You are in: eMedicine Specialties > Orthopedic Surgery > NEOPLASMS Solitary OsteochondromaArticle Last Updated: Jul 9, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Ian D Dickey, MD, FRCSC, Adjunct Professor, Department of Chemical and Biological Engineering, University of Maine; Consulting Staff, Adult Reconstruction, Orthopedic Oncology, Department of Orthopedics, Eastern Maine Medical Center Ian D Dickey is a member of the following medical societies: American Academy of Orthopaedic Surgeons, British Columbia Medical Association, Canadian Medical Association, and Royal College of Physicians and Surgeons of Canada Editors: Lynn A Crosby, MD, FACS, Chief of Shoulder Division, Professor, Department of Orthopedic Surgery, Wright State University School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Sean P Scully, MD, PhD, Professor, Department of Orthopedics, University of Miami; Dinesh Patel, MD, FACS, Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital; Harris Gellman, MD, Consulting Surgeon, Broward Hand Center, Voluntary Clinical Professor of Orthopedic Surgery and Plastic Surgery, Departments of Orthopedic Surgery and Surgery, University of Miami School of Medicine Author and Editor Disclosure Synonyms and related keywords: solitary osteochondroma, osteocartilaginous exostosis, solitary osteocartilaginous exostosis, solitary OCE, bone tumor, bone lesion, bone cancer, chondrosarcoma INTRODUCTIONSection 2 of 12
  Osteochondroma is the most common benign bone tumor. The tumor is often diagnosed as an incidental finding. Osteochondromas account for approximately 35% of benign bone tumors and 9% of all bone tumors. Most are asymptomatic, but they can cause mechanical symptoms depending on their location and size. As benign lesions, osteochondromas have no propensity for metastasis. In fewer than 1% of solitary osteochondromas, malignant degeneration of the cartilage cap into secondary chondrosarcoma has been described and is usually heralded by new onset of growth of the lesion, new onset of pain, or rapid growth of the lesion.1, 2, 3 History of the ProcedureHistorically and currently, most osteochondromas are incidental findings and are treated solely with observation. If they remain asymptomatic, they can be ignored. Lesions that create mechanical symptoms, become painful, begin to enlarge, or cause growth disturbance have historically been treated with surgical removal, and this remains the mainstay of treatment. ProblemOsteochondroma is a benign, cartilaginous neoplasm that is found in any bone that undergoes enchondral bone formation in its development. The World Health Organization (WHO) defines osteochondroma as a cartilage-capped bony projection on the external surface of a bone. It is found most commonly around the knee and the proximal humerus; however, it can occur in any bone. The osteochondroma may have a stalk (see Images 1-2) and be defined as pedunculated, or it may have a broad base of attachment and be considered sessile in nature (see Image 3). Whether sessile or pedunculated, the medullary canal of the stalk and the bone are in continuity by definition. Osteochondroma is a hamartoma, and patients most commonly present in the second decade of life. Osteochondromas grow until skeletal maturity; growth generally stops once the growth plates fuse.4 Slow growth from the cap may continue over time, as described by Virchow, but this usually stops by age 30 years. FrequencyThe actual frequency of osteochondromas is unknown because many are not diagnosed. Most are found in patients younger than 20 years (see Image 4). The male-to-female ratio is 3:1. Osteochondromas can occur in any bone that undergoes enchondral bone formation, but they are most common around the knee. EtiologyAlthough the exact etiology of these growths is not known, a peripheral portion of the physis is thought to herniate from the growth plate.5 This herniation may be idiopathic or may be the result of trauma or a perichondrial ring deficiency. Whatever the cause, the result is an abnormal extension of metaplastic cartilage that responds to the factors that stimulate the growth plate and thus results in exostosis growth. This island of cartilage organizes into a structure similar to the epiphysis (see Workup, Histologic Findings, below). As this metaplastic cartilage is stimulated, enchondral bone formation occurs, developing a bony stalk. The histology of the cartilage cap reflects the classic, defined zones observed in the growth plate—namely, a zone of proliferation, columniation, hypertrophy, calcification, and ossification. This theory is thought to explain the classic finding of the osteochondroma associated with a growth plate and growing away from the physis while maintaining its medullary continuity. The theory is also thought to explain the clinical behavior of the exostosis growing only until skeletal maturity. Genetic karyotyping has suggested that reproducible genetic abnormalities are associated with these benign growths and that they may actually represent a true neoplastic process, not a reactive one.6, 7 This research is in the early stages, and further investigation is necessary.8, 9, 10, 11 PathophysiologyOsteochondromas are located adjacent to growth plates and develop away from the growth plate with time because they are essentially isolated growth plates. They are affected by, and respond to, various growth factors and hormones in the same manner as epiphyseal growth plates; thus, growth of an osteochondroma should cease at skeletal maturity. ClinicalOsteochondromas are the most common benign bone tumors. They represent 35% of all benign tumors and 9% of all bone tumors. Most are diagnosed in patients younger than 20 years. A marked predilection for males exists; the male-to-female ratio is 3:1. Although they can be located almost anywhere in the skeleton, almost half of osteochondromas are found around the knee, in either the distal femur or the proximal tibia (see Image 4). Osteochondromas are most commonly diagnosed incidentally on radiographs obtained for other reasons. The second most common presentation is a mass, which may or may not be associated with pain. Most of these lesions do not need to be treated, and asymptomatic lesions can be safely ignored. When painful, however, they need to be evaluated properly. Pain is usually caused by a direct, mechanical, mass effect of the osteochondroma on the overlying soft tissue. This can result in an associated sac or bursitis over the exostosis. Irritation of surrounding tendons, muscles, or nerves can result in pain. Pain can also result from fracture of the stalk of the osteochondroma from direct trauma. The bony cap of the stalk may infarct or undergo ischemic necrosis. INDICATIONSSection 3 of 12
Asymptomatic lesions require no treatment and can be monitored initially with radiographs and subsequently by clinical examination. Further investigation is indicated if the patient presents with a painful lesion or develops pain or an increase in size of a preexisting lesion. Such changes may represent either a new mechanical symptom or malignant degeneration. MRI is very useful for investigating these changes. The most common causes of pain are bursa formation, impingement, fracture of the stalk, and malignant degeneration.12, 13, 14 Excision is the treatment of choice for symptomatic lesions. As with all lesions of muscle and bone, the physician must be confident of the diagnosis and well versed in the care of tumors, should the lesion in fact be malignant. If the surgeon has any doubt about the diagnosis of the lesion or the management of a potential malignancy, patient referral is the most appropriate course of action. In excising the lesion, it is important to avoid leaving any remnants of cartilage from the cap or any perichondrium, because this can allow recurrence. The reported rate of local recurrence is less than 2-5%.15 The risk of recurrence is thought by some to be higher in the skeletally immature; therefore, resection might best be delayed until skeletal maturity is reached. Great care must be exercised with lesions close to the physeal plate in the immature patient, because of the risk of growth plate arrest and subsequent deformity. RELEVANT ANATOMYSection 4 of 12
Osteochondromas can occur in many different locations in the body. Thus, a complete understanding of local anatomy is paramount to ensure that local structures are not harmed during surgical resection. Because these lesions arise from the metaphysis, particular care must be taken to avoid damage to the growth plate in the skeletally immature patient. CONTRAINDICATIONSSection 5 of 12
No frank contraindications to removal exist, but the surgeon should be aware that a large osteochondroma may in fact be a chondrosarcoma and should exercise appropriate caution. Removal by a surgeon who is not well versed in dealing with orthopedic malignancies may be a relative contraindication. WORKUPSection 6 of 12
Imaging Studies
Histologic FindingsGrossly, the stalk is contiguous with the intramedullary marrow. By definition, the medullary canal of the affected bone and the canal of the tumor are connected. The stalk is made up of mature bone. The cartilage cap, which tops the lesion and can be quite thick in children, is replaced by enchondral bone formation in maturing patients (see Images 9-10). On microscopic examination, the cartilage cap can exhibit varying amounts of cellularity. The cap has an overlying fibrous layer that contains mesenchymal cells, which are thought to be responsible for the lesion's growth.19 The cells in the cartilage are orientated vertically, as is found in a growth plate. In skeletally immature patients, the cells undergo enchondral bone formation (see Images 11-12). While no specific cartilage cap thickness is an absolute indicator of risk for malignancy, less than 4 cm generally is thought to be in the range of normal. Further, the cap should not thicken in persons older than 30 years. StagingOsteochondromas are benign lesions and can be staged under the Musculoskeletal Tumor Society (MSTS) staging for benign lesions, as follows:
Most osteochondromas are stage I or II. However, significant deformity secondary to mass effect can occur in areas such as the radioulnar joint and tibiofibular joint. While classification is not perfect, such lesions could be considered stage III lesions (see Image 13). These cases likely represent a pressure erosive process, rather than a truly invasive process (as the staging for benign lesions is defined), a subtle but distinct biologic process. In the rare case of malignant degeneration of the cartilage cap, the lesion is usually a low-grade chondrosarcoma that would be graded a low-grade extracompartmental lesion, MSTS stage IB. TREATMENTSection 7 of 12
Medical therapyNo medical therapy currently exists for osteochondromas. The mainstay of nonoperative treatment is observation because most lesions are asymptomatic. Lesions found incidentally can be observed, and the patient can be reassured. Surgical therapyThe treatment for symptomatic osteochondromas is resection. Care must be taken to ensure that none of the cartilage cap or perichondrium is left in the resection bed; otherwise, there may be a recurrence. Ideally, the line of resection should be through the base of the stalk; thus, the entire lesion is removed en bloc with its fibrous covering. Atypical or very large lesions should be investigated fully to exclude the remote possibility of malignancy. MRI is useful in assessing cartilage cap thickness. In the skeletally immature patient, care must be taken to avoid damage to the growth plate during the exposure and resection of the lesion. Preoperative detailsLocal anatomic constraints must be considered carefully so that the approach and resection do not damage nearby structures. CT scanning and MRI can be useful for lesions that arise from flat bones or that are located in difficult areas, such as lesions around the hip or scapula. Intraoperative detailsOnce the osteochondroma is exposed, dissection is limited to the base of the lesion so that an osteotome can be used to shear off the base at the level of the host bone cortex. Care is required to ensure that the resection neither violates normal host cortex by straying too deep nor leaves residual lesion by staying too shallow. The overlying bursa should be left intact, and the loose adhesive tissue should be dissected away so that the lesion and the bursa are removed en bloc. The resected surface of the host bone can be rasped smooth, and if needed, bone wax can be packed on the cut surface to stop bleeding. Once the specimen is removed and pathologic confirmation is received, the wound should be irrigated well and a surgical drain can be placed if needed. The drain should exit in line with the wound. Postoperative detailsMost osteochondromas allow the patient to return to activity as tolerated. However, after resection of a large sessile lesion, restriction of activities should be considered because the stress riser created by the violation of the cortex may increase the risk of fracture. Follow-upThe local recurrence rate after resection of osteochondroma is about 1.8%.20 Once the wound is healed, follow-up on an as-needed basis is reasonable if no associated bone deformity or potential growth-arrest concerns exist. COMPLICATIONSSection 8 of 12
Complications after surgical resection of osteochondromas are rare. Considerations include physeal disturbance or growth arrest, fracture, recurrence, incorrect diagnosis, and hematoma formation. OUTCOME AND PROGNOSISSection 9 of 12
For solitary osteochondromas, the outcome and prognosis after surgery are excellent, with excellent local control and a local recurrence rate of less than 2%.21, 22 The process is a benign one; thus, the prognosis is usually one of complete recovery. Poorer outcomes usually are related to the morbidity associated with the exposure required to remove the lesion or associated with secondary bone deformity, but the latter is usually observed in the multiple hereditary form of the disease.23, 24, 25, 26, 27, 28, 29 FUTURE AND CONTROVERSIESSection 10 of 12
Genetic karyotyping suggests that reproducible genetic abnormalities are associated with these benign growths and that they may represent a true neoplastic process, not a reactive one.6, 7 Research is in the early stages, and further investigation is needed.8, 9, 10, 11 Biologic therapies for osteochondromas may be possible in the future. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Solitary Osteochondroma excerpt Article Last Updated: Jul 9, 2008 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
