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Correlation of Wide-Awake Exploration and US-guided EMG to Confirming ECRL and ECRB Strength Prior to Tendon Transfer in Tetraplegic Patients
Brooke E Willborg, MD, James Meiling, DO, Andrea J Boon, MD, Marianne T Luetmer, MD, Peter C Rhee, MD; Kitty Y Wu, MD
Mayo Clinic, Rochester, MN
Introduction: Tetraplegic patients with extensor carpi radialis longus (ECRL) and brevis (ECRB) function may undergo nerve or tendon transfers utilizing one wrist extensor as a donor. Pre-operative confirmation of two strong and independent wrist extensors is critical but difficult based on physical examination alone. We describe two techniques - ultrasound-guided electromyography (US-EMG) and wide awake ECRL tenotomy - to assess wrist extension strength and hypothesize a strong correlation between these two methods.
Materials & Methods: Spinal cord injury (SCI) patients undergoing wide awake ECRL tenotomy or US-EMG assessment of ECRL and ECRB muscle activation were retrospectively reviewed. Inclusion criteria were patients with complete SCI, International Classification for Surgery of the Hand in Tetraplegia (ICSHT) group 2 or 3, or any patient with incomplete SCI. Patient demographics, pre-operative and intra-operative wrist extension strength, and pre-operative US-EMG results were recorded. Patients underwent EMG assessment of voluntary ECRL and ECRB activation with US guidance to confirm needle placement.
Results: Eight patients (4 male, 4 female; mean age 46 years, range 16-69 years) who underwent wide awake distal ECRL tenotomy and subsequent tendon transfers were included. Six patients had complete SCI (ICSHT group 3), one had transverse myelitis (ICSHT group 5), and one had central cord syndrome (ICSHT group 6). Patients underwent surgery at a mean of 50 months after injury (range 8 to 306). Pre-operative wrist extension strength was M4 in two patients, M4+ in two patients, and M5 in four patients. Following ECRL tenotomy, all patients demonstrated preserved wrist extension strength through ECRB alone (four M5, four M4 strength). All proceeded ahead with ECRL to flexor digitorum profundus tendon transfer for reconstruction of active grasp. Six of these patients also underwent pre-operative US-guided EMG of the ECRL and ECRB muscles. In all 6 cases EMG findings correlated with the intra-operative findings confirming two active wrist extensors.
Conclusions: US-EMG and wide awake ECRL tenotomy are both reliable methods for confirming the presence of two functional wrist extensors. While not required for any patients in this study, if wrist extension was lost after ECRL tenotomy, the ECRL could then be transferred to the ECRB for wrist centralization. The strong correlation between pre-operative EMG and intra-operative assessment supports the use of US-EMG as a non-invasive diagnostic tool in surgical planning.
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