Supraclavicular exposure

The surgical approach to NBPP inevitably begins in the supraclavicular region for exploration of the site(s) and extent of the brachial plexus lesion. In the vast majority of patients, supraclavicular exposure alone will suffice for a proper nerve repair and reconstruction. Surgery is performed under general anesthesia without the use of muscle blocking agents. The supraclavicular brachial plexus is exposed in the posterior triangle of the neck. Appropriate positioning of the patient is extremely important to facilitate the operation. The patient is positioned supine, and the head is turned toward the opposite direction with the neck in gentle extension (taking care to place the contralateral ear in the hole of a silicone head ring); the non-affected shoulder is positioned caudally to avoid compressing the cervical vascular structures. Neck extension is encouraged by placing a folded cotton cloth at the level of the lower cervical spine and upper thoracic spine in order to support the plane of the brachial plexus parallel to the floor; avoid narrowing the costoclavicular space with an excessively thick folded cloth. The affected arm lies completely in the sterile field and is supported at 45 degrees of abduction as close as possible to the edge of the operating table. For easier access to the dorsal aspect of the legs for harvesting sural nerve grafts, the length of the operating table is reduced as much as possible. The lower part of the face, neck, shoulder, chest and legs are prepared for surgery.

A curvilinear incision extending from the sternocleidomastoid muscle to the coracoclavicular joint is made approximately 0.5 cm (for lower plexus) to 1.5 cm (for upper plexus) above and parallel to the clavicle. The platysma is incised perpendicular to its fibers, and a generous subplatysmal dissection is performed. The external jugular vein is often encountered and must be retracted or ligated when necessary. The position of the spinal accessory nerve (SAN) is relatively superficial as it courses from the posterior aspect of the sternocleidomastoid muscle (2/3 of the distance from the sternum to the mastoid) toward its insertion in the trapezius. Identification of the SAN along its course is crucial to preserve trapezius function and to use its branches as a donor for potential nerve transfer. An intraoperative nerve stimulator can be used to identify and confirm this nerve.

The lateral margin of the sternocleidomastoid muscle is identified, with its sternal and clavicular heads. The lateral aspect of the clavicular head is released to facilitate exposure. The supraclavicular nerves (sensory nerves branches of the ansa cervicalis, C2–C4) are identified along their superficial cranial-caudal course. These nerves are likewise preserved for anatomical landmarks and for intraplexal transfers and, occasionally, for potential donors for nerve graft material. The supraclavicular nerves are followed proximally until the C4 spinal nerve root is identified. The cervical fascia/scalene fat pad is released from this parallel to the sternocleidomastoid muscle starting at the level of C4 in a cranial to caudal direction; at the retroclavicular level, a 90-degree turn parallel to the clavicle. The resulting cervical fascia/scalene fat pad can be mobilized for the operation then replaced at closure to cover the nerve grafts and coaptation sites after the reconstruction. The cervical fascia/scalene fat pad should be preserved as much as possible; i.e., coagulation should be avoided, as the vascular fat pad may contribute to revascularization of nerve grafts and may provide the optimal environment for the nerve elements. When releasing the fat pad during exposure of the left supraclavicular brachial plexus, one should preserve or ligate the thoracic duct to avoid chyle leakage. The transverse cervical artery and vein that run parallel to the clavicle ventral to the brachial plexus elements are retracted or ligated. The omohyoid muscle is identified between the superficial and deep cervical fascia along its course toward the suprascapular notch, and it can be tagged and retracted. Note that preserving this muscle to identify the suprascapular notch permits identification of the suprascapular nerve (SSN), especially in patients whose anatomy is distorted by trauma. Appropriate placement of intraoperative retractors can facilitate surgical exposure of the supraclavicular brachial plexus ( Figure 9.1 ).

Positioning of retractors for supraclavicular exposure of the right brachial plexus. The curved blade (solid black arrow) retracts the anterior scalene muscle. Care should be taken to avoid tension on the phrenic nerve (*). Another retractor blade (black dashed arrow) is used to push the clavicle downward.

From the C4 spinal nerve root, a branch from this nerve can be followed to the phrenic nerve, which derives from C3, C4, and C5. The phrenic nerve is dissected along its length on the ventral aspect of the anterior scalene muscle. One should carefully mobilize the phrenic nerve to preserve function of the diaphragm, which is especially important to infant respiration. Four pointers to facilitate safe identification of the phrenic nerve are as follows: (1) The phrenic nerve cannot always be seen directly because it is covered by the deep transverse cervical fascia; the transparency of this fascia varies depending on its thickness and any scar present. Nerve stimulation to identify the course of the phrenic nerve from medial to lateral over the surface of the anterior scalene muscle is extremely helpful and is, in our opinion, indispensable; (2) The phrenic nerve usually originates from C3 and C4 and occasionally has a thin C5 contribution. Because C4 is already identified at this stage, the phrenic nerve origin can be located at the caudal aspect of C4; (3) The artery and vein adjacent to the phrenic nerve should not be identified erroneously as the nerve; (4) We have occasionally encountered a separate auxiliary phrenic nerve at higher cervical levels.

The phrenic nerve courses lateral to medial toward the diaphragm, whereas contents of the plexus and the surrounding nerves course from medial to lateral. As the phrenic nerve approaches the lateral edge of the anterior scalene, the C5 spinal nerve root emerges; this is a reliable site for the identification of the C5 nerve root. The phrenic nerve is completely freed up in its trajectory ventral to the anterior scalene muscle to allow gentle medial retraction without significant traction. In some patients, the phrenic nerve may be adherent to the neuroma of C5. In such cases, leaving some neuroma scar tissue on the phrenic nerve so as to preserve diaphragmatic function is preferable to dissecting flush on the phrenic nerve and remove all the C5 neuroma. Resection or partial resection of the anterior scalene muscle is always performed to allow for optimal exposure of the proximal, intraforaminal part of the spinal nerve roots. During such proximal exposure, a pseudomeningocele that extends extra-foraminally may be encountered; every attempt should be made to identify such structures on CT-myelography or MRI.

Following the C5 root distally leads to the upper trunk, and following the upper trunk proximally will lead to the C6 spinal nerve root. The C6 spinal nerve root is located caudal and dorsal to the C5 spinal nerve root. The anterior tubercle of C6 can be very prominent (Chassaignac’s tubercle). The C7, C8, and T1 spinal nerve roots are sequentially more caudal and dorsal. A transverse cervical artery and vein cross the C7 spinal nerve root and can be ligated. Following the C7 spinal nerve distally will reveal the middle trunk. The C8 and T1 spinal nerves combine quickly to form the lower trunk, which is adjacent to the subclavian vessels. The roots of the lower trunk surround the first rib; therefore, care should be taken to avoid injury to the pleura.

The next step is to identify the SSN and the divisions of the upper trunk. The upper trunk can be seen to “split” into 3 separate structures – from lateral to medial, the SSN, the posterior division, and the anterior division. The SSN originates from the lateral aspect of the upper trunk and normally follows a slightly oblique cranial-caudal course toward the suprascapular notch (the omohyoid also attaches at the suprascapular notch). Caudal displacement of the superior trunk will alter trajectory of the SSN to a more horizontal direction.

Uncommonly, the NBPP lesion extends to the retroclavicular region. To facilitate adequate exposure, the surgeon can expand the retroclavicular space by fixed or mobile retraction with a lace passed immediately beneath the clavicle. Employing both supra- and retroclavicular views allows exposure and/or repair of the retroclavicular elements of the brachial plexus. Should a more extensive exposure of the retroclavicular brachial plexus be necessary, a clavicle osteotomy may be considered, although we have never done so.

Infraclavicular exposure

Infraclavicular extension of the lesion in NBPP is quite rare. The infraclavicular brachial plexus is exposed through the deltopectoral groove. The patient is placed in the supine position, and a linear incision is made from the clavicle toward the axilla, overlying the deltopectoral groove. The cephalic vein is visualized within the groove, and it can be retracted laterally or ligated. If needed, a portion of the pectoralis major muscle can be detached from the inferior surface of the clavicle and from the humerus. The cuff of tendon from the humerus is tagged to facilitate later repair.

The pectoralis major muscle is retracted caudally and the deltoid laterally, revealing the underlying coracoid process with its muscle attachments. Blunt dissection will separate the pectoralis minor from the coracobrachialis and the surrounding tissues. Once the pectoralis minor tendon has been isolated, it may be divided with later reapproximation, or the muscle may be retracted.

The infraclavicular brachial plexus elements lie immediately dorsal and caudal to the pectoralis minor. When the arm is at or lower than the plane of the shoulder, the most superficial structures are the lateral cord with its lateral branch leading to the musculocutaneous nerve (MCN) and its medial branch leading to the median nerve. The medial cord may be identified medial and slightly posterior to the axillary artery, and the lateral branch of the medial cord will lead to the median nerve (the medial branch continues down the arm as the ulnar nerve). Exposure of the posterior cord and its axillary and radial nerve branches is best accomplished in the region lateral and posterior to the axillary artery, in contrast to the medial posterior course that is frequently and erroneously depicted in schematic anatomical drawings. The axillary nerve branches from the posterior cord and runs through the quadrilateral space above the latissimus dorsi and teres major tendons; this nerve can be identified more easily by externally rotating the humerus.

Exposure of extraplexal nerves for nerve transfer procedures

When nerve transfers are appropriate, the donor nerves must be exposed. It is imperative that donor nerves have normal function; direct electrical stimulation intraoperatively can assess their function and aid in their identification. The SAN is a commonly employed donor nerve for neurotization to the SSN for restoration of shoulder function. The SAN can be located as it approaches and enters the anterior surface of the trapezius muscle as described above. The nerve gives off a proximal branch to the superior part of the trapezius muscle, which must be kept intact. The SAN is mobilized as distally as possible then transected. The proximal stump is then passed through the cervical fascia/scalene fat pad to allow for direct coaptation with the SSN.

Another commonly used donor nerve is the medial pectoral nerve (MPN); it is used for nerve transfer to the MCN for restoration of elbow flexion. The MCN can be identified in its course dorsal to the pectoralis major and minor muscles. Generally MPNs can be reached by retracting the pectoralis major muscle cranially through a low incision in the deltopectoral groove. The MPN originates from the medial cord, and its function remains intact in C5–C6 or C5/C6/C7 lesions. Intraoperative nerve stimulation is an indispensable step for identification of MPNs, because small vessels simulate their appearance and course. There are usually 2 individual MPN branches, and they should be cut as distally as possible then coapted to the MCN. The total cross-sectional area of the MPN branches may be less than that of the MCN, and if so, coaptation to a fascicle of the MCN is undertaken.

Another nerve transfer technique for restoration of elbow flexion uses intercostal nerves (ICNs) as donors and the MCN as recipient. We previously described the technique for ICN transfer in adults. We apply the same surgical technique in infants with NBPP. ICN 3-6 are exposed by means of an undulating skin incision over the ipsilateral chest. The incision starts at the anterior axillary line at the inferior border of the pectoralis major muscle and continues beneath the nipple, extending medially to the costosternal junction. The inferior part of the pectoralis major muscle is shifted upward, with partial detachment of its sternal insertion, if necessary. The rib attachments of the serratus anterior muscle usually remain intact. The main branch of the ICN is identified halfway in its ventral course between the external and internal intercostal muscles and dissected free over its entire anterior course. Care should be taken to keep the periosteum of the ribs intact in order to avoid rib cage deformities during growth. ICN motor responses are assessed using electrical nerve stimulation. If feasible, sensory branches are identified by their course toward the skin and left intact after they have been interfascicularly dissected from the main nerve. The ICNs are then transected as close as possible to the sternum to obtain sufficient length for direct coaptation to the MCN and are tunneled to the axilla. The infraclavicular and intercostal wounds remain separated from each other by an area of intact skin at the anterior axilla, facilitating wound closure and healing. In female infants, if the anatomical localization of sensory innervation to the nipple is uncertain, the third ICN is left untouched to preserve at least partial sensation to the breast. The MCN is cut proximally after freeing it from the lateral cord until fascicular intermingling is encountered. No attempt is made to identify the motor branches within the MCN. Before coaptation, the infant’s arm is abducted 90 degrees. The ICNs are coapted to the centrally located MCN fascicles by means of fibrin glue.

Intraoperative assessment of lesion severity in the brachial plexus

We determine severity of the lesion by assessing each clinically involved spinal nerve as follows. A distinction is made between axonotmetic and neurotmetic lesions including nerve root avulsions based on (1) visual evidence of nerve continuity at the intraforaminal level combined with preoperative knowledge of the presence or absence of root filaments on CT-myelography; (2) visual/microscopic assessment of the location and extent of neuroma formation; (3) selective electrical stimulation of all the involved spinal nerves using a bipolar electrode in combination with a 2.5-Hz pulse generator with increasing voltage (maximum 6 V).

We consider a spinal nerve root to be avulsed when nerve root filaments and the dorsal root ganglion are visible near the neural foramen. Note that upon initial inspection, the spinal nerve root may look completely normal. If so, and nerve root avulsion is suspected, examine the scalene muscles for scarring and fibrosis, which implies that proximal injury has occurred with a high probability of nerve root avulsion. Additionally, resection of a portion of the anterior scalene muscle may then reveal the avulsed rootlets proximal in the foramen. Direct stimulation of the nerve root generally does not yield distal muscle contraction. Additionally, it is useful to correlate the intraoperative findings with the absence of nerve rootlets as demonstrated by CT-myelography.

A lesion is considered to be neurotmetic when the following features are present: normal appearance of the nerve root at the intraforaminal level; a clear increase of the cross-sectional diameter at the juxta-foraminal level; abundant epineurial fibrosis; loss of fascicular continuity; increased density and increased length of the nerve elements with concomitant displacement of the trunks and divisions distally. Electrical stimulation of the spinal nerve proximal to the neuroma might cause weak muscle contractions that are detectable with palpation, but these contractions are not strong enough to move the limb. Resection of neurotmetic tissue is performed, and the proximal and distal stumps are prepared for nerve repair/reconstruction.

Care should be taken not to cut the small nerve branches that contribute to formation of the long thoracic nerve. They arise very proximally at the caudal aspect of C5 and C6 (and/or C7). These branches can additionally be used to differentiate between avulsion and neurotmesis. In the case of a root avulsion, no contraction of the serratus anterior muscle on direct stimulation will be found. In the case of neurotmesis, stimulation of these branches leads to contraction of the serratus anterior muscle, as the traction injury is usually located distal to the branch point. The most frequent finding is that a functionally intact long thoracic nerve branch exits from the neurotmetic part of the spinal nerve. Careful proximal dissection of the long thoracic nerve branch within the neurotmetic part of the spinal nerve usually reveals an essentially normal fascicle that can be dissected away from the neurotmetic tissue. Transection of the neurotmetic spinal nerve tissue/neuroma (in preparation for repair) should then be performed just distal to the exit of the long thoracic nerve branch. Proximal stumps are evaluated by frozen section for the presence of normal-appearing nerve fascicles. The total quantity of myelin in the entire cross-sectional area of the donor stump, which corresponds to the viability of the proximal stump, is expressed semi-quantitatively in quartiles: (a) <25%; (b) 25%–50%; (c) 51%–75%, (d) >75%. The neuropathologist can also assess for the presence of dorsal root ganglion cells (indicative of nerve root avulsion) and for the presence of fibrosis/neuroma in the proximal and distal stumps. In our institution, proximal stumps are considered viable as donors for nerve grafting when the total myelin quantity is ≥50% and preoperative CT-myelography demonstrates intact rootlets.

The spinal nerve root lesion is considered axonotmetic when neurolysis reveals no substantial increase in cross-sectional diameter of the brachial plexus elements, and limited epineurial fibrosis and good continuity of fascicular structure are present. Additionally, direct stimulation to the spinal nerve should result in limb movement; for instance, upon C5 stimulation, abduction and external rotation should be present, and upon C6 stimulation, elbow flexion against gravity with supination should be observed. Axonotmetic lesions are left in situ because spontaneous nerve regeneration is demonstrable with direct electrical stimulation, although limb movement clinically is yet absent. Axonotmesis is confirmed by the occurrence of good spontaneous recovery after at least 2 years of follow-up.