Question: My 4-month-old filly has been diagnosed with severe bilateral locked stifles. This condition came on quite suddenly from an unknown cause. I have been told she is too young for an operation and that I should allow her moderate exercise to strengthen her ligaments. This has been going on for three weeks and so far she has shown no improvement. Her stifles are locked almost all the time. Do you have any suggestions as to how I can help her?
Answer: A 4-month-old filly with bilateral locked stifles is very unusual. This phenomenon, called "upward fixation of the patella," occurs when one of the ligaments in the stifle (the medial patellar ligament) slips over a projection on the end of the femur (the medial condyle) and gets stuck in place. This can cause anything from mild hesitations in a gait to total rigidity of the joint.
Locking stifles is not a rare condition, but I don't think I have seen it in a foal this young. I would be interested in knowing your filly's breed and basic hind-end conformation. I suspect she is pretty straight through the stifle and hocks.
To address this issue, conservative therapeutic shoeing would be your best option over the long run. Also, I would take lateral radiographs to determine the palmar angle (PA), the angle between the bottom surface of the coffin bone and the ground. "Normal" can vary, but in most horses, the leading edge of the coffin bone is slightly lower than at the heel. If your filly has a five to eight degree PA and you raise it by four to eight degrees, you could certainly create enough flexion in the stifle to discourage upward fixation.
Most stifle shoes I have used for older horses created a PA of 20 to 30 degrees and had a rocker action that forced the toe to maintain this elevation. The shoes also have rocker action side to side.
If your filly continues to stay locked and becomes more difficult to correct each time she has a patella fixation, she will bruise the medial patellar ligament as well as the medial condyle, which can create further problems. At that point, the best option may be a medial patellar desmotomy (to sever the ligament so that it can no longer catch on the bone).
I hope this helps.
Ric Redden, DVM
The Redden International Consulting Service