I. Concept of cerebral palsy
The clinical syndrome arising from non-progressive brain injury caused by various reasons before, during and one month after delivery is known as cerebral palsy. The main manifestations are dysfunction of the central nervous system and motor system, specifically mental retardation, muscle weakness, muscle spasm, walking difficulties, abnormal gait, scissors and pointed foot gait.
Second, the purpose of cerebral palsy treatment.
The name of cerebral palsy makes the parents of the affected children unknowingly enter a misunderstanding. They always want to solve the problem of brain, and as a result, they adopt a series of treatments for brain, but their condition never improves. Although the root of cerebral palsy is in the brain, the brain lesion of children with cerebral palsy is static and irreversible, which means that the brain lesion cannot be solved, and the aim of cerebral palsy treatment should be directed at the limb dysfunction caused by the brain lesion.
III. The importance of selective posterior spinal nerve rhizotomy (SPR) in cerebral palsy rehabilitation.
Spastic cerebral palsy accounts for two-thirds of the total number of cerebral palsy. The presence of spasticity affects the normal muscle strength, leading to limb motor dysfunction and the occurrence of various deformities. Previous orthopedic surgical treatments generally seldom targeted spasticity, and were aimed solely at correcting deformities, often leading to recurrence of spasticity and deformities, with unsatisfactory results. Although rehabilitation training is an important and indispensable treatment for cerebral palsy, it has its limitations in terms of efficacy due to its inability to release spasticity.
SPR is a new neurosurgical technique that has been gradually developed in recent years, which is mostly used for the treatment of cerebral palsy spasticity. SPR surgery can effectively relieve limb spasticity and lay the foundation for limb orthopaedics and functional rehabilitation.
IV. Historical review of SPR
As early as the beginning of this century, Foerster (1908) first used posterior spinal nerve root amputation to treat limb spasticity, and he used complete amputation of the entire posterior root.
Half a century later, French scholar Gros (1967) improved Foerster’s procedure by cutting only a portion of the posterior root fibers in a certain proportion, with the result that although the sensory integrity of the limb could be preserved, the release of spasticity was not complete, so the procedure was not popularized.
In the late seventies, Fasano (1978), an Italian scholar, first reported that selective posterior rhizotomy using electrical stimulation successfully preserved the sensation of the limb while completely relieving the spasticity, and the postoperative follow-up revealed significant functional improvement in a significant number of cases. This successful experience gradually attracted the attention of scholars from all over the world, and Fasano also called this procedure functional posterior rhizotomy.
In the 1980s, SPR surgery was introduced to North America, and Peacock (1988) further improved Fasano’s surgical method by lowering the SPR surgical plane from the thoracolumbar segment (thoracic 12 and lumbar 1 and 2) to the lumbosacral segment (L2-S1) and operating at the cauda equina level, which reduced the risk of surgical injury to the spinal cone and reduced the surgical difficulty, and made the procedure popular in North America.
Our scholar, Professor Xu Lin, was the first to carry out the surgical treatment of cerebral palsy SPR in China and Asia in May 1990. The orthopedic department of Zhongyuan General Hospital successfully carried out this surgery in 1999 and achieved satisfactory results
V. New understanding of the mechanism of SPR antispasticity
The mechanism of increased muscle tone and muscle spasm caused by cerebral palsy lies in the weakening of downward conductive inhibition, increased excitability of r-motor neurons in the anterior horn of the spinal cord, increased sensitivity of the muscle shuttle, and hyperactivity of the detrusor reflex. Fibers emanating from r-motor neurons in the anterior horn of the spinal cord innervate intracartilaginous muscle fibers, regulating the length of the intracartilaginous muscles so that the receptors are often sensitive. This activity of r-motor neurons, which is transmitted through the muscle spindle to class Ia fibers in the nerve fibers, causes a-motor neuron activity and muscle contraction in a reflex process called the r-loop.
The purpose of SPR surgery is to selectively cut the afferent class Ia fibers from the muscle spindle and block the r-loop in the spinal cord reflex, thereby relieving the spasm of the limb. The posterior root of the spinal nerve contains several fiber components, and the Ia-like afferent fibers of the myenteric plexus are one of them. Their main morphological characteristics are myelinated, thick class A fibers with a diameter greater than 11 μm and fast conduction velocity.
Fasano used electrophysiological methods to identify the major fiber components in the posterior root nerve bundle and concluded that the low-threshold nerve bundle was composed mainly of class Ia afferent fibers, with fewer other fiber components, and was cut off intraoperatively.
From the difference in voltage used to electrically stimulate the nerve bundles to induce muscle contraction during SPR, the distribution of class Ia afferent fibers in the posterior root is not uniform, in other words, the number of class Ia afferent fibers contained among the nerve bundles in the posterior root is not equal, and the nerve bundles containing more class Ia afferent fibers show their low-threshold characteristics, while the nerve bundles with less class Ia afferent fibers have a high threshold to induce muscle contraction.
VI. SPR surgical method
General anesthesia with tracheal intubation, prone position, head low and hip high, posterior median lumbar incision, resection of the spinous process and push plate. The posterior median epidural incision is made longitudinally to reveal the cauda equina, and the segment of the spinal nerve root is judged according to the position of the intervertebral foramen, generally the L5 nerve root is the thickest. The posterior roots are generally wider and flatter than the anterior roots, lighter in color, and located on the posterior side of the anterior roots, so that gentle stimulation with a detachment hook will not cause muscle contraction.
The posterior roots were divided into two to four bundles according to the natural division line, and each bundle was stimulated with a nerve threshold meter. The threshold of each bundle was measured, and the bundle with the lower threshold was cut off, and the general cut-off ratio was L2-L330-40%, L5-S140-50%, and L4 was generally not cut off. The incision is flushed, the dura is sutured, a drainage tube is placed, and the incision is closed.
VII. Positioning of the spinal nerve
Since the anterior and posterior spinal nerve roots are concentrated in the cauda equina and lack fixed anatomic landmarks, it is difficult to distinguish the segments of the anterior and posterior spinal nerve roots, which can only be identified by the position of the nerve roots out of the intervertebral foramen.
According to this anatomical feature, Peacock’s modified SPR section was moved to the cauda equina level, five vertebral plates of L2-S1 were removed, the entire cauda equina was exposed, and the anterior and posterior roots of the left and right nerves were identified according to the position of the terminal filaments. Thus, the posterior spinal nerve roots are identified and protected to prevent injury to the nerves innervating the bladder and rectum.
The posterior roots of the spinal nerve also differ morphologically in many ways from segment to segment. The degree of thickness of the posterior roots varies greatly from segment to segment. The posterior and posterior roots of the spinal nerve gradually increase in diameter from L2 to L5, with L5 being the largest in Chinese, and then gradually decrease from S1 onwards, with the anterior and posterior roots of S2-S5 always located in the posterior median part of the cauda equina, on either side of the terminal filament.
Identification of anterior and posterior spinal nerve roots
1. Morphological comparison of the corresponding anterior and posterior roots
First, morphologically, the posterior root is thicker than the corresponding anterior root, and the posterior root is 3-5 times larger than the anterior root. The posterior root is composed of 2-3 nerve bundles, while the anterior root has only one nerve bundle. The number of nerve fibers in the corresponding anterior and posterior roots also differed significantly, with the posterior root containing an average of 311682 nerve fibers compared to 94983 in the anterior root.
For each pair of corresponding anterior and posterior roots, the location is more constant, with the anterior root located ventral to the posterior root in a free inferior direction. At 1-3 cm before the corresponding anterior and posterior roots penetrate the dura mater, the anterior and posterior roots floating in the cerebrospinal fluid are encased together by the sheath and penetrate the dura mater. Xu Lin called the apposition of the anterior and posterior roots before they penetrate the dura mater as the anatomical meeting point. The anterior and posterior roots are easily distinguished here.
2. Positioning of anterior and posterior roots in SPR: In SPR, the anterior and posterior roots of the spinal nerve need to be identified according to various morphological characteristics, among which the position of the anterior and posterior roots plays an extremely important role in the identification of the anterior and posterior roots. The anterior and posterior roots are distinguished by the fact that they are free and attached to each other before they emerge from the dura. The ventral nerve root is small and single stranded and is the anterior root, while the dorsal posterior root is significantly thicker than the ventral anterior root and contains multiple strands of nerve bundles.
IX. Localization of class Ia afferent fibers in the posterior roots
The posterior root of the spinal nerve contains a variety of fiber components, and the class Ia afferent fibers of the musculocutaneous plexus are one of them. Their main morphological characteristics are myelinated, thick class A fibers with a diameter greater than 11 μm and fast conduction velocity. As for the location of class Ia afferent fibers in the posterior root, the identification of class Ia afferent fibers from the posterior root has become a central issue in SPR.
Fasano used an electrophysiological method to identify the major fiber components in the posterior root bundle, and concluded that the low-threshold bundle consisted mainly of class Ia afferent fibers, with fewer other fiber components, and was cut off intraoperatively. Xu Lin performed a histological and histochemical study of the posterior root nerve fiber bundle at low threshold and concluded that the nerve fiber bundle at low threshold was composed mainly of myelinated class Ia afferent fibers, and the class Ia afferent fibers were positive for acetylcholinesterase reaction.
From the difference in voltage used to electrically stimulate nerve bundles to induce muscle contraction during SPR, the distribution of class Ia afferent fibers in the posterior root is not uniform, in other words, the number of class Ia afferent fibers contained among the nerve bundles in the posterior root is unequal, and nerve bundles containing more class Ia afferent fibers show their low-threshold characteristic, while nerve bundles with less class Ia afferent fibers have a high threshold for inducing muscle contraction.
X. Selective indications and contraindications
Posterior spinal nerve rhizotomy, SPR surgery, is a treatment for spasticity, but not for all cerebral palsy, and it is estimated that it is feasible in almost one third of cerebral palsy patients;
The indications for surgery are:
(1) Simple spasticity with muscle tone of grade 3 or higher;
(2) No obvious fixed contracture deformity or only mild deformity;
(3) preoperative spine and limbs have some motor ability;
(4) Normal or near-normal intelligence to facilitate postoperative rehabilitation training;
(5) Severe spasticity and rigidity, which affects daily life, care and rehabilitation training.
Contraindications to SPR should be noted for.
(1)Those who are mentally retarded and cannot cooperate with postoperative rehabilitation training;
(2) Weak muscle strength and low muscle tone;
(3) Tardive dyskinesia, ataxia and torsional spasm;
(4) Severe solid contracture deformity of the limbs;
(5) Severe spinal deformity and spinal instability.