AIM 2: The second aim will study the use of US in imaging the placement of IAS and response to this therapy in 20 subjects receiving IAS for treatment of active arthritis in large and medium joints. Patients less than 21 years old with a diagnosis of JIA per ILAR classification receiving IAS injections of the knee, wrist, elbow, or ankle as part of their standard medical care will be eligible. Non-eligible patients include subjects with a non-inflammatory diagnosis, such as mechanical joint disease, or a large joint effusion requiring additional therapeutic procedures, such as arthrocentesis. Informed consent and assent for children over 7 will be obtained. The targeted joint will be scored by a rheumatologist other than the PI using the Clinical Severity Score described above. Sedation may be provided per routine for joint injection. Routine process for joint injection will be followed. The pediatric rheumatologist performing the injection will use standard external clinical landmarks and palpation to identify the appropriate injection site. Triamcinolone hexacetonide with 1% unbuffered lidocaine will then be shaken to allow the introduction of air per GAS-graphy technique as described by Koski et al. and injected into the targeted joint. The PI, who will not perform any injections in this study, will obtain US imaging just prior and immediately following the joint injection. The rheumatologist performing the injection will be masked to US images. Each image will be obtained and recorded using EULAR specifications, saved under a subject code on the US machine hard drive, and scored by the PI and the consulting rheumatologist using the US Severity Score described above. For the second aim, I will also determine the presence or absence of steroid within the target joint capsule. The physician performing the physical exam, the subject, and the subject's guardian(s) will be masked regarding US results, including location of steroid within or around the joint space and sonographic recordings of joint pathology. Patient outcomes will be determined at 1 week, 4-6 weeks and 3-6 months by the Clinical Severity Score and by US using the US Severity Score described and developed in Aim 1. The clinician performing the physical exam and the sonographer will be masked to each other's scores.