# Establishment of a Periprosthetic Acetabular Bone Defect in an In Vivo Model
## 3 Results  
Using the abovementioned technique, surgery could be performed in all cases (\(n=27\)). The implantation of the available acetabular and femoral implants was possible in all cases. No operation had to be cancelled intraoperatively due to the inability to implant the femoral or acetabular components. No intraoperative complication occurred. The mean operation time was 178 \(\pm\) 32 min. There was no difference in operation time between our three groups. X-ray imaging before extubation confirmed the correct positioning of the implant in all cases. There were no signs of a periprosthetic femoral or acetabular fracture. The vital signs were continuously monitored until the first attempt of the sheep to get up. The postoperative analgesic and antibiotic medication could be administered until day 5 after surgery. Except for two sheep, all animals showed a pain-related/protective limping for 3 days, which they suspended spontaneously until day 5 after surgery. Those two animals showed clinical evidence of damage to the sciatic nerve, with a complete regression after 5 and 7 days postoperatively. In no case was it necessary to extend the application of the analgesic and antibiotic medication. The wound dressing, including the suture, was removed on the 17 th day after surgery. We could not detect a wound healing disorder in any case. After transferal to the external stables (12 th day) and before transferal to the pasture (21 st day), a clinical examination was performed by a veterinarian. Only in the absence of any signs of lameness and in the presence of a physiological gait pattern, transferal to the pasture was planned, which could be performed in all cases. We did not perform any kind of further clinical assessment in defined intervals until the end of the experiments, 8 months after surgery.  
During the course of the experiment, three postoperative complications (one complication per group; autologous cancellous bone group: periprosthetic fracture of the femur 10 days after surgery; Tutoplast(r) group: pneumonia 21 days after surgery; and NanoBone(r) group: cervical abscess with septic circulatory instability 22 days after surgery) occurred before the end of the standing time, which led to the termination of the animal experiment in those cases. This resulted in eight animals per individual group, which were available for test evaluation after a standing time of 8 months.  
For the remaining 24 animals, X-ray imaging after surgery and after 8 months did not show any sign of a postoperative heterotopic ossification. We could not detect a postoperative dislocation or migration of the acetabular implant. In no case were radiolucent lines visible in zones 1-3 according to [PERSON] nor was a migration \(\geq\) 2 mm of the acetabular component detectable.  
For the evaluation of the femoral component, we could not detect a secondary varus or valgus dislocation of the femoral stem in comparison to the longitudinal femoral axis; in addition, we could not detect a rotation or axial migration of the femoral component. An osteolysis surrounding the femoral stem or the cement was not visible.