A 17-year-old boy presents to the office with a mass on the lateral aspect of his right knee. He noticed the mass approximately 6 months ago and does not believe it has grown since then. He denies pain at rest, but he is starting to experience pain over the mass when running. On examination the patient has a firm, nontender, 2 cm mass over the lateral supracondylar femur. A positive Ober’s test is noted. Anteroposterior and lateral x-rays of the knee are obtained.
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The patient has an osteochondroma on the lateral supracondylar femur that is causing iliotibial band (ITB) tendinitis.
Osteochondroma, or osteocartilaginous exostosis, is a benign cartilaginous tumor that develops during childhood or adolescence. The tumor most commonly arises from the physes of the distal femur, proximal tibia, and proximal humerus but may occur at other sites. The tumor is essentially part of the physis that separates and continues to grow independently. Osteochondroma is the most common bone tumor, accounting for approximately 40% of all benign bone tumors. The tumor usually presents as a painless mass arising from the surface of the bone. Large tumors can cause pain by mechanical impingement and neurovascular compression. Osteochondromas will enlarge during skeletal growth and become latent during skeletal maturity.
Multiple hereditary exostoses is an autosomal-dominant condition characterized by multiple osteochondromas throughout the skeleton. Almost all patients with the condition will have developed multiple osteochondromas by the age of 12, and new lesions rarely develop after skeletal maturity. Patients with multiple exostoses may present with angular deformities in bone, growth disturbances, and limb-length discrepancies. Multiple sites of exostoses is associated with a higher rate of malignant transformation to chondrosarcoma, as is persistence of a cartilage cap measuring >2 cm after skeletal maturity. A patient with a solitary osteochondroma has a 1% chance of malignant transformation compared with a 10% chance in patients with multiple hereditary exostoses.
Radiographic examination alone can make the diagnosis of an osteochondroma; it will reveal an exostosis that may have a sessile (flattened) or pedunculated (stalk-like) appearance. The cortex of the lesion is continuous with the cortex of the native bone. The mass has a thin 2- to 3-mm cartilaginous cap that may be visualized radiographically as irregular calcifications. Magnetic resonance imaging is the best modality to measure the cartilage cap and assess for potential malignant transformation.
Treatment for osteochondroma includes observation in asymptomatic patients. Operative treatment may be indicated for patients with lesions that cause pain, mechanical impingement, deformity, or neurovascular compression. Operative treatment involves a marginal resection that includes the base of the stalk, the cartilage cap, and the overlying periosteum. Cartilaginous growth of >1.5 cm in a dormant osteochondroma or growth occurring after skeletal maturity may signify malignant transformation and surgical resection should be performed. The recurrence rate after marginal excision of a solitary exostosis is <5%.
Chondrosarcoma is a malignant cartilage lesion found more commonly in men (male-to-female ratio is 1.5 to 1) in their 40s to 80s. There are multiple subtypes with a variety of presentations, making it difficult to diagnose and treat. Chondrosarcomas are generally found in the metaphysis of long bones and typically present with a history of constant, progressive pain not relieved with rest.
Enchondroma is a solitary, benign intramedullary cartilage tumor, often occurring in the short tubular bones of the hands, feet, or proximal long bones. Typically, this tumor causes no symptoms and is found incidentally on radiographic examination performed for another complaint. They usually begin and grow in childhood; peak incidence is in the third decade of life and equal between men and women. The incidence of transformation of enchondroma to a malignant tumor is rare (1%).
Osteoid osteoma is a benign bone tumor, usually occurring in the proximal end of long bones. People of all ages can be affected. The male-to-female ratio is 2 to 3 to 1. They are small (<2 cm) but may have surrounding reactive bone formation. Typical presentation is a moderate-intensity, dull, aching pain that may or may not respond to nonsteroidal anti-inflammatory drugs. Most osteoid osteomas disappear after a few years.
Chondroblastoma is a rare benign bone tumor derived from chondroblasts. It is most commonly found in the epiphyses of long bones around the knee, hip, shoulder, or elbow. Although it can affect anybody, 80% occur by the age of 25 and males are twice as likely as females to be affected. The most common symptom is pain but may include joint stiffness, muscle atrophy, or gait disturbance. A chondroblastoma does have the potential to metastasize.
- Arkader A. Clinical and surgical approach to benign bone tumors in children. Orthop Knowledge Online J. 2012;10(1).
- Osteochondroma. Available at: http://www.bonetumor.org/tumors-cartilage/osteochondroma. Accessed July 13, 2015.
- Duke Orthopaedics. Oteochondroma/osteocartilaginous exostosis. Wheeless’ Textbook of Orthopaedics. Available at: http://www.wheelessonline.com/ortho/osteochondroma_osteocartilaginous_exostosis. Accessed July 14, 2015.