What is the SI Joint?

Do you know where the SI (Sacroiliac) Joint is on your horse? You hear about it all the time. It’s one of the most common places for horses to have pain, and therefore one of the most commonly injected joints. But do you actually know where it is and what it does?

The SI Joint is the link between the low back and the pelvis. Together with the Pubic Symphysis (which is in the front of the pelvis), it allows for locomotion. When a horse brings his leg in front of him (into flexion), the pelvis on that same side has to rock down and back. We refer to this as posterior-inferior motion of the pelvis at the SI Joint. Posterior (meaning backwards), and inferior (meaning downwards). In contrast, when he brings his leg back behind him (into extension), the pelvis on that side rocks down and forward. This is referred to as Anterior-Superior motion of the pelvis at the SI Joint. Anterior (meaning forward), and Superior (meaning up). In order for your horse to have proper movement in the hind end, the SI Joints (there’s one on each side), must be free and clear in both directions!

Many times, when a horse is short on a hind leg, the assumption is that the hip is at fault. However, the hip and SI Joint move together, and so if the leg isn’t moving properly, both joints need to be checked for proper motion. My experience has shown me that the vast majority of the time, it’s an SI joint issue…