The diagnostic potential of synovial effusion in meniscal pathology

During a 20-month period, 382 arthroscopies were performed and the type of washout fluid obtained was noted. When a torn meniscus was found, the fluid was macroscopically abnormal in 97.4% of cases. A crystal clear washout was associated with no demonstrable pathology in over half the cases, the remainder having mainly patellofemoral joint pathology and other articular lesions. Only 6.3% of those with a clear fluid washout had meniscal pathology. Of those with abnormal fluid, 68% had meniscal pathology, with a normal arthroscopic examination being found in only 8.5%. In addition, when the fluid from traumatic effusions was examined microscopically, a typical droplet containing lipid crystals was found to be present and to account for an oily macroscopic appearance. These data support the use of fluid irrigation of the knee as a screening test for intraarticular pathology, especially of the menisci, that may allow a reduction in the number of negative arthroscopies.