Morphometric study of the upper intercostal nerves: practical application for neurotizations in traumatic brachial plexus palsies.

UNLABELLED: The aim of the study was a morphometric evaluation of the intercostal nerves at different levels along their course in order to determine their adequacy in neurotizing the recipient nerves. The intercostal nerves were harvested from 5 cadavers. A biopsy of the nerve was obtained at 2 levels for each nerve in the parasternal region and at the level of the mid-axillary line. The musculocutaneous nerve was isolated at its origin from the lateral cord. Each harvested specimen was embedded in paraffin and sections were made using a microtome. These sections were then stained histochemically using HPS (Hematein, Phloxine, Safran). Real-time digitalisation of the video image under the microscope was performed. The sum of the different fascicular zones is the effective sensorimotor surface of the nerve at the level being studied.

RESULTS: Direct suture of the upper three intercostal nerves to the musculocutaneous nerve is always possible upto the axillary fossa. The sixth intercostal nerve can be delivered upto this level in only 50% of cases without dissection of the musculocutaneous nerve upto its entry into the coracobrachialis. The musculocutaneous nerve presents a mean surface area of 2.64 mm2 while the nerve to the biceps has a mean surface area of 0.34 mm2 i.e. a ration of 1/8. The mean surface area of the intercostal nerves at the parasternal level is 0.23 mm2 while that at the axillary level is 0.34 mm2. Thus a loss of 33% in surface area occurs between the axillary and the parasternal levels. Our study confirms the insufficiency between the surface area of the intercostal nerves and the different nerve trunks to be neurotized. The relationship between the surface area of the musculocutaneous nerve and the three intercostal nerves is 26.72% with a minimum of 17.2%. If a fourth intercostal nerve is added, this ratio nerves appears to be a superior technique. We were able to deliver the sixth intercostal nerve for a direct suture to the musculocutaneous nerve in only half the cases.