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Nerve Transfers for Wrist Extension in the Spastic Upper Extremity: an Anatomic Feasibility Study
Kitty Wu, MD, FRCSC1; Peter C. Rhee, MD2
1Mayo Clinic, Rochester, MN; 2Orthopaedic Surgery, Mayo Clinic, Rochester, MN

Hypothesis: In the spastic flexed wrist deformity, there is imbalance between the spastic wrist flexors and weak or paralyzed wrist extensors. Nerve transfers have the theoretical advantage of reducing the spasticity of the donor muscle while augmenting function of the recipient muscle. The aim of this study was to determine the anatomic feasibility transferring the motor branch to the FCU to the ECRB to restore balance in wrist function.
Materials & Methods: Five fresh frozen cadaveric upper extremity specimens were used for this study. A curvilinear bayonet incision within the antecubital fossa was used to identify the radial nerve as it emerged into the forearm between the brachialis and brachioradialis (BR). The motor branch to the FCU was identified through a separate incision splitting the two heads of the FCU muscle. The origin and number of branches, branching pattern, and muscle entry points to the FCU, BR, and ECRB were recorded and measured with reference to the interepicondylar line (IEL; - proximal, +distal). The motor branch of the FCU was then transferred and directly coapted to the ECRB.
Results: There were 1-3 branches to BR, entering the muscle at a mean distance of -2.1cm from the IEL (range -4cm to +1cm). There were 2-3 branches to the ECRL, entering the muscle at a mean distance of +1.1cm (range -1 to +4cm) and with a mean length of 5cm from its nearest branch point. There were 1-3 branches to the ECRB entering the muscle at a mean of +4.7cm (range +2cm to +8cm) and with a mean length of 6.5cm. There were consistently 2 branches to the FCU entering the muscle at a mean of +4.8cm (range +2 to +8cm) and with a mean length of 3.6cm from its branch point from the ulnar nerve. In all cases, a tension free, direct neurotization from either of the two FCU branches to ECRB could be performed.
Conclusions: Distal nerve transfer from the FCU to ECRB is anatomically feasible with primary coaptation. This may provide an effective strategy to better balance wrist function in patients with spastic wrist flexion deformity by decreasing tone in a spastic wrist flexor and subsequently augmenting or providing motor tone to a weak or paralyzed wrist extensor, respectively


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