Ultrasound-Guided Arthrocentesis

Excerpt

Acute monoarticular arthropathies are a common source for Emergency Department (ED) visits, with septic arthritis alone having an annual incidence of 10 per 100,000 patients in the United States. In the ED, the most critical of these arthropathies to diagnose and treat is septic arthritis. While lab values and vital signs may assist with the diagnosis of septic arthritis, the gold standard test is done via analysis of the synovial fluid following arthrocentesis. If the synovial fluid sample is concerning for septic arthritis, the patient should then be started on intravenous antibiotics, and orthopedics should be immediately consulted.

Arthrocentesis is a common procedure that is frequently performed in the ED as it has both diagnostic and therapeutic value. Traditionally, arthrocentesis was performed blindly using critical landmarks to aspirate effusions for comfort or diagnosis. However, using a landmark-based approach has some limitations due to variance in anatomy and effusion, with success rates ranging from 61 to 78% depending on the joint that is being assessed. Ultrasonography has been adopted as an adjunct for many emergent and urgent procedures, including arthrocentesis, as it adds some distinct advantages over a blind landmark-based approach.

The primary advantage of ultrasound (US) guided arthrocentesis offers the user direct visualization of the effusion. By visualizing the effusion and using an in-plane or out-of-plane needle technique, the clinician can perform arthrocentesis with greater accuracy and fewer attempts. Additionally, US-guided arthrocentesis can detect small effusions that potentially would not be assessed using a landmark-based technique due to an inability to aspirate small volume effusions. It has been found that the US can detect effusions as small as 4 ml of fluid in the joint space. Finally, studies have demonstrated that the US-guided arthrocentesis techniques allow the clinician to aspirate more volume and decrease a patient’s perceived pain scores during the procedure. Critically, the adoption of the US as an adjunct to arthrocentesis has also been shown to lead to quicker time to diagnosis and management of septic arthritis.

While perhaps intuitive, many of the aforementioned advantages make US-guided arthrocentesis relevant for managing arthropathies in the pediatric population. Pediatric patients will inherently have smaller joints, smaller joint effusion sizes, and potentially be less able to tolerate the discomfort during the procedure. Effusion detection with the US has been shown to have a diagnostic sensitivity and specificity of 80 and 90%, respectively. The overall sensitivity and specificity of US for the diagnosis of effusion in the pediatric population must be determined. Still, the assessment of the hip demonstrates the potential for US application in the assessment of pediatric arthropathy. Beyond diagnosis, multiple case reports have shown that US-guided arthrocentesis can be safely performed in the pediatric hip and knee.

While the literature is more robust at this time for the adult population, in general, US-guided arthrocentesis techniques may be used at most major joints of the body. Discussed below are common US-guided arthrocentesis techniques for all of the major joints of the upper and lower extremity. Some of the described techniques will have technical variations in the literature (i.e., in-plane vs. the out-of-plane US-guided arthrocentesis). This article will discuss the authors’ preferred approach, but additional techniques are in the literature. Finally, while this article focuses on using the US as an adjunct for arthrocentesis, many of these same techniques may be utilized for intra-articular joint injections in the appropriate clinical setting.