Answer: osteochondroma of the clavicle

Discussion:

An osteochondroma is a benign lesion that is often considered to be the most common type of bone tumor; however, it is actually a developmental physeal growth. Histological and experimental analyses have shown that osteochondroma originates in the cells of the growth plate. An osteochondroma is a developmental growth defect that occurs in the circumferential ring of the perichondrium, the ring of Ranvier, that covers the epiphyseal plate. The lesion may develop in any bone in which endochondral ossification occurs. In the long bones, it is likely to develop in the metaphyseal region of the most active growth cartilage. Primary bone tumors and tumor-like lesions of the clavicle are uncommon; Klein et al., in a review of the literature, found that only 0.45 percent of more than 13,000 primary bone tumors involved the clavicle. Nevertheless, almost every type of bone tumor and tumor-like lesion has been described in this location. Primary bone tumors of the clavicle are more likely to be malignant than benign. Smith et al., in a review of thirty-five primary bone tumors of the clavicle that had been treated at the Memorial Sloan-Kettering Cancer Center, reported only five benign lesions. A larger nationwide series from Japan, however, demonstrated that the occurrence of benign primary bone tumors of the clavicle was almost equal to that of malignant tumors.

Solitary osteochondromas accounted for 35 to 41 percent of all benign bone tumors in a series ranging in size from 2421 to 17,550 lesions. However, solitary osteochondromas of the clavicle constituted only 0.5 percent of the 748 solitary osteochondromas in the study by Unni, 0.5 percent of the 6200 solitary osteochondromas recorded in the Bone Tumor Registry in Japan, and 0.2 percent of the 1001 solitary osteochondromas in the review by Schajowicz. According to Smith et al., solitary osteochondromatosis accounted for only 3 percent (two) of fifty-eight primary bone tumors and tumor-like lesions of the clavicle.

The lateral end of the clavicle is closely surrounded by many structures, including the trapezius, deltoid, and supraspinatus muscles; the acromion; the scapular spine; the glenoid and coracoid processes; and the acromioclavicular, coracoacromial, and coracoclavicular ligaments. As a result of this complexity of the local anatomy, an osteochondroma that develops at the lateral end of the clavicle may produce a wide variety of symptoms.

Ogawa, K.; Yoshida, A.; and Ui, M.: Symptomatic osteochondroma of the clavicle. A report of two cases. J. Bone and Joint Surg., 81-A: 404-8, March 1999.