February 2018

Update: Orthotic care and physical therapy for DMD

Jennifer Wallace, PT, helps this boy with DMD stretch his gastrocnemius and Achilles tendon. (Photo courtesy the Duchenne Therapy Network.)

Lower extremity interventions can help boys with Duchenne muscular dystrophy (DMD) stay ambulatory for years—and improve outcomes in the condition’s nonambulatory phase.  Devices can address con­tractures and other issues, while stretching programs are key to maintaining flexibility. 

By Hank Black

Gene mutations in DMD short-circuit production or function of dystrophin, a protein that keeps muscle cells intact,1 and the disease is marked by unrelenting muscle-fiber degeneration and progressive muscle weakness.2 For this reason, lower extremity practitioners remain central to efforts to manage this disorder of X-linked recessive inheritance that affects 1 in 3600 boys (rarely, girls).3 The emergence of progressive contracture and gradual loss of functional muscle are indications for orthotic use and the beginning of physical therapy.4

“Every provider’s expertise is directed at getting patients with DMD up and moving for as long as possible,” according to Kirk Ferris, CPO, director of prosthetics and orthotics at Mary Free Bed Rehabilitation Hospital in Grand Rapids, MI.

Diagnosis usually comes as children exhibit clumsiness and other motor signs of muscle weakness. Gowers’ sign—having to “walk” hands up the thighs to achieve an erect position—is due to weakness in the pelvic girdle and lower extremities and is a cardinal alert to the disorder.

Lower extremity interventions are essential to maintaining patient’s ambulatory phase. As muscles deteriorate, most children with DMD who do not receive corticosteroid treatment will need a wheelchair by age 12 years; with treatment, children may walk functionally many years longer.5

“Every [lower extremity] provider’s expertise is directed at getting patients with Duchenne’s up and moving for as long as possible.” —Kirk Ferris, CPO

Orthotic intervention often begins when tightening muscles cause contractures and range-of-motion loss in the ankle, leading children to toe walk.6,7 Toe walking is a characteristic gait in this population, one that a recent study suggested is an adaptive, “voluntary” mechanism meant to increase stability, rather than pathology.8 Typically, a stretching program is initiated, with night splints and ankle foot orthoses (AFOs) prescribed to maintain gains from stretching.

Sara Rubinstein, CO, LO, TRS, orthotist and rehabilitation specialist at the Ann & Robert H. Lurie Children’s Hospital of Chicago, noted, “If the condition is apparent in infancy from genetic diagnosis with a known family history, then we have the chance to get involved when the child first develops his nighttime routine. The helpful trick is to get him to tolerate nighttime bracing before contractures are present and as early as possible to create normalcy in the routine of positional bracing.”

Adherence is an issue. Although experts recommend using night splints in the nonambulatory phase, parents reported stopping use of night splints at a mean age of 10.3 years, after a mean duration of use of 2.9 years.9

Orthoses: Day vs night use

Ciafaloni and colleagues found that, on average, 2.5 years pass between the appearance of the first signs and symptoms of DMD and a DMD diagnosis based on muscle biopsy or a DNA test. The average age at diagnosis for DMD is 5 years.10 Because of this diagnostic delay, many children with DMD are initially misdiagnosed and may present to specialized clinics already walking in an orthosis. But daytime, functional AFOs for DMD are controversial, and most practitioners limit the devices to nighttime use.

Townsend et al found daytime AFO use decreases ambulatory function and increases incidence of falls.11 That study has been criticized for using a dynamic, rather than an articulated, AFO and for not including kinematic assessments.

Sandra B. Smith, MS, PT, director of rehabilitation services at Shriner’s Hospital for Children–Tampa, in Florida, said: “Daytime AFOs are not usually tolerated due to the need for patients to adjust their center of gravity forward to balance, with increased plantar flexion at the ankle and increased lumbar lordosis, which occurs due to quad and gluteal muscle weakening.”

One recent small study of kinematics and kinetic gait assessment found potential benefit for daytime AFO12 use by children with DMD. Lead author Ana Claudia Mattiello-Sverzut, PT, MSc, PhD, said her group recommends daytime wear when less than 5° of dorsiflexion is present. The results indicate that daytime ambulation with an AFO minimized the biomechanical compensations typical of DMD.

“In addition, our recent unpublished study showed daytime AFO use decreases the incidence of falls and is well accepted by patients with DMD if they choose to wear it,” said Mattiello-Sverzut, professor of pediatric neurology at the University of São Paulo, Brazil.

Rubinstein noted the published study showed improvements in the 10-m walk test. “My experience, however, is this may not be the case after a full day in the device,” she said. The São Paulo group did call for further study into whether their result would hold up over time.

“Daytime AFOs may be used as resting splints for ambulatory patients as a supplement for those who are not able to tolerate the AFOs the recommended six hours at night,” according to Jennifer Wallace, PT, owner of Duchenne Therapy Network and education director for the nonprofit CureDuchenne, both in Los Angeles, CA.

Leslie Vogel, PT, of Seattle Children’s Hospital in Washington, pointed out that older nonambulatory patients are often allowed to choose when to wear devices. “They often choose daytime because by then it’s harder to reposition themselves in bed with an orthosis,” she said. Children with DMD often are on respiratory support at night, making repositioning more difficult.

“At night, the patient might get an articulated AFO with strapping to put a dynamic stretch to the ankle, but we use a solid AFO if they have plantar flexion contractions,” Vogel said. “In the nonambulatory stage of DMD, if the boy has a plantar flexion contracture, we may have him in ankle resting splints to prevent inversion and equinovarus.”

Rubinstein, however, prefers not to use strapping. “Our patients say strapping is cumbersome when caught in blankets and often wakes kids up,” she said. “Fewer moving parts with regular follow-up for necessary adjustments is ideal.”

Issues at the knee and hip

Another orthotic issue is how to address knee and hip flexion tightness. Rubinstein said, “We may tackle this problem with a knee immobilizer in conjunction with a positional AFO, but tolerance may be a challenge. More research is needed, but for now our bread-and-butter protocol is to use positioning and stretching programs with physical therapists to tackle the hip and knee tightness, with AFOs addressing the tendency for equinovarus contractures.”

Most orthoses for children with DMD are custom-made to accommodate the fibrotic nature of calf muscles in this population, Rubinstein said. “We are exploring a static, progressive, solid design that we can adjust as kids change throughout the year. If we can adjust the angle and keep the child comfortable, he ultimately will wear the braces longer.”

Rubinstein said, “Ideally, these boys will obtain a power wheelchair that accommodates standing. And if a KAFO [knee ankle foot orthosis] is considered, we do a trial period in knee immobilizers with PTs if a kid is highly motivated and starting to have increased falls, and as long as his ankle, knee, and hip joints are not too tight. If we feel he is a good candidate for therapeutic use of KAFOs in a stander, I’ll do a custom set with ground-reaction AFO portions.”

Design and construction of a KAFO, orthotists said, require great precision to avoid disrupting knee mechanics and affecting the activity of more proximal muscles.

“Because the muscles above the knee are affected before those below the knee, and weakness proceeds from proximal to distal, a poorly aligned AFO can create abnormal flexion moments at the knee and overwork the quadriceps,” according to Thomas V. DiBello, CO, FAAOP, director of clinical and scientific affairs at the Hanger Clinic in Houston, TX. “It’s a very delicate orthotic process that requires practitioners who are highly experienced in tuning and alignment. Functional orthoses such as this need to be designed carefully. Their use is controversial.”

Rubinstein added: “Tuning is crucial. It’s important to have an alignment that accommodates any contractures but allows the child to have a forward center of mass to balance over their base of support with weak hip extensors.”

Eric Weber, LCPO, at the Hanger Clinic in Seattle, WA, said, “KAFOs can be a useful treatment following surgical tendon release or lengthening. While in a standing frame or other safe condition, KAFOs provide a suitable base of support for proximal lower limb weakness.”

Weight gain, a frequent side effect of corticosteroid use, makes ambulation more difficult, and a nutritionist or dietitian is now included in multidisciplinary clinics. In a healthy child, weight gain would be countered with an exercise program. However, children with DMD must not overdo it, experts say, or they will suffer additional cell damage and muscle deterioration.

Molecular-based drugs enable production of the muscle protein dystrophin (represented above), which in DMD is blocked by gene mutations.

DMD medications

Much attention now is on the advent of molecular-based medications targeted at the underlying genetic defect of Duchenne muscular dystrophy (DMD) as well as on steroidal and nonsteroidal pharmaceuticals to control deterioration of the abnormal muscle.

Despite their side effects, prednisone and other corticosteroids add years of greater strength, ambulation, and survival to a population whose life was once limited to their early twenties.16 A 2014 study found steroid usage the most significant predictor of improved wheelchair-free survival. Now some patients are living into their fourth decade.17

“There’s a lot going on that’s exciting,” according to Michael D. Sussman, MD, a pediatric orthopedic surgeon in Oregon at Shrine Hospital for Children—Portland. “Until corticosteroid treatment became accepted practice nearly 20 years ago we had nothing to really change the course of the condition, and now we have the first approval of molecular-based pharmaceuticals specific to Duchenne,” he said.

Molecular therapies target different genetic defects and include gene transfer or gene editing techniques. Eteplirsen, for example, the only Food and Drug Administration-approved medication for DMD, delivers through intravenous infusion an exon-skipping molecular “patch” that masks exon abnormalities and allows dystrophin production. It increases skeletal muscle but is only indicated for the 13% or so of children with DMD who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping.18

Ataluren is an oral “protein restoration therapy” for treatment of DMD caused by a nonsense mutation (about 13% of DMD patients). It’s approved for use in DMD in the EU and has been granted orphan drug status in the US. It overcomes the mutation by forcing cells to ignore a premature stop signal, enabling the production of the full-length, functional protein.19

Smith said, “The therapist must monitor subjective signs of fatigue and continually reassess objective changes in function and symptoms during treatment sessions. Eccentric or high-resistance exercises should be avoided.”13 She said Shriners-Tampa recently opened a multidisciplinary clinic for children with DMD and other neuromuscular disorders. Such teams of professionals are becoming more common at major centers as subspecialties’ diagnostic and management options broaden.

Vogel recommends starting powered mobility earlier, before total loss of ambulation occurs. “The boys want to keep up with their peers but shouldn’t be overstressing their muscles. We tell families that if the boy’s legs are sore at night or the following day, they’ve overdone it and need to decrease either duration or intensity of exercise.”

In fact, Vogel said, “Repetitive exercises such as  leg lifts or sit-ups stress the same muscles. We view exercise more as simply activity. If they’re playing with peers, using a tricycle or bike with training wheels, or simply moving about, that’s about all they need. In addition, such activity provides more self-esteem and self-satisfaction than traditional exercise.”

Wallace said even a daily routine can become too stressful for boys with DMD. “Energy conservation becomes really important, especially for those aged seven to twelve years,” she said. “We want them to walk when they’re safely able to, but to use an electric scooter for those times they need to conserve energy to not deteriorate too quickly.” Changes may include avoidance of hills, for example, or a school schedule with classes closer together.

Stretching, surgery, and other interventions

Stretching programs are essential for maintaining the flexibility of the hip flexors, iliotibial band, hamstrings, and plantar flexors. This allows boys to remain upright longer and to later be positioned comfortably in a wheelchair, Vogel said. Parents are vital to success of stretching, which should be performed six times a week, Wallace added.

When the child is  aged 2 to 4 years, parents should start stretching the heel cords and hamstrings, Vogel said. “As they get into school, a stretch for hip flexors and iliotibial bands are added, and some kids are able do their own stretches,” she said.

Serial casting was once a treatment for later-stage DMD to help maintain heel-cord stretches, but now has gained favor as an earlier treatment, Wallace said.14

Guidance published in the March 2018 issue of Lancet-Neurology by a multidisciplinary group of experts recommended foot surgery to improve varus positioning and Achilles tendon surgery to improve dorsiflexion.15

Use of a standing frame should begin when the child can still take a few steps. (Photo courtesy of the Duchenne Therapy Network.)

Achilles lengthening may be employed in carefully selected patients—that is, the 10% to 15% whose ankles experience a contracture of approximately 30° and whose proximal muscles are still relatively strong, said Michael D. Sussman, MD, pediatric orthopedic surgeon in Oregon at Shriners Hospital for Children–Portland. Children with DMD, he added, are prone to falls and fractures. “These must be treated very aggressively with good fixation,” Sussman said.

Standing support has become an important part of DMD care, including postsurgically. Wallace and Vogel said that use of a standing frame should be started while the child can still take a few steps—an example of interventions now used earlier than in the past. “Standing frames provide stability to stay upright for homework, standing programs at school or therapy, as well as for improving respiratory care, and delaying the onset of scoliosis.”

Aquatic therapy and antigravity treadmills are heavily favored by physical therapists for children with DMD because they allow for more low- or no-impact exercise and are particularly useful for postsurgical rehabilitation, according to physical therapists interviewed for this article.

Overhead harness treadmills have fallen from favor, Wallace said, largely because the patient’s weight falls on harness straps that go through the groin area. One antigravity treadmill uses differential air pressure technology to provide lifting forces to reduce impact.

As Wallace conducts DMD educational sessions for other physical therapists around the country, she has noticed many regional differences in management. “My expectation is that these differences will largely disappear as new outcome measures and treatments are validated through clinical trials and as awareness of the progress made in Duchenne is raised through journals, conferences, and standards of care,” she said.

Hank Black is a freelance medical writer based in Birmingham, AL.

REFERENCES
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