The importance of a functional increase in dorsiflexion stiffness at the MTP joints during gait

Members do not see these Ads. Sign Up.

Ok I´ve been going on about this for awhile now - thought it was time for a discussion.

There have been many discussion about Functional Hallux Limitus FnHL and the roll it playes in changing of gait - Sagittial plane theory.

There have been discussions if the increase in dorsiflexion stiffness at the 1st MTP and we should include all MTP joints is from the results of mechanical stress- ie increase in internal and external plantarflexion moments at the MTP joint.

There have been discussions about the reverse windlass mechanism

I´m of the school of thought the an increase in dorsiflexion stiffness is the result not the cause.

Heres a little expriement I do when discussing this.

Now I believe that a change in the dorsiflexion stiffness of all MTP joints during gait maybe a good thing, by changing the length of the lever arm of the foot the loads placed on the Plantar fascia and triceps surea will increase and if this load does not lead to pathology we will have great energy return and more effective gait.

I believe it all comes down to timing andor load. So increasing the dorsiflexion stiffness at the MTP may be very important.

Thoughts ?

 

Careful with the experiment. Are you aware of Hicks' findings where tension in the fascia increased as force on the foot was more distally? Here's a more simple experiment, try to dorsiflex a hallux in a standing individual. Then have the individual lean forward (there will be more tension in the Achilles tendon and the weight will shift anteriorly.) The hallux will be more difficult to dorsiflex when leaning forward.

That made realize that there is another argument against Bosjen-Moller's short and long gear push off. Bosjen-Moller assumes push off at the met heads. There are a lot of people who have a deep impression in their sock liner under the hallux that is the result of high pressure there. So, a significant number of people will have their foot lever end more distally at the hallux.

I'd agree with load being important. Things break when placed under greater stress.

Eric

 

An indication of FnHL. The first metatarsal and hallux become one leaver instead of two resulting in the pressure over the Hallux into propulsion. (maybe)!

 

No was not aware that Hicks said that or forgot - need to re-read his papers again

What do you think of my idea that increased dorsiflexion stiffness at the MTP joints at certain stages of the gait cycle may have benefits - such as gretaer energy return ?

 

There are always trade offs. Trying to get more elastic energy out of the plantar fascia may lead to increased stress/ pain in the plantar fascia. I vaugely remember a paper looking at 1st MPJ power. This paper may give you some idea of how much the 1st MPJ can add to gait power.

To look at energy return you should look not at stiffness but joint power. They are somewhat related, but not the same thing. Power = moment x angular velocity. So, the toe would have to plantar flex to add power to gait. If elastic energy were stored in the fascia then it could be the source of the moment that creates the movement. However, if the fascia doesn't stretch a significant amount then it would not be producing power and if you saw plantar flexion it might be the muscles of the toe providing the moment for the power. If the STJ were to pronate, the windlas could "unwind" and create some plantar flexion moment and motion.

You could probably repeat the above discussion by looking at the plantar fascia and the midtarsal joint.


Eric

 

Thanks Eric stuff to consider - I´ll try and look for the paper.

 

Michael:

Sorry for the delay in replying. I've been very busy lately getting my first book ready to be reprinted.

I believe that more fully comprehending the weightbearing function of the plantar fascia is the key here toward developing a better understanding of how it performs the many functions for our foot and lower extremity, passively, without any muscular effort by the individual. In your analysis above, you note that one of the critical functions of the plantar fascia is to passively increase the plantarflexion moment at the metatarsophalangeal joints (MPJs) during the latter stages of the stance phase of gait. This increase in MPJ plantarflexion moment will increase the ground reaction force (GRF) being exerted by the plantar digit or, put another way, will increase the digital purchase force.

The passive function of the plantar fascia greatly contributes to the ability of the digits to participate in a plantar load-sharing arrangement with the metatarsal heads so that, during late midstance and propulsion, the plantar digits are able to reduce the plantar load on the metatarsal heads. Disrupting the plantar fascia function, such as occurs with a significant plantar plate tear, a plantar fasciotomy, a plantar fascia rupture, or even by a shortening of a metatarsal ray by fracture or surgery will decrease the digital purchase force and will likely also increase the GRF acting plantar to the metatarsal head. Such a loss of digital purchase force may, in itself, lead to painful conditions of the plantar metatarsal head. In addition, a loss of of plantar fascial integrity/passive tensile force may, over time, lead to digital deformity.

In the special case of the much larger diameter 1st MPJ that has plantarly located sesamoids (which significantly increase the plantarflexion moment arm of the plantar fascia at the MPJ), the effects of the plantar fascia on hallux purchase force (and also on 1st MPJ compression force) is very important. Any factor which increases the load on the first ray will likely also cause an increase in tensile force on the slip of the plantar fascia which attaches to the sesamoids and will increase hallux purchase force. First ray load may be increased by such factors as increasing the tension in the Achilles tendon (e.g. leaning forward as Eric mentioned) or increasing the internal STJ pronation moment (e.g. by increased peroneus brevis contractile force).

I have written quite extensively on these subjects previously in my three books and I feel that understanding the function of the plantar fascia is very important for both the non-surgical and surgical podiatrist.

Good discussion.:drinks

 

As I recall, Bojsen-Moller recognised this in one of his papers and called it something like "ultra-high gear". it might have been in:
Bojsen-Moller, et al.
Significance of free-dorsiflexion of the toes in walking
ACTA ORTHOPAEDICA SCANDINAVICA
Volume 50, Issue 4, 1979. Pages: 471

 

Interesting.
I have wondered sometimes whether elite level sprinters may utilise this... fully dorsiflex the medial column, create a hallux limitus... therefore effectively have a leaf spring? Part of this would be having the soft tissue physiology to do this without injury?
I believe Benno Nigg was very excited about research showing that a stiff sole sprint spike would bring down the world record. Perhaps the research was simply showing what sprinters do already without external help???

 

1st look forward to making my Kirby book set complete when the reprint comes out I guess there will be a 4th soonish as well - Thanks for taking the time to get the ideas down on paper.

as you and Eric have mentioned the increase in tension in the Achilles tendon will effect the tension in the plantar fascia and therefore all things being equal increase the Dorsiflexion stiffness at the MTP joints. This increase in tension in the Achilles will also be important in energy storage and return by my way of thinking. I had some PFD+s but I think Craigs getting some copyright stress but will post up the abstracts.

 

Craig do you remember Why B Nigg thought that it would aid the sprinter - ie the mechancial changes which occured?

I remember someone saying that a study found that sprinters also had a higher incidence of structural hallux limitus and this was thought to add performance.

 

For those who would like to have a read of the full text - click on this link -http://informahealthcare.com/doi/pdf/10.3109/17453677908989792

 

Michael:

The first book will be reprinted very soon. Actually, the first book is the largest and probably much more practically oriented than the second and third books. It has now been 24 years since I wrote my first Precision Intricast Newsletter. However, when I read the early newsletters, I can't say that my ideas have changed much during the past 20+ years, except for how I now describe the functional axes of the midtarsal joint.

BTW, I don't think that any fourth book will be here for at least another 3 years..... assuming I'm still alive and kicking in early 2014.:drinks