The effect of dynamic mechanical compression on nitric oxide production inthe meniscus

Objective: The menisci play an important role in the blomechanics of the kn ee, and loss of meniscal function has been associated with progressive dege nerative changes of the joint in rheumatoid arthritis as well as in osteoar thritis. However, little is known about the underlying mechanisms that link meniscal injury or degeneration to arthritis. Meniscal fibrochondrocytes r espond to environmental mediators such as growth factors and cytokines, but the influence of mechanical stress on their metabolic activity is not well understood. Nitric oxide (NO) is believed to play a role in mechanical sig nal transduction, and there is also significant evidence of its role in car tilage and meniscus degeneration. The goal of this study was to determine i f meniscal fibrochondrocytes respond to mechanical stress by increasing NO production in vitro. Design: Explants of lateral and medial porcine menisci were dynamically com pressed in a precisely controlled manner, and NO production, nitric oxide s ynthase antigen expression and cell viability were measured. The relative r esponses of the meniscal surface and deep layers to dynamic compression wer e also investigated separately. Results: Meniscal NO production was significantly (P <0.01) increased by dy namic compression in both the medial and lateral menisci. Dynamically compr essed menisci contained inducible nitric oxide synthase antigen, while unco mpressed menisci did not. Significant (P <0.05) zonal differences were obse rved in basal and compression-induced NO production. Discussion: Our findings provide direct evidence that dynamic mechanical st ress influences the biological activity of meniscal cells. These results su ggest that NO production in vivo may be in part regulated by mechanical str ess acting upon the menisci. Since NO affects matrix metabolism in various intraarticular tissues, alterations in the distribution and magnitude of st ress in the menisci may have important metabolic as well as biomechanical c onsequences on joint physiology and function. (C) 2001 OsteoArthritis Resea rch Society International.