Selective posterior rhizotomy (also called functional dorsal rhizotomy) is a neurosurgical technique being used increasingly to treat spasticity (tightness in the muscles that resists rapid movement), especially in children with cerebral palsy. The procedure evolved from work done in the late 19th century. It is based on the assumption that spasticity results from loss of the modulating influences of nerves from the brain on the spinal cord's reflex circuits.
There are a multitude of these reflex circuits, an example of which is the tendon jerk reflex (straightening of the leg in response to tapping the knee with a hammer). In this case, sensors within the large muscle in the front of the thigh perceive the stretching of the muscle, which results when its tendon is tapped by the hammer. A nerve impulse is sent to the spinal cord, where it stimulates a nerve which sends a signal back to the thigh muscle, causing it to contract and pull the leg straight. Nerves from the brain control these reflex circuits, allowing us to voluntarily move a muscle without its reflexively tightening up. With injuries to the spinal cord or brain (e.g., cerebral palsy), these descending nerves from the brain can be damaged, resulting in an alteration of the controlling influences on the reflex circuits. The result is a spreading activation of nerves within the spinal cord and a subsequent contraction of numerous muscles throughout the body. This creates the typical picture of limb spasticity.
Bracing
Physical Therapy—Bracing
Bracing is an important adjunct to therapy, and the physical therapist plays an important role in brace prescription. Bracing can change the biomechanical alignment of the foot and lower limb, thereby placing the muscles in a better position to work most efficiently. A muscle is most efficient (or strongest) at its mid range of contraction. The normal biomechanical alignment of the lower extremity places muscles at their mid ranges so they are most efficient during ambulation. Bracing can assist in this goal. Below is a list of braces commonly used post rhizotomy, followed by a brief description of each:
Long leg brace (pelvic band with single lateral detachable uprights, hinged joint ankle foot orthoses): This is the most common brace used post rhizotomy. This brace places the limb in a neutral alignment controlling the tendency for adduction (legs being too close together) and internal rotation (knees and feet turning inward) at the hip. At the same time, it places the limb at optimal alignment for muscle contraction. Over time, the brace can assist in changing the movement pattern by repetitively having the child move properly. Also, muscles will be strengthened as the child walks more frequently and for longer distances. Many children, with the assistance of this brace, have become community ambulators with good patterns of movement. The brace is detachable, allowing the child to just use the ankle foot orthosis to help carry over the new movement patterns without the assistance of the uprights. Detaching the brace should be done under the guidance of the physical therapist. Weaning off the uprights is a gradual process requiring the cooperation of the child, family, therapist and school teachers. Some children require control of hip internal rotation only. They have adequate ability to control hip adduction. In this case the pelvic band can be split with a joint in the middle. This allows the child more mobility to freely abduct (spread apart) his or legs, but the tendency to internally rotate is still controlled.
Hinge joint ankle foot orthoses: This brace controls foot position and allows ankle motion. Often the brace limits plantar flexion (pointing the toe). After rhizotomy, the hinge joint ankle foot orthoses is often recommended, as the child can now control and benefit from ankle motion during gait.
Anti-crouch ankle foot orthoses: This brace has an anterior shell. It assists in giving the child extension at the knee. This brace is appropriate for a child who tends to maintain a flexed knee position, but has good control and adequate range of motion at the ankle.
Solid ankle foot orthoses: This brace is often ordered for a very involved child with limited walking ability and dependence on a wheelchair. This brace maintains good alignment of the foot and prevents contractures from developing in the gastrocnemius soleus (calf) muscles.
Supra-malleolar orthotic: This brace ends just above the ankle bones. It is appropriate for a child who has good hip and knee control, but still requires minimal support of the ankle and foot.
Footplate orthotic: This is the least restrictive brace. It is given to a child who has good hip, knee and ankle control. It maintains good arch support of the foot.
The goal of bracing is to assist the child in becoming as independent as possible with good limb alignment. Walking for long periods in poor alignment can aggravate and worsen preexisting orthopaedic deformities, such as subluxed or dislocated hip joints. Changing bracing is a weaning process. Fatigue can be a big consideration. The child may be able to maintain good patterns of movement for only short periods of time; therefore, changing a brace may require many weeks of weaning to allow time for the child's limb to strengthen.
Treatment
Physical Therapy—Treatment
The therapist’s assessment includes the following areas:
- Muscle tone
- Joint mobility (passive range of motion, or PROM)
- Strength
- Biomechanical alignment
- Motor control
- Other influences
Motor tone: The therapist determines if there is any abnormal tone in the upper and lower extremities. Also, the therapist will evaluate the trunk tone. It is common that children with cerebral palsy generally have low-tone trunk musculature. Tonal influences should be assessed at rest and also during active movements. Treatment will revolve around inhibiting or relaxing muscles in which there is high tone and strengthening muscles where there is weakness and/or low tone.
Joint mobility (passive range of motion, or PROM): Passive range of motion in all joints should be assessed. Also, joint capsule range should be assessed. Where tightness and/or limitation exists, stretching and/or mobilization should be initiated. Muscle stretching should be done in two ways: passively, to gain more range, and then actively, to help maintain range gains. Active lengthening is most effective in maintaining the range gains achieved in therapy.
Strength: It is well documented that children with cerebral palsy have muscle atrophy or weakness. The weakness is present in all muscles but is most severe in the muscles that oppose the spastic muscles. After rhizotomy, muscle weakness is uncovered, therefore, strengthening is a major component to rehabilitation after rhizotomy. Strengthening will focus on two areas. First, the muscle must be strengthened through its full excursion of movement. Children with spastic cerebral palsy tend to move in mid-range of muscle excursion, and are therefore weakest at the end range of movement. Second, the muscle endurance must be built up. This can be accomplished by increasing repetitions of exercises, encouraging walking for longer distances, or bike or tricycle riding. We have begun using therapeutic electrical stimulation (TES) as an adjunct in muscle strengthening post rhizotomy.
Biomechanical alignment: This is a clinical assessment of bony structure. The therapist will assess the alignment of the bones in relation to other bony structures. Some bony alignment problems can be addressed and treated through bracing. For example, a child whose foot is very pronated will tend to compensate for the pronation by flexing at the knee and internally rotating and flexing at the hip. Proper bracing that corrects the foot posture will also help to correct the knee and hip joints. Some biomechanical alignment problems can be corrected only by changing the bony structure itself through orthopaedic surgery. Examples of corrective bony surgeries are varus derotation osteotomies of the femur or de-rotation osteotomies of the tibia.
Motor control: The therapist will observe how the child moves, and treatment will focus on changing or facilitating correct movement patterns. Some of these movement patterns are difficult to correct because they have been ingrained in the child's movement repertoire for years. Changing movement patterns can be likened to learning proper techniques for sporting activities (for example, learning and perfecting a golf swing or tennis serve). Learning the proper techniques for any motor activity requires a strong desire to achieve the proper movement pattern and the ability to concentrate on the movement pattern.
Other influences: Other influences that will affect the surgical outcome and are included in the therapeutic assessment include the child's integration of sensory information from the environment, the child's motivation level, and the child's cognitive level of function. Some children have aversions to certain types of sensory input, such as fear of heights or an aversion to some types of sensation, such as spinning motions, textures, and so on. Cognitive and motivation impairments can also limit treatment outcomes. A child who has difficulty understanding or cooperating with treatment may have compromised outcomes.