Introduction In our experimental design we evaluated the osteogenic potential of h-bone marrow (hBM), h-mesenchymal stem cells (hMSC), bone morphogenetic protein (BMP-7) and the combination hMSC plus BMP-7. The aim of the study was to define the capacity to elicit bone formation of expanded hMSC alone and associated with BMP-7

Material and methods A rat femoral segmental defect model was used in this study. 12 male athymic rats were used. The institutional Animal Ethics Committee approved the study. Athymic rats test graft groups consisted of: G1-autoclaved bone and h-BM; G2-bone and h-MSC; G3-bone with BMP-7; G4-bone and h-MSC with BMP-7. h-BM aspirates were harvested from iliac crests of patients undergoing to THA. A plate has been fixed on the femurs with four cerclage wires before a femoral gap of 6mm has been realized in the diaphysis. Gap was filled with different graft. Defect was evaluated at 2, 4, 8, 12 weeks after implantation with radiographs. Evaluation of bone graft has been done using a Cook classification. Histological study with toluidine blue and safranine O at 12 weeks has been performed in each group.

Results At 8–12 weeks after surgery G1 shown non visible new bone formation, G2 minimal new disorganized bone and G3 disorganized new bone bridging graft to host at both ends. The G4 group show significant new bone and graft remodelling. Histological analysis confirmed the rx results.

Conclusion The association hMSC plus BMP-7 determines a significant activation of the osteogenic activity at 8 weeks that may have a remarkable impact on the future orthopedic surgery strategies.

It has been shown that mesenchymal stem cells (MSCs) and BMP are involved in bone formation. The aim of the study was to evaluate the osteogenic potential of human bone marrow (hBM), human expanded MSC (hexp-MSC), BMP-7, and hexp-MSC plus BMP-7, to treat a rat femoral segmental defect.

Sprague-Dawley (SD) and athymic rats (Nu) were used. SD rats where used in order to define surgical technique. Nu rats groups consisted of: G1-autoclaved bone and human bone marrow (hMNC); G2-bone and hexp-MSC; G3-bone with BMP-7 only; and G4-bone and hexp-MSC with BMP-7. A plate was attached to the femoral diaphysis with two cerclage wires. Then a 6-mm femoral gap was made and filled with a different graft. At regular intervals, the femoral defect was evaluated with radiographs, using a modified six-grade Cook classification.

At 8 weeks G1 showed non-visible new bone formation; G2 minimal new disorganised bone; G3 disorganised new bone bridging the graft to host at both ends; and G4 significant new bone and graft remodelling. Histological analysis confirmed these results.

Our results showed that although the osteogenic activity may be improved by hMSC (G2) as well as by BMP-7 (G3), the association hexp-MSC plus BMP-7(G4) produced graft osteointegration at 8 weeks after surgery. This may have a remarkable impact on future orthopaedics surgery strategies.

Human mesenchymal stem cells (hMSC), residing in the bone marrow, can be purified, expanded in cell culture and under appropriate stimuli may differentiate along the osteogenic, chondrogenic and adipogenic lineages. The aim of this study was to investigate the expansion capability and differentiation potential of MSCs obtained from femur, pelvis and acetabular cancellous bone of aged patients in order to establish whether these cells, isolated and expanded in vitro, can be used in a new approach in orthopaedic revision surgery.

In this preliminary study we enrolled 33 patients undergoing hip arthroplasty in order to investigate CFU-F frequency, expansion ability and differentiation potential of hMSC derived from three different anatomical sites: femural, pelvic and acetabular cancellous bone (ACB).

CFU-F frequency (CFU-F/10 ⁶ MNC) was 63 for pelvis (range 7–122), 90 for bone (39–132) and 47.5 for femur (7–124).CFU-F frequency was higher in ACB than in either pelvis (p=0.04) or femur (p=0.001). The patients were divided into three age groups: G1 ≤50 years (n=6), G2 50 −65 years (n=11), and G3 ≥65 years (n=16); however, CFU-F frequency did not show any statistically significant difference, although the frequency was lower at higher age.

We expanded in cell culture MSC of 16 patients from the three considered sites until the fourth passage. At the first passage there was a higher MSC recovery in ACB (median 12%) than in pelvis (median 8%; p< 0.004) and femur (median 3.8%; p< 0.0004). MSC recovery from pelvis was higher than in femur (p< 0.04). At the second and third passage MSC expansion was found to be significantly higher in ACB than in pelvis alone (median 3.1 vs 1.6, p< 0.01; 1.8 vs 1.2, p< 0.005, respectively), while at the fourth passage it became higher than in pelvis and femur (median 2.6 vs 1.4, p< 0.03; 2.6 vs 1.6, p< 0.0, respectively). At each culture passage, cells showed MSC features as supported by flow cytometry and by the multilineage differentiation potential.

hMSCs seem to have higher frequency in close association with bone; moreover, they show an increased expansion ability in vitro which is still mantained in elderly patients. As these progenitors can differentiate in bone, they seem to be the best choice for the effective repair of bone defects in revision surgery.