Mechanical injury of explants from the articulating surface of the inner meniscus

Knee osteoarthritis is accelerated by damage to the meniscus, a fibrocartilage tissue that assists in load transmission. However, little is known about the mechanical or cellular response of the meniscus to injurious overloading. Here, in vitro studies explored injury to meniscal explants using a compressive overloading protocol that has been well characterized for articular cartilage. Cartilage samples were processed in parallel as a reference to the extensive literature on cartilage injury. Injured meniscal explants showed extensive cell death at the articulating surface but no gross tissue damage, while similar conditions of peak stress and strain resulted in cartilage surface fissures and cell death consistent with moderate overloading. Post-injury gene expression in meniscal explants indicated a decrease in seven of the nine catabolic and pro-inflammatory molecules surveyed, while cartilage experienced a downregulation in ADAMTS-5 and TNF-α only. These data demonstrated a resiliency of the meniscus to injury, and that an acute increase in catabolic activities is not necessarily a consequence of mechanical overloading.