A colleague recently asked for my opinion on a patient who suffered a midfoot fracture at the base of the fourth and fifth metatarsal shafts. The patient had no treatment at the time of the injury and healed with a large bone callus on the plantar surface of the metatarsals. These bone calluses create a large prominence on the plantar foot. This area is taking excessive pressure, leading to pain, keratoma formation and occasional skin breakdown. My colleague was looking for suggestions on an orthotic prescription for the patient’s foot.
Our primary orthotic goal is to transfer pressure off of the plantar prominence. We have a second goal of reducing friction in the area, which will help prevent callus formation and skin breakdown.
I recommended using a semi-rigid, vacuum-formed polypropylene orthosis. By using vacuum-formed polypropylene rather than direct-milled polypropylene, one can incorporate a sweet spot in the orthotic shell to accommodate for the plantar prominence.
I also recommended prescribing a standard heel cup and a wide width. The wide width will help to transfer pressure from the lateral foot to the medial foot. The heel was not everted so a standard heel cup is sufficient in this case. If the heel was everted, we could use a deep heel cup to reduce excessive eversion.
In regard to prescribing the aforementioned sweet spot accommodation, the location is based on the outline on the negative cast of the plantar prominence. If you are taking the images of the foot with a laser scanner, instead of marking the plaster negative cast, you could place felt on the foot at the site of the prominence. This will show up on the laser scan and mark the area of the prominence.
I also recommended using a cushioned top cover. In this situation, the clinician prescribed a diabetic top cover. The patient is not diabetic but the diabetic top cover has both a layer of Poron for cushion and a layer of Plastazote for accommodation. This should help cushion and accommodate the plantar prominence. The clinician prescribed the top cover to be glued on the heel only. This means that the cover was only glued in the heel cup area of the orthosis, leaving the anterior two thirds of the cover unglued. This allows access to the sweet spot so the clinician can easily add more accommodation if necessary. Once one is sure the patient is comfortable, the clinician can glue down the top cover to the rest of the orthosis.
The contralateral foot orthosis was essentially the same prescription but without the sweet spot and there is no need to glue the top cover heel portion only. For the contralateral foot, one can prescribe the top cover to be glued all the way down.
Finally, after the patient has worn the orthosis for couple of weeks, we will be able to see on the cover where the most wear is occurring. This will be indicative of increased pressure and friction in this area. At this point, I would suggest adding a PTFE patch (ProLab Orthotics) on the dorsum of the top cover to reduce localized friction.
Editor’s note: Dr. Huppin is the Medical Director of ProLab Orthotics, the distributor of the PTFE Patch™. This blog was originally published at http://prolaborthotics.com/Default.aspx?tabid=90&EntryID=499  and has been adapted with permission from Lawrence Huppin, DPM, and ProLab Orthotics. For more information, visit www.prolaborthotics.com  .