Midtarsal joint: current thinking

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Afternoon.

Can someone point me in the right direction for a reasonably cohesive summary of current thinking around the midtarsal joint kinetics. I am aware the two axis model fell out of favour some time ago as it wasn't supported in the research.

I am presently becoming interested in lesser toe deformity as it pertains to ulceration, (bulk of my job). Have some theories around tendon activity based on STJ axis and knee posture but would like to have a greater understanding of MTJ influence on the forefoot in closed chain.

Also, can someone offer me a brief entry level explanation around the metatarsal parabola, its importance and effects around forefoot and toe kinetics? I tried to read a couple of articles by someone called Demp the other day and felt like i was reading an ancient text written by advanced lifeforms.

Thanks much

 

MTJ kinetics. The midtarsal joint is essentially a planar joint with an envelope of motion. The envelope is volume of space the distal part can occupy relative to the proximal part. The motion of the distal part is limited by ligaments. The ligaments are longer in some places and shorter than others. The longer the ligament, the more motion in the direction of the ligament. (The largest motion available is usually in the direction of motion described by he oblique axis). The plantar ligaments prevent excessive dorsiflexion of the forefoot on the rearfoot. This is important when the rearfoot plantar flexes with ankle joint plantarflexion. I don't feel that the midtarsal joint is relevant for plantar ulcer formation except in Charcot foot where the plantar ligaments are torn/elongated and the talar head causes significant plantar pressure.

Metatarsal parabola. The relative lengths, or plantar flexed position, of the metatarsal can contribute to the explanation of where the callus/ulcer is. There has been a lot of talk about stiffness in stead of position. But position and stiffness are related. If you plantar flex a metatarsal and then apply a dorsiflexion load initially, the stiffness is really low and the metatarsal dorsiflexes easily. After some dorsiflexion motion, the plantar ligament tension will increase and the stiffness of the ray/metatarsal will increase. If the stiffness of one metatarsal increases in a more plantar flexed position than another metatarsal, the one with the more stiffness at a given position will have more load and be more likely to cause callus/ulceration. Cavanagh had a good paper correlating x-ray measurements with plantar pressure. The results, as I recall, were pretty much as you would expect. The longer metatarsals tended to have higher plantar pressures under them. My sense is that Demp complicates the issue unnecessarily. I'm willing to listen to those who think Demp's explanation adds to the discussion.

 

Eric. My general thinking around forefoot ulceration, which has yielded positive outcomes for patients last 12 months, is that 1st MPJ ulcerations are almost always rectifiable at the rearfoot (Medial wedging in a medially deviated axis) or lateral forefoot (plantarflexed 1st ray due to p.longus activity in lateral axis') if there is ROM at the 1st MPJ. Similarly 5th MPJ ulcerations are generally fixable with mobilising the lateral column or posting laterally dependent on foot type/presentation.

I do come across ulcerations to the 2th-4th as stand alone pressure areas and these have been more difficult for me to wrap my head around. Often times these present with toe contracture which I have theorised may be caused by the relative pulls of EDL & FDL with one having increased power to increase either supination/pronation dependent on the foot type. Occasionally, we also see the randomly dropped metatarsal whereby the 2nd, 3rd or 4th has plantarflexed relative to the rest. Do you therefore feel that this is more a presentation around ligament damage & OA at the midfoot. I accept that these things can/do happen and I suppose what I am looking for is how to recognize the cause so that I can identify and prevent this happening for people in the future.

I'm glad to hear that you thought Demp complicates the matter as I felt like i needed to complete a masters in advanced mathematics just to get past the first page I do have a working theory that those with 5th met head loading in lateral axis over 1st met head may be dictated by metatarsal length. Would seem that stiffness in the lateral column could be driven by p.longus pulling so hard around the cuboid to plantarflex the 1st. Are there any general considerations you take from the metatarsal length when factoring in insole designs or is the bulk of the offloading still achieved at the rearfoot/lateral forefoot for most people.

Thanks as always

 

I haven't thought much about cause or predicting who is going to have a sub 2,3, 4 metatarsal ulcer. When the patient comes in with a callus there, or their sock liner has high wear, then I worry about it. Although I have seen enough 4th met head ulcers after 5th ray amputations that I would consider a fifth met amputation a risk factor for further amputaiton.

The general metatarsal length rule that I have is that when I'm treating windlass related pathology (functional hallux limitus) I will generally use a reverse Morton's extension. If I see a long 2nd or a callus sub 2 I will use a forefoot valgus wedge instead.