December 2010

AFO choices for PTTD grow clearer

By Cary Groner

Posterior tibial tendon dysfunction (PTTD) continues to bedevil clinicians treating patients for whom a conservative, nonsurgical approach is indicated. Although extensive research has supported treatment with AFOs, few controlled trials have been conducted, and the choice between articulated and solid designs has largely remained a matter of individual preference.

That situation is changing, fortunately, as consensus has begun to emerge about which design is most suited to certain patient types. In a study presented at the International Foot and Ankle Biomechanics (i-FAB) conference in Seattle in 2010, researchers from SUNY Upstate Medical University in Syracuse, NY, tested 10 subjects with Stage II PTTD under four conditions: (1) shoe only; (2) shoe with a custom solid AFO; (3) shoe with a custom articulated AFO; and (4) shoe with an off-the-shelf AFO.

The kinematic variables were hindfoot inversion, forefoot plantar flexion, and forefoot adduction. The researchers reported that any given effect from the AFO on hindfoot inversion and forefoot plantar flexion was dependent on the phase of stance. Although none of the AFOs significantly affected forefoot abduction and considerable inter-subject variability was seen relative to the other two measures, custom articulated AFOs “provided the greatest correction of flatfoot deformity while maintaining ankle motion and push-off function,” according to the researchers.

“The components of the flatfoot deformity we see in PTTD include hindfoot eversion, a lower medial longitudinal arch, and forefoot abduction,” said Christopher Neville, PT, PhD, an assistant professor of physical therapy education at the university, who presented the findings at the i-FAB meeting. “If we can correct those mechanical defaults, we can have direct effects on the tendons and ligaments supporting the foot. We’re achieving clinical utility by controlling some of these foot postures, but we’re failing to correct others, such as forefoot abduction.”

The finding that AFOs affect hindfoot and medial longitudinal arch motion to varying degrees throughout stance was not unexpected, Neville said.

“For instance, the medial longitudinal arch may be the most important when the patient is really putting weight on it. That may be the time we want to correct it the most, and we’re seeing correction at that time, in midstance,” he said. “So the effects are not consistent all the way across stance, but we wouldn’t expect them to be.”

Practitioners will also likely not be surprised to learn of the inability of the AFOs to control forefoot abduction in the SUNY study, given that motion in the transverse plane is an ongoing clinical challenge. David Levine, DPM, CPed, who practices in Frederick, MD, said most AFO designs have trouble affecting the transverse plane.

“As a practitioner, you can try to deal with that by modifying the shoe to maintain the foot in better alignment,” Levine said.

In-shoe foot orthoses may offer another possible solution to address forefoot abduction, Neville said.

It’s worth noting that the SUNY study results may only be applicable to patients with Stage II PTTD. Clinically, disease progression and symptom severity definitely affect decisions about AFO design for PTTD patients, Levine said.

“Which design will work for an individual depends on the amount of deformity present, on the pain level and on the foot structure,” he said.

Levine and Neville agreed that, in general, a nonarticulated AFO is much more difficult for patients to tolerate than an articulated one. Articulated devices may have the added benefit of facilitating muscle activation, which could effectively serve as an alternate means of biomechanical correction.

“The data I’ve collected suggest that the correction of some of these foot postures are better if we allow the ankle to move,” Neville said. “One thing that’s changing is that we realize that the muscles that control our foot posture are important, and if we restrict them by putting on a solid brace, the muscles can’t fire and move the joint. We may actually get some correction and control of foot movement just by allowing the muscles to do what they’re supposed to do.”

Sponsored by an educational grant from American Orthopedics Manufacturing Corporation

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