1st MPJ ulcerations in high risk 'pes cavus' feet

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Hi.
I see a number of ulcerations to the 1st MPJ in (some) pes cavus feet.
My working theory is;
- significantly laterally deviated STJ requiring high activity of peroneus longus which consequently plantarflexes 1st ray due to insertion on med cuneiform and 1st met.
- plantarflexed first ray coupled with calcaneal inversion makes for maximally engages windlass mechanism due to elevation of medial column.
- little saggital plane motion left available at 1st MPJ due to maximal windlas engagement and position of 1st met predisposes to large amount of sheer as external leg rotation drives transverse plain motion at propulsion.
I have had some (anecdotally) good results with heel raises and lateral posting to encourage pronation to relax the windlass prior to propulsion & reduce peroneus longus workload in the hope it relaxes pull on the 1st met.
I faced some push back as appeared counter intuitive to attempt to load the medial column with a 1st met head ulceration. Despite this, it does appear to work well in those I have trialled it with, whether it is because of my rationale or something entirely different.
So, my questions are; do you believe the rationale is reasonable. Would you post lateral on the rearfoot even though this is medial to STJ (thinking K.Kirby SALRE) or would a valgus forefoot post be more appropriate.
My goal is to improve outcomes for these difficult to treat patients so all ideas welcome and any recommendations for further reading would be gratefully received.
Lastly, is there a risk of throwing out knee kinematics by attempting to collapse (partially) the medial arch in this patient group.
Many Thanks, Dan

 

yep. BUT, invariably orthotic prescription is often about compromises and this is one of them!

 

Indeed. Thanks Craig. I officially stole the term pes pancakeus from you as well fyi

 

I agree that a laterally deviated STJ axis can lead to peroneal activity and that can lead to late stance phase pronation. This late stance phase pronation will lead to high medial forefoot loads. High medial forefoot loads will increase tension on the plantar fascia causing a functional hallux limitus.

I disagree with the notion that a lateral wedging will cause an increase in medial forefoot loads. If you make the forefoot valgus wedge big enough, you will eventually run out of range of motion of the STJ and MTJ and you will get an increase in pressure laterally. It is theoretically possible that a smaller lateral wedge would be enough to stop the peroneal activity causing the late stance phase pronation.

When you see pronation, it may be caused by ground reaction force or it may be caused by muscle.

On whether to do just forefoot or forefoot and rearfoot wedging. You need to think in terms of center of pressure. Even if your rearfoot lateral wedge is still medial to the STJ axis (still causing supination) The center of pressure will be moved more laterally and this will decrease the supination moment from the ground. A foot with its entire heel medial to the STJ axis location would be quite an outlier and quite rare.

 

Thanks for the response and for clarifying the rearfoot posting. Intuitively I assumed a lateral post would still reduce supination but I've struggled to rationalise these concepts as I learn.

RE; the peroneal activity driving the late stance phase pronation. Could the high activity of peroneus longus just to maintain eversion in standing still result in and explain contracture and presence of the dorsiflexed first ray. I (again anecdotally and admittedly, subjectively) have noted a reduction in first ray plantarflexion and medial arch height in the patient's I issued lateral forefoot and rearfoot posts and a small heel raise. Although less pronounced, it does seem to correct to some extent, similar to a forefoot supinatus when the rearfoot is posted medial to the STJ.

Also, how would you guage the appropriate amount of forefoot valgus wedging to reduce peroneal activity without overcooking STJ pronation. Or is it simply a matter of start small and see how you go.

Appreciate your help

 

Might be a good idea to send high risk ulcerated patients to a High Risk Foot clinic that is equipped and experienced with the type of pathology you describe.
Regards
Ros Kidd

 

In a foot with a STJ axis position lateral enough for the ground to cause supination, There must be a moment from some source to keep the foot from supinating to end of range of motion. Peroneus longus is a very interesting muscle because it simultaneously plantar flexes the first ray and pronates the STJ. Its function varies with STJ axis position. I've been meaning to write this paper. I created a mechanical model of peroneus longus and gave it three different positions of the STJ axis. In the most lateral position contraction of the peroneus longus the plantar flexion of the first ray effect overcame the pronation effect and the model supinated with first ray plantar flexion range of motion. When the model had the axis in the intermediate position, the STJ pronated, increasing the load on the first met head. The dorsiflexion load from the ground on the head of the metatarsal was matched by the plantar flexion load from the tendon and there was no motion of the ray as the whole foot everted. In the most medial position of the axis, ground reactive force created a grater dorsiflexion moment than the plantar flexion moment from the tendon. The rearfoot everted and the metatarsal dorsiflexed with pull of the peroneus longus muscle.


If you started with someone with a laterally positioned axis, it is unlikely that peroneus longus is causing the arch lowering. On the other hand, a much simpler explanation is that peroneus brevis is acting to keep the forefoot flat on the floor in response to the supination moment from the ground. This increases ground reaction force on the metatarsal head and ground reaction force causes the arch flattening/ dorsiflexion of the medial column.

I have written about the maximum eversion height test here on the arena.

https://podiatryarena.com/index.php?threads/maximum-eversion-height-test.69635/

 

Thanks for the response. I work within this service in the NHS and regrettably find that appropriate management for these patients is sorely lacking. Hence my renewed interest and continued study into biomechanics to change what I see as a failure within this service. I see a number of arbitrarily prescribed TCCs with simply some form of cushioning under the first MPJ. Re-ulceration rates are high. Since I have changed the intervention and scaled it within our service, this is no longer the case. I would like to refine and justify this process, hence the enquiry

 

I look forward to reading that when you do. Sounds as though that answers a lot of my questions. Appreciate your help, that's cleared up a lot

I do use the maximum eversion test you described. Thanks for that pearl of Wisdom, it's serving me well at present