Functional lesser toe deformity.

Members do not see these Ads. Sign Up.

Functional lesser toe deformity, is there such a thing and can it contribute to falls in the older population?

What I mean by "functional lesser toe deformity" is probably best understood by looking at the foot on the left of the included image. When the intrinsic foot musculature of a foot is weak and demands are placed on the foot, the foot will collapse in such a way that the lesser toes adopt a hammer toe position . This effectively shortens the foot and reduces the base of support, likely compromising balance.

In my experience ( I am not qualified in foot and ankle biomechanics but I have been involved in university studies around the subject) where the lesser toes of a foot collapse under load they can easily be strengthened so that they do not.

 

Does it make a difference if toes adopt a hammer toe configuration only under load, for example when balancing or walking, or if the configuration is present even at rest and the toes cannot straighten at the MTPJs ? I suspect not. That is to say, toes which collapse under load will have the same overall effect on gait and balance as toes which are in a permanent hammer toe configuration.

We know that lesser toe deformities are associated with an increase in falls risk , but are clinicians dealing with falls in the elderly failing to do anything about toe weakness? Are lesser toe intrinsic muscle deficits being ignored and toes being left to collapse under load giving functional toe deformity?

Some really promising falls prevention programmes exist but as far as I can see none directly address intrinsic foot muscle weakness.

 

Which muscles prevent the toes from adopting a hammer toe/ claw toe configuration when proximal part of the foot is under the most load. Some feel that the flexor digitorum brevis has a role to play in this but others think that activation of the FDB encourages hammer toe configuration. The same certainly cannot be said for the lumbricals or the interossei. The lumbrical for example, both flex the distal phalanx of the lesser toes and extend the interphalangeal joints. If the lumbricals are strong enough and " switched on " as they are during balance and walking on a flat surface the toes will not collapse . Collapsing lesser toe structure may be indicative of weak intrinsics generally, but certainly means an effective shortening of the foot and presumably impaired balance .

How would you strengthen the lumbricals ? By moving the toes around the MTPJs against resistance whilst keeping the interphalangeal joints straight .

Calf raises will not strengthen the lesser toes and toe curls certainly wont strengthen muscles like the lumbricals or interossei since this action requires bending at the toe joints.

 

An error in the post above "The lumbrical for example, both flex the distal phalanx of the lesser toes and extend the interphalangeal joints." should read "The lumbricals, for example, both plantar flex the lesser toes at the MTPJs and extend the interphalangeal joints "

How might we tell if a persons intrinsic foot musculature is weak, for example an older person or someone with diabetes? One test that might be done under supervision is as follows -

An early marker for intrinsic atrophy could be what the toes do during Vele's forward lean . Often with neuropathy, the more distal musculature is affected soonest . If an individual with straight, relaxed toes, but weak lumbricals and interossei, loads up the fore foot then the toes will collapse into a hammer toe or curled configuration.

Toes that remain straight under load are better at assisting in balance than toes that curl or hammer ( more force applied to ground further from the COP, ie longer lever arm. Also, research has shown that the FDB generates more muscular force when the toes remain straight at the IPJs rather than curling or going into a hammer toe configuration. )

From experience, if you strengthen the IFM of a foot that collapses when the forefoot is loaded, then the collapsing stops.

I have included an image that shows a hammer toe configuration. The PIP will not "pop up" if intrinsics attached to the base of the 1st phalanyx are strong enough, regardless of the action of the FDB.

 

For a dentist who has spent a huge amount of time studying feet, you should know anatomy and terminology better. The number refers to which toe. The phalanx is delineated by proximal, intermediate, or distal. What intrinsic muscles do think insert on the base of the proximal phalanx of the the lesser toes? I don't know of any.

I would agree that the lumbricals can plantar flex the proximal phalanx at the metatarsal phalangeal joint.

Your term collapse rankles my sensibilities. Collapse implies that gravity is causing the motion that you see in the picture you posted. You would get the same motion (dorsiflexion of proximal phalanx, plantar flexion of intermediate phalanx and hyperextension of the distal phalanx) if you put your feet on a wall and gripped with your toes like the person did in the picture in the first post in this thread. That motion is caused by active contraction of a muscle.

I would agree that lumbrical contraction could counter act the moments created by EDB and contracting both EDB and lumbricals simultaneously might be able to get you straight toes.

We should also look at the amount that straight versus hammered toes could change COP. Take a 250 mm foot and look at the difference in length of the foot with hammered versus straight toes. The difference is what 10mm? That's a 4% difference. Ankle plantar flexors are much more important for AP balance.

 

Dorsal Interossei Eric ?
Insertion

The two heads of each muscle form a central tendon which passes forwards deep to the deep transverse metatarsal ligament.[1] The tendons are inserted on the bases of the second, third, and fourth proximal phalanges[2] and into the aponeurosis of the tendons of the extensor digitorum longus[3] without attaching to the extensor hoods of the toes.[1]

 

Hi Eric ,
I ran into a firewall problem with the last post so couldn't complete it.

Muscles which insert on the base of the proximal phalanxes of the lesser toes include the lumbricals, the plantar interossei, the dorsal interossei, flexor digiti minimi brevis and abductor digiti minimi ( a large muscle as intrinsics go). To use your own words "you should know anatomy .. better."

The lumbricals do plantar flex the proximal phalanx at the metatarsal phalangeal joint.

I like the term since it conveys the idea of structural failure under load due to weakness. "Buckle" would also be a good term.

Eric , would you expect strong, healthy toes to go into a hammer toe configuration during Veles forward lean or remain straight at the PIP joint ?

 

Eric, you are not alone in thinking that the lumbricals of the foot do not attach at the bases of the proximal phalanges of the lesser toes, with a number of anatomy sites making this mistake, but in fact they do. This allows these muscles to extend the IPJs, plantarflex the toes at the MTPJs and adduct toes 2 through to 5.

In view of the above comment, I think it would be a good idea to revise the intrinsic muscles of the foot with a particular emphasis on those that insert onto the bases of the proximal phalanxes of each of the lower toes, before expanding on how this anatomy impacts on toe function and deformity.

Each lesser toe has at least 3 such attachments, not none, and they are likely crucial when it comes to lesser toe deformity.
Muscles inserting onto the base of the proximal phalanx of each lesser toe-

2nd toe
1 lumbrical on medial aspect of base as well as extensor hood
2 dorsal interosseous inserted into medial aspect of base
3 dorsal interosseous on lateral aspect of base

3rd toe
1 dorsal interosseous – inserted on lateral aspect of base of proximal phalanx (pp)
2 plantar interosseous – inserted on medial aspect of base pp
3 lumbrical - medial aspect of base pp

4th toe
1 dorsal interosseous -lateral aspect base pp
2 plantar interosseous – medial aspect base pp
3 lumbricals - medial aspect base pp

5th toe
1 lumbrical -medial aspect of base pp
2 plantar interosseous- medial aspect of base pp
3 flexor digitorum minimi- base pp
4 abductor digiti minimi -base pp

In short , most of the intrinsic muscles of the foot insert onto the bases of the proximal phalanxes of the lesser toes .



Note on the short and long toe extensors

Eric,you said "I would agree that lumbrical contraction could counter act the moments created by EDB and contracting both EDB and lumbricals simultaneously might be able to get you straight toes."

There seems to be a persistent misunderstanding abroad concerning the way the toe extensor muscles contribute to foot biomechanics during gait, with some believing co-contraction of the toe flexors and extensors is a thing. In fact, they are largely separable as ably demonstrated in Co-ordination of intrinsic and extrinsic foot muscles during gait Zelik et al 2014-

“Conclusions: The sequential peak activity of MTP flexors followed by MTP extensors suggests that their biomechanical contributions may be largely separable from each other and from other extrinsic foot muscles during walking.”

During Veles forward lean I would be very surprised if a healthy foot shows much toe extensor activity at all.

When I say “straight toes” some dorsiflexion at the distal PIP, to give a toe wink effect would, be found in a healthy strong foot. Thank you for allowing me to clarify this.

When Vele’s forward lean is done by a person with weak intrinsic foot muscles, and weak lumbricals and interossei in particular, hammer or claw toes will form transiently with the extension of the proximal phalanges at the MTPJs.

In my experience, this tendency to collapse can be reversed with foot strengthening exercises where the toes remain “straight” at the proximal IP joint, extended at the distal IP joint, and flex around the MTPJs against resistance
Could flexible hammer and claw toes be treated using this exercises method? I have no evidence but believe it may well be possible.


Eric ,you said " Ankle plantar fkexors are much more important for AP balance "
Perhaps you would benefit from reading this paper from 2029

Toe weakness and deformity increase the risk of falls in older people Karen J Mickle et al 2009
Interpretation
Reduced toe flexor strength and the presence of toe deformities increase the risk of falling in older people. To reduce this risk, interventions designed to increase strength of the toe flexor muscles combined with treatment of those older individuals with toe deformities may be beneficial

 

Can functional lesser toe deformity contribute to the risk of plantar plate tears?

Well, flexible lesser toe deformities, like hammer and claw toes, are thought to contribute to the risk of tears and these can be caused by weak intrinsic foot musculature.

If flexible toe deformities can increase the risk of plantar plate tears during activities like sports, then it seems logical to me to conclude that "functional lesser toe deformities" will increase the risk by the same mechanisms.

It is important to remember that the majority of the intrinsic muscles of the foot insert onto the bases of the proximal phalanxes of the lesser toes. These muscles seem to be largely ignored by some clinicians ,which is extraordinary give their importance to foot mechanics.

If functional lesser toe deformities increase the risk of plantar plate tears, wouldn't it be wise to reverse these deformities, where present, by strengthening the lumbricals and interossei ?

 

Other common foot problems that are associated with lesser toe deformities include -
Morton's Neuroma and Metatarsalgia

. If, for example, flexible lesser toe deformities contribute to these conditions, then won't functional lesser toe deformities do the same ? (" Functional lesser toe deformities "is an expression I have coined to describe toes which adopt a hammer toe/claw toe configuration when under load. Or at least I think it was me that first coined it!)

It would appear that many conditions may be traced back to weakness in the lumbricals and interosseus muscles since when healthy these act to help keep the toes straight under load at the interproximal joints and flex the toes around the MTPJs.

Worth noting also, if the toes collapse under load then the flexor digitorum longus, which functions isometrically, will not be able to function as well as it does if the IP joints don't "fail" . Functional hammer toes cannot apply the same level of force to the substrate as healthy toes which do not collapse/buckle, although developed hammer toes ,where the tendon of the flexor digitorum longus becomes shortened ,may be better at applying force. This may in part explain the possible progression from "functional lesser toe deformity" to flexible hammer toe deformity.

 

Some might say, "if lesser toe deformity can be reversed or prevented by strengthening exercises then where is the evidence?"

That would be a fair enough question. In my view, which I believe is supported by the evidence, you need to strengthen the lumbricals ,interossei and FDB if you want to prevent functional lesser toe deformity or prevent it getting worse. Toe curling exercises will get you nowhere since these involve turning the lumbricals and interossei "off" to allow flexion the IP joints (these muscles straighten the IP joints) .

Functional foot strengthening exercises like hopping or calf raises may also fail if loading the toes during such exercises causes a collapse of the toes into a hammer toe configuration from the start . The very muscles you are trying to target are not in use during the exercises if the toes display functional lesser toe deformity. You might even be strengthening the flexor digitorum longus which might cause weakening of the lesser toe intrinsics.

Previous research has shown extrinsic foot muscle strengthening done before intrinsic strengthening can cause significant intrinsic foot muscle weakening.
Ketachi et al Differential effects of intrinsic- versus extrinsic-first corrective exercise programs on morphometric outcomes and navicular drop in pediatric flatfoot

If you come across a subject who's toes collapse under load, I believe it may be wise to address this at once or certainly before embarking on functional exercises based around collapsing toes. A foot may need to function properly before it can be strengthen uniformly.

If anyone is working on research concerning functional exercises and the intrinsic foot muscles they could do worse than take cognisance of this thread.

Get the foot working properly, with toes staying straight and flexing around the MTPJs ,then strengthen the whole.

 

So if you read one site that says one thing and another site that says another how do you choose which one is mistaken?

Sarafian's text the Anatomy of the foot is one place to look. The book has the pictures of the dissected feet to prove that the guy did look closely at the anatomy.

On the lumbricles: Sarafian p.247 "The lumbicle tendons are located on the plantar and tibial aspects of the corresponding deep transverse intermetatarsal ligament. ... At the distal end of the deep transverse intermetatarsal ligament the lumbrical tendon is directed anteriorly and dorsally. It joins the extensor hood and most of the fibers remain concentrated on the tibial border distally, reaching the extensor medial and lateral slips. Few fibers insert on the base of the proximal phalanx. "

The lumbricals are able to plantar flex the proximal phalanx not because they attach to the base of the phalanx, but because of the downward pull, from the tendon, on the hood. It has this downward pull because the tendon goes inferior to the transverse metatarsal ligament. (The interosseous muscles are dorsal to the transverse intermetatarsal ligament)

It is not just that the muscles insert on the base, it is very important where on the base of the phalanx that they insert.


What I needed to have said was that I don't know of any muscles that insert on the plantar base of the proximal phalanx. Muscles that insert on the medial or lateral sides (Plantar and Dorsal interossei) are not able to create a plantar flexion moment when the toes are straight. As the proximal phalanx moves relative to the metatarsal the direction of pull changes. When the toe is dorsiflexed the attachment of the tendon moves dorsally and this gives the tendon a dorsiflexion lever arm. In my dissections of feet with hammertoes I've seen interosseous muscles that only have a dorsiflexion action because the toe sits dorsiflexed.

In short, strengthing the lumbricals would potentially increase a source of plantar flexion moment at the MPJ to counteract the weight bearing action of FDB which is to cause dorsiflexion of the MPJ. The interosseous muscles would not be helpful for this.

 

I can see why someone wanting to sell something would like to call normal function of a muscle structural failure. The "load" that causes the motion is tension in the FDB tendon.

I would expect a foot with a strong healthy FDB to go into hammertoe configuration. You might be able to train someone to simultaneously contract their lumbricals at the same time as they contract the FDB so that their toes might stay straight.

I can put my hand on a table and create the hammertoe shape, or not, depending on which muscles I contract, or relax. It is a voluntary muscle.

 

Good to see that you have gone away and read up on the anatomy of the foot although your comments about the contribution the interosseus muscles make to plantar flexion at the MTPJs seem to be merely your opinion and not supported by the literature.

Depending on circumstances ( contraction state of associated muscles), the flexor digitorum brevis flexes the lesser toes at the PIP joint and also at the MTPJs .

You contend the contraction of the FDB would give a hammer toe configuration. However, the lumbricals and interossei are active at the same time as the FDB during gait on a flat surface, and these ( lumbricals and interossei) act to extend the interproximal joints of the toes. If the interproximal joints are being extended then, without question ,the FDB will flex the lesser toes at the MTPJs. That is what makes these muscles so important .

You think we have to train this ? Why are you using your hand and not your foot ? A hand is not a foot.

 

Lesser toe deformities like hammer or claw toes involve flexion at one or both of the joints between the 3 bones that make up each of the toes 2-5 ,the IP joints .Hammer toes also involve extension at the toe knuckle joint or MTPJ.

The lumbricals and interossei act to extend the IP joints and flex the toes around the MTPJ's and so strong healthy lumbricals and interossei will tend to allow the foot to function with straight toes that flex/extend around the MTPJ's during gait or manoeuvres such as Vele's forward lean.

The actions of the flexor digitorum longus and flexor digitorum brevis (FDB) will change along with lumbrical /interossei activity. For example, lack of activity in the lumbricals/interossei may see contraction of the FDB produce a hammer toe configuration ( flexion at the PIP and extension at the MTPJ's) but simultaneous activity in these 3 muscles will result in straight toes flexing around the MTPJ's .

Weakness in the muscles which hold the toes straight ( extended )at the IP joints will, IMO, lead first to "functional lesser toe deformity "and then, depending on the demands placed on the foot, perhaps to flexible deformity and then fixed deformity as the foot adjust to strength deficits.

Weak feet may not exhibit flexible lesser toe deformity if gait is adjusted by the CNS to avoid the usual later stages of toe off, however, "functional lesser toe deformity" will probably be present.

Back to the 1st sentence in this thread " Functional lesser toe deformity, is there such a thing and can it contribute to falls in the older population? "

I think there is, but then I am not a foot health care professional, as Eric has pointed out.

With regard to the simultaneous contraction of the toe extensors and flexors, Zelik 2015 et al found that-

"peak MTP flexor activity occurred significantly before peak MTP extensor activity during walking (P < 0.001)." And that" The sequential peak activity of MTP flexors followed by MTP extensors suggests that their biomechanical contributions may be largely separable from each other and from other extrinsic foot muscles during walking.
Paper https://doi.org/10.1007/s00421-014-3056-x

So, at least in the initial stages of hammer toe claw toe formation, an imbalance between extensors and flexors is unlikely to be the cause since these muscles are active at different phases of gait. The timing of activity in the extensors changes as deformity worsens .

Anyway, one of the major causes of lesser toe deformity ,lumbrical /interossei weakness . How can you tell if this is present ? Place the toes under load and look for IP flexion ,or buckling under load .

 

There is literature that supports the idea that the interossei will dorsiflex the toes when the toes are in a dorsiflexed position. I have seen this when pulling on the tendons in a cadaver. What literature do you have that says that the interossei plantar flex the MPJ?

Would you agree that the interosseous muscles inert on the side, and not the bottom of the proximal phalanx?

Sometimes the lumbricals and interossei are not active at the same time as the FDB. For evidence look at the picture you posted in post #9

 

Could you supply a reference for literature that supports the idea of the interossei acting to dorsiflex the toes at the MTPJ's ? I would be very interested to read it.

For example Dorsal Interossei of Feet : Wheeless' Textbook of Orthopaedics https://share.google/e9yuqZnHzG4Y4OZ8Z
On the dorsal interossei
" Action:
- assists in flexing the proximal phalanx and extending the middle and distal phalanges.
- abducts the toes from the longitudinal axis of the 2nd toe."

In the picture, the hammer toe configuration is caused by FDB contraction and the lack of force production from the lumbricals and interossei. I have taken to calling this type of toe buckling/collapse as "functional lesser toe deformity" .
People with healthy feet do not walk in such a way that the toes "claw up"/"hammer"at toe off.

I have read texts that advocate lumbrical/ interossei strengthening through toe curls/towel curls . Since this involves flexion at the IP joints, and the lumbricals, dorsal interossei and plantar interossei all extend these joints, I fail to see how such exercises could work. Trying to correct toe deformities caused by deficiency in plantar IP extensors, using toe curls, may actually make things worse . IMO such exercises are at best, useless for the purpose.

 

Since I appear to be introducing a new concept in this thread ,it is worth repeating that I am not a qualified foot health care professional and nothing I say is meant to be medical advice. Instead, the thread is aimed at researchers. The opinions I have expressed on the short foot exercise are by no means accepted by all, they are just my opinions.

That said, “Functional lesser toe deformity” may be a wide spread and largely undiagnosed problem with many believing the foot adopting, for example, a hammer toe configuration under load, is healthy and normal. I believe it is a clear sign of intrinsic foot muscle weakness and, if it is very common, then so is toe flexor weakness. A recent study of younger people found that their toe flexor strength increased by 57% after 6 months walking around in minimal footwear.

The lumbricals and interossei are small muscles but their function is vital to overall foot mechanics.

How would these muscles be strengthening ? Well ,the doming exercise looks like a good idea to me.