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EVALUATION OF A NON-INVASIVE TECHNIQUE FOR PATELLAR KINEMATIC ANALYSIS



Abstract

Purpose of the study: The issue of patellar kinematics remains a difficult problem for patellar resurfacing during conventional or computer-assisted knee surgery, yet adequate knowledge is required for appropriate orientation of the patellar cut and insert positioning. The purpose of this study was to develop a non-invasive tool for in vivo kinematic analysis of the patellar tract and to compare results with the gold-standard invasive method.

Material and methods: A special experimental set-up designed for this study enabled experimental simulation of load-bearing flexion-extension cycles of the knee joint. Range of motion from 0 to 102° was imposed with a computer-controlled motor. The analysis was conduced on 14 complete lower limb cadaver specimens. Patellar kinematics was analyzed for each knee simultaneously with two systems: a non-invasive method using a low-dose stereoradiographic scan linked to a 3D reconstruction software; and the reference system using tripodes implanted on the patella and radio-opaque spherical markers. Six degrees of freedom were considered: three translations and three rotations. Sequential kinematic recordings were made by calculating the position of a patellar landmark in relation to a femoral landmark.

Results: The mean difference between the results obtained with the two systems was less than 1 mm for anteroposterior and vertical translations, greater for mediolateral translations. It was less than 2° for patellar flexion-extension, to the order of the motion itself for abduction-adduction, and to the order of 5° for horizontal tilt.

Discussion and conclusion: The non-invasive technique proposed here appears to be reliable for patellar translations and flexion, but need further improvement for tilt and adduction-abduction. This is particularly true for the 45° to 90° range of motion because of the difficult problem of determining the contours of the patella. Further developments for this tool are under way.

Correspondence should be addressed to SOFCOT, 56 rue Boissonade, 75014 Paris, France.