Mesure d'indentation et d'épaisseur sur les surfaces articulaires du genou de rat après une déchirure méniscale médiane

(En anglais seulement) Dr. Evseenko from University of Southern California contacted us to incorporate mechanical testing into one of his studies: “How does medial meniscal tear (MMT) affect the joint in a rat model”. A major challenge in characterizing the outcome of this degenerative model is related to the very small size of the samples. To demonstrate the performance and sensitivity of our mechanical mapping technique in detecting potential osteochondral changes a few weeks following surgery, our scientists – in collaboration with Dr. Evseenko’s lab – designed a short pilot study.

Following our procedure for the importation of biological samples, 2 closed murine knee joints from the same animal (right contralateral control joint and left joint with the MMT surgery) were shipped overnight to our facility. Upon arrival, our study director, experienced with handling small animal joints, carefully extracted the tibial plateaus, distal femurs and patellas. Each articular surface was then attached onto our multiaxial mechanical tester (Mach-1 model v500css equipped with a 17N multiaxial load cell, a spherical indenter (D=0.5 mm) and a 26G needle probe) to perform automated indentation and thickness mappings. Following these non-destructive tests, samples were fixed, packaged and shipped back for subsequent histological analyses.

Using the normal stress-relaxation curves (normal spherical indentation) and the load vs displacement curves (needle penetration), analyses were performed to calculate instantaneous modulus (MPa) and cartilage thickness (mm) at each position of the mapping. These high-resolution mappings (≈80 positions/surface) allowed the detection of stiffer regions (suggesting bone exposure) surrounded by abnormally softer cartilage in the medial side of the tibial plateau and femoral condyles (kissing lesion) of the treated left knee, when compared with the untreated right control knee. Mappings of the tested patellas also revealed a drastic decrease of cartilage stiffness of the treated knee compared to the control. These pilot results demonstrated the potential of this technique in understanding the functional impairment in knee joints following MMT surgery and in following the evolution of the induced degeneration.

This pilot study (from the sample reception to preliminary report submission) was completed within 2 days. Dr. Esveenko has given his consent to publish this case study.