Excerpt from Clavus

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Background

Clavus is a thickening of the skin due to intermittent pressure and frictional forces. These forces result in hyperkeratosis, clinically and histologically. This extensive thickening of the skin may result in chronic pain, particularly in the forefoot; in certain situations, this thickening may result in ulcer formation. The word clavus has many synonyms and innumerable vernacular terms, some of which are listed in the Table below; these terms describe the related activities that have induced clavus formation.

Synonyms include the following: callosity, a hyperkeratotic response to trauma; corn, heloma, or a circumscribed hyperkeratotic lesion that may be hard (ie, heloma durum) or soft (ie, heloma molle); and callous, callus, or a diffusely hyperkeratotic lesion. Localized callosities of the soles, which do not resolve, are termed plantar callus, heloma, tyloma, keratoma, or plantar corn.¹ When callosities occur over 1 or more lateral metatarsals, they are termed intractable plantar keratoses.²

Clinically, all these lesions look like hyperkeratotic or thickened skin. Maceration and secondary fungal or bacterial infections are a common overlying feature in heloma molle and diabetes. Plantar helomas tend to have a central keratin plug, which, when pared, reveal a clear, firm, central core. The most common sites for clavus formation are the feet, specifically the dorsolateral aspect of the fifth toe for heloma durum, in the fourth interdigital web of the foot for heloma molle, and under the metatarsal heads for calluses.³

Pathophysiology

The shape of the hands and feet are important in clavus formation. Specifically, the bony prominences of the metacarpophalangeal and metatarsophalangeal joints often are shaped in such a way as to induce overlying skin friction. As clavus formation ensues, friction against the footwear is likely to perpetuate hyperkeratosis. Toe deformity, including contractures and claw, hammer, and mallet-shaped toes, may contribute to pathogenesis. Bunionettes, ie, callosities over the lateral fifth metatarsal head, may be associated neuritic symptoms due to compression of the underlying lateral digital nerves. Furthermore, Morton toe, in which the second toe is longer than the first toe, occurs in 25% of the population; this may be one of the most important pathogenic factors in a callus of the common second metatarsal head, ie, an intractable plantar keratosis. Chronic or repetitive motion may also induce clavus formation, as is seen in computer users (ie, "mousing" callus).

Frequency

United States

The clavus is a common disorder because of the frequency of usage of occlusive footwear and participation in repetitive activities, such as running.

Mortality/Morbidity

Extensive thickening of the skin may result in chronic pain, particularly in the forefoot; in certain situations, ulcer formation may result. Clavus may be a sign of underlying neuropathy due to diabetes or neuroborreliosis, or due to the deformities of rheumatoid arthritis. In the case of neuropathy, a clavus may hide ulceration or denote abnormal neurovasculature of the feet. In the case of rheumatoid arthritis, clavus may enhance the pain of deformed joints.

Race

Any race may be affected.

Sex

Clavus is more common in women than in men because of their use of occlusive and poorly fitted footwear.

Age

Anyone can have a clavus, but most individuals acquire the risk factors for clavus formation after puberty because of the onset of traumatic footwear use, repetitive motion injuries, and progressive foot deformities.

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