Are other diagnostic studies useful in the evaluation of chronic monoarticular arthritis?
• Arthroscopy: Arthroscopy allows direct visualization of many important articular structures and provides the opportunity for synovial biopsy in all large and some medium-sized joints. It is particularly useful for diagnosing internal derangement of the knee.
• Synovial biopsy: Microscopic evaluation with culture of synovial tissue is useful in the diagnosis of benign and malignant tumor, fungal and mycobacterial infection, and foreign-body synovitis.
• MRI of the joint: Useful in diagnosing avascular necrosis of bone, internal derangement of the knee, osteomyelitis, and destruction of periarticular bone.
• Universal primer: Synovial fluid can be tested for bacteria, fungi, and mycobacterial infections that cannot be grown in culture. The 16S rDNA sequence is a gene encoding small subunit ribosomal RNA. This gene contains conserved sequences of DNA common to microbial organisms as well as divergent sequences unique to each microbial species. When a small piece of this sequence is used as a primer in a polymerase chain reaction (PCR) assay, it acts as a universal primer for nonselective amplification of microbial DNA in the patient’s synovial fluid. Once the DNA has been amplified, the PCR product is then stained with ethidium bromide and visualized by electrophoresis on an agarose gel. If microbial DNA is identified, it can then be directly sequenced to identify the species. Bacterial, fungal, and mycobacterial organisms can be detected with this testing, but not viral organisms.