Repair of critical-size bone defects using bone marrow stromal cells: a histomorphometric study in rabbit calvaria. Part I: Use of fresh bone marrow or bone marrow mononuclear fraction

Objectives The aim of this study was to compare the bone healing observed after the use of (1) a scaffold enriched with fresh bone marrow, (2) a scaffold enriched with bone marrow mononuclear fraction, and (3) a scaffold alone. Material and methods Twenty one rabbits were randomly divided into three groups of six animals and 1 group of 3 animals. Bilateral 12-mm diameter defects were created in the animals' parietal bones. In Control Group, the defects were filled with a xenograft alone (n=6); in Group 1, with a xenograft enriched with fresh bone marrow (n=6); in Group 2, with a xenograft enriched with bone marrow mononuclear fraction (n=6) and in Unfilled Group, nothing was grafted (n=3). In Groups 1, 2, and Control, one of the calvarial defects was randomly covered with a barrier membrane. The rabbits were sacrificed 8weeks after surgery, and their parietal bones were harvested and analyzed histomorphometrically. Results The histomorphometric analysis showed no difference between Group 1 and the Control Group regarding non-vital mineralized tissue area, but Group 2 showed a statistically significant higher percentage than the Control Group (P<0.05) for both situations, with membrane (21.24 +/- 3.78% and 13.52 +/- 3.00%, respectively) and without membrane (20.91 +/- 2.01% and 13.08 +/- 1.72%, respectively). Group 2 showed the highest percentage of vital mineralized tissue area, followed by Group 1 and the Control Group (P<0.05) for both situations, with membrane (28.17 +/- 3.19%; 21.14 +/- 7.38% and 13.06 +/- 5.24%, respectively) and without membrane (21.13 +/- 0.55%; 12.45 +/- 6.34% and 6.56 +/- 1.20%, respectively). Group 2 showed the lowest percentage of non-mineralized tissue area, followed by Group 1 and Control Group (P<0.05) for both situations, with membrane (50.59 +/- 6.64%; 58.75 +/- 7.14% and 73.41 +/- 6.87%, respectively) and without membrane (57.97 +/- 1.91%; 71.74 +/- 6.63% and 80.37 +/- 2.67%, respectively). The sides in which the defects were covered with the barrier membrane showed better bone healing compared with the uncovered sides, in all groups (intragroup comparison, P<0.05). The Unfilled Group specimens showed no bone formation. Conclusions Both methods using bone marrow stromal cells contributed to enhancing bone healing, especially that using the bone marrow mononuclear fraction. The use of a barrier membrane seemed to have a synergistic effect.