Pathophysiology of osteoarthritis: evidence against the viscoelastic theory.

OBJECTIVES Whether changes in the hyaluronan moiety of synovial fluid are associated with osteoarthritis (OA) is unresolved experimentally, notwithstanding frequent statements in the literature that the disease leads to degraded hyaluronan. We evaluated this hypothesis by comparing the molecular weight and concentration of hyaluronan in synovial fluid from patients with and without OA. METHODS Synovial fluid was obtained by needle aspiration from patients with advanced OA (Kellgren-Lawrence Grade IV) and from patients with no radiological or arthroscopic evidence of OA. The distribution of the molecular weight of hyaluronan was measured using both gel electrophoresis and size-exclusion chromatography, and hyaluronan concentration was determined by immunosorbent assay and differential refractometry. RESULTS The distributions of molecular weight were highly variable within each group of patients; the average distributions, however, were identical in the 2 groups. The average concentration of hyaluronan also did not differ statistically between the 2 groups. CONCLUSIONS We found no evidence of hyaluronan degradation in synovial fluid of patients with OA. Commonly expressed opinion in the literature to the contrary may have resulted from a failure to adequately consider the limitations of previous experimental studies.