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Title: Reconstruction of a Failed 1cm Ulnar Nerve Conduit.
PNS ID: 110316-1, Published: 3/16/2011, Updated: 4/5/2011.

Author(s): Simone W. Glaus MD, Andrew Yee BS, Susan E. Mackinnon MD.
Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, St. Louis, MO.

Abstract: This 20-year-old right hand dominant woman lacerated her ulnar nerve when she accidentally pushed her hand through a pane of glass. Two weeks following the injury, her right ulnar nerve was reconstructed at an outside institution using a 4mm diameter, 1cm long collagen conduit. The small finger FDS tendon, flexor carpi ulnaris tendon, and ulnar artery were also repaired. Upon presenting to our institution six months following her injury, the patient had no ulnar nerve function and a non-advancing, painful Tinel’s sign at the mid-portion of the surgical scar. She elected to undergo re-exploration and reconstruction of the ulnar nerve. The ulnar nerve was decompressed through Guyon’s canal. The area of injury and previous reconstruction were resected and reconstructed with a medial antebrachial cutaneous nerve cable graft. The results following this reconstruction are pending long term follow-up due to the recent presentation of this case. The patient, however, reports significant reduction in her ulnar nerve-related pain.

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History

A 20 year-old right-hand dominant female sustained a laceration to the ulnar aspect of her middle and distal right forearm upon accidentally falling through a window pane. At initial presentation, the patient was felt to be neurovascularly intact, including in the ulnar nerve distribution; her laceration was washed out and primarily closed. Upon follow-up with a hand specialist later that week, the patient complained of numbness in the ulnar digits, as well as weakness and pain in the hand. On physical examination, the patient lacked ulnar distribution pinprick sensation, demonstrated weak abduction of the digits, and was unable to cross her fingers. Perfusion to the hand was adequate. An ulnar nerve laceration was suspected, and the patient was taken to the OR for exploration approximately 2 weeks later. Lacerations to the ulnar artery and nerve were found, as well as to the flexor carpi ulnaris (FCU) tendon and small finger flexor digitorum superficialis (FDS) tendon. Under microscope visualization, the nerve stumps were trimmed back until healthy fascicles were present. A 1 cm gap was present between the nerve ends, which could not be re-approximated without tension. A 4 mm diameter commercially available collagen conduit was used to bridge the gap and was secured with 8-0 nylon epineural sutures. Additionally, the patient received tendon repairs and microsurgical ulnar artery repair. Postoperatively, the patient had no complications but failed to demonstrate ulnar nerve recovery. Approximately 3 months after her initial repair, she was referred to our institution.

Physical Examination

Complete intrinsic muscle atrophy and clawing of the ring and small fingers were present in the right hand. Sensory exam revealed no light touch sensation and no functional two-point discrimination in the right ulnar nerve distribution. Two-point discrimination in the median nerve distribution was 4-5 mm. Motor exam showed a positive Froment’s sign, inability to cross the fingers, pinch strength of 6 lb, and grip strength of 40 lb. Pinch and grip on the left were 15 lb and 65 lb, respectively. Tinel’s sign was present in the mid portion of the patient’s scar (non-advancing).

Diagnostic Testing

No diagnostic testing was performed given the patient’s physical examination, which was clearly consistent with a complete right ulnar neuropathy.

Management

Pre-operative: The patient was maintained in a protective splint for her ulnar clawing.

Surgical: Re-exploration was performed under 4.5x loupe magnification. The ulnar nerve was first identified in Guyon’s canal and decompression of Guyon’s canal was performed, along with decompression of the deep motor branch distally. The ulnar nerve was then followed proximally until the site of prior conduit reconstruction was reached. The conduit was excised; breadloafing through the conduit revealed dense scar tissue. Once the nerve had been cut back to healthy fascicles, a 4 cm gap was present. The medial antebrachial cutaneous nerve (MABC) was harvested through a separate incision. The topography of the ulnar nerve was mapped out both proximally and distally to ensure appropriate matching of sensory and motor components. Three cables of MABC, each 5 cm in length, were used to reconstruct the ulnar nerve under the operating microscope using 9-0 nylon microsutures. Fibrin glue was also used at the repair sites. The posterior branch of the MABC was reconstructed in an end-to-side fashion to the sensory side of the median nerve, whose sensory component was identified by its lack of motor activity with intraoperative nerve stimulation.

Post-operative: A pain pump placed intraoperatively was used for 3 days. The patient was then started on nortriptyline and referred for hand therapy. Initial hand therapy included scar mobilization and silicone sheeting, ulnar gliding exercises, passive range of motion exercises, and use of a hand-based ulnar nerve palsy splint.

Patient Outcomes

Two months postoperatively, sensory exam revealed no light touch sensation in the right ulnar nerve distribution. Pinch and grip strength were 4 and 20 lbs, respectively, compared to 12 and 65 lbs on the left. Tinel’s sign with ulnar radiation was present 3 cm proximal to the wrist crease. Given the typical nerve regeneration rate of one mm per day, or one inch per month, a longer period of follow-up is required to observe ulnar nerve recovery. This follow-up is pending.

Discussion

Important aspects of this case include: (1) using nerve autografts (the undisputed gold standard) for bridging gaps in critical nerves such as the ulnar nerve; (2) mapping out the motor and sensory topography of the injured nerve prior to grafting to ensure grafting of proximal sensory components to distal sensory components and proximal motor components to distal motor components; and (3) reconstructing the donor nerve (MABC) by transferring its distal stump to the side of an intact sensory nerve.

References

Ray WZ, Mackinnon SE. Management of nerve gaps: autografts, allografts, nerve transfers, and end-to-side neurorrhaphy. Exp Neurol. 2010 May; 223(1): 77-85.
 
Pfaeffle HJ, Waitayawinyu T, Trumble TE. Ulnar nerve laceration and repair. Hand Clin. 2007 Aug; 23(3): 291-9.
 
Brown JM, Yee A, Mackinnon SE. Distal median to ulnar nerve transfers to restore ulnar motor and sensory function within the hand: technical nuances. Neurosurgery. 2009 Nov; 65(5): 966-77. (Description of topographical mapping of the ulnar nerve)