Restoration of intrinsic hand function by superficial radial nerve: an anatomical study

BACKGROUND

The contralateral seventh cervical (cC7) nerve root transfer represents a cornerstone technique in treating total brachial plexus avulsion injury. Traditional cC7 procedures employ the entire ulnar nerve as a graft, which inevitably compromises its restorative capacity.

OBJECTIVE

Our cadaveric study seeks to assess this innovative approach aimed at preserving the motor branch of the ulnar nerve (MBUN). This new method aims to enable future repair stages, using the superficial radial nerve (SRN) as a bridge connecting cC7 and MBUN.

METHODS

We undertook a comprehensive dissection of ten adult cadavers, generously provided by the Department of Anatomy, Histology, and Embryology at Fudan University, China. It allowed us to evaluate the feasibility of our proposed technique. For this study, we harvested only the dorsal and superficial branches of the ulnar nerve, as well as the SRN, to establish connections between the cC7 nerve and recipient nerves (both the median nerve and MBUN). We meticulously dissected the SRN and the motor and sensory branches of the ulnar nerve. Measurements were made from the reverse point of the SRN to the wrist flexion crease and the coaptation point of the SRN and MBUN. Additionally, we traced the MBUN from distal to proximal ends, recording its maximum length. We also measured the diameters of the nerve branches and tallied the number of axons.

RESULTS

Our modified approach proved technically viable in all examined limbs. The distances from the reverse point of the SRN to the wrist flexion crease were 8.24 ± 1.80 cm and to the coaptation point were 6.60 ± 1.75 cm. The maximum length of the MBUN was 7.62 ± 1.03 cm. The average axon diameters in the MBUN and the anterior and posterior branches of the SRN were 1.88 ± 0.42 mm、1.56 ± 0.38 mm、2.02 ± 0.41 mm,respectively. The corresponding mean numbers of axons were 1426.60 ± 331.39 and 721.50 ± 138.22, and 741.90 ± 171.34, respectively.

CONCLUSION

The SRN demonstrated the potential to be transferred to the MBUN without necessitating a nerve graft. A potential advantage of this modification is preserving the MBUN's recovery potential.

Nerve Transfer of Brachialis Branch to Anterior Interosseus Nerve Using In Situ Lateral Antebrachial Cutaneous Nerve Graft in Tetraplegia

PURPOSE

Reconstruction of finger motion is a therapeutic goal in tetraplegic patients. Although nerve transfer of the brachialis branch of the musculocutaneous nerve to the anterior interosseus nerve has been previously described, this results in unreliable reinnervation because the donor nerve is proximal to the target muscle. We describe an alternative technique in which nerve transfer is performed using the lateral antebrachial cutaneous nerve as a vascular in situ nerve graft. The clinical results are reported.

METHODS

Nine upper limbs of 6 patients (mean age 25 years) with tetraplegia were subjected to brachialis-to-anterior interosseus nerve transfer using the lateral antebrachial cutaneous nerve as a vascular in situ nerve graft, at a mean of 6 months after injury. Additional supinator branch transfer to the posterior interosseous nerve was performed for 6 upper limbs and to the flexor digitorum superficialis motor branch for 1 upper limb.

RESULTS

At a mean of 2 years of follow-up, thumb and finger flexion strength scored M3-M4 in 5 of the 9 limbs according to the Medical Research Council scale. Key pinch and grip pinch averaged 0.6 kg (range, 0-1.0 kg) and 2.2 kg (range, 0-8 kg), respectively. No donor-site deficit was observed.

CONCLUSIONS

Brachialis-to-anterior interosseus nerve transfer with an in situ lateral antebrachial cutaneous nerve graft can be used to reconstruct thumb and finger flexion in tetraplegic patients. Combined with supinator-to- posterior interosseous nerve transfer, simultaneous active extension of the fingers can be achieved.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic V.

The role of vascularization in nerve regeneration of nerve graft

Vascularization is an important factor in nerve graft survival and function. The specific molecular regulations and patterns of angiogenesis following peripheral nerve injury are in a broad complex of pathways. This review aims to summarize current knowledge on the role of vascularization in nerve regeneration, including the key regulation molecules, and mechanisms and patterns of revascularization after nerve injury. Angiogenesis, the maturation of pre-existing vessels into new areas, is stimulated through angiogenic factors such as vascular endothelial growth factor and precedes the repair of damaged nerves. Vascular endothelial growth factor administration to nerves has demonstrated to increase revascularization after injury in basic science research. In the clinical setting, vascularized nerve grafts could be used in the reconstruction of large segmental peripheral nerve injuries. Vascularized nerve grafts are postulated to accelerate revascularization and enhance nerve regeneration by providing an optimal nutritional environment, especially in scarred beds, and decrease fibroblast infiltration. This could improve functional recovery after nerve grafting, however, conclusive evidence of the superiority of vascularized nerve grafts is lacking in human studies. A well-designed randomized controlled trial comparing vascularized nerve grafts to non-vascularized nerve grafts involving patients with similar injuries, nerve graft repair and follow-up times is necessary to demonstrate the efficacy of vascularized nerve grafts. Due to technical challenges, composite transfer of a nerve graft along with its adipose tissue has been proposed to provide a healthy tissue bed. Basic science research has shown that a vascularized fascial flap containing adipose tissue and a vascular bundle improves revascularization through excreted angiogenic factors, provided by the stem cells in the adipose tissue as well as by the blood supply and environmental support. While it was previously believed that revascularization occurred from both nerve ends, recent studies propose that revascularization occurs primarily from the proximal nerve coaptation. Fascial flaps or vascularized nerve grafts have limited applicability and future directions could lead towards off-the-shelf alternatives to autografting, such as biodegradable nerve scaffolds which include capillary-like networks to enable vascularization and avoid graft necrosis and ischemia.