The orthopilot navigation system for primary bicontact total hip replacement

Aim: Navigated implantation of the cup and stem components enables additional parameters to be recorded for joint reconstruction. The results and reproducibility of the implant position were studied in a consecutive series of implantations with femoral transmitter (femoral C-clamp) close to the hip joint. Method: 107 consecutive cementless THA operations with the Orthopilot Software THA 2.0 were analysed. The preoperative planning for cup and stem position were compared with the intraoperative data from the navigation system and the postoperative radiograph. Cup inclination and anteversion, leg lengths and offset changes and the rotation position of the Bicontact stem were investigated. Results: 98% of the radiological cup positions were within 42.5 +/- 10 degrees inclination and all cases were within 10 +/- 10 anteversion. The navigation system recorded 83% of the relative leg length changes with an accuracy of +/- 5 mm. 15% were in a range of +/- 10 mm. In 77% of the operations, the Bicontact stem or the Bicontact B osteoprofiler could be positioned in the position measured by the Orthopilot of 5 of the box osteotome (i.e. medullary cavity opening). In 20% the deviation was +/- 10 degrees. 73% of the arthroplasties gave a relative offset change in a range of 10 mm. A tendency to medialisation of the hip joint centre was seen in 62% of the procedures. The mean was a small offset change of only 1.2 mm with a high standard deviation of 17.8 mm. Conclusion: The navigated implantation of stem and cup components with a femoral transmitter close to the joint leads to reproducible results. The distribution of femoral offset and leg length changes corresponds to clinical experience. Analysis of the radiographs does not appear sufficiently accurate for all the recorded parameters.