Background
Intractable plantar keratosis (IPK) is a focused, painful lesion that commonly takes the form of 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. Although the diagnosis of IPK is made clinically, the differential diagnosis includes plantar verrucous carcinoma and epidermal inclusion cyst. The pain associated with IPK can limit ambulation and also cause compensatory changes in gait.
IPK is 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.
Anatomy
A plantar or dorsally displaced metatarsal alters the pressure pattern in the forefoot, and an 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.
IPKs beneath the great toe are somewhat different. Beneath the first metatarsophalangeal (MTP) joint are two small bones called sesamoids, which are 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.
The metatarsal parabola, or cascade, should be assessed when surgical intervention is under consideration. 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 weightbearing 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.
Pathophysiology
The pathophysiology of IPK involves an impairment of normal weightbearing 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.
Etiology
A focused area of pressure on the plantar fat pad, typically resulting from a dropped—or, more correctly, plantarflexed—metatarsal, causes IPK. In such cases, the metatarsal head lies in a plane lower than the surrounding metatarsals, focusing exaggerated weightbearing 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 weightbearing stress shifted to them, and this shift can cause an IPK. A hypermobile first ray shifts weightbearing 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.
Epidemiology
IPK is not uncommon, but its exact frequency remains to be defined.
Prognosis
A successful outcome is based on accurately identifying the etiology of the IPK and clearly establishing realistic expectations. If the underlying cause is not addressed, the outcome will be poor and the patient unhappy.
Conservative, nonoperative treatments should not be discounted: Often, they are all that is required for patient relief. A study by Kang et al found that the use of metatarsal offloading pads reduced peak pressures and improved subjective pain responses in patients.
History
The patient with intractable plantar keratosis (IPK) reports pain in the plantar aspect of the forefoot, which is aggravated by weightbearing. Pain is exacerbated when the individual is barefoot; for instance, Thai monks who walk barefoot have more foot problems (including IPK) than those who work with shoes. 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.
Physical Examination
On physical examination, the IPK typically appears in one of two presentations. A focused, discrete IPK is the more common presentation and is 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.
The other, less common 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. Cysts can arise in IPK or can even cause other related conditions, such as plantar fasciitis.
Imaging Studies
Weightbearing radiography should be performed for IPK. Images are reviewed for possible fractures, metatarsal avascular necrosis (AVN), or accessory sesamoids. The metatarsal parabola should be noted, as well as the sagittal plane of the metatarsal heads on the FtAx view.
A radiopaque marker can be used to indicate the exact location of the lesion in the soft tissue.
Medical Therapy
First-line medical treatment of IPK includes the following:
Surgical Therapy
Surgical options
Surgical treatment of IPK can involve the following:
Paring of callus tissue and removal of the central core of the lesion
Sesamoid planing, with protection of the flexor attachments - This is done in lesions below the first metatarsal
Complete tibial or fibular first-ray sesamoidectomy - This is avoided if possible, but it may be necessary in cases of an enlarged sesamoid, sesamoid arthrosis, or nonunion of fracture; care should be taken to reestablish soft-tissue balance of the first metatarsophalangeal (MTP) joint so as to prevent a varus deformity
Distal metatarsal osteotomies - Variations include minimal incision or percutaneous transverse osteotomy of the metatarsal neck, chevron osteotomy, oblique sliding osteotomy, dorsal closing wedge, partial or total resection of the metatarsal head, intramedullary decompression, and lesser-rays condylectomy at osteotomy; in the past, most of these osteotomies were not fixated, but the current norm is to use internal fixation, employing either screws or wires, with possible percutaneous wiring as well.
Proximal metatarsal segmental resection - This involves removal of the proximal metatarsal bones to shorten the overall length of the metatarsal and translate the head more proximally
Data have been published on the clinical outcomes of isolated periarticular osteotomies involving the first metatarsal to treat hallux rigidus.
Preparation for surgery
Patients should be appropriately counseled on the risks and benefits of surgery and the expected postoperative course. Operative risks include infection, neurovascular damage, nonunion, wound dehiscence, toe destabilization, recurrence of lesion, and development of a transfer lesion. The patient should be made aware of the likelihood of recurrence or transfer lesion development. The patient must have appropriate expectations. An informed surgical consent is obtained.
The clinician must determine the cause of the IPK because this dictates the surgical correction. Associated pathologies, such as hammertoe contracture, should be addressed at the same sitting if they are causative to the painful IPK.
Intractable plantar keratosis (IPK) is a focused, painful lesion that commonly takes the form of 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. Although the diagnosis of IPK is made clinically, the differential diagnosis includes plantar verrucous carcinoma and epidermal inclusion cyst. The pain associated with IPK can limit ambulation and also cause compensatory changes in gait.
IPK is 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.
Anatomy
A plantar or dorsally displaced metatarsal alters the pressure pattern in the forefoot, and an 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.
IPKs beneath the great toe are somewhat different. Beneath the first metatarsophalangeal (MTP) joint are two small bones called sesamoids, which are 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.
The metatarsal parabola, or cascade, should be assessed when surgical intervention is under consideration. 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 weightbearing 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.
Pathophysiology
The pathophysiology of IPK involves an impairment of normal weightbearing 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.
Etiology
A focused area of pressure on the plantar fat pad, typically resulting from a dropped—or, more correctly, plantarflexed—metatarsal, causes IPK. In such cases, the metatarsal head lies in a plane lower than the surrounding metatarsals, focusing exaggerated weightbearing 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 weightbearing stress shifted to them, and this shift can cause an IPK. A hypermobile first ray shifts weightbearing 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.
Epidemiology
IPK is not uncommon, but its exact frequency remains to be defined.
Prognosis
A successful outcome is based on accurately identifying the etiology of the IPK and clearly establishing realistic expectations. If the underlying cause is not addressed, the outcome will be poor and the patient unhappy.
Conservative, nonoperative treatments should not be discounted: Often, they are all that is required for patient relief. A study by Kang et al found that the use of metatarsal offloading pads reduced peak pressures and improved subjective pain responses in patients.
History
The patient with intractable plantar keratosis (IPK) reports pain in the plantar aspect of the forefoot, which is aggravated by weightbearing. Pain is exacerbated when the individual is barefoot; for instance, Thai monks who walk barefoot have more foot problems (including IPK) than those who work with shoes. 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.
Physical Examination
On physical examination, the IPK typically appears in one of two presentations. A focused, discrete IPK is the more common presentation and is 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.
The other, less common 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. Cysts can arise in IPK or can even cause other related conditions, such as plantar fasciitis.
Imaging Studies
Weightbearing radiography should be performed for IPK. Images are reviewed for possible fractures, metatarsal avascular necrosis (AVN), or accessory sesamoids. The metatarsal parabola should be noted, as well as the sagittal plane of the metatarsal heads on the FtAx view.
A radiopaque marker can be used to indicate the exact location of the lesion in the soft tissue.
Medical Therapy
First-line medical treatment of IPK includes the following:
- Padding - A doughnut-type cutout pad can be placed directly over the lesion; this allows the IPK to sit in the center and be offloaded by the surrounding pad
- Shoe modifications - A low-heel shoe reduces the amount of weight shifted toward the forefoot and can be more forgiving on the foot; a shoe with a wide, soft toe box that does not crowd the toes is also recommended
- Oral nonsteroidal anti-inflammatory drugs (NSAIDs) - These are occasionally used but typically are not very effective
- Injectable anti-inflammatory medications - Steroid injection into or around an IPK is not recommended; it can create fat-pad atrophy and further exacerbate the plantar foot pain
- Orthotic devices - These are typically accommodative or offloading and are soft so as to help cushion the area; if the IPK is secondary to a hypermobile first ray, a rigid Morton extension may be used to help focus more of the weightbearing force onto the medial column of the foot
- Moisturizing lotions or creams - These can be effective in softening the keratosis and reducing pain; some prescription creams include mild lactic acid to help remove callus tissue
- Pumice stones and callus removers - These should be used with caution in certain patients; they are typically used in the shower or bath, when the skin is soft; reducing the overall mass of the lesion usually provides some symptomatic relief
- Foot baths
- Scrub brushes
- Paraffin baths to reduce callus buildup
- Botulinum toxin - This may be a treatment for IPK
- More effective and invasive treatments include debridement. In a study by Jain et al, platelet-rich plasma injections were more effective than corticosteroid injections for the treatment of plantar fasciitis; such injections might work for IPK.
Surgical Therapy
Surgical options
Surgical treatment of IPK can involve the following:
Paring of callus tissue and removal of the central core of the lesion
Sesamoid planing, with protection of the flexor attachments - This is done in lesions below the first metatarsal
Complete tibial or fibular first-ray sesamoidectomy - This is avoided if possible, but it may be necessary in cases of an enlarged sesamoid, sesamoid arthrosis, or nonunion of fracture; care should be taken to reestablish soft-tissue balance of the first metatarsophalangeal (MTP) joint so as to prevent a varus deformity
Distal metatarsal osteotomies - Variations include minimal incision or percutaneous transverse osteotomy of the metatarsal neck, chevron osteotomy, oblique sliding osteotomy, dorsal closing wedge, partial or total resection of the metatarsal head, intramedullary decompression, and lesser-rays condylectomy at osteotomy; in the past, most of these osteotomies were not fixated, but the current norm is to use internal fixation, employing either screws or wires, with possible percutaneous wiring as well.
Proximal metatarsal segmental resection - This involves removal of the proximal metatarsal bones to shorten the overall length of the metatarsal and translate the head more proximally
Data have been published on the clinical outcomes of isolated periarticular osteotomies involving the first metatarsal to treat hallux rigidus.
Preparation for surgery
Patients should be appropriately counseled on the risks and benefits of surgery and the expected postoperative course. Operative risks include infection, neurovascular damage, nonunion, wound dehiscence, toe destabilization, recurrence of lesion, and development of a transfer lesion. The patient should be made aware of the likelihood of recurrence or transfer lesion development. The patient must have appropriate expectations. An informed surgical consent is obtained.
The clinician must determine the cause of the IPK because this dictates the surgical correction. Associated pathologies, such as hammertoe contracture, should be addressed at the same sitting if they are causative to the painful IPK.