Intractable Plantar Keratosis


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. IPKs are thought to occur in two major forms: discrete and diffuse. [1Typically, they develop beneath one or more lateral metatarsal heads or under another area of pressure. [2345]

Although the diagnosis of IPK is made clinically, the differential diagnosis includes plantar verrucous carcinoma [6and epidermal inclusion cyst. [7 The pain associated with IPK can limit ambulation and also cause compensatory changes in gait.

IPK is often treated successfully with nonoperative care. For those lesions that continue to cause pain after failure of appropriate nonoperative treatment, surgical intervention may be indicated. 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. [8]

Hatcher et al 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. [9]

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 the metatarsal head, is frequently reported. Dreeben et al found complete relief of symptoms in 67% of 45 patients in whom this method was used. [10Young and Hugar likewise used the chevron osteotomy, and they achieved an 87.5% success rate in resolving symptomatic IPK. [11]

A later 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 weightbearing 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. [12 

As with any surgical procedure, not all operative approaches to IPK are 100% successful, and each comes with its own series of complications; thus, the decision to proceed with surgical intervention should be made judiciously. [13]

For patient education materials, see the Foot, Ankle, Knee, and Hip Center.

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. (See the image below.) 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. [1415]

Plantar aspect of foot with arrow pointing to callPlantar aspect of foot with arrow pointing to callus.

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. (See the image below.)

Radiograph shows relatively longer 3rd metatarsal.Radiograph shows relatively longer 3rd metatarsal.

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 can become 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. (See the image below.)

IPK under 2nd and 3rd metatarsal heads.IPK under 2nd and 3rd metatarsal heads.

Other causes of IPK include tight or poorly fitting shoes, hammertoe deformity, long lesser metatarsals, hypertrophic plantar metatarsal head condyles, malunion of metatarsal fracture (see the image below), accessory sesamoids, and first-ray hypermobility.

Radiograph shows malunited 4th metatarsal neck fraRadiograph shows malunited 4th metatarsal neck fracture and relatively longer 2nd and 3rd metatarsals.

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.

Plantar keratosis can be linked to obesity and diabetes; the association was found in about 10% of patients studied in a series of 109 patients in Spain. [16]

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. [17]

Mann and Wapner reported on tibial sesamoid shaving in 10 patients with symptomatic IPK below the first metatarsal. At an average follow-up of 52.6 months, nine of the 10 patients reported good to excellent results, and one described results as fair. [12]

For the more typical lesser-metatarsal IPK, one of the various metatarsal procedures may be used. The difficulty with the majority of the metatarsal osteotomies is the unpredictable degree of dorsal displacement. Intraoperatively, it is difficult to accurately gauge the level of the metatarsal heads in the sagittal plane. The use of internal fixation reduces the chance that weightbearing will cause unwanted dorsal displacement.

Kiviniemi et al treated 25 plantar callosities in 13 patients (mean age, 48 years; five male, eight female) with transverse distal metatarsal osteotomy. Osteotomies united primarily in 24 cases and in one after revision. Twenty-three of the callosities healed, two of them after an oblique repeat osteotomy; follow-up extended 7 years. In four of the treated feet, eight hammertoe deformities developed in the involved rays. In five of the feet, eight plantar callosities developed outside the operated rays. [18]

The distal chevron is reported in multiple studies. Kitaoka and Patzer reviewed 21 feet that had undergone chevron osteotomy on the lesser metatarsals; the mean follow-up period was 4 years. Sixteen feet were labeled as good, two as fair, and three as poor. Transfer metatarsalgia occurred in three feet (14%). [19]

Idusuyi et al found that although the single oblique lesser-metatarsal osteotomy may be successful, 50% of the patients studied continued to have some degree of pain, and most patients had limitations in footwear. [20]

A study by Grimes and Coughlin on the Weil osteotomy concluded that a proximal shift of the distal osteotomy may also shift in a plantar direction. They recommended that if a shift of more than 5 mm is needed, a 2-mm-thick blade be used to allow for some dorsal displacement, in order to prevent plantar pressures. [21]

Another study on the clinical results of the Weil osteotomy found relief of plantar pain in 97% of patients treated, at a follow-up of 26 months. [22]

Proximal metatarsal segmental resection involves resection of a cylindrical segment of proximal metatarsal bone approximately 0.5 cm long. Spence et al reported good results in 54 patients operated on with this procedure. [23]

Overall, surgical intervention for lesser-metatarsal IPK should be undertaken with caution. Pontious et al reviewed 29 patients who altogether had undergone 40 V-shaped osteotomies for IPK. The overall effectiveness was quite limited, and there were multiple complications. More than 42% of the patients developed transfer lesions, 10% had recurrence, and 25% reported lack of toe purchase. 


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. [25 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 [5 other related conditions, such as plantar fasciitis.


Laboratory Studies

Standard preoperative tests are indicated.

Pedobarography provides numeric information regarding dynamic and static foot pressure. However, one study found the diagnostic validity of pedobarography to be low for intractable plantar keratosis (IPK) related to metatarsophalangeal (MTP) dislocation in rheumatoid arthritis. [27]

Imaging Studies

Weightbearing radiography should be performed for IPK. Anteroposterior (AP), lateral (LAT), and forefoot axial (FtAx) projections are best. 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.

If the lesion is overlying the first MTP sesamoids, the FtAx view is useful for evaluating for fracture of the sesamoid, as well as for gauging the overall size of the sesamoid.

A Harris mat can be used to determine pressure areas.

Other Tests

Nerve conduction studies, electromyography (EMG), and noninvasive vascular testing may be used if indicated on the basis of the clinical history. However, these tests are rarely indicated in the workup of IPK.

Histologic Findings

Analysis of a biopsy specimen of IPK will show hyperkeratosis and inflammation.



Approach Considerations

Detailed history, meticulous clinical assessment, and radiographic evaluation should be used to assess the causes and extent of intractable plantar keratosis (IPK). Lesions recalcitrant to nonoperative care and routine debridement can be considered for surgery.

Indications for surgical treatment of IPK 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

Absolute contraindications for surgical correction of an IPK include the following:

  • Local infection
  • Vascular insufficiency
  • Painless lesion
  • Neuropathy

Relative contraindications include the following:

The future of IPK treatment must focus on more accurate identification of the underlying pathology of IPK. The enhancement of nonsurgical means of treatment and the refinement of surgical options also are critical. Computerized force plates can aid in understanding the pressure distribution on the foot and thus create better offloading orthotics.

The high rate of transfer metatarsalgia and recurrence of IPK suggests that surgical intervention should be undertaken with caution. Surgery is more successful when a specific etiology can be determined. Performing prophylactic surgery on an asymptomatic foot because of irregularities seen on radiography is highly controversial and is not recommended.

In a study by Zhao et al, pelvis adjustment combined with Dong's extraordinary points helped abate 21 cases of refractory calcaneal pain, and it may have the potential to help treat IPK. [28]

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 therapies - Steroid injection into or around an IPK is not recommended, on the grounds that it can create fat-pad atrophy and further exacerbate the plantar foot pain; other injectable modalities have been tried, but results to date have not been promising [29]
  • 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 [30]

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. [31]

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 or valgus plane 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 [8; 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 [3233]
  • 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. [34]

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.

Operative details

There are various surgical approaches to the correction of an IPK. The authors' preferred technique includes either a plantar condylectomy of the metatarsal head or a double-cut Weil oblique osteotomy of the metatarsal head. Either approach is well suited to monitored anesthesia care (MAC) with a regional popliteal or ankle block. An ankle Esmarch or tourniquet can be used, provided that this does not cause contracture of the long toe flexors.

A dorsally based linear incision is marked just medial or lateral to the extensor tendon over the involved MTP joint. Sharp dissection through the skin and fascia tissue is performed, with care taken to protect any cutaneous nerves. The incision is deepened, and the extensor complex is elevated and protected either medially or laterally. The capsular tissue is sharply incised, and minimal release of the collaterals is performed to enhance exposure. The involved toe is plantarflexed to expose the metatarsal head.

If a plantar condylectomy is to be performed, the plantar capsular attachments must be released with a blade. Care should be taken to protect the long flexor tendons beneath the metatarsal head. The plantar condyles are identified, and one is typically larger than the other. A microsagittal saw is used to remove the condyles in a thin plantar osteotomy made parallel to the weightbearing surface (plantar one-third of the metatarsal head).

The small sliver of bone, including the condyles, is then removed. A hand rasp can be used to smooth any rough edges. A percutaneous Kirschner wire (K-wire) is driven through the length of the toe and across the involved MTP joint down the metatarsal. This is important for allowing the plantar capsule to adhere to the cut bone surface and preventing MTP destabilization.

If the involved metatarsal is plantarflexed or elongated, a double-cut Weil osteotomy is instead performed. The microsagittal saw is used to make a 30° osteotomy at the superior aspect of the metatarsal head-neck junction angled from distal-dorsal to proximal-plantar. Two blades are stacked together to create a controlled wedge resection. The width of each blade cut is approximately 1 mm; thus, two blades together create a 2-mm wedge. This allows some dorsal displacement of the metatarsal head in a controlled fashion.

The metatarsal head is also translated slightly proximal along the osteotomy to shift the head away from the pressure area, and it is fixated with a small screw. An aggressive proximal shift must not be made, because this can shift the head in a plantar direction as it follows the angle of the osteotomy. Again, a percutaneous K-wire is used to splint the toe and maintain alignment of the MTP joint.

The extensor tendon sling and capsular tissue are repaired with 2-0 absorbable suture. Subcutaneous closure is performed with 2-0 absorbable suture, and the skin is closed with 4-0 nonabsorbable suture of choice. The IPK is then debrided from the plantar forefoot, and the central core should be completely removed.

A compressive dressing is applied, and the tourniquet is released. Before leaving the operating room, the physician should confirm that the toe's vascularity is intact.

Postoperative Care

The patient is placed in a rigid postoperative shoe and allowed to bear weight on the heel to tolerance. The dressing is kept clean and dry and is changed in 7-10 days. At that point, the sutures are removed if adequate healing has taken place. Postoperative radiography is performed to confirm alignment of the toe and/or osteotomy.

The patient must remain in the postoperative shoe until the K-wire is removed and adequate healing of the osteotomy is observed. Typically, the K-wire is left in place for 4 weeks and then removed in the office.

At 6 weeks postoperatively, follow-up radiography is performed to assess the healing of the osteotomy. The osteotomy typically requires 6-8 weeks to heal enough to allow migration out of the surgical shoe and into a comfort shoe. Once the patient is in a comfort shoe, postoperative exercises of the toe are encouraged, to restrengthen the toe and prevent loss of purchase, or floating, of the toe.

Typically, patients are able to return to all activities without restriction by 12 weeks.

Complications

Postoperative complications of surgical therapy for IPK include the following:

  • Edema
  • Recurrence of IPK
  • Pain
  • Numbness
  • Stiffness of the involved MTP joint
  • Shortening of digits or metatarsals
  • Malposition
  • Nonunion
  • Delayed union
  • Transfer lesions
  • Vascular complications

Long-Term Monitoring

Appropriate shoe wear is important in preventing recurrence of the IPK. The patient should again be counseled on wearing shoes with enough room in the toe box and a reasonable heel height. Custom orthotics may be beneficial in supporting the foot, and specific modifications can be made to off-load the surgical area.

Periodic follow-up should be made to monitor for recurrence of the IPK or development of transfer lesions.



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