The biological reaction in metallosis and pseudotumor generation after metal on metal total hip arthroplasty or corroding metal implants remains unsettled. Clinically, still lethal cases appear with massive bone loss and metal ions are suspected to be responsible for this inflammatory reaction, solid metal wear particles instead are usually not observed in the common literature. The aim of this study was to compare the biological reactions of metal ions and metal wear particles in a murine in vivo model. Metal ions (CoCr), metal particles (CoCr), polyethylene particles (UHMWPE) and phosphate buffered saline (PBS) were injected into the left knee joint of female BALB/c mice. 7 days after injection, the microcirculation was observed using intravital fluorescence microscopy, followed by euthanasia of the animals. After the assessment of the knee diameter, the knees underwent histological evaluations of the synovial layer. Throughout all recorded data, CoCr particles caused higher inflammatory reactions compared to metal ions and UHMWPE particles. The mice treated with the solid particles showed enlarged knee diameters, more intensive leukocyte–endothelial cell interactions and an elevated functional capillary density. Pseudotumor-like tissue formations in the synovial layer of the mice were only seen after the exposition to solid CoCr particles. Even if the focus of several national guidelines concerning metallosis and pseudotumor generation is on metal ions, the present data reveal that solid CoCr particles have the strongest inflammatory activity compared with metal ions and UHMWPE particles in vivo

Autologous bone grafting is a standard procedure for the clinical repair of skeletal defects, and good results have been obtained. Autologous vascularized bone grafting is currently the procedure of choice because of high osteogenic potential and resistance against reabsorption. Disadvantages of this procedure include limited availability of donor sites, clinical difficulty in handling, and a failure rate exceeding 10%. Allografts are often used for massive bone loss, but since only the marginal portion is newly vascularized after the implantation non healing fractures are often reported, along with a graft reabsorption. To overcome these problems, some studies in literature tried to conjugate bone graft and vascular supply, with encouraging results. On the other side, several studies in literature reported the ability of bone marrow derived cells to promote neo-vascularization. In fact, bone marrow contains not only hematopoietic stem cells (HSCs) and MSCs as a source for regenerating tissues but also accessory cells that support angiogenesis and vasculogenesis by producing several growth factors. In this scenario a new procedure was developed, consisting in an allogenic bone graft transplantation in a critical size defect in rabbit radius, plus a deviation at its inside of the median artery and vein with a supplement of autologous bone marrow concentrate on a collagen scaffold. Twenty-four New Zealand male white rabbits (2500–3000 g) were divided into 2 groups, each consisting of 12 animals. Surgeries were performed as follow:. −. Group 1 (#12): allogenic bone graft (left radius) / allogenic bone graft + vascular pedicle + autologous bone marrow concentrate (right radius). −. Group 2 (#12): sham operated (left radius)/ allogenic bone graft + vascular pedicle (right radius). For each group, 3 experimental time: 8, 4 and 2 weeks (4 animals for each time). The bone used as graft was previously collected from an uncorrelated study. An in vitro evaluation of bone marrow concentrate was performed in all cases, and at the time of sacrifice histological and histomorphometrical assessment were performed with immunohistochemical assays for VEGF, CD31 e CD146 to highlight the presence of vessels and endothelial cells. Micro-CT Analysis with quantitative bone evaluation was performed in all cases. The bone marrow concentrate showed a marked capability to differentiate into osteogenic, chondrogenic and agipogenic lineages. No complications such as infection or intolerance to the procedure were reported. The bone grafts showed only a partial integration, mainly at the extremities in the group with vascular and bone marrow concentrate supplement, with a good and healthy residual bone. immunohistochemistry showed an interesting higher VEGF expression in the same group. Micro CT analysis showed a higher remodeling activities in the groups treated with vascular supplement, with an area of integration at the extremities increasing with the extension of the sacrifice time. The present study suggests that the vascular and marrow cells supplement may positively influence the neoangiogenesis and the neovascularization of the homologous bone graft. A longer time of follow up and improvement of the surgical technique are required to validate the procedure

The feasibility of bone transport with bone substitute and the factors which are essential for a successful bone transport are unknown. We studied six groups of 12 Japanese white rabbits. Groups A to D received cylindrical autologous bone segments and groups E and F hydroxyapatite prostheses. The periosteum was preserved in group A so that its segments had a blood supply, cells, proteins and scaffold. Group B had no blood supply. Group C had proteins and scaffold and group D had only scaffold. Group E received hydroxyapatite loaded with recombinant human bone morphogenetic protein-2 and group F had hydroxyapatite alone.

Distraction osteogenesis occurred in groups A to C and E which had osteo-conductive transport segments loaded with osteo-inductive proteins. We conclude that scaffold and proteins are essential for successful bone transport, and that bone substitute can be used to regenerate bone.