# Establishment of a Periprosthetic Acetabular Bone Defect in an In Vivo Model
## 2 Materials and Methods
### Anaesthesia and Surgical Technique  
The prepnedication was carried out by an intramuscular injection of 0.1 mg of Ketamin(r) 10% (Serumwerk Bernburg AG, Bernburg, Germany)/10 kg body weight and 0.1-0.3 mg of xylazine 2% (Serumwerk Bernburg AG, Bernburg, Germany)/kg body weight, followed by an immediate induction of anesthesia with 3-8 mg of pentobarbital/kg body weight (Narcoren(r), Merial GmbH, Halbergmoos, Germany). The endotracheal intubation was performed with a laryngoscope (endotracheal tube, Hi-Lo Lanz(r), Mallinckrodt medical inc., Athlone, Ireland, diameter 8.5-9.5 mm). The inhalation anesthesia was carried out with isoflurane (Alfa Aesar GmbH & Co., KG, Karlsruhe, Germany) and an oxygen-nitrogen oxide mixture at a ratio of 1:3. In order to achieve a sufficient depth of anesthesia, isoflurane was initially flooded in at a concentration of 1.5-3.0% by volume; to maintain anesthesia, it was reduced to an average of 0.8-1.0% by volume. For perioperative antibiotic therapy, an intravenous dose of 2.5 mg of Baytril(r) (Bayer Vital GmbH, Leverkusen, Germany)/kg body weight was administered. Intraoperative analgesia was performed through the intramuscular application of 6 ug of buprenophrine (Merck Healthcare, Darmstadt, Germany)/kg body weight. The animals were placed in a lateral position on the right side of the body. We always performed surgery of the left hip joint. The lateral surgical approach to the hip joint was performed after taking into account the specific anatomy of the sheep [6,11]. In detail, a 10-cm-long incision centered over the greater trochanter was performed (Figure 2A), followed by a parallel incision of the fascia lata between the tensor fasciae lata muscle and the gluteus medius muscle (Figure 2B). Afterwards, the gap between those two was used to access and visualize the gluteus profundus muscle (Figure 3A), which was subsequently split in line of its fibers. Two Hohmann retractors were used to visualize the joint capsule. Afterwards, a T-shaped dissection of the ventral capsule was performed, followed by a careful preparation of the acetabulum to gain a good overview of the cup. Here, it is essential to resect the ventral aspect of the joint capsule, including its femoral and acetabular insertion for the best possible overview. After establishing an overview of the situs, osteotomy of the femoral neck (Figure 3B) can be performed with an oscillating saw 1.0-1.5 cm proximal from the lesser trochanter. Two Hohmann retractors can be placed around the femoral neck to protect the surrounding tissue. To visualize the fossa acetabuli, a sharp curette can be used to remove remaining soft tissue or remnants of the ligamentum capitis femoris. For the initial bony preparation of the acetabulum, we used a 28-mm reamer. Reaming was always performed perpendicular to the body's longitudinal axis. Subsequently, reamers  
Figure 1: Display of the used implants: cemented monobloc implant made of CoCrMo (Aesculap, Tuttlingen, Germany) (**A**) and acetabular reinforcement ring out of pure titanium (ARR; [PERSON], Weisendorf, Germany) (**B**). up to 32 mm in diameter were used for the final preparation ([PERSON], Weisendorf, Germany). Special attention was paid to retain the subchondral bone lamella. Afterwards, a defined bone defect, measuring 1.5 \(\times\) 1.5 \(\times\) 1.5 cm (\(\sim\)3.375 cm\({}^{3}\)), was created in the load-bearing cranial area of the acetabular cavity (Figure 4A) using a custom-made drilling template with a depth stop. For this augmentation (Figure 4B, Table 1), the prepared autologous or allogeneic bone chips were impacted in the bone defect step by step using the impaction bone grafting technique analogous to the surgical procedure in humans [12; 13; 14]. After augmentation of the bony defect, the revision implant was implanted to bridge the defect. A primarily stable situation was achieved with the help of three 6.5 \(\times\) 25 mm cancellous screws ([PERSON], Weisendorf, Germany) at the acetabular rim (Figure 5A).