Nerve Transfer for Restoration of Elbow Flexion: The Modified Oberlin Procedure

10.1055/b-0034-78103

Nerve Transfer for Restoration of Elbow Flexion: The Modified Oberlin Procedure

Frances Sharpe, David J. Slutsky, and Milan Stevanovic

Restoration of elbow flexion remains the first reconstructive priority in treating patients with injury to the upper roots of the brachial plexus (C5–C6 and C5–C6–C7). In the setting of root avulsion or an otherwise irreparable lesion, nerve transfer has been used to restore function. In 1994, Oberlin et al described the use of a fascicle of the ulnar nerve transferred to the musculocutaneous nerve (MCN) branch to the biceps brachii for reconstruction of elbow flexion.1 Since the introduction of this transfer, excellent functional results have been reproduced in other centers. The double fascicular transfer was subsequently described for reinnervation of both the biceps and brachialis to improve the strength of recovered elbow flexion.2,3

Indications

Oberlin and double fascicular nerve transfers for elbow reconstruction are indicated in lesions of the brachial plexus involving C5 and C6 or C5, C6, and C7 root injuries.
Some global or mixed plexus injuries can be treated by this method if there is adequate clinical recovery in the lower roots.
It can be used for deficits resulting from postradiation neuritis of the brachial plexus.
It is indicated for nerve reconstruction in patients who present with a significant delay from their time of injury, since the neurorrhaphy is placed close to the target muscles, and for older patients who may have poor outcomes with more conventional techniques. British Medical Research Council (BMRC) classification M4 motor strength has been recovered in patients as old as 66 years of age.4

Contraindications

The absolute contraindication for this nerve transfer is a global brachial plexus palsy with no recovery of ulnar nerve function.
A relative contraindication is a global palsy that subsequently recovers lower nerve root function, since the transfer requires intact function of the C8–T1 nerve roots.
Outcomes are unpredictable after more than 1 year from injury.

Examination and Imaging

A prerequisite for the transfer requires intact function of the C8–T1 nerve roots. A preoperative clinical examination for motor strength of the flexor carpi ulnaris (FCU) and flexor carpi radialis (FCR) is imperative. Surgical alternatives to this technique should be used if a patient does not have at least grade 4 BMRC strength in these muscles.
If it is anticipated that the patient will need tendon transfers for distal hand function, using either FCU or FCR, it should be kept in mind that this nerve transfer has the potential to weaken these muscles.
A preoperative electromyogram (EMG), even in late cases, may be useful to evaluate the muscle for potential for reinnervation. The absence of fibrillation potentials in a denervated muscle would suggest that the muscle has become fibrotic and is no longer capable of reinnervation.

Relevant Anatomy

The MCN is the terminal branch of the lateral cord of the brachial plexus, containing donor fascicles from C5, C6, and C7 roots. The nerve leaves the lateral cord near the inferior margin of the pectoralis minor muscle and pierces the deep surface of the coracobrachialis, giving off the motor branch to this muscle as it travels through the muscle substance. It emerges from the superficial surface of the coracobrachialis muscle at an average of 7.7 cm distal to the tip of the acromion,5 subsequently giving off branches to the biceps and brachialis muscles, then terminating as the lateral antebrachial cutaneous nerve (LABCN).
The dominant nerve pattern to the biceps is a single muscular branch, which arises between 12–13 cm distal to the acromion or 18 cm proximal to the medial epicondyle.5,6 This main branch quickly divides into secondary branches, which then supply the short and long heads of the biceps independently ( Fig. 16.1 ).

Anatomy of the MCN in the medial arm. The relationships to the biceps and brachialis muscles as well as the median and ulnar nerves are shown. (Courtesy of Frances Sharpe, David J. Slutsky, and Milan Stevanovic.)

Approximately 4.5 cm distal to the branch to the biceps is the muscular branch to the brachialis, estimated at 17.5–18 cm distal to the acromion or 13.5 cm proximal to the medial epicondyle ( Fig. 16.1 ). The internal topography of the MCN shows a consistent pattern of orientation, with the fascicle groups to the biceps, brachialis, and LABCN located from lateral to medial, respectively. The fascicles to the biceps are grouped and can be separated proximally from their point of exit from the main nerve for a distance of 4–6 cm. Similarly, independent motor fascicles to the brachialis could be separated from the MCN for an average of 5–9 cm proximal to the take-off of the branch to the brachialis, with a wide range between different specimens.
Variations of the branching patterns of the MCN have been described by several authors. These branching patterns to the biceps and brachialis and their relative frequencies are illustrated in Fig. 16.2 . These variations may need to be accommodated in the surgical technique.
Other described variations of the MCN include communicating branches between the median nerve and the MCN (typically occurring proximal to the branch to the brachialis), absent MCN, and fusion with the median nerve. In most cases, when this variant is present, the motor branches to the biceps and brachialis originate from the median nerve7 ( Fig. 16.3 ).
The internal anatomy of the proximal median and ulnar nerves allows donor fascicles to be harvested without measurable donor deficit. Despite the plexiform arrangement with multiple intrafascicular interconnections, fibers from the peripheral branches pursue a localized course in the nerve for variable, though often considerable, distances.
Care is taken to harvest those motor fascicles that predominantly contribute to expendable muscle donors. Thus, in the median and ulnar nerve, we try to isolate fascicles that principally innervate the extrinsic muscle flexors, specifically fibers that are predominantly to the flexor carpi ulnaris (FCU) from the ulnar nerve and to the flexor carpi radialis (FCR) from the median nerve.
Motor fascicles for the FCU should generally be anterolateral or anterocentral.8 Motor fascicles from the median nerve are also located anteriorly, with fascicles predominantly supplying pronator teres situated anterolaterally, and FCR fascicles lying anterior and slightly medially. Deep (posterior) to the FCR fascicles are fascicles to the flexor digitorum superficialis (FDS) and profundus (FDP). More posteriorly on the medial side are the fascicles that make up the anterior interosseous nerve.
The biceps muscle receives its innervation from the MCN, except in cases of anatomic variations noted above. The dominant nerve root supplying the biceps is C6, with some contribution from C5. The brachialis muscle is a dually innervated muscle in more than 80% of cases, with the lateral third to half receiving innervation from the radial nerve. From the MCN, it is supplied principally by C6, and from the radial nerve, it is supplied principally by C7.

Pearls

In selecting donor motor fascicles from the ulnar nerve, the fascicles that produce the strongest contraction of the FCU or the FDP to the ring and little fingers with intraoperative stimulation are harvested.
It is preferrable to select synergistic muscles for nerve transfer.
Motor fascicles for the FCU should generally be antero-lateral or anterocentral.
Motor fascicles from the median nerve are also located anteriorly, with fascicles predominantly supplying pronator teres situated anterolaterally, and FCR fascicles lying anterior and slightly medially.

The branching patterns of the MCN and the percentage of various branching patterns to the biceps and brachialis muscles. Most common is the Type 1 pattern, with a single branch from the MCN that then ramifies. (Based on the work of Chiarapattanakom et al, and reproduced with their permission.5)

One of the anatomic variations seen in the MCN, with the median nerve connecting to the MCN. (Courtesy of Frances Sharpe, David J. Slutsky, and Milan Stevanovic.)

Surgical Technique

The patient is placed supine on the operating table with the arm placed on a hand table. The entire extremity and shoulder girdle should be prepped into the operative field. Clear communication with the anesthesiologist is necessary before and throughout the procedure to ensure that only short-acting paralytic agents are used for the induction of anesthesia. The paralysis should resolve shortly after the start of the procedure.
The dissection should be done under wide-field loupe magnification. The surgical incision on the medial side of the arm is facilitated by placing the shoulder in external rotation. The line of the incision lies between the midpoint of the axilla and the medial epicondyle, correlating with the bicipital groove. The incision starts approximately three finger breadths from the axilla (at the level of the distal edge of the insertion of the pectoralis major into the humerus) and extends to approximately three finger breadths proximal to the medial epicondyle ( Fig. 16.4 ). If necessary, the incision can be extended proximally into the axilla and distally toward the medial epicondyle.
The skin and subcutaneous tissues are dissected down to the level of the brachial fascia. This is opened in line with the skin incision on the posterior edge of the biceps. The ulnar and median nerves are easily identified just deep to the brachial fascia ( Fig. 16.5a,b ). The medial brachial and medial antebrachial nerves lie within the surgical dissection and should be protected ( Fig. 16.5a ).
The biceps muscle is retracted laterally away from the humerus, gently lifting and rotating the biceps to be able to see the deep surface of its medial edge ( Fig. 16.6 ). The MCN will lie on the deep surface of the medial edge of the biceps and is often covered by a thin layer of fascia and fatty tissue ( Fig. 16.7 ). Careful dissection of the MCN is performed from proximal to distal, until the first motor branch to the biceps is identified. This branch usually enters the middle third of the biceps, close to one of the dominant vascular pedicles to the biceps from the brachial artery ( Fig. 16.8a,b ). The vascular pedicle travels more transversely than the nerve and should be preserved ( Fig. 16.6 ). Further distal dissection of the MCN is done to evaluate the pattern of innervation to the biceps.
The majority of patients (62%) have a single branch from the MCN that bifurcates to supply separately the short and long heads of the biceps muscle (Type 1 pattern) ( Fig. 16.2 ). However, a substantial percentage of patients have two, and less commonly three, separate branches from the MCN.
After identifying all the branches, proximal interfascicular dissection of the nerve should be done, separating the fascicles to the biceps as far proximally as possible. When there is more than one branch to the biceps, it is sometimes possible through proximal interfascicular dissection of the MCN to identify a single motor fascicle that can be used for neurorrhaphy.
In cases where a single motor fascicle cannot be identified, two donor motor fascicles from the ulnar nerve should be used for nerve transfer. Proximal interfascicular dissection of the MCN is performed under loupe magnification.

Surgical incision in bold solid line. Dotted line represents the anatomical location of the ulnar nerve. (Courtesy of Frances Sharpe, David J. Slutsky, and Milan Stevanovic.)

Pitfalls

The harvest of fascicles from an intact functioning nerve raises the concern of causing deficits in the donor nerve distribution. To date, no long-term deficits have been reported from these techniques.
Dr. Oberlin has reported two anterior interosseous nerve palsies, which did not recover (personal communication). In these cases, he had difficulty in identifying a donor fascicle from the median nerve that was size-matched to the branch of the MCN to the brachialis muscle. Rather than performing an interfascicular dissection, he elected to use the “large” fascicle from the median nerve, with the resultant distal deficit.

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