The accuracy and reliability of a novel handheld dynamic indentation probe for analysing articular cartilage

This study investigates the accuracy and reliability of a novel handheld indentation system designed to ascertain the dynamic biomechanical properties of articular cartilage. A series of standard elastomers were assessed with both the handheld indentation system and a bench-top dynamic indentation system to assess the accuracy of the instrument. Interoperator and intraoperator experiments were undertaken to investigate the reliability of the system when used by an individual operator and by five different operators. Intraclass coefficients (Rho) were derived using a random effects model. The system was then used to ascertain the topographical variation in the shear moduli and phase lag of articular cartilage across normal ovine tibial plateaux. The system was shown to be highly accurate (R-2 = 0.97), and had excellent reliability when measuring the dynamic shear modulus of articular cartilage (interoperator Rho = 0.75, intraoperator Rho = 0.79). Measurement of static shear modulus was less reliable (interoperator Rho = 0.15, intraoperator Rho = 0.52), but may be improved by monitoring the load applied to the instrument by the operator. The instrument was used to differentiate between different regions of cartilage and generated a topographical map of an ovine tibial plateau. The cartilage located beneath the menisci was 200-500% stiffer than the cartilage that was not covered by the menisci, while the phase lag was almost constant (10 degrees +/- 2 degrees SD) over the entire tibial plateau. The system was shown to be an accurate and reliable tool for rapidly assessing the dynamic biomechanical properties of articular cartilage, while being small enough to be used arthroscopically.