Journal of the American Podiatric Medical Association • Vol 99 • No 6 • November/December 2009 519 Exostoses are isolated, slow-growing, benign osteo- chondral tumors that can appear in every bone of the skeleton. They have been proposed to be a variant of osteochondroma, 1 although their clinical, radiologic, and pathologic features are diverse. 2-4 Exostoses that appear in the distal phalanx of the toes and affect the nail unit are called subungual exostoses. Although these lesions can appear in any digit, the big toe of the foot is the most common location. The presence of a subungual exostosis is usually interpreted as a reactive process rather than as a neoplastic one. It has been described as an acquired deformity in which trauma and microtrauma seem to be the most important etiologic factors. 2-9 Although no studies, to our knowledge, have investigated the possible causes of subungual exostosis, it is thought that the use of high-heeled, narrow shoes; athletic en- deavors; previous nail surgery; and first-ray disorders such as hallux valgus and hallux limitus 2-7 can accel- erate development of the disorder. Epidemiological- ly, subungual exostoses occur most frequently in the fourth and fifth decades of life and are more com- mon in women than in men. 4 Clinical Classification Patients with subungual exostosis can have different clinical presentations depending on when they seek care and factors such as nail trauma and previous treatments. Because of the variety of lesions of the nail unit that can accompany this disorder, it is often unrecognized or misdiagnosed as other conditions of the nail plate such as onychocryptosis. In addition, although radiographic evaluation is paramount in the diagnosis of subungual exostosis, the radiographic lateral view demonstrates an elevated hallux (Fig. 1), which usually presents smaller lesions compared with the intraoperative findings because of the radiolucen- cy of its fibrocartilaginous cap, 4, 10-12 making the diag- nosis more difficult. For these reasons, clinical signs and symptoms should be combined cautiously with radiographic findings to make an accurate diagnosis. We 4 have described four different clinical scenar- ios for subungual exostosis on the basis of the clini- cal appearance of the toe and nail plate and associat- ed disorders at the time of examination (Table 1). In type I or mild deformity, pain exists in the pulp of the toe associated with subungual exostosis. This defor- mity is frequently associated with distal subungual helomata with no major nail plate disorders (Fig. 2). Patients often seek care at this stage because of the Subungual exostosis is a slow-growing, benign outgrowth of normal bone under the nail that affects the nail unit. The most common location in the foot is the dorsal surface of the distal phalanx of the big toe. Clinically, it can appear in combination with a variety of nail disorders, masking the underlying bone condition, which is frequently unrecognized or misdiagnosed. A new classification system for these lesions is proposed on the basis of the clinical signs and symptoms present during examination and the associated disor- ders of the nail plate. Also, a therapeutic algorithm that describes surgical approaches to the different presentations of this disorder is presented. (J Am Podiatr Med Assoc 99(6): 519-524, 2009) *Escuela Universitaria de Enfermería, Fisioterapia y Podología, Universidad Complutense de Madrid, Madrid, Spain. †Department of Podiatry, Universidad Europea de Madrid, Madrid, Spain. ‡Enfermería, Universidad Complutense de Madrid, Madrid, Spain. Dr. Fernández Morato is now in private practice, Madrid, Spain. Corresponding author: Francisco Javier García Carmona, DP, Escuela Universitaria de Enfermería, Fisioterapia y Podología, Avda. Universidad Complutense de Madrid, Ciu- dad Universitaria, s/n, Madrid 28040, Spain. (E-mail: carmona @enf.ucm.es) A Proposed Subungual Exostosis Clinical Classification and Treatment Plan Francisco Javier García Carmona, DP* Javier Pascual Huerta, DP† Diana Fernández Morato, DP‡ BASIC SCIENCE REVIEW