Meningomyelocele

Determination of Level

Determining the level of neurologic involvement in meningomyelocele is crucial. It permits the evaluation of the following five major functional criteria:

Determination of the extent of muscular imbalance around each of the major joints of the lower extremity
Evaluation of the degree and character of any deformity
Assessment of remaining function and the need for bracing or surgery
Evaluation of bladder and bowel function
Baseline analysis for long-term follow-up

Although the defect frequently causes a total loss of innervation below it, this is not always so. In many cases, there will be partial innervation of several levels below the major level of involvement, or partial denervation of several levels above it. It is therefore necessary to determine not only the level that seems to be primarily involved but also the extent to which other levels may be affected. The level of involvement can be determined through muscle testing, sensory testing, reflex testing, examination of the anus, and evaluation of bladder function.

It is easier to test a newborn infant than a child. In the infant, the skin can be pinched to provide a painful stimulus and the muscle being tested can be palpated for contraction: the muscle will either react (positive indication of muscle function) or will remain inactive (indication of no muscle function). Although it is difficult to grade muscle strength accurately in an infant, it will be evident from palpation and observation whether the muscle is functioning at a minimum of grade 3: movement possible against gravity, but not against resistance by the examiner. The infant’s muscular function can also be tested by appropriate electrodiagnostic studies such as electromyography and muscle stimulation tests. Children are more difficult to test because they may refuse to respond, forcing the examiner to test many times to obtain an accurate evaluation. In addition, muscle grading is a necessity as soon as it is possible, especially when a child is old enough to cooperate, because the child may lose muscle power or the cord level of involvement may ascend, reducing functional capacity. As a result of such shifting involvement, further evaluation and surgical intervention may be necessary.

Deformities that result from meningomyelocele are usually caused by muscle imbalance. If the muscles around the joint are not working or if all muscles are functioning equally well, deformities seldom develop. It is usually when a muscle is working either unopposed or against a weakened antagonist that a deformity occurs. A mild muscle imbalance acting over a prolonged period of time may produce a deformity. Development of muscle imbalance after birth as a result of the involvement of additional neurologic levels may also lead to deformities. They may also appear as a result of postural problems if braces or splints are incorrectly applied, if the limbs remain constantly in one position until they become fixed, or if the patient is allowed to lie in one position in the crib (in most instances, the hips flex, abduct, and externally
rotate; the knees flex; and the feet move into a few degrees of equinus).

Once a fixed deformity has developed, it tends to remain, even if the muscular imbalance disappears. For example, if nerve roots higher than the original lesion become involved, an existing deformity will usually not correct itself even though the previously unopposed muscle has ceased to function.

Evaluate the neurologic or cord level of involvement by motor testing each of the joints of the lower extremity. Then review the information within the broader concepts of neurologic levels to establish the diagnosis (Table 5-1).

The following meningomyelocele examination will evaluate each possible level of involvement from L1-L2 to S2-S3, its functional deficits, and its potential for causing deformity (Fig. 5-1).

L1-L2 Neurologic Level (L1 Is Intact, L2 Is Not)

Motor Function

Hip

Flexion:	absent
Extension:	absent
Adduction:	absent
Abduction:	absent

No function; there may be some hip flexion from the partial innervation of the iliopsoas (T12, L1-L3).

TABLE 5-1 MOTOR TESTING FOR NEUROLOGIC LEVEL

JOINT	ACTION	LEVEL
Hip	Flexion Extension Adduction Abduction	T12, L1-L3 S1 L2-L4 L5
Knee	Extension Flexion	L2-L4 L5,S1
Ankle	Dorsiflexion (ankle extension) Plantar flexion (ankle flexion) Inversion Eversion	L4, L5 S1, S2 L4 S1

Knee

Extension:	absent
Flexion:	absent
No function,	no deformity

Foot

Dorsiflexion:	absent
Plantar flexion:	absent
Inversion:	absent
Eversion:	absent

No function; if there is any deformity, it may be a result of either the intrauterine position, a loss of function where there was once a muscle imbalance, or a crib position that has produced hip and knee flexion contractures and equinovarus deformity of the foot. The foot normally has a few degrees of equinus when at rest, a position that may become fixed.

Sensory Testing

There is no sensation below the L1 band, which ends approximately one-third of the way down the thigh (Fig. 5-2).

FIGURE 5-1 Meningomyelocele.

FIGURE 5-2 Lumbar sensory dermatome.

Reflex Testing

None of the deep tendon reflexes of the lower extremity function. Occasionally, reflex activity may occur as a result of the functioning of a portion of the cord below the involved neurologic level (intact reflex arc).

Bladder and Bowel Function

The bladder (S2-S4) is nonfunctioning, the patient is incontinent, the anus is patulous, and the anal wink (S3, S4) is absent. It should be noted that sacral sparing is not uncommon at any level. Lesions that give a pattern of involvement in the sacrally innervated leg muscles but adequate innervation of the sphincter muscles are also common.

L2-L3 Neurologic Level (L2 Is Intact, L3 Is Not)

Motor Function

Hip

Flexion:	partial
Extension:	absent
Adduction:	partial
Abduction:	absent

Flexion is considerable, because the iliopsoas is almost completely innervated. There is, in addition, a hip flexion deformity because the iliopsoas is unopposed by the major hip extensor, the gluteus maximus (S1, S2). There is a small degree of hip adduction, with a corresponding slight adduction deformity because the adductor group (L2-L4) is partially innervated and is unopposed by the main hip abductor, the gluteus medius (L5, S1).

Knee

Extension:	partial
Flexion:	absent

The knee is not deformed in spite of the small amount of function of the knee extensor, the quadriceps (L2-L4). There is no significant clinical function.

Foot: No function, no muscular deformity, except as mentioned earlier.

Sensory Testing

There is no sensation below the L2 band, which ends two-thirds of the way down the thigh.

Reflex Testing

None of the lower extremity reflexes are functioning.

Bladder and Bowel Function

There is no function of the bladder and bowel. The patient cannot urinate in stream; the patient is only able to dribble urine. A stream may appear if the patient is crying, as a result of the tightening of the rectus abdominus muscle and the corresponding increase in intra-abdominal pressure.

L3-L4 Neurologic Level (L3 Is Intact, L4 Is Not)

Motor Function (Fig. 5-3)

Hip

Flexion:	present
Extension:	absent
Adduction:	present
Abduction:	absent

FIGURE 5-3A, B Neurologic level L3-L4: motor function.

The hip has flexion, adduction, and lateral rotation deformities.

Knee

Extension:	present
Flexion:	absent

The knee is fixed in extension by the unopposed quadriceps.

Foot

Dorsiflexion:	absent
Plantar flexion:	absent
Inversion:	absent
Eversion:	absent

There are still no active muscles in the foot.

Sensation Testing

Sensation is normal to the knee. Below the knee, there is no sensation (Fig. 5-4).

FIGURE 5-4 Neurologic level L3-L4: sensation, reflex, and bladder and bowel function.

Reflex Testing

There may be a slight, but obviously diminished, patellar reflex (L2-L4), because the reflex is primarily L4.

Bladder and Bowel Function

No function.

L4-L5 Neurologic Level (L4 Is Intact, L5 Is Not)

Motor Function (Fig. 5-5)

Hip

Flexion:	present
Extension:	absent
Adduction:	present
Abduction:	absent

The hip has both flexion and adduction deformities, because the iliopsoas (T12-L3) and adductor muscles (L2-L4) are still unopposed.

FIGURE 5-5A, B Neurologic level L4-L5: motor function.

Such an unopposed adduction may over time result in a dislocated hip and, eventually, a fixed flexion-adduction deformity. For ambulation, full leg bracing will be necessary, including the use of a pelvic band, because the hip is unstable without extension and abduction. Surgery is also a possible solution.

Knee

Extension:	present
Flexion:	absent

The knee has an extension deformity as a result of the unopposed action of the quadriceps. The main knee flexors, the medial and lateral hamstrings (L5 and S1), are denervated. An extended knee is
relatively stable, and future bracing is not necessary. However, because the hip must be braced (unless surgery is performed), the knee is also braced.

Foot

Dorsiflexion:	partial
Plantarflexion:	absent
Inversion:	partial
Eversion:	absent

The only functioning muscle in the foot is the tibialis anterior (L4) because everything else is innervated by L5, S1-S3. The insertion of the tibialis anterior on the medial side of the foot at the first metatarsal-cuneiform junction causes the foot to be dorsiflexed and inverted. In this position, the foot is both unbalanced and unstable, and the tibialis anterior may have to be surgically released. The foot is not plantigrade and is without sensation; thus, skin breakdown may occur. Bracing is necessary, but fitting shoes and getting the foot into a brace may be difficult if some correction is not achieved.

Sensory Testing

Sensation extends to the medial side of the tibia and foot. The lateral aspect of the tibia (L5) and the middle and lateral portions of the dorsum of the foot are anesthetic (Fig. 5-6). A pinprick is the most effective way to test infants for sensation; if there is sensation, the child cries or moves the extremity. A triple response to the pinprick (flexion of the hip and knee, dorsiflexion of the foot) should not be confused with motor function at these joints. Such a general triple reflex response may occur even if the patient is completely paralyzed.

FIGURE 5-6 Neurologic level L4-L5: sensation, reflex, and bladder and bowel function.

Reflex Testing

The patellar reflex (predominantly L4) functions, whereas the tendon of Achilles reflex (S1) does not. If there is hyperactivity in the tendon
of Achilles reflex, a portion of the cord below the original lesion has developed with intact nerve roots, without connection to the rest of the cord. Thus, the S1 ankle reflex arc is intact, and only the inhibitory and controlling factor of the brain is missing.

Bladder and Bowel Function

Neither the bladder nor the bowel functions.

L5-S1 Neurologic Level (L5 Is Intact, S1 Is Not)

Motor Function (Fig. 5-7)

Hip