We studied 105 patients who received a total hip arthroplasty between June 1985 and August 2001 using freehand positioning of the acetabular cup. Using pelvic CT scan and the hip-plan module of SurgiGATESystem (Medivision, Oberdorf, Switzerland), we measured the angles of inclination and anteversion of the cup. Mean inclination angle was 45.8°±10.1°(range: 23.0-71.5°) and mean anteversion angle was 27.3°±15.0°(range: −23.5°to 59.0°). We compared the results to the "safe" position as defined by Lewinnek et al. and found that only 27/105 cups were implanted within the limits of the safe position.We conclude that a safe position as defined by Lewinnek et al. [13] was only achieved in a minority of the cups that were implanted freehand.

Optimal orientation of the acetabular component of a total hip prosthesis is an important factor in determining the early and long-term result of a total hip arthroplasty (THA). Conventional positioning of the cup component is usually done using a free-hand method, or with the help of a mechanical acetabular alignment guide. However, these methods have proven to be inaccurate, and a great variation in orientation of the cup is found postoperatively. In this study, we wished to determine if the variability of the abduction angle of acetabular cups could be reduced with the use of computer navigation. The abduction angles of the acetabular components of three groups of 50 THAs were assessed. In the first group, a free-hand method was used to position the cup component. This group was operated in the period before we started using computer navigation for hip surgery. In the second group, CT-based computer navigation was used to plan and help position the cup. The third group consisted of 50 THA cases in which a free-hand method was used to position the cup, although these procedures were performed in the period after we had begun using the Computer Assisted Surgery (CAS) system. The variability in cup abduction angle was assessed in all three groups and compared. There was a significant reduction in variability in the CAS group compared to the first group. There was also a reduction in variability in the CAS group compared to the third group, although this was not statistically significant. It is concluded that the use of computer navigation helped the surgeon to place the cup component with less variability of the abduction angle, and, more importantly, we found that no cups were placed in the more extreme positions (outliers).

Optimal orientation of the acetabular component of a total hip prosthesis is an important factor in determining the early and long-term result of a total hip arthroplasty (THA). Conventional positioning of the cup component is usually done using a free-hand method, or with the help of a mechanical acetabular alignment guide. However, these methods have proven to be inaccurate, and a great variation in orientation of the cup is found postoperatively. In this study, we wished to determine if the variability of the abduction angle of acetabular cups could be reduced with the use of computer navigation. The abduction angles of the acetabular components of three groups of 50 THAs were assessed. In the first group, a free-hand method was used to position the cup component. This group was operated in the period before we started using computer navigation for hip surgery. In the second group, CT-based computer navigation was used to plan and help position the cup. The third group consisted of 50 THA cases in which a free-hand method was used to position the cup, although these procedures were performed in the period after we had begun using the Computer Assisted Surgery (CAS) system. The variability in cup abduction angle was assessed in all three groups and compared. There was a significant reduction in variability in the CAS group compared to the first group. There was also a reduction in variability in the CAS group compared to the third group, although this was not statistically significant. It is concluded that the use of computer navigation helped the surgeon to place the cup component with less variability of the abduction angle, and, more importantly, we found that no cups were placed in the more extreme positions (outliers).

Level IV. Prospective prognostic study.

Using computer-assisted surgery a significantly higher reproducible cup position can be obtained. Long time survey may present a lowering of the rate of early and late complications caused by better prostheses alignment in the follow up.