Abstract 15

KINEMATIC JOINT MEASUREMENTS USING SINGLE-PLANE RSA

J.L. Ioppolo^1,2, N. Börlin³, M.D. Baratz⁴, B. Nivbrant^1, C.R. Bragdon^4, M.G. Li^1, R.I. Price^3, H. Malchau^4, D.J. Wood¹ and W.H. Harris⁴

¹Department of Surgery (Orthopaedics), University of Western Australia
²Medical Technology and Physics Department, Sir Charles Gairdner Hospital
³Department of Computing Science, Umeå University, Sweden
⁴Orthopaedic Biomechanics & Biomaterials Laboratory, Boston, MA, USA

Skeletal kinematics are able to yield significant insight into the patient factors, surgical techniques and design of implants used for the management of joint replacement patients. This project involved the basic scientific development of a clinical system for the measurement of skeletal kinematics. Radiostereometric Analysis (RSA) is the established "gold-standard" for measuring the long-term migration of prosthetic hip and knee joint components with respect to underlying bone. However, the use of conventional RSA to perform measure skeletal kinematics is limited. In addition, no clinical methods currently exist for measuring the in-vivo wear of polyethylene tibial components.

The precision and accuracy of this novel RSA fluoroscopy system was determined in-vitro using two international standard reference phantoms and a single-plane General Electric Flexiview (OEC9800) fluoroscope. A method for determining knee joint wear was evaluated by analysing the instantaneous tibiofemoral centre of rotation over a shortened knee flexionextension cycle of a woodcut knee phantom implanted with total knee replacement components.

The accuracy of RSA fluoroscopy is proportional to the pixel size of the image intensifier and was approximately 200 microns in the proximal-distal and anterior-posterior directions and approximately 700 microns in the medial-lateral direction. The lower threshold for the in-vitro measurement of statistically significant polyethylene tibial component wear was 400 microns.

The technique offers the independent and accurate assessment of the in-vivo kinematics of joint implants designed by different manufacturers. Results of this work will assist the surgical decision making and implant design processes by offering direct evidence of the characteristic in-vivo skeletal kinematics of a particular implant.

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