Recently presented minimally invasive endoscopic surgical techniques demonstrated the feasibility of implanting standard osteosynthesis plates for pelvic fractures. The reconstruction and internal fixation of complex acetabular fractures is still challenging. The goal of this study is to introduce a divisible implant, with a positive-locking in situ linking mechanism for plate osteosynthesis, making it possible to stabilize large and complex acetabular fractures with involvement of the quadrilateral surface. Standard implants were used to recreate a base design. Using computer-aided design, a three-dimensional standard implant was divided into two parts, so they could be re-allocated in situ. A critical objective was to reduce the cross section of each part (clearance gauge). To connect the separated parts in situ, a new linking mechanism (cone in cone) was created. The new construct also features self-stabilization, self-centering, reinforced positional movement, and preloading effects. A linking system for plate osteosynthesis was developed entitled PEGASOS (“percutaneous endoscopic guided acetabulum-stabilizing osteosynthesis system”). Endoscopic implantation and in situ linking could be performed in a human cadaver. Therefore, we could demonstrate that buttressing the quadrilateral surface of the acetabulum could be performed minimally invasive using a divisible suprapectineal buttress plate. We created a linking mechanism to couple two plates in situ. This mechanism enables an extremely strong, positive-locking connection, whereas its geometric shape allows for different relative movements during the locking procedure, with a single screw.