The "positive wink sign" is actually the wrong way round, IMO.

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Recently, I came across something the author called the "positive wink sign". I believe that the author, a well respected educator , has gotten it wrong in this particular instance, and that the positive wink sign is actually an indicator of general intrinsic foot weakness, and not strength.


Part of the article in which the author views a hammer toe configuration under load as a sign of healthy intrinsic musculature :

"While toe strength can be measured with dynamometers and/or the paper grip test, the easiest way to evaluate strength in the FDB is by instructing a standing patient to push their toes into the floor with as much force as possible. When FDB is weak, their second through fifth toes remain stationary while the distal phalanx plantarflexes (Fig. 1B). Conversely, when FDB is strong, the intermediate phalanx plantarflexes, creating a visible crease between the intermediate and distal phalanx, which I refer to as a “positive wink sign” (Fig. 1A). A negative or absent wink sign typically indicates weakness not just of the FDB, but of all the intrinsic muscles of the arch." Dr Tom Michaud

 

Gerrard, would you agree that different foot muscles do different things? Would you also agree that when someone contracts one of those muscles that you would see motion that muscle should produce? Modeling of the EDB shows plantar flexion of the PIPJ and extension of the DIPJ, which appears to be what what the author you quoted described as the "wink" sign. This would seem contrary to your contention that the wink sign is a a sign of general foot weekness. The wink sign would be a sign of EDB strength and contraction, and no contraction of the muscle that extends the PIPJ. Foot, and hand, specialists should know that the lumbricals cause extension of the PIPJ and DIPJ.

 

The sort of hammer toe appearance shown in this picture, a " positive wink sign", is not a sign of intrinsic foot strength but rather weakness. If the lumbricals and plantar and dorsal interossei are strong and healthy, the lesser toes will remain straight under load. In addition, it has been shown that the flexor digitorum brevis is more active, and can thus develop more force, if the toe remains straight at the PIP joints and the entire toe flexes as a unit around the MTPJ .

I have personally seen toe/foot strengthening take people from a positive wink sign, to no positive wink sign, as their feet get stronger.

It is worth noting that another recent paper showed that extrinsic foot muscle exercises, like calf raises, may reduce intrinsic muscle strength . Toe curls were not included in this study but are primarily an extrinsic foot muscle exercise, so perhaps this exercise also weakens the intrinsics. Toe curls by there very nature require toe PIP flexion and are very unlikely to strengthen the lumbricals, interossei, abductor hallucis or flexor hallucis brevis.

 

You have lost me Eric . The positive wink sign is elicited when a person leans forwards and puts the toes under load . This is, to an extent, mimicking the phase of gait which exists as a person transitions between mid stance and toe off, or just before heel of, if you like . My understanding is that, in a healthy foot, the FDB is not active at this point.

 

Why do you think FDB is not active at that point? If you see a motion that is caused when a muscle contracts, why would you think that muscle is not active?

 

Because the research indicates that the FDB is not active at that point.
Coordination of intrinsic and extrinsic foot muscles during walking

• November 2014
• European Journal of Applied Physiology 115(4)

DOI:10.1007/s00421-014-3056-x

• Source
• PubMed

Authors:

Karl E Zelik

• Vanderbilt University

 

One, the activity described at the beginning of the post is not walking.
Two muscle contraction is under central nervous system control and a person chooses (sub consciously) to contract muscles. Just because it was not active in one study does not mean that it could be active.

 

Correct, that's what I said . "This is, to an extent, mimicking the phase of gait which exists as a person transitions between mid stance and toe off, or just before heel of, if you like . My understanding is that, in a healthy foot, the FDB is not active at this point."

I should imagine most people have no idea what the muscles in their feet are doing as they walk. Ask most people to move the toes of their feet independently and they struggle, even when looking at them and concentrating hard . Many struggle with the short foot exercise .

Oh it is active in some situations ,I have no doubt . For example, intrinsic minus feet.

 

A number of structures help stiffen the foot at push off including the intrinsic foot muscles and the plantar fascia( via the windlass mechanism) . The windlass mechanism is engaged as the toes are dorsiflexed, but what if the toes are not straight but deformed, reducing the lever arm of the toes and so reducing the windlass effect. In such cases the extensors may lend a hand ,as it were, by becoming active earlier in stance and pulling the base of the proximal phalanx dorsally, thus adding to tension in the PF and foot stiffness .
Thus you could have a foot which engages the windlass mechanism in mid stance via toe extensor contraction . Please see below.

 

When foot bears weight the arch will lower and tighten the plantar fascia. This effect is more pronounced in some feet. In some feet the plantar fascia can be palpated and felt to be tight. When this happens there is an increase in resistance to toe dorsiflexion compared to when the fascia is not tight. The fascia can contribute to arch stiffness without dorsiflexion of the toes.

 

I agree.

The consequences of weak intrinsic foot musculature may or may not included toe deformity . Recent research has shown that anaesthetizing this group of muscles will alter gait, so the foot may not need to stiffen in the same way as it did pre anesthetic.
Pts with a diabetes related intrinsic minus foot may not have toe deformities if they have developed alternative walking strategies such as a shuffling gait.

That said, 60% of older people have lesser toe deformities and this likely greatly impacts the likelihood of falls, negatively impacts patients, and costs the NHS a fortune.

Incidentally, you may be correct about the action of the FDB acting to produce a hammer toe appearance when the toes are placed under load, but it is worth noting that the FDB is activated most when resistance exercises are performed with straight toes moved around the MTPJs ( without flexion at the PIP joints), not during toe curling exercises.

 

During toe off, the lesser toes are dorsiflexed by ground reaction forces and the plantar fascia is wound around the MTPJs, engaging the windlass mechanism and helping to stiffen the foot.

However, if the toes collapse under this load then the lever arm ( full length of toe ) is reduced in length and the winding action is reduced . Small though the lumbricals and interossei are, weakness in these muscles can have far reaching consequences.

Claw or hammer toe configurations give shorter lever arms .

 

The flexor digitorum longus is thought to function isometrically during the stance phase of gait, but how can it do this if, when put under load, the toes collapse into a hammer or claw toe configuration.

The toes make up a substantial part of the length of the foot and toe collapse will see the insertion point of the FDB, at the base of the distal phalanx, ineffectually drawn back towards the muscle origin in the lower leg. IMO collapsing toes will also compromise the ability of the quadratus plantae to apply force and support the medial longitudinal arch of the foot as well as the overall curvature of the foot which is vital to its function.

It is also known that the flexor digitorum brevis is less active during toe curling activities and is more active when the toes are flexed around the MTPJs, without flexion at the PIP joints, as happens during toe curling activities.

In short, weakness in the lumbricals and interossei could compromise the effectiveness of the windlass mechanism, and FDB ,FDL and QP function, leading to problematic changes in gait patterns.

Changes in gait which might be found would include shorter steps, shuffling gait, wider foot placement or, with the intrinsic minus foot of diabetics, a high stepping gait.

Such changes in gait might tax the intrinsics less giving further strength deficits and a lead to a circle of IFM weakning and gait modification.

It's worth repeating, 60% of older people have lesser toe deformities. This might be a modifiable risk factor for falls and addressing it could save the NHS a fortune.

( It has to be said that in a recent review among foot experts, a consensus was reached on appropriate foot strengthening exercise and these did not include toe curling activities. )

The lumbricals and interossei, small, but vital.

 

FDB should read FDL