Synovial Joints Like the Knee and Hip

Synovial joints like the knee and hip are qualified by their possessing a liquid that serves as a lubricant; that liquid is called synovia or synovial fluid. The fluid is surrounded by the synovium, which is the soft connective tissue that holds the synovial fluid. Whereas the synovium is actually permeable to water, the synovial fluid is far more viscous. Furthermore, a synovial membrane generates the synovial fluid. The name synovia comes from the words syn (like) and ovium (egg), due to its thick, stringy consistency resembling that of egg white (Laptiou, 2014). With age, the synovial fluid may become thinner, leading to insufficient lubrication and symptoms such as reduced range of motion, painful movements, stiffness, and swelling. Other classes of tissue that comprise the synovial joint system include the bone and cartilage, as well as the surrounding tensile tissues and ligaments. (Lapitou, 2014). Repair of synovial joints depends on the interaction of these various parts. So long as both the hyaline and fibrocartilage surrounds bone, the bone itself remains able to respond to various stressors including impacts.

The aging process impacts the amount of synovial fluid being produced by the synovial membrane and stored in the synovium. One of the most common effects of the weakening of synovial fluid is osteoarthritis. Osteoarthritis is known to have a genetic component (Sandell, 2012). However, trauma such as that experienced by athletes can also result in the activation of the synovium in the healing response. Whenever the equilibrium in the synovial joint is compromised, inflammation and other responses initiate the healing process. Because synovium is a reactive tissue, it is integral in the process of repairing synovial joints (Pavlovich, 2008). When damage occurs, synovial cells cause a "fibroblast-like response enhancing healing," (Pavlovich, 2008, p. 1). Moreover, healing can be facilitated by applying radiofrequency pulses to the synovium, thus enhancing meniscal repair (Pavlovich, 2008, p. 1). Verbruggen et al. (2007) found that restoring the balance of catabolic cytokine can also promote osteochondral repair. Progressive research in the application of stem cells shows how the future of synovial joint repair therapy may appear. For instance, mesenchymal stem cells (MSCs) are the "multipotent precursors of connective tissue cells that can be isolated from many adult tissues, including those of the diarthrodial joint," and "have emerged as a potential therapy" for osteoarthritis (Barry & Murphy, 2013, p. 584).