Osteofibrous Dysplasia 

Osteofibrous dysplasia is a rare, nonneoplastic condition of unknown etiology that affects the long bones. It frequently is asymptomatic.^[1]

Most lesions of osteofibrous dysplasia affect the cortex of the tibia, predominantly the middle third of the diaphysis, as seen in the image below. The cortex often is expanded and thinned, with multiple radiolucencies mixed with intervening areas of sclerosis. The second most common site of involvement is the fibula.

Numerous cases of osteofibrous dysplasia affecting the tibia have been reported. Sweet et al reported 30 cases, with ipsilateral fibular involvement in 5 cases (17%).^[2] In another study of 10 children with tibial lesions, one case (10%) showed ipsilateral fibular involvement. Campanacci and Laus reported 35 cases; the tibia was affected in each case, with ipsilateral involvement of the fibula in 4 cases (11%).^[3] Further, 22 of 35 lesions (63%) affected the middle third of the tibial diaphysis. Ishida et al found 11 of 12 lesions (92%) in the tibia, with one lesion in the ulna.^[4] Most of these tibial lesions affected the proximal diaphysis.

Bilateral involvement is rare. However, in a study of 5 children by Ozaki et al, one child presented with bilateral lesions of both ulnae and tibiae.^[5] The tibia was affected in the remaining 4 children, with one having ipsilateral fibular involvement.

Wang et al reported one case of a lesion affecting the radius, and Schlitter reported the case of a lesion in the humerus.^{[6, 7]}

Osteofibrous dysplasia of the mandible, which occurs exclusively in adults, commonly is referred to as ossifying fibroma.

Frangenheim first described the lesion in 1921 and reported it as a congenital osteitis fibrosa.^[8] Subsequently, Kempson reported 2 cases affecting the tibia of young children and named the lesion ossifying fibroma.^[9] In 1981, Campanacci and Laus studied 35 cases and coined the term osteofibrous dysplasia of the tibia and fibula.^[3] They proposed this term to replace the use of ossifying fibroma because of the supposed congenital origin of the condition, the histologic resemblance to fibrous dysplasia, and the apparent exclusive involvement of the tibia and fibula.^[10] Osteofibrous dysplasia is occasionally referred to as Campanacci syndrome.

Frequency

Osteofibrous dysplasia usually is diagnosed in children under 10 years, with a peak incidence in children aged 1-5 years. Several occurrences in newborns have also been reported.^{[11, 12]} Adults diagnosed with de novo osteofibrous dysplasia have been reported, the oldest patient being age 39 years at diagnosis.^[2]

The reported mean age at diagnosis has been variable. Sweet et al and Ishida et al reported an average age over 10 years.^{[2, 4]} In contrast, Komiya and Inoue, Ozaki et al, and Campanacci and Laus reported an average age younger than 10 years.^{[3, 5, 13]}

No significant sex preponderance has been reported consistently, although several studies have found a slight male predilection. Sweet et al reported 16 males in their 30 patients.^[2] Campanacci and Laus noted that 21 of 35 patients (60%) in their series were male.^[3] This represents the largest reported sex preponderance. In contrast, Park et al reported 38 males and 42 females in their series of 80 patients.^[14]

The etiology of osteofibrous dysplasia, as well as the cell of origin, is unknown. Only one description of familial osteofibrous dysplasia has been reported.^[15]

Osteofibrous dysplasia has been postulated to arise from a fibrovascular abnormality. Johnson proposed a relationship between osteofibrous dysplasia and adamantinoma on the basis of a common causative factor — namely, a fibrovascular defect.^[16] According to this theory, osteofibrous dysplasia results from an abnormality in the Haversian canals, whereas adamantinoma develops secondary to a defect of intramedullary vasculature.

Komiya and Inoue reported similar findings and suggested a deficiency in blood flow within the periosteum as the etiologic factor in osteofibrous dysplasia.^[13] Bridge et al investigated the cytogenetics of osteofibrous dysplasia.^[17] They reported trisomy 12 in 2 distinct specimens from a lesion in an 11-year-old boy and trisomy 7, 8, and 22 in another boy. Studies of adamantinoma have revealed trisomy 7 and 12, suggesting a relationship between osteofibrous dysplasia and adamantinoma.

Sherman et al reported the coexistence of adamantinoma and osteofibrous dysplasia in the same patient, providing additional evidence of a relationship between these 2 entities.^[18] Several other abnormalities have been found within adamantinoma lesions; consequently, these chromosomal anomalies may not be pathogenetic.^{[19, 20]} On the other hand, Sakamoto et al have shown mutations at the Arg 201 codon in persons with fibrous dysplasia but not in persons with osteofibrous dysplasia, suggesting a different pathogenesis for each lesion.^[21]

Classically, osteofibrous dysplasia has been described as painless, with a localized, firm swelling of the tibia as the presenting complaint. The tibia frequently is bowed anteriorly or anterolaterally.^[22]

Park et al reported that of 80 patients, 25% complained of pain, 12.5% had a pathologic fracture, 8.8% presented with tibial swelling, and 6.2% presented with deformity.^[14] Sweet et al reported that 18 of 30 patients (60%) presented with complaints of pain, 13 (43%) with swelling, and 4 (13%) with deformity.^[2] One lesion was an incidental finding.

Komiya and Inoue reported similar presenting complaints in a series of 10 cases.^[13] Ishida et al reported a duration of symptoms in 11 of 12 patients ranging from 2 months to 5 years, with an average of 14 months; one lesion was asymptomatic.^[4] Of 3 newborns with osteofibrous dysplasia of the tibia, 2 had swelling and 1 had pathologic fracture.

Differential diagnosis

The differential diagnosis of osteofibrous dysplasia includes monostotic fibrous dysplasia, nonossifying fibroma, and adamantinoma. Fibrous dysplasia can be differentiated on the basis of several characteristics. Generally, it occurs in patients older than 10 years, more commonly affects the femur and ribs, and does not resolve spontaneously.

Radiographically, fibrous dysplasia appears as an intramedullary lesion with a ground-glass appearance.^[23] On histologic examination, fibrous dysplasia is not bordered by active osteoblasts and is cytokeratin-negative.^[24] Cytogenetically, fibrous dysplasia is related to anomalies affecting chromosomes 3 and 5. Sakamoto et al found that immunoreactivity for osteonectin in bone matrix is seen more commonly in osteofibrous dysplasia.^[25] Nonossifying fibroma can be distinguished from osteofibrous dysplasia by several typical features. Nonossifying fibroma predominantly is a metaphyseal lesion. Histologically, it is characterized by a storiform pattern of spindle cells with scattered multinucleated giant cells, is not bordered by active osteoblasts, and is cytokeratin-negative.

More challenging is the distinction between osteofibrous dysplasia and adamantinoma.^[26] Accurate differentiation between these 2 lesions is essential for correct diagnosis and appropriate treatment. Adamantinoma has a similar predilection for the cortex of long bones, particularly the tibia, and may have radiologic and histologic findings similar to those of osteofibrous dysplasia.^{[27, 28]} However, adamantinoma can be distinguished from osteofibrous dysplasia by the presence of soft-tissue extension, intramedullary involvement, periosteal reaction in the absence of pathologic fracture, and the histologic finding of hyperchromatic epithelial islands. Adamantinoma typically manifests with a larger, more painful lesion and is usually found in patients older than 10 years.

However, as suggested by Kuruvilla and Steiner, it is likely that osteofibrous dysplasia is part of the morphologic spectrum of adamantinoma.^[29] Kanamori et al found that extra copies of chromosomes 7, 8, 12, 19, and 21 recur in adamantinoma.^[30] These aneuploidies may be useful in differentiating adamantinoma from osteofibrous dysplasia.

Due to the high recurrence rate, many authors advocate nonoperative treatment of the lesion until after skeletal maturity is reached, at which time marginal resection and bone grafting may be performed without increased risk of recurrence. For patients of any age, surgical correction of associated deformities may be required. Surgery may be indicated if the lesion is aggressive or if the patient experiences multiple pathologic fractures. Resection of large portions of the lesion usually is not necessary and only increases susceptibility to recurrent fractures.

The tibia is a tubular long bone with a triangular shape in cross section. The bone is surrounded by 4 fascial compartments. The anteromedial surface lies subcutaneously and therefore has no soft-tissue protection. The primary center of ossification appears at 7 weeks of gestation. The proximal ossific nucleus appears soon after birth and fuses with the metaphysis at approximately age 16 years. The distal ossific nucleus appears at age 2 years and fuses at age 15 years. In some, separate centers of ossification exist for the medial malleolus and tibial tubercle.

The vascular supply to the tibia is provided predominantly by the posterior tibial artery, from which the nutrient artery enters the tibia at the origin of the soleus muscle along the oblique line of the tibia. The nutrient artery of the tibia has 3 ascending branches and 1 descending branch. The distal aspect of the tibia is supplied by periosteal anastomoses that enter the bone adjacent to the ankle joint.

Though nonoperative management is recommended in patients who are skeletally immature, there are no absolute contraindications to surgical intervention in children, with the exception of any underlying medical or anesthetic issues. Operative management is not recommended in patients who are skeletally immature, because of the high recurrence rate following resection and curettage and because of the predisposition to fracturing after the bone has been weakened by biopsy. Pathologic fracture does not necessarily require surgical management, since cast immobilization frequently results in good healing.