There are a few foot and ankle surgical procedures that I consider a slippery slope with tremendous uncertainty regarding poor cost versus reward ratios. One of these procedures is the surgical treatment for intractable plantar keratosis via a lesser metatarsal osteotomy.
Only in the rare instances in which the metatarsal is truly elongated or plantarflexed from either trauma or adjacent iatrogenic metatarsal shortening should you employ a lesser metatarsal osteotomy. The metatarsal parabola is a very delicate concept and alteration of this is fraught with complications. Complications such as transfer metatarsalgia, transfer lesions, stress fractures, lack of digital purchase and metatarsophalangeal joint stiffness are common results of lesser metatarsal osteotomies.
Most often, intractable plantar keratosis is a result of either the retrograde force due to a rigid or semi-rigid digital deformity, or a sub second lesion due to a hypermobile first ray. These are the true etiologic components of the intractable plantar keratosis, not the lesser metatarsal. The component surgeons often overlook is the relationship of equinus to intractable plantar keratosis formation. Clearly, equinus is directly related to hypermobility of the first ray and pronatory changes of the foot, which can result in flexor stabilization hammer digit formation. Additionally, equinus causes increased loading of the forefoot, resulting in elevated peak pressures.
No matter the pathology, I believe you must treat the underlying etiology as well as the symptoms. In the case of intractable plantar keratosis, there is the symptomatic dermatologic lesion and the underlying etiologic pathologic condition(s). To be clear, the vast majority of these have nothing to do with the lesser metatarsal.
Can one treat intractable plantar keratosis non-surgically? When is surgical intervention required? Are lesser metatarsal osteotomies required to alleviate the intractable plantar keratosis? These are important questions that require careful consideration. Without a truly thoughtful examination of these questions, the patients entrusted to our care can fall down the slippery slope of uncertainty that accompanies altering the lesser metatarsal parabola.
We can treat intractable plantar keratosis non-surgically when there is no associated rigid digital hammertoe deformity. I like to treat the dermatological condition with topical 40% salicylic acid pads and debridement. Typically, the intractable plantar keratosis will resolve in three to four weeks of treatment. If equinus is present, one must also address this with dorsiflexion bracing for one hour per day, usually for two to three months. Finally, one must treat any underlying biomechanical deformity. Use custom orthoses to treat a pronatory pathology associated with intractable plantar keratosis formation. Examples of pronatory pathologies would be a sub-second metatarsal lesion due to a hypermobile first ray or flexible hammer digit syndrome. One may treat semi-rigid hammer digit syndrome through digital splinting.
Surgical intervention becomes much more likely when there is an associated rigid hammer digit to the intractable plantar keratosis. You can treat the lesion and the equinus either surgically or non-surgically. One must treat all components for successful resolution.
The metatarsal parabola is critical regarding forefoot biomechanics and proper maintenance will best serve you and your patients. Podiatric surgeons can treat intractable plantar keratosis conservatively under the right circumstances. The key to successful conservative resolution is treating the symptomatic dermatologic lesion and the underlying etiologic lesion. By carefully examining the underlying pathologies, one can achieve consistent results without a metatarsal osteotomy, which one should reserve for a truly plantarflexed or elongated metatarsal.