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96 7 Arthrocentesis Technique

7.2 Risks and Contraindications

Generally, there is little risk with appropriately performed arthrocentesis; however, iatrogenic
damage to the joint and joint sepsis are possible complications. The overall incidence of joint sepsis
after arthrocentesis and intra‐articular administration of medications in horses has been reported
to be less than 0.1% or 1 case per 1279 injections (Steel et al. 2013), but this has not been studied in
dogs. To avoid the risk of contamination, arthrocentesis should not be performed when any
evidence of infection/pyoderma is present in the area. Additionally, arthrocentesis should be
performed under sterile conditions and with appropriate restraint/sedation.

7.3 Restraint

We recommend that sedation be used to ensure that the best synovial fluid samples are obtained in
a pain‐free manner that reduces patient stress during the procedure. There are anecdotal reports of
performing canine joint taps without any or with only mild sedation using topical lidocaine–
prilocaine cream (EMLA); however, these creams require 30–60 minutes of contact time (van
Oostrom and Knowles 2018). Although joint taps are commonly performed without sedation in
horses, canine joints are much smaller, and sedation helps reduce iatrogenic damage to the joint
structures. Clinicians should choose a sedation method that they are comfortable with, provide
adequate analgesia for the procedure, and minimize patient motion to ensure atraumatic aspira-
tion of joint fluid. Please refer to Chapter 8 for specific sedation recommendation when joint fluid
aspiration is combined with diagnostic joint anesthesia (e.g. joint block).

7.4 Site Preparation

All arthrocentesis sites should undergo a standard aseptic preparation process prior to acquiring a syno-
vial sample. The goal of the aseptic skin preparation is to reduce gross contamination as well as the
transient bacterial flora on the skin. Hair should be removed (clipped) from an area of approximately
5 cm × 5 cm (for a medium‐sized dog) prior to cleaning and aseptic preparation. The size of the prepared
site may vary by joint, size of dog, and/or clinician preference. The removal of hair helps reduce tissue
contamination during arthrocentesis in horses; however, Wahl et al. (2012) found that angled insertion
of the needle (at 45° to the skin) through unclipped hair results in the least amount of hair (not tissue)
contamination. Additionally, the authors of this study suggested that hair debris is more likely to con-
tain bacteria and cause sepsis and, therefore, recommended that (for horses) hair clipping may not be
beneficial. However, since this has not yet been studied in dogs, when performing arthrocentesis on
dogs, we recommend clipping hair prior to cleaning and aseptically preparing the insertion site.

7.5 Equipment

The equipment needed for arthrocentesis is readily available in most clinical environments. Sterile
disposable syringes and hypodermic needles of varying sizes will be needed along with sterile
gloves, glass slides for evaluation, culture medium (ideally pediatric blood culture flasks), hair
clippers, and sterile preparation materials. General recommendations are listed in Table 7.1.
When selecting needles, clinicians should remember that joint fluid is viscous and smaller bore
needles (e.g. 25 g) can make aspiration difficult. However, larger gauge needles appear to be associ-
ated with an increased risk of contamination (Waxman et al. 2015). Therefore, needle size should