IN-DEPTH: ULTRASONOGRAPHY IN LAMENESS DIAGNOSIS


pensory ligament during a pre-purchase ultrasound exam. Therefore, it is imperative to evaluate the entire length of the suspensory ligament in both the transverse and the longitudinal (long-axis) planes. Information obtained on the transverse view allows the practitioner to evaluate ligament edges, struc- ture, and cross-sectional area (CSA). Informa- tion obtained on the long-axis view evaluates fiber pattern.2 It is important to note that lesions are usually identified in both planes, unlike artifacts that are usually noted in one plane. Visible scar tissue commonly develops at 3 to 6 months post injury, and is appreciated as hyperechoic lines with a short length when scanning in the long-axis view. In the transverse view, focal hyperechoic regions indicate scarring in the suspensory ligament. Cal- cification in the suspensory ligament may also ap- pear about 6 months post injury, and will appear as a hyperechoic area casting an acoustic shadow be- neath. Although the clinical exam is of utmost im- portance in the pre-purchase exam, swelling at the origin is often difficult to appreciate due to the loca- tion of the suspensory ligament between the splint bones. Evaluation with ultrasound can provide valuable insight to the ligament’s integrity in this location. One benefit to using the CSA measure- ments in the pre-purchase exam, is the determina- tion between a suspensory ligament with more muscle and fat fibers versus a lesion. A normal suspensory ligament may have areas of hypoechoge- necity but a normal CSA. An abnormal ligament will have areas of hypoechogenecity and an abnor- mal CSA.


3. Materials and Methods


One of the most challenging aspects of the pre- purchase ultrasound is the inability to properly prepare the horse. The majority of clients are not willing to allow you to clip the limb to the best of your ability so as not to draw attention to the limb in the future. Fortunately, many high-level sport horses are kept impeccably groomed, and the hair is routinely short. Additionally, the inability to se- date the horse can also be challenging. It is not uncommon for the horse to be currently competing in an Fe


´de ´ration Equestre Internationale (FEI) set-


ting and therefore cannot receive medication. In the transverse view, the suspensory origin is imaged before the suspensory can be visualized separating from metacarpal 3/metatarsal 3 (MC3/MT3). This location has the suspensory origin fibers. The fore- limb origin shape will be bilobed compared to the hind limb’s triangular shape. Taking measure- ments in the pre-purchase exam is highly variable and controversial, but it has benefits. The CSA in warmbloods is highly variable and larger than other breeds. Again, this should be evaluated in conjunc- tion with the clinical picture. If using the CSA measurements in a pre-purchase ultrasound exam, it is useful to compare limb to limb, However, this


may add to some confusion considering that bilat- eral suspensory desmitis is common in sport horses. Many publications report the forelimb origin CSA to be 80 to 100mm2 and the hindlimb origin CSA at 80 to 100 mm2. The practitioner must take into ac- count the size of the horse being evaluated as it is not uncommon in sport horses to see normal suspen- sory origins of the forelimb with a CSA approxi- mately 120 mm2 and a hindlimb origin CSA approximately 150 to 180 mm2 CSA. The body of the suspensory ligament is commonly reported at 80 to 100 mm2 in the forelimb and 100 to 120 mm2 in the hindlimb; however, typical sport horses often range from 120 to 150 mm2. Note that the body of the suspensory should be the same throughout, and may be larger than the origin. After the bifurca- tion, the CSA is reported to be 60 to 80 mm2, but is commonly 100 mm2 in the sport horse. The sus- pensory branches should be oval shaped and have a very defined edge. Loss of edge definition can de- note chronic stress. The insertion of the suspen- sory branches will be larger than the more proximal aspect of the branch. The insertional CSA is re- ported at 100 to 120mm2 and is commonly 130mm2 in the sport horse. The medial and lateral branches should be of similar size. The suspen- sory ligament insertion should be imaged where the entire ligament inserts into the bone. When using the CSA in the pre-purchase exam, it is helpful to compare the measurement of the CSA to the vertical width in the long-axis view. These measurements should be similar, and are easily compared in the split-screen views. Other views to consider include oblique views of the forelimb suspensory origin and the flexed view. Many fore- limb lesions occur on the medial aspect of the ligament, so obtaining images that are oblique will completely image the suspensory origin in the forelimb. Imaging the suspensory origin in the flexed view will evaluate the bone more efficiently.


4. Conclusion


The sport horse pre-purchase exam has become more complex with more information provided to the buyer to help them reach a decision. Ultra- sound of the four limbs has become the standard of practice in a sport horse pre-purchase exam. This exam is used as a reference point and al- though ultrasound is highly variable depending on patient and operator, implementing a consistent method of examining the suspensory ligament, can provide the practitioner much-needed infor- mation. Using measurements to compare one limb to another while relying on fiber pattern in- formation from both the transverse and long axis, the veterinarian can provide a solid baseline of the integrity of the suspensory ligament at the time of the exam. With this valuable insight, the practi- tioner can use this information in conjunction with the clinical findings to develop a more accu- rate impression of the sport horse during the pre-


AAEP PROCEEDINGS  Vol. 64  2018 7


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