# Effect of Systemic Zoledronic Acid Dosing Regimens on Bone Regeneration in Osteoporotic Rats
## 3 Results
### Descriptive Histological Evaluation of Bone Defects  
Saling group: the light-microscope images shown in Figure 2 confirmed the osteogenic character of the femoral condylar bone, which was characterized by the presence of sparse and discontinuous bone trabeculae, with bone marrow in between these trabeculae. The remaining bovine bone particles could easily be recognized. Bone ingrowth into the defect area was very limited and mainly restricted to the edge of the defect. At the defect boundary, bone had grown into the spaces between the particles, and these particles were surrounded for their major part by newly formed bone. Bone ingrowth did not proceed into the center of the defect, which was filled with fibrous tissue between the bovine bone particles. Osteoclast-like cells were observed in close contact with the bovine bone particles (Figure 3).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Osteoporotic Condition**} \\ \hline
**Groups** & **Samples Numbers** & **Included in Analysis** & **No. Histological Sections** \\ \hline ZA-Pre & 6 & 6 & 18 \\ ZA-Post & 6 & 6 & 18 \\ ZA-Pre+Post & 6 & 5\# & 13 \\ Saline & 6 & 6 & 18 \\ \hline \hline \end{tabular} \#one sample was excluded due to microscopic scan failure.  
\end{table}
Table 1: Number of samples used for histological evaluation and histomorphometric measurements.  
Figure 2: Representative histological sections of specimens from different study groups showing a transverse section through the femoral condyle, perpendicular to the long axis of the cylindrical bone defect. A circular region depicting the region of interest (ROI) is shown separately as an offset image for each group.  
ZA-Pre group and ZA-Post group: the histological sections in Figure 2 of ZA-Pre and ZA-Post specimens showed a very similar appearance. At low magnification, the femoral condylar bone was denser and more uniform compared to that of the saline control group (Figure 2). In addition, the size of the intra-trabecular space was reduced. Bovine bone particles could still easily be recognized (Figure 3). In contrast to the saline control group, bone had grown throughout the bone defect in these treated groups. The majority of the bovine bone particles was surrounded by a layer of bone, which was in tight contact with the surface of the bovine bone particles. Bone marrow-like tissue was present within the newly deposited bone. Only very few osteoclast-like cells were observed (Figure 3).  
ZA-Pre+Post group: light-microscopy analysis of specimens of the ZA-Pre+Post group showed that the density of the femoral condylar bone was increased compared with specimens of the saline control group. On the other hand, histological examination revealed a wide variation in bone defect healing compared to the ZA-Pre and ZA-Post groups. In three specimens, bone formation into the defect space was similar to that observed in ZA-Pre and ZA-Post specimens. Bone had grown from the defect border between the bovine bone particles and was surrounding these particles. However, in two specimens, no bone ingrowth into the defect space had occurred. The bovine bone particles were still present but were surrounded by fibrous tissue.