The role of arthroscopy in the differential diagnosis of osteoarthritis of the knee.

The arthroscope, currently used in OA mostly as a tool to deliver surgical therapy, can play an important diagnostic role in patients with knee pain for whom OA is part of the differential diagnosis. Concepts that may seem foreign to clinicians who take care of patients with knee OA (that is, of arthroscopy as a purely diagnostic tool and of knee OA as a clinical situation for which a differential diagnosis might be rendered) are supported by an appreciation for the heterogeneity of conditions of which OA is a part as well as an awareness of the pathoanatomic complexity of symptomatic knee OA as revealed by recent MRI and arthroscopy studies. Inspection of the perplexing OA knee with one of the newly available needle arthroscopes in an ambulatory office setting may be preferable to referral for conventional operating room--based arthroscopy, as this new technique adequately delineates intra-articular anatomical abnormalities (for which surgical therapy is not always indicated) and provides saline lavage to the joint (considered by many as a major factor in the improvement of symptoms reported by many patients with knee OA after arthroscopy). At present arthroscopy can serve to aid differential diagnostic efforts in five clinical situations involving knee OA: painful swollen knee with normal radiographs and noninflammatory fluid, clinical and radiographic OA with pain out of proportion to radiographic findings and refractory to conventional medical therapy, chronic stable (radiographic) OA with profound worsening of symptoms, OA with predominate "mechanical" symptoms, and OA with unexpected synovial fluid characteristics. Future use of needle arthroscopy in knee OA could serve to define the intraarticular correlates of pain in OA, to identify specific subgroups of knee OA upon which prospective randomized testing of arthroscopic surgical interventions could be conducted, and to quantitatively assess the effects of new treatment modalities on articular cartilage and other intraarticular structures.