Technical noteArthroscopic assessment of human cartilage stiffness of the femoral condyles and the patella with a new tactile sensor
Introduction
The articular cartilage is composed of chondrocytes, the extracellular matrix, and its interstitial fluid. In the extracellular matrix, proteoglycans primarily determine the compressive stiffness of the cartilage [1], [2], whereas collagen fibers determine the tensile property of the cartilage [3]. It has been suggested that a decrease in the proteoglycans content and an increase in the amount of fluid might initially alter the cartilage structure, resulting in a softening of the cartilage [1], [4]. If the proteoglycans content decreases, fissures and cracks appear in the cartilage. Finally, the cartilage deteriorates and degenerates. Determining the stiffness of cartilage is important for detecting the first signs of cartilage degeneration. Many devices and much equipment have been developed to measure the stiffness of cartilage samples obtained in vitro or by autopsy [2], [5], [6], [7], [8]. However, there have been few studies on the stiffness of cartilage in living humans [9], [10].
Omata and Terunuma developed a new type of tactile sensor to detect the hardness and softness of an object [11]. The method involves measuring a change in resonance frequency when a vibrating ceramic transducer touches the surface of the object. This tactile sensor has been clinically used to determine the elasticity of the hand, myocardium, bladder, and penis in the field of medicine or urology [12], [13], [14], [15], [16], [17]. It provides useful information on physical and pathological characteristics such as hardness and/or softness in healthy conditions or in diseases.
With this tactile sensor, qualitative measurement of the cartilage stiffness can not only provide useful information for diagnosing early degenerative changes under arthroscopic control, but can also predict surgical or medical outcomes. The purpose of this study was to measure the cartilage stiffness of human femoral condyles and patella under arthroscopic control, and to determine the relationship of stiffness to gender and the grade of cartilage degeneration.
Section snippets
Materials and methods
The Review Board at our institution approved the use of human subjects for this research. From 1998 to 2000, 105 knees (51 right, 54 left) in 74 patients (39 men, 35 women) with traumatic cartilage injury (25 knees), osteochondritis dissecans (14 knees), osteoarthritis (13 knees), meniscal injury (11 knees), anterior or posterior cruciate ligament injury (six knees), bipartita patellae (three knees), and symptomatic plica synovialis (two knees) were enrolled in the study. The average age of the
Results
The plot of the method of Bland and Altman showed that mean difference of the cartilage stiffness in the system was 0.01 with 95% confidence interval, −0.20 to 0.22. The mean difference in the observers, and in an observer were −0.04, and −0.03, with 95% confidence interval −0.23 to 0.16, and −0.25 to 0.20, respectively. These results indicated the reproducibility, and inter- and intra-observer reliability of the measurement.
The value of stiffness observed in grade 0, I, II, III and IV was
Discussion
The results of the present study demonstrated that the new tactile sensor is capable of measuring the stiffness of the joint cartilage under arthroscopic control and of detecting the difference in stiffness between intact normal and diseased (injured) cartilage. In addition, we have presented data on the stiffness of normal living human cartilage, indicating that cartilage stiffness of the patella is lower in women than in men.
A number of studies have previously demonstrated cartilage stiffness
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