Traumatic injuries of the brachial plexus are complex injuries that have a profound impact on the life of patients.

These injuries can be caused by root avulsion or injury at the level of trunks, fascicles or segmental brachial plexus structures and require a long interposition grafts > 10 cm, and if the surgical intervention is delayed there is always the fear of denervation of the motor end plate ^[1,2]. This forces surgeons to look for a way to restore innervation closer to the affected muscles, and so nerve transfers are introduced.

In traumatic upper type injury to the brachial plexus the restoration of flexion in the elbow joint is of paramount importance ^[3,4].

Christoph Oberlin in 1994 described the transfer of one or more nerve fascicles from the ulnar nerve to the motor branch of the biceps brachii muscle as an intraplexial donor ^[5].

Susan Mackinnon later reported direct transfer of motor fascicles from the ulnar and median nerve to the motor branches of biceps brachii and brachialis muscles ^[6].

In Bulgaria, this surgical technique was introduced and validated by Margarita Kateva ^[3,4,7,8].

In the present study we present a current treatment method for restoring flexion in the elbow joint after traumatic injury to the brachial plexus. For this purpose, fascicular nerve transfers were used, and in rare cases, when necessary, augmentation to the nerve transfer was added such as muscle transposition.

The study covers the period from 2014 to 2022 and includes 23 patients, 18 of whom are men and 5 are women. All 23 patients were operated on in the Clinic of Hand Surgery and Reconstructive Surgery at Sofiamed University Hospital. 17 of these patients were operated on using the end-to-end neurotization technique of the motor branches to brachialis and biceps brachii muscles, using median and ulnar nerve as donor fascicles. The remaining 6 patients were operated on with end-to-side nerve transfer using the same donor nerves. Mean age at surgery was 35.08 years, with the youngest patient being 16 years old and the oldest 62 years old. The average follow-up period was 4.7 years - from 3 to 5 years. Postoperative results of restored elbow flexion were evaluated on MRC scale (Medical Research Council) and dynamometry comparison of the affected upper limb to the contralateral one (Figure 6).

Surgical approach is made on the medial surface of the arm at the border between the biceps brachii muscle and triceps brachii muscle (Figure 1). When the skin, subcutaneous tissue and fascia are dissected, the biceps is carefully dissected and the neurovascular bundle is identified, which is then dissected to the distal third of the brachium. Musculocutaneus nerve is then dissected and traced along the medial surface of the biceps. In the distal direction, the motor branches are found and dissected sequentially first to the biceps brachii muscle and then to the.brachialis muscle (Figure 3). With intraoperative neurostimulation, we confirm whether the nerve is totally dysfunctional or has some potential for recovery. Therefore, it is important to communicate preoperatively with the anesthesiologist to ensure that only short-acting muscle relaxants are used intraoperatively. Next, the median and ulnar nerve are dissected and traced in the middle third of the arm. To determine the level of intrafascicular dissection of the donor nerves, we use the corresponding level of separation of the motor recipient nerves to the biceps brachii muscle and distally to the brachialis muscle. In case the level of separation of the donor fascicles from the median and ulnar nerve has already been determined, we begin with electrical stimulation of individual fascicle bundles, as follows: the operator stimulates several bundles one by one with an electrical stimulator, while the assistant holds both hands on the patient’s fingers and wrist. Usually, there is one bundle that responds to stimulation with the most pronounced FCU (flexor carpi ulnaris) function for the ulnar nerve and FCR (flexor carpi radialis) for the median nerve. The choice of donor fascicle–recipient pairing was individualized intraoperatively based on anatomical proximity and tension-free coaptation. Both median (FCR) and ulnar (FCU) fascicles were used interchangeably for reinnervation of the biceps and brachialis motor branches.

This bundle is dissected intraneurally using a microdissector under microscopic magnification, then resected distally with microscissors and directed to the recipient motor nerve, where a microsurgical suture is performed with 9/0 atraumatic suture (end-to-end, end-to-side) without tension (Figure 4). We cover the coaptation site with tissue glue (Figure 5). Layered suture. Bandage. Since there is no tension at the site of the micronerve suture, no specific immobilization should be applied postoperatively except for a sling for a period of 14 days.

Surgical treatment of clinical case: Infraclavicular and axillary revision with neurolysis of brachial plexus + fascicular nerve transfer: FCR fascicles of median nerve-motor branch to biceps brachii muscle end-to-end; FCU fascicles of ulnar nerve-motor branch to brachialis muscle end-to-end.

All 23 patients were operated on in the Hand Surgery and Reconstructive Surgery Clinic at Sofiamed University Hospital using the fascicular nerve transfer method. 17 of these patients were operated on using the end-to-end neurotization technique of the motor branches to brachialis and biceps brachii muscle, with median and ulnar nerve being used as donor fascicles. The remaining 6 patients underwent end-to-side (perineurial window) nerve transfer using the same mentioned donor nerves. Decision on the end-to-side nerve transfer was made on the intraoperative electrostimulation and partial motor reaction of the recipient muscles. The final functional results achieved are as follows: M4 – 15 patients, M3 – 5 patients, M2 – 3 patients were assessed using the MRC scale. Elbow flexion strength was additionally quantified using a MuscleMeter® (MAT) dynamometer. The flexion strength in the elbow joint was on average 53% of that of the contralateral side. Three patients underwent additional Steindler flexoroplasty. There were no donor side morbidity except from 5 patients who suffered transitory paresthesia of ulnar and median nerve.

The MRC scale was used for clinical assessment of postoperative results, as well. In our series, 87% of patients achieved ≥ M3 flexion in the elbow joint.

The most commonly used nerve transfer technique for restoring elbow flexion in upper type brachial plexus palsy (Erb type C5, C6/C7) is fascicular nerve transfer, which was first presented in Paris in 1994 by Christophe Oberlin ^[5]. He described the transfer of one or two nerve fascicles from the ulnar nerve to the motor branch of the biceps brachii muscle, using 10% of the ulnar nerve fascicles, which were randomly selected because at this level the sensory and motor fascicles are mixed with interfascicular connections, forming a plexiform structure ^[3]. Later, the idea of selective fascicle transfer was developed by using a nerve stimulator intraoperatively (most often the fascicles for FCU). This prevents denervation to the intrinsic muscles innervated by the ulnar nerve. Good results were also shown by Leechawengvongs in Thailand, who reported his experience with 26 of 32 patients (81.3%) regaining elbow flexion (M4) after the Oberlin I transfer ^[9]. In both studies, none of the patients showed permanent ulnar nerve deficiency ^[5,9].

Oberlin used this transfer in adults, and the first report of its effective use in infants with upper obstetric palsy was made by Al-Qattan in 2002 ^[10]. Despite the enthusiasm for the success of the Oberlin I method, many authors report the need for additional surgical interventions, such as Steindler flexoroplasty, to achieve greater strength in elbow flexion ^[6,11,12]. In search of a solution to the problem and avoiding such additional interventions, the trend of reinnervation of the m. brachialis with a view to stronger flexion is beginning to enter world practice. In 2003, Susan MacKinnon in St. Louis and Christophe Oberlin in Paris described a new technique, which is a fascicle transfer (FCU) from the ulnar nerve to the motor branch of the biceps brachii muscle end-to-end and a transfer from the median nerve (FCR) to the motor branch of the brachialis muscle end-to-end ^[6].

In 2005, Oberlin reported 15 of 15 patients (100%) who restored M4 flexion at the elbow joint, and Mackinnon reported 6 of 6 (100%) who achieved M4, with no patient in either study showing permanent sensory or motor deficits in the donor nerves ^[6]. Later, several other authors reported significantly better results with the Oberlin II/Mackinnon than with the Oberlin I ^[6,13]. However, there are also authors who show similar results with the two techniques ^[14]. In 2014 Socolovsky and colleagues divided 40 patients into 2 groups, in which both approaches were applied, and concluded that there were insignificant differences in postoperative outcome ^[15]. Nevertheless, there is a strong premise to assume that the Oberlin II/Mackinnon is the functionally superior method, considering that the brachialis muscle is the primary flexor of the elbow joint and its reinnervation is likely to result in improved postoperative strength ^[16,17]. This is why, when possible, our team prefers to perform double fascicular nerve transfer to utilize maximum potential of donor nerve options for restoration of elbow flexion in traumatic plexus injuries.

Nowadays, regarding the improvement and development of the surgical technique for nerve transfer to restore flexion in the elbow joint, R. Shahriar-Kamrani and colleagues propose in 2025 to add neurotization of brachioradialis muscle to the Oberlin II technique ^[18].

Considering the complications, most authors who applied the classical or modified Oberlin technique agree on the opinion that there are no subjective complaints from patients, motor and/or sensory deficit in the area of the donor nerve ^[4,5,6,14]. There are reported cases of transient sensory complaints in the area of the ulnar nerve, but they resolve quickly and do not cause discomfort ^[16,17]. Regarding grip strength, some weakness may be observed in the early postoperative period, which is subsequently restored. There are even cases in which postoperative power grip indicators exceed preoperative measurements. One possible explanation of this from the authors is that patients with regained elbow flexion start to use the affected upper limb and their hand more in their daily life ^[11].

Severe traumatic lesions of the brachial plexus are debilitating injuries requiring specific diagnosis and treatment. Nerve transfers represent a reliable and effective surgical intervention for restoring elbow flexion in patients with brachial plexus injuries. Younger patients and those with partial injuries without root avulsion tend to demonstrate better results as refer to literature, which emphasizes the importance of early diagnosis and individualized surgical planning. These findings confirm the usefulness of nerve transfers as a cornerstone in the surgical treatment of brachial plexus injuries, which necessitates the continued improvement and adoption of personalized approaches to optimize outcomes in these patients. The implementation of surgical treatment by a well-trained and experienced interdisciplinary team is a key moment for improving the final functional results.