Arthrocentesis, or joint taps, is the collection of synovial fluid. It is commonly performed to diagnose or rule out conditions such as immune-mediated polyarthritis or IMPA, and so is an important procedure for the veterinary nurse to be aware of, to provide the best possible care to the patient throughout the procedure, and in the post-procedure period.

Today we’re looking at what arthrocentesis is, how it is performed, what you need for the procedure, and what we should consider in the recovery period. Ready to jump in? Let’s go…

When is arthrocentesis performed?

Joint taps are indicated in patients with joint disease of unknown cause, if there is pain on joint manipulation, if effusion is present within the joint, or if there is heat local to the joint. They may be performed in patients with pyrexia of unknown origin (in order to rule-out an IMPA causing the increase in temperature), and in patients with a suspected immune-mediated or infective/septic arthritis. Repeat centesis may be performed to monitor response to therapy.

Arthrocentesis is contraindicated in patients with coagulopathies.

What equipment is required?

Equipment required for arthrocentesis includes:

• Anaesthetic and monitoring equipment

• Clippers

• Chlorhexidine skin scrub solution

• Sterile chlorhexidine-in-alcohol or final scrub applicator

• 2-10ml syringes x 10

• 22-23g needles of appropriate length (normally 5/8” for smaller patients, and 1-1.5” for large patients) x 10

• Sterile gloves for clinician x 2 pairs

• Sterile fenestrated drape x 6 (or one per centesis site, if less joints are being sampled)

• EDTA blood tubes x 6 (or one per site) for cytology

• Microscope slides x 1 box; lay out 5-10 slides for each joint, pre-labelled with the joint and side being sampled.

• Slide holders x 6-10 (or 1-2 per site)

• Blood culture bottle or bacteriology swab for culture

• Pencil (for slide labelling)

• Permanent marker (for tube labelling)

• Hairdryer (if available - for drying slides)

As with bone marrow aspirates, having a separate nurse to assist the clinician, support the site and prepare samples is advised, in order to prevent disruptions in anaesthetic monitoring and maximise patient safety throughout the procedure.

How is arthrocentesis performed?

A number of joints are commonly sampled, particularly where diffuse disease is present (e.g. in IMPA patients). This is usually a combination of the carpus, elbow, stifle and/or tarsus on both the left and right sides.

1. A 5x5cm area over the needle insertion site is clipped and aseptically prepared, as for any other surgical procedure. It is useful to clip and scrub all sites being sampled on that side of the body before sampling begins; that way, a quick repeat and final scrub can be performed on each joint just before they are sampled, saving time.

2. The clinician drapes the site and the assistant supports the site as the needle is inserted into the sampling site. For each joint, the exact locations are:

   1. Carpus: the dorsal aspect of the limb/joint

   2. Tarsus: dorsolateral aspect of the limb/joint

   3. Stifle: the medial aspect of the joint/limb

   4. Elbow: the caudolateral aspect of the joint/limb

3.  Once synovial fluid has been collected, the nurse places a drop on each slide and creates synovial fluid smears. A drop of fluid should be placed either on a bacteriology swab, or in a blood culture bottle for bacterial culture; any remaining synovial fluid should then be placed in EDTA in case additional tests are required.

4. Synovial fluid is very viscous and takes time to dry. This can cause drying artefacts to occur on the slides – thoroughly air-drying the slides ASAP after preparation, or drying them carefully with a hairdryer can help minimise this. Ensure your samples are labelled in some way before moving on to the next joint; this is especially important where many joints are being sampled!

5. Repeat for all other joints on that side.

6. Turn the patient, clip and aseptically prepare any sites on the second side whilst the clinician re-gloves.

7. Repeat sample collection and preparation for all joints requiring sampling on the second side.

What are the potential complications?

Potential complications of arthrocentesis include joint infection, joint haemorrhage and iatrogenic damage to the cartilage within the joints.

What are the post-procedure nursing considerations?

Patients with immune-mediated polyarthritis, or other arthropathies, are often painful and in some cases reluctant or unable to move, due to joint pain and swelling. Regular pain assessment, administration of appropriate analgesia and recumbency care where necessary are vital areas of nursing care for these patients. Bedding should be soft and padded, using orthopaedic mattresses where available, to maximise their comfort in the clinic.

IMPA results in pyrexia in most cases. Unless their temperature reaches an excessive level (>40-40.5*C), they should not be cooled. This is because pyrexia is an increase in the body’s temperature set point, rather than a failure of the normal thermoregulatory mechanisms (like in hyperthermic patients).

Immune-mediated polyarthritis is treated with immunosuppressive medications; these patients should be barrier nursed, as these medications can cause bone marrow suppression and immunocompromise. As many of the medications have cytotoxic or teratogenic effects, staff members handling the patient, their medications or their excretions should wear appropriate PPE.

So that is a brief overview of arthrocentesis, what is involved, and the vital role of the medical nurse! Have you assisted with joint taps before, or seen them performed? Let me know your experiences below!

References:

1. Bexfield, N. and Lee, K. 2014. BSAVA Guide to Procedures in Small Animal Practice. 2nd Ed. Gloucester: BSAVA.

2. Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.

3. Specht, A and Guarino, A. 2019. Canine Immune-Mediated Polyarthritis: Meeting the Diagnostic and Therapeutic Challenges. Today’s Veterinary Practice, available from https://todaysveterinarypractice.com/canine-immune-mediated-polyarthritis-meeting-the-diagnostic-and-therapeutic-challenges/