Surgery in the Dorsal Roots for Children with Cerebral Palsy

Muscle responses to radicular stimulation during lumbo-sacral dorsal rhizotomy for spastic diplegia: Insights to myotome innervation

OBJECTIVE

Most of knowledge on muscle radicular innervation was from explorations in root/spinal cord pathologies. Direct and individual access to each of the lumbar-sacral -ventral and dorsal- nerve roots during dorsal rhizotomy for spastic diplegia allows precise study of the corresponding muscle innervation. Authors report the lumbo-sacral segmental myotomal organization obtained from recordings of muscle responses to root stimulation in a 20-children prospective series.

METHODS

Seven key-muscles in each lower limb and anal sphincter were Electromyography (EMG)-recorded and clinically observed by physiotherapist during L2-to-S2 dorsal rhizotomy. Ventral roots (VR), for topographical mapping, and dorsal roots (DR), for segmental excitability testing, were stimulated, just above threshold for eliciting muscular response.

RESULTS

In 70% of the muscles studied, VR innervation was pluri-radicular, from 2-to-4 roots, with 1 or 2 roots being dominant at each level. Overlapping was important. Muscle responses to DR stimulation were 1.75 times more extended compared to VR stimulation. Inter-individual variability was important.

CONCLUSIONS

Accuracy of root identification and stimulation with the used method brings some more precise information to radicular functional anatomy.

SIGNIFICANCE

Those neurophysiological findings plead for performing Intra-Operative Neuromonitoring when dealing with surgery in the lumbar-sacral roots.

Dorsal rhizotomy for children with spastic diplegia of cerebral palsy origin: usefulness of intraoperative monitoring

OBJECTIVE The utility of intraoperative neuromonitoring (ION), namely the study of muscle responses to radicular stimulation, remains controversial. The authors performed a prospective study combining ventral root (VR) stimulation for mapping anatomical levels and dorsal root (DR) stimulation as physiological testing of metameric excitability. The purpose was to evaluate to what extent the intraoperative data led to modifications in the initial decisions for surgical sectioning established by the pediatric multidisciplinary team (i.e., preoperative chart), and thus estimate its practical usefulness. METHODS Thirteen children with spastic diplegia underwent the following surgical protocol. First, a bilateral intradural approach was made to the L2-S2 VRs and DRs at the exit from or entry to their respective dural sheaths, through multilevel interlaminar enlarged openings. Second, stimulation-just above the threshold-of the VR at 2 Hz to establish topography of radicular myotome distribution, and then of the DR at 50 Hz as an excitability test of root circuitry, with independent identification of muscle responses by the physiotherapist and by electromyographic recordings. The study aimed to compare the final amounts of root sectioning-per radicular level, established after intraoperative neuromonitoring guidance-with those determined by the multidisciplinary team in the presurgical chart. RESULTS The use of ION resulted in differences in the final percentage of root sectioning for all root levels. The root levels corresponding to the upper lumbar segments were modestly excitable under DR stimulation, whereas progressively lower root levels displayed higher excitability. The difference between root levels was highly significant, as evaluated by electromyography (p = 0.00004) as well as by the physiotherapist (p = 0.00001). Modifications were decided in 11 of the 13 patients (84%), and the mean absolute difference in the percentage of sectioning quantity per radicular level was 8.4% for L-2 (p = 0.004), 6.4% for L-3 (p = 0.0004), 19.6% for L-4 (p = 0.00003), 16.5% for L-5 (p = 0.00006), and 3.2% for S-1 roots (p = 0.016). Decreases were most frequently decided for roots L-2 and L-3, whereas increases most frequently involved roots L-4 and L-5, with the largest changes in terms of percentage of sectioning. CONCLUSIONS The use of ION during dorsal rhizotomy led to modifications regarding which DRs to section and to what extent. This was especially true for L-4 and L-5 roots, which are known to be involved in antigravity and pelvic stability functions. In this series, ION contributed significantly to further adjust the patient-tailored dorsal rhizotomy procedure to the clinical presentation and the therapeutic goals of each patient.

Keyhole interlaminar dorsal rhizotomy for spastic diplegia in cerebral palsy

BACKGROUND

The efficiency and safety of dorsal rhizotomies for cerebral palsy lie in the accuracy of radicular identification together with selectivity of root sectioning. Two different exposures are currently in use. The first is extended laminotomy/laminectomy from the upper lumbar level to the sacrum, which allows accurate identification of all L2-S2 roots/rootlets. The second is limited laminotomy exposing the conus/cauda equina at the thoracolumbar junction; this less invasive method limits accessibility to the roots. To optimize the accuracy and selectivity while minimizing invasiveness, the authors developed a tailored interlaminar procedure targeting the radicular levels involved in the harmful components of spasticity directly and individually.

METHODS

Six patients with spastic diplegia at different levels of the Gross Motor Functional Classification System were selected. In each patient, two to three interlaminar spaces, preselected according to planning, were enlarged in the "keyhole" fashion, respecting the spinous processes and interspinous ligaments. Ventral root stimulation identified the radicular level. Dorsal root stimulation evaluated its implication in the hyperactive segmental circuits, helping quantify the percentage of rootlets to be cut.

RESULTS

There were neither wound-related nor general complications. At 1 year of follow-up, X-ray examination did not reveal kyphosis or instability. In all children, the excess of spasticity was reduced. The Ashworth score decreased from 3.2 on average to 0.6 postoperatively (range: 2-4 to 0-2). Regarding the functional status at 1 year of follow-up for the three ambulatory children, the Gillette ability-to-walk score increased from 3/10 on average to 7.3/10 postoperatively (range: 2-4 to 7-8). For the three non-ambulatory children, abnormal postures, painful contractures and ease of care were much improved.

CONCLUSION

Keyhole interlaminar dorsal rhizotomy (KIDr) offers direct intradural access to each of the ventral/dorsal roots, thus maximizing the reliability of anatomical mapping and allowing individual physiological testing of all targeted roots. The interlaminar approach minimizes invasiveness by respecting the posterior spine structures.