How To Perform Ultrasound-Guided Arthrocentesis and Injection of the Equine Scapulohumeral (Shoulder) Joint

The equine shoulder joint can be a significant and severe source of lameness in horses. The proximal location and complex anatomy of the surrounding area often make arthrocentesis of this joint a challenge to the practitioner. Use of an ultrasound-guided injection technique can greatly facilitate the ease and accuracy of shoulder joint injection in the horse. Assuring the correct placement of anesthetic or therapeutic medications in the joint will allow for a confident and accurate assessment of the response to diagnostic analgesia and intra-articular medications. Authors’ addresses: University of Georgia, Veterinary Biosciences and Diagnostic Imaging, 501 DW Brooks Drive, Athens, GA 30602 (Selberg); and 2716 Landmark School Road, The Plains, VA 20198 (Allen, Norvall, Johns); e-mail: ktselberg@gmail.com.

1. Introduction

The shoulder or scapulohumeral joint is a ball and socket joint with the chief movement of extension and flexion. It is mainly stabilized by four muscles and their tendinous attachments: the supraspinatus, infraspinatus, subscapularis, and teres minor. Unlike joints with similar movements, there are no collateral ligaments. Instead, there are relatively small glenohumeral ligaments. Although lameness related to the shoulder joint in horses is less common than that associated with the distal limb, when present it often causes significant lameness and decreased performance.^1,2 A thorough understanding of the pertinent clinical anatomy and the available techniques for arthrocentesis of the shoulder joint is necessary when performing diagnostic analgesia or administering intra-articular medications. In addition to radiography, ultrasound examination of the shoulder joint provides additional important diagnostic information. It also can help facilitate safe and accurate arthrocentesis or injection of the joint. 

Both traditional (blind) and ultrasound-guided techniques for shoulder joint injection have been described.^3,4 A recent comparison of ultrasound-guided versus non-guided attempts at intra-articular shoulder injection revealed that blind techniques resulted in a 50% extra-articular injection rate and more attempts at needle repositioning for successful injection.⁵ Practitioners frequently use aspiration of joint fluid as criteria for confirmation of correct needle placement. However, in diseased joints synovial proliferation and joint capsule fibrosis may obstruct the bore of the needle, thereby precluding aspiration of synovial fluid. Redirecting the needle multiple times to aspirate fluid may lead to fenes,tration of the joint capsule and extravasation of the local anesthesia or medication. Current techniques for ultrasound-guided injection of the shoulder describe needle placement in the joint in a transverse plane.⁴ However, the articular margins of joints are also effectively visualized in the sagittal (para) plane (longitudinal axis), perpendicular to the joint. Ultrasound-guided needle placement in the equine shoulder is accurate, safe, and easily performed. Assuring correct placement of anesthetic or therapeutic medications in the joint will allow for confident and accurate assessment of the response to diagnostic analgesia and administration of intra- articular medications. This paper and presentation will demonstrate how to use ultrasound guidance to accurately and safely perform intra-articular injection of the shoulder joint in horses.

2. Materials and Methods

Ultrasonographic evaluation of the shoulder should be performed before sterile preparation of the injection site to accurately identify joint margins and suitable access sites to the joint. Horses may be lightly sedated with xylazine HCl (75–100 mg, IV) for the procedure with minimal impact on subsequent lameness evaluation.⁶ Optimal visualization of the joint is achieved by clipping the hair over the entire shoulder region with a no. 40 clipper blade. The skin should be washed and ultrasound gel applied. The joint should be examined at the highest frequency possible (7–12 MHz) at a scanning depth of 4 to 6 cm. A linear or curvilinear ultrasound transducer will provide optimal images, allowing ultrasound guidance of needle penetration into the joint.

The biceps brachii tendon is often the most easily identifiable structure upon initial ultrasound examination. To visualize the tendon, the ultrasound transducer is placed on the point of the shoulder in the transverse plane. As the biceps tendon passes over the humerus, through the bicipital groove, it is bilobed. The lateral aspect of the biceps tendon is bordered by the greater tubercle of the humerus (Fig. 1). The greater tubercle consists of the cranial and caudal parts (Fig. 2). The cranial part forms the lateral border of the bicipital groove and serves as an attachment for the lateral branch of the supraspinatus muscle. The caudal part serves as an attachment for the infraspinatus muscle. The lateral aspect of the caudal portion of the tubercle is covered in cartilage, over which the tendon of the infraspinatus passes. Subjacent to the infraspinatus tendon lies a small bursa, which is often not seen during examination when pressure is applied to the ultrasound transducer. From the cranial greater tubercle, the joint is visualized by rotating the transducer 90° and moving slightly caudally and proximally, between the cranial and caudal portions of the greater tubercle. The joint margin is most easily visualized in the (para) sagittal plane or long axis of the limb. Along the cranial aspect of the scapulohumeral joint, there is a synovial recess to which a needle can be easily directed. This is the synovial recess, which is preferred by the author; however, the joint can be accessed from the lateral and caudal aspects as well.
 

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