Faculty Bibliography

The disadvantages of autogenous bone grafts has prompted a search for a dependable onlay bone graft substitute. A combination of tricalcium phosphate, a resorbable ceramic, and osteogenin, an osteoinductive protein, was evaluated as an onlay bone graft substitute in a rabbit calvarial model. Twenty-eight tricalcium phosphate implants (15 mm diameter x 5 mm; pore size, 100-200 microns) were divided into experimental and control groups and placed on the frontal bone of 14 adult New Zealand White rabbits. In the experimental animals, 185 micrograms of osteogenin was added to each implant. In the control animals, the implants were placed untreated. Implants were harvested at intervals of 1, 3, and 6 months, and evaluated using hematoxylin and eosin histology, microradiography, and histomorphometric scanning electron microscope backscatter image analysis. At 1 month there was minimal bone ingrowth and little tricalcium phosphate resorption in both the osteogenin-treated and control implants. At 3 months, both the osteogenin-treated and control implants showed a modest increase in bone ingrowth (8.85 percent versus 5.87 percent) and decrease in tricalcium phosphate (32.86 percent versus 37.08 percent). At 6 months, however, the osteogenin-treated implants showed a statistically significant increase in bone ingrowth (22.33 percent versus 6.96 percent; p = 0.000) and decrease in tricalcium phosphate (27.25 percent versus 37.80 percent; p = 0.004) compared with the control implants. The bone within the control implants was mostly woven at 6 months, whereas the osteogenin-treated implants contained predominantly mature lamellar bone with well-differentiated marrow. All implants maintained their original volume at each time interval studied. The tricalcium phosphate/osteogenin composite, having the advantage of maintaining its volume and being replaced by new bone as the tricalcium phosphate resorbs, may be applicable clinically as an onlay bone graft substitute

We report an unusual case of Ewing's sarcoma of the humerus with epithelial differentiation. This rare finding has recently been documented in this type of tumor.

The principle of distraction osteogenesis, well-established in the enchondral bones of the axial skeleton, has recently been applied to the membranous bones (mandible, cranium) of the craniofacial skeleton in the experimental animal and in the human. In the craniofacial skeleton, however, the technique has been used only to lengthen bone in a direction along its major axis, i.e., unidimensional distraction. A canine model is presented to demonstrate the feasibility of distracting membranous bone away from its dominant axis, i.e., multidimensional distraction. Four mongrel dogs, 5 months of age, were the subjects of this study. Two osteotomies were made in the zygomatic arch, and the bone-lengthening device was fixed to the zygoma. After 7 days of external fixation, the osteotomized segment was lengthened 1 mm/day away from the long axis of the bone for 15 days. External fixation was then maintained for a minimum of 4 weeks, after which the dogs were sacrificed. Craniofacial CT with three-dimensional reconstruction documented multidimensional bone lengthening, and histologic analysis of the specimen confirmed the presence of new cortical bone in the expanded areas. Refinement in technique and miniaturization and internalization of the bone-lengthening device may allow for more precise changes in the amount and direction of lengthening, thus making distraction osteogenesis more widely applicable for use in the human craniofacial skeleton

Intracapsular and paraarticular chondromas are rare benign tumors. The authors report four such lesions, three of which occurred about the knee and one at the hip. Radiographs showed calcified soft-tissue masses in the infrapatellar region of the knee in three patients. In the hip, the lesion was not visible on conventional radiographs. Three lesions originated from the joint capsule and one was extracapsular. These lesions should be differentiated from synovial chondromatosis and other calcified lesions occurring about the joints. After local excision, the tumors usually do not recur.

We present 20 examples of fibro-osseous lesions of bone, characterized by the presence of varying numbers of rounded calcified structures (calcified spherules). In the past, such lesions have been regarded as ossifying fibromas or cementifying fibromas, the latter because of their histologic similarity to jaw lesions known by that name. In the present series, six lesions showed, in addition to the calcified spherules, typical histologic features of fibrous dysplasia, while a further seven showed atypical bony structures that also suggest a link with fibrous dysplasia. This study has led us to conclude that these lesions of the extragnathic skeleton, containing rounded calcified spherules, represent a variant of fibrous dysplasia.

The appearance on magnetic resonance imaging (MRI) of 16 cases of pathologically proven eosinophilic granuloma were reviewed retrospectively and correlated with the radiographic appearance of the lesion. The most common MR appearance (ten cases) was a focal lesion, surrounded by an extensive, ill-defined bone marrow and soft tissue reaction with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, considered to represent bone marrow and soft tissue edema (the flare phenomenon). The MRI manifestations of eosinophilic granuloma, especially during the early stages, are nonspecific, and may stimulate an aggressive lesion such as osteomyelitis or Ewings sarcoma, or other benign bone tumors such as osteoid osteoma or chondroblastoma.

Twenty-seven cases of an unusual, poorly recognized destructive hip arthropathy with radiographic findings of rapid severe joint destruction are presented. Radiographic findings mimicked those of other disorders such as septic arthritis, rheumatoid and seronegative arthritis, primary osteonecrosis with secondary osteoarthritis, or neuropathic osteoarthropathy, but none of the patients had clinical, pathologic, or laboratory evidence of these entities. All patients underwent hip arthroplasty, and osteoarthritis was confirmed at pathologic examination. Rapid progression of hip pain and disability was a consistent clinical feature. The average duration of symptoms was 1.4 years. Radiographs obtained at various intervals before surgery (average, 18 months) in nine patients documented rapid hip destruction. Involvement was unilateral in 89% (24 of 27 cases). Twenty patients (83%) were elderly women. The authors postulate that these cases represent an uncommon, rapidly destructive subset of osteoarthritis

Pathological examination of the resected femoral heads from approximately 2000 total hip replacement operations carried out at the Hospital for Joint Diseases from 1984 to 1989 identified the presence of osteonecrosis in 345 patients (377 femoral heads). In 232 patients the osteonecrosis, referred to as "idiopathic," had occurred in the absence of a subcapital fracture. The present paper describes the pathology of the necrotic lesions in these 232 patients. The use of undecalcified sections and microradiography provides evidence of bone marrow calcification which, at the margin of the lesion, is sufficient to influence the radiographic features of the lesion significantly. Although a subchondral fracture is an almost constant feature of osteonecrosis when it occurs in a femoral head with a normal articular cartilage, no such fracture was found in cases in which osteonecrosis had occurred in an osteoarthritic joint.

The Swarm rat chondrosarcoma has been the subject of extensive biochemical studies. However, to our knowledge, there are no previous reports in the literature on transplantation of this tumor into bone. This article describes the natural history of the tumor when implanted into the bone of the rat, and correlates its histological growth pattern with its radiological appearance. Our results showed that the tumor grows slowly in the bone. The rate of intramedullary growth, however, was variable and was not the same in all the animals. Its growth pattern resembles human chondrosarcoma, with extensive invasion of the marrow and cortex. In the first few weeks after implantation, the only radiological changes noted were mild medullary radiopacities. At a later stage, 12-14 weeks postimplantation, as the tumor infiltrated the bone, significant radiological abnormalities were observed in the medullary cavity and cortex. Periosteal reaction was seen after the tumor invaded the cortex with the production of a soft-tissue mass. Distant dissemination was rare; only 1 of 24 rats developed pulmonary metastases. The Swarm rat chondrosarcoma is a well-differentiated malignant tumor that histologically resembles well-differentiated human chondrosarcoma. Transplanted into bone, it may be useful as an experimental model for comparative studies with human chondrosarcoma.