Ultrasonography of the Back and Neck

Ultrasonography of the Back and Neck

Marcus Head

Ultrasonographic assessment of the back and neck has added significantly to our ability to clinically evaluate these areas and provides imaging of the axial skeleton which complements radiography and scintigraphy. It also has the advantage that, in the axial skeleton, ultrasonography can be accomplished with most if not all ultrasound machines, compared to scintigraphy and the majority of axial skeleton radiography which can only be accomplished in a hospital setting. Although ultrasound examination of the back is limited to the epaxial structures, ultrasonographic assessment is useful in a wide variety of investigations, from trauma to poor performance.


Reasons for performing ultrasound assessment of the back and neck are varied but the commonest indication in non-Thoroughbred practice is evaluation of reduced performance due to suspected back or neck pain. These investigations can be time-consuming and frustrating, but the use of ultrasonography enables a greater number of differential diagnoses to be considered. Lower motor nerve signs, such as muscle atrophy or abnormal “stringhalt-like”| gaits, which may be caused by lumbosacral nerve compression, can also be evaluated. In Thoroughbred racehorses, indications also include evaluation of stress fractures known to occur in the back.


Clipping is often necessary, although not in fine coated horses – a 5 cm wide strip extending from the withers to behind the tubera sacrale should be prepared. It should be widened over the caudal thoracic and lumbar regions to allow imaging of the facet joints.

A high-frequency linear probe is the most useful for superficial structures but imaging the facet joints requires a lower-frequency curvilinear or sector probe. Imaging can be difficult in patients with significant subcutaneous fat or thick skin.


The main areas that can be imaged are:

  • Supraspinous (SSpL) and interspinous ligaments along with the dorsal aspects of the spinous processes
  • Sacroiliac ligaments
  • Caudal thoracic and lumbar intervertebral (facet) joints
  • Epaxial musculature

Supraspinous and Interspinous Ligaments

The tough, fibrous SSpL connects the summits of the dorsal spinous processes and is easily visualized using a linear transducer. Its appearance is similar to other ligaments or tendons, with a striated fiber pattern evident when viewed longitudinally. The ligament lies in close apposition to the interspinous ligaments, whose fibers may run at a different angle, and this can cause off-incidence artifacts if care is not taken. The correct technique involves dynamic assessment of the ligament, tilting the probe forward and backward along its long axis to appreciate the slight curve/angle change of the fibers as they insert onto the DSPs (a standoff pad is therefore very useful). In addition, care should be taken that it is the SSpL being imaged, as the strong aponeurosis of the longissimus muscle has a prominent tendon-like appearance just to the left and right of midline (Figure 9.1). Transverse images of the ligament can be obtained simply by rotating the probe and are useful to corroborate potential injury identified longitudinally.

Figure 9.1 Care should be taken when imaging the supraspinous ligament (SSpL) that the transducer is midline (position 2). The aponeurosis of the longissimus muscles will appear as a striated, fibrous structure mimicking the ligament if the transducer is positioned to the left or right (position 1).

The supraspinous ligament often appears hyperechogenic relative to the interspinous ligament and this can lead to errors in concluding that there is damage to the SSpL, when in fact it is normal interspinous ligament tissue. As well as this, the fibers of the SSpL alter their angle of orientation slightly as they insert upon the oblique dorsal surfaces of the DSPs. This can lead to misinterpretation due to off-incidence artifacts. The SSpL is larger and more fibrous as it progresses caudally; images in the lumbar region are generally more consistent between individuals but there is a wide variation in “normal” appearance. This may be due to operator factors, anatomical idiosyncrasy, or previous but currently insignificant injury.

Interpretation of potential lesions follows the same basic principles as with other ligaments or tendons, with attention paid to size, echogenicity, and fiber pattern particularly (Figure 9.2). A certain degree of caution needs to be exercised when interpreting the appearance of the SSpL: it seems that a degree of dystrophic, possibly age-related change, is evident in some horses and not necessarily indicative of disease. In addition, sites of injury rarely recover a normal appearance and regions of hypoechogenicity may not relate to current pathology. In almost all cases, evidence of injury will need to be confirmed with other techniques, such as diagnostic anesthesia.

Figure 9.2 Longitudinal images of the supraspinous ligament (SSpL) and associated dorsal spinous processes (DSPs). Note the disruption to the longitudinal fiber pattern of the ligament, the close apposition of the DSPs, and the new bone production on the image to the left. Comparison with the adjacent interspinous region (to the right) can be helpful.

It is easy enough to infiltrate local anesthetic around the “injury” and ascertain whether this alters the horse’s movement/behavior, although there can be difficulties in reproducing that behavior consistently enough to allow this. Bear in mind that the ultrasonographic appearance of most SSpL injuries changes little with time and false positives can be a problem. This also makes follow-up of genuine lesions difficult. SSpL abnormalities are common in areas of significant impingement of the dorsal spinous processes.

An assessment of the health of the DSPs is also possible during examination of the SSpL, in relation to their dorsal bony contour (well-spaced or close, smooth or roughened, presence of osteophytes, etc.). However, as only the very superficial part of these structures can be visualized, the technique is only supplementary to radiography and scintigraphy.

It is practical to begin by performing a rapid, general appraisal of the ligament, running from cranial to caudal in the longitudinal plane. After this, move back to the cranial extent of the prepared area and scan longitudinally, identifying and recording areas of interest. If pathology is suspected, transverse scans (Figure 9.3) are used to try to ascertain the significance of changes. Suspicious areas should be marked, most easily by a short clip in the coat, to allow subsequent diagnostic anesthesia.

Figure 9.3 Transverse scans of a normal supraspinous ligament (SSpL) as an adjunct to longitudinal scans to ascertain the significance of changes seen on longitudinal images.

The Caudal Thoracic and Lumbar Facet Joints

The anatomy of the thoracic and lumbar joints differs makes imaging of the more cranial thoracic joints more difficult due to their proximity to the dorsal spinous processes (Figure 9.4). Fortunately, most pathology occurs in the last thoracic and cranial lumbar joints, which are easily imaged in horses without excessive subcutaneous fat or thick skin. The technique is compromised severely in patients with these last factors and in some horses it is impossible to obtain diagnostic images.

Figure 9.4 Postmortem specimen of the caudal thoracic intervertebral articulations (IVAs) viewed dorsally. Note their proximity to the dorsal spinous processes.

The technique aims to identify the articulation of the cranial articular process of one vertebra as it interdigitates with the caudal (and medial) process of the vertebra ahead of it (Figures 9.5 and 9.6). The first image to acquire is with the probe (a lower frequency curvilinear, ideally) at right angles to and just to the side of midline (Figure 9.7). By counting the ribs and following them up, the operator can get an idea of the vertebrae being imaged. Moving the probe backward (and, therefore, with the haircoat) the joints will appear and disappear from the field of view as the transducer heads caudally. Normal joints appear as the corner of a box, close to the junction of dorsal and transverse spinous processes. In thin-skinned horses and with high-quality equipment, it is common to be able to identify the individual cranial and caudal processes of each joint as well as the joint space. Disease of the intervertebral articulations (IVAs) results, regardless of the inciting cause being a stress fracture or osteoarthritis, in enlargement of the joint and the loss of this definition, with new bone production, which may progress to joint ankylosis (Figure 9.8). The ultrasound appearance is as if someone has stuck a ball onto the corner of the box, which takes on a rounded shape. It is important to compare adjacent joints on the same side of the horse to establish the validity of changes and also to compare the left and right sides.

Figure 9.5 Postmortem specimen of the lumbar intervertebral articulations (IVAs) viewed dorsolaterally. Note that they are more easily discernible than the thoracic IVAs.

Figure 9.6 Postmortem specimen of the lumbar intervertebral articulations (IVAs) with their finger-like cranial and caudal projections interlocking.

Figure 9.7 A frontal plane ultrasound image superimposed on an anatomical specimen showing the technique to image the caudal thoracic and lumbar IVAs.

Figure 9.8 Osteoarthritis (OA) can be identified as enlargement and rounding of the IVA. The diseased joint is on the left of this image and is compared to the normal contralateral joint on the right.

Longitudinal images, obtained by placing the transducer parallel to and just to the side of midline, can enable adjacent joints to be imaged in the same field of view (Figure 9.9

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Nov 6, 2022 | Posted by in EQUINE MEDICINE | Comments Off on Ultrasonography of the Back and Neck

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