Key Insights On Intractable Plantar Keratoses
The third thing I look for is whether there are hammertoes. If a hammertoe is present, I determine whether the hammertoe corresponds to the affected metatarsal head that has an intractable plantar keratosis.
Finally, I perform a thorough examination of the first ray/great toe joint to determine whether there is any dysfunction such as hallux valgus, hallux limitus/rigidus and/or hypermobility.
Before I even look at an X-ray, I have gathered enough information as to why this patient has an intractable plantar keratosis. Indeed, it is critical to understand the entire biomechanical picture as opposed to just looking at X-rays and coming to the conclusion that the patient has a plantarflexed metatarsal.
We can characterize biomechanical reasons for intractable plantar keratoses by foot type. Typically, I find that the pes valgus foot type with an insufficient first ray will have a hyperkeratotic lesion under the second and sometimes third metatarsal heads. The pes cavus foot type will tend to have tripod landing with high pressures on the heel and underneath the first and fifth metatarsal heads.
Therefore, hyperkeratosis under the first and fifth metatarsal heads is common in the pes cavus foot type. The foot type with a higher arch in addition to underlying metatarsus adductus will tend to have lesions under the fourth and fifth metatarsal heads. Additionally, these patients may have calluses and/or pain under the styloid process of the fifth metatarsal.
Hammertoe deformities can also contribute to the formation of an intractable plantar keratosis. This is due to the retrograde buckling forces applied to the respective metatarsal. This in turn leads to increased skin pressures under that metatarsal head. This is most notable with rigid hammertoes that are non-reducible.
After gathering all of the biomechanical information, review X-rays to finalize the assessment. The anterior posterior view is best to visualize the length pattern of the metatarsals. The most commonly accepted normal metatarsal parabola pattern is when the first and third metatarsals are the same length with the second metatarsal slightly longer. There is a gradual step down among the third, fourth and fifth metatarsals. Certainly, there are normal anatomic variations but this is what I tend to regard as the “normal” foot.
Having a relatively plantarflexed metatarsal can also cause increased pressures that lead to an intractable plantar keratosis. One can best view sagittal plane relationships of the metatarsals on X-ray with the oblique view and sesamoid axial view.
The lateral view is sometimes difficult to ascertain sagittal plane position of the metatarsals due to overlap of the bones. I find the lateral view is beneficial for determining plantarflexion of the first metatarsal in comparison to the second metatarsal by evaluating the dorsal cortices in relationship to one another.
Pertinent Pearls On Developing A Surgical Plan
It is my opinion that intractable plantar keratoses are not solely caused by biomechanical influences or structural deformities, but most likely a combination of the two.
To that end, surgery planning is difficult since the intractable plantar keratosis may be in part due to multiple factors. For example, how do you address the lesion that is located under the second metatarsal head in a patient who has hallux valgus, a long second metatarsal and a non-reducible hammertoe? Those who believe in the structural etiology would recommend shortening the second metatarsal. Those who believe in the biomechanical etiology would recommend a bunionectomy to restore function of the first ray and repair of the hammertoe to reduce retrograde buckling.