Hip Subluxation in a Horse

A 10 year-old mare presented for sudden onset hind limb lameness. The mare was non-weight bearing on the right hind limb and within 24 hrs there was significant swelling centered over the right gluteal region. In Figure 1, the pelvis of a horse is pictured to identify the left (bottom blue arrow) and the right (top blue arrow) coxofemoral joints. In Figure 2 and 3, the pelvis has been rotated slightly to picture the area that is most commonly ultrasounded to assess the coxofemoral joint space. In Figure 3, the red line corresponds to the junction of the pelvis and the femor. The blue arrow corresponds to the coxofemoral joint space.

Figure 1

Figure 2

Figure 3

Figures 4 and 5 illustrate the views captured via ultrasound exam of the equine pelvis. This area is very difficult to adequately radiograph in a standing horse hence the ultrasound exam provides an opportunity to assess the coxofemoral joint space of a horse. As in Figure 3, the red line in Figure 5 corresponds to the juction of the pelvis and femur (coxofemoral joint space) which is also highlighted by the blue arrow. In the normal exam, the only bone structures commonly noted are the pelvis (long white line at bottom of view) and the greater trochanter of the femur (small white line at the top right of the image).

Figure 4

Figure 5

Figures 6 and 7 correspond to the right coxofemoral joint space of the lame horse. There is clearly and extra curved line in the image that corresponds to the "head" of the femur. Normally, the head of the femur is NOT visualized because it is within the acetabulum that makes up the coxofemoral joint. The ultrasound findings below are consistent with a subluxation of the coxofemoral joint space and very likely fracture of the acetabulum!  This injury carries a very poor prognosis for an adult horse; however, in miniature horses or very small ponies, surgical correction exists as an option with a guarded prognosis.

Figure 6

Figure 7