Vascularized Ulnar Nerve Graft
Breidenbach and Terzis first introduced the free vascularized ulnar nerve graft (VUNG) in 1981 based on the superior ulnar collateral artery (SUCA) for cases with lower brachial plexus avulsion.1 Bonney et al used the ulnar nerve as a vascularized nerve graft but transferred it based on the ulnar artery.2 Lebreton et al described a detailed anatomical study of the VUNG based on the SUCA in 1983.3 At present, the VUNG is frequently used as donor nerve graft for reconstruction of a brachial plexus injury (BPI). Terzis and Kostopoulos reported the large series of the VUNG for reconstruction of BPI.4 They concluded that the VUNG is the appropriate solution for BPI with C8 and T1 root avulsion, with outcomes that are superior to those achieved with conventional nerve grafts.
The VUNG based on the SUCA has an adequate blood supply, which is necessary to hasten axonal regeneration. Dissection of the graft is relatively easy because the pedicle′s location is anatomically constant.
The indication for a vascularized nerve graft would include proximal lesions, long nerve defect, and scarred recipient bed. The strongest evidence in favor of vascularized nerve graft is in the use of large-caliber nerve grafts, such as the ulnar nerve, to prevent central necrosis.
This technique should be selected if there is definite evidence of a preganglionic injury to the C8 and T1 roots in BPI. Breidenbach and Terzis proposed the use of a VUNG as an interposition nerve graft between the proximal and distal stumps of the median nerve in selected cases of upper-extremity replantation.1
Hattori et al reported the use of a VUNG for reconstruction of a large defect of the median or radial nerve after severe trauma of upper extremity in cases where there is a hopeless prognosis for ulnar nerve repair.5
Irreversible fibrosis of target end organs can compromise the result and is a contraindication to this procedure.
The ulnar nerve has an extrinsic blood supply consisting of multiple dominant systems: the SUCA, the inferior ulnar collateral artery (IUCA), the posterior ulnar recurrent artery, and the ulnar artery. However, the entire length of the ulnar nerve can survive based only on the SUCA and its venae comitantes.1,3
Taylor′s group examined the blood supply of the upper limb and classified peripheral nerves according to their suitability for microvascular free transfer, with type A being the best and type E being the worst ( Fig. 13.1 ).
The ulnar nerve is supplied by the brachial and the ulnar angiosomes. In the arm, the ulnar nerve is type C as it courses distally with the superior ulnar collateral artery on its surface. As it passes behind the medial epicondyle, the ulnar nerve is nourished by the anastomotic system formed by the superior ulnar collateral and posterior ulnar recurrent arteries and the blood supply is a type E pattern. In the forearm, the ulnar nerve receives a type A supply as it accompanies the ulnar artery, receiving many characteristic Y-shaped arteriae nervorum. In the hand, the ulnar nerve has a type E blood supply pattern again6 ( Fig. 13.2 ).
The SUCA arises from the medial aspect of the brachial artery at the mid portion of the arm. The venae comitantes of the SUCA arising from the venae comitantes of the brachial artery are identified at the similar or more distal level of the SUCA. The SUCA pierces the intermuscular septum from the anterior to posterior compartment and courses 3 to 4 cm before joining the ulnar nerve. The external diameter of the SUCA varies from 0.8 to 2.0 mm. According to the anatomical study of Lebreton et al, the SUCA was present in 47 of 50 upper extremities.3
In the arm, the superior ulnar collateral artery runs on the ulnar nerve together with the corresponding vein. Around the elbow, the venous drainage appears to be directly to nearby veins. In the forearm, the ulnar nerve is supplied directly by the ulnar artery, and its venous drainage is to the periarterial venous plexus ( Fig. 13.2 ).