Originally Posted by footphysio

My head literally hurts trying to grasp all this biomechanical information. I am trying to make sense of it all as this way of thinking is relatively new to me. All this talk about FncHL, COM and compensations makes me think of a current client I have and several past clients with the same characteristics. The past few replies may help to explain the biomechanics behind their pathologies. May be some of you could help me put this together.

This fellow I am seeing is extremely fat (Simon opened the flood gates for being completely frank). He presents with distal Achilles pain. He has an out toed gait with a midfoot strike and pushes off through the lateral rays rather than the 1st ray. He has a FncHL, forefoot valgus and medially deviated STJ. My thinking here ( after reading the last few posts) is first of all, ff valgus leads to FncHL by way of Davids Smith's explanation. FncHL leads to decreased forward progression. His centre of his extremely large mass is pushing down on his medialy deviated STJ giving a strong pronation moment. His plantar flexors are now working really hard to plantar flex and supinate, especially since his windlass mechanism will not assist due to the FncHL (hence Achilles pain). In the end he out toes and pushes off through his lateral toes because he cannot go through 1st ray due to pain. He also has really tight gastroc/soleus. I'm not sure how I can tie that in other than it causing the midfoot strike and contributing to the pronation and outtoeing as well as his Achilles pain.

So, to help this man would a logical first step (other than professional dietary advice) be to use an orthotic ff valgus post?

BTW, does this type of gait seem to be common with obese people? I may be noticing a trend in my relatively short time in practice.

Originally Posted by Simon Spooner

So the tissue under stress is the achilles. What is the function of the achilles and what forces would cause it to be excessively stressed? What would be the best way to reduce said stresses?

Originally Posted by Craig Payne

Interesting you should raise this. I was going to start a thread on it at some stage.

For some time I struggled with the rationale for using foot orthoses in achilles tendonitis. None of the risk factor studies showed xs foot pronation as a risk factor.... etc etc .... BUT, so many claim clinical success with the use of foot orthoses.

Then I got thinking ... what is the function of the muscles attached to the achilles tendon? If they do not have to work as hard, then the loads through the achilles would be reduced.

The function of the muscles are:
1. Provide a plantarflexory moment at the ankle joint
2. Provide a supinatory moment at the STJ
(ignore the gastroc effect at the knee for now)

So if we are to reduce loads in the achilles tendon with a foot orthotic, then we need to reduce those moments....ie incorporate design parameters into the foot orthotic to change those moments.

A heel raise has been the mainstay of achilles management, but I not so sure it actually reduces the plantarflexory moment (I think Sharon Dixon's study showed that, even thou it was a very small sample size). - a heel raise shortens the distance between origin and insertion, but I just can't see how that would reduce how hard the calf muscles have to contract during gait

I can't think of a foot orthotic prescription variable that would reduce the plantarflexion moment.

A heel raise may reduce the supinatory moment (we showed a ~12% decrease in supination resistance force with a 1cm heel raise)

Certainly and 'anti pronatory' motion orthotic will reduce the supinatory moment (doesn't actually matter if it changes the motion or not), as long as the moment is reduced --> less load on the achilles as calf muscle do not have to contract so much to provide the supinatory moment at the STJ.

SO, I now think there is a theoretical rationale for using foot orthoses in achilles tendon problems ... we just need data to back it up. Shannan Munteanu, in the Dept here, has funding for a RCT of foot orthoses in achilles tendonitis ..so watch this space.

Originally Posted by Simon Spooner

For those not familiar with the study Craig refers to its here:
http://www.uni-duisburg-essen.de/~qp...cr/Dixon05.pdf

The peak achilles force decreased in their sample but not significantly. However, the rate of loading was significantly decreased by the heel lifts- the authors suggest that rate of loading may be clinically important. Due to the visco-elastic nature of the achilles, the heel lift should result in a more compliant (less stiff) achilles.

This study also found similar results but without the timing differences:
http://cat.inist.fr/?aModele=afficheN&cpsidt=3484945
"The results showed that, typically, a small initial dorsiflexion moment took place changing into a larger plantarflexion moment before 20% of stance phase. The magnitude and time of occurrence of the initial dorsiflexion moment were significantly affected by heel height changes, but the maximum plantarflexion moment and its time of occurrence were not significantly affected. The results did not support the speculation that a heel lift generally decreases the Achilles tendon loading during running. However, single subject analyses indicated that for two subjects the plantarflexion moments decreased with increasing heel height"

This is another study of interest here:
http://linkinghub.elsevier.com/retri...66636202001960

Originally Posted by David Smith

Craig

You wrote


This is how I see it,
In the foot where a heel lift is required the range of dorsiflexion motion is at its maximum as the leg approaches vertical in mid stance. The muscle can extend no more and the tendon starts to tension. At the point where internal tension is too high some kind of compensation will take place to reduce internal stress and strain. In diagram A) (only considered the relevant forces for simplicity) the example 1) has increased tension in the ach tendon, which causes or is caused by anterior progression of the plantar CoF and a corresponding slowing of the CoM progression. In example 2) the tendon can reach the same point in gait with less tension, therefore the CoM is decelerated less (0.9m/s^2 - V's - 1.0M/s^2) .
In the second diagram the heel lift allows the foot to achieve the same relative dorsiflexion RoM but allows the CoM to progress forward so that its line of action is forward of the ankle. Whereas the diagram without heel lift (top) requires the CoM to move another 5dgs or more anterior and in its present position gravity induces moments that resist saggital Plane progression of the CoM over the ankle fulcrum. The Ach tendon is in the same state of tension in both diagrams, however to achieve the desired forward progression the top diagram foot must make some compensation to allow this. This may be extra pronation, as you have pointed out the GSC thru the Ach tendon must exert more force to recover to supination from a more pronated position. So even with a compensatory action the ach tendoon is still under more strain without a heel lift than with it.
So while it intuitively appears that the shortening of insertion to origin is the reason for reduced tension, it may actually be more that the change in CoM position relative to the foot fulcrum is the key. Does this seem to make sense to you?







Cheers Dave Smith

Originally Posted by Kevin Kirby

Simon and Craig:

I don't see how heel lifts don't alter the tension within the Achilles tendon. I have seen heel lifts immediately reduce the pain in hundreds of patients with Achilles tendinopathy and retrocalcaneal bursitis and immediately reduce the pain in children with Sever's disease. If the heel lifts are not reducing the tensile force within the Achilles tendon, then how do you explain the near instantaneous reduction in pain in these patients when they first start walking with heel lifts?

Originally Posted by Kevin Kirby

Dave:



Good to see your diagrams. I did a nearly identical drawing about 20 years ago to explain how heel lifts reduced Achilles tendon tensile forces.



I believe that heel lifts probably have a much greater effect in reducing Achilles tendon tension on those patients that have a relatively shortened gastrocnemius-soleus complex (GSC) than in those patients that have the more normal 10 degrees of ankle joint dorsiflexion. The central nervous system (CNS) is unlikely to compensate for a short GSC by inefficiently attempting to lengthen the GSC with increased out-of-phase muscular activiation of the ankle joint dorsiflexors (e.g. anterior tibial muscle) during late midstance phase. However, the CNS may easily compensate for a normal to long GSC complex that has a heel lift added by increasing the contractile activity of the GSC to the exact level of ankle joint plantarflexion moment that is required for smooth progression of the center of mass over the planted foot.

Originally Posted by Simon Spooner

Kevin,

Don't shoot the messenger. I agree. I have also successfully employed heel lifts in association with other prescription variables in the treatment of the conditions you list.



I would also tend to agree that the research really needs to look at symptomatic subjects.



The paper at the last link I included in my previous post appears to address the issue of variation in dorsiflexion "flexibility" at the ankle and this too demonstrated no differences in ankle joint moments or kinematics during walking between those with high "flexibility" and low "flexibility" (I'm not sure how they determined "flexibility" as I don't have the full text, however I assume they are measuring range of motion or joint stiffness). From the information in the abstract these results appear to challenge the ideas presented by Dave and previously by yourself, it also challenges my own prior learning and experiences too. Interesting.

Originally Posted by Kevin Kirby

Probably the best way to model the effect of heel lifts on Achilles tendon tension is to consider that the tensile force within the Achilles tendon at the instant of heel off is a combination of both passive mechanical factors and active mechanical factors. Passive mechanical factors include what we commonly measure when we perform a nonweightbearing ankle joint dorsiflexion examination, with no muscular activation, which I call passive ankle joint plantarflexion stiffness. Active mechanical factors include the increase in Achilles tendon tension that arises from central nervous system (CNS) activation of the gastrocnemius-soleus complex (GSC) during heel off, which I call active ankle joint plantarflexion stiffness.



My hypothesis is that subjects with high passive ankle joint plantarflexion stiffness will show a significant reduction in ankle joint plantarflexion moments during late midstance with the addition of a heel lift whereas those subjects with low passive ankle joint plantarflexion stiffness will show little to no reduction in ankle joint plantarflexion moments with the addition of a heel lift. The passive stiffness within the GSC can not be significantly decreased by the CNS since the passive GSC stiffness is determined by the viscoelastic nature and relative length of the GSC and Achilles tendon. However, the stiffness of the GSC may be significantly increased by CNS activation of the GSC to incrementally increase the GSC stiffness, and therefore also incrementally increase the magnitude of ankle joint plantarflexion moment during late midstance, as the task demands. This hypothesis certainly makes sense from the clinical effects that I have seen on treating Achilles tendon disorders with heel lifts over the years.

Originally Posted by Craig Payne

I not disagreeing with the use of heel lifts for severs and achilles tendon probs, its just the simplistic rationale for their use I struggle with.



Simplistically, if i was to stand and then raise on my toes, x load goes through the achilles tendon; if I added a heel raise (to shorten the distance between origin and insertion) and the raise up on my toes, I can't see how that reduces the load in the achilles tendon ?



There is no doubt that heel raises help clinically, but by other mechanisms (shock absoprtion; STJ moments; etc)

Originally Posted by efuller

Hi all,



We should carefully clarify the condition we are talking about. In static stance with an ankle that dorsiflexes to 0 degrees, I would expect immediate relief with a heel lift in static stance. (A 3.5mm orthotic could act as a heel lift.) Now, in gait, I would not expect much difference in tension if there is equal power output when comparing the lift to not lift condition. Benno Nigg was involved with a study that looked at inverse dynamics and heel lifts and saw no difference in ankle plantar flexion moment with and without the lift.



Cheers,



Eric

Originally Posted by Simon Spooner

Second link in my previous post. here again:

http://cat.inist.fr/?aModele=afficheN&cpsidt=3484945

Originally Posted by Kevin Kirby

Eric:



In the hundreds of times I have seen patients with Achilles tendon symptoms, they report that walking with a heel lift makes their symptoms improve. The symptoms don't seem to be that significant with just standing. The symptoms are caused by walking and especially running. If this common clinical observation is not caused by a decrease in Achilles tendon tension, then what do you expect causes this finding? Also, how would I measure in my clinic if there is equal power output when comparing a lift to no lift condition?



Even though I am aware of the literature, my 25 years of treating these symptoms in countless patients indicates to me that the most likely cause of the reduction of symptoms with a heel lift in patients with Achilles tendon pathology is due to a reduction in Achilles tendon tension. Could the peroneals and deep flexors be more active and the gastrocnemius-soleus be less active with a heel lift?

Originally Posted by Simon Spooner

I guess what we are attempting to achieve with the heel lift is to alter the length/ tension relationship of the muscles. The net length/ tension curve being the result of the passive and active components. The current issue of the Journal of Applied Biomechanics includes two articles relating to this. Here is the abstract from the second paper:



"For a physiologically realistic range of joint motion and therefore range of muscle fiber lengths, only part of the force-length curve can be used in vivo; i.e., the section of the force–length curve that is expressed can vary. The purpose of this study was to determine the expressed section of the force–length relationship of the gastrocnemius for humans. Fourteen male and fourteen female subjects aged 18–27 performed maximal isometric plantar flexions in a Biodex dynamometer. Plantar flexion moments were recorded at five ankle angles: -15°, 0°, 15°, 30°, and 40°, with negative angles defined as dorsiflexion. These measurements were repeated for four randomly ordered knee angles over two testing sessions 4 to 10 days apart. The algorithm of Herzog and ter Keurs (1988a) was used to reconstruct the force–length curves of the biarticular gastrocnemius. Twenty-four subjects operated over the ascending limb, three operated over the descending limb, and one operated over the plateau region. The variation found suggests that large subject groups should be used to determine the extent of normal in vivo variability in this muscle property. The possible source of the variability is discussed in terms of parameters typically used in muscle models."- JAB, 24(3), August 2008, Reconstruction of the Human Gastrocnemius Force–Length Curve in Vivo: Part 2—Experimental Results. Samantha L. Winter, John H. Challis



The length-tension relationship should be altered through the addition of a heel-lift, shifting the curve to the right of the length (x) axis. i.e. by removing tension in the muscle via the heel-lift it should be similar in effect to a muscle that is functionally long and weak as described by Yanda. So maximal force is then produced at a different point within the joint range of motion, with relative weakness in inner range. The results of the above study suggest that individuals gastroc/ soleus function at varying points within the curve also. The proportional change in muscle groups length/tension that is achieved through lifting the heel may vary among individuals despite the use of identical heel-lifts as per the Dixon and other studies. Indeed, this may go some way to explaining the variable results obtained in the Nigg study. Of note also is that none of the studies thus far have examined the longer term effects of heel-lifts, only immediate response.



Thinking out-loud, so I hope it makes sense.

Originally Posted by Dananberg

Yanda's influential thinking on muscular strength during phases of gait is most important in understanding what the effect of heel lifts actually accomplish.



Classically, the clinical test of Posterior tibial tendon (PT) rupture or even dysfunction is the single sided heel raise. Considering the normal nature of the Achilles tendon/muscle is this case, the inability to raise onto one's toes when the PT is removed from the equation, raises the question as to what functional structures cause (allows?) heel lift. If we change position of the foot via a heel lift, and this, from a Yanda perspective, changes muscle function in either the PT, peroneals or both, it is that change that relieves the strain on the Achilles tendon and thus decreased symptoms?



As Simon said....just thinking out loud.



Howard

Originally Posted by Simon Spooner

I started thinking a little outside of the box on this one. We wear shoes with variable heel height differentials, women especially. Basically, the heel of a shoe is the equivalent to the heel lift on the orthoses. So what does the research which has compared walking in low flat shoes with high-heeled shoes conclude about the effects of heel height on ankle plantarflexor moment? Two minute google search and the first hit:

http://www.japmaonline.org/cgi/content/abstract/93/1/27



Kinetics of High-Heeled Gait



Meltem Esenyel, MD*, Katlen Walsh, Judith Gail Walden, MPH* and Andrew Gitter, MD*



A within-subject comparative study of walking while wearing low-heeled sports shoes versus high-heeled dress shoes was performed to identify and describe changes in lower-extremity joint kinetics associated with wearing high-heeled shoes during level overground walking. A volunteer sample of 15 unimpaired female subjects recruited from the local community underwent quantitative measurement of sagittal and frontal plane lower-extremity joint function, including angular motion, muscular moment, power, and work. When walking in high-heeled shoes, a significant reduction in ankle plantar flexor muscle moment, power, and work occurred during the stance phase, whereas increased work was performed by the hip flexor muscles during the transition from stance to swing. In the frontal plane, increased hip and knee varus moments were present. These differences demonstrate that walking in high-heeled shoes alters lower-extremity joint kinetic function. Reduced effectiveness of the ankle plantar flexors during late stance results in a compensatory enhanced hip flexor "pull-off" that assists in limb advancement during the stance-to-swing transition. Larger muscle moments and increased work occur at the hip and knee, which may predispose long-term wearers of high-heeled shoes to musculoskeletal pain. (J Am Podiatr Med Assoc 93(1): 27-32, 2003)



This study from Kevin's research colleague Stephen Piazza seems to concur with my musings on length/ tension: http://www.gradsch.psu.edu/diversity..._henderson.pdf



"In high heel gait and standing, many muscles located in the lower extremities and

the back are overly worked due to the plantar flexion of the foot. Muscles are at their

peak for force generation when they are at resting length. When muscle length increases or decreases beyond its resting length, muscle force production decreases in a bell shaped form. This relationship is seen in high heel wearers. When the heel is raised, as in wearing high-heeled shoes, muscles fibers that innervate the muscles along the leg are shorten. The shortened muscles are now inconsistent with its resting length-tension relation resulting in less force production. Esenyel et al. (2001), found “… the exaggerated plantar flexed position of the ankle joint places the gastro-soleus muscle at a shortened and thus less favorable position on its muscle length-tension curve. Under such conditions, the plantar flexion musculature is in a less advantageous position for power and work generation and consequently less propulsive abilities. (Esenyel et al.,2001)



And also seems to agree with the out-loud thoughts of Howard and to the idea that it is the supinatory effect of the heel lift that may be significant: read the discussion!



So the question then becomes, why do we see changes in ankle kinetics and kinematics with high-heeled shoes but not with heel lifts? Is it because the heel lift studies looked at running while the heel height trials have focused on walking?



Food for thought, I hope.

Originally Posted by efuller

To address the topic of the thread: Achilles tendon supinator or pronator of the STJ.

The Achilles tendon has a much longer lever arm at the Ankle joint as compared to the STJ. Tension in the tendon will create simultaneous moments at both joints. The plantar flexion moment at the ankle will shift the center of pressure more anterior "faster" than it will shift it laterally. The STJ axis, most of the time is oblique to the foot and an anterior shift of the center of pressure will put the center of pressure more lateral to the location of the STJ axis in the standing foot. So, the anterior shift in the center of pressure, in many feet, will create a greater pronation moment from ground reaction force than the direct supination effect of the tendon about the STJ.

This does not really address the heel lift question though.

Cheers,

Eric Fuller

Originally Posted by Simon Spooner

Thanks Eric, I take your point. Why would this relate to the lateral head of gastrocnemius greater than the medial head? Also of note is the lateral shift in orientation of the STJ axis that should occur with supination which should counter this effect.

Originally Posted by Simon Spooner

How can the lateral head of the gastrocnemius be an evertor and presumably by its exclusion, the medial head is then considered to be an invertor, when the muscles action is through the achilles tendon insertion?

Anyone?

Originally Posted by Simon Spooner

Got that. but why just the lateral head?

Originally Posted by Simon Spooner

Something to consider over the weekend? I found this while looking into the effects of heel lifts on ankle plantarflexor moment in the biomechanical explanation thread

"Both the lateral gastrocnemius and peroneals are muscles that help eversion of the
heel."

Paula D. Henderson, Dr. Stephen J. Piazza: A Biomechanical Evaluation of Standing in High- Heeled Shoes. http://www.gradsch.psu.edu/diversity..._henderson.pdf

How can the lateral head of the gastrocnemius be an evertor and presumably by its exclusion, the medial head is then considered to be an invertor, when the muscles action is through the achilles tendon insertion? The achilles position relative to the STJ axis should determine whether the force generated by the muscle results in supination or pronation moment. When I went to school the gastroc/ soleus complex was an invertor except in grossly medially deviated STJ axes. Since these guys were looking at high heel shoes that should have supinated the foot and therefore translated the STJ axis laterally, how does the lateral head act as an evertor?

Anyone?

Originally Posted by fatboy

I've been trying to find the evidence for the 30 -150 degree rotation of the achilles tendon and this book states:

http://books.google.co.uk/books?id=6... tates&f=false

"during their descent the fibres internally rotate... so the inital posterior surface of the soleus attaches on the medial aspect... and the gastrocnemius attaches on the lateral aspect"

maybe it's the rotation of the achilles tendon fibres that cause the problem.
.

Originally Posted by fatboy

I've been trying to find the evidence for the 30 -150 degree rotation of the achilles tendon and this book states:

http://books.google.co.uk/books?id=6... tates&f=false

"during their descent the fibres internally rotate... so the inital posterior surface of the soleus attaches on the medial aspect... and the gastrocnemius attaches on the lateral aspect"

maybe it's the rotation of the achilles tendon fibres that cause the problem.

A laterally 'attached' tendon (to the Sub-talar joint) would provide an eversion / pronation moment?!

how you would test the rotation of the achilles clinically in patients i have no idea.

i wonder if it's too late to take up a career that doesn't make my brain ache, or should i go back to the way i was taught and just add a 2 degree varus rearfoot post to everything.

Originally Posted by Kevin Kirby

To give an approximate estimate of Achilles tendon tensile force, simply multiply the magnitude of ground reaction force acting under the forefoot at late midstance/propulsion by a factor of two, and that will give you a good estimate of the tensile forces within the Achilles tendon. So in running, for a 180 pound individual that is pushing off the ground with 1.5 times body weight of force at the forefoot just before heel off, the Achilles tendon is likely subjected to approximately 500 pounds of force. The force will increase within the Achilles tendon with faster running speeds and increased body mass.

Therefore, it isn't exactly rocket science understanding why Achilles tendon injuries occur. The amazing thing is trying to understand why Achilles tendon injuries don't occur more frequently!!

Originally Posted by fatboy

You've just re-affirmed all the reasons i don't run... and i was about 12 yrs old when i was last 180lbs.

Another factor in achilles tendinopathy is the increase in plantarflexion when having to walk / run uphill.

Originally Posted by Simon Spooner

Plantarflexion or dorsiflexion uphill?

Kevin, I am interested in braids versus spirals- are the fibres braided, i.e. plaited at that level of microscopy- woven between each other, or spiralled around each other?

Originally Posted by Simon Spooner

Plantarflexion or dorsiflexion uphill?

Kevin, I am interested in braids versus spirals- are the fibres braided, i.e. plaited at that level of microscopy- woven between each other, or spiralled around each other?

Originally Posted by fatboy

Plantarflexion, as the foot is more dorsiflexed when going uphill.

Originally Posted by Kevin Kirby

Simon:
only the Achilles tendon has a spiral arrangement of all the tendons in the human body. Fascinating to imagine why that is, isn't it?

Originally Posted by Simon Spooner

How does spiralling influence the biomechanical properties of the tendon?

Originally Posted by Kevin Kirby

The spiral arrangement of Achilles tendon fibers is the standard anatomical configuration of the Achilles tendon. How many ropes have you seen that are arranged with their fibers parallel and straight, with no braiding or spiral arrangement?

Achilles tendinitis so commonly occurs probably because of the huge loads this tendon is forced to bear (it is the largest tendon of the body) and the relative lack of blood flow to the narrow section of the Achilles tendon about 3-6 cm superior to the calcaneus.