Nerve Transfers to Rebalance the Spastic Wrist: An Anatomical Feasibility Study.
PURPOSE Spastic wrist flexion deformities result from an imbalance between spastic wrist flexors and weak or paralyzed wrist extensors. Nerve transfers offer the potential to restore this balance by combining neurotomy of the spastic donor nerve with reinnervation of the paralyzed recipient muscle. This study evaluated the anatomic feasibility of addressing the spastic wrist flexion deformity by transferring a motor branch from the flexor carpi ulnaris (FCU) to the extensor carpi radialis brevis (ECRB) and/or longus extensor carpi radialis (ECRL). METHODS Ten fresh-frozen cadaveric upper-extremity specimens were dissected. Motor branches to the FCU were identified through an incision between its two heads. The radial nerve branches to the ECRL and ECRB were exposed via a separate curvilinear incision within the antecubital fossa. The number of motor branches, muscle entry points, and length available for nerve transfer was recorded for each motor branch relative to the interepicondylar line (IEL). RESULTS The ECRL received one to three motor branches, entering the muscle at a median distance 1.6 cm distal to the IEL (range: 4 cm proximal to 6.4 cm distal). The median branch length available for transfer was 3.8 cm (range: 1.5-7.0 cm). The ECRB received one to three motor branches, entering the muscle at a median of 2.7 cm distal to the IEL (range: 1.7-8.0 cm distal). The median maximal branch length was 5.5 cm (range: 4.0-9.0 cm). The FCU had two to three motor branches, median muscle entry point 2.5 cm distal to the IEL (range 0 to 8.0 cm distal), and median maximal branch length of 3.3 cm (range: 1.6-5.2 cm). Direct, tension-free coaptation of the FCU to ECRB motor nerve was feasible in 90% specimens and the FCU to ECRL motor nerve in 50% of specimens. CONCLUSIONS FCU to ECRB nerve transfer was anatomically feasible in the majority specimens and may offer a possible surgical option to rebalance resting wrist posture and function in patients with spastic wrist flexion deformities. TYPE OF STUDY/LEVEL OF EVIDENCE Diagnostic, IV.