The repeated sampling bone chamber: a new permanent titanium implant to study bone grafts in the goat

We developed a repeated sampling bone chamber (RSBC) and tested its suitability for studying various aspects of the bone allograft incorporation process under reproducible nonload-bearing experimental conditions in a large vertebrate. Our chamber is made of commercially pure titanium and is designed to allow bone or tissue ingrowth into a removable hollow inner core. Three chambers per animal were randomly implanted in the tibias of 10 goats and were harvested every 8 weeks. In experiment 1, two chambers were filled with a fresh-frozen structural allograft or a chip allograft, and one was left empty. In experiment 2, all chambers were left empty to measure intra- and interanimal variation. The results were evaluated by histomorphometry. Clinical results of four growth factor experiments also are presented. Using this model, we conducted 60 harvest operations (median, 4/animal; range, 2 to 8). In experiment 1, more soft tissue ingrowth and osteoclasts were measured in the chambers with allograft (P < 0.005 and P < 0.03 respectively). Bone ingrowth was scant, with no significant differences between chip graft, structural graft, and empty control chamber. Thus, the bone graft did not show any osteoinductive or osteoconductive properties. Experiment 2 indicated consistent tissue ingrowth, with greater interanimal variation than variations among the chambers in any goat. Our method forms a means of studying gradual tissue and bone ingrowth into bone grafts. The inherent low amount of bone ingrowth makes this model suitable for studying bone-inductive substances. Repeated sampling in the same animals lowered the intersample variability and reduced the number of animals that were required.