Empty Fig 1. A) Im gap packed B) Post-harves Fig 2. Gap (grey) and Calcium Based Fillers Pro 1 Lim, L Z; + 1,2 Bo +Divisions of 1 Experimental Medicine and 2 O Introduction: Revision arthroplasty surgery often involves loss o cavitary defects that result in suboptimal implant f stability, and reduced potential for biologic fixation o Several types of biomaterials have been proposed fo substitutes for autogenous bone graft; these include c (CaP) and calcium sulfate (CaS) compounds. formulations of Ca-based biomaterials have been porosity and bio-degradation characteristics that enco cells, blood supply and osteoconduction, all of which bone regeneration. The purpose of this study was to i healing potential of two different Ca-based materials in model using porous titanium implants. Materials and Methods: Gap-type intramedullary implants were fabricated f pure titanium with a 5mm diameter central porou diameter solid end and central spacers to create two s regions between host bone and porous metal implant (Fig 1). The titanium foam core was 55% porous with an average pore size of 400μm. One gap filling material was a commercial formulation of nanocrystalline apatitic CaP (Etex Corp, MA). The CaS material was in the form of small granules ranging between 20-400 μm in diameter. Adding sterile saline to the materials at the time of surgery produced compounds with handling characteristics conducive to molding and shaping into the implant gap regions. Prior to compound was relatively soft and paste-like while th was harder and more putty-like. The proximal 3mm i manually filled with either CaP or CaS, leaving the di controls. Six dogs underwent bilateral surgery, each implant containing each material into the left or right (institutionally approved protocol). After 12 weeks, harvested to yield 6 sets of paired data from each anim with CaS. The humeri were scanned with a high voltag microCT (μCT) scanner to obtain 18μm thick seri complete bone-implant construct. The resulting 1000 of each gap were used to quantify the extent of reso based materials and bone formation within the implan as a volume percentage of the gap. Specimens w embedded in acrylic and undecalcified transverse se imaged with backscattered scanning electron micros enable analysis of bone growth within the 3mm gaps the porous implant regions. Statistical comparisons paired and unpaired Student's t-tests and multiple two models, with p≤0.05. Results: MicroCT quantified both native bone and residual C the gaps, without discriminating one material from the with time zero, the total material within CaP-filled gaps diminished by a mean volume of 25%±13% (Fig 2). Compared with time zero, the total material within CaS-filled gaps diminished by a greater mean volume of 49%±7% (p=0.001). Compared with CaP at 12 wks, the CaS material resorbed into a more porous scaffold within and on which new, interconnected trabeculae had formed in continuity with surrounding host bone (Figs 3, 4). Empty gaps were only 5% ± 1% filled at 12 wks (p=0.001). y CaP CaS mplant with proximal with CaS material. st radiograph. p filling at time zero d at 12 weeks (blue). omote Bone Defect Healing Around Porous Titanium I obyn, J D; 2 Okyere, M J; 3 Barralet, J E; 2 Bobyn, K M; 2 Tanzer, M Orthopaedics, Faculty of Medicine, 3 Faculty of Dentistry, McGill Univers [email protected] of bone stock and fit, reduced initial of porous implants. or defect filling as calcium phosphate Medical grade n developed with ourage invasion of h are necessary for investigate the gap n a canine implant from commercially us rod and 11mm separate 3mm gap o setting, the CaS he CaP compound implant gaps were istal gaps empty as dog receiving one proximal humerus the humeri were mal comparing CaP ge, high resolution ial images of the 0 serial CT images orption of the Ca- nt gaps, expressed were subsequently erial sections were scopy (BSEM) to s as well as within were made using o-level hierarchical CaS or CaP within e other. Compared Fig 3. Images from μ CT scans of CaP-filled gap zero. B) Longitudinal and C) transverse images Fig 4. Images from μ CT scans of CaS-filled gap zero. B) Longitudinal and C) transverse images BSEM images more clearly showed th predominantly filled by the material, with and around the material pores (Fig 5). In most of the CaS had resorbed by 12 week with dense bony trabeculae connecting surrounding host bone (Fig 5). CaP-fille apposition at the porous implant perimete although the latter was associated with a ingrowth (p=0.04). Discussion: Previous studies have shown that a 3m in the proximal humerus does not spontan weeks. At time zero both Ca-based materi By 12 weeks both materials resorbed and the gap, on and within the porous im surrounding host bone. The CaS resorb facilitating more gap filling with new bon that the CaP compound is a more mec property that could be advantageous in re strength is important. Longer implantation additional resorption of the CaP and repla Significance: While possessing different properties both Ca-based materials demonstrated po within a clinically relevant time frame. Acknowledgments: Canadian Institutes for Health Resear Canada, Etex Corporation. Fig 5. Transverse BSEM images of A) CaP implant after 12 weeks (the darker grey is bone arrows show bone in the implant pores. Implants sity, Montreal, Canada p. A) Longitudinal image at time at 12 weeks. p. A) Longitudinal image at time at 12 weeks. hat CaP-filled gaps remained h some new bone formation in n contrast, BSEM revealed that ks, with most of the gaps filled the porous implant core with ed implants showed more bone er than the CaS group (p=0.06) a greater mean extent of bone mm gap around a porous implant neously heal with bone after 12 ials filled almost the entire gap. d new bone was evident within mplant and in continuity with bed to a much greater extent, ne. It should be noted, however, chanically resistant material, a evision surgery where construct n periods would likely result in acement with new bone. and resorption characteristics, otential for use in gap healing rch, National Research Council P-filled implant and B) CaS-filled e, lighter grey is residual CaS). Red Poster No. 0979 • ORS 2012 Annual Meeting