Importance de la distribution spatiale des propriétés mécaniques du cartilage articulaire dans les études animales

Methods: The three species (rat, rabbit and sheep) used in this study are widely chosen in cartilage regeneration and repair studies [3]. Mechanical properties were mapped ex vivo, using a novel technique allowing for automated indentation mapping (Mach-1 v500css, Biomomentum Inc.) of visually normal tibial plateau and femoral condyles (right and left joints) from three rats (aged 8 weeks, female, 0.62 lbs), three rabbits (aged 13-14 weeks, male, 6-7 lbs) and one sheep (aged 4-5 years, male, 100-140 lbs). The multiaxial mechanical tester indents the articular surface at each position (at least 50 positions per articular surface) by moving a spherical indenter (radius=0.5 mm) along a vector perpendicular to the surface while measuring the resulting load. Subsequently, the thickness was measured with an adapted version of the needle technique [4]. The instantaneous modulus at each position was obtained by fitting the load-displacement curve (with corresponding thickness) to an elastic model of indentation [5].

Results: High-resolution maps (Fig. 1) of the thickness and the instantaneous modulus for the tibial plateau and femoral condyles of the three species were generated. The average thickness and instantaneous modulus are shown in Table 1. Measured thickness agrees with those reported in the literature [6]. The spatial distribution of thickness and instantaneous modulus reveals a large difference between regions covered and not covered by the meniscus and also between the medial and lateral sides for both articular surfaces. Effectively, a thinner and stiffer cartilage can be observed in regions in contact with the meniscus while a thicker and softer cartilage is observed on the rest of the surface whereas this topographic pattern is more striking in tibial plateau than femoral condyles.