Use of MRI for volume estimation of tibialis posterior and plantar intrinsic foot muscles in healthy and chronic plantar fasciitis limbs. (2012)

Abstract
BACKGROUND:
Due to complexity of the plantar intrinsic foot muscles, little is known about their muscle architecture in vivo. Chronic plantar fasciitis may be accompanied by muscle atrophy of plantar intrinsic foot muscles and tibialis posterior compromising the dynamic support of the foot prolonging the injury. Magnetic resonance images of the foot may be digitized to quantify muscle architecture. The first purpose of this study was to estimate in vivo the volume and distribution of healthy plantar intrinsic foot muscles. The second purpose was to determine whether chronic plantar fasciitis is accompanied by atrophy of plantar intrinsic foot muscles and tibialis posterior.
METHODS:
Magnetic resonance images were taken bilaterally in eight subjects with unilateral plantar fasciitis. Muscle perimeters were digitally outlined and muscle signal intensity thresholds were determined for each image for volume computation.
FINDINGS:
The mean volume of contractile tissue in healthy plantar intrinsic foot muscles was 113.3 cm(3). Forefoot volumes of plantar fasciitis plantar intrinsic foot muscles were 5.2% smaller than healthy feet (P=0.03, ES=0.26), but rearfoot (P=0.26, ES=0.08) and total foot volumes (P=0.07) were similar. No differences were observed in tibialis posterior size.
INTERPRETATIONS:
While the total volume of plantar intrinsic foot muscles was similar in healthy and plantar fasciitis feet, atrophy of the forefoot plantar intrinsic foot muscles may contribute to plantar fasciitis by destabilizing the medial longitudinal arch. These results suggest that magnetic resonance imaging measures may be useful in understanding the etiology and rehabilitation of chronic plantar fasciitis.

My comments:

Researcher’s noted that foot intrinsic muscles were 5% smaller on the painful foot of people with plantar fasciitis. In this study they compared the good foot to the bad foot on the same person. However, I would expect the relative atrophy to be greater when compared to healthy controls. In my physical therapy office, I have noticed people with plantar fasciitis haven weakness in both legs, with the painful side often being the worst. Still, it’s a very interesting study. The authors pointing out that plantar fasciitis isn’t just an injury associated with a loss of range of motion, but one associated with a loss of foot intrinsic muscle strength that can benefit from strengthening as well as typical rehabilitation programs that focus solely on morning foot stretches and orthotics (which turn out to do a lot less good than people think), was an interesting point.