Key Insights On Intractable Plantar Keratoses

Due to their unique presentation, intractable plantar keratoses can be challenging to treat and can be particularly painful. This author reviews the biomechanical causes of intractable plantar keratoses, offers pearls on making a diagnosis and provides a guide to surgical techniques for various iterations of the condition.

Metatarsalgia is one of the more common conditions we treat on a daily basis. Corns and calluses are hyperkeratotic lesions located over bony prominences. In the sub-metatarsal region, one may develop an intractable plantar keratosis, which clinically appears as if there is a corn within a callus.

   These hyperkeratotic lesions can be exquisitely painful and, as the name suggests, can be difficult to eradicate. Initial treatment for these often includes: debridement of the hyperkeratotic lesion; the use of topical keratolytic agents; and the use of accommodative padding and/or accommodative orthotic devices.

   I will generally use felt accommodative padding to offload the corresponding metatarsal head to resolve pain. If this technique is beneficial, the patient may do well with an accommodative orthotic device with a metatarsal pad and appropriate sub-metatarsal accommodation. I will recommend a stiff-soled shoe, which in my experience reduces sub-metatarsal pressures. If there is a significant equinus deformity of the Achilles tendon complex, then aggressive stretching and the use of night splinting may be beneficial to reduce sub-metatarsal pressures.

   When conservative treatments are ineffective in managing pain associated with these lesions, then one may consider surgery. Since these skin lesions are secondary to pressure points, the entire goal of any treatment including surgery is to reduce pressure from the underlying bone.

   Before considering surgery, it is paramount that you are certain of the diagnosis of intractable plantar keratosis. Other circumscribed skin hyperplasias that may mimic the intractable plantar keratosis include tyloma (biomechanical callus), verruca plantaris and porokeratoses.

   Warts have a characteristic appearance, which will include black dots in the lesion, a lack of normal skin lines and pinpoint bleeding upon debridement. Porokeratoses can sometimes have the appearance of verruca and intractable plantar keratosis. When you are uncertain, a biopsy can confirm the diagnosis. Certainly, we manage verruca and porokeratoses differently than the osseous surgical procedures for intractable plantar keratosis.

   After making a diagnosis of intractable plantar keratosis and excluding infectious skin conditions such as warts and other benign skin lesions such as porokeratoses, one can formulate a surgical plan. Assuming that the conservative treatments have been ineffective, surgery can be another treatment option.

   We have all learned that the main surgical procedures of the metatarsals, if you will, for intractable plantar keratosis include either shortening of the metatarsal, raising a metatarsal or a condylectomy. Certainly, excision of the intractable plantar keratosis alone will be ineffective. We all tell our patients something to the effect that “calluses are not skin problems but rather bone problems that show up in the skin.” At times, one may excise the skin lesion in addition to bone surgery.

A Guide To The Physical Exam And Precipitating Biomechanical Factors

When examining the foot with an intractable plantar keratosis, the first thing I do is look at the foot type. I make a mental note as to whether it is a high arch or a low arch.

   The second thing I look for is the length pattern of the toes. I want to know if there is a long second toe, which would be suggestive of a Morton’s foot type.

   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.

   Certainly, there are other factors to consider when developing a surgical plan. In the older population, there may be lack of fat padding to the sub-metatarsal region. In this patient population, I am more likely to perform something simple such as addressing a structural problem versus a more global functional reconstruction.

   For example, a geriatric patient with an intractable plantar keratosis under the fifth metatarsal head generally does well with a fifth metatarsal head resection. Obviously, I would not entertain this procedure in a young and/or highly active patient.

   It is difficult for me to come up with a foolproof algorithm for you to determine the ideal surgical procedure(s) for intractable plantar keratoses. I would like to share with you the way I think about surgery for this condition. In my mind, I feel the simplest way to come up with a treatment plan depends on the location of the skin lesion.

   To illustrate, for intractable plantar keratoses under the first metatarsal head, I will generally consider a Jones tenosuspension if there is a flexible contracture at the interphalangeal joint and/or metatarsophalangeal joint. However, if there is a rigid plantarflexed first metatarsal, then I will do a dorsiflexory base wedge osteotomy. This scenario typically occurs in the pes cavus foot type. I rarely do anything with the sesamoids, such as sesamoid planning or sesamoidectomy.

   When the skin lesion is under the fifth metatarsal head, one should assess for a plantarflexed first metatarsal. Additionally, I will determine whether there is in an associated tailor’s bunion deformity. If there is a significant plantarflexion deformity of the first metatarsal (forefoot valgus), I will consider a dorsiflexory base wedge osteotomy of the first metatarsal to reduce compensatory stress on the fifth metatarsal head (i.e., remove the “teeter-totter” effect).

   If there is no structural sagittal plane deformity of the first metatarsal, I will typically address the fifth metatarsal with an osteotomy at the neck to dorsiflex and also medialize the bone if there is an associated tailor’s bunion.

Treating Intractable Plantar Keratoses Under The Central Metatarsals

The most difficult area to address and come up with an appropriate surgical plan for is typically the intractable plantar keratosis under the central metatarsals. When the hyperkeratotic lesion is under the second and third metatarsals, it is typically due to a pes valgus foot type with an insufficient first ray.

   There may also be concomitant hammertoe deformities and structurally long metatarsals. I typically will stabilize the medial column with a first ray procedure, fix the hammertoe(s) with digital stabilization (proximal interphalangeal joint fusion) and shorten/elevate metatarsal heads as needed, depending on the radiographs.

   A hyperkeratotic lesion under the fourth metatarsal head is typically a scenario similar to the lesion under the fifth metatarsal head. I will assess for a plantarflexed first metatarsal and determine whether that is causing lateral overload. If so, I will address the first metatarsal as I have previously described. If there is a hammertoe deformity and/or structural problem with the fourth metatarsal, I will perform an osteotomy of the metatarsal with hammertoe repair.

Other Keys To Appropriate Procedure Selection

When shortening metatarsals, I typically prefer a distal neck osteotomy. Generally, I will do a Weil type osteotomy. If I need to shorten the metatarsal more than 3 to 4 mm, then I will typically do a step down Z osteotomy.

   To raise metatarsals, I typically do a distal V osteotomy or “tilt up” procedure. If I need significant dorsal elevation, I will do a dorsiflexory base wedge osteotomy.

   Typically, I reserve condylectomies and isolated fifth metatarsal head resections for geriatric patients or for patients who cannot mentally or physically handle reconstructive surgery.

   Iatrogenic deformities of the forefoot tend to be the most challenging for surgical reconstruction. Intractable plantar keratoses are common after failed bunion surgeries and with prior lesser metatarsal osteotomies. Excessive shortening of the first metatarsal and/or dorsiflexion of the capital fragment following bunion surgery leads to lesser metatarsal overload. This often leads to intractable plantar keratosis under the second and sometimes third metatarsal heads.

   Surgical management generally includes lengthening and plantarflexion of the first metatarsal as well as shortening the affected metatarsal in the central rays. A sagittal Z osteotomy works well for small amounts of lengthening and plantarflexion of the first metatarsal. In scenarios in which a significant amount of lengthening is necessary, bone grafting and/or callus distraction may be indicated.

   Don’t forget about the pan metatarsal head resection. This is a time-tested method for resolving chronic metatarsalgia and intractable plantar keratoses. This procedure should always be in the back of your mind as a salvage procedure for severe metatarsal derangements, revision of failed surgery or in the older patient with less physical demand.

   It is easy to fall into the mental mindset that a patient has a callus because of a “dropped metatarsal.” It is a disservice to your patient simply to recommend a condylectomy or metatarsal osteotomy that may be doomed to failure without addressing other biomechanical causes. Always consider multiple reasons for the cause of the intractable plantar keratosis.

In Conclusion

Rather than just assuming the intractable plantar keratosis is due to a long metatarsal or plantarflexed metatarsal, physicians should evaluate the condition globally with respect to arch type, concomitant deformities and biomechanical influences. Don’t forget to have the patient get out of the treatment chair and walk for you to assess his or her gait.

   Hopefully, a treatment that addresses functional faults and structural deformities will lead to good outcomes for your patients with resolution of pain and accompanying intractable plantar keratoses.

   Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is in private practice in Phoenix. He is also a faculty member of the Podiatry Institute.

   Dr. Fishco pens a monthly blog for Podiatry Today. For more info, visit https://www.podiatrytoday.com/blogs/william-fishco-dpm-facfas .