February 2016

Extension correction: AFO design improves PTTD mechanics

In the moment: O&P

The two orthotic devices used for testing: the standard-length AFO (left) and the AFO with lateral extension (right). (Reprinted with permission from Neville C, Bucklin M, Ordway N, Lemley F. An ankle foot orthosis with a lateral extension reduces forefoot abduction in subjects with stage II posterior tibial tendon dysfunction. J Orthop Sports Phys Ther 2016;46(1):26-33.)

The two orthotic devices used for testing: the standard-length AFO (left) and the AFO with lateral extension (right). (Reprinted with permission from Neville C, Bucklin M, Ordway N, Lemley F. An ankle foot orthosis with a lateral extension reduces forefoot abduction in subjects with stage II posterior tibial tendon dysfunction. J Orthop Sports Phys Ther 2016;46(1):26-33.)

By Larry Hand

When a lamp cord doesn’t quite reach an outlet, you reach for an extension cord. So when a custom ankle foot orthosis (AFO) didn’t quite provide the corrected forefoot abduction desired in patients with post­erior tibial tendon dysfunction (PTTD), researchers from Syracuse, NY, added a lateral extension.

Investigators from State University of New York Upstate Medical University found that an AFO with a lateral extension was associated with significantly greater forefoot abduction than a standard AFO while maintaining control over hindfoot inversion and eversion. The findings were published in the January 2016 issue of the Journal of Orthopaedic & Sports Physical Therapy.

“What has been lacking in findings from previous studies is this particular foot kinematic of forefoot abduction, which is noted in subjects with PTTD,” said Christopher Neville, PT, PhD, associate professor of physical therapy. “What we’ve seen is that the forefoot abduction wasn’t corrected well. This study looked at a new component of a device, being this lateral extension, as an attempt to try to correct that one piece that was missing. In summary, the findings are that it seems to do that. It also seems to maintain correction of the medial longitudinal arch height.”

Neville and colleagues evaluated the gait of 15 people with stage II PTTD under three conditions: a standard nonarticulated custom AFO, the same AFO with a lateral extension, and a shoe-only control condition.

Both AFOs consisted of a 3-mm polypropylene shell inside a leather cover. The standard AFO ended just proximal to the metatarsals; with the lateral extension added during fabrication, the experimental AFO rounded the fifth meta­tarsal head.

Each participant wore one AFO for an hour per day, alternating AFOs from one day to the next, for an average of eight days. Laboratory testing consisted of walking trials along a 5-m walkway at a self-selected speed, with the AFO conditions tested in random order.

The AFO with the lateral extension resulted in significantly greater forefoot adduction (1.3°) than the standard AFO (-1.3°) and the shoe-only condition (-2.8°).

Both AFOs were associated with more hindfoot inversion at terminal stance than the shoe alone, but the extended AFO also resulted in more hindfoot inversion at loading response than the shoe only. Both AFOs also improved upon the shoe-only condition in terms of forefoot plantar flexion, but the extended AFO was associated with more forefoot plantar flexion than the standard AFO.

The findings could have important clinical implications, Neville said.

“For me, as a practitioner, if I saw people that I thought had really significant forefoot abduction as part of the deformity, then this would be a good brace component to use,” Neville said.

Adding the lateral extension did not adversely affect the fitting of the AFOs in the shoes used in the study, but shoes with a wide toe box are needed, he said.

“I think people should think about this as a concept. A lateral extension can likely be added to many orthotic designs to achieve greater control of excessive forefoot abduction,” Neville said.

Leigh Davis, MSPO, CPO, prosthetist and orthotist at Children’s Healthcare of Atlanta, GA, and treasurer of the American Academy of Orthotists & Prosthetists, agreed.

“It’s really important for us as orthotists to know what specific orthotic design features are important for this patient population,” Davis said.

The potential utility of the new design feature may extend beyond the PTTD population, she said.

“I think it’s applicable to a lot of patient populations,” Davis said. “They’re really showing that a long lateral border can change the position of the forefoot. I think that anyone could integrate this right away into practice for any patient who has a forefoot abduction tendency and utilizes an AFO.”

Source:

Neville C, Bucklin M, Ordway N, Lemley F. An ankle foot orthosis with a lateral extension reduces forefoot abduction in subjects with stage II posterior tibial tendon dysfunction. J Orthop Sports Phys Ther 2016;46(1):26-33.

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