Cryoneurolysis of Anterior and Posterior Divisions of the Obturator Nerve

Abstract

This feature is a unique combination of text (voice) and video that more clearly presents and explains procedures in musculoskeletal medicine. These videos will be available on the journal’s Website. We hope that this feature will change and enhance the learning experience. Walter R. Frontera, MD, PhD Editor-in-Chief URL: https://links.lww.com/PHM/B825 A scissoring and often painful gait sequelae to spastic hip adduction can be detrimental to an individual’s ability to ambulate.1 In addition, the spasticity may impede catheterization and cause poor perineal hygiene and ensuing skin or bladder infections and impaired sexual function may arise.2 Hip adduction spasticity may occur in neurological disorders, including spinal cord injury, traumatic brain injury, cerebral palsy, hereditary spastic paraparesis, and multiple sclerosis.1 Interventions that target the obturator nerve can relieve pain, decrease spasticity, and improve hygiene for 3 mos.1 The obturator nerve arises from the lumbar plexus and diverges into anterior and posterior branches.2 The anterior branch courses between adductor longus and brevis muscles, as well as supplies motor innervation to the adductor longus, adductor brevis, gracilis, and sometimes the pectineus.2 The posterior branch travels between the adductor brevis and magnus muscles supplying adductor magnus and brevis and occasionally the obturator externus and adductor longus.2 The obturator nerve supplies sensory innervation to the hip and knee joints and medial thigh.2 Historically used for analgesia, cryoneurolysis is a novel, adjuvant treatment for problematic spasticity.3 Cryoneurolysis of the musculocutaneous, radial, and tibial nerves has led to improvements in Modified Ashworth Scale, Modified Tardieu Scale, and gait.3 Cryoneurolysis engages a specialized probe with a tip capable of freezing to colder than −60°C.3,4 By positioning the probe’s tip on the selected nerve, a limited zone of axon and myelin disruption is created.3,4 Subsequently, the slow breakdown of the axon occurs—a phenomenon known as axonotomesis and Wallerian degeneration. The process preserves the epineural tube; thus, the nerve can regenerate over time. Case reports showed a reduction in spasticity maintained at a final 17-mo follow-up.3 Before cryoneurolysis, a diagnostic nerve block with 2% lidocaine is performed. This will cause a temporary nerve block and predict whether the longer lasting cryoneurolysis can be successful, ensure there is no significant sensory disturbance, or unwanted weakness. To localize the obturator nerve for cryoneurolysis, we propose two approaches using ultrasound guidance and electrostimulation: transverse and longitudinal. The patient is supine with their hip slightly abducted. TRANSVERSE The probe is advanced lateral to medial at 45 degrees. The obturator vessels appear with the anterior divisions arising above and the posterior below the vessels (Figs. 1A–C). Color Doppler can enhance localization (Fig. 1D).FIGURE 1: Ultrasound visualization of the obturator nerve (anterior and posterior branches). A, Anterior division of the obturator nerve, visualized using the transverse approach. B, Ultrasound probe placement and entry point for the transverse approach. C, Posterior division of the obturator nerve, visualized using the transverse approach. D, Localization of the blood vessel using color Doppler. E, Ultrasound probe placement and entry point for the longitudinal approach. F, Anterior and posterior branches of the obturator nerve visualized with the longitudinal approach.LONGITUDINAL APPROACH The transducer is sagittal along the anteromedial thigh, and the probe is advanced in-plane cephalad 45 degrees. The anterior branch is visualized at the plane separating adductor longus and brevis. The posterior branch is targeted by advancing the probe and initiating the freezing sequence in the hyperechoic fascia between the adductor brevis and magnus (Figs. 1E, F). To treat muscles innervated by each branch of the obturator nerve, the probe is repositioned between lesions. To ensure the nerve lesion interrupts innervation to all spastic adductor muscles, we recommend creating at least two lesions along the length of each branch.3 E-stimulation at less than 1 mA is essential for accurately targeting the desired branches and not the muscle bellies.3 Further studies are required to validate the safety and efficacy of the approach.

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