O

Table 2. Surgical targets for spasticity in the peripheral nervous system

Ablative

Procedure

Target

Efficacy

Morbidity

Afferent of

Efferent

Yes Yes

Yes Yes No

Posterior rhizotomy

Selective posterior lumbosacral rhizotomy

Anterior rhizotomy

Peripheral (selective) neurectomy

Peripheral nerve or motor-point block

Entire posterior nerve root L2-S2 Selected posterior rootlets (EMG-guided)

L2-S2

Anterior nerve roots (lumbosacral or cervical)

Peripheral nerve or motor branch

Peripheral nerve or muscle group

Good for spasticity

Excellent in selected cases

Good for spasticity

Good in selected cases (tibial or musculocutaneous n.) Provides temporary relief

Unacceptable sensory loss

Potential for sensory loss; inadequate relief spasticity

Unacceptable flaccid paralysis and muscle atrophy

Sensory loss; weakness

Causalgia, permanent dysesthesias or nerve deficit

Table 3. Surgical targets for spasticity in the central nervous system

Procedure

Target

Efficacy

Morbidity

Ablative

Stereotactic thalamotomy

Pulvinar or VL nucleus of thalamus

Poor

Potential neurological deficit

Stereotactic dentatotomy

Dentate nucleus of cerebellum

Variable

Potential neurological deficit

Cordectomy

Low thoracic spinal cord

Variable

Complete motor, sensory loss; bladder dysfunction

Myelotomy

Descending motor tracts in thoracolumbar spinal cord

Variable, may be indicated for severe spinal-cord injury

Potential sensory deficit, bowel/ bladder dysfunction

DREZotomy

Dorsal root entry zone of lumbar spinal cord

Similar to selective posterior rhizotomy

Increased risk of weakness, sensory loss

Nonablative

Intrathecal baclofen pump

Subarachnoid space

Good

Catheter-related problems; infection; respiratory failure

Deep brain stimulation

Basal ganglia

Experimental

Risk of deep hemorrhage, system complications

Cerebellar stimulation

Cerebellum

Variable

Infection; device failure

Spinal-cord stimulation

Dorsal columns of spinal cord, thoracic or cervical

Variable

Infection; device failure

This destroys nociceptive and myotactic fibers, sparing the lemniscal fibers and resulting in interruption of the spinal reflex arc.

Selective Posterior Rhizotomy

Selective posterior rhizotomy interrupts the afferent limb of the stretch reflex at the posterior spinal nerve root or rootlet level. The original procedure as described by Foerster in 1913 involved complete division of posterior roots from L2 to S2, sparing L4 for knee extension, but resulted in unacceptable proprioceptive and sensory deficits. The modern procedure involves selective division of posterior rootlets demonstrating abnormal intraoperative electromyogram (EMG) responses to stimulation.

Preoperative Evaluation

Careful preoperative evaluation and patient selection is of foremost importance in ensuring good functional outcomes. Because selective posterior rhizotomy only addresses spasticity, it is indicated only for patients in whom spasticity is the major type of motor dysfunction. Attention is given to assessment of the patient's muscle tone, range of motion, posture, gait and functional capacity. The degree of spasticity should be measured objectively (Table 4). It is important to confirm that the disturbance in muscle tone is due to spasticity and not to weakness, dystonia or rigidity, which do not respond well to rhizotomy. Rhizotomy may exacerbate weakness in children who have undergone previous procedures such as tenotomy, tendon lengthening or neurectomy. The ideal candidate for rhizotomy is a spastic diplegic child who is able to ambulate independently with a scissoring gait, flexed hips and knees, and an equinus foot posture. Significant fixed contractures or weakness should not be present. Low-functioning, severely affected spastic quadriplegic patients may also benefit from rhizotomy because the procedure may also facilitate care and prevent progressive contractures or skeletal deformities.

Operative Technique

The patient is positioned prone with EMG needle electrodes placed into five muscle groups of each leg and the external anal sphincter muscle. Long-acting neu-romuscular blocking agents are avoided because intact neuromuscular activity is required for intraoperative EMG. An L2 to S1 laminectomy or laminotomy is performed to expose the entire cauda equina. The posterior nerve rootlets between L2

Table 4. Ashworth spasticity scale

Grade Description

Table 4. Ashworth spasticity scale

Grade Description

1

Normal Tone

2

Slight increase in tone, a palpable "catch" in passive flexion

or extension

3

Moderate increase in tone, difficult passive movements

4

Marked increase in tone, very difficult passive movements

5

Rigid in extension or flexion

and S2 are electrically stimulated and selectively divided based on intraoperative EMG responses and visual/tactile observation of muscle responses. In a typical rhizo-tomy procedure, between 50 and 75 rootlets are stimulated and, depending on the degree of spasticity, between 25% and 50% are then divided. There are usually 2 to 4 posterior rootlets at the L2 level, with an increasing number at each subsequent level down to S1, where there are usually between 8 and 11. The S2 root is the first to be smaller than the preceding root and usually contains 2 to 6 very fine rootlets.

Postoperative Care

The child is nursed lateral-recumbent or supine to reduce the chance of incisional CSF leakage. A Foley catheter is continued for several days to keep the dressing dry. Physical therapy for bed mobility is started at postoperative day 3, and increased to out-of-bed transfers and gait therapy at postoperative day 5.

Expected Outcomes and Potential Complications

Reduction of spasticity can be observed clinically immediately after surgery. Many published studies have documented decreased spasticity and improvements in ambulation, functional ability and balance while sitting and standing. Intelligent, ambulatory children with spastic diplegia who have good trunk control and no significant weakness generally do best. Follow-up studies demonstrate preserved long-term functional improvement and reduction of spasticity and acceptable complication rates. Dysesthesias and paresthesias are common in the postoperative period but are usually temporary and not disabling. Inadequately relieved spasticity is another potential complication, followed by infection, fever, cystitis and CSF leakage.

Peripheral Neurectomies

Similar to neuromuscular blockade, surgical division of the peripheral nerve innervating a spastic muscle weakens muscle contraction. This may provide a long-term reduction in spasticity, but often at the cost of undesirable side effects such as weakness, atrophy and sensory loss because the peripheral nerve contains both motor and sensory fibers. Nevertheless, the most common procedure performed in the upper extremity for spasticity is neurectomy of the musculocutaneous nerve to relieve spastic elbow flexion. Peripheral neurectomies in the lower limbs include the anterior obturator neurectomy for excessive hip adduction, and tibial neurectomy for spastic calf muscles causing excessive ankle extension. Preoperative motor block often provides a good correlation with the expected postoperative result and should be performed prior to neurectomy.

Chronic Intrathecal Baclofen Infusion

Centrally-mediated side effects of baclofen, such as confusion and drowsiness, often limit effective oral administration. However, intrathecal administration can achieve higher concentrations of baclofen in the spinal subarachnoid space with less severe CNS side effects. Over the past decade, indwelling programmable pumps have been implanted for the delivery of intrathecal baclofen. There is reported long-term effectiveness in patients with spasticity arising from spinal-cord injury, hypoxic and traumatic brain injury, multiple sclerosis and CP.

Preoperative Evaluation

A test dose of intrathecal baclofen by lumbar puncture is used to assess for efficacy. The typical dose is 50 ^g, but may be modified based on patient size. If a satisfactory decrease in spasticity is observed, the placement of a permanent pump for continuous infusion of baclofen should be considered. When successful, the effect on spasticity in the lower extremities usually begins in 2 hours, peaks at 4 hours, and returns to baseline in about 8 hours. A limitation of the test dose procedure is that although the brief effect on lower extremity spasticity can be quantified with a neurologoical exam, functional improvements are difficult to quantify without actual engagement in everyday motor tasks.

Operative Technique

The pump and reservoir are placed in a subcutaneous pocket above the rectus fascia in the lower abdomen, and the catheter is tunneled subcutaneously to the lumbar spine and introduced into the lumbar subarachnoid space. For the relief of upper extremity spasticity, the catheter may be directed more cephalad to the midthoracic level. Two pump sizes are available: the standard pump with an 18 cc reservoir, and a smaller pump with a 10 cc reservoir (for smaller children, i.e., less than 18 kg). Pump battery life is roughly 5 years and the rate of infusion or concentration of baclofen can be easily adjusted when the pump reservoir is accessed percu-taneously for refills.

Expected Outcomes and Potential Complications

Complication rates vary in reported series, but catheter-related problems and side effects from baclofen toxicity are common. In one large series there was a 29% re-operation rate (19 procedures in 15 of 66 patients), mainly for catheter-related problems such as occlusions, fractures, punctures and displacement. Other complications include side effects from intrathecal baclofen such as hypotonia, urinary retention, worsened constipation, nausea and drowsiness. Symptomatic respiratory compromise has been reported at a rate of approximately 10%, and coma is rare.

Advantages of intrathecal baclofen include the reversible, nonablative nature of the procedure, highly effective reductions in lower extremity spasticity, and improvements in overall function. Disadvantages include the costly nature of pump refills, pump replacements for battery failure, and the high complication rate of the system. Sudden withdrawal of high-dose intrathecal baclofen in the setting of mechanical pump or catheter failure can be dangerous, sometimes necessitating temporary lumbar subarachnoid catheter infusions of baclofen until the pump system can be revised. Severe overdoses are treated by giving ventilatory support, stopping the pump, and draining of 30 to 50 cc of CSF to clear the baclofen.

Central Procedures for Spasticity

Implanted Stimulators

Early reports of success with chronic electrical stimulation of the cerebellum in an attempt to modify cerebellar outflow and increase inhibitory influences on the

anterior horn motor neuron have not been substantiated. Reports of epidural dorsal spinal cord stimulation applied to spasticity patients have described variable results.

Stereotactic Procedures

Stereotactic lesions in the cerebellum that interrupt outflow from the dentate nucleus may result in diminished muscle tone by reducing the unbalanced excitatory influences on the anterior horn cells. Published series are conflicting, with the consensus opinion favoring cerebellar nuclei-lesioning procedures for hyper-kinetic disorders such as athetosis, chorea, tremor and ballismus rather than spas-ticity treatment.

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