In situ measurement of articular cartilage deformation in intact femoropatellar joints under static loading

The deformational behavior of articular cartilage has been investigated in confined and unconfined compression experiments and indentation tests, but to date there exist no reliable data on the in situ deformation of the cart ilage during static loading. The objective of the current study was to perf orm a systematic study into cartilage compression of intact human femoro-pa tellar joints under short- and long-term static loading with MR imaging. A non-metallic pneumatic pressure device was used to apply loads of 150% body weight to six joints within the extremity coil of an MRI scanner. The cart ilage was delineated during the compression experiment with previously vali dated 2D and 3D fat-suppressed gradient echo sequences. We observed a mean (maximal) in situ deformation of 44% (57%) in patellar cartilage after 3 1/ 2 h of loading (mean contact pressure 3.6 MPa), the femoral cartilage showi ng a smaller amount of deformation than the patella. However, only around 7 % of the final deformation (3% absolute deformation) occurred during the fi rst minute of loading. A 43% fluid loss from the interstitial patellar matr ix was recorded, the initial fluid flux being 0.217 +/- 0.083 mu m/s, and a high inter-individual variability of the deformational behavior (coefficie nts of variation 11-38%). In conjunction with finite-element analyses, thes e data may be used to compute the load partitioning between the solid matri x and fluid phase, and to elucidate the etiologic factors relevant in mecha nically induced osteoarthritis. They can also provide direct estimates of t he mechanical strain to be encountered by cartilage transplants. (C) 1999 E lsevier Science Ltd. All rights reserved.