Accuracy and repeatability of cementless total hip replacement surgery in patients with deformed anatomies.

The present study is aimed to assess the repeatability of orthopaedic surgeons in planning total hip replacement surgery, and the Planned-vs.-Achieved accuracy obtainable with a conventional unassisted surgical procedure. A CT-based surgical planning system called Hip-Op was used for pre-operative planning the pose of the cementless components. The study group included only patients affected by severe deformities of the hip joint. In the repeatability study three surgeons were asked to repetitively plan the same three cases in a blind way. There was agreement among surgeons and also consistency for each surgeon in planning the implant position, while the most expert surgeon was more repeatable in planning the implant orientation. For all patients of the study group, the Planned-vs.-Achieved accuracy was computed as the difference between the spatial position of both prosthetic components derived from the post-operative CT scans and that achieved by the surgeon in the pre-operative planning. The average differences for the stem were lower than 5 mm for the position, and lower than 5 degrees for the orientation. For the socket the average differences increased to 8 mm and 10 degrees. The study shows the need for a more informative planning environment and for intra-operative supports, especially when deformed anatomies are involved.