Researchers at Brigham Young University evaluated the effect of passive hallux adduction (pushing the big toe outwards, towards the other toes) on blood flow in the lateral plantar artery. They hypothesized that this positioning would result in decreased blood flow in the artery, which supplies the plantar fascia. They proposed that the abductor hallucis muscle may play a role in this arterial compression. The abductor hallucis runs along the medial aspect of the foot and moves the big toe away from the second toe. Putting the abductor hallucis in a lengthened position may compress the posterior tibial artery, which feeds the lateral plantar artery. Evidence is emerging that the persistent nature of plantar fasciitis may be a result of decreased blood flow to the plantar fascia, which slows healing. Poor fitting running shoes that are too narrow across the forefoot could cause passive hallux adduction and could be a contributing factor to the development and persistence of plantar fasciitis.
From a biomechanical perspective, hallux valgus reduces the amount of available extension at the 1st MTP joint. 1st MTP extension is essential for normal push off during running, and if it is not available, the body will steal motion from somewhere else (such as the increased knee frontal plane motion and increased foot pronation seen in the Stoneham study). While the results from the Stoneham paper are from barefoot runners, the results could be applied to shod runners as well. If a runner has hallux valgus, they will steal motion from another joint, regardless of whether they are barefoot or shod. A shod runner may be more likely to compensate at the knee, particularly if a shoe has a high amount of toe spring that exceeds that person’s available 1st MTP extension range of motion. The simplest thing a runner can do to reduce their risk of developing hallux valgus is to ensure they are wearing shoes (both running and casual) that are wide enough for their forefoot.