Why is a split better than a cut for problematic stifle ligaments? Peter Green MRCVS looks at the latest research

Young horses in particular can experience problems with the mechanism in the stifle that locks the kneecap, or patella, on to the bottom of the femur.

Sometimes the patella gets stuck in the locked position or is not released efficiently when the horse wants to move.

The result is a stiff, straight, fixed back leg that can look quite alarming and can upset the horse, or a snatching action of the back leg as the patella snags on the bone and then flips off.

The condition is known either as “upward fixation” or “delayed release” of the patella. Many young horses grow out of it, and in older animals the condition often resolves as the horse gets fitter.

If it is persistent, surgery is an option. The traditional technique is to cut the thick ligament on the inside of the stifle that links the patella to the tibia. This ligament is an important part of the locking system and if it is cut, the problem is solved. But cutting risks making the patella unstable.

In a more recent technique, the ligament is not cut but split lengthways. This seems to induce a change in the way the ligament functions and prevents unwanted locking or snagging.

Vets in Texas have just published the results of this ligament-splitting operation in 64 horses who had delayed release problems. When they were followed up after surgery, 60% were completely cured, 30% were improved and 10% were not helped by the operation.

The results are not as good as those obtained with the old-fashioned ligament-cutting operation, but there is no risk of causing damage. If it doesn’t work, the ligament can always be cut later.