Page 136 - Canine Lameness

108 8 Diagnostic Joint Anesthesia

8.4 Intra-articular Anesthetic Instillation

The basic principles (including patient positing and preparation) used with arthrocentesis (Chapter 7)
apply when using DJA. However, given the possibility of performing injections into normal joints,
great attention to detail is required to avoid iatrogenic trauma to the joint. Ultrasound‐guided injec-
tions may help improve the accuracy of injections and reduce trauma to the cartilage. A technique
description for canine ultrasound‐guided injection of the coxofemoral joint is available (Bergamino
et al. 2015). Ultrasound guidance allows to place the needle more superficially in the joint, thereby
causing less trauma. Furthermore, confirmation of placement of the anesthetic into the joint can be
confirmed by observing distention of the joint capsule. If ultrasound guidance is not available, prior
to instilling the anesthetic agent, joint fluid should be aspirated to confirm the location of the needle.
In the case that joint fluid is unable to be aspirated, the needle should be slightly withdrawn, redi-
rected, and aspiration attempted again. If joint fluid still cannot be aspirated, then careful instillation
of the anesthetic agent can be performed. This should be done gradually and with great care to
ensure that no resistance is met during instillation. If the needle is correctly located in the joint space,
regardless of the aspiration of joint fluid, there should be no resistance met upon instillation of the
anesthetic agent. Following instillation of the anesthetic agent, the joint flexion and extension should
be performed to distribute the anesthetic throughout the joint (Van Vynckt et al. 2012a).
Because it is widely available and has a preferred safety profile for intra‐articular use, 2% mepiv-
acaine (i.e. 20 mg/ml Carbocaine®) is the recommended anesthetic agent for DJA in dogs. The use
of lidocaine or bupivacaine for DJA is not recommended at this time as they may cause more local
irritation when compared to mepivacaine (Van Vynckt et al. 2010). The recommended dose is
1.5 mg/kg instilled into a single joint (approximately 1–4 ml). A total dose of 5 mg/kg per dog and a
total volume of 4 ml should not be exceeded (Van Vynckt et al. 2010, 2012a).

8.5 Lameness Evaluation and Interpreting the Effect
of Diagnostic Joint Anesthesia

The localization of lameness to a specific joint with DJA is based on a change in lameness following
instillation of the anesthetic. A positive response is when lameness improves, and a negative response
is when the lameness is unchanged or worsens. Various grading scales are available, as described in
Chapter 1. Currently available research used an 11‐point numerical rating scale (with 0 = no lame-
ness and 10 = non‐weight‐bearing) and a change of 2 scores was considered a positive response. As
such, an approximately 20% improvement in degree of lameness should be used if other scoring
systems are used. Ideally, objective gait analysis (Chapter 2) is used before and after DJA.
Lameness evaluation is recommended to begin seven minutes after the reversal agent is admin-
istered if an α₂‐adrenergic receptor agonist is administered (Protocol A) for sedation (Figure 8.1).
If a neuroleptanalgesia with an opioid is administered (Protocol B), then it is recommended that
evaluation begins two minutes after the anesthetic agent is instilled. Regardless of sedation proto-
col, dogs should be evaluated at frequent intervals. The dogs should be walked continuously for the
first five minutes after the initial evaluation. If an improvement in lameness is not seen during that
time period, then repeat evaluations should be performed approximately every 5 minutes for a
maximum of 30 minutes after injection (Van Vynckt et al. 2011, 2012a). An improvement in lame-
ness at any time point during those 30 minutes is considered a positive response. The use of video
recordings may aid in lameness evaluation by providing an ability to compare time points as well
as providing material for secondary observers, if needed.