Using Ultrasound Exam as an Aid to Document Clinical Findings

Take Home Message—Evaluating a horse’s musculoskeletal system requires the equine practitioner to go through a series of tests which aim to document an anatomical region as the source of pain. Many imaging methods exist, but the ultrasonography exam is very dynamic and may allow the practitioner to see if clinical findings and lesions are active or recent.

I. Introduction

Many imaging techniques exist for horses such as radiography, ultrasonography, thermography, CT scanner, bone scan and MRI. MRI is the gold standard; however, there are some less expensive and accurate techniques that allow us to identify a clinical lesion. The ultrasonography exam is an accurate technique to evaluate soft tissues.

II. Principles of the ultrasonographic exam

This is an imaging technique using a beam of ultrasound coming from and returning to a transducer (or probe). In the first years of practicing in orthopedics, this has been the way of evaluating any type of lump seen or palpated superficially regarding a potential musculoskeletal disease. Nowadays, this technique is widely used to evaluate pain in deeper structures, abnormal heat or pain in superficial structures such as flexor tendons, or to evaluate a positive response to an anesthetic local block. This technique became easier with increased knowledge of the anatomy and a good positioning of the probe to progressively assess soft tissues such as tendon, ligaments, capsule, and surfaces of bone or joints.

Structures Important to Document on a Clinical Exam

Many of these structures may look abnormal on this imaging method, so if the ultrasonography (U/S) is a “prolongation” of the practitioner’s hand, it has to be related to a source of pain to palpation or pressure, a response to a local block, and finally should be used to document a deep structure that has an abnormal motion or restriction of movement (example of the axial skeleton).

A Structure Painful upon Pressure or Palpation

Tendon, ligaments or muscles are the very first structures to be evaluated by U/S techniques regarding musculoskeletal issues in horses. As a clinician, the veterinarian would use the probe of their ultrasound system as a “prolongation” of their hand to see what they’re palpating. Thus, the practitioner would assess the type of thickening and zone of sensitiveness, in relation or not, to echogenic changes of the soft tissue. This is where the relevance of core lesions are detected that could not be evaluated by external palpation.
 

A Structure Responding to a Local Block

The best example is the local joint block responding positively with many potential structures locally involved such as cartilage surface, capsule, collateral ligament, and surrounding soft tissue.

Upon the clinical findings, the practitioner must differentiate the soft tissues and potential instability of a joint. Before blocking, it is useful to perform an U/S evaluation to determine if blocking the joint is safe. Again, signs of instability can be related to permanent synovitis and/or joint distension, especially if it appears as the horse exercises. Attention should first be given to the collateral ligaments which are the main stabilizing structures of many joints. Other soft tissue structures surrounding the joint should then be examined carefully before making a final diagnosis.

The upper scan on the right of Fig. 4 shows a transverse view of the dorsal capsule, where thickening can be seen more medially (left side of the picture).
 

The 2 scans on the lower right side of Fig 4 show a longitudinal view (left) which shows a remodeling of the collateral ligament with bone irregularity on proximal phalanx. The right view shows just a moderate thickening of the same ligament. These structures must be distinguished to determine if joint instability could be caused by a lesion.

The suspensory ligament is an important structure that may be inconsistently painful on palpation. Clinical evaluation of the suspensory ligament (palpation of the insertions, the body, or branches) can provide information if this is a cause of lameness. The branches are easily palpable, but the proximal insertion and first part of its body has become a major pattern in our everyday clinical evaluation. A local block will give us a clue about its clinical relevance. U/S imaging is a major tool in this scenario. For example, it is now offered as a crucial evaluation for horses with no local pain as part of a pre-purchase exam.
 

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