Objectives: Development a giant cell tumor model arising from the mutated mesenchymal cells present in its stroma. This establishes the pathogenic mechanism of giant cell tumor, and allows the evaluation of the possible role of biphosphonates and retinoic acid in medical therapy of giant cell tumor of bone.

Introduction: In previous studies our group has shown that mesenchymal stroma contains mesenchymal cells capable of recruiting osteoclasts, and lacking capacity to undergo osteoblastic differentiation. These cells represent the actual neoplastic component of the tumor. In the current study, an attempt was made to establish a giant cell tumor in an animal model by injection of these cells.

Methods: 6 Balb/C named mice were used. The mice were kept in a laminar flow hood and injected when they were 4 weeks old. The injection was in an intra-osseous location into the distal femur. The cell inoculum consisted of 1 million stromal cells. The cells were derived from a grade III giant cell tumor occurring in the hip joint of a 30 years old woman. The mice were kept for 2 months and than sacrificed.

Results: A lytic lesion similar to that occurring in humans developed. The tumor consisted of stromal cells with interspersed osteoclasts. These were identified as being of host origin by mice-specific monoclonal antibodies. The tumor penetrated the cortex but did not infiltrate the articular cartilage. Metastases were not observed.

Discussion: Giant cell tumor of bone is typified by osteolytic bone destruction mediated by osteoclasts. In previous studies, our group has shown that the proliferation rate of the stromal component correlates closely with prognosis and grade of the tumor. The stromal component was shown to consist of pre-osteoblasts that fail to differentiate into osteoblasts, but instead recruit giant cells (osteoclasts), mediating bone destruction. Addition of retinoic acid in culture induces osteoblastogenesis cells by blocking AP-1. The current study confirms in an animal model that indeed the stromal cells are capable of osteoclast recruitment and bone destruction. This animal model might allow development of medical remedies to this tumor.

Study design: An experimental human study of retrieval material.

Objectives: Assessment and evaluation of the involvement of TNFα and Nitric oxide in sciatic pain.

Summary and background data: It appears that the inflammation produced by the herniated fragment is at least partially related to the sciatic pain. TNFα was found to be expressed by herniated nucleus polposus of rats and exogenous TNFα applied in vivo to rat nerve root produced neuropathologic changes and behavior deficit that mimicked experimental studies with herniated nucleus polposus (HNP) applied to nerve roots. Nitric oxide was shown to be involved in the mechanism that produce mechanical and thermal hyperalgesia in rats. Nitric oxide synthesis can be induced by different cytokines among them TNFα and is mediated by the enzyme Nitric oxide synthase. The current study was performed in order to evaluate the possible mechanism of action of TNFα in human herniated discs and define the relationship between nitric oxide and TNFα production by human discs.

Methods: Six herniated fragments of lumbar discs were compared to a similar number of normal intervertebral discs removed during spinal fusion procedures of the lumbar and thoracic spine for the presence of TNFα and the expression of Nitric oxide synthase.

Results: TNFα was expressed by chondrocytes of the herniated fragments but not by the same cells in normal discs. Similar expression pattern was noted for nitric oxide synthase. Both materials were not expressed in the healthy discs.

Conclusions: TNFα appears to be related to pain mechanism of disc herniation. It’s effect is mediated through Nitric oxide. It is well known that NSAIDs are relatively inefficient in modulating TNF-related pain. This might explain the lack of efficacy of currently used medications.

Methods of study: Prospective Controlled Animal Study.

Objectives: Evaluation of the feasibility of embryonal epiphyses transplantation in a xenogeneic model for reconstruction of adult articular cartilage in a rabbit model.

Introduction: Articular cartilage reconstruction has been the goal for many years of orthopaedic research. Current acceptable techniques include the use of allografts, autologous chondrocytes transplantation and osteochondral cylinder grafting. Reconstruction of articular cartilage defects using adult osteochondral allografts is an established clinical procedure, whose principal drawback is lack of lateral integration of the grafts to the surrounding tissue. Autologous chondrocytes transplantation is a sophisticated technique requiring cell culture and a staged operation. Its main draw back is the lack of mechanical strength early on and the prolonged rehabilitation period. This study was conducted in order to evaluate the possibility of using embryonal epiphyses as a cartilage reconstruction tissue.

Methods: A xenogeneic human to rabbit sub-acute osteochondral defect model was designed to evaluate the possibility of allogeneic implantation in humans. The following procedures were performed (n=5): transplantation of: 1. live epiphyses, 2. live epiphyses with autogeneic periosteum, 3. devitalized epiphyses, and 4. devitalized epiphyses with autogeneic articular chondrocytes.

A fifth control group did not receive any implant. Animals were followed for 3 months after transplantation and than sacrificed. The histological specimens were evaluated by image analysis after immuno-histochemical stains were performed (including the following antigens – collagen type II, collagen type I, collagen type III, collagen type X, S-100, alkaline phosphatase, osteocalcin, osteopontin, nitric oxide synthase).

Results: Animals in groups 1 and 2 had a viable reconstruction of the articular surface with little evidence of rejection and without pannus formation. Animals in groups 3 and 4 became severely arthrotic and the graft was resorbed. Nitric oxide synthase accumulation was reduced in group 1 and 2 as compared to groups 3, 4, and 5, indicating a joint preserving function of the epiphyseal grafts.

Discussion: Epiphyseal grafts appear to be a feasible procedure for reconstruction of articular cartilage defects even in a xenogeneic model. The restoration of articular cartilage even with a xenogeneic graft appears to prevent nitric oxide synthesis and the resulting destruction of unafflicted articular cartilage. This is a major pathway leading to secondary osteoarthritis after joint injury. Blocking this pathway might prevent degenerative changes.