In vivo characterization of indentation stiffness of articular cartilage in the normal human knee

Previous laboratory measurements showed topographical variation in the prop erties of articular cartilage in several animal species and in humans, In t his study we characterize for the first time the topographical variation of the stiffness of the human knee articular cartilage in vivo using a novel arthroscopic indentation instrument. The instrument indicates the stiffness in the form of force (Newtons) by which the tissue resists the constant de formation (300 mu m) produced by the small (l-mm diameter) cylindrical inde nter. Measurements mere carried out at eight sites in the knee joint of 20 persons who had intact cartilage in the arthroscopic examination. The stiff est cartilage (5.6 +/- 1.2 N, mean +/- SD) was located in the lateral condy le of the femur, whereas the softest cartilage (2.4 +/- 0.8 N) was in the m edial plateau of the tibia, In general, the cartilage stiffness was higher in the femur than in the tibia (p < 0.01) or in the patella (p < 0.01),In t he femur, the condyles were stiffer than the patellar surface (p < 0.01). T he stiffness variation was consistent with earlier biphasic indentation ana lyses of laboratory measurements with the knee joint cartilage of cadavers, This study provides baseline data for characterization of cartilage stiffn ess in pathological situations or follow-up of the cartilage quality after surgical interventions. (C) 1999 John Wiley & Sons, Inc.