How to Perform Arthrocentesis of the Compartments of the Stifle of the Horse

1. Introduction

The stifle is the largest and the most complex of all the articulations of the horse and is composed of two joints, the femoropatellar and the femorotibial.1 The femorotibial joint is composed of two compartments, the lateral femorotibial and medial femorotibial. The femoropatellar joint is the most spacious of the three compartments. It communicates directly with the medial compartment of the femorotibial joint in about 65% of horses, but it seldom communicates directly with the lateral compartment.²  Because of the uncertainty of anatomical or functional communication between the compartments of the stifle^2–5  and because inflammation of these joints may result in obstruction of the anatomical communications,⁶  a common recommendation is that all three compartments be injected with local anesthetic solution to accurately evaluate response to intra-articular analgesia of the stifle during an evaluation for lameness.^3,6,7 

2. Materials and Methods

One technique of centesis of the femoropatellar joint is to insert a 1.5-inch (3.8-cm), 18- to 20-gauge needle between the middle and medial patellar ligaments or between the middle and lateral patellar ligaments, 1 to 1.5 inches (2.5 to 3.8 cm) proximal to the palpable proximal aspect of the tibial tuberosity. The needle is inserted parallel to the ground through the large fat pad between the patellar ligaments and joint capsule (Fig. 1). The procedure can be performed with the limb flexed or bearing weight,² but performing centesis with the limb flexed requires a longer (3.5-cm) needle and an assistant to hold the limb.⁷ With this technique, fluid can seldom be aspirated if the joint is not distended with fluid. The volume of local anesthetic solution recommended for injection varies from as little as 10 mL⁶ to as much as 100 mL.⁸
 

Another technique of centesis of the femoropatellar joint involves inserting the hypodermic needle into the lateral cul-de-sac of the joint.⁹ Using this technique, a 1.5-inch (3.8-cm), 18- to 20-gauge needle is inserted perpendicular to the long axis of the limb, approximately 2 inches (5 cm) proximal to the palpable lateral edge of the lateral tibial condyle, just caudal to the caudal edge of the palpable lateral patellar ligament (Fig. 2). The needle is inserted until its tip contacts bone and then withdrawn slightly.
 

[...]