What it is
The cranial cruciate ligament runs diagonally through the middle of the knee and stops the shin bone from sliding forward under the thigh bone. In dogs it tends to wear slowly from within over months or years, so a tear that seems to happen in one leap during play may have been building for a long time. A partly torn ligament lets the knee wobble a little with every step, which irritates the joint and wears the cartilage. The cartilage cushions inside the knee, the menisci, can be damaged too.
Heavier dogs, dogs carrying extra weight and dogs whose quiet weeks alternate with sudden bursts of hard exercise put more strain on the ligament.
Living with an unstable knee means watching how your dog moves: whether it sits squarely, gets up evenly from lying down, and copes with stairs and jumping into the car. Steady, regular exercise and a healthy body weight put less load on both knees, which matters because the other knee can be affected too.
Signs you may notice
- Sudden hind leg limp
- Only toe-touches with a hind leg
- Sits with a leg out sideways
- Stiff after rest
- Thickened, swollen knee
- Reluctant to jump or climb stairs
The dog may suddenly start limping or stop putting weight on a hind leg altogether, or limp only now and then, especially after rest or heavy exercise. You may notice that it sits with the leg stuck out to the side and that the knee looks thickened.
When to see a vet
If your dog suddenly stops putting weight on a hind leg, contact a vet soon. A limp that keeps coming back after rest or exercise is also worth booking a visit for.
This is general information, not veterinary advice. For your own dog's health, tests and treatment, see a vet.