Intractable Plantar Keratosis 

Intractable plantar keratosis (IPK) is a discrete, focused callus, usually about 1 cm, on the plantar aspect of the forefoot. Typically, IPKs occur beneath one or more lateral metatarsal heads or under another area of pressure.^{[1, 2, 3, 4]}

Intractable plantar keratoses (IPKs) are often treated successfully with nonoperative care. Those lesions that continue to cause pain may require surgical intervention. Various surgical procedures have been described for treatment of IPK, ranging from partial metatarsal excisions to metatarsal osteotomies and shortening procedures or, in the case of the first ray, sesamoid surgery.

Henri DuVries reported on metacondylectomy in 1953. This technique involves removal of a portion of articular surface of the metatarsal and the plantar condyle. The procedure completely resolved the lesion in 79% of patients and was associated with a 93% patient satisfaction rate.^[5]

Hatcher and colleagues presented a thorough review of 238 various metatarsal osteotomies used in the correction of IPK. The overall success rate was only 56.5%; this was thought to be due to the fact that transfer lesions occurred in almost 40% of the patients.^[6]

Several different distal osteotomies are described, including the dorsal V (or chevron) osteotomy, the tilt-up wedge osteotomy, and the free-floating osteoclasis technique.

The chevron osteotomy of the distal metatarsal, with dorsal displacement of metatarsal head, is frequently reported. Dreeben and colleagues found complete relief of symptoms in 67% of 45 patients in whom this method was used.^[7] Young and Hugar likewise used the chevron osteotomy, and they achieved an 87.5% success rate in resolving symptomatic IPK.^[8]

A more recent modification of the DuVries technique is to remove just the plantar condyle, through a dorsal approach. This significantly reduces the chance of transfer lesions, because no change is made to the weight-bearing metatarsal parabola.

An isolated IPK beneath the first metatarsal is often caused by a hypertrophic sesamoid bone. Historically, this was treated with tibial or fibular sesamoidectomy. Sesamoid shaving or planing has met with good success and fewer complications.^[9]

The intractable plantar keratosis (IPK) is a focused, painful lesion directly beneath a weight-bearing portion of the foot. This pain can limit ambulation and also cause compensatory changes in gait.

Frequency

Intractable plantar keratosis is not uncommon, but its exact frequency requires further definition.

A focused area of pressure on the plantar fat pad, typically resulting from a dropped, or, more correctly, plantarflexed, metatarsal, causes intractable plantar keratosis (IPK). In such cases, the metatarsal head lies in a plane lower than the surrounding metatarsals, focusing exaggerated weight-bearing stress on this area.

Other causes of IPK include tight or poorly fitting shoes, hammertoe deformity, long lesser metatarsals, hypertrophic plantar metatarsal head condyles, malunion of metatarsal fracture, accessory sesamoids, and first-ray hypermobility. In poorly fitting shoes, the toes may become buckled in a tight toe box and create a retrograde hammertoe effect. This forces the toe on top of the lesser metatarsal head and drives the head down against the plantar fat pad. Long lesser metatarsals also have added weight-bearing stress shifted to them, potentially causing an IPK. A hypermobile first ray shifts weight-bearing stress laterally and potentially overloads the plantar fat pad.

An IPK beneath the first metatarsal head is often caused by hypertrophy of either the fibular or tibial sesamoid. Other possible causes include a plantarflexed first ray, a hammered great toe, a cavus foot deformity, or excessive pronation.

The pathophysiology of intractable plantar keratoses involves an impairment of normal weight bearing and a resultant increase in the thickness of the stratum corneum of the sole of the foot. As the lesion develops, the central portion invaginates and becomes extremely painful.

The patient with intractable plantar keratosis (IPK) reports pain in the plantar aspect of the forefoot, which is aggravated by weight bearing; pain is exacerbated when the individual is barefoot. Patients often report a sensation similar to walking on a marble. Most have had this lesion for many years and have tried various home remedies. Sometimes, patients provide a confusing history of a possible foreign-body lesion or of having warts.

On physical examination, the IPK typically appears in 1 of 2 presentations. A focused, discrete IPK is more common and seen directly overlying a bony prominence. This lesion is approximately 1 cm, with a hyperkeratotic rim and a painful, white center core. There is rarely any erythema, edema, or suspicion of infection. This lesion occurs as an isolated IPK or as several discrete, isolated IPKs.

Another type of presentation is a more diffuse buildup of keratotic tissue, called a diffuse IPK or tyloma. This frequently is seen spanning across the plantar aspect of several metatarsal heads and does not have the focused central core.

The indications for surgical treatment of intractable plantar keratosis include the following:

• Failure of periodic debridement, padding, and accommodative shoes
• Continued pain and loss of function that a patient cannot tolerate
• Patient acceptance of the risks and benefits of surgery

When plantar or dorsally displaced, a metatarsal alters the pressure pattern in the forefoot, and an intractable plantar keratosis (IPK) can form in the area of increased pressure. Typically, this is beneath one of the lesser metatarsal heads and can be exacerbated by a hammertoe deformity or hypertrophic metatarsal condyles. These condyles are small protuberances on the plantar flare of the metatarsal head that serve as a soft-tissue attachment point. In some cases, these condyles become enlarged and cause focused pressure beneath the metatarsal head.^[10]

IPKs beneath the great toe are somewhat different. Beneath the first metatarsophalangeal (MTP) joint are 2 small bones called sesamoids, embedded within the soft tissues. The toe flexors pass underneath the first MTP joint, and the sesamoids act as a fulcrum, similar to the patella in the knee. The sesamoids also help to absorb pressure under the foot during standing and walking, and they ease friction in the soft tissues under the toe joint when the big toe moves. Malalignment of or a fracture in the sesamoids can contribute to the development of IPK.

Consider the metatarsal parabola, or cascade, when considering surgical intervention. In the typical cascade, the second digit is longer than (or sometimes as long as) the first, followed in length by, from longest to shortest, the third, fourth, and fifth digits. This permits the natural transition of weight-bearing forces across the forefoot. If this cascade is altered, either in metatarsal length or in the metatarsal head position in the sagittal plane, this can create an IPK.

Absolute contraindications to surgical correction of an IPK include local infection, vascular insufficiency, painless lesion, and neuropathy. Relative contraindications include diabetes, avascular necrosis (AVN) of the metatarsal head, or hypermobile first ray.