Spinal accessory nerve transfer to the suprascapular nerve to restore shoulder function in brachial plexus injury: Management nuances
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.250725
Source of Support: None, Conflict of Interest: None
Abduction, along with external rotation, are the two most important functions of the shoulder joint, which are virtually involved in all cases of brachial plexus injury (BPI), except isolated C8-T1 injuries. The shoulder movement is important for achieving the prehensile function among patients with complete paralysis of brachial function. Management of shoulder palsy in BPI has always been a reconstructive challenge. Various procedures like nerve reconstructions, muscle transfers and joint arthrodesis are available, for both early and late cases. The judicious use of these practices can lead to a favourable outcome.
The shoulder abduction has two components, an initiation till 15 degrees by the supraspinatous muscle, supplied by the suprascapular nerve; and, further elevation by the deltoid muscle supplied by the axillary nerve. External rotation is performed by the infraspinatous muscle, supplied by the terminal branches of suprascapular nerve. The suprascapular nerve is involved in 98% of brachial plexus lesions, either through the preganglionic C5–C6 injury, or in more distal lesions, an injury between the upper trunk and the notch, or due to injury at the notch level. In one-third of axillary nerve lesions, there is an associated injury to the suprascapular nerve. It is not uncommon that the branch to the supraspinatus is avulsed from the muscle, while the longer branch to infraspinatus muscle has been stretched or ruptured. The short length of the supraspinatus branch is believed to play a role in this pattern.
Today, nerve transfers have replaced intra-plexal reconstructions as the primary modes of nerve repair in upper trunk injuries. A pure C 5-6 injury presenting early, is treated by a combination of the Oberlin, Somsak and spinal accessory to suprascapular nerve transfer (SASNT) procedures to restore adequate shoulder and elbow function.
However, an intra-plexal neurotisation is of value in total palsies with avulsion of the lower roots (C7–C8–T1). With only one or two ruptured roots available in the inter scalene area, it is not possible to graft the whole of the plexus. In such cases, surgery must be performed early (at 6 weeks to 3 months) and our approach should be to aim for re-innervation of the proximal territories. Patients must be counselled that they will have definitive paralysis of the hand.
The indications for an early intervention include a flail limb with severe deafferentation pain, the presence of pseudomeningoceles on magnetic resonance (MR) myelography, a positive Horner's sign, and an associated diaphragmatic palsy. These signs indicate severe trauma to the plexus with little or no potential for spontaneous recovery. An early intervention, in such cases, is expected to regain some useful functions.
The results depend on the anatomo-pathological lesions. When only one root (C5) can be grafted, the choice would be to repair the anterior part of the upper trunk with the C5 root, and the suprascapular nerve by neurotization with the spinal accessory nerve, which is divided distal to the origin of the branches for the superior and middle parts of the trapezius. The goal is to obtain stabilization of the shoulder, an active shoulder adduction, flexion of the elbow and protective sensation in the forearm and palm.
When there are two roots (C5 + C6) which can be grafted, it is also possible to graft some parts of the posterior cord to augment radial or axillary nerve function. It is desirable to connect the anterior plane of the roots with the anterior plane of the plexus, and the posterior plane of the roots with the posterior plane of the plexus, in order to respect the cortical topography and to avoid co-contractions between antagonist muscles.
Considering the ease of harvest, minimal donor site morbidity, and long length availability, we most frequently use the sural nerve as a nerve graft. In cases of T1–C8–C7 avulsion, it is possible to use a vascularized ulnar nerve graft (either free or pedicled) when the aspect and size of C5 or C5 and C6 are good and when the length of the nerve defect is longer than 15 cm. However, all this is always supplemented with SASNT.
Thus, SASNT is a very important transfer procedure in any brachial plexus reconstruction. Restoration of the shoulder abduction provides a greater range of motion to the arm and forearm. While the aim is to achieve about 30 degree shoulder abduction with a useful external rotation, the results are variable and dependent on various intrinsic and extrinsic factors. Shoulder stability, a subjective perception by the patient, is the bare minimum requirement. Stability refers to the perception that patient has in not feeling a weakness of the subluxating shoulder, even when the limb is not supported by a pouch arm sling. This stability improves the elbow function after nerve repair. The patient is able to use and position the elbow joint better with a stable shoulder joint. This again is essential for late cases where the trapezius transfer or shoulder arthrodesis is preferred before performing any form of muscle transfer (functioning free muscle transfer [FFMT] or latissimus dorsi) for improving elbow flexion. In the context of a meta-analysis, Merrell et al., reported that the best nerve transfer for restoration of shoulder abduction was the spinal accessory to suprascapular nerve.
It has been a common observation that obese (those with a high body mass index) and/or elderly patients, as well as those with concomitant injuries and co-morbidities, tend to have poorer results even in expert hands. Such patients should be counselled before undertaking any reconstructive procedure.
Suturing for SASNT in the neck is always done at a depth, making tension-free co-optation unreliable and difficult. We use multiple innovations to improve the nerve co-optation. Firstly, we use an absorbable hemostatic gel sponge as a base and a filler in the neck over which the cut ends of both nerves are rested before suturing (Personal communication from Prof S. Gaba in 2017). The sponge reduces the depth of the cavity, making the suturing tensionless and easy, which is always done under an operating microscope. Secondly, the suturing technique used is outside-in and outside-in producing an inversion at the suture line, unlike the regular outside-in and inside-out, which produces tissue eversion. This prevents fascicles from popping out of the repair site. Another variation that we have incorporated in our technique for the management of pan BPI patients is the use of the posterior approach for SASNT in selected cases. Many times, with severe traction injuries, the suprascapular nerve is retracted down and is not found by the standard supraclavicular approach. Its proximal part may also be involved in the scar tissue and a distal transection near the healthy nerve will need a graft, which usually has poorer results. Furthermore, the suprascapular nerve may be injured at two or three levels with its concurrent involvement at the suprascapular notch and the spino-glenoid notch. Considering all these factors, some authors even concluded that the reanimation of shoulder function in patients with severe brachial plexus traction injury, following the suprascapular nerve neurotization, had a disappointingly low success rate.
Double level lesions, especially at or distal to the scapular notch, may be one of the reasons for poorer results following the SASNT repair, especially in cases with pan-brachial plexus injuries. Hence, for cases with concomitantly severe trauma, scapular or shoulder injuries, or delayed presentations (>6 months), we selectively utilize the posterior approach, as advocated by Bhandari et al.
Moreover, in the anterior approach, transection of the spinal accessory nerve at the proximal level can lead to denervation of the upper trapezius, which plays an important role in shoulder function. In the posterior approach, the distal transection spares the important branches to trapezius and preserves its function of shoulder stabilization and elevation.
All those patients in whom the SASNT procedure is performed, a 9-0 monofilament repair is done, that is reinforced with tissue glue. A prolonged neck immobilization with a soft collar for atleast 3-4 weeks, along with a pouch arm sling, is used in all cases.
Patients with injuries that we were able to be reconstruct with both root grafting and nerve transfers had the best function. These results suggest that the combined use of nerve transfers and root grafting may enhance outcomes in the repair and reconstruction of C5-C6 injuries of the brachial plexus.
To conclude, restoration of shoulder stability and abduction is an important goal in the rehabilitation of patients with devastating brachial plexus injuries. Suprascapular and axillary nerves are the target nerves in achieving these functions. Results of nerve transfers have shown that neurotisation of the suprascapular nerve provides more reliable and effective abduction than direct neurotisation of the axillary nerve., Suprascapular neurotisation also restores external rotation that maximizes abduction by preventing the impingement of the greater tuberosity of humerus against the coracoacromial arch. Conventionally, spinal accessory to suprascapular nerve transfers have been performed by the anterior approaches. The results of these procedures in restoring shoulder function following anterior transfers are variable. The posterior approach can be a useful alternative in late as well as severe cases, and in patients with a concomitant scapular injury. Poor results due to a double level injury to the suprascapular nerve can also be improved upon with the posterior approach. All efforts should be made to produce a tension-free co-optation without a nerve graft in the neck during the SASNT procedure. The adjunctive use of inverted suturing, an operating microscope, avoiding operating in the depth of the surgical field, ensuring a prolonged neck immobilization and the use of tissue glue, help in producing optimal results. Proper patient selection and patient counselling are essential for an effective, long-term psychological and physical rehabilitation of patients with BPI.