279. COMPARISON OF TWO METHODS FOR EVALUATING TOTAL KNEE ARTHROPLASTY KINEMATICS: WHAT CAN BE EXPECTED FROM 2D FLUOROSCOPY?

Abstract

Purpose of the study: Comprehension of total knee arthroplasty (TKA) kinematics is primordial for improving the functional outcome and longevity of these prostheses. Several methods are available for evaluating knee kinematics. The purpose of this study was to determine the accuracy of the 2D fluoroscopic method in vitro, taking optoelectronic analysis as the gold standard.

Material and methods: In order to compare these two techniques, a posterior stabilised prosthesis was implanted on dry bones. The lateral ligaments were modellised with two elastic bands. Thirty flexion movements were imposed consecutively. The kinematics of this prosthetic model were recorded simultaneously using the fluoroscope and a computer-assisted surgery system. The technique used for the fluoroscopic analysis was based on the detection of the contours and projective geometry algorithms. The statistical analysis measured differences and correlations between the two systems using the root mean square (RMS) method and interclass coefficients of correlation (ICC) in addition to Bland and Altman analyses.

Results: Three hundred thirty six relative implant positions were analysed for 30 flexions from −8 to 132 degrees. The objective RMS were to the order of one degree for flexion, varus and tibia rotation. Conversely, there was a difference of 2.43±3.17 mm for the mediolateral distance (ML). Similarly the ICC were to the order of 0.9 for the six degrees of freedom of the model with the exception of ML displacement where the ICC was 0.106. These analyses were confirmed by the Bland and Altman analysis which revealed an underestimation of the ML distance by the fluoroscopic method in greatest internal rotation.

Discussion: This study is the first using a realistic model to evaluate the kinematic data provided by 2D fluoroscopy in comparison with conventional navigation data. The results show a good agreement between the two techniques and a small difference in measures excepting for the ML plane. The results are less satisfactory than those reported in the literature where data were obtained from computer simulations.

Conclusion: 2D fluoroscopy of the TKA kinematics provides precise data. Nevertheless, the limits and inaccuracies of this technique should be recognized. This study is a prerequisite for in vivo 2D fluoroscopy.