Arthrocentesis is a procedure performed to aspirate synovial fluid from a joint cavity. It is used both diagnostically and therapeutically. While arthrocentesis is deemed to be a minor surgical procedure, there is always the potential to injure blood vessels, nerves, and tendons. Thus, the procedure should only be performed by healthcare workers who do have knowledge of the anatomy of joints. To minimize the risk of injury, the extensor surface of the joint should be in extension with minimal flexion.
Anatomical considerations include:
Therapeutic: Large and painful joint effusions can be aspirated for pain relief. Also, can be used for intra-articular injection of certain medications (primarily steroids). Evaluate response to treatment.
Diagnostic: Synovial fluid analysis can provide physicians with an unequivocal etiology of acute arthritis, specifically to differentiate between septic arthritis and an inflammatory cause of bloody mono-arthritis.
The procedure can be done in the clinic or the minor operating room.
No absolute contraindications. Relative contraindications include overlying cellulitis (potential intra-articular seeding of bacteria), coagulopathy/bleeding disorders, joint prosthesis (preferably performed by orthopedic surgery), acute fracture, adjacent osteomyelitis, and uncooperative patient.
Skin cleansing solution (betadine, chlorhexidine, etc.), skin marking pen, sterile gloves, sterile gauze, 1% lidocaine, 10 cc syringe, 30cc to 60 cc syringe, 18 g and 27 g needle, specimen tubes (cell count, gram stain, and culture, and crystal analysis).
The procedure may usually be performed without an assistant. If the patient is anxious or special circumstances are predicted, an existent will make it much easier to perform the procedure.
Patients who are anxious, in pain, or unable to cooperate with the procedure might require an assistant and procedural sedation. It is highly recommended that some type of local anesthesia be utilized. For most surgeons, lidocaine 1% is used to numb the skin. It is important to avoid deep injections with the local anesthetic because there is a risk that it may alter the synovial fluid analysis.
The clinician or medical care professional must obtain informed consent. A timeout should be performed to confirm patient and correct joint. The most important step is having the patient lay in a comfortable position with the affected knee fully extended or flexed at 15 to 20 degrees with a towel roll under the knee. This position helps to facilitate procedure success by ensuring quadriceps muscle relaxation. The clinician should then locate the patella. The clinician may mark it with a marking pen.
The knee is the largest synovial cavity in the body and can easily be accessed from either the medial or lateral aspect, and superior, inferior at the midpoint of the patella.
Sterilize area and drape in typical sterile fashion.
Choose the approach, then use a small syringe and small bore needle, draw up lidocaine and anesthetize superficial skin and then deeper tissue in the projected trajectory of joint aspiration to anesthetize the track.
“Milking” or compressing the joint can help facilitate aspiration of fluid.
Transfer fluid to specimen tubes. Remove the needle from joint and place bandage over the insertion site.
If the needle placement is poor or if the synovium is thickened, it may result in a dry tap.
Hemarthrosis can occur if a large needle damages a blood vessel when multiple attempts are made. In most cases, the hemarthrosis presents within a few hours after the procedure. It is often associated with pain, stiffness, and swelling of the joint. The majority of hemarthrosis are self-limited and resolve within a few weeks. If the patient has a coagulopathy, it may need to be corrected, and consultation with a hematologist may be helpful.
If arthrocentesis is performed through an infected area of skin to look for a septic joint, the patient must be given antibiotics promptly. If the fluid is frankly purulent, admission is recommended.
Arthrocentesis is performed for identification of the etiology or pain relief, injection of medications, or effusion drainage. To avoid complications, the clinician should be familiar with the anatomy. The risk of complications can be minimized by using an appropriate technique.
Crystal analysis is usually an important result of a successful knee aspiration. Most commonly, the clinician differentiates gout (negatively birefringent urate crystals), pseudogout (weakly positive birefringent crystals), and an infectious process.
Synovial fluid associated with septic or infectious joint effusion is as follows:
The knee joint is often aspirated as an outpatient. However, in most cases, the primary care provider or nurse practitioner should always consult with the orthopedic surgeon on management because there are many causes of a swollen knee. To avoid complications, the knee should only be aspirated by healthcare workers familiar with the anatomy.