This retrospective review is of 7 patients with a osteoid osteoma of a phalanx. The ages ranged between 1 and 35. Three involved the proximal phalanx, two the middle phalanx and two the distal phalanx. These patients exhibited atypical clinical, radiographic and histological characteristics. Five of seven patients had pain, but were not specifically relieved with aspirin. Two patients had a painless swelling or a macrodactyly. One patient had a monoarticular arthritis of the PIP joint associated with a proximal phalanx lesion. Two patients had clubbing of the digit associated with a lesion of the distal phalanx but only one was painful. Radiographically, only one patient had a lucency of the phalanx upon initial presentation, but it lacked surrounding reactive bone that is typically seen in the long bones of the lower extremity; one patient subsequently developed a typical lucency with surrounding sclerosis. Four patients had minimal or no radiographic findings. A one-year old had a fusiform expansion of the proximal phalanx more typical of an osteochondroma with radial deviation of the digit. Histologically, the lesion was less well demarcated than typically seen in other bones between the nidus and the reactive bone. In six of seven patients, the nidus tissue gradually blended with the cancellous bone and many did not have a rim of reactive bone.
This study outlines the atypical nature of osteoid osteomas of the phalanx. The lesion may not be painful or relieved with aspirin, there maybe clubbing of the distal phalanx, synovitis or even macrodactyly. There are no typical imaging findings that would be diagnostic and the histology can be challenging since there is often no reactive bone surrounding the nidus. It behooves the clinician to keep osteoid osteoma in the differential diagnosis for atypical findings of digits.