Definition

Arthrogryposis multiplex congenita (AMC) is a congenital anomaly in the newborn involving multiple curved joints (see Fig. 674-1 on the Nelson Textbook of Pediatrics website at www.expertconsult.com ). Arthrogryposis is a descriptive term and not an exact diagnosis, as there are as many as 300 possible underlying causes.

Figure 674-1 Arthrogryposis multiplex congenita. A 32-wk premature boy with severe multiple congenital contractures and severe congenital neuropathy.

(From Hosalkar HS, Moroz L, Drummond DS, et al: Neuromuscular disorders of infancy and childhood and arthrogryposis. In Dormans J, editor: Pediatric orthopedics: core knowledge in orthopedics, Philadelphia, 2005, Mosby, pp 454–482.)

The incidence of classic AMC is approximately 1/3,000 live births, and the three main groups include classic AMC, in which the limbs are primarily involved and the muscles are deficient or absent (amyoplasia) (Fig. 674-2); arthrogryposis in association with major neurogenic (brain, spinal cord, anterior horn cell, or peripheral nerve) or myopathic (congenital muscular dystrophy, myopathy, toxic myopathy) dysfunction; and arthrogryposis in association with other major anomalies and specific syndromes such as diastrophic dysplasia and craniocarpotarsal dystrophy (Table 674-1).

Figure 674-2 Child with amyoplasia. In the upper extremity, the shoulders are internally rotated, the elbows are extended, the wrists are flexed and ulnarly deviated, the fingers are stiff, and the thumbs are positioned in the palm. In the lower limbs, the hips may be dislocated, the knees are extended, and the feet have severe equinovarus contractures.

(From Bamshad M, Van Heest AE, Pleasure D: Arthrogryposis: a review and update, J Bone Joint Surg Am 91[Suppl 4]:40–46, 2009.)

Clinical Features

Multiple rigid joint deformities are present with defective muscles and normal sensation. There is rigidity of several joints in each case, resulting from both short tight muscles and capsular contractures. Pterygium may be present on the flexor aspects of contracted joints (Fig. 674-3). There is often an absence or fibrosis of muscles or muscle groups. There is normal intellectual development in most cases. All four limbs are involved in the classic form (AMC), but the condition can also occur in the upper or lower limbs. An autosomal dominant variant called distal arthrogryposis involves the hands and feet with severe deformation but with only minor contractures more proximally; scoliosis is a possible development. To date, 10 different distal arthrogryposes have been described. They are classified according to the proportion of features they share (Table 674-2). In addition to the multiple joint contractures, the lack of skin creases (cylindrical or tubular limbs) and deep dimples over the joints are very characteristic (Fig. 674-4). There is dislocation of joints, most commonly the hip but occasionally the knee; the trunk is rarely affected. Other congenital anomalies such as cryptorchidism, hernias, and gastroschisis can occur.

Figure 674-3 Fixed flexion of the knees in a boy with arthrogryposis multiplex congenita.

(From Hosalkar HS, Moroz L, Drummond DS, et al: Neuromuscular disorders of infancy and childhood and arthrogryposis. In Dormans J, editor: Pediatric orthopedics: core knowledge in orthopedics, Philadelphia, 2005, Mosby, pp 454–482.)

Table 674-2 CURRENT LABELS AND OMIM NUMBERS FOR THE DISTAL ARTHROGRYPOSIS SYNDROMES

OMIM, Online Mendelian Inheritance in Man.

From Bamshad M, Van Heest AE, Pleasure D: Arthrogryposis: a review and update, J Bone Joint Surg Am 91 Suppl 4:40–46, 2009.

Figure 674-4 Characteristic lack of skin creases and tubular limbs.

(From Hosalkar HS, Moroz L, Drummond DS, et al: Neuromuscular disorders of infancy and childhood and arthrogryposis. In Dormans J, editor: Pediatric orthopedics: core knowledge in orthopedics, Philadelphia, 2005, Mosby, pp 454–482.)

Etiology

AMC is multifactorial in etiology. Factors liable to produce immobility of the fetus can contribute to congenital contractures. Some of these include structural abnormality of the uterus (bifid, large fibroids), oligohydramnios, increased intrauterine pressure, mechanical compression of the fetus, weak fetal movements, breech presentation, and prematurity. Inflammatory or infective etiology has also been postulated, including inflammation in the joint, muscle, spinal cord, or brain; rubella in early pregnancy; and infection with unknown viruses. A dominant theory is that the primary condition is patchy degeneration of the anterior horn cells occurring in the early months of gestation. A pregnant mother treated with curare for severe tetanus gave birth to an arthrogrypotic baby.

Diagnosis

Clinical examination remains the best modality for establishing the diagnosis of arthrogryposis. We have found a few factors that are often useful in making a diagnosis. Although not absolute criteria, they are helpful when considered in combination.

Unlike paralytic disorders, joint deformities of AMC are usually stiff or rigid from the beginning, with incomplete passive range of motion. Deformities of arthrogryposis tend to be symmetric.

The severity of contractures tends to increase as one reaches the periphery of the limb. The more proximal joints tend to be less involved, and the trunk is often spared. The most severe deformities tend to occur in the hands and feet.

The orthopedist, neurologist, geneticist, and pediatrician must participate in diagnosing and managing this condition. Radiographs of the involved extremities with joint involvement are recommended. These can demonstrate congenital bony abnormality and loss of subcutaneous fat and muscle. Radiographs of the whole spine identify any vertebral anomalies. CT and MRI of the brain and spine are useful in establishing or ruling out structural central nervous system (CNS) involvement. Electromyography and nerve conduction studies are of limited value and have been used to differentiate the peripheral neuropathic from the myopathic variants.

DNA diagnostic tests to distinguish the various congenital myopathies and/or dystrophies are not widely available, and thus skeletal muscle biopsy may be needed when a primary myopathic disorder is suspected. In such case, care must be taken to avoid malignant hyperthermia. Plasma creatine kinase may be estimated to exclude myopathic disorders. This is best checked on the 3rd day of life or after, once any transient initial increase in creatine kinase from the birth process has subsided. If a prenatal ultrasound scan detects an absence of fetal movement, especially in combination with polyhydramnios, the diagnosis of arthrogryposis can be suspected. Histologic analysis reveals a small muscle mass with fibrosis and fat between the muscle fibers. Myopathic and neuropathic features can overlap in the same specimen. The periarticular soft tissues are fibrotic. Genetic consultation, with chromosome analysis and collagen studies, should be considered in cases in which a distinct peripheral neuromuscular disorder is not readily apparent.

The differential diagnosis is shown in Table 674-3.

Prognosis

Most children with arthrogryposis require therapy; an estimated 80% of children with amyoplasia receive therapy services into their adolescence. Limb deformities that restrict function often require surgical treatment; in one series, 76% of children received surgery of the foot, >30% surgery of the knee, 25% surgeryof the elbow, and nearly 20% surgery of the hip. The clinician should be able to derive a general prognosis and treatment plan once the diagnosis of AMC is established. Vigorous occupational therapy and use of hand splints and serial casting can improve the range of motion and functional use of the hand in many cases of AMC in which the etiology is not a progressive disorder (amyoplasia). Surgery, in selected cases, is necessary to obtain a more neutral positioning of the wrist and fingers so the limited degree of strength can be used to optimal biomechanical advantage.

Corrected deformities are quite common and occur with growth in a limb in which the periarticular structures are incapable of stretching. Arthrogrypotic children have certain positive factors that must be used in their successful management.

Joint instability is not a problem in AMC, unlike other paralytic conditions.

With a coordinated and team approach in management, there often is little deterioration from the condition at birth. There is commonly central sparing and a relatively normal trunk.

The child with normal CNS findings can be expected to have reasonably normal intelligence and, with enough motivation, can contribute to successful management.

Principles of Orthopedic Management of Patients with Arthrogryposis and Multiple Congenital Contractures

Patients should be seen as early as possible, and treatment of the deformities should be started early because some respond remarkably well to physiotherapy, stretching, and splinting.

Muscle balance is usually less of a problem than in other paralytic neuromuscular conditions and is easier to achieve. Muscle balance should be possibly established if there are functioning muscles available for transfer. Recurrence of deformity is the rule because the dense, inelastic soft tissues about the joints do not properly elongate with growth. These structures are considered the key to successful management of arthrogryposis in the growing child. The maximal, safely obtainable correction should be achieved at the time of surgery. The use of wedging or corrective casts after surgery is of little additional benefit.

Lower Limbs

Foot Involvement

The most severe deformities in arthrogryposis are known to occur in the foot. The rigid foot deformity is usually the clubfoot or equinovarus deformity and, less commonly, a congenital vertical talus deformity. The goal of treatment is conversion of the rigid deformed foot into a rigid plantigrade foot.

Correction of the hindfoot takes precedence over the forefoot. Serial stretching (casting) sometimes produces a degree of correction. Once it is clear during the course of treatment that conservative treatment will not be successful, surgery should be considered, preferably when the child is ready to walk.

An extensive posteromedial and posterolateral release is recommended. If the foot fails to correct with even the most extensive soft-tissue release or relapses quickly within 2-3 yr, talectomy may be considered. The Ilizarov technique and apparatus do offer an opportunity to correct these deformities by gradual distraction and neohistiogenesis (Fig. 674-5). Applications of this fixator in the pediatric foot have been fairly successful and satisfactory. In the case of older children with neglected or relapsed equinovarus deformity, correction can be best obtained by triple arthrodesis. In rare cases of recurrence of the deformity after triple arthrodesis (at the level of the ankle), a pantalar arthrodesis may be offered by an easy conversion of the triple arthrodesis.

Figure 674-5 Ilizarov fixation device for correction of ankle contracture.

(Courtesy of Dr. Richard Davidson, Children’s Hospital of Philadelphia.)

Upper Limbs

Unlike management of lower limbs, where independent walking is the main goal, management of upper extremities in arthrogryposis requires considerable caution because the prognosis for successful treatment depends more on the extent of deformity and on the patient’s intelligence. The minimal requirements for the patient are ability to feed and attend to personal hygiene.

Again, in contrast to the lower limbs, where surgery cannot be postponed due to risk of delayed walking, operations on upper limbs can be postponed for several years. Interestingly, arthrogrypotic children develop a remarkable ability to get about well with their upper limbs in spite of the complexities of these deformities, developing a surprising amount of dexterity. Therefore, surgical intervention, if any, should be weighed very carefully in these cases.

Spine

In consistency with the principle that the severity of the stiffness and deformity increases toward the periphery of limbs and that the more central or proximal areas are less involved, a straight, supple, and well-balanced trunk is an important asset. Scoliosis occurs commonly in arthrogryposis because of a high incidence of congenital curves (Chapter 671).