Total knee arthroplasty three-dimensional kinematic estimation prevision. From a two-dimensional fluoroscopy acquired dynamic model.

INTRODUCTION: To determine six-degree of freedom of total knee arthroplasty kinematics (TKA), optimized matching algorithms for single fluoroscopic image system may be used. Theoretical accuracy of these systems was reported. Nevertheless, all reports were done under idealized laboratory experimental conditions. The aim of this study was to evaluate the "true" accuracy of a flat panel single plane video-fluoroscopy system based on computed-assisted design (CAD) model matching and compare it to TKA kinematics obtained from optoelectronic measurements as gold standard. HYPOTHESIS: The estimation of the error produced by 2D/3D fluoroscopic registration in daily practice is misjudged in most available laboratory reports. MATERIAL AND METHODS: The experimental set-up used a TKA implanted into femoral and tibial cadaver bones. Thirty flexions were simultaneously registered using single plane fluoroscopy and an active optical tracking system. Kinematics registered were compared using the root mean square error (RMS), the concordance correlation coefficient and Bland & Altman plot analysis. RESULTS: The mean range of motion of flexion during the experiment was 106°. The respective RMS for flexion, varus-valgus and internal-external rotation were 0.68, 0.67 and 1.02°. The respective RMS for antero-posterior, medio-lateral and proximo-distal displacement were 1.3, 2.4 and 1.06 mm. Extreme values of the measured error concerning medio-lateral displacement were -5.4 and 22,1mm. DISCUSSIONS: Analysis found some outliners in all degree of freedom with a systematic error and larger standard deviation than already published data. One should make sure that during the experiment the motion of interest is in the in-plane direction. Moreover, this study brings out the true threshold detection of this type of analysis.

Arthroscopic medial meniscectomy on stable knees.

We reviewed 74 partial medial meniscectomies in 57 patients with stable knees, to assess the long-term functional and radiological outcome. The International Knee Documentation Committee score and the residual laxity were assessed in both knees. At the time of surgery the mean age of the patients was 36 +/- 11 years and the mean follow-up was 12 +/- 1 years. All had a limited medial meniscectomy. The anterior cruciate ligament was intact in all cases. The meniscal tear was vertical in 95% and complex in 5%. The posterior part of the meniscus was removed in 99%. A peripheral rim was preserved in all cases. After 12 years 95% of the patients were satisfied or very satisfied with their knee(s). Objectively, 57% had grade A function and 43% were grade B. The outcome correlated only with the presence of anterior knee pain at final follow-up. In the 49 cases of arthroscopic meniscectomy for which there was a contralateral normal knee there was narrowing of the 'joint-space' in 16% of the operated knees. There was no correlation between this and other parameters such as age or different meniscal pathologies.