A common model for studying acute mechanical damage in cartilage is to impact an isolated osteochondral or cartilage specimen with a metallic impactor. mechanical properties, smaller decreases in chondrocyte viability, higher total proteoglycan content, and less histologic structural damage, as compared to the impacted MOC specimens. If metal-on-cartilage impact conditions are to be utilized for modeling of articular injuries and post-traumatic osteoarthritis, the differences between COC and MOC impacts must be kept in mind. preparations. Most commonly, impaction of an osteochondral or cartilage Tosedostat inhibitor specimen has been Tosedostat inhibitor performed with a metallic impactor. In clinical practice, articular fractures and cartilaginous injuries are the result of supra-physiologic causes transferred between two cartilaginous surfaces. Material and structural differences between two impacting osteochondral structures, compared to a metallic impactor striking cartilage, would be expected to impact stresses and stress rates of switch during the impact. These differences in mechanical impact characteristics would in turn impact the deformation of the cartilage during impact, and therefore the pathologic strains encountered by the chondrocytes at the time of injury. The objective of this study was to compare the cartilage injury characteristics of a cartilage-on-cartilage (COC) impact model to those of a conventional metal-on-cartilage (MOC) impact model. The first hypothesis was that with the same delivered impact energy per unit area, cartilage stresses and stress rates of switch would be less for COC impacts compared to MOC impacts. The second hypothesis was that compared to MOC-impacted specimens, COC-impacted specimens would exhibit less structural damage, less mechanical property change, less chondrocyte death, and less chondrocyte metabolic dysfunction. Methods Osteochondral specimens measuring approximately 25 mm square and approximately 8 mm solid were excised from skeletally mature (12C24 month) bovine lateral tibial plateaus, from sites where meniscus did not cover the articular cartilage. Each specimen was attached to its own stainless steel plate using polycaprolactone as a mechanical bonding agent. Attachment of the C1qtnf5 plate through its reference corner holes automatically indexed the specimen to a reproducible position within all screening fixtures and microscopes, and allowed weight applications, measurements, and harvesting cuts to be made in known, reproducible locations (Physique 1). The osteochondral specimens were impacted with the same delivered energy per area, using either a metallic (n = 18) or cartilage (n = 16) impactor. The impact behavior, mechanical properties, chondrocyte viability, cell metabolism, and structural damage of the specimens were determined. Open in a separate window Physique 1 A) Schematic of osteochondral specimen on base plate, and locations of the B) mechanical assessments (circles) and imaging (xs), C) cuts for biochemistry assessments, and D) cuts for histological slides around the osteochondral specimens. The impact area in the center of the specimen is usually indicated by shading. Impact behavior The metal impactor (Physique 2A) was a brass cylinder having a flat end with a rounded edge and an impact diameter of 5.5 mm. The cartilage impactors (Physique 2B) were obtained from the femoral condyle apposing Tosedostat inhibitor each test specimen, using a mosaicplasty harvesting system (Mosaicplasty DP-Disposable Harvesting System, Smith & Nephew Endoscopy, Andover, MA). Four or five osteochondral plugs were punched, and the plug that was the flattest and that experienced a cartilage surface most perpendicular to the plug sides was chosen as the cartilage impactor for the specimen. The plugs were 6.5 mm in diameter and approximately 15 mm in length. Each plug was press-fit into a brass sleeve, leaving approximately 3 mm of cartilage and subchondral bone outside the sleeve. The opposite end of the plug was braced by filling the remainder of the brass sleeve with polycaprolactone. This sleeve was in turn press-fit into a brass sphere, which was then secured within the drop tower prior to impact. Open in a separate window Open in a separate window Physique 2.