New research confirms foot muscle atrophy and toe deformities

It is surprising how long it has taken for significant steps to be made in understanding the relationship between foot muscle strength and foot function.

The most recent exciting paper has come from one of the world leaders in the research of intrinsic muscles and their implications in toe deformities. Karen Mickle from Victoria University, Australia has been extraordinarily productive over the last 10 years with her use of diagnostic ultrasound and dynamometers. She has collaborated with some well known researchers too including Chris Nester and Hylton Menz.

The most recent paper to have come forth from Karen has just been published in Arthritis Care & Research.

Essentially the results of this paper have confirmed what has long believed to be the case i.e. if you have toe deformities such as hallux valgus and claw toes,  you are likely to have atrophic (smaller and weaker) muscles. If you have hallux valgus you have a smaller abductor hallucis, if you have lesser toe deformities (claw toes) then you had atrophy and weakness in the intrinsics attached to these.

This study collected data from 44 older adults (>60 years) with either toe deformities or not (controls). They then underwent ultrasound assessment to look at the size of the muscles in their feet with a standardized ​protocol. 

What was particularly interesting in this study was that virtually every muscle examined (of which there were 7 different muscles examined) was atrophic relative to the controls, bar flexor hallucis longus. Take a look at the chart below:
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The tricky part of this research then leads us to the next important question. Does the atrophy occur because of the toe deformity or does it lead to the toe deformity? Current evidence​ would point to the latter, which suggests specifically in relation to hallux valgus that prevention through exercise should happen in the early stages to stop the progression of the deformity. Once the abductor hallucis muscle moves under the 1st metatarsal it acts as a weak flexor instead of an abductor.

References:

1. Mickle, Karen J., and Christopher J. Nester. "Morphology of the Toe Flexor Muscles in Older Adults With Toe Deformities." Arthritis care & research 70.6 (2018): 902-907.​
2. Mortka, Kamila, Przemysław Lisiński, and Agnieszka Wiertel-Krawczuk. "The study of surface electromyography used for the assessment of abductor hallucis muscle activity in patients with hallux valgus." Physiotherapy theory and practice (2018): 1-6.