Contralateral C7 Nerve Transfer
So far, nerve transfer is the optimal treatment for restoring critical motor or sensory function of paralyzed upper limb caused by brachial plexus avulsion injury (BPAI). During the nerve transfer procedure, a total or partial section of an intact but less important nerve is coapted to the distal of an injured peripheral nerve. Contralateral C7 (CC7) nerve root is a relatively new, controversial, but important donor.
In 1986, Gu et al first introduced the CC7 nerve root transfer for treatment of total BPAI.1 Since then, this procedure has been increasingly adopted and become one of the major treatments for BPAI. Although there are controversies on cutting off a normal nerve root without any neurologic sequelae in the donor limb, this technique has been gaining wider and wider acceptance with growing experience.
Indications
Patients who had traction injury of unilateral upper limb with root avulsions of unilateral brachial plexus.
CC7 nerve root transfer is particularly indicated when ipsilateral donor nerves are injured and unavailable for transfer.
CC7 nerve root transfer could be one of the series of multiple nerve transfers for treatment of total BPAI, together with accessory nerve transfer, phrenic nerve transfer, intercostal nerve transfer, and other possibilities.
CC7 nerve could also be a donor nerve of free muscle transplantation, such as free gracilis muscle transplantation by innervated median nerve.
Contraindications
CC7 nerve transfer should not be used when the patient has associated injury in the contralateral upper limb or around the shoulder.
Examination
Electrophysiologic studies, such as electromyography (EMG) and nerve conduction studies, are performed to identify BPAI and integrity of CC7 preoperatively. Intraoperative exploration and direct sensory evoked potential (SEP) are performed to confirm root avulsions of brachial plexus. Integrity of CC7 could be further confirmed by recording action potentials from the latissimus dorsi muscle and the triceps in intraoperative EMG testing.
Relevant Anatomy
The C7 nerve contains 27,213 ± 5,417 myelinated nerve fibers, more than the total number of all available extraplexus donor nerves,2 thus adequate power for transfer.
The C7 nerve consists of both motor and sensory fibers. But more motor fibers are located in the posterior division, while more sensory fibers are located in the anterior division, especially the medial part. This provides a basis for selective CC7 nerve transfer.
There is cross-innervation from the upper or lower trunk of the brachial plexus in C7-innervated muscles; thus, no single muscle is dominated by C7 alone. Muscles controlled by C7 can be compensated for by other nerve roots. Therefore, cutting off the entire or partial C7 nerve root in isolation does not result in significant functional loss of any individual muscle.
Surgical Technique
Preparation of CC7 Nerve Root
The patient is placed in supine position with the head toward the affected side after execution of general anesthesia.
A ~ 7 cm transverse incision is made 2 cm parallel to and above the contralateral clavicle. The transverse cervical vessels and omohyoid muscle are ligated or retracted to one side. All five roots are explored, and the anatomic configuration of brachial plexus is identified by gross observation and intraoperative EMG testing.
The CC7 nerve root is determined by intraoperative EMG testing and detecting action potentials elicited from the latissimus dorsi muscle and the triceps as well as observing shoulder adduction and elbow and wrist extension by using intraoperative microstimulation with a direct current stimulator. Thereafter, the contralateral C7 is dissected as distally as possible and then severed for transfer ( Fig. 22.1 ).
Preparation of Nerve Grafts
Several methods are adopted in connecting CC7 and the injured brachial plexus: pedicled ulnar nerve graft, ulnar nerve graft with vessel anastomosis, free or vascularized sural nerve graft, and direct neurorrhaphy.
Pedicled Ulnar Nerve Graft
In total BPAI patients, the ulnar nerve and its dorsal cutaneous branch on the affected side are severed at the wrist level and dissected proximally. The superior ulnar collateral artery of upper arm segment is also harvested, together with the ulnar nerve ( Fig. 22.2 ).
The distal end of the ulnar nerve is drawn to the supraclavicular region on the unaffected side through a cross-chest subcutaneous tunnel. The distal end is coapted to the CC7 nerve root in the first stage of this surgery while the other end of the pedicled ulnar nerve graft is coapted to the recipient nerve, such as the median nerve, radial nerve, musculocutaneous nerve, or thoracodorsal nerve of the injured side at the second stage ( Fig. 22.3 ).
The second stage can be performed when nerve regeneration has reached the axilla of the affected side, as decided by clinical and physiological studies as follows:
Tapping along the route of ulnar nerve until Tinel sign can be elicited at ipsilateral axilla
Eliciting SEP from scalp while stimulating along the route of subcutaneous ulnar nerve, which demonstrates successful nerve regeneration
Estimation based on previous experiences and the nerve growth rate of 1 mm per day, suggesting an optimal interval of 4–8 months between the two stages to obtain best outcomes in both motor and sensory recovery.
Pitfalls/Complications
Sensory abnormality of donor limb is the most common complication. Most experienced temporary paresthesia in the median nerve innervated area of the donor limb. Paresthesia, mostly numbness, frequently affects the distal index finger (74%), followed by middle finger (58%), and thumb. In a few cases, paresthetic area also includes the ring finger, volar palm, and radial area of the contralateral forearm. The sensory abnormalities spontaneously recovered within 2 weeks to 3 months.
Temporary mild motor deficits of extensor weakness in the elbow, wrist, or fingers in the healthy upper limb are also a main complication after CC7 nerve transfer but less common than sensory deficit. Usually, complete functional recovery was noted within 2 weeks to 2 months after surgery.
Theoretically, the anatomic variation of prefixed or postfixed brachial plexus with involvement of C4 or T2 contribution may result in considerable complications of upper limb paralysis after CC7 nerve transfer, although it is rare. Adequate exposure of all five roots and intraoperative EMG testing are effective and necessary preventions to avoid function deficits in the donor limb.
Related posts:
Reconstructive Nerve Transfer Options for Restoration of Pronation
Accessory to Suprascapular for Shoulder Abduction and External Rotation
Supinator Nerve Transfer for Reconstruction of Thumb and Finger Extension
Brachial Plexus: Use of the Da Vinci Robot
Nerve Transfer for Restoration of Elbow Flexion: The Modified Oberlin Procedure
Transfer of Triceps Motor Branches for Axillary Nerve Reconstruction
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