Comparative study of mechanical strength of callus after bridging of segmental bone defects with the use of allografts in immunodeficient mice

Bone grafts are widely used for the coverage of bone defects resulting after several types of surgical interventions. Different types of bone-graft substitutes have been developed and are on the market worldwide. Thus, it´s important to evaluate their osteoinductive and osteoconductive potential. We used 20 mature immuno deficient male SCID mice (severe combined immune deficiency - NOD.CB17-Prkdcscid/J strain) aged 6-8 weeks, divided into 4 groups (A, B, C, D). A segmental bone defect equal to the quadruple of the right femur diameter (4mm) was created. In group A the defect was covered using demineralized bone matrix (DBM) (GRAFTON DBM Gel, 0.5 cc, Osteotech), in group B using cancellous allograft (Cancellous chips, 1cc, Osteopure) and in group C using a combination of DBM and cancellous allograft. Finally in group D the coverage of the bone defect was achieved using an osteoconductive biocomposite of cortical fibers suspended in a resorbable, porous polylactide-co-glycolide scaffold (Plexur™ P Bone Void Filler, Osteotech). All animals from each of the four experimental groups were sacrificed at the end of the 8th week. Both femurs of every animal were ressected and tested on SHIMADZU Autograph tester (AGS-500NJ standard Unit, Shimadzu Corporation, Tokyo, Japan) against bending force in order to determine the mechanical strength of the callus compared to the normal femur. In groups B and D the strength of the callus against bending force was 63% and 65% respectively compared to the strength of the normal bone. In groups A and C these measurements were 49% and 44% respectively. Cancellous bone allograft and Plexur™ P showed the highest rates of callus strength, consisting a valuable solution for the coverage of bone defects.