The Rigid Flat Foot: Do you know what you are actually dealing with ?

In these 5 photos of a client with a flat arch we see some great opportunity to discuss some of the clinical issues and clinical thinking that needs to occur.  As usual we write our blog posts on the fly with a principle at hand that we want to drive home, or in this case “into the ground”.  There are many more clinical issues with this type of foot and its problems, so today’s list and dialogue is not meant to be exhaustive.  But, if you take one thing away from this case, it should be that not all flat feet can take a stability shoe or an orthotic. So, if you are in the mind set that “when it is flat, jack it up (the arch)” and “when it is high (the arch), cushion it” hopefully you will open your eyes a bit to the reality that it just is not that simple.  IF you want to learn more about these issues we have purposefully put together the National Shoe Fit program for stores and doctors/therapists so they can learn more about the anatomy of the feet and shoes and how to pair them up to create the best recipe for a person.  

Now, onto this case.

In this case you should notice a few things. 

1- the rigidity of the flat foot as portrayed in the photo where we are pushing up with our thumb on what once was the peak of the arch (yes, there are 5 photos in this case, click on one to enlarge or scroll) . We are attempting to push up, but the midfoot is completely rigid. This is a classic Rigid Flat Foot Deformity, A Rigid Pes Planus if you will. 

2- There is a prominence at the navicular bone, both top (dorsal) and bottom (plantar) aspects of the foot (see photo of my hand with finger and thumb indicating these areas). The plantar prominence is the actual naviular bone (mostly) that has become weight bearing (termed “weight bearing  navicular” and crudely by some as a dropped navicular, a term we dislike). And the dorsal prominence is a dorsal crown of osteophytes. This means a dorsal ridge of bone has formed at the navicular-1st cuneiform bone/joint interval because of the constant and repetitive compression of the two against each other dorsally as midfoot arch collapse occurred repeatedly and then became a fixed permanent entity.

3- The hyper dorsiflexion range at the 1st MTP joint (the big toe). This range is excessive at actually was able to exceed 90 degrees (see photo) !  Even at rest the hallux (big toe) is extended suggesting the volume of dorsiflexion it gets all the time.  By the way, there was little to no hallux 1st MPJ joint plantarflexion (downward bend), not in a foot this flat. In fact most of that is from the contracture of the short extensors of the toes as noted by the photo showing the hammer toe formation (hammer toe = contractured short extensor myotendon, and to the long flexors as well). Hammer toes are almost always seen in a flat foot presentation, to a degree.

Now, lets put some things together (but a reminder, this is a single principle today, there are many more issues here).

Today’s Principle: Passing the Buck

Normally we need to have just slightly greater than 90 degrees of ankle mortise dorsiflexion to progress the body over the ankle.  Put in other words, we need to be able to get the tibia slightly past vertical (perpendicular to the ground, hence 90+ degrees). Depending on the reference, anywhere from 15-25 degrees past that 90 degree vertical, thus 105 to 120 degrees) is the goal.

If an ankle cannot get that range, the range must be achieved either proximal or distal to that joint, ie. Passing the Buck beyond the ankle mortise joint.  Proximally, one can hyperextend the knee to enable the body mass to pass sagittally over the ankle but a better strategy (arguably) is to compensate distally via collapsing the arch and pronate more than normally through the midfoot putting undue stress and strain into the plantar fascia and over time eventually collapsing the arch and creating the dorsal and plantar bony prominences we mentioned in #2. By dropping the arch, the subtalar joint exceeds its ranges and the talus and navicular collapse medially and plantarwards. 

When the arch drops to the planus stage the tibia is passively thrust forward achieving the necessary forward tibial progression to get body over and past the ankle to enable forward progression. 

Remember, this pes planus will dorsiflex the long metatarsal bone (meaning make it parallel to the ground). This will screw up the 1st Metatarsal-phalangeal joint function and  impair the Windlass Mechanism of Hicks at the big toe (translation, it will impair the sesamoids, possibly leading to sesamoiditis, and change the normal toe function and its tendons.  This is seen both in the pes planus foot and in hallux rigidus turf toe presentations where the big toe loses its  normal ranges as compared to this case here).

So, the normal range can as for the buck to be passed proximally into the kinetic chain or distally. Which one would you want, if you had to chose?  It is a tough choice, luckily the body decides for us.  IF you consider that luck !

Regardless, one has to stand in awe that the body will find a way to get the range elsewhere when it cannot find it in the primary motor pattern.  And when the range has to be gained elsewhere, the muscular function has to change as well and prostitute the normal kinetic chain motor patterns. 

Here is a tougher question for you. Would you want this phenomenon on one side and be uniliaterally compromising (and thus have to compensate on the opposite side) the kinetic chain or bilaterally and have the asymmetry on both sides ?  That is a tough one. There is no good choice however.

*So, a flat RIGID foot.  If you jam an agressive orthotic (or possibly even a motion control shoe) under this foot it could very likely be painful to those rigid bony prominences and it will remove the client’s “passing the buck” compensation. Now the forces may have to revert to the proximal strategy at the knee.  So, when do YOU go with the orthotic or motion control shoe ? When it comes to the feet, use your head.  And, consider the Gait Guys, National Shoe Fit DVD program.  Email us at : thegaitguys@gmail.com