SDR evolved from the more radical, nonselective dorsal rhizotomy that Foerster first described in the early 1900s as a means of interrupting aberrant spinal reflex arcs responsible for spastic paralysis. In its original form, the entire dorsal (sensory) root, or a significant portion of it, was transected at one or more spinal levels in an effort to quell hyperreflexia. Although tone was reliably reduced, the procedure was hampered by frequent numbness, proprioceptive loss, and occasional ataxia—limitations that ultimately spurred refinement toward a selective, function-preserving strategy. ^,,

Modern SDR is a microsurgical technique in which the involved dorsal roots—typically spanning L1-S2 in ambulatory children with CP and C5-T1 in selected cases of upper-limb spasticity—are divided into 3- to 5-rootlet fascicles under the operating microscope. Each rootlet is stimulated electrically while recordings of a lower-threshold electromyography (EMG) are obtained from target muscles; rootlets that elicit abnormally high-amplitude or widespread motor responses are considered “spastic” and are sharply sectioned, whereas physiologic rootlets are preserved. Some centers supplement EMG with direct clinical observation of limb movement during stimulation, reasoning that concordance between electrophysiologic and macroscopic hyperactivity increases the specificity of the selection process. By excising only those afferent fibers that demonstrably drive hyperexcitability, SDR aims to attenuate (Group Ia afferent fibers [Ia])-mediated facilitation of α-motor neurons in the ventral horn while maintaining sufficient proprioceptive input for coordinated volitional movement. Several large series in pediatric CP have documented durable reductions in Ashworth and Tardieu scores, improved gait kinetics, and enhanced gross motor function lasting more than a decade after surgery, with sensory deficits limited to patchy hypesthesia that rarely affects daily activities. ^,, SDR may be beneficial in carefully selected patients with spasticity not related to CP, prompting a reconsideration of traditional surgical inclusion criteria.

Investigation of cervical SDR for upper-extremity spasticity is more recent but encouraging: Bertelli and colleagues ^, reported meaningful gains in dexterity, grasp, and pinch strength after C5–C8 rhizotomies, with negligible sensory morbidity—findings that they attribute to generous overlap among adjacent dermatomes and residual dorsal-root afferents. A systematic review encompassing 112 children with upper-limb involvement likewise demonstrated significant improvements in Melbourne and QUEST scores after lumbosacral SDR, suggesting that reduced proximal tone may indirectly benefit distal function.

Simple, nonselective dorsal rhizotomy still has a role when intraoperative monitoring is unavailable or when extensive multilevel disease mandates a broader intervention. Advocates of the traditional technique argue that all rootlets innervating a spastic muscle are pathologic and should therefore be divided en bloc, citing comparable tone reduction and improved operative efficiency. ^,, However, studies have failed to show superiority over monitored SDR, and the potential cost in sensory function has led most contemporary centers to favor the selective approach. ^,,

Controversy persists regarding the reliability of EMG criteria: some studies have shown that rootlets deemed “physiologic” can still contribute to postoperative tone, whereas others report equally favorable outcomes when rootlets are cut at random. ^, These discrepancies likely reflect heterogeneity in stimulation parameters, anesthetic regimens, and patient selection. Ongoing refinement of neurophysiologic thresholds and incorporation of high-density motor-unit mapping may further enhance selectivity in the coming decade.

In summary, SDR represents a focused, physiology-guided evolution of dorsal rhizotomy that balances robust spasticity reduction with preservation of protective sensation and purposeful movement. Although lower-limb applications in CP remain its most established indication, emerging evidence supports carefully selected use at cervical levels for upper-extremity spasticity that is refractory to pharmacologic agents, chemodenervation, or peripheral nerve procedures. When integrated into a comprehensive rehabilitation program, SDR can yield durable functional gains and facilitate subsequent orthopedic or reconstructive interventions.

The idea of crossing a healthy cervical root to the paretic side was first explored in brachial-plexus repair. Gu and colleagues first used the entire C7 root as a donor for total plexus avulsion, noting its large motor axon count. A decade later the same team extrapolated the idea to central hemiplegia, reasoning that (1) severing the pathologically hyper-afferent C7 root on the affected side would reduce spastic input and (2) coapting it with the intact C7 root from the contralateral side would provide a fresh corticospinal channel to strengthen the weak muscles. Zheng and colleagues confirmed the therapeutic promise in a 36-patient randomized trial: cC7 transfer plus task-oriented rehabilitation improved the Fugl-Meyer upper-extremity (UE-FM) score by 17.7 ± 4.5 points versus 2.6 ± 3.2 with rehabilitation alone at 12 months. A recent systematic review by Luo and colleagues included 384 patients with central spastic paralysis (192 receiving cC7 transfer and 192 undergoing rehabilitation alone) and found significantly greater improvements in Fugl-Meyer and ROM scores in the surgical group. Spasticity was also markedly reduced, with no major adverse events reported. Despite some limitations, the investigators concluded that cC7 transfer shows promising efficacy and warrants further investigation.

Surgical technique and route choice

In cC7 transfer for spastic hemiplegia, through a supraclavicular exposure, the donor C7 root is dissected as distally as possible at the level of the trunk or divisions, preserving adjacent roots and cords. On the recipient side, the corresponding C7 root or a target distal nerve is exposed for coaptation. Two surgical routes have been described. The earlier method involves creating a subcutaneous tunnel across the anterior chest and neck, where a nerve graft—commonly a sural nerve cable or autologous ulnar nerve—is interposed between the 2 C7 stumps ( Fig. 1 ). The graft length typically ranges from 15 to 18 cm and necessitates 2 neurorrhaphies, with associated risks of tension, delayed regeneration, and donor morbidity. ^, More recently, the prespinal (retroesophageal) route has gained favor. This approach entails careful dissection along the prevertebral space, passing posterior to the esophagus and anterior to the vertebral column, often requiring detachment of the anterior scalene and elevation of the longus colli. The resulting tunnel permits a direct, around 4- to 6-cm path that allows for end-to-end coaptation without grafts in most patients. ^,, Microsurgical neurorrhaphy is performed under magnification using epineurial or group fascicular sutures, frequently supplemented by fibrin glue. Cadaveric and clinical studies confirm that the prespinal route achieves a shorter, more linear trajectory than the subcutaneous route, minimizing the need for interposition grafts while maintaining vascular safety and functional alignment. ^, Donor-site morbidity following the entire C7 harvest for cC7 transfer is generally mild and transient. One study of 63 patients observed that, although some experienced long-term sensory disturbances, objective measures of motor function and dexterity in the donor limb remained unaffected, and no permanent deficits were reported.

cC7 nerve transfer using the left C7 root as the donor and the ulnar nerve as an interposition graft. The donor ulnar nerve is shown bilaterally after subcutaneous tunneling, before epineural coaptation with the donor C7 root on the left and the recipient nerve on the right.

A simplified approach—ipsilesional C7 neurotomy (involving only transection without cross-grafting)—has regained interest as a potential method to reduce spasticity ( Fig. 2 ). The affected C7 root is divided proximally near the dorsal-root ganglion, immediately interrupting the pathologic afferent signal that fuels spasticity. In a 2022 pilot series of 4 chronic hemiplegic patients who underwent simple C7 transection, UE-FM scores increased by a mean of 7 points and Modified Ashworth Scale (MAS) decreased by 1 to 1.5 grades within 6 months, with no donor-side morbidity. Early reports suggest the operation can be completed in less than 60 minutes through a single supraclavicular incision, making it attractive where cross-transfer resources are limited. Nonetheless, the absence of new efferent fibers means motor recovery relies solely on cortical plasticity rather than axonal regeneration. Crucially, no level I trials have yet compared cC7 transfer with simple C7 transection. Robust randomized studies are needed to determine whether the added complexity and donor-root morbidity of cC7 transfer translate into clinically meaningful advantages over transection alone.

Dissection of the left “spastic” C7 root, prepared for transection to reduce ipsilateral spasticity. The patient’s head is positioned on the right side of the image.

HSN represents a microsurgical refinement of Stoffel’s 1913 “partial neurotomy” and the hyponeurotization technique popularized by Brunelli and Brunelli in 1983. ^, By excising only the hyperexcitable motor fascicles while sparing at least one-third of the volitional fibers and all sensory branches, the procedure interrupts the pathologic stretch reflex arc while preserving useful strength. Systematic anatomic work and intraoperative quantitative EMG have transformed HSN into an evidence-based option for focal spasticity after stroke, CP, TBI, SCI, and multiple sclerosis. Midterm and long-term series consistently document tone reduction lasting greater than 3 years and compatibility with fractional tendon lengthening, tendon transfers, or staged botulinum toxin.

Indications for HSN include focal upper-limb spasticity in patients with preserved voluntary control, particularly when conservative treatments like botulinum toxin have failed or provided only temporary relief. Ideal candidates are individuals with upper motor neuron syndromes who present disabling hypertonia but retain sufficient residual strength. Preoperative EMG and diagnostic nerve blocks (eg, with botulinum toxin) help confirm the dynamic and reversible nature of the spasticity, ensuring appropriate surgical targeting. The presence of muscle and/or joint contractures may necessitate adjunct procedures, such as tendon lengthening, tenotomy, or joint arthrolysis, to optimize functional outcomes. ^,

The authors outline the indications and surgical options for HSN based on the anatomic regions associated with upper-limb spasticity.

Shoulder spasticity

Management of shoulder spasticity in upper motor neuron syndromes often targets the classic deformity of internal rotation and adduction, typically driven by spastic overactivity in the pectoralis major, latissimus dorsi, teres major, and, in select cases, subscapularis. A practical algorithm begins with distinguishing dynamic spasticity from fixed contracture.

In cases dominated by spasticity, nerve-specific strategies can be used alone or in combination with muscle-based procedures. The pectoralis major is often affected and may be managed through tenotomy in cases of severe contracture, tendon lengthening when contracture is mild, or HSN of the medial and lateral pectoral nerve branches in cases characterized by isolated spasticity ( Fig. 3 , [CR] ). Decq and colleagues first denervated the lateral and medial pectoral nerves in 5 adults (3 stroke, 2 SCI). They reported mean gains of 30° abduction and 50° forward flexion with pain relief and no donor-site weakness. HSN can be safely and efficiently performed for the treatment of spasticity of the latissimus dorsi muscle, too. In a recent combined cadaveric and clinical study, Lin and colleagues identified 1 to 3 consistent motor branches of the thoracodorsal nerve entering the latissimus dorsi at 25% to 70% of humeral length. In the clinical part of the study, selective neurectomy of 2 branches in 10 poststroke patients resulted in a mean reduction of 1.8 points on the MAS and an average improvement of 39° in active shoulder abduction. Notably, all patients retained sufficient latissimus function to maintain tasks, such as wheelchair propulsion, underscoring the functional safety of partial thoracodorsal denervation for shoulder spasticity relief. Teres-major neurectomy can further correct persistent internal rotation. ^, Subscapularis HSN is rarely performed in CP because deep exposure risks glenohumeral instability; most pediatric teams favor extra-articular tendon lengthening or chemodenervation instead.

Branches of the medial and lateral pectoral nerves to the pectoralis major muscle ( arrow ) dissected and prepared for HSN in cases of spasticity without fixed muscle contractures.

Elbow flexor and extensor spasticity

Elbow spasticity is a common manifestation of upper motor neuron syndrome that significantly impairs functional reach, self-care, and limb positioning. It typically presents as a flexion deformity driven by overactivity of the biceps, brachialis, and brachioradialis muscles, often accompanied by co-contraction of flexors and extensors, which further limits voluntary motion and functional use.

Preoperative assessment may include imaging studies, such as elbow radiographs and computed tomographic scans, alongside functional evaluations like dynamic electromyography (dEMG) and selective nerve blocks. dEMG is particularly useful in identifying coactivation patterns of elbow flexors and extensors, whereas diagnostic nerve blocks help differentiate between spasticity and fixed soft tissue or joint contractures. When spasticity is the dominant component and no significant contracture is present, a temporary response to nerve block or botulinum toxin can confirm surgical candidacy and guide target selection. In patients who retain voluntary motor control, HSN of the musculocutaneous nerve (MCN) effectively reduces spasticity in the biceps and brachialis muscles. Preoperative assessment can determine whether the brachioradialis muscle needs to be addressed. ^, Cadaveric studies have shown that the MCN typically gives off between 1 and 5 branches to the biceps, which enter the muscle at 18% to 64% of humeral length, and 1 to 3 branches to the brachialis at 35% to 75%. This map indicates the surgical exposure: the MCN is followed from the coracobrachialis split distally to 75% of arm length, permitting selective fascicular resection while preserving sensory fibers ( Figs. 4 and 5 , [CR] ). HSN of the radial nerve can be used to reduce spasticity in the brachioradialis muscle. The brachioradialis typically receives 1 to 4 motor branches, which are carefully dissected, and about 70% to 80% of their fibers are removed to reduce muscle overactivity while preserving function. The prospective 42-limb series by Leclercq and colleagues confirmed durable tone relief over 31 months and stressed retaining at least 20% to 30% fascicular section to preserve strength.

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