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Title: Reconstruction of a Failed Nerve Wrap for an Ulnar Nerve Neuroma Resection.
PNS ID: 110318-1, Published: 3/18/2011, Updated: 4/6/2011.

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 55-year-old right-hand dominant male physician had a painful granular cell tumor partially removed from his ulnar nerve. The excised portion of the nerve was reconstructed with a nerve wrap. It was thought at the time of surgery that the nerve biopsy originated from the sensory component of the ulnar nerve; however, post-operatively the patient was found to have normal sensation and complete loss of ulnar intrinsic motor function. Upon presenting to our institution, the patient had complete ulnar intrinsic atrophy of the right hand with a positive Froment’s sign, ring and small finger clawing, and inability to abduct or adduct the fingers. The patient elected to have the surgical site re-explored with a plan to use an autologous motor nerve graft to reconstruct the motor component of the ulnar nerve. At surgery, the ulnar nerve was decompressed through Guyon’s canal. The normal functioning sensory component of the ulnar nerve was protected while the area of nerve injury and previous nerve wrap reconstruction were excised. The nerve gap was reconstructed with a 5.5 cm graft using the obturator motor nerve to the gracilis muscle as a nerve graft. The results following this reconstruction are pending long term follow-up due to the recent presentation of this case.

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History

A 54 year-old right-hand dominant male developed extreme sensitivity over the course of months at the right ulnar nerve proximal to wrist crease. There was no history of trauma, and physical examination was normal except for a positive Tinel’s and pain over the area of complaint. EMG was normal. MRI showed a small area of fusiform swelling of the ulnar nerve, most consistent with a benign mass. The patient underwent exploration and was found to have fusiform swelling within what was identified as the sensory fascicular group, which was stuck to the motor fascicular group. The sensory and motor fascicular groups were separated, and multiple biopsies were taken of the lesion. Intraoperative stimulation revealed the motor component to be intact. A nerve conduit was applied as a wrap to the sensory component to keep it separate from the motor fascicular group. Immediately postoperatively, the patient demonstrated complete ulnar intrinsic motor palsy with normal ulnar sensory function. This was felt to likely be a first or second degree injury from dissection of the components prior to biopsy. An ultrasound was obtained approximately 2 weeks postoperatively which showed no evidence of constriction, laceration, or defect. An EMG was obtained approximately 2 months postoperatively which showed evidence of a severe ulnar nerve injury at the distal wrist. The patient was referred to our clinic at that time. Of note, the patient’s profession required very fine and precise motor control of his fingers, making this palsy devastating to his career.

Physical Examination

Complete intrinsic muscle atrophy and clawing of the ring and small fingers were present in the right hand. Sensory exam revealed moving and static two-point discrimination of 5 mm in the median and ulnar nerve distributions bilaterally. Motor exam showed a positive Froment’s sign, an inability to cross the fingers, a pinch strength of 3 lb, and a grip strength of 70 lb. Pinch and grip on the left were 18 lb and 80 lb, respectively. Tinel’s sign was present just proximal to the wrist crease, at the site of the patient’s scar.

Diagnostic Testing

Repeat EMG: Right ulnar motor nerve conduction study from the abductor digiti minimi (ADM) showed normal onset latency, normal conduction velocity, and a very small distal compound muscle action potential (CMAP) amplitude. Right ulnar motor nerve conduction study from the first dorsal interosseous (FDI) showed no CMAP. 2+ to 3+ fibrillations and positive sharp waves were present in the right ADM and FDI. Severely reduced recruitment of motor unit potentials (MUPs) was noted at the ADM, and no voluntary MUPs were present at the FDI. Right ulnar sensory testing was normal.

Management

Preoperative: The preoperative plan was to perform a re-exploration with decompression of the ulnar nerve through Guyon’s canal, removal of the tumor, and autologous nerve grafting of affected sensory and motor components. Repeat EMG testing was performed prior to re-exploration.

Surgical: Re-exploration of the right ulnar nerve was performed via the patient’s previous incision, which was extended proximally and distally. The ulnar nerve was identified in Guyon’s canal and was decompressed through Guyon’s canal and at the deep motor branch distally. Intraoperative stimulation of the deep motor branch produced no motor function. The deep motor branch of the ulnar nerve was then traced proximally to identify the sensory and motor topography. Additionally, the dorsal cutaneous branch of the ulnar nerve was identified in the proximal incision and traced distally to identify sensory and motor topography. Carefully proceeding into the area of previous surgery, the nerve wrap was identified around the motor component of the ulnar nerve. This was neurolysed away from the sensory component and resected. Meanwhile, a second surgeon harvested the gracilis branch of the left obturator nerve to serve as an autologous graft of motor origin. A motor donor nerve was chosen for its potential benefit in regeneration over a sensory nerve graft, given the patient’s professional need to recover absolutely as much function as possible. After complete removal of the prior conduit wrap reconstruction and the tumor in its entirety, a defect of 5.5 cm remained. This gap was grafted using the harvest gracilis branch of the obturator nerve, which provided a good size match and tension-free repair. The proximal graft repair site was at a level 6 cm proximal to the wrist crease.

Post-operative: The patient’s pathology revealed a granular cell tumor, which was completely excised.

Patient Outcomes

The patient experienced no complications following surgery. One month postoperatively, the patient’s sensory exam was normal (unchanged from preoperative exam). Motor exam showed a pinch strength of 8 lb, and a grip strength of 58 lb, compared to 18 lb and 70 lb on the left. Further follow-up is 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

Reliable topographical mapping of the ulnar nerve can be performed in two ways—using either the dorsal cutaneous branch or the deep motor branch as a landmark:

(1) Distal to the takeoff of the dorsal cutaneous branch (DCU), the sensory component of the ulnar nerve makes up about 60% of the nerve cross-sectional area, and the motor component that continues as the deep motor branch makes up the remaining 40%. Proximal to the takeoff of the DCU, the motor fascicular group is “sandwiched” between the DCU medially (i.e., ulnarly) and the main sensory component of the ulnar nerve laterally (radially). The DCU branches off from the main ulnar nerve about 10 cm above the wrist crease. As it travels distally, the motor component turns into the deep motor branch of the ulnar nerve (DMB) and moves from lying medial to the sensory portion of the ulnar nerve, to travelling under the sensory component as it turns around the hook of the hamate, where it finally assumes a position lateral to the sensory component. There is an intraneural cleavage plane between the motor and sensory groups, as well as between the main ulnar nerve and the DCU, that is easily discernible using micro-pickups. Tapping across the surface of the nerve, micro-pickups will “fall” into the intraneural cleavage plane. Often, there is also a streak of fatty tissue or a micro-vessel that also delineates this cleavage plane.

(2) Alternatively, the motor and sensory components can be clearly delineated by tracing the DMB proximally to identify the motor fascicular group. In the forearm, at or proximal to the level of the wrist, the larger sensory component of the ulnar nerve will lie most laterally (i.e., most radially) compared to the motor component, and above 10 cm proximal to wrist level, there will also be a smaller fascicular group present on the most medial (ulnar) aspect that is the DCU.

References

Polatsch DB, Melone CP Jr, Beldner S, Incorvaia A. Ulnar nerve anatomy. Hand Clin. 2007 Aug; 23(3): 283-9.
 
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)
 
Magill CK, Moore AM, Mackinnon SE. Same modality nerve reconstruction for accessory nerve injuries. Otolaryngol Head Neck Surg. 2008 Dec; 139(6): 854-6. (Use of a motor autograft to repair a motor nerve defect)