A misunderstanding about hallux valgus

[Gerrard Farrell]

Subject Hallux valgus (HV), also known as a bunion, is one of the most common forefoot deformities. HV manifests with the proximal phalanx deviating laterally and the first metatarsal head deviating medially

The misunderstanding-

Quote from Physiopedia but a widely held view-

"It ( adductor hallucis ) is a key intrinsic muscle of the foot. Due to the pull on the lateral aspect of the first digit, the adductor hallucis may contribute to hallux valgus deformities."

IMO the above statement is more wrong than right . The idea that adductor pull on the the lateral aspect of the first digit seems to be based around the idea that the pull on the hallux somehow levers the 1st MTPJ medially giving rise to HV or a bunion ,but this idea is demonstrably wrong.
image.png

Here we see the pull of the adductor hallucis in blue and a medially deviated 1st met head . However a simple model shows that adductor pull actually resist medial deviation.

In the video below the pen in my hand represents the 1st metatarsal ,the pen attached to it by the elastic the toe, the dental floss the adductor hallucis, and the radio the adjacent toes . Note how adductor activity reduces hallux valgus angle it does not increase it .

https://www.youtube.com/watch?v=rGQEGUZleZs

[Gerrard Farrell]

Here is a link to a video showing the adductor hallucis acing to reduce HAV angle during the doming exercise.

https://www.youtube.com/watch?v=uHBJH5pD3aM

[Gerrard Farrell]

Some have written that hallux valgus has a genetic component and that is probably true ,however it is a rare condition in unshod populations. It seems to me then that although the morphology of the bones of the foot have a role to play, the condition does not develop without the influence of modern footwear.

Here is a quote from a paper on the subject-

"Hallux valgus (HV) is a common deformity characterized by progressive lateral deviation of the great toe at the first metatarsophalangeal joint (1^st MTPJ). It commonly associates with a painful overlying soft-tissue prominence, the “bunion”. A recent systematic review estimated the prevalence of HV to be 23% in adults aged 18 to 65 years. It becomes more frequent with increasing age and is more prevalent in women than men. Several potential risk factors for HV have been identified. Various mechanical factors are thought to associate with HV including metatarsal length and head-shape, first ray hypermobility and foot posture. HV is rare in unshod populations but associates with wearing high-heeled or narrow shoes." E Roddy 2011

I strongly suspect than modern footwear gives an increased HAV angle and also an imbalance between the intrinsic and extrinsic toe flexors. The footwear weakened adductor hallucis, which normally acts to reduce hallux valgus progression, becomes less effective at doing this, and the increased hallux valgus angle, produced by footwear, increases the mechanical advantage of the flexor hallucis longus which then contributes to the progression of hallux valgus and bunion formation.