Model-Based RSA

Model-Based RSA enables you to assess the micromotion of implants in Roentgen Stereophotogrammetric Analysis (RSA) radiographs without attaching markers to the implant. However, there are still markers needed to mark the bones.

In addition to this, Model-Based RSA is also able to perform conventional RSA with markers attached to the implants.

The 3D-viewing interface facilitates an intuitive analysis and allows advanced visualisation and reporting of results.

The Fluoroscopy module of Model-based RSA allows you to assess skeletal and endoprosthetic kinematics in fluoroscopic images using tantalum markers and/or 3D-models of implants.

Method

Model-Based RSA requires 3D-models of prostheses. In general, the manufacturer's original CAD-models are used for this. For each size that will be included in a clinical study, that particular CAD-model has to be added to the software. Confidentiality and quality is guaranteed by encryption of the implemented models in the software.

Reversed engineered (RE)-models can also be used in Model-Based RSA and have shown to be more accurate than CAD-models (Kaptein et al., 2003). The components are laser scanned and converted into a 3D-model.

The accuracy of the models, CAD and/or RE-models, needs to be assessed in a phantom study before starting a clinical study. Based on this accuracy a power analysis for the clinical study can be performed.

Developments

Model-Based RSA software will be extended with a module allowing you to assess skeletal and endoprosthetic kinematics in fluoroscopic images using tantalum markers (Garling et al., 2005) and/or 3D-models of implants.

Publications

• Hurschler C, Seehaus F, Emmerich J, Kaptein BL.
  Accuracy and precision of a model-based RSA technique for measuring implant migration.
  J Biomech 2006; 39 Suppl 1: S129.
• Kaptein BL, Valstar ER, Spoor CW, Stoel BC, Reiber JH, Rozing PM.
  Model-based-RSA of a hip stem using geometrical shape models.
  J Biomech 2006; 39 Suppl 1: S514.
• Kaptein BL, Valstar ER, Stoel BC, Rozing PM, Reiber JH.
  A new model-based RSA method validated using CAD models and models from reversed engineering.
  J Biomech 2003; 36(6): 873-882.
• Kaptein BL, Valstar ER, Stoel BC, Rozing PM, Reiber JH.
  Evaluation of three pose estimation algorithms for model-based roentgen stereophotogrammetric analysis.
  Proc Inst Mech Eng 2004; 218(4): 231-238.
• Kaptein BL, Valstar ER, Stoel BC, Rozing PM, Reiber JH.
  A new type of model-based Roentgen stereophotogrammetric analysis for solving the occluded marker problem.
  J Biomech 2005; 38(11): 2330-2334.
• Valstar ER.
  Digital roentgen stereophotogrammetry. Development, validation, and clinical application.
  Thesis, University of Leiden, The Netherlands, 2001.
• Valstar ER, Gill R, Ryd L, Flivik G, Borlin N, Karrholm J.
  Guidelines for standardization of radiostereometry (RSA) of implants.
  Acta Orthop 2005; 76(4): 563-572.
• Valstar ER, Jong FW, Vrooman HA, Rozing PM, Reiber JH.
  Model-based stereogrammetry of orthopaedic implants.
  J Biomech 2001; 34(6): 715-722.
• Valstar ER, Vrooman HA, Toksvig-Larsen S, Ryd L, Nelissen RGHH.
  Digital automated RSA compared to manually operated RSA.
  J Biomech 2000; 33(12): 1593-1599.