Fibroosseous [corrected] pseudotumor of the digit: a clinicopathologic study of 43 new cases.

Myositis ossificans (MO) is a reactive zonal fibroosseous lesion in skeletal muscle of the proximal extremities and trunk of young patients. It generally matures over several weeks to form a peripheral rim of bone. Fibroosseous pseudotumor of the digits (FOPD) is a similar reactive lesion of the digits, which is reportedly less well organized. Cases up to year 1980 were previously reported from our institution. We examined new cases of FOPD since 1980 and addressed the relationship of this lesion to both myositis ossificans and other distal extremity fibroosseous lesions. Fifty-two cases coded as FOPD or MO limited to the hands and feet, from 1980 to the present, were retrieved from our files. Nine cases were excluded due to incomplete material or rediagnosis as other lesion. Materials reviewed included radiologic images and pathologic material. Forty-three cases of FOPD were included. All cases were in the fingers, except for 1 toe case, with the proximal phalanx of the index finger the most commonly affected site. Duration of lesions was radiologically estimated to range from 2 to 6 weeks. Age of patients ranged from 10 to 64 years (mean and median of 40 years). Sixty percent of cases occurred in women. Morphologically, half of these lesions had a zonal organization, with mature woven bone peripherally and immature woven bone centrally; all bone demonstrated osteoblastic rimming. Clinically, 6 patients had known antecedent trauma, yet edema and pain of the digit were noted in all. Novel findings were that patients often had occupations requiring repetitive manual labor. Cases of FOPD were diagnosed and treated by simple excision. Three patients had residual disease, subsequently resected, without any recurrences. Fibroosseous pseudotumor of the digits is a distinctive, benign, reactive myofibroblastic and osseous zonal lesion that occurs in the finger of mainly adult patients, many with occupations that require repetitive manual use. Imaging can date these lesions, determine their exact location, and help with diagnosis. These lesions are the superficial and distal counterparts of MO. It is important to understand the morphology of FOPD to distinguish this type of lesion from other benign and malignant fibroosseous lesions.