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© 1999 The Journal of Bone and Joint Surgery, Inc. Symptomatic Osteochondroma of the Clavicle. A Report of Two Cases* , TOKYO, JAPANInvestigation performed at the Department of Orthopaedic Surgery, School of Medicine, Keio University, Tokyo
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 defect19. A solitary osteochondroma is encountered more frequently than are multiple hereditary osteochondromas18,25. This defect may develop in any bone in which endochondral ossification occurs, but the principal locations are the long bones, especially the femur, the humerus, and the tibia18,25. The lesion rarely occurs in the clavicle. Although it typically presents as an asymptomatic slow-growing osseous mass, symptoms resulting from various causes may occur after local expansion4,5,8,9,13,18,23,25,26. We report the cases of two patients who had a painful solitary osteochondroma that was located at the lateral end of the clavicle.
CASE 1. A twenty-six-year-old man who worked as a clerk was seen in July 1995 because of a three-year history of pain in the left shoulder. The pain occurred with movement but not at night or at rest. The patient reported no history of trauma to the shoulder. The lateral end of the clavicle bulged slightly upward, but no instability was noted. The supraspinatus and infraspinatus muscles were slightly atrophic, and both were rated as grade 4 of 5 on manual muscle-testing, but tenderness and a palpable defect of the rotator cuff were absent. The active range of motion of the left shoulder was reduced, compared with that of the right shoulder, by 15 degrees in elevation and by 20 degrees in external rotation. The impingement sign, which is elicited by forced elevation of the arm against the acromion with simultaneous stabilization of the scapula, was negative, but forceful horizontal adduction was noted to be very painful. Radiographs showed a large osseous mass projecting from the inferior surface of the lateral end of the clavicle toward the supraspinous fossa (Figs. 1-A and 1-B). Plain tomograms revealed that the medullary cavity of the osseous mass was continuous with that of the clavicle, and computed tomographic scans demonstrated that the osseous mass abutted the posterior aspect of the coracoid process as well as the inferior aspect of the supraspinous fossa (Figs. 1-C and 1-D). Electromyography revealed no involvement of the suprascapular nerve.
An operation was performed to decompress the mass and thereby reduce the pain. An incision was made along Langer's lines, beginning at the coracoclavicular interval and extending posteriorly to the scapular spine. The lesion was approached by splitting the trapezius muscle parallel to its fibers, beginning at the posterior margin of the acromioclavicular joint. The supraspinatus muscle was noted to be compressed posteriorly by the smooth posterior wall of the osseous mass, and the anteroposterior diameter of the muscle was found to be reduced to approximately one-half of its normal size. After the lesion had been resected, it was noted that the posterolateral half of the trapezoid ligament, which had been adjacent to the mass, had been disrupted, probably as a result of attrition. The conoid and transverse suprascapular ligaments and the suprascapular nerve and vessels were neither compressed nor disrupted. Examination of histological sections of the excised tissue revealed findings that were consistent with the diagnosis of an osteochondroma (Fig. 1-E).
Postoperatively, a small portion of the tumor remained embedded within the inferior surface of the clavicle. However, the pain was no longer present and the range of motion and muscle strength of the left shoulder returned to normal within six months after the procedure. When the patient was seen approximately two and a half years postoperatively, in April 1998, there was no obvious expansion of the remaining tumor and there had been no recurrence of the symptoms. CASE 2. A thirty-nine-year-old man who worked as a computer technician was seen in December 1996 because of a one-year history of pain in the right shoulder. The patient reported that the pain occurred when he served or volleyed the ball while playing tennis. One month before the examination, the pain had begun to occur even during activities of daily living. The patient reported no history of trauma. A round bulge was visible anteromedial to the acromioclavicular joint. An osseous mass with a smooth surface was palpable at this location; the mass extended from the anterior aspect of the lateral end of the clavicle to the superior aspect of the coracoid process. There was exquisite tenderness in the region where the mass was in contact with the coracoid process. The range of motion of the right shoulder was reduced, compared with that of the left shoulder, by 10 degrees in external rotation, by 60 degrees in horizontal adduction, and by the ability of the outstretched thumb to reach three fewer vertebrae in internal rotation. Radiographs and tomograms showed an osseous mass consisting of a cortex that was continuous with that of the anteroinferior surface of the clavicle and a spongiosa that was continuous with that of the clavicle. The mass protruded toward the coracoid process and its distal end made contact with the superior surface of that bone, presenting a joint-like appearance (Fig. 2-A).
An operation was performed to decompress the mass in order to relieve the pain. A transverse skin incision was made along the inferior border of the lateral one-fourth of the clavicle. The lesion was approached by detaching the lateral one-half of the proximal portion of the deltoid from the clavicle. The osseous mass originated three millimeters medial to the acromioclavicular joint. It had a broad base, measuring 2.5 by 1.0 centimeter, on the inferior surface of the clavicle and was covered with a smooth cortex. The distal end of the mass was adjacent to the horizontal portion of the coracoid process. This area was covered by a thin fibrous capsule, similar to that of a joint. A small amount of mucous fluid exuded when the fibrous capsule was incised. The contact surfaces of the osseous mass and the coracoid process were smooth and shiny, like joint cartilage. Osteophytes had formed on the medial margin of the contact surfaces of both structures. Resection of the entire osseous protuberance revealed that the coracoacromial ligament was completely absent. However, the coracoclavicular and coracohumeral ligaments were intact and did not appear to have been affected by the mass. Examination of histological sections revealed that the mass consisted of normal cortical bone and spongiosa. Endochondral ossification was absent, although a thin layer of degenerated and fibrillated fibrocartilage was present at the tip of the protuberance (Fig. 2-B). These findings were consistent with the diagnosis of an osteochondroma in which growth had terminated.
The patient had no pain postoperatively, and the range of motion of the shoulder returned to normal within six months after the operation. When the patient was seen approximately one and a half years after the procedure, in June 1998, there had been no recurrence of the tumor or the symptoms.
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 clavicle11. Nevertheless, almost every type of bone tumor and tumor-like lesion has been described in this location2,10,12,21. Primary bone tumors of the clavicle are more likely to be malignant than benign17,20. 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 lesions21. 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 tumors10. Solitary osteochondromas accounted for 35 to 41 percent of all benign bone tumors in series ranging in size from 2421 to 17,550 lesions10,18,24. However, solitary osteochondromas of the clavicle constituted only 0.5 percent of the 748 solitary osteochondromas in the study by Unni25, 0.5 percent of the 6200 solitary osteochondromas recorded in the Bone Tumor Registry in Japan10, and 0.2 percent of the 1001 solitary osteochondromas in the review by Schajowicz18. 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 clavicle21. When the clavicle is preformed during the embryonic period, primary ossification takes place by intramembranous ossification without a preceding endochondral stage6. From the end of the embryonic period, the clavicle grows in a fashion similar to that of a long bone of the cartilage type, except that the growth zones at both the acromial and the sternal end resemble those of articular rather than epiphyseal cartilage6. Even after birth, these cartilaginous growth areas remain at both ends. It is not certain whether a secondary ossification center develops at the acromial end, although one does develop at the sternal end6,15,22. Histological and experimental analyses have shown that osteochondroma originates in the cells of the growth plate3,14. An osteochondroma is a developmental growth defect that occurs in the circumferential ring of the perichondrium, the ring of Ranvier, that covers the epiphyseal plate19. 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 cartilage18. The cartilaginous growth area of the sternal (medial) end of the clavicle contributes 70 to 80 percent of the longitudinal growth of that bone and is more active than that of the acromial (lateral) end15. However, among the six previously reported cases of osteochondroma of the clavicle of which we are aware and in which the origin was identified, two lesions developed in the medial aspect, one developed in the middle third, and three developed in the lateral aspect of the bone1,7,21. Osteochondroma may become symptomatic as a result of a fracture of the stalk16, an overlying bursa accompanied by an inflammatory reaction4, malignant transformation18,25, a vascular injury8,9,13, compression of peripheral nerves or the spinal cord5,23, and impingement against soft tissue26. However, we are aware of only one other patient, a forty-seven-year-old woman reported on by Vander Maren et al., who had a symptomatic osteochondroma of the clavicle27. Those authors suggested that the pain in their patient was the result of mechanical irritation of the supraspinatus muscle by the osteochondroma, which had developed in the lateral aspect of the bone. The pain described by one of the patients in the present study (Case 1) was probably caused by mechanical irritation of the supraspinatus muscle, the inferior aspect of the supraspinous fossa, the coracoid process, and the trapezoid ligament as a result of the direct contact between these structures and the exostosis. In the second patient (Case 2), an osteochondroma that had stopped growing impinged against the coracoid process and may have caused the pain as well as the disturbance of movement between the clavicle and the scapula. 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.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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