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For a patient with pain following a previously undiagnosed sesmoid fracture, would you be more interested in an orthotic designed to limit the range of motion of MP joint or an orthotic to reduce the force on the sesmoid region of the foot?

 

radiograph

 

This is a good example of tissue stress approach to biomechanics.

I can make the case for doing both. In your x-ray there is gapping between the two fragments. That would imply that this is an avulsion injury caused by tension rather than a crush injury. You can use the windlass mechanism to model how various treatments would affect tension on the sesamoids. The sesamoids will be placed under tension when the medial slip of the plantar fascia is under tension.

In gait, at heel lift, there is a relative dorsiflexion of the hallux on the metatarsal. This would appear to be a movement that would increase tension within the plantar fascia. So a rigid shoe might prevent increase in tension in the plantar fascia. A shoe with a rocker tip will also tend to be more rigid than a shoe without a rocker tip and this also something that would tend to decrease tension in the plantar fascia.

In stance, ground reaction force will tend to dorsiflex the first metatarsal. One of the structures that resists this dorsiflexion is tension in the plantar fascia/ sesamoids. So, if you reduced force on the first met head you would reduce tension in the fascia. A reverse Morton's extension (e.g. 1/8" cork under metatarsal heads 2-5) would tend to decrease the load on the first met head.



Eric