Patellar cartilage deformation in vivo after static versus dynamic loading

The objective of this study was to test the hypothesis that static loading (squatting at a 90 degrees angle) and dynamic loading (30 deep knee bends) cause different extents and patterns of patellar cartilage deformation in v ivo. The two activities were selected because they imply different types of joint loading and reflect a realistic and appropriate range of strenuous a ctivity. Twelve healthy volunteers were examined and the volume and thickne ss of the patellar cartilage determined before and from 90 to 320s after lo ading. using a water excitation gradient echo MR sequence and a three-dimen sional (3D) distance transformation algorithm. Following knee bends, we obs erved a residual reduction of the patellar cartilage volume (-5.9 +/- 2.1%; p < 0.01) and of the maximal cartilage thickness (-2.8 +/- 2.6%), the maxi mal deformation occurring in the superior lateral and the medial patellar f acet. Following squatting, the change of patellar cartilage volume was -4.7 +/- 1.6% (p < 0.01) and that of the maximal cartilage thickness -4.9 +/- 1 .4% (p < 0.01), the maximal deformation being recorded in the central aspec t of the lateral patellar facet. The volume changes were significantly lowe r after squatting than after knee bends (p < 0.05), but the maximal thickne ss changes higher (p < 0.05). The results obtained in this study can serve to validate computer models of joint load transfer, to guide experiments on the mechanical regulation of chondrocyte biosynthesis, and to estimate the magnitude of deformation to be encountered by tissue-engineered cartilage within its target environment. (C) 2000 Elsevier Science Ltd. All rights re served.