Accuracy of Suspensory Ligament Measurements via Ultrasound

When it comes to equine injuries in the proximal (upper) suspensory ligament (PSL), many veterinarians rely on ultrasonography (US) to diagnose and monitor the problem. But obtaining accurate US measurements of the PSL could be a challenge, even for experienced operators, according to the results of a recent German study.

"Despite recent improvements in the diagnosis of proximal suspensory desmitis using a combination of advanced imaging modalities such as computed tomography, scintigraphy, and magnetic resonance imaging, US remains the imaging technique used most frequently," said Johanna Zauscher of the equine clinic at the Free University of Berlin Faculty of Veterinary Medicine and lead researcher of the study.

The researchers aimed to evaluate inconsistencies within and between two experienced US operators while they measured several dimensions of the PSL using US longitudinal and transverse scans. On two separate occasions, the operators imaged and then measured multiple PSL dimensions (thickness from front to back [DP]; length from outside to inside [lateromedial]; cross-sectional area; and circumference) in all four limbs of eight horses.

Altogether, each operator took 588 forelimb and 364 hind-limb measurements. Upon analyzing the data, the research team found multiple discrepancies both within and between the two operators. Key findings included:

  • "Excellent" levels intra- and interoperator agreement for DP measurements using a longitudinal scan;
  • "Acceptable" levels of agreement for the DP thickness on the transverse scan; and
  • "Considerable variation" in other US measurements of the PSL, both intra- and interoperator.

In reference to the excessive variation in measurements, the team noted, "A limb will never be in exactly the same position as it was during an earlier examination and when the load on tendons and ligaments changes, this alters the US appearance and consequently the results of measurements."

Zauscher recommends that, if US is selected diagnosing and treating PSL injuries, operators, have experience and "good knowledge of the anatomy."

The study, "The proximal aspect of the suspensory ligament in the horse: How precise are ultrasonographic measurements?" will appear in an upcoming issue of the Equine Veterinary Journal. The abstract can be viewed online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.