adaptive process that takes place during limb motion. As that limb moves the pathway through which the nerves run shorten or lengthen. If the limb is flexed to the trunk, the nerve is shortened, or lax, in its pathway. When the nerve is lengthened along its pathway the nerve is first straightened, then stretches and finally performs an untwisting. Peripheral nerve fibers are arranged in a spiral fashion to allow an unwinding to take place during the lengthening process. This unwinding process allows the nerve to lengthen without putting stress on the actual nerve fibers. Two articles will be examined for measuring the longitudinal excursion at the median nerve. Both use different techniques to determine nerve motion. One relied on electrode tips being placed in the median nerve and the motion of the electrodes was measured relative to the motion of the arm. The second study used ultrasound imaging to measure the longitudinal motion of the median nerve.
The first article (1) examined motion of the median nerve at a point halfway between the shoulder and the elbow in fifteen subjects. Both active and passive motions of the arm were performed, which produced an angulation of the end of the electrode along the long axis of the nerve. The free end motion of the electrode was measured with calipers to the nearest .5 mm. The recorded movements of the median nerve at this location were no different in regards to active or passive motion. Their study found that the greatest amount of longitudinal motion of the median nerve occurred with extension of the wrist and fingers at 7.4 mm distally. Flexion of the elbow produced 4.3 mm of proximal nerve motion.
Four of the subjects also had measurements taken at the wrist. The authors found that with flexion of the index or middle finger the median nerve moved 4 to 5 mm in a proximal direction. They also stated that soft-tissue interference made the measurement for motion of the nerve with wrist hyperextension unreliable, but estimated that the nerve moves distally approximately 10 to 15 mm during this motion.
The second article (2) looked at the longitudinal excursion of the median nerve using ultrasonography in patients with carpal tunnel syndrome. The authors designed a jig for the participants arm to rest in. The patient was lying supine with the shoulder at 45 degrees of abduction, elbow flexed to 45 degrees, and neck at neutral position. The elbow was in some instance for testing purposes moved to full extension. The ultrasound transducer was placed longitudinally at the wrist of the participants so that a clear image of the carpal tunnel contents could be acquired. Images of the median nerve and the tendons of the flexor digitorum superficialis muscle were taken during flexion and extension motions of the of the metacarpophalangeal joints of the tested extremity. The direct longitudinal motion of the nerve was measured as well as the motion of the flexor digitorum superficialis. Movement of the nerve relative to the flexor digitorum superficialis was also measured calculated.
The results of the study appear to support the hypothesis that patients with a diagnosis of carpal tunnel syndrome show a decrease in longitudinal excursion of the median nerve. Motion of the median nerve through the carpal tunnel with the elbow extended for the control group (no CTS diagnosis) was 11.2 mm, where the patient group was 8.3 mm. This study was limited in data regarding motion of the median nerve at other points of the body. This study also only looked at the longitudinal motion of the median nerve in a distal direction, not proximal, when compared to the previous study.
Both of the studies give good supportive evidence that longitudinal motion of the median nerve is important part of its accommodation, and the reduction of that motion may play some role in the symptoms associated with median nerve entrapment. The author of the first study suggested that proximal and distal sliding of the nerves through the site the nerve slides through may cause damage to the nerve at these locations and reduced or restricted sliding at that point. The author suggest this would be greater in people using their arms for repetitive tasks over extended periods of time. Further studies need to be performed that will look at the longitudinal motion of the median nerve at possible entrapment sites and if that motion can be influenced by motion based soft-tissue techniques in symptomatic individuals.
1. McLellan D, Swash M. Longitudinal sliding of the median nerve during movements of the upper limb. Journal of Neurology, Neurosurgery and Psychiatry 1976;39:566-570.
2. Hough A, Et. Al. Reduced longitudinal excursion of the median nerve in carpal tunnel syndrome. Arch Phy Med Rehabil 2007;88:569-576.