The ideal treatment method regarding various defect sizes after local aggressive tumor resection is unknown. We investigated the biomechanical properties of metaphyseal defect filling regarding different defect sizes and fixation methods.

Ninety-one sheep tibias were divided into five groups as 21 tibias per four study groups and 7 tibias in the control group. Study groups were further divided into three subgroups according to 25%, 50% and 75% metaphyseal defect size. Control group tibias were left intact. In study group 1, a metaphyseal defect was created and no further process was applied. Metaphyseal defects were filled with cement without fixation in group 2. Cement filling and fixation with 2 screws were performed in group 3. In addition to cement filling, plate-screw fixation was performed in group 4. Axial loading test was applied to all tibias and the results were compared between study subgroups and control group.

Plate-screw fixation was found to have the best biomechanical properties in all defect sizes. Load to failure for screw fixation was found to be significantly decreased between 25% and 50% defect size (P<0.05). However, load to failure for isolated cement filling was not affected from defect size (p>0.05).

In conclusion, size of the defect predicts the fixation method in addition to filling with cement. Filling with cement in metaphyseal defects was found to be biomechanically insufficient. In addition to filling with cement, additional screw fixation in less than 25% defects and plate-screw fixation in more than 25% defects may decrease tibial plateau fracture or metaphyseal fracture risk after local aggressive tumor resection.

Purpose: Current research is focusing on the imitation of the optimal osteoconductive and osteoinductive properties of bone graft. We used in this study a β-trical-cium-phosphate scaffold impregnated with an osteogenetic transglutaminase (plasmatransglutaminase, FXIII, (Fibrogammin®)). Methods: Release study: 27 & #946;-TCP discs (8x10mm) were impregnated with 10, 40 and 100 IU of FXIII. The release was measured with ELISA.|Animal study: A bilateral tibial metaphyseal defect (8.5 x 20 mm) was performed in eighteen adult sheep. The defects were filled with a & #946;-TCP cylinder (chronOS®, Synthes) in 16 sheep and left unfilled in 2 sheep (control group). The cylinders were impregnated with autologous venous blood, autologous bone marrow aspirate from the sternum and 125 IU FXIII in 4 sheep each or left unfilled and a daily dose of 1250 IU FXIII administered iv. over 14 days. After 6 and 12 weeks QCT, histology and histological analysis was performed. Results: Release study: We found a linear release of FXIII with a plateau after 48 h. Until then on average 18% of the total dose was release from the scaffold. Animal study: The QCT analysis found unspecific changes in all group without any clear results regarding remodeling of the scaffold. The histological analysis showed the best bone ingrowth after 6 weeks in the bone marrow group and after 12 weeks in the local F XIII with on average 10% more bone ingrowth than in any other group. The best remodeling of the inner area in the scaffold was also seen in the local F XIII group. Conclusions: FXIII is only partially released from a β-TCP scaffold. At least 80% of the dose remains in the scaffold after 48h. F XIII has a good osteogenetic property which is at least as good as bone marrow and better than venous blood; however a local application of F XIII is preferable to iv. administration. It stimulates osteoblast migration and proliferation in a β-TCP scaffold and causes a remodelling on the inside of the scaffold. Funding: Commerical funding. Funding Parties: Grant by the AO Research Institute Davos, Switzerland and Synthes, Oberador, Switzerland