Cranial cruciate ligament rupture is the most common cause of hind-leg lameness in dogs and occurs in cats too (though less often).

The ligament inside the knee (stifle) that stops the shinbone from sliding forward tears or frays over time. The knee becomes painful, unstable, and develops arthritis quickly.

Surgery is the gold standard for most dogs and many cats because it restores stability, slows arthritis, and helps pets return to normal activity. Small cats and very small dogs may do well with conservative therapy, but the best functional recovery is expected with the surgery.