ZiMT Journal Club March 2021: Dr. Frank Seehaus / Roentgen Stereophotogrammetric Analysis (RSA) – Limits and opportunities for assessing implant safety
Dr. Frank Seehaus, Chair of Orthopedics with Orthopedic Surgery, FAU
Aseptic implant loosening is one of the five most common causes of implant revision in hip and knee arthroplasty . The assessment of implant anchoring over time is carried out in orthopedics using imaging methods, which aid in assessing the movement between the implant and the bone surrounding the implant. If there is a relative movement between the implant and the bone, it is referred to as migration. In order to be able to determine migration in the tenths of a millimeter range, special measuring methods are required. The Roentgen Stereophotogrammetric Analysis (RSA) is currently the so-called gold standard for the in vivo assessment of implant anchoring [2, 3]. Long-term clinical studies have shown that increased implant migration observed in the first two postoperative years strongly correlates with later aseptic loosening [4, 5]. The implant migration measured with the RSA can therefore be regarded as a reliable component in the assessment of implant safety (context: loosening).
The RSA method has been successively further developed – the so-called model-based RSA variant was introduced. In addition to surface models of the implants, an implant model based on geometric basic bodies (cylinders, spheres, …) can also be generated and used to determine migration. The validation of the RSA method [6, 7] as well as the identification of limits and possibilities in clinical use  is the subject of research of the working group at the Chair of Orthopedics with Orthopedic Surgery.
 Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) Hip, Knee & Shoulder Arthroplasty: 2019 Annual Report. Adelaide: AOA, 2019.
 Sundfeldt M, Carlsson LV, Johansson CB, Thomsen P, Gretzer C (2006) Aseptic loosening, not only a question of wear: a review of different theories. Acta Orthop 77:177-197.
 Valstar ER, Gill RH (2006) Radiostereometric analysis in orthopaedic surgery: editorial comment. Clin Orthop Relat Res 448:2.
 Ryd L, Albrektsson BEJ, Carlsson L, Dansgard F, Herberts P, Lindstrand A, Regner L, Toksviglarsen S (1995) Roentgen Stereophotogrammetric Analysis as a Predictor of Mechanical Loosening of Knee Prostheses. J Bone Joint Surg-Br. 77b:377-383.
 Karrholm J, Borssen B, Lowenhielm G, Snorrason F (1994) Does early micromotion of femoral stem prostheses matter? 4-7-year stereoradiographic follow-up of 84 cemented prostheses. J Bone Joint Surg-Br. 76-B:912-917.
 Xu J, Cao H, Sesselmann S, Taylor D, Forst R, Seehaus F (2020). Model-Based Roentgen Stereophotogrammetric Analysis Using Elementary Geometrical Shape Models: Reliability of Migration Measurements for an Anatomically Shaped Femoral Stem Component. Appl Sci. (Basel) 10(23):8507.
 Wu J, Forst R, Hong Y, Kang Z, Xu J, Seehaus F (2020) Assessment of polyethylene wear in THA using Model-Based Roentgen Stereophotogrammetric analysis – an experimental phantom-model setup. Z Orthop Unfall 158(S01): 39 – 40.
 Xu J, Sonntag R. Kretzer JP, Taylor D, Forst R, Seehaus F (2020). Model-based Roentgen Stereophotogrammetric Analysis to monitor in vivo the Head-Taper junction in Total Hip Arthroplasty – and they do move. Materials (Basel). 13(7):1543.