Abstract
Objective
The optimal positioning of the acetabular component is a relevant prognostic factor in total hip arthroplasty (THA). Because of substantial errors of manual technique in cup placement even with experienced surgeon, computer aided navigation system has been developed in recent years. However, existence of the hardware around acetabulum likely deteriorates the accuracy of the navigation system, namely in revision THA case and postoperative status of pelvic fracture. Here we report a case who we successfully performed THA using CT based navigation system although there were multiple hardware around acetabulum due to osteosynthesis for the previous pelvic fracture.
Case presentation
A forty-one years old man presented with intolerable hip pain with severe radiographic osteoarthritic findings in left hip joint. He had sustained left pelvic fracture and posterior hip dislocation due to traffic accident and undergone osteosynthesis using multiple plates and screws when he was forty years old. However, progressive collapsing of femoral head and acetabulum occurred. Then, we indicated THA for his situation and planned to apply the CT based navigation system (Stryker CT based hip Ver.1.1 softwear and Cart II system). Preoperative workup revealed incomplete union of posterior and superior acetabular wall and we had to retain plates and screws for the stable fixation of acetabular cup. The existence of the hardware made it complicated to perform three dimensional planning and templating. Meticulous surface editing of pelvis to exclude the metal artifact and fibrocartilagenous tissue was needed to achieve accurate surface registration. In the operation room, we had to use unusual way of registration to complete two steps of registration. In the first step (roughly matching between patient's physical pelvic surface and edited pelvic surface in work station using corresponding 5 points), we utilized head of screw and hole of the plate which we could easily identify intraoperatively, in addition to ASIS and innominate groove. In the second step (strict matching using more than 30 points of pelvic surface), we had to identify the pelvic bony surface, as excluding the metal surface and fibrocartilagenous tissue such as fracture callus. These efforts enabled us to accomplish substantial accuracy of registration with RMS of 0.5 mm. Final cup orientation at the end of surgery was 41° of inclination and 25° of anteversion. Postoperative CT scan revealed that cup placement angle was 40° of inclination and 25° of anteversion, almost identical with intraoperative value.
Conclusion
Our experience showed that CT based navigation system provided accurate placement of the acetabular component in a case having multiple hardware as well as in normal primary THA. Although we need additional efforts such as meticulous preoperative planning, extra operation time, CT based navigation system has great advantages to minimize the mal-placement of the cup in complicated case.
