05/28/2013    Kevin A. Kirby, DPM

We Walk in a Tripod Fashion: CA Podiatrist (Robert Phillips, DPM)

To further add to the excellent points made by
Dr. Phillips about the importance of weight-
bearing function of the metatarsal rays, I
believe that the biggest misconception most
podiatrists have about the metatarsals is that
they somehow have a “locking position”, where
they will not dorsiflex further under increasing
dorsiflexion loading forces. This is certainly
not the case, and, unfortunately, seems to be a
myth that is perpetuated from one generation of
podiatrists to the next.

The metatarsal rays do not “lock”, like the
ratcheting wrench, in a “fully dorsiflexed
position” where they remain in one position even
with increasing loads acting upon them. Rather,
the metatarsal rays should rather be thought of
as “leaf springs”, as in the rear suspensions of
trucks, where there are infinite adjustment
positions depending on the load being applied to
those springs at any given instant in time. In
this way, each metatarsal ray, when subjected to
increased ground reaction force, will dorsiflex
just enough to allow the metatarsal head to
remain in contact with the weightbearing surface.

Therefore, every metatarsal ray, depending on its
dorsiflexion stiffness, will dorsiflex so that
the plantar forefoot is congruent to any surface
irregularities of the ground. This spring-like
ability of each metatarsal ray to be able to
conform to the irregularities of the ground
results from the viscoelastic nature of the
supporting plantar ligaments, plantar fascia,
plantar intrinsic muscles and extrinsic muscles
of the plantar arch. In addition, the central
nervous system, continually processes afferent
data from the plantar skin, joint and tendon
receptors and from visual and balance receptors
to determine the optimal efferent motor activity
to the lower extremity musculature in order to
allow the metatarsal rays, and the foot as a
whole, to function optimally during each selected
weightbearing activity.

Metatarsal rays that “lock” into a “fully
dorsiflexed position” could never mechanically
provide the infinite adjustments that are
necessary for the foot and lower extremity to
function in the wide variety of human bipedal
activities required during athletic and other
daily weight-bearing tasks. Rather, metatarsal
rays, with spring-like mechanisms, are necessary
to allow the foot and lower extremity to function
optimally in all of our daily weight-bearing
activities (Kirby KA: Foot and Lower Extremity
Biomechanics III: Precision Intricast
Newsletters, 2002-2008. Precision Intricast,
Inc., Payson, AZ, 2009, pp. 75-84).

Kevin A. Kirby, DPM, Sacramento, CA,
kevinakirby@comcast.net

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