Skives

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Evening

I've been requesting medial heel skives recently as I continue to try but a few things - great effect.

Can anyone offer any insights as to what general circumstance would dictate what degree of medial heel skive you are requesting?

Furthermore, any experience with lateral heel skives for the lateral STJ pts? I generally request lateral forefoot posting to pronate STJ with moderate plantar expansion into the arch - as lateral to the axis. Have excellent results with this but still a few stubborn patients with heavy Callus to 5th mets after 4-6 weeks even though they are no longer ulcerating. I recently requested a 4 degree lateral heel skive but this actually increased lateral loading of 5th met I believe as it was too much bulk on medial aspect of the STJ axis, in this particular gent. I thought a 2mm lateral skive might just give a subtle nudge to the calc at heel strike without being enough to influence inversion? Any additional ideas or is this just as good as it gets for these patients - a 4 week return, forever?

Cheers, Dan

 

I rank the amount of deviation of the STJ axis. The feet where the axis projects to a small portion of the heel get the maximum, I don't go higher than 6mm. Those with the axis projecting just medial to the first met head get 2mm. On smaller heels you should reduce the amount because when you file the cast the skive goes all the way across and as you file down 6mm you will be removing so much heel that you will be reducing arch height.

Remember the Coleman block test, which gives you the same information as the maximum eversion height test. There are two reasons for high lateral pressure. The two types are an over supinator foot type (laterally deviated STJ axis) and the second type is a varus foot that has limited eversion range of motion (or large amounts of tibial varum). The varus foot will not be able to lift the lateral forefoot off of the ground without rotating the leg in the frontal plane. Most of the time the lateral axis foot will be able to evert without moving the tibia (There are some rare lat axis feet that do not have eversion available.)

With high pressures sub 5th met head look for high lateral arch and try to increase pressure along the lateral column proximal to the fifth met head and possibly all the way back to the lateral heel.

What you are doing with wedging is trying to shift the location of center of pressure under the foot. There can still be a CNS response seen as change in muscular activity. I've seen it a lot more, not in the above situation, but when a subject with a lateral axis is given a medial skive and then you will see more pronation.

 

Cheers Eric.
So it's a no to lateral skives in your opinion.
Need to go back and look RE Coleman block test just to understand it but the max eversion test seems much more practical for the daily.
I think I will try rearfoot lateral posts at a lesser degree than the forefoot lateral posting and try to cast mildly pronated, see how I go with these gents. Regrettably, it's NHS and all our custom stuff gets sent off. As I say by, and large I've been getting great results with patients my department has struggled with for years following your previous advice so I appreciate your input.
By varus foot are you referring to a fixed, relatively inflexible deformity. Or are we talking a normal STJ axis put in a significant varus position by tib varum. I do have one gent with no eversion and it is a nightmare to stop him ulcerating.
Can you theorise a reason for the CNS response in lateral axis with a medial skive. Additional pronation would be a desirable outcome if it's reproducible across patients.

 

If you use the maximum eversion height test, don't bother reading about the coleman block test. They give the same information and you only need to know about it if you are and academic.

I use lateral skives, and lateral forefoot "posting" (valgus forefoot wedge) in a patient with a laterally positioned axis. I was trying to make the point that not all feet with high lateral forefoot loads have laterally positioned STJ axes.

Casting pronated: What this does for you is increase the amount of forefoot valgus and gives you a slightly lower arch height. If your lab does the classic Root forefoot valgus post, this should increase the forefoot valgus wedge effect in the orthotic. I recently had an interaction in the lab where there was no forefoot valgus wedge effect and the lab claimed it was accounted for in the cast. An orthotic with a forefoot valgus intrinsic post, when placed against the foot when the foot is in the casting position, will curve away from the foot at the distal lateral edge.

Yes tibial varum creates a "varus" foot. When I say varus foot I'm talking about the foot that has no eversion height in stance and when try to put your fingers under the first metatarsal, you can. When you try to put your fingers under the fifth metatarsal you cannot. These feet can have a normal amount of subtalar joint range of motion, but the maximally everted position is still inverted, so not all varus feet have a "fixed" deformity.

In a lateral STJ axis foot the ground tends to cause a supination moment. (The center of pressure of ground reactive force is more likely to be medial to the axis.) When you shift the center of pressure more medially with a medial heel skive, there will be increased supination moment from the ground and the CNS does not like this because the foot is being pushed toward an inversion ankle sprain. The CNS will activate the peroneal muscles more causing a pronation motion. When this happens the pronation moment from the peroneals will have to be larger than the supination moment from the ground.

 

Got you.

Don't count me out of academia yet doing a second PGCert in diagnostic radiology then I'll be going back for a full MSc in clinical biomechanics next year. Certainly couldn't envision myself undertaking research but I definitely enjoy reading it and understanding the why behind what I see.

Interesting RE; medial skives and increased pronation - does make logical sense. I had been considering the proprioceptive effects since you explained sinus tarsi, medial axis and counterintuitive lateral ankle sprains. I do suspect that if that feedback loop becomes engrained into the muscle memory you may have a mare adjusting to any barefoot sport whereby the skive is gone but the increased peroneal drive persists. For the right person though it might be a logical add in particularly, I would imagine, if increased peroneal strength would be desirable as a long term goal.

Thanks again, keeps me thinking