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A knee arthrocentesis is a minor surgical procedure to aspirate synovial fluid from the knee joint. The procedure has diagnostic and therapeutic uses as it drains fluid and diagnoses the etiology of the underlying knee pathology. During arthrocentesis, blood vessels, nerves, and tendons can always be injured. Clinicians with extensive knowledge of the knee's anatomy, training, and credentialing should perform the procedure. Throughout this activity, participants explore the diagnostic and therapeutic aspects of knee arthrocentesis while also addressing potential risks associated with this minor surgical intervention, such as hazards to blood vessels, nerves, and tendons. By the end of the course, clinicians have a better understanding of the indications, contraindications, and potential complications related to knee arthrocentesis, enabling them to make informed decisions in clinical practice. Beyond mastering procedural techniques, participants also receive comprehensive guidance on the medical management of synovial fluid analysis, facilitating the interpretation of commonly ordered lab studies. Furthermore, this course emphasizes the importance of an interprofessional team approach in enhancing competence and patient care. Collaborating with colleagues from various specialties ensures a holistic approach to patient management during in-office visits, emergency department encounters, or operating room procedures. Objectives: Identify the different techniques commonly used when performing a knee arthrocentesis. Determine the indications for knee arthrocentesis. Differentiate the various complications that can arise after performing a knee arthrocentesis. Highlight the importance of collaborative teamwork and coordinated care among interprofessional team members to perform knee arthrocentesis, contributing to improved clinical care. Access free multiple choice questions on this topic.

A knee arthrocentesis is a minor surgical procedure to aspirate synovial fluid from the knee joint. The procedure has diagnostic and therapeutic uses as it drains fluid and diagnoses the etiology of the underlying knee pathology. During arthrocentesis, blood vessels, nerves, and tendons can always be injured. Clinicians with extensive knowledge of the knee's anatomy, training, and credentialing should perform the procedure. The knee is the largest synovial cavity in the body and is easily accessible from either the medial or lateral aspect and superior or inferior to the midpoint of the patella. The patient can be supine or sitting, but fluid is more easily aspirated in the supine position. To minimize the risk of injury, the joint's surface should be in extension with minimal (20°) flexion under ultrasound guidance, as this approach improves aspiration volume, accuracy rates, and pain scores.[1][2][3][4]

Complications can arise from local trauma, including damage to nearby structures, pain, infection, and reaccumulation of effusion. If the needle placement is poor or the synovium is thickened, it may result in a dry tap and a need to redirect the needle or change the approach. When the needle's angle is changed during the procedure, the needle is withdrawn to the skin surface. Changing the angle in the deeper soft tissue or knee joint can cause the needle bevel to tear through soft tissue and adjacent structures, causing lacerated tissue and bleeding.[10][11] Hemarthrosis can occur if a large needle damages a blood vessel on multiple attempts. In most cases, hemarthrosis presents a few hours after the procedure; this is often associated with joint pain, stiffness, and swelling. The majority of hemarthrosis is self-limited and resolves within a few weeks. Results from a study evaluating the risk of complications in patients taking Dabigatran showed an incidence of hemarthrosis of less than 1%, and other recommendations suggest that anticoagulation does not need to be discontinued. [12][13][14] Another uncommon complication is an arterioarticular fistula. If the patient has a coagulopathy, it may need to be corrected before the procedure is performed, and consultation with a hematologist is warranted. However, under certain circumstances, like the evaluation of a potential septic arthritis, the procedure might need to be performed regardless of anticoagulant use status. The hemarthrosis risk is still low under those circumstances. If an arthrocentesis is performed through an infected skin area to look for a septic joint, prescribing antibiotics is the standard of care. If fear of an infected joint is evidenced, the cost of treatment delay is greater than joint aspiration through overlying cellulitis.[15] In the absence of overlying cellulitis, the risk of inoculation still exists. Although rare, reported rates are around 1 in 2034 to 1 in 3500 procedures.[16]

A knee arthrocentesis is often an outpatient procedure in the emergency department or operating room. However, in most cases, a primary care clinician, physician assistant, or nurse practitioner should consult the orthopedic surgeon. To avoid complications, only clinicians familiar with the indications, anatomy, and understanding of potential complications should aspirate the knee.