Sunday-November 19, 2017 
    
      Home | Procedures | Pre-Surgery Form | Registration | Search | About Us  
 
FORBES magazine names YourSurgery.Com as one of it's "Best of the Web"
 
Selective Dorsal Rhizotomy
A treatment for spastic cerebral palsy

Selective dorsal rhizotomy (SDR) is a procedure for the treatment of spasticity in some children with cerebral palsy. The incidence of cerebral palsy ranges from 2 - 2.5 per thousand school-age children. Of these children about 75% will have a spastic variety. Some of these children may benefit by reducing their spasticity through selective dorsal rhizotomy.

Anatomy

  • The normal lumbar spine is composed of five building blocks called vertebrae that sit on the sacrum, which is the back part of the pelvic bone. (Figure 1)
  • Each vertebra is constructed of a body, lamina, and pedicles, which surround an opening, the spinal canal.(Figure 2)
  • A spinous process extends posteriorly (towards the back) from the lamina in the midline
  • Separating any two vertebral bodies is a soft elastic material called a disk. (Figure 3). There are five lumbar disks
  • On each side of the back of the spinal canal and linking one vertebra to the next are a series of small joints called facets
  • Through the spinal canal pass the nerve roots that emerge from the end of the spinal cord (conus medullaris) and go to form the nerves to the legs. (Figure 4)
  • Each root exits the spinal canal through a 'hole' in the side of the canal formed by two adjacent vertebrae called a foramen
  • The roots float in fluid and are contained within a fibrous sac called the dura
  • Each nerve root is composed of a dorsal (back) and ventral (front) portion. The dorsal roots conduct sensation (pain, temperature and position as well as sensation from muscles and tendons) and enter the spinal cord along its dorsal side. (Figure 5) The ventral roots conduct impulses from the spinal cord to muscles
  • A sensory nerve from muscle or tendon enters the spinal cord and connects directly to a motor nerve going to the same muscle (called a monosynaptic reflex arc). This reflex is modified by impulses from the brain and other levels of the spinal cord that result in maintaining normal muscle tone (Figure 5)
  • Both the dorsal and ventral roots are made up of smaller fibers called rootlets
  • With normal tone, muscles that move a limb in one direction (agonist muscles) are balanced by muscles that move the limb in the opposite direction (antagonist muscles)
Figure 1 - There are five lumbar vertebrae. The disks are numbered according to the number of the vertebra above it. Figure 2 - Construction of a typical lumbar vertebra.
Figure 3 - Two adjacent vertebrae showing a disk and intervertebral foramen with exiting nerve root. Figure 4 - Cross-section through a vertebra showing the spinal canal and nerve roots of the cauda equina.
Figure 5 - Diagrammatic representation of a monosynaptic reflex arc composed of a sensory neuron from muscle and tendon going into the spinal cord and connecting to a motor neuron exiting the spinal cord going to muscle. Stimulating the tendon causes the muscle to contract. The long tracts represent neurons that pass up and down the spinal cord and modify the action of the reflex arc. Injury to these tracts usually causes the reflex arc to become hyperactive (spastic). © T. Graves

Pathology

  • Spasticity is an increase in muscle tone at rest caused by a lesion in the brain or spinal cord above the level of the monosynaptic reflex arc
  • The form of the injury varies and includes tumor, stroke and trauma. A common abnormality seen in children with cerebral palsy is periventricular leukomalacia in which there are changes in the white matter of the brain that surrounds the ventricles (the spaces within the brain filled with fluid-see Shunt for Hydrocephalus)
  • The increase in muscle tone resulting in spasticity tends to affect some muscle groups more than their antagonists. For example, in the legs the muscles that flex the hips, knees and ankles tend to overcome the action of their antagonists
  • Continued severe spasticity leads to contractures (shortening) of agonist muscles and even bone deformity
  • In cerebral palsy, spasticity is of the 'tonic' type in which continued muscle contracture activates the antagonist muscles to contract. Selective dorsal rhizotomy appears to particularly help with this type of spasticity

History and Exam

  • There are two general types of spasticity- spastic diplegia and spastic quadriplegia
  • Spastic diplegia
    1. The child generally has good mental function
    2. The child is usually born prematurely
    3. Spasticity occurs in both arms and legs but primarily in the legs
    4. There may be weakness that is masked by the spasticity
  • Spastic quadriplegia
    1. The child frequently has a severe mental handicap and is unlikely to achieve independent living
    2. The child is usually born full term with a specific lesion occurring at or near birth
    3. Spasticity occurs about the same in all limbs
    4. There may be weakness that is masked by the spasticity

Tests

  • MRI may show periventricular leukomalacia
  • X-rays of the back may show scoliosis while those of the limbs may show bone deformity

Non-surgical Treatment

  • Medications. There are a variety of medications that are effective to some degree. Frequently the dose of medication required may cause significant drowsiness
  • The two most common medications used to reduce spasticity are Baclofen and Tizanidine Hydrochloride
    1. Baclofen (brand name Lioresal®) is both a muscle relaxant and antispasticity agent
      • Inhibits both monosynaptic and polysynaptic (multi-connection) reflexes at the spinal cord level
      • It has general CNS depressant properties. Because of this frequently the oral doses needed to produce an adequate effect at the spinal level are not well tolerated
      • Baclofen may be given directly into the fluid (cerebrospinal fluid, CSF) that surrounds the spinal cord (intrathecal administration). This permits effective concentrations of Baclofen around the spinal cord with blood plasma concentrations 100 times less than when given by mouth
      • Baclofen is indicated for the treatment of severe spasticity. Long term infusion is obtained by an implantable pump. This has become a common mechanism of treatment for spasticity but should be reserved for those unresponsive to oral therapy
      • Technical complications with pump implantation can be as high as 25% and include infection, catheter problems and CSF leak. The pump needs to be refilled routinely and changed when battery life is low
      • Abrupt withdrawal can result in high fever, altered mental status, exaggerated rebound spasticity, muscle rigidity, rhabdomyolysis (breakdown of muscle), multiple organ failure and even death
    2. Tizanidine hydrochloride (brand name Zanaflex®) reduces spasticity by increasing inhibition of motor neurons (nerve cells)
      • It is a short acting drug that peaks 1 to 2 hours after being taken by mouth and lasts 3 to 6 hours
      • 48% of patients report sedation and in 10% it is severe
      • Other adverse affects include hypotension (low blood pressure), liver injury and hallucinations or psychotic like symptoms
  • Botulinum toxin acts by causing a neuromuscular blocking effect
    1. To treat spasticity botulinum toxin has been found useful in multiple sclerosis, cerebral palsy, stroke, traumatic brain injury and spinal cord injury
    2. In cerebral palsy the reduction in strength and spasticity is temporary and in most patients lasts only 3 to 6 months
  • Orthopedic surgery has no influence on spasticity itself. It is directed at correcting secondary problems that result from spasticity such as muscle contractures and bone deformities
    1. It is most effective when used in combination with treatments aimed at reducing spasticity
    2. It can restore contracted muscles to their appropriate length and realign the bony skeleton so that the muscles can work better. Without treating the underlying spasticity, muscles will contracted again and the bony deformities will reoccur over time
    3. Tendon lengthening is associated with a decrease in muscle strength
  • Physical therapy is an important part of therapy of a child with cerebral palsy
    1. Increases the range of motion of joints by aggressive stretching of tight muscles to reduce contractures
    2. Reduction of reflex spasticity by a continuing rehabilitation program involving the home caregiver, usually the parents
    3. The physical therapist is an integral part of the team that decides whether SDR surgery should be performed

Indications/Contraindications

  • Selecting the appropriate patient is one of the most important aspects of successful selective posterior rhizotomy
  • Both groups of patients with cerebral palsy may be considered for SDR
  • The group with spastic quadriplegia is frequently dismissed as a candidate for SDR because these children with severe cerebral palsy are typically mentally handicapped, bedridden and depended upon caretakers
    1. The primary goal of SDR in this child is to improve caretaking such as positioning and changing a diaper
    2. SDR also reduces pain and reduces caloric consumption
    3. The goal is not to allow the child to walk or crawl. In fact, because spasticity can look like muscle movement, after the operation overall "movement" may be decreased
  • The group with spastic diplegia is usually intelligent, motivated and primarily spastic
    1. The primary goal of SDR in this child is to improve movement and gait. It will not make the child's legs normal. It will require a lifetime of physical therapy or exercise and maintenance of a healthy weight for this to be effective
    2. Screening evaluation assesses strength, range of motion, walking with and without shoes or braces, standing, bench sitting, floor sitting, sitting to standing, creeping, reaching, grasping, range of motion, and isolated joint movements
    3. The ideal candidate is purely spastic, has good underlying muscular strength, is motivated and has the appropriate family support to commit to lengthy postoperative rehabilitation therapy
    4. Typically boys range from ages 3 to 17 and girls range from ages 3 to 13
    5. Patients should not be operated on before three years of age. Between 3 and 5 years is ideal
    6. Because spasticity can look like muscle movement, after surgery overall "movement" may be decreased and require intensive therapy to maintain a good pattern of movement
      • The child may go backwards and start to crawl again before subsequently walking
      • The child may require a walker, braces or other assistive devices (cane) for mobility
      • The operation is not a cure. While it will reduce the need for further orthopedic surgery, it will not eliminate the need for orthopedic surgical treatment
  • SDR cannot be successful in the nervous disorders with non-spastic muscular contractions such as athetosis or chorea

Surgical Procedure

  • A lifetime of therapy and a commitment to an active lifestyle are critical to the long term success of this operation
  • Children who undergo SDR often have significant medical problems such as underlying lung and feeding problems. These problems make the procedure and general anesthesia riskier. These children may develop lung or gastrointestinal problems that prolong their stay and make them more critically ill. Any underlying medical conditions are evaluated to decrease the risk of the general anesthetic
  • The operation is done under light general anesthesia without the use of muscle relaxants than might interfere with electromyographic (EMG) monitoring during the surgery
  • Electrodes are placed in the muscle groups of the lower extremities
  • A urinary catheter is placed for drainage
  • The child is placed in the prone position (face down)
  • An incision is made in the midline from the level of the first lumbar (L1) vertebrae to the upper sacrum following which the muscles are elevated off of the spinous processes and lamina of L1 to L5
  • The laminae from L1 to L5 are cut as wide as possible with a bone cutting tool (Figure 6) and the laminae with attached ligaments removed as a single unit. The laminar unit is put aside to be replaced at the close of the operation
  • The lamina of S1 is removed but not preserved
  • The dura is opened in the midline (Figure 7), the cauda equina exposed and CSF removed by gentle suction (Figure 8)
  • The S1 and S2 nerve roots are identified anatomically and by electrical stimulation by EMG
  • The dorsal root is then separated from the ventral root from L2 to S1 on both sides (Figure 9 and Figure 10)
  • Threshold electrical response for each dorsal root is determined following which the dorsal root is separated into rootlets
  • The rootlets are stimulated individually and muscle movement and EMG responses noted. Rootlets causing abnormal responses are cut
  • One variation of the procedure involves doing a limited laminectomy over the conus medullaris at the L1 - L2 level and identifying all the posterior roots at this level
  • The dura is sutured closed
  • The laminar unit is then replaced and secured with sutures placed through the bone (laminoplasty). (Figure 11) In some cases the laminae are not replaced (laminectomy)
  • All bleeding is controlled and the muscles and skin brought together with sutures
Figure 6 - The laminae are cut as wide as possible with a bone cutting tool and the laminae with attached ligaments removed as a single unit. © T. GravesFigure 7 - The dura is opened in the midline. © T. Graves
Figure 8 - The dura is spread to expose the cauda equina and the individual roots that exit at each spinal level. © T. GravesFigure 9 - Each nerve root is separated into its dorsal and ventral roots and the dorsal root separated into its individual rootlets. © T. Graves
Figure 10 - Photos taken at surgery. Left. Individual nerve root isolated from the rest of the cauda equina and separated into dorsal and ventral roots. Courtesy A. Marlin, MD. Figure 10 - Right. The dorsal root is separated into individual rootlets. Courtesy A. Marlin, MD
Figure 11 - The lamina are replaced and secured with sutures. © T. Graves

Complications

  • The most common long-term complication is spotty sensory loss in the lower extremities and hypersensitivity (increased sensitivity) of the feet
  • The ability to move the legs may be worse after surgery. Especially since spasticity can look and behave like underlying muscle strength. When the spasticity is removed, there can be less overall movement of the legs. Although this is an operation on the "feeling" nerves (the dorsal roots), there is a risk of the "moving" nerves (ventral roots) being damaged during surgery and this could directly affect motor function. The chance of this occurring is less than one percent, but it is not zero. Intensive therapy is required to build normal muscle and to learn how to move the legs. It is like getting a new set of legs and learning how to use them all over again
  • There may be some areas of abnormal sensation and the feet may actually be hypersensitive (more sensitive when standing on a cold floor, for example). Complete loss of sensation in an area is also possible with this surgery, but less likely (<1% chance)
  • Bowel and bladder function may be altered such that if the child urinates independently, the child may permanently require intermittent catheterization to empty the bladder. The volume of urine held by the bladder, the ability to stay dry between catheterizations and bowel function may all be permanently changed by the surgery. Immediate though usually transient retention of urine occurs in less than one percent of cases
  • Sexual function may be permanently altered by the surgery. Males may not have erectile function as a result of the surgery. Females may have reduced sensation in the genitals
  • Scoliosis and/or spinal instability may develop or progress after the operation and this could require a major orthopedic operation some time in the future. Scoliosis, which is common in cerebral palsy, can also occur in the long-term after surgery. It is difficult to relate this to the laminectomy itself though in large numbers of laminectomies, this complication does occur, but is least frequent in lumbar laminectomies
  • SDR will not completely eliminate all the spasticity, nor will it fix any underlying orthopedic abnormalities. This operation will not make the legs normal
  • While it is known that this operation will reduce the overall number of orthopedic procedures required in a lifetime, it will not eliminate the need for orthopedic procedures in the future
  • There is a small chance of CSF leaking from the dura, which holds the spinal cord and nerve roots. If this develops, there is an increased risk of infection. Rarely, a second procedure may be required to repair the leak. If a leak develops, the hospital stay is usually longer to allow for treatment. CSF leak occurs in less than one percent of cases
  • There is less than a 1% risk of infection with this operation. If an infection develops it can be serious, like meningitis, although this is uncommon. If the patient has a shunt for associated hydrocephalus, it can become infected secondarily and require treatment
  • The blood loss associated with this operation does not usually require a transfusion, but there is always a possibility of a transfusion with this or any operation

Postoperative care

  • Pain control is very important. Intravenous narcotics are usually necessary for 12 to 36 hours
  • Sometimes dysesthesias (abnormal sensations) are present for the first two or three days after surgery. These are usually treated with steroids, bed cradles and stockings
  • As soon as pain tolerance allows physical therapy is begins. The program is planned preoperatively depending on the functional goals in each case. In order to achieve maximal gains, a well structured rehabilitation program is essential

After care

  • Patients with cerebral palsy tend to be weak. An intensive rehabilitation program is initially essential to obtain maximal function
  • After this is done, continued exercise and participation in functional activities are essential to maintain strength and continue functioning at maximal potential
  • The exact type of rehabilitation program will be dependent on the functional goals, the child's circumstances and resources available