Surgery for Intractable Spasticity

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Chapter 122 Surgery for Intractable Spasticity

Spasticity is defined as a velocity-dependent resistance to passive movement of a joint and its associated musculature. It is characterized by hyperexcitability of the stretch reflex related to the loss of inhibition from descending supraspinal structures. Spasticity should not be treated just because it is present, as it may be useful for compensating for loss of motor power. Spasticity must only be treated when excess tone leads to functional losses, impairment of locomotion, or deformities. Functional neurosurgery should be considered when its harmful components cannot be controlled by physical therapy and medications.

Surgical procedures must be performed so that excess of tone be reduced without suppressing useful muscular tone or impairing any residual motor/sensory functions. In patients who retain some residual or masked voluntary motility, the aim is to re-equilibrate the balance between paretic agonist and spastic antagonist muscles so that surgery results in improvement in—or reappearance of—voluntary motor function. In patients with poor residual function, the aim is to stop evolving orthopedic deformities and to improve comfort.

Methods are classified according to whether their impact is general or focal and whether the effects are temporary or permanent (Fig. 122-1). They include intrathecal baclofen (ITB) therapy and botulinum toxin injections, along with lesioning operations aimed at peripheral nerves, dorsal roots, the spinal cord, and the dorsal root entry zone (DREZ).

FIGURE 122-1 Managing spasticity. Management is based on whether excess of spasticity is focal or general and permanent or temporary.

Because spasticity features and their consequences differ from one patient to another, the first step is to define the objective or objectives of the treatment for every patient: improvement in function, prevention of deformities, alleviation of discomfort and pain—in other words, what can be gained and what will not be obtained by surgery. These issues must be explained to the patient, relatives, and caregivers within the frame of a multidisciplinary team.

The guidelines given in the present chapter have been built from personal surgical experience of more than 1000 adult patients and more than 150 children with cerebral palsy over the last 25 years. A strong anatomic–physiologic basis and knowledge of the history and evolution of concepts about surgery for spasticity are important prerequisites before starting to deal with these complex patients.¹^–⁴

Surgical Techniques

Intrathecal Baclofen Therapy

The placement of an intrathecal drug pump assures regional delivery of medications in the cerebrospinal fluid (CSF) surrounding the spinal cord for spasticity. Baclofen is a γ-aminobutyric acid B analogue, and direct delivery to the intrathecal CSF avoids the blood–brain barrier.⁵

ITB therapy can be preceded by a test to screen for adequate response to the medication. The common standard procedure is as follows: The patient receives a bolus of 25 to 50 μg of baclofen via lumbar puncture or via a temporary lumbar catheter connected to a subcutaneous access reservoir. In the absence of a positive response, indicated by a two-point reduction in the patient’s Ashworth score 4 to 8 hours following administration, the bolus dose is increased in 25-μg increments up to a maximum bolus of 100 μg. Once a positive response is observed without unacceptable loss of function, the patient is considered to be a candidate for pump implantation. However, the bolus dose response is a poor guide to the likely daily infusion rate that will be needed subsequently. The “bolus method” can be read as “false-negative responses” in the sense that it may produce a brutal or exaggerated loss of motor power and muscle tone, which might be interpreted by the patient as a decrease in functional status. This holds especially true for the patients with the ability to walk. Therefore, the bolus test should be replaced by a continuous infusion test, using an external automatic injection pump connected to a line implanted into a subcutaneous reservoir. The test should last several days so that functional capabilities can be reliably evaluated. The initial postimplantation infusion dose depends, in part, on the effective screening dose. Typically, the initial starting dose is double the effective screening dose. The dose is then increased daily by 10% to 30% until the desired effect is achieved. The most useful criterion for dose adjustment is effective suppression of the hyperactive reflexes, such as tendon jerk, clonus, spasms, cramps, and decrease of muscle tone. Once the effective dose has been stabilized, the administration of the drug can be fine-tuned. A programmable pump allowing cyclic dose adjustments makes it possible to provide levels that correlate with the daily variability of spastic symptoms. The Synchromed pump (Medtronic, Minneapolis, MN) is the most frequently used. A detailed and well-illustrated description of the surgical technique of implantation can be found in Penn and Kroin’s article.⁶

According to a literature review of the main published series, the ITB dosage varies between 167 and 462 μg/day (average 298 μg/day), with an Ashworth score decreasing from between 3 and 4 to between 0.5 and 1.8.

A serious risk of ITB therapy is overdose, which could be irreversible because of the lack of true baclofen antagonists; therefore, this technique requires great care. Other complications include mechanical catheter migration or occlusion and infection, which require revision or removal of the system, respectively. The advantage of the ITB method is reversibility of effects. However, high cost, necessity of periodic refilling and reprogramming the pump, and geographic dependence are limitations to this conservative method.

ITB is particularly indicated for patients with severe spasticity from a spinal cord origin, especially if painful spasms are present—such as in advanced multiple sclerosis or after spinal cord injury, when physical therapy and rehabilitation do not succeed in preventing the harmful components of spasticity from appearing. ITB may also be indicated for hyperspasticity due to brain stem lesions.

In recent years, ITB therapy has joined the neurosurgical armamentarium to treat cerebral palsy patients. Due to the large size of the available pump, ITB therapy cannot easily be performed in children under 6 years of age. Children with associated choreoathetosis, hypotonia of neck and trunk, obesity, poor motivation, and/or severe multiple deformities are poor candidates for ITB therapy. For cerebral palsy patients, adequate doses (i.e., ones effective on the excess of tone that do not produce motor weakness) are often difficult to establish.

Selective Peripheral Neurotomies

Peripheral neurotomies were introduced for treatment of the spastic foot in 1912 by Stoffel.⁷ Peripheral neurotomies were made more selective by using microsurgical dissection and mapping with intraoperative electric stimulation to better identify the function of individual nerve fascicles⁸^–¹¹ (Fig. 122-2). Neurotomies consist of partial sectioning of one or several motor fascicles corresponding to the muscle or muscles in which spasticity is considered excessive. They act by interrupting the segmental reflex arch on both its afferent and its efferent pathways. Neurotomies must not involve sensory nerve fibers; even their partial section could be responsible for paresthesias and deafferentation pain. Motor branches must be clearly isolated from the nerve trunk; motor fascicles have to be dissected and identified within the nerve trunk proximally to the formation of their corresponding identifiable branch. Empirically, it is agreed that to be effective, neurotomies should section around 50% to 80% of all motor fascicles to the targeted muscles.

FIGURE 122-2 Selective peripheral neurotomy: microsurgical technique (example with median neurotomy). Operative microsurgical views show the steps of neurotomy as an example for the pronator teres, the muscular branch of the median nerve. A, After opening the epineurium, the (two) fascicles of the muscular branch for the pronator teres are identified with bipolar electric stimulation. B, According to the preoperative evaluation and subsequent program for this particular patient, 50% of the (motor) fascicles are resected, 5 mm long, to prevent regrowth of fibers.

Principles

Techniques

Surgery at the Lower Limb

Obturator Neurotomy for the Spastic Hip

Obturator neurotomy, which targets adductor muscles, should be proposed to diplegic children with cerebral palsy when walking is hampered by crossing of the lower limbs or to paraplegic patients to facilitate perineal toilet and self-catheterization.

The incision can be performed along the body of the adductor longus at the proximal part of the thigh or transversely at the hip flexion fold, centered on the prominence of the adductor longus tendon. In addition to its more aesthetic appearance, the later incision facilitates adductor longus tenotomy when necessary (Fig. 122-3A). To rapidly locate the anterior branch of the obturator nerve, which is the target, the dissection is conducted laterally to the adductor longus muscle body. The posterior branch, situated more deeply, should be spared to preserve the hip-stabilizing muscles (Fig. 122-3B).

FIGURE 122-3 Obturator neurotomy. A, The skin incision for a (right) obturator neurotomy on the relief of the adductor longus (AL) muscle (1) or at the hip flexion fold centered on the prominence of the AL tendon (2) gives a cosmetic advantage. B, Dissection of the anterior branch (AB) of the right obturator nerve (ON). The AL is retracted laterally, and the gracilis (G) is retracted medially. The AB is found anterior to the adductor brevis. B shows the adductor brevis nerve (1 and 2), AL nerve (3), and G nerve (4 and 5). The posterior branch (PB) of the ON lies under the adductor brevis and should be spared.

Hamstring Neurotomy for the Spastic Knee

Hamstring neurotomy is indicated in children with spastic diplegia to counter the accentuation of the flexion deformity of the knees observed with growth. The transverse incision is performed at the gluteal fold, centered on the groove between the ischium and the greater trochanter (Fig. 122-4A). After crossing the gluteus maximus, the sciatic nerve is identified in the depth of the incision. The branches to the hamstring muscles are isolated at the border of the nerve, primarily based on responses of the semitendinosus muscle, which is the major muscle responsible for spasticity (Fig. 122-4B).

FIGURE 122-4 Hamstring neurotomy. A, The skin incision for a hamstring neurotomy (on the right side) is located on the midline between the ischial tuberosity (IT) and the greater trochanter (GT) (1). A transverse incision can also be performed at the gluteal fold (2), centered on the groove between the IT and the GT for better aesthetic results. B, Dissection of the right sciatic nerve (SN), under the piriformis muscle (P), after passing through the fibers of the gluteus maximus muscle (GM). The epineurium of the nerve is opened, and fascicles for hamstring muscles (HF) are localized in the medial part of the nerve trunk. IGN, inferior gluteal nerve; IGA, inferior gluteal artery.

Tibial Neurotomy for the Spastic Foot

Tibial neurotomy, the most frequently neurotomy used, is indicated for the treatment of varus spastic foot drop with or without claw of toes.¹⁰ It consists of exposing all motor branches of the tibial nerve at the popliteal fossa (i.e., the nerves to gastrocnemius and soleus, tibialis posterioris, flexor hallucis longus, and flexor digitorum longus). The soleus has usually been demonstrated to be almost fully responsible for the pathogenesis of spastic foot drop, allowing sparing of gastrocnemius.¹² The incision can be vertical on either side of the popliteal fossa or transverse in the popliteal fossa. The latter gives a better aesthetic result and allows tenotomy of the gastrocnemius fascia insertion if necessary (Fig. 122-5A).

FIGURE 122-5 Tibial neurotomy. A, The skin incision for a (right) tibial neurotomy can be a vertical incision on either side of the popliteal fossa, extending inferiorly (1), or a transverse incision in the popliteal fossa (2) for a better aesthetic result. B, Dissection of the tibial nerve, and dorsal view of the right popliteal region. B shows the tibial nerve (1) and peroneal nerve (2). The sensory sural nerve (3) lies superficially just beneath the subcutaneous aponeurosis between the two gastrocnemius muscles. The medial gastrocnemius (MG) and lateral gastrocnemius (LG) nerves (4) may arise either separately from both sides of the tibial trunk or posteriorly from a common origin, sometimes including the sensory sural nerve. Each gastrocnemius nerve usually divides into two distal branches when approaching the muscle. The two soleus (S) nerves (5) may arise from a common origin or quite separately from the tibial nerve. The posterior tibialis nerve (6), like the S nerve, originates from the ventrolateral aspect of the tibial nerve but does so more distally, at the level of the S arch. Sometimes, it may originate from a common trunk with the inferior branch of the S nerve. The distal trunk of the tibial nerve (7) contains five to eight fascicles averaging 1 mm in diameter each; two thirds of them are motor fascicles, and one third are sensory ones.

The first nerve encountered is the (sensory) medial cutaneous nerve of the leg; situated adjacent to the saphenous vein, it must be spared. More deeply, the tibial nerve trunk, from which the nerves to the gastrocnemius emerge, is easily identifiable. The superior soleus nerve is situated in the midline, just posterior to the tibial nerve. The effect of a soleus neurotomy is assessed by the immediate intraoperative disappearance of ankle clonus. Then by retracting the tibial nerve trunk medially, the other branches can be identified by electric stimulation as they emerge from the lateral edge of the tibial nerve trunk. The most lateral branch is the popliteal nerve, followed by the tibialis posterior nerve and finally by the inferior soleus nerve and the flexor digitorum longus nerves. Some fascicles, often larger, can give a toe flexion response via intrinsic toe flexors (Fig. 122-5B); however, neurotomy of these branches is not recommended if they cannot be clearly individualized at this level—the more so because they may be mixed with sensory fascicles.

Anterior Tibial Neurotomy for Permanent Extension of the Extensor Hallucis

Anterior tibial neurotomy is indicated to treat the so-called permanent Babinski sign, which makes it difficult to wear shoes. A vertical incision is centered on the junction between the tibialis anterior and the extensor hallucis at the middle third of the leg. The tibial nerve is situated deeply between these two muscles, and the neurotomy is performed on the motor branch to the extensor hallucis.

Femoral Neurotomy for the Spastic Quadriceps

The quadriceps muscle is often spastic, which can interfere with gait by limiting knee flexion during the swing phase. Given its “strategic” importance in maintaining upright posture, a motor block is an essential part of the preoperative evaluation. The neurotomy concerns the motor branch to the rectus femoris and vastus intermedius muscles. The incision is horizontal at the hip flexion fold (Fig. 122-6A). The dissection passes medial to the sartorius muscle body and exposes the motor branches of the femoral nerve, first the nerve to the rectus femoris and then, more deeply, the nerve to the vastus intermedius (Fig. 122-6B). Electric stimulation is essential, given the large number of sensory fascicles of this nerve that must be spared.

FIGURE 122-6 Femoral neurotomy. A, The skin incision for a (right) femoral neurotomy, below the inguinal ligament laterally to the femoral artery (FA) (1) or horizontal at the hip flexion fold (2), gives a better aesthetic result. B, Dissection of the right femoral nerve (FN) and its branches, after opening the anterior fascia of the psoas muscle (P). The bipolar stimulation allows identification of the two or three branches to sartorius muscle (S) and three or four branches to rectus femoris muscle, which produces flexion of the hip. The nerve to the vastus intermedius can be found more deeply. FV, femoral vein.

Surgery at the Upper Limb

Pectoralis Major and Teres Major Neurotomies for the Spastic Shoulder

Neurotomy of collateral branches of the brachial plexus innervating the pectoralis major or the teres major are indicated for spasticity of the shoulder with internal rotation and adduction.¹³ For the pectoralis major, the skin incision is made at the innermost part of the deltopectoral sulcus and curves along the clavicular axis. Then the clavipectoralis fascia is opened and the upper border of the pectoralis major muscle is reflected downward. Close to the thoracoacromialis artery, the ansa of the pectoralis muscle is identified with the aid of a nerve stimulator. For teres major, the skin incision follows the inner border of teres major, from the lower border of the deltoid muscle posterior head to the lower extremity of the scapula. The lower border of the long portion of brachii triceps constitutes the upper limit of the approach. The dissection goes deeply between teres minor and major muscles. In the vicinity of the subscapularis artery, the nerve ending on teres major is identified. The nerve is surrounded by thick fat when approaching the anterior facet of the muscle body.

Musculocutaneous Neurotomy for the Spastic Elbow

Spasticity of the elbow with flexion depends on the biceps brachii and the brachialis muscles. The skin incision is performed longitudinally, extending from the inferior edge of pectoralis major, medial to the biceps brachii, and down to 5 cm (Fig. 122-7A). The superficial fascia is opened between the biceps laterally and the brachialis medially. The brachial artery and median nerve exit medially. The dissection proceeds in this space where the musculocutaneous nerve lies anterior to the brachialis muscle (Fig. 122-7B). Opening the epineurium allows the fascicles of the nerve to be dissected; the motor fascicles are distinguished from the sensitive ones using nerve stimulation.