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I was just reading a piece about metatarsus adductus where it said that the STJ axis is laterally deviated in a foot with a this deformity. Is this always the case? Would anyone care to comment?

 

If the rearfoot, mid foot, is the same, then a foot with more metadductus will tend to have a more laterally deviated STJ axis. The STJ axis is determined by the facets of the talocalcaneal joint. They are not always the same.
I have a large degree of metarsus adductus and was one of the more medially deviated subjects in Kevin's paper on the anterior axial projection paper. I have what is called a skew foot where the midfoot is abducted on the rearfoot. So, the abducted midfoot makes the bases of the metatarsals more lateral and the metatarsus adductus may not bring the forefoot back under the STJ axis. (Let me know if you understand that last one. Different wording may help.)

Eric

 

I let u know that I didn't get the last concept

could u use other words?
thanks fabio

 

Yes, if you could elaborate or use different wording so I can picture it. I'm just thinking about a particular client who, if I cover most of the midfoot and toes and simply considering the arrangement of the hindfoot, appears to have a medially deviated STJ axis.

 

We've got three foot segments. Rearfoot (talus calcaneus), Midfoot (lesser tarsals) and the metatarsals.
So the STJ axis roughly runs from the posterior lateral aspect of the heel through the talar head. So if there is abduction of the lesser tarsus relative to the rearfoot that will place the forefoot more lateral to the STJ axis. Or you could look it as the rearfoot adducting relative to the midfoot and exposing more talar head medially. Abduction of the midfoot is the same thing ass adduction of the rearfoot relative to the mid foot. So, the mid foot is pointing laterally relative to the rearoot. Now compare that to the situation where the midfoot was straight ahead relative to the rearfoot. When the midfoot is abducted this will create a more medially positioned STJ axis when compared to the rest of the foot.

Now we can add on the metatarsals. If you have an abducted mid foot and abducted metatarsals then your are going to have a really medially deviated STJ axis. However, if you have an abducted midfoot and a metatarsus adductus there can be somewhat of a canceling effect. In some feet with a large amount of abducted rearfoot a large amount of metatarsus adductus, the metatarsus cannot overome the mid foot abdcuted position. So it is possible to have a large metatarsus adductus angle and a medially positioned STJ axis.

Hope this helps.
Eric

 

Thanks Eric! I now have a more clear image in my head. The original piece I was reading had it wrong in that not all cases of metatarsus adductus will have a laterally deviated STJ axis. I don't suppose you, or anyone else for that matter, have a photo to share of a foot which is described by your final paragraph; abducted rearfoot, large amount of metatarsus adductus, medially deviated STJ axis.

 

Here it is. I hope it comes through as attached file

 

We are making shoes for a pnt with a foot just like the one in the picture at the moment. He cannot take any abductory force on the distal hallux which is the main reason he has come to us for bespoke orthopaedic footwear. In order to not make the shoe look like a banana, we've given him a wide toe shape.

 

The person in the picture has an "A" width foot, but needs "D" width shoe to be comfortable. Starting with a wider forefoot would probably create the need for custom.

 

Yes, thank you Eric, that is what is happening with my patient. If his foot was straight he could wear a narrow fitting but if he wears a wide fitting to accommodate the shape, his foot will feel unsupported.

Perhaps you help me with some use of language here. One condition that we come across commonly is what we call a 'forefoot equinus,' that is, in the saggital plane the lesser tarsus is on a plantar grade angle to the calcaneus and the talus. Another way to put it is there is a high lateral arch. The result is a tendency to mid-tarsal joint pronation so that the cuboid can weight bear. Classically the patient will have heavy wear on the heel seat and under the met heads of the insole of his/her shoe but the label will be as new as the day the shoe was bought.

We treat this condition by simply making the heel seat horizontal even though there is say a 1/4" (30mm) heel height. I'm sure you see this condition all the time. My question is, how would you describe it, that is what name do you give to it?
Bill

 

It is helpful when describing feet to say whether you are talking about weight bearing or non weight bearing. I think I understand what type of foot you are talking about. Let me know if I get it right.

A flexible cavus foot is one where non weight bearing you will see the foot assume a a very high arched position with plantar flexion of the forefoot on the rearfoot. When this patient is in the chair you can apply an upward force to the metatarsal heads and the forefoot will dorsiflex and will appear to have a normal or low arch. In stance the foot will have a normal or low arch. (Well, it could have a high arch, but the arch is certainly lower than non weight bearing.)

The problem these feet have is that during swing phase they assume the high arched position and when the forefoot hits the ground, ground reaction force will try to flatten the arch and frictional forces will attempt to prevent the forefoot from sliding further away from the heel, which is the motion that is need to allow the arch to flatten.

I'm still working on how to treat this foot. I'm certain that a normal neutral position non weight bearing cast will not work as the orthotic will have too high of an arch. An orthotic with a slippery top cover and slippery socks might help prevent the forefoot pain these patients often get. Also, a tight shoe that tries to flatten the arch during swing phase. The shoe would have to apply an upward force on the heel and forefoot and a downward force on the top of the foot.

Hope this helps.
Eric

 

Thanks Eric. I'll research some examples from my files and get back to you soon. Bill

 

A foot with a metatarsus adductus deformity, all other things being equal, will have a more laterally deviated subtalar joint (STJ) axis, when compared to a foot with a metatarsus rectus. In fact, often times, clinically we see patients with a high degree of metatarsus adductus have increased tendency toward peroneal tendinopathy, inversion ankle sprains and 5th metatarsal fractures. This is likely related to their abnormal transverse relationship of their metatarsals relative to their foot's STJ axis.

In a metatarsus adductus, as the metatarsal are more adducted toward the contralateral foot, so will the weightbearing metatarsal heads also become more medially located relative to the STJ axis in the metatarsus adductus foot. As the metatarsal heads become more medially located and/or less laterally positioned relative to the STJ axis, then when ground reaction force (GRF) acts on the metatarsal heads in the metatarsus adductus deformity, the mechanical actions of GRF will tend to produce greater magnitudes of STJ supination moments and/or lesser magnitudes of STJ pronation moment when compared to the metatarsus rectus foot. This increase in STJ supination moments caused by the abnormal transverse plane deformity relative to the STJ axis that is present in metatarsus adductus deformity is the most coherent mechanical explanation for the increased risk of peroneal tendinopathy, inversion ankle sprains and 5th metatarsal fractures in these types of feet.

I have covered these biomechanical concepts quite extensively in my 2001 paper on the subtalar joint axis location and rotational (SALRE) theory of foot function (Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001). I believe if you sat down and read the paper in full, you would much better understand the concepts that I describe above. I would be happy to e-mail my paper to you if you contact me privately: kevinakirby@comcast.net

I have attached Figure #21 from my paper to better illustrate these concepts.

Hope this helps.:drinks

 

Thank you Dr. Kirby. I have been trying to get my hands on that particular paper and will email you for it. In the meantime, and this may be described in the paper already, how would I approach the creation of a CFO for a foot type such as this when the symptoms are not at all laterally located but rather plantar/medial heel and apex of MLA? My initial thoughts were medial heel skive and lateral forefoot posting/ reverse Morton's.

 

Assuming the use of CFO, what considerations would have been made in the casting of these feet and the fabrication of the devices?

 

You have the problem of a curved lateral boarder of a foot and a relatively straight shoe. If you make the orthotic the shape of the foot it may not fit will against the lateral aspect of the shoe. If you make the lateral side of the orthotic straight you will often get irritation sub styloid processs on the foot. So, make sure the device does not irritate the styloid.

A lot of labs will straighten the orthotic out because they will assume that you adducted the forefoot on the rearfoot while casting.

Eric