Benefit of in-joint anesthesia queried in canine arthroscopy

By Sarah Guy

Measurements of gait and lameness after arthroscopy in dogs show no evidence that either intra-articular (IA) bupivacaine or morphine provide an analgesic effect in the immediate postoperative period, despite bupivacaine having some effect on pain, report researchers.

The findings indicate that peak vertical force (PVF) divided by body weight, the PVF measured in the contralateral limb, and the PVF divided by the time taken to unload the limb, all significantly decrease over time following surgery regardless of treatment.

The results are contrary to existing data that show IA bupivacaine is a superior analgesia to morphine in the postoperative period after knee arthroscopy, say Matthew Gurney (Northwest Surgeons, Cheshire, UK) and colleagues.

However, the team does report that "pain scores were significantly higher at both time points in the no treatment group compared to baseline and in morphine-treated dogs at the 4-hour time point compared to baseline pain scores." And while the overall changes in pain score were low, "any increase in an individual's pain should be viewed as clinically important."

Indeed, pain scores did not increase significantly in the bupivacaine group, supporting an analgesic effect with this drug, they remark in the Journal of Small Animal Practice.

A total of 29 dogs with unilateral thoracic limb lameness underwent elbow arthroscopy. Ten dogs were randomly assigned to treatment with IA bupivacaine, 10 with IA morphine, while nine received no treatment.

Gurney and co-workers report a mean PVF index of 7.7 N/kg in the dogs' lame limbs, and a mean 10.5 N/kg in their contralateral limbs before surgery, which decreased (nonsignificantly) to 6.1, 6.6, and 6.4 N/kg in the no treatment, bupivacaine, and morphine groups, respectively, by 24 hours postsurgery.

The rate of limb unloading - measured using kinematic and force plate analysis while the dogs were moving at trotting speed on a runway - decreased significantly after surgery, from a respective mean of 1915, 1745, and 1644 N/s in the no treatment, bupivacaine, and morphine groups at 0 hours postsurgery to 1318, 1591, 1125 N/s in those groups at 24 hours postsurgery.

In contrast, while limb loading measurements showed a trend toward decreasing over time, the difference was not significant, suggesting that "the unloading phase of the gait cycle is more painful and is a parameter worthy of further work in future studies," comment Gurney et al.

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