Effects of increased chronic loading on articular cartilage material properties in the lapine tibio-femoral joint.

Methods of producing relevant and quantifiable load alterations in vivo with which to study load-induced cartilage degeneration analogous to osteoarthritis are limited. An animal model was used to investigate the effects of increased chronic loads on articular cartilage. Mature rabbits were randomized into one of three experimentally loaded groups and a fourth unoperated control group.

The effect of coordinate system choice and segment reference on RSA-based knee translation measures.

Roentgen stereophotogrammetric analysis (RSA) can be utilized to accurately describe joint kinematics, but even when measuring small displacements within radiographically discernible structures, standardized reference frames are imperative for useful comparison across patients and across studies. In the current paper, accurately controlled laboratory models demonstrated the considerable influence that a mere 1.9-cm offset of the origin of the coordinate system from the rotation axes could exert on translation measures when rotations were occurring.

Material properties of articular cartilage in the rabbit tibial plateau.

The material properties of articular cartilage in the rabbit tibial plateau were determined using biphasic indentation creep tests. Cartilage specimens from matched-pair hind limbs of rabbits approximately 4 months of age and greater than 12 months of age were tested on two locations within each compartment using a custom built materials testing apparatus. A three-way ANOVA was used to determine the effect of leg, compartment, and test location on the material properties (aggregate modulus, permeability, and Poisson's ratio) and thickness of the cartilage for each set of specimens.

In vivo loads in the medial compartment of the rabbit knee.

Background: The compressive loads produced in the medial compartment of a rabbit knee during hopping are unknown, and necessary for the development of an animal model to study unicompartmental osteoarthritis.

Methods: In an effort to obtain such data, a surgical procedure was developed to insert a pressure sensor into the medial tibial compartment of a New Zealand white rabbit knee joint, and an inactive sensor of the same thickness into the lateral tibial compartment. After the rabbits recovered from anesthesia, contact pressure was measured as the rabbits hopped.

Ankle eversion torque response to sudden ankle inversion Torque response in unbraced, braced, and pre-activated situations.

In 13 young ankle stable subjects, ankle eversion torque and peroneal EMG were simultaneously recorded in response to sudden ankle inversion. The eversion torque response was bi-phasic. The initial development of torque, which was responsible for 30% of the maximal eversion torque response, was observed 135 ms after the start of platform rotation and correlated well with the onset of the automatic postural peroneal EMG response.