Solitary Osteochondroma Treatment & Management


Background

Osteochondroma 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. [1It is found most commonly around the knee and the proximal humerus; however, it can occur in any bone.

Osteochondroma is the most common benign bone tumor. Osteochondromas account for 20-50% of benign bone tumors [2and 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. [345]

Historically 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. Biologic therapies for osteochondromas may be possible in the future.

Anatomy

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.

The osteochondroma may have a stalk and be defined as pedunculated, or it may have a broad base of attachment and be considered sessile. Whether the neoplasm is sessile or pedunculated, the medullary canal of the stalk and the bone are in continuity by definition. [6]

Pathophysiology

Osteochondroma is a hamartoma, and patients most commonly present in the second decade of life. Osteochondromas 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.

Osteochondromas grow until skeletal maturity; growth generally stops once the growth plates fuse. [7 Slow growth from the cap may continue over time, as described by Virchow, but this usually stops by age 30 years.

Etiology

Although the exact etiology of these growths is not known, a peripheral portion of the physis is thought to herniate from the growth plate. [8This 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 Histologic Findings). 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, 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. [910This research is in the early stages, and further investigation is necessary. [11121314]

Heinritz et al reported on the clinical findings and results of molecular analyses of the EXT1 and EXT2 genes—mutations of which lead to multiple osteochondroma—in 23 patients. [15In 17 of the 23 patients, novel pathogenic mutations were identified (11 in the EXT1 gene; six in the EXT2 gene). According to the authors, findings of this study extend the mutational spectrum and understanding of the pathogenic effects of EXT1 and EXT2 mutations.

There is also evidence that various microRNAs (miRNAs) are abnormally expressed in osteochondroma tissues; some of them also participate in several major signaling pathways. [16Thus, it is possible that regulation of miRNA expression may eventually become part of the treatment of osteochondroma. 

Epidemiology

Osteochondromas are the most common benign bone tumors, representing 20-50% of all benign tumors [2and 9% of all bone tumors. However, their actual frequency is not known, because many osteochondromas are not diagnosed. Osteochondromas can occur in any bone that undergoes enchondral bone formation, but they are most common around the knee. Most are diagnosed in patients younger than 20 years (see the image below). A marked predilection for males exists (male-to-female ratio, 3:1). [17Survivors of childhood cancer may be more likely to have these lesions. [18]

Solitary osteochondroma. Anatomic and age distribuSolitary osteochondroma. Anatomic and age distribution of solitary osteochondromas.

Prognosis

For solitary osteochondromas, the outcome and prognosis after surgery are excellent, with excellent local control and a local recurrence rate of less than 2%. [19202122 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. [23242526272829]

Florez et al performed a retrospective study of 113 solitary osteochondromas (most frequently located in the distal femur) that were treated between 1970 and 2002. Six patients had a recurrence after treatment, and in two patients, the lesions became malignant and developed into chondrosarcoma. The authors noted that relapse of the exostosis is rare, occurring in approximately 2% of resections, and that growth of an osteochondroma or the presence of pain in older patients suggests a possible malignancy.

Clinical Presentation


History and Physical Examination

Although osteochondromas can be located almost anywhere in the skeleton, almost half of them are found around the knee, in either the distal femur or the proximal tibia (see the image below). [30]

Solitary osteochondroma. Anatomic and age distribuSolitary osteochondroma. Anatomic and age distribution of solitary osteochondromas.

Osteochondromas are most commonly diagnosed incidentally on radiographs that were 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 need not be treated, and asymptomatic lesions can be safely ignored. When painful, however, they must 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. [3132 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.

Osteochondroma may be associated with pseudoaneurysm of an extremity artery (eg, the popliteal artery), commonly evidenced by pain and swelling. [333435]

Osteochondromas of the spine, though rare, can give rise to symptoms of compressive myelopathy.


LABORATORY INVESTIGATIONS


Plain Radiography

Plain radiography is the mainstay of imaging for osteochondroma. Good-quality radiographs should be obtained in two perpendicular planes to characterize the lesion fully. Classic radiographic features include orientation of the lesion away from the physis and medullary continuity. [40 (See the images below.)

Solitary osteochondroma. Anteroposterior radiograpSolitary osteochondroma. Anteroposterior radiograph of a pedunculated osteochondroma of the distal femur.
Solitary osteochondroma. Lateral radiograph of a pSolitary osteochondroma. Lateral radiograph of a pedunculated osteochondroma of the distal femur. Orientation is away from the growth plate, and medullary continuity is clear.
Solitary osteochondroma. Anteroposterior radiograpSolitary osteochondroma. Anteroposterior radiograph of sessile osteochondroma of the humerus.

CT and PET

In certain bones, such as the pelvis and the scapula, computed tomography (CT) is a useful adjunct to localize the lesion. CT localization can be useful in planning resection. [41 (See the images below.)

Solitary osteochondroma. CT scan of the pelvis depSolitary osteochondroma. CT scan of the pelvis depicting a massive solitary osteochondroma.
Solitary osteochondroma. CT scan of the same sessiSolitary osteochondroma. CT scan of the same sessile osteochondroma of the humerus as in Image 6.

Purandare et al studied the role of whole-body fluorodeoxyglucose (FDG) positron emission tomography (PET)-CT in evaluating sarcomatous transformation of osteochondromas in 12 patients with a diagnosis of osteocartilaginous lesions, [42 with the following results:

  • Seven patients with histopathologic evidence of sarcomatous transformation to grade II chondrosarcoma had moderate-to-high FDG uptake
  • One patient with a dedifferentiated chondrosarcoma had a focus of very intense uptake
  • Four patients with histopathologic or clinical diagnosis of a benign osteocartilaginous lesion had low FDG uptake
  • FDG uptake was also noted in an asymptomatic osteochondroma, which on histopathology revealed a grade II chondrosarcoma

Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is needed only in cases where malignancy is a concern or where relevant soft-tissue anatomy must be delineated. MRI is the modality of choice for assessing cartilage cap thickness (see the image below). Although not an absolute indication, cartilage cap thickness is related to malignancy. Thick cartilage caps (>4 cm) are suggestive of malignant degeneration, especially when they are associated with pain.

Solitary osteochondroma. MRI of sessile osteochondSolitary osteochondroma. MRI of sessile osteochondroma of the femur demonstrating the thickness of the cartilage cap.

Bone Scanning

As a rule, bone scans are not useful in the workup of osteochondromas or in preoperative planning for resection. [43]

Histologic Findings

Grossly, the stalk is contiguous with the intramedullary marrow (see the images below). 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.

Solitary osteochondroma. Gross osteochondroma specSolitary osteochondroma. Gross osteochondroma specimen at the time of resection. Bone stalk and overlying membrane on cartilage cap.
Solitary osteochondroma. Cut surface of surgical oSolitary osteochondroma. Cut surface of surgical osteochondroma specimen. Cartilage cap and underlying bone with medullary continuity.

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. [44The cells in the cartilage are orientated vertically, as in a growth plate (see the image below).

Solitary osteochondroma. High-power view of benignSolitary osteochondroma. High-power view of benign cartilage cells arranged in vertical growth plate pattern.

In skeletally immature patients, the cells undergo enchondral bone formation (see the image below). Although no specific cartilage cap thickness is an absolute indicator of risk for malignancy, a thickness of less than 4 cm generally is thought to be in the range of normal. Furthermore, the cap should not thicken in persons older than 30 years.

Solitary osteochondroma. Histology of cut osteochoSolitary osteochondroma. Histology of cut osteochondroma specimen. Cartilage cap and orientation of enchondral bone formation.

Staging

Osteochondromas are benign lesions and can be staged according to the Enneking or Musculoskeletal Tumor Society (MSTS) classification for benign lesions, as follows:

  • Stage 1 (latent) - Inactive or static lesions
  • Stage 2 (active) - Actively growing lesions
  • Stage 3 (aggressive) - Actively growing lesions that are locally destructive/aggressive

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 (see the image below); although the classification is not perfect, such lesions could reasonably be considered stage III. These cases likely represent a pressure-erosive process rather than a truly invasive one (as the staging for benign lesions is defined), a subtle but significant biologic distinction.

Solitary osteochondroma. Radiograph demonstrating Solitary osteochondroma. Radiograph demonstrating the deformation of the distal tibiofibular joint in a patient with a solitary osteochondroma.

In the rare case of malignant degeneration of the cartilage cap, the lesion is usually a low-grade chondrosarcoma that would be staged as a low-grade extracompartmental lesion (MSTS stage 1B).

Solitary Osteochondroma Treatment & Management


Approach Considerations

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. Magnetic resonance imaging (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. [454647]

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%. [4849 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.

No frank contraindications for removal exist, but the surgeon should be aware that a large osteochondroma may in fact be a chondrosarcoma and should therefore exercise appropriate caution. Removal by a surgeon who is not well versed in dealing with orthopedic malignancies may be a relative contraindication.

Biologic therapies for osteochondromas may be possible in the future.

Medical Therapy

No 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 Therapy

The 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 skeletally immature patients, care must be taken to avoid damage to the growth plate during exposure and resection of the lesion. In a small study evaluating surgical outcomes of pediatric patients with digital osteochondroma (average age, 3.6 years), early surgical treatment was recommended for those with nonepiphyseal metaphysis of the bone to improve motion and prevent further finger deformity; tumor excision, potentially including part of the articular surface, was recommended for laterally oriented tumors that included less than one third of the joint surface. [5051]

Preparation for surgery

Local anatomic constraints must be considered carefully so that the approach and resection do not damage nearby structures. Computed tomography (CT) 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. [52

Operative details

Once 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. If needed, a surgical drain can be placed, ideally exiting in line with the wound.

Postoperative Care

Most 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.

Complications

Complications after surgical resection of osteochondromas are rare. Considerations include the following:

  • Physeal disturbance or growth arrest
  • Fracture
  • Recurrence
  • Incorrect diagnosis
  • Hematoma formation

Long-Term Monitoring

The local recurrence rate after resection of osteochondroma is about 1.8%. [53 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.




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