Muscle weakness and instability associated with Charcot-Marie-Tooth disease in children can be addressed with ankle foot orthoses, research suggests, but practitioners should be aware of the limitations of AFOs in this patient population, as well as the ever-present challenge of compliance.
Recognizing device limits is key.
By Shalmali Pal, Lower Extremity Review July 2011
In a 2010 paper in the Journal of Child Neurology, Kristy Rose PhD and Joshua Burns PhD of the University of Sydney found marked differences in ankle range, dorsiflexion strength, and muscle imbalance between preschool age CMT patients and healthy age-matched controls. However, there were no significant differences in foot structure, inversion, eversion, or plantar flexion strength.
These findings underscore the two main goals of AFO use in CMT management: Maintain ankle dorsiflexion and compensate for muscle weakness and instability. An ancillary goal is to encourage compliance.
However, an overarching principle needs to be kept in mind when working with AFOs in orthoses, namely that bracing cannot correct the equinus deformities that are characteristic of CMT, cautioned Grant Scheffers, a research honors student at the University of Sydney. Scheffers is conducting his research under the guidance of Burns and Rose at the Institute for Neuroscience and Muscle Research, part of the Children’s Hospital at Westmead.
CMT is a progressive neuropathy that depends, to some extent, on tendon length. But lengthening or transferring tendons to correct foot alignment in CMT requires surgery.
“Orthoses cannot correct the ankle weakness and muscle balance, but they can be prescribed to compensate for muscle weakness and ankle instability,” Scheffers said. “The evolution of the cavus deformity in children with CMT is thought to be related to selective atrophy and weakness of the peroneus brevis, tibialis anterior, and intrinsic foot muscles, which orthoses cannot correct.”
In fact, determining the limits of AFOs in CMT should be the first step, according to a 2010 review article in Clinics in Podiatric Medicine and Surgery. Researchers from the International Center for Limb Lengthening at Baltimore’s Sinai Hospital emphasized that before an AFO is fitted, contractures must be reduced to a point at which a child can achieve a neutral ankle position and a plantigrade foot within the AFO.
The Baltimore group recommended the following general criteria for AFOs in CMT:
- The AFOs should capture the leg just below the knee and include the foot to control the equinus deformity;
- The AFOs can include ankle dorsiflexion assist;
- Solid AFOs should be used in children who have severe hypertonia and no ankle range of motion;
- Once adequate tone reduction has been achieved with static AFOs, prearticulate AFO can be substituted.
Of course, patient compliance with orthoses is a perpetual struggle, and CMT patients are no exception. A 2008 Italian study in the European Journal of Physical & Rehabilitation Medicine noted that only five of 25 CMT patients used AFOs, and three of those five said they hated their devices. The study further concluded that CMT patients shun AFOs because they feel the devices highlight their disability, are uncomfortable, and are not essential for daily living.
A June paper by Margaret Phillips PhD and colleagues in Disability and Rehabilitation: Assistive Technology found that AFO use among 15 CMT patients was influenced by concerns about pain and discomfort as well as aesthetics.
The patient populations in both of these studies were adults, but compliance issues can be exacerbated in younger patients who simply do not have the maturity to comprehend the value of AFOs.
“Having talked to adults who had [AFOs] as children, including some in this study, the main impression is that they didn’t have the same level of understanding of the use of orthotics. Having had to wear them as children almost seems to have put them off wearing them in adult life in some cases,” said Phillips, a clinical associate professor in rehabilitation medicine at Royal Derby Hospital in Nottinghamshire, UK.
Recent advances in AFO materials, such as lightweight thermoplastics and carbon fiber, have gone a long way toward improving compliance, Scheffers said. In the pediatric population, colors and designs can alleviate cosmetic concerns, he added.
The results from compliance studies emphasize the importance of a systematic, individualized approach to AFO prescription whereby only the least restrictive type of orthoses is prescribed for a particular individual, Scheffers stressed.
Source Lower Extremity Review
Factors associated with foot and ankle strength in healthy preschool-age children and age-matched cases of Charcot-Marie-Tooth disease type 1A, Rose KJ, Burns J, North KN. J Child Neurol. 2010 Apr;25(4):463-8. doi: 10.1177/0883073809340698. Epub 2009 Aug 11.