Ablative Surgery for Spasticity

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CHAPTER 90 Ablative Surgery for Spasticity

Spasticity can be defined as a velocity-dependent resistance to passive movement of a joint and its associated musculature. Spasticity is characterized by hyperexcitability of the stretch reflex related to the loss of inhibitory influences from descending supraspinal structures. Spasticity should not be treated just because it is present because it may serve to compensate for loss of motor power. Rather, spasticity should be treated only when excessive tone leads to functional disability, impaired locomotion, or deformities. Neurosurgical intervention should be considered when the disability cannot be reduced by physical therapy and medications alone.

Management of spasticity includes not only intrathecal baclofen therapy and botulinum toxin injections but also destructive surgery directed at peripheral nerves, dorsal roots, the dorsal root entry zone (DREZ), and the spinal cord. Methods of surgical management are classified according to whether their impact is general or focal and whether the effects are temporary or permanent (Fig. 90-1).

FIGURE 90-1 Managing spasticity. Management is based on whether the spasticity is focal or generalized and whether the effect of treatment is permanent or transient.

Neurodestructive procedures must be performed so that excessive tone is reduced without suppressing useful muscular tone or impairing any residual motor/sensory functions. In patients who retain some masked voluntary motility, the aim is to re-equilibrate the balance between paretic agonist and spastic antagonist muscles so that treatment results in improvement in (or the reappearance of) voluntary motor function (Fig. 90-2). In patients with poor residual function preoperatively, the aim is to halt the evolution of orthopedic deformities and improve comfort.

FIGURE 90-2 Gait analysis. Preoperative polyelectromyography shows desynchronized activity in the triceps surae, with abnormal co-contractions of the tibialis anterior and triceps surae (left). After tibial neurotomy (right), muscular activity reappears in the tibialis anterior with normal alternation between contraction of the triceps surae at the end of the stance phase and contraction of the tibialis anterior during the swing phase.

Our team has treated more than 1000 patients with spasticity over the past 20 years. We believe that teams dealing with spasticity should have all of the technical modalities at hand.¹ Intrathecal baclofen therapy, which is discussed in detail in another chapter of this book, is indicated primarily for paraplegic or tetraplegic adult patients with diffuse spasticity, especially of spinal origin, although it can also be used to treat spasticity related to cerebral palsy in older children. Ablative operations are indicated for focal spasticity of the limbs when treatment with botulinum toxin injections proves insufficient. Peripheral neurotomy is justified when harmful spasticity affects one or a few muscular groups. A preliminary test consisting of an anesthetic block may help in the decision-making process by mimicking the effect of the neurotomy. When harmful spasticity affects an entire limb or in the setting of hemiplegia or paraplegia, surgery directed at the dorsal roots (dorsal rhizotomy) or the DREZ (microsurgical DREZotomy) may be the solution. Complementary orthopedic operations are frequently needed in patients with associated irreducible contractures, tendon retractions, joint deformities, or any combination of these problems.

Selective Peripheral Neurotomy

Peripheral neurotomy was introduced for the treatment of a spastic foot by Stoffel.² Later, peripheral neurotomy was made more selective by using microsurgery and mapping via intraoperative electrical stimulation to better identify the function of individual nerve fascicles (Fig. 90-3).³^,⁴ Neurotomy consists of partial sectioning of one or several of the motor branches (or fascicles) corresponding to the muscle or muscles in which spasticity is considered excessive and works by interrupting the segmental reflex arc in both its afferent and efferent limbs. Neurotomy must not include sensory nerve fibers because even partial sectioning of them can result in deafferentation pain. Either motor branches must be clearly isolated from the nerve trunk, or the fascicles must be dissected and identified within the nerve trunk several centimeters proximal to the formation of an identifiable branch. On an empirical basis it is agreed that neurotomy must include sectioning of approximately 50% to 80% of all the branches to a targeted muscle for it to be effective.

FIGURE 90-3 Selective peripheral neurotomy: microsurgical technique (median neurotomy shown as an example). Operative microsurgical views show the steps in neurotomy for the pronator teres muscular branch. A, The muscular branch of the pronator teres is identified by electrical motor stimulation. B, In line with the preoperative evaluation and subsequent plan for this particular patient, 50% of the isolated motor fascicles are resected, 5 mm in length, near the muscle to ensure that only its muscular branches are divided. C, The proximal stump is coagulated with bipolar forceps to prevent the regrowth of fibers.

Surgical Principles *

Surgical Techniques

Surgery on the Lower Limb *

Obturator Neurotomy for the Hip

Obturator neurotomy eliminates spasticity of the adductor muscles. It is often proposed for diplegic children with cerebral palsy when crossing or “scissoring” of the lower limbs hampers their walking. It can also be performed on paraplegic children to facilitate perineal washing, toilet, and self-catheterization. The incision can be made along the body of the adductor longus at the proximal portion of the thigh or transverse in the hip flexion fold, centered on the prominence of the adductor longus tendon. In addition to its more aesthetic appearance, the latter incision facilitates adductor longus tenotomy when necessary (Fig. 90-4A). The dissection is conducted lateral to the adductor longus muscle body to rapidly locate the anterior branch of the obturator nerve. The posterior branch is situated more deeply and should be spared to preserve the hip-stabilizing muscles (Fig. 90-4B).

FIGURE 90-4 Hamstring neurotomy. A, The skin incision for 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 made in the gluteal fold (2) centered on the groove between the ischial tuberosity and the greater trochanter 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 (GM). The epineurium of the nerve is opened and fascicles for the hamstring muscles (HF) are located at the medial part of the nerve trunk. IGA, inferior gluteal artery; IGN, inferior gluteal nerve.

Hamstring Neurotomy for the Knee

Hamstring neurotomy is indicated for children with spastic diplegia to counter the accentuation of flexion deformity of the knees observed with growth. A transverse incision is made in the gluteal fold, centered on the groove between the ischium and greater trochanter (Fig. 90-5A). After crossing the fibers of the gluteus maximus, the sciatic nerve is identified in the depth of the incision. Branches to the hamstring muscles are isolated at the border of the nerve, primarily based on motor evoked responses of the semitendinosus muscle, which is often the major muscle responsible for spasticity (Fig. 90-5B).

FIGURE 90-5 Obturator neurotomy. A, Skin incision for right obturator neurotomy along the relief of adductor longus (1) or in the hip flexion fold centered on the prominence of the adductor longus tendon (2), which gives a cosmetic advantage. B, Dissection of the anterior branch (AB) of the right obturator nerve (ON). The adductor longus (AL) is retracted laterally and the gracilis (G) medially. The nerve is anterior to the adductor brevis (AB). 1 and 2, adductor brevis nerve; 3, adductor longus nerve; 4 and 5, gracilis nerve. The posterior branch (PB) of the obturator nerve lies under the adductor brevis (AB) and should be spared.

Tibial Neurotomy for the Foot

Tibial neurotomy is indicated for the treatment of varus spastic footdrop with or without claw toes. It consists of exposing all motor branches of the tibial nerve at the popliteal fossa (i.e., nerves to the gastrocnemius and soleus, tibialis posterior, popliteus, flexor hallucis longus, and flexor digitorum longus). In a majority of patients, the soleus is almost completely responsible for the pathogenesis of spastic footdrop, so the gastrocnemius may be spared.⁸ The incision can be made vertical on either side of the popliteal fold and extended inferiorly or transversely in the popliteal fossa to yield a more aesthetic result. In addition, the latter incision allows high tenotomy of the gastrocnemius fascial insertion to be performed at the end of the procedure if necessary (Fig. 90-6A).

FIGURE 90-6 Tibial neurotomy. A, Skin incision to expose the tibial nerve. A vertical incision is made at the right popliteal fossa (1), or a transverse incision is made in the popliteal fossa fold (2) for a better long-term aesthetic result. B, Dissection of the tibial nerve, dorsal view of the right popliteal region. 1, Tibial nerve; 2, peroneal nerve. The sensory sural nerve (3) lies superficially just beneath the subcutaneous aponeurosis between the two gastrocnemius muscles. The medial and lateral gastrocnemius nerves (4) may arise either separately from the 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. One or two soleus nerves (5) may arise from a common origin or separately from the tibial nerve. The posterior tibialis nerve (6), like the soleus nerve, originates from the ventrolateral aspect of the tibial nerve, but more distally at the level of the soleus arch (5). Sometimes it may originate from a common trunk with the inferior branch of the soleus 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 with a third being sensory fascicles. LG, lateral gastrocnemius; MG, medial gastrocnemius; S, soleus.

The first nerve encountered is the sensory medial cutaneous nerve of the leg, which is located immediately anterior 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. An effective soleus neurotomy is marked by the immediate intraoperative disappearance of ankle clonus. By retracting the tibial nerve trunk medially with a traction adhesive tape, the other branches can then be identified by electrical 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 flexor digitorum longus nerves. Some fascicles, often larger, can give a toe flexion response via the intrinsic toe flexors (Fig. 90-6B). However, neurotomy of these branches is not recommended if they cannot be clearly individualized because they may be mixed with sensory fascicles.

Anterior Tibial Neurotomy for the Extensor Hallucis

This procedure is indicated for the treatment of permanent extension of the hallux (permanent Babinski sign), which makes wearing shoes difficult. It may sometimes be indicated after unjustified sectioning of the flexor hallucis tendon in which a disequilibrium is created that favors the extensor. 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 Quadriceps

Femoral neurotomy is indicated to treat excessive spasticity of the quadriceps muscle. This 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 involves the motor branch to the rectus femoris and vastus intermedius muscles. A horizontal incision is made in the hip flexion fold (Fig. 90-7A). 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. 90-7B). Electrical stimulation is essential given the large number of sensory fascicles of this nerve that must be spared.

FIGURE 90-7 Femoral neurotomy. A, Skin incision for right femoral neurotomy, below the inguinal ligament, lateral to the femoral artery (1) or horizontal in the hip flexion fold (2) for better aesthetic results. B, Dissection of the right femoral nerve (FN) and its branches after opening the anterior fascia of the psoas muscle (P). Bipolar stimulation allows identification of the two or three branches to the sartorius muscle (S) and the three or four branches to the rectus femoris muscle, which produces flexion of the hip. The nerve to the vastus intermedius can be found more deeply. FA, femoral artery; FV, femoral vein.

Surgery on the Upper Limb

Pectoralis Major and Teres Major Neurotomy for the Shoulder

Neurotomy of collateral branches of the brachial plexus innervating the pectoralis major or the teres major is indicated for spasticity of the shoulder with internal rotation and adduction.⁹ For the pectoralis major, the skin incision is made at the innermost part of the deltopectoral sulcus and curves along the clavicular axis. The clavipectoralis fascia is then opened and the upper border of the pectoralis major muscle reflected downward. Close to the thoracoacromialis artery, the ansa of the pectoralis muscle is identified with the aid of a nerve stimulator. For the teres major, the skin incision follows the inner border of the teres major from the lower border of the posterior head of the deltoid muscle to the lower portion of the scapula. The lower border of the long portion of the brachii triceps constitutes the upper limit of the approach. The dissection is carried deep between the teres minor and major muscles. In the vicinity of the subscapular artery, the nerve ending on the teres major is identified. The nerve is surrounded by thick fat when approaching the anterior facet of the muscle body.