February 2018

Measures of ankle weakness reveal varied CMT gait patterns: Gait profile should guide orthotic design

Kids with CMT wearing an SMO/AFO with a toe-off device (left) and a hinged AFO (right). (Photo courtesy of David B. Misener, CPO.)

By Keith Loria

Gait-pattern classification derived from functional measures of ankle weakness can be used to assess progression of Charcot-Marie-Tooth (CMT) disease and to guide clinical decision-making about treatment strategies, such as orthotic design and strength-training programs, according to a study from the University of Sydney in Australia, published in 2017.

Using 3D motion analysis, researchers examined gait patterns in 60 children with CMT aged 6 to 17 years (26 girls, 34 boys) and assessed differences between them and 50 healthy controls based on the CMT Pediatric Scale of functional ankle dorsiflexion and plantar flexion weakness.

Researchers split data into subgroups denoting increasing severity of dorsiflexion and plantar flexion weakness and found three distinct gait patterns at the ankle in kids with CMT: a near-normal gait pattern, with the only difference between kids with CMT and controls being a reduced maximum ankle dorsiflexion in stance; reduced maximum ankle dorsiflexion in swing (foot drop); and increased peak dorsiflexion and reduced ankle power generation. The third, most severely affected group, also had an increased mean sagittal plane knee extensor moment, indicating ground reaction force remaining behind the knee throughout stance.

Contrary to previous studies, there were no signs of reduced ankle power or compensation through “steppage gait” in this population with mild to moderate CMT.

“Kids vary considerably in weakness in dorsiflexors early in CMT and in plantar flexors later on.”
—Ken Cornell, CO

“The paper shows many individuals with CMT do not fit a specific gait profile, and that’s significant to orthotics because it’s so critical to do proper evaluations of their gait and of their needs to develop a proper device plan,” David B. Misener, CPO, who practices with Clinical Prosthetics and Orthotics in Albany, NY, told LER: Pediatrics.

Long-term follow-up, for example, Misener said, is needed for children who fall into the study’s third group to monitor for development of crouch gait, which could occur because of the increasing ankle dorsiflexion, knee flexion, and knee extensor moment in stance.

All children with CMT had a significantly worse gait profile score than controls. Primary deviations at the ankle showed significantly reduced ankle dorsiflexion in stance, reduced maximum ankle dorsiflexion during swing and at initial contact, reduced ankle dorsiflexion moment in loading response, and reduced external thigh-foot angle in midstance. There were no signs of reduced ankle plantar flexion or ankle power generation at push-off.

Compared with controls, children with CMT also demonstrated a significantly reduced external thigh-foot angle in the transverse plane, indicating altered foot alignment. Deviations at the knee included increased knee flexion at initial contact, increased peak knee flexion in loading response, and increased maximum knee flexor moment in single support compared with controls. At the hip, children with CMT showed reduced hip abductor moment in terminal stance and reduced internal hip rotation during midstance.

Misener noted that the study recognized loss of range of motion (ROM), and said tight plantar flexion seems to be common yet sometimes overlooked in CMT, though the finding is critical from a therapy and patient awareness perspective. “Individuals can be trained by physical therapy to stretch tight muscles and tendons,” he said. “From a bracing perspective, these tight muscles and tendons can be accommodated within a custom insert or AFO.”

Ken Cornell, CO, who practices with Cornell Orthotics & Prosthetics in Peabody, MA, said orthotists needs information like that provided by the study, which was published last July in Gait & Posture, to understand the needs of children with CMT.

“This study certainly proves we can no longer simply expect our CMT children aged eight to fourteen to have simple foot drop with progressing classic equinovarus foot and ankle deformities based on their diagnosis,” Cornell said. “They will vary considerably in weakness in dorsiflexors early on in the disease and plantar flexors later on. Each patient will require a thorough evaluation, and classification should be based on dorsiflexion and plantar flexion function.”

Cornell points out that, since the 1980s, physicians have known that muscles innervated by the longest peripheral nerve axons are affected first in CMT patients.

“These types of conditions are now commonly referred to as length-dependent neuropathies,” Cornell said. “If the disease has progressed to a point where the much shorter nerves innervating the plantar flexors high up in the calf are affected, one will need a brace design to manage plantar flexor weakness as well as dorsiflexor weakness.”

Among several noteworthy takeaways Cornell found in the study were data revealing reduced control of the tibia over the foot throughout stance phase due to plantar flexion weakness.

“This indicates that it is the soleus controlling knee flexion throughout stance, not the quadriceps,” Cornell said. “This reinforces the need for ground reaction for these patients—an AFO to provide ground reaction for heel rise and proprioception for loss of balance. However, excessive crouch posture in static standing may be associated with proprioceptive loss and a strategy for improved balance.”

Misener noted: “I was a little disappointed on when they suggested bracing should be used—only after [the patient presents with] pain—and think they missed the mark. A ROM loss would likely not occur unless there was also a muscle imbalance.”

He said it’s critical for orthotists to be aware of gait abnormalities and address them appropriately with bracing—whether it’s as simple as a foot insert or a device with more aggressive muscular control, such as a fixed AFO to limit the amount of ankle dorsiflexion in stance, provide stability to the foot, and assist movement of the ground reaction force in the front of the knee during stance.

Keith Loria is a freelance writer in northern Virginia.

Source:

Wojciechowski E, Sman A, Cornett K, et al. Gait patterns of children and adolescents with Charcot-Marie-Tooth disease. Gait Posture 2017;56:89-94.

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