Brachialis Branch to Radial Nerve Transfer for Reanimation of Wrist and Finger Extension: An Anatomical Feasibility Study.

Abstract

The motor branch to the brachialis muscle has been described as a versatile donor in upper limb nerve reconstruction. This includes patients with peripheral nerve injuries and tetraplegia. However the anatomic feasibility of transfers from the musculocutaneous nerve to radial nerve branches around the elbow has not been systematically evaluated. This study aims to assess this feasibility. Such a transfer may be particularly relevant in patients with high-level tetraplegia or in patients with spastic upper limb involvement, in which selective denervation of spastic elbow flexors could be combined with nerve transfer to paretic wrist and/or finger extensors. Sixteen fresh-frozen cadaveric upper limbs were dissected to establish the feasibility of transferring a motor branch of either the biceps or brachialis muscle onto the branch of the extensor carpi radialis longus (ECRL), the extensor carpi radialis brevis (ECRB), the posterior interosseous nerve, or an intraneurally dissected radial nerve fascicle. Donor and recipient nerve lengths were measured, and the feasibility of tension-free coaptation was assessed. Axon counts were obtained from selected donor and recipient nerves. Biceps branches were anatomically unsuitable as donors, and ECRB and posterior interosseous nerve branches were unsuitable as recipients. Direct brachialis-to-ECRL transfer was feasible in three of 16 specimens, whereas transfer from a brachialis branch to an intraneurally dissected radial nerve fascicle was feasible in all specimens. In these intraneural transfers, at least one brachialis branch was preserved in 15 of 16 upper limbs, thereby minimizing functional donor muscle deficit. Axon counts demonstrated favorable donor-to-recipient ratios for both the brachialis-ECRL and brachialis-intraneural transfers, with median (interquartile range) values of 0.92 (0.65-1.37) and 0.71 (0.41-0.88), respectively. Brachialis-to-radial nerve transfer is anatomically feasible, particularly via intraneural fascicular coaptation, while preserving donor muscle function. This approach may provide a novel option for restoring wrist and finger extension in patients with upper limb spasticity, including selected cases of high-level tetraplegia or brachial plexus palsy.