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AAOS Now

Published 6/1/2008
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Jennie McKee

ARM stretching device reduces ankle stiffness

Flat foot treatment holds foot in inversion during ankle dorsiflexion

“Flat foot deformity can be associated with contracture of the triceps surae muscle, and a corresponding reduction in dorsiflexion of the ankle, especially if the subtalar joint is inverted. Therefore, a stretching regimen where the hindfoot is held in inversion could be effective in reducing ankle stiffness,” said Vinod K. Panchbhavi, MD, of the University of Texas Medical Branch, during his presentation at the American Foot and Ankle Society’s 2008 Specialty Day.

According to this hypothesis, patients with flat feet who used a device that holds the subtalar joint in inversion and allows for dorsiflexion force to be applied to the ankle joint would be able to stretch the triceps surae muscle more effectively than stretching the tight heel cord in a straight, sagittal plane.

Obtaining the baseline measurements
The researchers recruited 15 healthy volunteers for the study. The physical examination to determine flat foot used the too-many-toes sign, hindfoot valgus, and forefoot adduction as indicators of the condition. All of the patients were older than age 18 years, had no additional pathology, and had sustained no injuries in the past 2 years.

The researchers randomly divided the volunteers into a control group (seven participants) and a treatment group (eight participants). Baseline ankle dorsiflexion stiffness in both groups was quantified in a pretest that used a Torque Range of Motion (TROM) device to measure ankle stiffness. To use the TROM, participants placed their foot on a foot plate connected to a laptop. As the ankle was moved up and down, ankle stiffness was displayed as angle (degrees) versus torque (Newton meters) on an output screen.

Stretching with the ARM device
For 6 weeks (4 weeks under the supervision of the physical therapists involved in this study and 2 weeks on their own), the treatment group used an Ankle Range of Motion (ARM) device for stretching. The device allows the patient to hold the foot in an inverted position with ankle dorsiflexion. The foot is strapped to a foot plate that has four cords attached to it. The other ends of the cords are attached to a ring that the patient uses to manipulate the foot (
Fig. 1).

Patients moved their foot into the desired position until they felt a tolerable “pulling” sensation. They held the position for 30 seconds at a time over the course of 10 minutes, three times per week.

After 6 weeks, researchers measured ankle stiffness again. TROM data were input into a custom-designed program within a spreadsheet; in addition, statistical analysis was performed using paired and independent t-tests. The results of the t-tests were followed up with Bonferroni correction at the .0125 level of significance.

Treatment group has impressive results
A comparison of the pretest and posttest results showed a statistically significant decrease (p=.003) in ankle dorsiflexion stiffness in the treatment group when compared with the control group, indicating that stretching with the ARM device decreased dorsiflexion stiffness.

“If we stretch this tight heel cord in a straight sagittal plane, such as in a closed chain or weight-bearing program, it can cause further adduction of the talus and accentuate the deformity,” said Dr. Panchbhavi.

“A device that can hold the foot in inversion during ankle dorsiflexion in an open chain, non–weight-bearing fashion can provide a safer, more effective stretch of the heel cord.”

As noted by Dr. Panchbhavi, the study was limited by its small sample size.

Dr. Panchbhavi’s mentor, Saul G. Trevino, MD, worked with him on this study, as did Katie Hendricks, PT; Dana Zander, PT; and Casi Baker, PT. Disclosure information for the authors can be found online at www.aaos.org/disclosure

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org