Diagnosing Coxofemoral Subluxation with Ultrasound

Subluxation (partial dislocation) of the coxofemoral joint between the femur and pelvis in horses is rare; only two cases have been reported in the literature. However, six cases were seen at the University of California, Davis, in a three-year period, suggesting that perhaps this problem is somewhat more common than previously thought. At the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla., Suzanne Brenner, DVM, an intern at UC Davis, discussed a technique for diagnosing these subluxations with ultrasound.

Radiographs have been considered the gold standard for diagnosing pelvic disorders, she noted. But the views needed to identify subluxation require the horse to be on its back under general anesthesia, while ultrasound in the standing horse is much quicker, carries less risk to the horse, and can provide a solid diagnosis. All six of the UC Davis cases were diagnosed with ultrasound.

Affected horses were quite lame (mostly grade 4/5, with one exhibiting grade 3 lameness), with an acute onset of lameness in five horses and insidious (slow) onset in one horse. Crepitus (a bone-grinding noise), muscle atrophy, and pelvic asymmetry were seen in some horses, but only one case had all three signs. No horses had external (outward) rotation of the distal (lower) limb, which has been noted in other reports of the condition. All six cases showed clear displacement of the head of the femur on ultrasound, and five horses had associated acetabular (coxofemoral joint rim) fractures and severe joint effusion (fluid swelling).

Four of the affected horses were euthanized, and only one of the remaining two horses is comfortable at the walk, leading investigators to conclude that the prognosis for this condition is not favorable.

"Coxofemoral subluxation should be considered when a hind limb lameness is suspected to originate from the pelvic region," Brenner concluded. "Diagnosis can be readily and safely obtained through the use of dynamic ultrasound in the standing horse if weight-bearing and resting views are performed."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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