Clinical Validation of Model-based RSA for a Total Knee Prosthesis

Roentgen stereophotogrammetric analysis generally is accepted as the most accurate method to measure prosthesis migration. A disadvantage of the method is it requires markers in the bone and the prosthesis. Model-based roentgen stereophotogrammetric analysis circumvents the need for markers on prostheses by fitting virtual projections of a three-dimensional surface model of a prosthesis to its actual projections in the roentgen image. We confirmed a model-based roentgen stereophotogrammetric analysis for a tibial component. Using implants with attached markers, we compared model-based roentgen stereophotogrammetric analysis with marker-based roentgen stereophotogrammetric analysis. In addition, we assessed precision of the model- based roentgen stereophotogrammetric analysis with a phantom experiment. The precisions for translations of marker- based and model-based roentgen stereophotogrammetric analysis were 0.06 and 0.11 mm, respectively, and for rotations, the precisions were 0.20° and 0.23°, respectively. The precisions of model-based roentgen stereophotogrammetric analysis calculated from the phantom data were 0.08 mm for translations and 0.13° for rotations. Although model-based roentgen stereophotogrammetric analysis is less precise than marker-based roentgen stereophotogrammetric analysis, its precision is still acceptable for most clinical applications, especially where markerbased roentgen stereophotogram- metric analysis has practical limitations.

Level of Evidence: Level II, prognostic study. See the Guide lines for Authors for a complete description of levels of evidence.