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1060 Arthrocentesis

• ± Red top tube, Culturette, or culture • Stifle
medium–containing vial ○ Assistant steadies the joint in a neutral
VetBooks.ir Anticipated Time ○ The joint is entered from the front to
position.
• ± Purple top tube for extra joint fluid
either medial or lateral side of the patel-
15-30 minutes
lar tendon, directing the needle caudally
toward the center of the tibial plateau.
Preparation: Important • Place needle on syringe while maintaining
Checkpoints sterility; the glove wrapper can be used to
• Have patient fasted for sedation set open syringes on. Aspirate and expel a
• Choose joints to sample bit of air to break the seal on the syringe
○ For polyarthritis, typically sample 2-4 joints. before performing the tap.
○ Carpi, tarsi, and stifles are most accessible. • Again palpate the landmarks on the asepti- A
○ Other joints sampled if there is a specific cally prepared joint.
indication to do so (e.g., if a single joint • Determine the angle of the joint space, and
is effusive/painful, it should be sampled) insert the needle, trying to avoid hitting the
○ Joint swelling often feels “puffy”; these cartilage. Most of the time when you enter
spots are best to tap. the joint space, you can tell there is a rubbery
• Label slide and place on tray for quick access; feel, and you do not hit a hard surface (bone).
include joint name/side (e.g., right carpus) The needle goes in deeper when in the space
and patient ID on slide label. than if over bone.
• If you do hit hard bone, gently pull the
Possible Complications and needle back a tiny bit, and move slightly, B
Common Errors to Avoid tapping along the way to reach the joint space
• Inability to retrieve fluid: effusive joints are when the bone ends (this is only millimeters).
best. May not be able to get sample from • When the needle seems to have gone deep
every joint to enter the joint space, gently aspirate on
• Blood contamination of sample: release the syringe without moving the needle
negative pressure before needle withdrawal. (movement causes bleeding).
If gross blood contamination seen, sample • If you do not get fluid right away, be patient,
another joint and wait at least 15-30 seconds before letting
• Hemarthrosis (rare with precautions): off the negative pressure. Joint fluid can be
coagulopathy or < 40,000 platelets are viscous, and especially when using a 25-gauge C
contraindications. needle, it can take a moment to produce fluid.
• Introduction of bacteria (rare): aseptic • For cytology, only a very tiny volume is ARTHROCENTESIS Schematic representation of
technique is crucial required, and you can stop after you see recommended sites for arthrocentesis in the dog and
• Torn joint capsule (rare): sedation to prevent fluid in the needle hub. Culture takes only cat. A, Carpus: partially flex joint. Palpate and enter
movement a bit more volume. Stop when you have the craniomedial aspect of carpometacarpal or radiocarpal
space. B, Hock: cranial approach. Palpate space
amount of fluid needed to reduce the risk
Procedure of blood contamination. between tibia and tibiotarsal bone on craniolateral
surface of hock; insert needle in shallow, palpable
• While waiting for sedation to take effect, • Release negative pressure, and pull the needle space. C, Hock: lateral approach. Partially flex joint,
shave target joints, and perform preliminary straight out as quickly as possible. If you and insert needle under (distal to) lateral malleolus
skin cleaning. aspirate while removing the needle, blood of fibula. (Reprinted with permission from Nelson RW,
• Don sterile gloves while an assistant performs contamination is likely. et al: Small animal internal medicine, ed 4, St. Louis,
aseptic skin prep on the joint. Keep glove • If the only fluid is in the needle hub, remove 2009, Mosby, pp 1122-1124.)
wrapper clean to use as a sterile field. the needle from the syringe, and fill the
• Carpus syringe with air. Reattach to the needle with • Submit samples for cytologic assay and any
○ Assistant should flex the carpus fully. sample in hub. other planned testing.
○ Palpate the cranial surface of the joint • Expel the contents of the needle, bevel side
for a natural depression on the cranio- facing down, onto the microscope slides (a Alternatives and Their
medial aspect of the carpometacarpal or very tiny drop per slide is adequate). Use a Relative Merits
radiocarpal space, with the tendons of the clean slide to make a gentle smear. • Joint radiographs: demonstrates bone erosion
extensor carpi radialis and common digital • If culture is required, a drop of fluid can be if present
extensor on either side. Depending on the placed on a Culturette, or fluid can be added • Bone scan: can identify which joints are
degree of joint effusion, this very small to culture media. Large volumes (>0.1 mL) inflamed/diseased
space (1-4 mm, depending on patient size) are occasionally obtained from large, effusive • Synovial biopsy: invasive technique useful
may be pushed out rather than a divot in. joints. Extra volume can be placed in a red top if joint capsule thickened or deformed
• Tarsus (hock) tube for culture submission or other analysis. • Arthroscopy: invasive technique to explore
○ Assistant steadies the joint in a somewhat • The same procedure is repeated on another diseased joint, usually reserved for biopsy
flexed position. 1-3 joints, depending on clinical indication. or planned therapeutic procedure
○ Medial and lateral access to the tarsal joint
is available from the caudal aspect of the Postprocedure Pearls
joint. • Assess gross appearance of joint fluid (clear Be patient during aspiration because joint fluid
○ The lateral and medial malleoli of the distal or turbid, color, blood contamination) is viscous and can be slow in coming.
tibia are palpated for a depression that • Assess viscosity while fluid is expelled from
occurs medial and caudal to each one. the needle or by placing a drop on one slide, AUTHOR: Matthew Haight, CVT
EDITORS: Leah A. Cohn, DVM, PhD, DACVIM;
The depression is more or less sunken, covering with another, and separating the Mark S. Thompson, DVM, DABVP
depending on degree of effusion. two. Normal synovial fluid is thick and sticky.
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