Other Neuromuscular Conditions and Spina Bifida



Other Neuromuscular Conditions and Spina Bifida


Kenneth J. Noonan, MD, MHCDS

Robert M. Kay, MD1


1Guru:











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Tips for Recognizing Neuromuscular Conditions

The array of diagnosable neuromuscular conditions presenting in children is interesting but sometimes intimidating. Most of this information is generally toward the periphery of most orthopaedic surgeons’ knowledge. Stay out of trouble by knowing a few common threads in these conditions that can help you identify a child with a potential neuromuscular condition. Also, don’t be afraid to ask parents what syndrome their child has and ask them to enlighten you. Parents like doctors who are not know-it-alls but are willing to learn from them.


A common scenario occurs when parents bring a child to an orthopaedic surgeon because the child walks funny, falls down, wants to be carried when walking far, or some other seemingly innocuous complaint. Ninety-nine percent of the time, it is age appropriate, but this chapter may help with the other 1%. Delay in diagnosis can have serious implications. In addition to delaying treatment of the child’s condition, it can also result in transmitting the same disease to younger siblings; as an example, before Duchenne muscular dystrophy (DMD) is diagnosed, 20% of families already have conceived a second child. Do not hesitate to examine the parents (subtle cavovarus feet, café au lait spots, etc.) and ask for a family history. Many parents have unrecognized subtle forms of the same disease as their child. This aids in diagnosis of the child.









Figure 17-1 A: This child with a cavus foot has an underlying neuromuscular disorder. In children with unilateral foot deformity, consider spinal pathology as more likely; with bilateral foot deformity, consider underlying neuromuscular disease is more common. B: A child with bilateral cavovarus feet with Charcot-Marie-Tooth disease. C: Claw toes are also an indication of an underlying neuromuscular disease.



General Principles of Treatment

Do not become focused on one body part as many neuromuscular conditions have multiple orthopaedic implications. For example, a child with Charcot-Marie-Tooth (CMT) disease may present to you with a foot deformity, but do not forget there is an increased risk of scoliosis1 and hip dysplasia.2,3 This raises an important point even for pediatric orthopaedic surgeons who feel comfortable seeing children with neuromuscular conditions. Each condition has its own unique pitfalls, and it is probably worthwhile to quickly review literature on a child’s condition prior to instituting treatment. For example, children with various muscular dystrophies have widely variable prognoses. Know the natural history and expected function of the condition prior to planning surgery as many of these children may never be expected to walk, or even live very long, which may influence whether surgery is indicated. If a muscle biopsy is required, biopsy the weak muscle—i.e., the deltoid, for shoulder girdle weakness.






Fractures

Children with neuromuscular disease and decreased ambulation are at an increased risk for osteopenic fractures. In an insensate area, fractures are often not appreciated at the time of injury and present late as a swollen, red, and warm limb that is often mistaken for infection by the inexperienced. To make things even more confusing, the child may present with a fever and abnormal laboratory studies. This scenario unfortunately occurs in children who have severe communication challenges (Figs. 17-2, 17-3 and 17-4).

Fracture care in these children is quite different than in otherwise normal, active children. First, mobilization should begin as early as possible. If a child with progressive weakness and increasing difficulty in walking (e.g., 11-year-old boy with Duchenne muscular dystrophy) is in a long leg cast that prevents walking for 6 weeks, the child may lose so much muscle strength that he never walks independently again. You do not want to contribute to that. Second, immobilize for as little a time period as possible. Immobilization leads to localized osteopenia. These children already have some degree of osteopenia to begin with; following immobilization, fractures at other areas in the limb are quite possible. One of the editors (D.L.S.) assumed care of a spina bifida patient who spent 11 months in lower extremity casts for multiple fractures at different locations. Third, these children often have abnormal sensation; soft-tissue problems from cast sores are more likely to occur, and less likely to be recognized, than in the general population.







Figure 17-2 Radiograph of a femur of a nonambulator with cerebral palsy who has sustained multiple femur fractures. The clinical and radiographic appearance of this fracture may be confused with infection.






Figure 17-3 A: This boy with thoracic-level spina bifida presented with a chief complaint of (painless) leg swelling. The leg was warm to touch. B: Radiographs demonstrate copious new bone formation. C: To make matters even more confusing, when children with spina bifida fracture through the growth plate, there may be no callus formation. Clinically, this young girl with thoracic-level spina bifida had motion through the Salter I fracture of the distal femur.

We have found less-rigid immobilization is a useful technique for fracture care in nonambulatory children with neuromuscular conditions. This can be accomplished with semirigid fiberglass and/or significant padding, such as polyurethane foam. This decreases osteopenia secondary to immobilization, lessens the chance of a secondary fracture at the edge of a rigid cast, and decreases skin problems from poorly sensate soft tissues rubbing against the edge of a hard cast. The good news in this situation is that there’s often rapid and overwhelming callus formation and the child’s demands usually do not require anatomic reduction.








Figure 17-4 Nonambulators with osteopenia frequently have fractures of the distal femoral metaphysis. Have a high index of suspicion when children who were in a hip spica cast for hip surgery present with increasing pain shortly after the spica cast was removed.






Figure 17-5 This young man with severe Charcot-Marie-Tooth disease has bilateral cavovarus feet (A) with clawing of his fingers (B). (Used with the permission of the University of Wisconsin Division of Pediatric Orthopaedics.)




Duchenne Muscular Dystrophy

Duchenne is the most common of the muscular dystrophies, and many other types of muscular dystrophy are less severe. The level of creatine phosphokinase (CPK) may be 20 to 200 times normal in children with DMD but can be elevated for patients with other forms of muscular dystrophy as well as many other types of muscle disease. The CPK may be elevated by birth in normal children, but should return to normal quickly. DMD is not that rare, occurring in 1 in 3500 births, so there is a good chance most orthopaedic surgeons will encounter a new patient at some point in their career. While DMD is X-linked and thus occurs only in boys, it can occur in a child with Turner syndrome (XO), and other forms of muscular dystrophies can occur in girls. Rarely, girls can prevent with a DMD phenotype in the setting of the Lyon hypothesis, in which there is inactivation of one of the two X chromosomes. Mental retardation may be present; just because a boy has mental retardation doesn’t mean he doesn’t have muscular dystrophy. Perhaps the greatest way to stay out of trouble in DMD is to make it a practice to do Gower’s test on all 3- to 6-year-old boys with gait abnormalities other than torsion (see Fig. 2-1 in Chapter 2).








Figure 17-6 Pseudohypertrophy of the calf in the setting of weakness suggests Duchenne muscular dystrophy.

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Jan 30, 2021 | Posted by in ORTHOPEDIC | Comments Off on Other Neuromuscular Conditions and Spina Bifida
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