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Simon

You wrote
Oh no my mistake FHB probably doesn't do anything to the hallux IPJ.

Dave

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Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.

Simon

You wrote
1) Medial displacement and external rotation of the 1st ray similar to that seen in HAV.

2) Possibly they could be balanced by -

A) Adductor hallucis = adduction or lateral displacement in terms of body midline plus some internal rotation.

B) Ext Hallucis brevis lateral displacement and some internal rotation. but with unwanted extension.

C) Plantar fascia to balance unwanted extra extension.

Dave

__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.

Simon, Eric and David:

Sorry I haven't been able to contribute to this interesting thread earlier. I've been setting up a new computer.

The plantar intrinsics obviously have important functions for the foot, but certainly they don't have the muscle strength to contribute greatly to gait function as do the extrinsic muscles of the foot. I consider the plantar intrinsics, as a whole, to play an assistive role for reducing the passive tensile forces within the plantar ligaments and plantar fascia, for resisting longitudinal arch flattening (i.e. increasing the forefoot dorsiflexion stiffness), for maintaining digital purchase and for preventing digital deformities.

Together the deep flexors and peroneus longus are the only extrinsic muscles of the foot that cause a forefoot plantarflexion moment which will not only resist longitudinal arch flattening but will also increase forefoot dorsiflexion stiffness. The plantar intrinsics, plantar ligaments and plantar fascia all work together synergistically, along with the deep flexor and peroneus longus muscles, to perform these same functions.

Can the foot function without the plantar intrinsics? Yes, an individual could probably walk and even run for some time without plantar intrinsic muscles. However, the loss of the function of the plantar intrinsic muscles would tend to, over time, cause flattening of the longitudinal arches, would tend to lead to digital deformities and would tend to make the subtalar joint more pronated during weightbearing activities.

It must be remembered, when we observe a foot that has a normal appearance and has good gait function, this is due to a delicate balance of all the muscles, ligaments and bones of the foot and lower extremity interacting in harmony with each other and the central and peripheral nervous systems to produce and maintain this normal structure and function. Certainly, the loss of muscles even as small and seemingly insignificant as the plantar intrinsic muscles will upset this harmonious balance within the body and increase the risk of painful pathology, deformity and abnormal gait function occurring over time.

__________________
Sincerely,

Kevin

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Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College

e-mail: kevinakirby@comcast.net

Private Practice:
107 Scripps Drive, Suite 200
Sacramento, CA 95825 USA
My location

Voice: (916) 925-8111 Fax: (916) 925-8136
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I have been thinking about this for some time in regards to symptoms at the anterior calcaneal tubercles. Simon you mentioned that the intrinsics are contractile tissue and when the extrinsics are not functioning correctly we will get an overload of these intrinsics. This should then increase its contractile force at its origins, and in my mind makes a lot more sense that this is the cause of the common plantar heel pain and not so much as the origin of the plantar fascia. I also think that when these intrinsics are functioning normally, they are going to contribute to the windlass mechanism extensively and mainting and increasing the MLA height during propulsion.

Hope that makes sense... in a hurry.

Ben