November 2011

Early stage rearfoot eversion effects bolster theory of PTTD progression

In the moment: Sports medicine

Two measures of pronation typically associated with later stages of posterior tibial tendon dysfunction are also apparent in its earliest stage, according to University of Calgary research with possible implications for early intervention.

Investigators analyzed static anatomical foot structure, ankle invertor muscle strength, and walking kinematics in 12 runners with stage 1 PTTD and 12 matched asymptomatic runners.

Peak rearfoot eversion angle during walking was significantly greater in magnitude and more prolonged in runners with PTTD than in their healthy counterparts, findings consistent with earlier studies of patients with later-stage PTTD. This supports the prevailing theory that PTTD is progressive, and suggests a kinematic progression in which increased rearfoot pronation in early-stage PTTD leads to later-stage midfoot and forefoot motion issues.

Seated arch height index (AHI) was also significantly lower in runners with PTTD, but the difference was small and other structural measures, including standing AHI, did not differ significantly between groups. Other variables, including ankle invertor strength and peak medial longitudinal arch angle during walking gait, also were not significantly different between groups despite having been reported in patients with later-stage PTTD in earlier studies.

The University of Calgary study, published in the October issue of the Journal of Orthopaedic & Sports Physical Therapy, specifically looked at walking gait to make comparisons to other studies. Further research is needed to determine whether the same rearfoot eversion variables are affected during running and whether interventions designed to control rearfoot motion in runners might be effective against PTTD, according to Melissa Rabbito, MSc, CPed, a research associate in the university’s kinesiology department and first author of the study.

Footwear-based intervention is one example.

“Motion control shoes have been shown to reduce rearfoot eversion in running. However, most of our subjects fell within the limits of ‘normal’ arch height index while standing, so motion control shoes would not have been recommended based on their foot structure,” Rabbito said. “Footwear would definitely be something to consider in this population, but we need to know more about how the PTTD foot acts in a shoe.”

Switching to a forefoot-strike pattern might not necessarily be the answer either.

“Altering the foot strike pattern could reduce the amount of pronation/eversion during running,” Rabbito said. “But the tibialis posterior is also a major plantar flexor of the ankle and could potentially still suffer from overuse in forefoot strikers due to the increased amount of time in a plantar flexed position.”

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