The myth of toes curling to grip the ground

Not sure what you mean here Eric . Are you saying there is no lever arm ?

I have been showing the figure in question purely because you refuse to post the radiograph from which you say you measurements have been taken .

Looking at your model ( the unused digit which you won't show ) you have no lever arm and no moment arm in either of your digits. How are you measuring lever arm ? From where to where ?

You said so earlier in the thread Eric -

"Toe curling will occur if there is not the perfect amount of contraction of the lumbricles, short flexors and long flexors. Contraction of the long flexors can produce hammertoes/claw toes."

What is most interesting about your model to me is that both of the digits lack any moment arm for the FDB at the MTPJ .

I have been trying to provide evidence of what causes very weak toes to collapse under load throughout this thread .Your counter arguments have been unpersuasive and, on a number of occasions, evasive.

 

What evidence do you have that the moment arm of my model is inaccurate? An accurate model reproduces reality. The model reproduces the reality of collapsed toes.

 

The fact that the model has almost no lever arm at the MPJ is exactly the point. That is the reality of the situation. An FDB with a small lever arm at the MPJ will create collapsed toes.

One way to measure lever arm is to measure the distance from the line of action of force to the axis of rotation. I described this already in post #78.

Another way to measure lever arm of a tendon is to move the joint through a certain number of degrees of motion and then measure the distance the tendon travels. This is similar to a bicycle wheel with multiple sprockets. The bigger the sprocket the farther the chain will move with a given amount of rotation of the wheel.

 

Below is your video.

The two digits are materially different with regard to the extra ring on the digit not being activated . Which of the two are you proposing as an accurate model ? The version being illustrated in motion or the version not in use ? If you can answer this I can more accurately reply to your question. If you see the digit with the extra proximal ring close to the hinge as being the more accurate, could you show a video of this?

I am happier relying to more a precise question.

 

Eric, with regard to the figure below where would you estimate the axis of rotation to be?

 

Eric, as previously stated, I can't find an MRI scan of the lesser toe MTPJs that is open access so will just go with the 1st MTPJ seen in the scan below .

I have marked in an approximation of the axis of rotation in yellow and the moment arm in green . As you can see the moment arm is far from negligible as it is in your model. Also the angle of pull of the short toe flexors is greater than 30 degrees to the long axis of the proximal phalanx .

So my model is functionally more correct than yours but I still would not rely on it. Since your model is so inaccurate and your free body analysis is likely also way off , it can be concluded that you have yet to offer any evidence that the toe collapse seen in the picture is the result of increased FDB activity.

This unsupported notion, that isolated contraction of the FDB will produce dorsiflexion at the MTPJ , is held by others in the podiatry profession, but where did it first come from? Has the idea simply sprung from very poor models?

 

Gerry, look at the model again. The lever arm of the tendon relative to the joint axis in the model is actually bigger than the one in your picture. A rough estimate of 2cm thick for a metatarsal head the center of rotation is roughly in the center of the metatarsal head so that would make the lever arm 1cm. My model has a lever arm of roughly 1.5 cm. Why do you think the lever arm in the model is negligible?

As to your criticism of my model not going through the eye screw on the base of the proximal phalanx: If tendon did go through that eye screw that would decrease the lever arm of the tendon at the MPJ. Gerry, you can't have it both ways. You can't criticize the model for having to small a lever arm at the MPJ and also criticize it for not using an even smaller lever arm.

Come on Gerry, at least put in the time to make an argument. Say why my analysis is way off.

Gerry, would evidence that FDB activation causes the hammertoe configuration (toe collapse) reduce the value of your intrinsic foot muscle strengthening machine because you could not claim that it prevents hammertoes?

The model is evidence that FDB tendon force produces toe collapse. Your criticism of the model (negligible lever arm) is wrong. The model produces the exact same motions seen in toe collapse. You have not provided an alternate explanation of toe collapse that makes any sense (muscle weakness cannot cause the motion of toe collapse).

 

Eric ,
Where I have talked about "moment arm" you seem to have read "lever arm" . They are not the same thing !

 

They can be the same. Go ahead and explain why you think the difference matters.

 

But they are not the same here and should not be used interchangeably. Please explain why you think the difference does not matter. After all, it is your mistake .

 

Lever arm and moment arm can be considered to be the same when there is a 90 degree angle between the force and the lever. They can be interchangeable be in this case.

This moment arm/ lever arm criticism is irrelevant to the mistake you made was saying that the moment arm in my model was negligible. The moment arm of the tendon in the model can be seen in the video in the non weight bearing portion of the video. After the PIPJ has reached its end of range of motion, the moment arm at the MPJ becomes the distance from the string to the wire that is the joint axis. This moment arm is able to plantar flex the phalanges of the model when non weight bearing. However weight bearing, tension in the FDB tendon will cause the collapsed hammertoe position.

 

Nowhere in the video you produced is there a 90 degree angle between the force and the lever. You used the wrong terminology, we all make mistakes, let's move on.

In an earlier post, and in complete contradiction to the quote above, you said;

"The fact that the model has almost no lever arm at the MPJ is exactly the point. That is the reality of the situation. An FDB with a small lever arm at the MPJ will create collapsed toes."

Eric, you are tying yourself in knots because you are trying to defend a poor model.

 

Gerry, you are playing both sides again. You complained that I didn't use a smaller lever arm in the video and you are also claiming that it should be a larger lever arm. The FDB has a small lever arm (as stated in the quote) at the MPJ. With no resistance to plantar flexion FDB can create a small moment to plantar flex the MPJ. When the foot is on the ground, the ground provides resistance to plantar flexion of the MPJ. When the FDB contracts it creates a plantar flexion moment on the intermediate phalanx. The head of the phalanx cannot go into the ground so the back end of the phalanx goes up and this dorsiflexes the MPJ.

In our discussion so far the best explanation of the cause of toe collapse is tension in the FDB tendon.

 

Nope ,that would be you . In fact you are even playing with 2 different models and refuse to pick one as your "best representation".

Now we are getting somewhere . The FDB has a larger moment arm in real life than in your models where it is near
negligible ( or as you put it " almost no lever arm" ) at the ranges of motion under consideration . Remember, any distance between the wire axis and the line of pull on the ligament (string ) measured on your models must be scale down before comparisons can be made with in vivo measurements . Nobody has toes 12-13 inches long .

You said "In our discussion so far the best explanation of the cause of toe collapse is tension in the FDB tendon."

No Eric, that is only your opinion backed by an inaccurate model and a fee body diagram that you refuse to show anyone .
Do you have any better evidence ?​

 

You have not presented a better explanation. The model exactly creates the motion seen in vivo.

 

You presented a better explanation in post #23 .
You said "Contraction of the long flexors can produce hammertoes/claw toes"

Your model can be manipulated to produce a number of outcomes including the one seen in my video .

 

What I believe we have established then Eric, is that based on a proportionally representative model, isolated contraction of the FDB will plantarflex the proximal phalanx of the lesser toe and not cause it to dorsiflex.

Further evidence is required and would probably best be provide by using exactly the same experimental set up as was used by Luke Kelly in one of his PhD papers where the foot was placed under load and then the FDB was activated via direct electrical stimulation. From memory he found that navicular height increased but made no mention of collapsing toes .

If surgical techniques are linked to the belief that FDB contraction can cause hammer toes then might it be prudent to ask Kelly what he found with regard to proximal phalanx movement and then, if necessary, investigate further ?

 

On the general theme of "toes don't curl to grip the ground " , here is a link to a twitter post involving a footprint being made in a particulate substance. Even when moving through mud our toes remain straight and move around the MTPJ's ,they do not curl for grip.

IMO exercises such as marble pick ups and towel curls are non functional and research which measures foot strength with toe grip dynamometers is misguide since the foot does not work by gripping as a hand would grip.

link to twitter post showing animation built in part from actual mud /foot interactions.

https://twitter.com/FarrellGerrard/status/1618958345054064641?s=20&t=Zw9KpNcI5MN1RFEePw29zA

 

So going back to the picture at the start of this thread we can see the toes adopting a "hammer toe position" under load.
The lumbricals flex the toes around the MTPJs and extend the toes at the interphalangeal joints ( keep the toes straight rather than collapsed ) . Some people seem to think that the configuration the toes have adopted in the photograph means strong intrinsics, but how can that be the case for the lumbricals if the toes are not straight/ extended at the interphalangeal joints ?
Seems to me that no matter what way you cut it, if your toes look like the photograph under load, you have an underlying intrinsic foot muscle weakness, be it the lumbricals or all of them.

How anyone can think the toes are designed to "crumple up" under load is a mystery to me.

 

Different muscles have different functions. Some intrinsics straighten the toes, other intrinsics (and some extrinsics) flex the toes. Different things will happen with different forces in the tendons. The video demonstrated that FDB can cause flexed "crumpled" toes.

?Designed? Now that is a loaded statement? Who is the designer that made toes that crumple? Evolutionarily, it would make sense that the toe flexors would be stronger than the toe extensors when examining walking. The flexors are resisting ground reaction force; the extensors are only moving the weight of part of the toes during swing so that the toes can clear the ground. So. with simultaneous equal contraction the action of the flexors should win, creating "crumpled" toes. Not a mystery.

 

Eric,
Are you suggesting that the toes have evolved to adopt a hammer toe configuration when under load, that the hammer toe configuration is the functional norm during toe off ?

 

Yes. (Load = contraction of FDB muscle)

No.

 

Ok, are you saying that the toes of healthy feet adopt a hammer toe configuration during certain phases of gait, walking/running?

 

I'm saying that when the FDB overpowers the lumbricals the toes will achieve the hammertoe configuration like in the picture you showed at the start of the thread and in the video of my model. Someone with healthy feet could learn to contract their FDB to create the hammertoe appearance.

 

So let's say someone with strong healthy feet has not undergone a volitional learning process to contract their FDB to create the hammertoe appearance. Are you saying that you would generally expect their toes to adopt a hammer toe position during gait ?

 

If you did see hammertoes during gait they would be using their FDB more than if you did not see hammertoes during gait.

 

But do you see hammer toes during gait in people with strong, healthy, feet? I feel you are fixating on FDB and not answering the question.

 

So to answer my own question, since it looks like Dr Fuller is not going to respond, no, you don't see hammer toes during gait with strong, healthy, feet. If toes were evolved to collapse into a hammer toe configuration under load, then hammer toes would not be constitute a deformity, would they? If the toes are loaded and a hammer toe configuration ensues ,then the toes/foot are weak. Strengthen them appropriately and they will not collapse.

I suspect the toes of many of the patients seen by foot health care professionals collapse under load and so this is seen as the norm. It's only the norm for feet made weak by shoes or other detrimental factors.

 

Gerrard, do not put words in my mouth. I ignored the question because I had answered it in a previous post. I though you were trolling, rather than being serious, when you said that I was fixating on FDB when in your post, that I was replying to, you mentioned FDB.

 

I didn't, I answered the question and made clear it was my answer and not yours : "So to answer my own question, since it looks like Dr Fuller is not going to respond, no, you don't see hammer toes during gait with strong, healthy, feet."

The question was not-

"If you did see hammertoes during gait would they be using their FDB more than if you did not see hammertoes during gait." ,

The question was-
"So let's say someone with strong healthy feet has not undergone a volitional learning process to contract their FDB to create the hammertoe appearance. Are you saying that you would generally expect their toes to adopt a hammer toe position during gait ?"

No, not trolling. My question does not require specific mention of FDB. And you have still not answered the question, which basically requires a yes or no answer.

​

 

Eliminating neurological deformities, infections and trauma, almost axiomatically, I have found that toe gripping is secondary to gravity drive pronation. Stabilize the excessive pronation, toe gripping attenuates.

 

Pretty clear that orthotics can help people who pronate excessively and develop problems related to this . Also, clear to me that the vast majority of people who walk across the threshold of podiatry offices have feet far weaker than they should be.

A good test would be supervised loading of the toes. If they collapse into a hammer toe configuration, strengthen.

It's a simple test that most older people would fail and so clinicians, not confident about foot strengthening methods, are likely to resist its validity. That may be acceptable for now but probably won't be for much longer, given the studies underway at La Trobe.

Increasingly, orthotic use in isolation is being discouraged.

 

Digital loading was my test of choice to determine the etiology of toe gripping (functional hammer toeing).

Specifically with Rothbarts Foot and the PreClinical Clubfoot deformity, using the indicated proprioceptive insole, the functional hammer toeing significantly attenuated.

Unfortunately, it is not uncommon that generic insoles are frequently prescribed to treat the Dx of abnormal pronation. However, abnormal (gravity drive) pronation is a Symptom, not a primary etiology! The healthcare provider must first determine the cause of the abnormal pronation and treat that cause directly with the appropriate orthotic/insole/proprioceptive insole.

I would venture that a good number of the members on this forum do Not follow that protocol. The wrong orthotic is used and hence the disappointing outcomes. That is why, currently, the use of orthotic alone to treat functional hammer toeing is discouraged.

 

Poorly developed foot muscles send poorer proprioceptive signals to the brain and are less able to carry out the mechanical duties they evolved for . Surely you are not claiming your insoles cause instantaneous muscle growth! The CNS can't get top performance out of rubbish muscles.

 

With regard to toes collapsing into a hammer toe configuration when under load if the intrinsics are weak, I feel the thread does not mention either the lumbricals enough, and the plantar and dorsal interossei are not mentioned at all.
I have focused on the flexor digitorum brevis when perhaps weakness in this muscle is not the key to hammer toes.( Time will tell and I suspect research clarifying this will soon be available. )

But for a hammer toe configuration to form when the forefoot is under load, the proximal interphalangeal joint needs to flex and there are muscles that specifically oppose interphalangeal joint flexion whist flexing the lesser toes at the MTPJ. These include ; the lumbricals
the dorsal interossei
the plantar interossei .

With hammer toe, we have extension of the proximal phalanx at the MTPJ and flexion at the proximal interphalangeal joint . The lumbricals, dorsal interossei and plantar interossei help to prevent hammer toe formation by flexing the proximal phalanx at the MTPJ and extending at the proximal interphalangeal joint .

In short, hammer toes are not going to form if these muscles are strong and active. How do you strengthen these muscles ? Well certainly not with picking up pencils, grabbing a squidgy ball with your toes ,or toe curling activities since these activities require movements at the MTPJs and interphalangeal joints that are opposite to those that these muscles produce .

If the toes collapse under load the points of insertion of the long toe flexors can shift towards their origins reducing effectiveness .

Toe curling activities, especially if done with increasing resistance, will likely promote muscle imbalances in the foot.

How do you strengthen the intrinsics in a way that will include the lumbricals and interossei ? By keeping the toes straight and moving them around the MTPJs ,because that's what these muscles have evolved to do.

 

Ok , so let's say Eric is right and a strong FDB will not pull the entire proximal phalanx, base included, down towards the ground . Muscles like the lumbricals and dorsal and plantar interossei certainly will , if strong enough . These muscle will also tend to keep the toes straight and so will not be strengthened by exercises like toes curls or grabbing a ball with your toes .

The lumbricals and interossei have a key role to play in foot function and would appear to be greatly underappreciated.

 

I recently read an opinion piece, written by a senior foot health care professional, on the subject of lesser toe deformity.

The lumbricals and dorsal and plantar interossei were not mentioned once, and yet these muscles are known to extend the PIP joints of the lesser toes and plantar flex the toes around the MTPJs, thus acting as plantar flexors of the proximal phalanx. I do not believe you can write any sort of balanced piece on the subject of lesser toe deformity and omit the lumbricals and interossei.

Karen Mickle has done some valuable research into the relationship between toe deformity, muscle weakness, balance and falls, and this is clearly a very important area. Too often, it seems to me, hammer and claw toes are seen as important only if they cause the patient discomfort and the effects of such deformities on long term balance are not properly considered.

It has been estimate that 60% of older people have lesser toe deformities, and, whilst many may not suffer discomfort from such deformities, this does not mean that their presence, or the muscle weakness that they are associated with, are without consequence. The intrinsic foot muscles play a hugely important role in generating toe flexor force and this measure is closely linked to falls.

Are toe deformities linked to intrinsic muscles weakness/atrophy? Here is what Mickle et al found when they investigated :

"Objective: Despite suggestions that atrophied, or weak toe flexor muscles are associated with the formation of toe deformities, there has been little evidence to support this theory. This study aimed to determine whether the size of the toe flexor muscles differed in older people with and without toe deformities. Methods: Forty-four older adults (>60 years) were recruited for the study. Each participant had their feet assessed for the presence of hallux valgus or lesser toe deformities. Intrinsic and extrinsic toe flexor muscles were imaged with an ultrasound system using a standardised protocol. Assessor blinded muscle thickness and cross-sectional area was measured using Image J software. Results: Participants with lesser toe deformities (n=20) were found to have significantly smaller quadratus plantae (p=0.003), flexor digitorum brevis (p=0.013), abductor hallucis (p=0.004) and flexor halluces brevis (p=0.005) muscles than the participants without any toe deformities (n=19). Female participants with hallux valgus (n=10) were found to have significantly smaller abductor hallucis (p=0.048) and flexor halluces brevis (p=0.013) muscles than the female participants without any toe deformities (n=10;

Worth noting; patients with lesser toe deformities (hammer and claw toes) were found to have more atrophied flexor digitorum brevis muscles than those without such deformities

 

Can the toe curl exercise make toe deformities worse over time?

Well, toe curls involve flexion at the PIP joints, and the lumbrical and interossei muscles extend the toes at these joints. Weakness in these muscles, which help to keep the toes straight and flex around the MTPJ, will not be addressed with toe curls.

Recently, a study (1) showed that extrinsic foot muscle exercises, performed by children with flat feet, can actually weaken the intrinsic foot muscles whilst strengthening the extrinsics, unless a prior program aimed at the intrinsics is performed before extrinsic training is undertaken.

The extrinsic exercises included inversion against resistance and calf raises. (It may be that calf raises contribute to intrinsic foot muscle weakening, if performed without proper intrinsic exercises being done first. )

Toe curls were not part of the program in Kedabchi et al, but I would categorize toe curls as an extrinsic foot muscle exercise.
Could toe curls, a staple foot strengthening exercise for more than 100 years, actually lead to intrinsic foot muscle weakening and progression of toe deformity rather than helping to prevent it ?

IMO, this needs looked at as a matter of great urgency.
(1) Differential effects of intrinsic- versus extrinsic-first corrective exercise programs on morphometric outcomes and navicular drop in pediatric flatfoot

Scientific Reports volume 14, Article number: 31393 (2024) Cite this article

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Abstract
Although the connection between muscular strength and flatfoot condition is well-established, the impact of corrective exercises on these muscles remains inadequately explored. This study aimed to assess the impact of intrinsic- versus extrinsic-first corrective exercise programs on muscle morphometry and navicular drop in boys with flexible flatfoot. Twenty-five boys aged 10–12 with flexible flatfoot participated, undergoing a 12-week corrective exercise program, with a shift in focus at six weeks. Ultrasound imaging measured muscle thickness and cross-sectional area (CSA), and the navicular drop test assessed flatfoot severity. The results demonstrated a significant interaction between exercise type and sequencing on muscle morphometry. Initiating with intrinsic exercises led to sustained improvement, even after transitioning to extrinsic exercises, while extrinsic-first exercises caused deterioration in intrinsic muscle morphometry, which was recovered after transitioning to intrinsic exercises. Statistical analysis revealed significant improvements in muscle thickness and CSA over time, particularly when initiating intrinsic exercises first. The intrinsic-first group also exhibited a more pronounced reduction in navicular drop. In conclusion, initiating corrective exercises with intrinsic muscles proved more effective in improving foot muscle morphometry and reducing navicular drop in boys with flatfoot. Therefore, commencing correction with intrinsic muscle exercises is recommended before progressing to extrinsic muscle exercises.