Model-based Roentgen Stereophotogrammetric Analysis (RSA) of polyethylene implants

Fedra Hossein Zadeh Zaribaf, Lennard A. Koster, Bart L. Kaptein, Elise C. Pegg, H S Gill

Research output: Contribution to journalArticlepeer-review


Model-based Roentgen Stereophotogrammetric Analysis (RSA) is able to measure the migration of metallic prostheses with submillimeter accuracy through contour-detection and 3D surface model matching techniques. However, contour-detection is only possible if the prosthesis is clearly visible in the radiograph; consequently Model-based RSA cannot be directly used for polymeric materials due to their limited X-ray attenuation; this is especially clinically relevant for all-polyethylene implants. In this study the radiopacity of unicompartmental Ultra-High Molecular Weight Polyethylene (UHMWPE) knee bearings was increased by diffusing an oil-based contrast agent into the surface to create three different levels of surface radiopacity. Model-based RSA was performed on the bearings alone, the bearings alongside a metallic component held in position using a phantom, the bearings cemented into a Sawbone tibia, and the bearings at different distances from the femoral component. For each condition the precision and accuracy of zero motion of Model-based RSA were assessed. The radiopaque bearings could be located in the stereo-radiographs using Model-based RSA an accuracy comparable to metallic parts for translational movements (0.03 mm to 0.50 mm). For rotational movements, the accuracy was lower (0.1∘ to 3.0∘). The measurement accuracy was compared for all the radiopacity levels and no significant difference was found (p=0.08). This study demonstrates that contrast enhanced radiopaque polyethylene can be used for Model-based RSA studies and has equivalent translational measurement precision to metallic parts in the superior-inferior direction.
Original languageEnglish
Article number104201
JournalMedical Engineering & Physics
Early online date3 Jul 2024
Publication statusE-pub ahead of print - 3 Jul 2024


The authors would like to thank Zimmer-Biomet for providing the Oxford Partial knee components used for the analysis; David Canepa Talamas and the metrology team in the Department of Mechanical Engineering at Bath for performing the reverse engineering of the radiopaque bearings; and the team in the Department of Orthopaedics at Leiden University for enabling the RSA analysis.


  • Imaging
  • Model-based RSA
  • Radiopaque UHMWPE
  • Unicompartmental knee bearing

ASJC Scopus subject areas

  • Biophysics
  • Biomedical Engineering


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