The partial truth about the Foot Tripod. The HEXApod.

The gait guys have talked about the foot tripod for a very long time. But the truth of the matter is that it is really a HEXApod. HEXA means 6. And when the foot is properly orientated and engaged on the ground, the 5 metatarsal heads and the heel should all be engaged with the ground, truly making it an asymmetrical hexapod. In an ideal scenario, the foot would be most stable if it looked like the strange symmetrical hexapod above with the contact points equally distributed around a center point. But that is not the human foot and this version of a hexapod is far simpler and likely inferior to the foot hexapod when human locomotion is to be attempted. The human foot is engineering marvel when it works properly.  

Perhaps the best example of what I mean by the foot being a HEXApod is in the pressure diagram above. In that first picture, on the right of that picture, we see multiple pressure points under the metatarsal heads of the right foot.  Minus the missing 1st metatarsal head pressure point (taken over by increased flexor hallucis longus activity represented by increased pressure at the big toe),  this pretty much confirms that the foot is not a tripod, rather a hexapod. The theory of the tripod, the 1st and 5th metatarsal heads and the heel, is only crudely accurate and honest. In this picture case, this person has increased lateral foot weight bearing (possibly why the 1st MET head pressure is absent) and possibly represented by pressure under the base of the 5 metatarsal. This is not normal for most people and if this person could get the 1st MET head down, they might even have a HEPTApod foot structure because of the 5th metatarsal base presentation (which sometimes represents peroneal muscle weakness). 

Where did we lead you astray after all these years of “tripod” talk ? We have always discussed the foot tripod. We have always discussed the imperative need to keep the limb’s plumb line forces within the area represented by the tripod.  If your forces fall more laterally within the tripod, as in this first discussed picture, one is at increased risk of inversion events and the myriad of compensations within the entire body that will occur to prevent that inversion. So again, why the tripod?  Well, it is easier to understand and it serves our clients well when it comes to finding active foot arch restoration as seen in this video of ours here.  But, the truth of the matter is that all of the metatarsal heads should be on the ground. The 2nd METatarsal is longer, the 3rd a little shorter, and the 4th and 5th even a little short than those. With the 1st MET shorter, these 5 form a kind of parabolic arc if you will. Each metatarsal head still should contact the ground and then each of those metatarsals should be further supported/anchored by their digits (toes) distally.  So the foot is actually more truly a HEXAPOD. Take the old TRIPOD theory we have always spoken about and extend a curved line beyond the forefoot bipod points (1st and 5th metatarsals) to incorporate contact points on the 2, 3 and 4th metatarsal heads. These metatarsals help to form the TRANSVERSE arch of the foot. It is this transverse arch that has given us the easily explainable foot TRIPOD because if a line is drawn between just the shorter 1st and 5th metatarsals, we do not see contact of the 2-4 metatarsal heads when we only look for pressure between these two bipod landmarks, but the obvious truth is that the 2-4 metatarsals are just longer and extend to the ground further out beyond this theoretical line drawn between the 1st and 5th MET heads.   

So, the foot is a HEXAPOD. Make no mistake about it. It is more stable than a tripod because there are more contact points inside the traditionally discussed foot tripod model. And frankly, the tripod theory is just a lie and just too fundamentally simple, unless you are an American 3 toed woodpecker.

Dr. Shawn Allen,     www.doctorallen.co

one of the gait guys

Keeping it Objective.

For clinicians and some die hard foot geeks, we often like to keep things objective. What could be more objective than an angular measurement? A few important measurements when examining or radiographing feet can give us information about clinical decision making (not that we suggest radiographs for mensuration purposes unless you are a surgeon, but when they are already available, why not put them to good use ?). When things fall outside the accepted range, or appear to be heading that way, these numbers can help guide us when to intervene. 

Hallux valgus refers to the big toe headed west (or east, depending on the foot and your GPS). In other words, the proximal and distal phalanyx of the great toe (hallux) have an angle with the 1st metatarsal shaft of typically > 15 degrees. This angle, called the Hallux Valgus Angle (HVA above) is used to judge severity, often for surgical intervention purposes but can guide conservative management as well. 

Metatarsus Primus Varus (literally, varus deformity of the 1st metatarsal) often accompanies Hallux Valgus. It describes medial deviation of the 1st metatarsal shaft, greater than 9 degrees. This angle is called the intermetatarsal angle and is measured by the angle formed by lines drawn parallel along the long axis of the 1st and 2nd metatarsal shafts. 

One other measurement is the Distal Metatarsal Articular Angle, which measures the angle between the metatarsal shaft and the base of the distal articular cap (ie, where the cartilage is) of the 1st metatarsal. This typically should be less than 10 degrees, preferably less than 6 degrees. Remember, these are static angles, things can change with movement, engagement, weight bearing strategies and shoes. What you see statically does not always predict dynamic angles and joint relationship.s

Are you doing surgery? Perhaps, as a last resort. Hallux valgus and metatarsus primus varus can be treated conservatively.

How do you do that?

The answer is both simple and complex.

The simple answer is: anchor the head of the 1st ray and normalize foot function. This could be accomplished by:

  • EHB exercises to descend the head of the 1st metatarsal
  • exercise the peroneus longus, to assist in descending the head of the 1st metatarsal
  • short flexor exercises, such as toe waving, to raise the heads of the lesser metatarsals relative to the 1st
  • work the long extensors, particularly of the lesser metatarsals to create balance between the flexors and extensors
  • consider using a product like “Correct Toes” to normalize the pull of the muscles and physically move the proximal and distal phalanyx of the hallux
  • wear shoes with wide toe boxes, to allow the foot to physically splay
  • consider using an orthotic with a 1st ray cut out, to help descend the head of the 1st metatarsal

This is by no means an exhaustive list and you probably have some ideas of your own. 

The complex answer is that in the above example, we have only included conservative interventions for the foot and have not moved further up the kinetic (or neurological chain). Could improving ankle rocker help create more normal mechanics? Would you accomplish this by working the anterior leg muscles, the hip extensors, or both? Could a weak abdominal external oblique be contributing? How about a faulty activation pattern of the gluteus medius? Could a congenital defect or genetic be playing a role? We have not asked “What caused this to occur in the 1st place?”

Examine your patients and clients. Understand the biomechanics of what is happening. Design a rehab program based on your findings. Try new ideas and therapies. it is only through our failures that we can truly learn.

The Gait Guys

references used:

http://www.bjjprocs.boneandjoint.org.uk/content/90-B/SUPP_II/228.3

http://www.slideshare.net/ANALISIS/hallux-valgus-2008-pp-tshare

http://www.orthobullets.com/foot-and-ankle/7008/hallux-valgus

http://www.slideshare.net/bahetisidharth/hallux-valgus-31768699?related=1

When the big guy heads medially….Game Changer

Lately we have been seeing a lot of bunions (hallux valgus). While doing some research on intermetatarsal angles (that’s for another post) we came across the nifty diagram you see above. 

Regardless of the cause, as the 1st metatarsal moves medially, there are biomechanical consequences. Lets look at each in turn. 

  • the EHB (extensor hallucis brevis) axis shifts medially. this muscle, normally an extensor of the proximal phalanyx, now becomes more of an abductor of the hallux. It’s secondary action of assisting the descent of the head of the 1st metatarsal no longer happens and it actually moves the base of the proximal phalanyx posteriorly, altering the axis of centration of the joint, contributing to a lack of dorsiflexion of the joint and a hallux limitus
  • Abductor hallucis becomes more of a flexor, as it moves to the plantar surface of the foot. Remember, a large percentage of people already have this muscle inserting more on the plantar surface of the foot (along with the medial aspect of the flexor hallucis brevis), so in these folks, it moves even more laterally, distorting the proximal phalanx along its long axis (ie medially) see this post here for more info
  • Flexor hallucis brevis moves more laterally. Remember this muscle houses the sesamoid bones before inserting onto the base of the proximal phalannx; the medial blending with the abductor hallucis and the lateral with the adductor hallucis. Because the sesamoid bones have moved laterally, they no longer afford this muscle the mechanical advantage they did previously and the axis of motion of the 1st metatarsal phalangeal joint moves dorsally and posterior, contributing to limited dorsiflexion of that joint and a resultant hallux limitis. The lateral movement of the sesamoids also tips the long axis of the 1st metatarsal and proximal phalanyx into eversion. In addition, the metatarsal head is exposed and is subject to the ground reactive forces normally tranmittted through the sesamoids; often leading to metatarsalgia. 
  • Adductor hallucis: this muscle now has a greater mechanical advantage  and because the head of the 1st ray is not anchored, acts to abduct the hallux to a greater degree. The now everted position of the hallux contributes to this as well

As you can see, there is more to the whole than the sum of the parts. Bunions have many biomechanical consequences, and these are only a small part of the big picture. Take you time, learn your anatomy and examine everything that has a foot!

See you in the shoe isle…

Ivo and Shawn

pictures from: http://www.orthobullets.com/foot-and-ankle/7008/hallux-valgus and http://www.stepbystepfootcare.com/faqs/nakedfeet/

When the big guy heads medially….Game Changer

Lately we have been seeing a lot of bunions (hallux valgus). While doing some research on intermetatarsal angles (that’s for another post) we came across the nifty diagram you see above. 

Regardless of the cause, as the 1st metatarsal moves medially, there are biomechanical consequences. Lets look at each in turn. 

  • the EHB (extensor hallucis brevis) axis shifts medially. this muscle, normally an extensor of the proximal phalanyx, now becomes more of an abductor of the hallux. It’s secondary action of assisting the descent of the head of the 1st metatarsal no longer happens and it actually moves the base of the proximal phalanyx posteriorly, altering the axis of centration of the joint, contributing to a lack of dorsiflexion of the joint and a hallux limitus
  • Abductor hallucis becomes more of a flexor, as it moves to the plantar surface of the foot. Remember, a large percentage of people already have this muscle inserting more on the plantar surface of the foot (along with the medial aspect of the flexor hallucis brevis), so in these folks, it moves even more laterally, distorting the proximal phalanx along its long axis (ie medially) see this post here for more info
  • Flexor hallucis brevis moves more laterally. Remember this muscle houses the sesamoid bones before inserting onto the base of the proximal phalannx; the medial blending with the abductor hallucis and the lateral with the adductor hallucis. Because the sesamoid bones have moved laterally, they no longer afford this muscle the mechanical advantage they did previously and the axis of motion of the 1st metatarsal phalangeal joint moves dorsally and posterior, contributing to limited dorsiflexion of that joint and a resultant hallux limitis. The lateral movement of the sesamoids also tips the long axis of the 1st metatarsal and proximal phalanyx into eversion. In addition, the metatarsal head is exposed and is subject to the ground reactive forces normally tranmittted through the sesamoids; often leading to metatarsalgia. 
  • Adductor hallucis: this muscle now has a greater mechanical advantage  and because the head of the 1st ray is not anchored, acts to abduct the hallux to a greater degree. The now everted position of the hallux contributes to this as well

As you can see, there is more to the whole than the sum of the parts. Bunions have many biomechanical consequences, and these are only a small part of the big picture. Take you time, learn your anatomy and examine everything that has a foot!

See you in the shoe isle…

Ivo and Shawn

pictures from: http://www.orthobullets.com/foot-and-ankle/7008/hallux-valgus and http://www.stepbystepfootcare.com/faqs/nakedfeet/

Did you see this in our recent blog post here ? a reader made us look closer. Did you catch it ?
The clients right foot appears to have a dropped 1st met head. (we hate this term, because it is not accurate and is a sloppy clinical description). In this still photo it appears plantarflexed.  But in this video, consider the descended 1st met head as due to the disuse or weakness of the EHL muscle (extensor hallucis longus) of the 1st toe. Or, is this in fact a compensated forefoot varus ? Sure looks like it. But with all that anterior compartment weakness (as we discussed in the previous blog post link above) it could just be a mirage. In the photo above, in a normal foot the rearfoot plane (greenline) should parallel the forefoot line (orange line). In this case, in this actively postured foot (thus some inaccuracy here, we are merely making a teaching point from the photo) the upslope of the orange line suggests a forefoot varus. This would be true if the first Metatarsal head also was on this line, but you can see that it has its own idea. This represents, in theory (regarding this photo), a compensated forefoot varus. But remember, this client is  holding the foot actively in this posture. A true hands on assessment is needed to truly define a Forefoot varus, and whether it is anatomic, flexible, rigid or in many cases, just a learned functional posturing from weakness of the flexor/extensor pairing of the 1st metatarsal complex or from other weaknesses of the other forefoot evertors.  It gets complicated as you can see.

As always, knowledge of the anatomy and functional anatomy allows for observation, and observation leads to understanding, which leads to answers and then remedy implementation. Our thoughts, knowing the case, is that this is a functional appearance illusion of a compensated forefoot varus due to the EHL, EDL and tibialis anterior weakness (anterior compartment) and how they play together with the flexors. One must be sure to assess the EHL when examining the foot. Test all of the muscles one by one.  We have been talking about toe extensors for a long time, they can be a paramount steering wheel for the forefoot and arch posture. Podcast 71 talks about this Forefoot varus, and you should care.
In a 2009 study by Reynard et al they concluded: 

  • “The activity of extensor digitorum longus muscle during the swing phase of gait is important to balance the foot in the frontal plane. The activation of that muscle should be included in rehabilitation programs.” (1)

here is the video again.

Have a burning desire to learn more about forefoot varus, here are 25 blog post links from our last few years. And/or you can take our National Shoe Fit program (downloadable links below).

Knowing what you are seeing during your exam and gait analysis can only truly come from coupling your observations with a clinical exam.  Anything less is speculation and guess work.  It is gambling, and this is not Vegas baby, this is someone’s health.

Shawn and Ivo, The Gait Guys

________________

National Shoe Fit Certification Program:

Gait Guys online /download store (National Shoe Fit Certification and more !) :

http://store.payloadz.com/results/results.aspx?m=80204

1. Foot (Edinb). 2009 Jun;19(2):69-74. Epub 2008 Dec 31. Foot varus in stroke patients: muscular activity of extensor digitorum longus during the swing phase of gait.  Reynard F, Dériaz O, Bergeau J.

Other web based Gait Guys lectures:

www.onlinece.com   type in Dr. Waerlop or Dr. Allen,  ”Biomechanics”Reference

Welcome to rewind Friday, Folks. We always seem to be talking about bunions, and receive quite a few questions on them. This brief video discusses where they come from.

Enjoy!

The case of the missing toes.

OK, a bit dramatic but as you can see in the plantar view above, all you can see is the toe pads, the rest of the digit shafts are hidden.  

This is a classic example of a foot imbalance. We have talked about this many times before but the attached video link here  ( http://youtu.be/IIyg7ejYNOg ) shows it very well.  Read on.

There is shortness and increased resting tone in the short toe extensors (EDB, extensor digitorum brevis) and long toe flexors (FDL=flexor dig. longus) with insufficiency in the short flexors and long extensors. This pairing creates a hammer toe effect.  In the video, you can see that these toes are showing early hammering characteristics, but not yet rigid ones. The key word there is, “yet” so this is still a correctable phenomenon at this point.  You can also clearly see the distal migration of the metatarsal fat pad. The fat pad has migrated forward of the MET heads and is being pulled forward by the excess tension in the long toe flexors. As this imbalance in the toe flexors and extensors develops, the forefoot mechanics get impaired and the lumbricals (which anchor off off the FDL) become challenged. Their contributory biomechanics, amongst other things, help to keep the fat pad in place under the metatarsal heads. You can see in this video link above that by proximally migrating (towards the heel) just the fat pad back under the MET heads the resting mechanics of the toes changes, for the better.  

Remember the other functions of the lumbricals ?  their other major functions, namely: thinking from a distal to proximal orientation (a closed chain mode of thinking), they actually plantarflex the metatarsal on the fixed phalynx, assist in dorsiflexion of the ankle, and help to keep the toes from clawing from over recruitment of the flexor digitorum longus.

Here is another blog post we did on a similar presentation.http://thegaitguys.tumblr.com/post/14766494068/a-case-of-plantar-foot-pain-during-gait-this

Proper balance of the toe flexors and extensors, and their harmony with lumbricals and fat pad amongst other things will give healthy long flat toes that can help the proximal biomechanics of the foot.  If you have neuromas, metatarsalgia, hammer toes, claw toes, migrating toes, bunions or hallux valgus amongst many other things, this might be a good place to start.   

There are exercises that can help this presentation, but understanding “the why” is the first step.

Shawn and Ivo

The Gait Guys