Hyperselective Neurectomy for Spastic Flexion-Pronation Deformity of the Forearm and Wrist Using Local Anesthesia without a Tourniquet.

BACKGROUND

Spasticity in the upper limb following stroke or traumatic brain injury substantially impairs function and quality of life by affecting the flexor and adductor muscles. Spasticity commonly presents with deformities such as shoulder adduction and internal rotation, elbow flexion, forearm pronation, wrist flexion, finger flexion, and thumb adduction-commonly referred to as "thumb-in-palm" deformity. As the spasticity is incurable, surgical interventions aim to improve function and aesthetics, and facilitate daily care. Procedures such as tendon transfers and fractional lengthening can be limited by persistent spasticity, which may mask the underlying pathology, leading to misjudgments during surgery. Hyperselective neurectomy (HSN) is a surgical technique targeting specific motor nerve branches to reduce spasticity while preserving voluntary function. Traditionally performed with the patient under general anesthesia, HSN presents challenges, as the relaxed muscles may obscure the degree of spasticity. Performing HSN with the patient receiving local anesthesia and without the use of a tourniquet offers real-time evaluation of muscle function, enabling precise surgical adjustments and minimizing unnecessary nerve resection. Additionally, HSN provides flexibility to incorporate tendon transfers or fractional lengthening intraoperatively, as appropriate.

DESCRIPTION

With the patient under local anesthesia, a longitudinal incision exposes the median and ulnar nerves from the elbow to the forearm. The median nerve branches innervate the pronator teres, flexor carpi radialis (FCR), flexor digitorum profundus (FDP), and flexor digitorum superficialis (FDS), while the anterior interosseous nerve innervates the flexor pollicis longus. The ulnar nerve innervates the flexor carpi ulnaris (FCU) and FDP, with branches arising near the medial epicondyle. Selective neurectomy targets two-thirds to three-quarters of the nerve fascicles responsible for spastic movements, preserving sufficient fascicles for voluntary control. For example, patients with flexion-pronation deformities and weak wrist dorsiflexion may benefit from neurectomy of the pronator teres and wrist flexor branches. No cauterization is applied proximal to the nerve stumps in order to avoid further complications. The surgeon can also consider tendon transfers, such as transferring the extensor carpi ulnaris (ECU) to the extensor carpi radialis brevis (ECRB) in order to enhance wrist dorsiflexion. After partial neurectomy of the flexor pollicis longus, the patient can demonstrate thumb extension intraoperatively. The use of local rather than general anesthesia allows continuous feedback from the awake patient, ensuring accurate spasticity reduction and helping to assess the need for further interventions. Intraoperative neurostimulation aids in accurately identifying motor branches and avoiding sensory nerves. This method enables fine-tuning of the neurectomy to achieve optimal outcomes without excessive nerve resection that could compromise muscle strength.

ALTERNATIVES

Alternative treatments for spasticity include physical therapy, oral medications, botulinum toxin injections, and intrathecal baclofen pumps. However, these options may have limited efficacy, have side effects, or require more studies.

RATIONALE

Selective neurectomy offers several advantages over other treatments. (1) A targeted approach. Unlike systemic medications or generalized nerve blocks, HSN specifically addresses the nerves responsible for spasticity, sparing other muscles. (2) A long-lasting effect. Whereas medications and botulinum toxin provide temporary relief, HSN offers longer-lasting spasticity reduction. (3) Functional improvement. The procedure enhances specific movements, such as wrist dorsiflexion and thumb extension. It also allows for intraoperative tendon transfer as needed in order to address persistent deformities. HSN is not typically a first-line treatment but is considered when nonoperative treatment has failed. HSN is particularly suitable in patients with focal spasticity who retain some voluntary control and who possess sufficient passive range of motion. The procedure may also be combined with single-event multilevel surgery for more comprehensive upper-limb reconstruction.

EXPECTED OUTCOMES

Patients undergoing HSN can expect substantial reduction in spasticity and improved functional range of motion. In a prospective trial including 18 HSN procedures involving the pronator teres, Leclercq et al. reported significant improvements in forearm resting position and spasticity parameters at the latest follow-up. Similar procedures on wrist flexors, including the FCR, FCU, and pronator teres, have shown moderate wrist extension improvement without compromising flexor strength. Hysong et al. reported that House scores improved from 2.2 to 3.4 on average and that surgical goals were achieved in 93% of patients, with no postoperative complications or permanent strength loss reported. Although outcomes may vary according to individual patient factors, HSN provides long-lasting improvements in function and spasticity control, contributing to higher patient satisfaction. Additional tendon transfers may further enhance outcomes.

IMPORTANT TIPS

Ideal candidates for HSN exhibit focal spasticity that is unresponsive to nonoperative treatments, with functional wrist and finger flexors and weak extensors.Local anesthesia without a tourniquet allows for real-time nerve stimulation and precise identification of target branches, enabling the patient to actively participate in intraoperative assessments before and after the neurectomy.A curvilinear incision ensures adequate exposure and identification of individual nerve branches.Target only the motor fascicles causing spasticity while preserving sensory branches in order to maintain function.Tendon transfers, such as ECU to ECRB, enhance wrist dorsiflexion.Postoperative rehabilitation is crucial to prevent complications and maximize functional gains.Anatomical variations can complicate nerve identification.Excessive fascicle resection may result in unintended muscle weakness.Inadequate resection may not sufficiently reduce spasticity.Potential complications include infection, hematoma, nerve injury, and chronic pain.

ACRONYMS AND ABBREVIATIONS

PT = pronator teresHSN = hyperselective neurectomyECU = extensor carpi ulnarisECRB = extensor carpi radialis brevisFCR = flexor carpi radialisFDP = flexor digitorum profundusFDS = flexor digitorum superficialisFPL = flexor pollicis longusEPL = extensor pollicis longusEDM = extensor digiti minimiECRL = extensor carpi radialis longusWALANT = wide awake local anesthesia no tourniquetFCU = flexor carpi ulnaris.