An upward fixation of the patella is a condition in which the horse’s patella, or kneecap, is caught or trapped on the bottom portion of the horse’s femur just above the stifle joint; this prevents the horse from flexing the leg. You may have heard some people say the affected horse is stifled, but the correct term is upward fixation of the patella. The condition can be found in any breed of horse but commonly occurs in ponies and miniature horses and is due to the horse’s anatomy. It commonly occurs in horses with straight hind limbs and those with poor muscling that allows the patella to be more mobile; the patella gets trapped on the femur and will not release. It is also commonly seen in horses that are not exercised because muscle tone decreases.
Many years ago, the condition was treated surgically. One of the patellar ligaments was cut and although this was effective, complications did develop. It was found that after this surgery, damage to the kneecap itself could occur so the surgery was not as popular. However, we now believe the kneecap damage can be prevented by resting the horse for 8 weeks after surgery. Other treatments include injecting the ligaments with various substances to inflame them and make them thicker, which prevents the kneecap from getting caught on the femur. Another surgery reported on several years ago was splitting the patellar ligament with a blade rather than completely cutting it. In this procedure, stab incisions are made in the ligament to cause it to thicken versus cutting it entirely. A recent study conducted by surgeons in Copenhagen found that over 97% of the horses in their study responded to this surgery with no post-operative complications.