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Prevalence of Crystals in Knee Osteoarthritis: Experience From Patients Undergoing Arthroscopic Procedures

C oexistence of calcium-containing crystals and osteoarthritis (OA) has been reported in many studies and has led researchers to question their interrelationship. Reported prevalence of calcium-containing crystals in OA patients ranges from 22% to 60%. Most studies derived their data from synovial fluid analysis or by the presence of radiographic evidence of chondrocalcinosis, which may not be robust assessments of prevalence. The purpose of this study was to elucidate the prevalence of calcium-containing crystals using direct arthroscopic inspection in knee OA patients who underwent arthroscopic procedures over the course of a 10-year period. Arthroscopic irrigation had previously been used as a therapeutic consideration for patients with OAwho had not responded to other medications before being shown to be ineffective by a Veterans Administration controlled trial. Around that same time, our group was actively involved in an interventional trial to test the efficacy of arthroscopic irrigation in addition to its use in our practice. The study did not demonstrate an effect of irrigation on arthritis severity as measured by aggregate WOMAC (Western Ontario & McMaster Universities Osteoarthritis Index) scores, the primary outcome variable; however, in a hypothesis-generating post hoc analysis of the effect of positively birefringent intraarticular crystals on arthroscopic irrigation, our group showed that patients with and without intra-articular crystals had statistically significant improvements in pain assessments and aggregate WOMAC scores 12 months after arthroscopy. Patients with crystals had statistically greater improvements in pain. Using data from our prior study procedures, we describe the prevalence of crystals and their association with inflammatory findings and cartilage destruction.