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Selective Dorsal Rhizotomy Surgery for the Treatment of Pediatric Spastic Cerebral Palsy
∗Portions of this section on the “History of Selective Posterior Rhizotomy” have been reproduced from the previous Schmidek and Sweet SDR chapter by Drazin et al.
Cerebral palsy (CP) is the most common motor disability in children, occurring in 1.5 to 4 per 1000 live births in the United States. The incidence is rising as a result of increasing survival rates of very-low-birth-weight premature infants, the population at highest risk for the diagnosis. Spastic diplegic and quadriplegic CP are the most common subtypes of the disorder; nearly 80% of all patients with CP are affected by spasticity. Traditionally, medical and surgical management has been directed by physiatrists, physical therapists, and orthopedic surgeons at the muscle contractures and bony deformities caused by the effect of spasticity on the growing child. Interventions aimed at impacting the primary pathology within the nervous system itself have greater potential for sustained spasticity control and reducing rates of secondary complications; neurosurgeons have taken a lead role in this approach over the last 50 years. This chapter discusses the modern operative technique of selective dorsal rhizotomy (SDR) for the treatment of spastic CP in childhood.
Treatment of Spastic Cerebral Palsy
It is recognized that spasticity typically arises in the context of perinatal damage to the periventricular and subcortical white matter due to presumed hypoperfusion and reperfusion injury that alters the excitatory and inhibitory influences on the spinal cord alpha motor neurons primarily responsible for muscle tone; because the fibers descending from the motor cortex traveling closest to the ventricle project to the legs, spastic diplegia is seen most often. The resulting imbalance creates hyperactivity of both target and antagonistic muscle groups, which manifests clinically as a velocity-dependent, increased resistance to passive stretch. Over time, this impairment of voluntary motor activity limits mobility and causes abnormally shortened muscles, long tendons, and muscle contractures. If left untreated, the muscle stiffness progresses as the child grows and often leads to significant bone and joint deformities.
Spasticity has been managed for decades with oral medications that modify neurotransmitters at the spinal cord level, including baclofen, diazepam, and dantrolene, among others. For some patients, these drugs are effective at reducing spasticity, though systemic side effects such as sedation and risk of withdrawal can limit their use in others. Intramuscular injection of botulinum toxin A into affected muscles has been shown to provide durable relaxation and reproducible benefit, particularly in young children, and can be repeated every few months as needed. Intrathecal administration of baclofen through an implanted programmable infusion system permits delivery of the drug directly to the central nervous system and has been proven to reduce spasticity with decreased systemic side effects. Unfortunately, this procedure in the pediatric CP population is associated with a high rate of morbidity, including wound infection, pump malfunction, and risk of baclofen overdose or withdrawal.
Selective Dorsal Rhizotomy
The first documented attempt at treating spasticity by cutting posterior spinal rootlets in humans was made by Foerster in 1905 and was based on the studies by Sherrington that showed resolution of spasticity via this same approach in cats whose brain stems had been sectioned from their spinal cords. , Foerster subsequently introduced electrical stimulation to identify the levels of the nerve roots encountered during surgery and achieved successful spasticity reduction in a large group of patients. It wasn’t until 50 years later, however, that Gros described the technique of partial deafferentation of the sensory rootlets in an effort to decrease rates of undesirable loss of proprioception.
In the 1970s, Fraioli and Guidetti used work by Sindou documenting the location of the entry site of the 1A sensory fibers at the spinal cord level to further refine the rhizotomy by performing a hemisection of nerve rootlets. , In 1978, Fasano and colleagues reported their procedure of SDR that involved dividing rootlets based on electromyographic (EMG) responses to electrical stimulation. They found that, unlike normal roots, the stimulation of “abnormal” roots caused a tetanic contraction that often persisted after cessation of the stimulus; by cutting the abnormal roots and saving the normal ones, they achieved long-term reduction in spasticity with preserved proprioceptive sensation. ,
This technique was further modified and popularized by Peacock and colleagues, who classified and graded EMG responses in greater detail to facilitate improved functional selection of rootlets for division or preservation; this characterization included EMG responses that persisted after the stimulus ceased, clonus, contraction of muscles in the contralateral extremity, and contraction of muscles not normally in the myotome innervated by the stimulated root. , Peacock moved the site of surgery from the conus medullaris to the cauda equina and performed the evaluation of rootlets at their exit zones from the dural sac, where the identification of lower sacral rootlets and the separation of dorsal from ventral roots could be performed more easily. Park subsequently advocated dorsal rhizotomies at the level of the conus through a minimally invasive approach to decrease the long-term risk of spinal deformity and reported equally good outcomes.
Numerous clinical studies have shown that SDR is a safe and effective treatment in the management of spastic CP. Although some contemporary neurosurgeons perform lumbar dorsal rhizotomies without electrophysiologic guidance, this text focuses on the selective partial deafferentation of the L1–S2 roots based on intraoperative EMG responses via a single-level laminectomy at the conus medullaris.
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