Modern patient management in rheumatology: interventional musculoskeletal ultrasonography

Abstract

509 performed in an X-ray department and involves radiation exposure. Ultrasound allows accurate and reproducible identification of the anterior part of hip joint and periarticular tissues. Musculoskeletal ultrasonography (MSUS) can detect small or deeply located effusions not found on clinical examination. Cadaveric studies show that ultrasound can detect effusions of as little as 1 ml of fluid in hip joints and 2 ml of fluid in the ankle. MSUS can also provide information on the precise location, structure and extent of palpable effusions in addition to delineating surrounding tissues such as skin, vessels and nerves. This allows the safest route of injection to be identified and provides useful information on the depth to which the needle must be inserted. Thus MSUS improves detection and aspiration of joint effusions. Intraarticular effusion is a recognized classification criteria for knee—but not hip—OA. However, hip effusion has been demonstrated by ultrasonography in OA. Effusions are usually differentiated from solid structures, as they are anechoic though they can appear hypoechoic if they contain reflective particles. MSUS may also detect intraarticular and intrabursal septae or complex multiloculated structures but cannot differentiate between inflammatory or non-inflammatory effusions, septic arthritis or haemarthrosis. Synovial proliferation also appears hypoechoic, though fluid can be confirmed by compression and/or displacement with transducer pressure. Newer techniques for differentiating between solid structures and effusions are in development, particularly in inducing and detecting acoustic streaming in breast cysts using real-time ultrasonography. Interventional ultrasound is a reliable and safe technique. The indications and contraindications for ultrasound guided joint and soft tissue injections are essentially the same as for unguided injection though most operators also use a combination of antiseptic liquids, sterile gels, sterile gloves, sheaths, condoms, or sterile latex and nonlatex materials to cover the probe and maintain a sterile field. Some operators do not use a sterile covering on the probe, arguing the transducer does not come in close contact with the needle. Future developments in ultrasound technology such as cableless transducers and combined ultrasound injection probes will make aspiration and injection of the joint even easier. Aspiration of joint and bursal effusion and intraarticular and soft tissue injection are performed routinely as diagnostic and therapeutic procedures in clinical rheumatology. Only a few studies have examined the accuracy of intraarticular and soft tissue injection. These studies demonstrate a surprisingly low rate of accurate needle placement. Using an admixture of steroid and radiological contrast material, Eustace et al. found that only 37% of subacromial and glenohumeral joint injections were accurately placed while Jones et al. could only confirm intraarticular needle placement in 56 (52%) out of 108 joint injections. In both studies the accuracy of injection of the two most commonly injected large joints (shoulder and knee) was poor. In de Quervain’s tenosynovitis, the larger, more superficial abductor pollicis longus tendon sheath was accurately injected in 84% of cases while the smaller, deeper extensor pollicis brevis tendon sheath was accurately injected in only 32% of cases. In all three studies, accurately placed injections were associated with a superior clinical outcome. Confirmation of accurate needle placement is usually obtained by free aspiration of synovial fluid. However, a ‘dry tap’ usually occurs in non-inflammatory joint disease such as osteoarthritis (OA), soft tissue injection, smaller joints or when a small effusion is present. Diagnostic aspiration may also be indicated in the absence of palpable effusion when septic or crystal arthritis is suspected. With the advent of the use of intraarticular sodium hyaluronate in the management of knee OA, rheumatologists are required to accurately inject into an increasing number of ‘dry joints’, leading to a need for alternative strategies to confirm needle placement. A thorough knowledge of the surface anatomy of joints can be applied to improve the accuracy of joint injection. The knee can be reliably accessed from many different approaches. However other less superficial joints—such as the hip—are also affected by OA, and imaging may be required to accurately access the joint space. Fluoroscopic guidance is recommended for hip injection, but must be