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Title: Reconstruction of a Failed Nerve Wrap for an Ulnar Nerve Laceration.
PNS ID: 110323-1, Published: 3/23/2011, Updated: 4/22/2011.

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: A 53-year-old right-hand-dominant woman lacerated her left ulnar nerve on broken glass five months before she presented to our institution. Her ulnar nerve was reconstructed by an outside institution with a nerve wrap 7mm in diameter and 2cm in length. Upon examination at our institution, she had no recovery of ulnar nerve function. An ultrasound showed an apparent 7mm gap in the ulnar nerve. The patient's main complaint was severe pain in the ulnar nerve distribution. A strong Tinel’s sign was present at the level of the nerve repair with no advancement. She also had significant hypersensitivity in the ulnar nerve distribution. An exploration and an ulnar nerve repair with a medial antebrachial cutaneous nerve graft were elected. At the time of the surgery, it was noted that the deep motor branch had not been decompressed and was not involved in the initial nerve reconstruction. Two months post-operatively, there was an advancing Tinel’s sign and resolution of pain. The long-term results following this reconstruction are pending due to the recent presentation of this case.

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History

A 53 year-old left-hand dominant female sustained a laceration to her volar right wrist at the level of Guyon’s canal when she accidentally fell onto broken glass. The wound was sutured at the time of injury, but the patient had persistent numbness in the ulnar nerve distribution and complained of inability to spread her fingers. On exam, the patient was found to have decreased ulnar light touch sensation and weakness of the interosseous muscles. Approximately 2 weeks after her initial injury, the patient was taken to the OR for exploration. The ulnar nerve was found to be completely lacerated, with approximately 1 cm of gaping between the nerve ends. The nerve ends were trimmed and re-approximated with the wrist in flexion. A primary epineurial repair was performed, followed by wrapping of the nerve with a 7 mm diameter, 2 cm long collagen nerve wrap. The patient was maintained in a short arm cast with the wrist in slight volar flexion for 3 weeks postoperatively. The patient did not recover substantial motor or sensory function by two and a half months postoperatively and underwent electrical studies and ultrasound. EMG showed no conduction through the ulnar nerve at the level of the wrist and 2+ fibrillations in the first dorsal interosseous and abductor digiti minimi muscles. Ultrasound revealed a 7 mm gap in the repair site. The patient was seen in our clinic approximately 5 months after her injury.

Physical Examination

Intrinsic muscle atrophy was present in the right hand. Sensory exam revealed moving and static two-point discrimination of 3-4 mm in the median nerve distribution and 6 mm in the ulnar distribution. Motor exam on the right showed no ulnar intrinsic function, a pinch strength of 4 lb, and a grip strength of 34 lb. Pinch and grip on the left were 14 lb and 65 lb, respectively. Tinel’s sign was present at the site of the nerve repair, and the patient had hypersensitivity in the ulnar nerve distribution of her hand. Normal extrinsic ulnar motor function was present.

Diagnostic Testing

No further diagnostic testing was indicated. Please see initial history for EMG and ultrasound findings obtained prior to referral.

Management

Preoperative: None.

Surgical: Re-exploration of the right ulnar nerve was performed via extension of the patient’s previous incision proximally and distally. The prior reconstruction and nerve wrap were identified. The proximal ulnar nerve entered the wrap, and the sensory component of the ulnar nerve exited the wrap. However, the deep motor branch had not been explored and had not been included in the reconstruction. Guyon’s canal was completely released. The deep motor branch was identified. Proximally, the ulnar nerve was traced until the dorsal cutaneous branch (DCB) was found to be intact. This allowed for topographical mapping of the ulnar nerve (at the level of the DCB, the motor fascicular group lies sandwiched between the DCB and the sensory fascicular group). When the nerve wrap and scar tissue were excised so that healthy fascicles were seen, a gap of approximately 6 cm remained. Through a separate incision, the medial antebrachial cutaneous nerve (MABC) was harvested to serve as an autograft. 3 cables of MABC total, each 6 cm in length, were used to graft the ulnar nerve, taking care to match the motor fascicular group to the deep motor branch (one cable) and the sensory fascicular group to the sensory component distally (two cables). The distal end of the (anterior) branch of the MABC, which had been harvested, was reconstructed to the posterior cutaneous branch of the MABC in and end-to-side fashion. A Marcaine pain pump was placed intraoperatively at the time of wound closure.

Post-operative: The pain pump was removed 3 days postoperatively. The patient was instructed to rest her wrist for an additional 10 days prior to starting active range of motion. She was provided with a neutral wrist splint to wear at night, given her tendency to sleep with the wrist hyperflexed.

Patient Outcomes

At 7 weeks postoperatively, the patient’s pinch and grip on the right were 6 lb and 30 lb, compared to 14 lb and 55 lb on the left. Tinel’s sign had advanced by approximately 1 inch. Physical therapy is ongoing and longer term results are pending. 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.

Discussion

For any laceration of the distal ulnar nerve, correct alignment of the sensory and motor topography is essential to optimizing recovery. By tracing out the deep motor branch to identify the distal continuation of the motor fascicular group, and by finding the dorsal cutaneous branch proximally to identify the level at which the motor fascicular group is sandwiched between the dorsal cutaneous branch and the sensory fascicular group, the topography can be appropriately mapped prior to nerve repair. Additionally, depending on the level of the injury, this will also ensure that all components are adequately reconstructed (i.e., tracing out the deep motor branch in this case would have revealed that it had been severed).

References

Polatsch DB, Melone CP Jr, Beldner S, Incorvaia A. Ulnar nerve anatomy. Hand Clin. 2007 Aug; 23(3): 283-9.
 
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)