No abstract

Articular cartilage is a highly hydrated fibre composite material that provides a resilient, lowfriction bearing surface covering bones where they articulate. The literature suggests that the tissue becomes increasingly elastic, less viscoelastic, as the loading rate increases, i.e. that hysteresis, the energy lost between loading and unloading, will decrease with increasing strain-rate. Here we show, using a controlled impact, that hysteresis increases with strain rate. No fluid was lost during the deformation and the ratio of the radial to the axial strains, Poisson's ratio, measured using highspeed video recording, increased as the tissue was deformed, starting close to zero and tending towards that for an isovolumetric deformation. The decreasing coefficient of restitution, a measure of the hysteresis, was modelled using a non-linear viscoelastic element, as a first approximation. These results indicate that the tissue remains viscoelastic with increasing strain rate, dissipating energy which might otherwise generate cracks in the matrix.

The experiences and feelings of physical therapists treating patients with NSLBP include conflict among their pain beliefs, attitudes, and working partnerships with patients. Treatment decisions may be influenced when physical therapists modify their beliefs and attitudes to reduce this sense of conflict. Improving physical therapist communication skills may help decrease feelings of conflict, enhance working relationships, and encourage a more consistent approach toward patients with NSLBP.

No abstract

Impact injury to a joint is a known risk factor for the subsequent development of secondary osteoarthritis. An in vitro model, employing a drop-tower loading machine, was used to examine the effect of an impact load on isolated articular cartilage explants from human and bovine femoral heads. Two different types of impact experiment were performed. In the first, 4 mm diameter explants were loaded using a plane-ended impactor. In the second, a modified impactor was developed that had a central 4 mm diameter plane-ended indentor which was used to load the centre of 8 mm diameter explants. This enabled the unloaded outer ring of each explant to be compared with the loaded central core. The modulus values measured using the impactor were found to be higher, compared with the indentor in both species. Scanning electron microscopy showed that cartilage surrounding the loaded central region of the 8 mm explants protected the indented tissue, and these explants showed less damage than the 4 mm samples that were fully impacted. In addition, human cartilage was found to be less damaged than bovine, possibly as a consequence of the different structure as well as of a greater thickness. Both the source of the tissue and the nature of the impact affected the type of damage observed.