Purpose: Filling bone defects is a major challenge in orthopaedic surgery. One of the therapeutical alternatives to combined autologous bone grafts and bone substitutes is to use a biomaterial carrying bone stem cells. The purpose of this study was to test a hybrid biomaterial in a major bone loss model in the rabbit.

Material and methods: The study material was the AN 69 hydrogel (Hospal). Twenty-four rabbits were divided into four identical groups of six individuals. Each animal underwent a unilateral resection measuring 2 cm in the mid third of the cubitus: group 1 simple resection; group 2 resection and centromedullary pin; group 3 resection, centromedullary pin and biomaterial; group 4 resection, centromedullary pin, biomaterial with bone marrow stem cells. Animal were sacrificed at six weeks. A radiograph was obtained immediately after surgery and at sacrifice. The study parameters were: new bone formation, bone healing, bone remodelling. Each criteria was assessed with a mean score (Werntz score). A pathology examination was performed in all cases to study new bone formation, polylmere degradation and inflammation.

Results: The overall radiographic score was group 1 = 2, group 2 = 8, group 3 = 24, group 4 = 42 for a maximum 62 points. Histologically, there was nonunion after simple pinning with formation of a defective callus. The nonunion persisted after pinning and hydrogel without cell seeding. New bone formation was moderate and predominated on the borders of the bone resection. After pinning associated with cell seeded hydrogel, an osteogenic lamina arose from the hydrogel network. This osteogenesis was continuous with osteogenesis originating from the bone section cut.

Discussion: These findings demonstrate that associated a hydrogel with bone stem cells can produce more significant bone formation than in controls, confirming the animal model. Treatment of major bone loss and aseptic osteonecrosis after curettage could be proposed with this new biomaterial combining a hydrogel and CD34+ stem cells in humans.

Purpose: Joint cartilage repair is one of the most widely studies aspects of orthopedic care. The tissue’s intrinsic capacity to repair degenerative, inflammatory or trauma-induce damage is low. The purpose of this study was to report early results obtained with an allograft using a hybrid biocartilage in the rabbit.

Material and methods: Chondrocytes obtained by successive enzymatic digestion of joint cartilage from the knee joint were implanted via medial arthrotomy into an osteo-cartilaginous knee defect measuring 4 cm in diameter and 3 mm in depth produced by trepanation of the tronchlea. Both knees were operated in six adult New Zealand rabbits. After eight weeks, the animals were assessed clinically then sacrificed. The femoral condyles were removed for histological study. All grafted joints were mobile and had normal function without risk of self-mutilation.

Results: The joint samples did not show any evidence of effusion. The implant site was still visible macroscopically and presented a cartilaginous surface continuous with the healthy cartilage. After HES staining, the distal pole of the implant was found to be colonised with young cartilage continuous with the trochlear cartilage. Enchondral ossification appeared to be present in the distal part of certain cartilaginous nodules with a bony lamina continuous with the adjacent subchondral bone. There was no evidence of an inflammatory reaction of the synovial and the patellar cartilage was normal.

Discussion: These preliminary results of a hybrid biocartilage graft combined with cartilage surface reconstruction and osteointegration of the deep implant without in vivo supply of growth factors are encouraging. The safety of the supporting material was demonstrated. We are currently working on developing an autograft from progenitor cells.