Summary Subchondral bone plays a role in the pathogenesis of osteochondral damage and osteoarthritis in horses and humans. Osteochondral fragmentation and fracture, subchondral bone necrosis and osteoarthritis are common diseases in athletic horses, and subchondral bone is now thought to play an integral role in the pathogenesis of these diseases. There have been numerous research efforts focused on articular cartilage damage and its pathogenesis, yet comparatively little effort focused on subchondral bone pathology or the coordinated disease states of the osteochondral tissues. The purpose of this report is to review the current understanding of osteochondral disease in all species and its application to equine research and practice. It can be concluded from this review that our current understanding of osteochondral disease is based on clinical and pathological sources; and that the lack of information about joint tissue adaptation and disease has hampered objective studies of osteochondral tissues.

Fracture surfaces of both monotonic and fatigue loaded bone cement samples were examined to investigate the fractographic characteristics of PMMA. Classic cleavage step river patterns were observed on all monotonically loaded samples, running downstream in the direction of crack propagation. All fatigue cracks initiated at internal pores and the direction of crack propagation of many cracks was discernible. Porosity, pore size, and pore size distribution were found to affect the crack initiation and fatigue behavior of bone cement. Statistical analysis revealed a strong negative correlation between two-dimensional porosity present on the fracture surfaces and the cycles to failure. The fractographic observations of these fatigue samples elucidate one reason why porosity reduction by centrifugation or vacuum mixing increases the fatigue life of PMMA bone cement.

Thirty-eight cemented acetabular components that had been clinically implanted in client-owned dogs were retrieved postmortem and analyzed for mechanical stability, volumetric wear, and articular surface damage. Comparison of the results from this study with similar studies on autopsy-retrieved human components will provide insight into the adequacy of the dog as a model for human total hip replacement (THR). The canine average volumetric wear rate (6.7 +/- 4.2 mm(3) per year) was an order of magnitude lower than similar studies of human components; however, articular surface damage was considerably different from, and more severe than, that reported in the literature for human acetabular components. The incidence of mechanical loosening of the canine acetabular component was high, with 20 of 38 (52.6%) testing as loose. There was a positive correlation between articular surface damage and mechanical loosening of the acetabular component, but there was no significant correlation between volumetric wear and mechanical loosening, as seen in human retrieval studies. Initial failure events for the canine acetabular component appear to be mechanical in nature. Differences between human and canine acetabular components with regard to wear volume, articular surface damage, and mechanical loosening need to be taken into account when one is designing studies using dogs as the animal model for human THR.

Knotting method does influence the structural properties of suture materials and should be considered when tying knots under tension.

This study is the first description of the extensive porosity which is preferentially located at the cement-prosthesis interface of cemented femoral components of total hip replacements. The observation is important because the interfacial porosity may decrease the strength of the cement-femoral prosthesis interface and jeopardize the mechanical integrity of the cement mantle. We examined the cement-metal interfaces from a multiplicity of in vivo and in vitro specimens using both optical and scanning electron microscopy. These samples included several stem designs, implants made from either Co-Cr or Ti alloy, implants made with a variety of surface finishes and both centrifuged and uncentrifuged cement. All in vivo and in vitro samples had marked porosity in the cement focally concentrated at the cement-metal interface. The amount of porosity at the interface greatly exceeded the amount of general porosity found throughout the bulk cement. Centrifuging did not affect the interfacial porosity, and neither did alloy nor surface finish. The presence of these pores may be explained by the rheological characteristics of the cement.