The arterial supply of the ulnar nerve and cubital tunnel ischaemia

Abstract

Background: The ulnar nerve is a major nerve in the upper limb and is susceptible to injury, particularly in the region of the cubital tunnel. A suspected mechanism of injury at this site is ischaemia. Whilst this can be caused by mechanical stress (stretching, compression) on the nerve in the tunnel, there may also be fundamental differences between and within individuals in the arterial supply of the nerve in this region. The nature of the arterial supply to the ulnar nerve has received relatively little attention, and a more detailed understanding could aid in the diagnosis, treatment and prevention of ischaemic injury to the nerve. Aims: The first aim of this study was to investigate the extrinsic arterial supply to the ulnar nerve by dissection. The second aim was to analyse the intrinsic arterial anatomy of the ulnar nerve in the cubital tunnel by semi-quantitative histology. Methods: Twelve cadaver upper limbs (paired upper limbs from six body donors; four female, two male; age range 66 – 90 years) were dissected to record the presence of visible arterial branches contacting the ulnar nerve and their arteries of origin. The distances between bony landmarks and the origins of the major arterial branches supplying the ulnar nerve were measured, together with their diameters. For the study of intrinsic arterial supply, 5µm thick histological sections of the nerve were taken from standardised sites within the cubital tunnel and 5cm proximally and distally. The sections were stained with haematoxylin and eosin, and the combined total cross-sectional area (CSA) of all arteries with a minimum CSA of 80µm² was measured. This was then expressed as a percentage of the total nerve CSA. Results: The extrinsic arterial anatomy of the ulnar nerve was found to be very variable. The superior ulnar collateral artery (SUCA), inferior ulnar collateral artery (IUCA), posterior ulnar recurrent artery (PURA), brachial and ulnar arteries all contributed, although SUCA was the most consistent of these (9 of 12 specimens). There were no detectable branches from the anterior ulnar recurrent artery (AURA). Variations were found in the extrinsic arteries of some specimens: four limbs had high proximal brachial bifurcations; two had unusual SUCA origins; and in nine the PURA and AURA originated from a common stalk. The mean CSA of arteries within the ulnar nerve in the cubital tunnel was not significantly different from standardised sites proximal and distal to the tunnel (cubital tunnel vs. proximal, p=0.76; cubital tunnel vs. distal, p=0.24). However, in two specimens with aberrant SUCA origins there was a significantly greater proportion of CSA occupied by arteries in the cubital tunnel. Extrinsic and intrinsic supply were found to have a direct positive relationship in nine of the 12 specimens: the greater the number of arterial branches supplying the ulnar nerve and the larger their diameter, the greater the proportional CSA of the intraneural arteries. Conclusions: The extrinsic arterial supply of the ulnar nerve is very variable. The SUCA, IUCA, PURA, brachial and ulnar arteries all contribute but the SUCA is most consistent between individuals. The intrinsic arterial supply (as determined by the proportion of CSA occupied by intraneural arteries) does not appear to be significantly different in the cubital tunnel compared to adjacent proximal and distal sites. Accepting the relatively small sample size in this study, these results suggest that the nature of the intrinsic arterial supply to the nerve is unlikely to be a major factor in the predisposition to ulnar nerve ischaemia, but the variability of the extrinsic arterial supply of the nerve could be important.