REGIONAL VARIATIONS OF INDENTATION STIFFNESS AND THICKNESS OF NORMAL RABBIT KNEE ARTICULAR-CARTILAGE

The rabbit knee is frequently used as an experimental model for cartil age repair, but the choice of different joint regions for such studies makes comparisons between methods difficult. Furthermore, there is on ly limited information available about the regional variations of the biomechanical properties in normal rabbit knee articular cartilage. In the present study in situ indentation tests were used to map the shor t-term stiffness and thickness of articular cartilage at seven locatio ns (anterior and posterior areas of the medial and lateral femoral con dyles, the patellar groove, and the central areas of the medial and la teral tibial plateaus) in nine normal rabbit knee joints. Short-term c artilage stiffness was described by elastic moduli under ramp loading and 15-s creep conditions. The moduli were calculated according to Hay es' single-phase elastic model. A moderate positive correlation (r = 0 .54) between cartilage stiffness and thickness was found for rabbit fe moral cartilage, but was not confirmed for tibial cartilage, which had the thickest, but also the softest cartilage of all areas. The cartil age in the patellar groove and the medial compartments of both femoral condyles and tibial plateaus was stiffer and thicker than that in the lateral components, similar to previous findings in dogs. However, th e dog femoral cartilage was found to be stiffer at the anterior than a t the posterior regions, but we found the opposite in the rabbit. Thes e dissimilarities between animal models may be caused by different joi nt loading characteristics. Accordingly, in rabbits repair processes i n the more anterior femoral areas with less stiff cartilage may not be comparable to repairs in more posterior areas where cartilage is stif fer. (C) 1996 John Wiley & Sons, Inc.