Owners describe it to me almost word for word. “Every so often she’s running along and just skips a step — lifts a back leg up, gives it a little kick or a stretch, then carries on like nothing happened.” They have usually decided it is a harmless quirk. Often it is not. That skip is the textbook sign of a kneecap slipping out of place, and ignored for long enough it drives one of the most common causes of arthritis in the canine knee.
What’s Actually Happening in the Knee
The kneecap — the patella — is a small bone that sits in a groove at the bottom of the thigh bone (the femur). The big thigh muscle attaches to the top of the patella; a strong ligament runs from the bottom of it down to the shin bone. When the muscle contracts, the patella glides up and down its groove like a pulley, and that mechanism is how the dog straightens its leg.
For the system to work, three things have to line up: the groove must be deep enough, the bones must be straight, and the soft tissues must pull the patella in a straight line. In a dog with patellar luxation, one or more of those is off. Usually the groove is too shallow, the alignment of the leg bones is slightly rotated, or both. The result is that the kneecap pops sideways out of its groove — most commonly to the inside of the leg (medial luxation).
When the patella is out, the dog cannot straighten the knee properly, so the leg locks up for a stride or two. That is the skip. Then the dog extends or shakes the leg, the kneecap slides back into the groove, and normal walking resumes. The dog feels little or nothing in that moment, which is exactly why owners dismiss it.
Both the Little Dogs and the Working Lines
Patellar luxation has a reputation as a toy-breed problem, and it is certainly very common in small dogs. But it is a genuine issue across herding breeds too. Smaller herders and crosses get it often, and it shows up in the working lines of larger breeds as well — Australian Shepherds, Shelties, Border Collies, and the smaller-framed shepherds. In bigger, more athletic dogs the lateral (outward) form becomes relatively more common and tends to be associated with more significant bony deformity.
It is largely developmental and has a heritable component, which is why it matters for anyone breeding. The conformation that predisposes a dog to a luxating patella — the shallow groove, the slight bow or rotation of the limb — is passed on. This puts it firmly in the same category as the other joint conditions worth screening for before breeding, alongside hip dysplasia and the scoring schemes that go with it.
The Grading System, and Why It Decides Treatment
Vets grade patellar luxation from I to IV, and the grade is the single most useful thing for deciding what to do.
- Grade I: The kneecap sits normally most of the time. You can push it out of the groove during an examination, but it pops straight back on its own. Often no clinical signs at all — frequently an incidental finding.
- Grade II: The kneecap luxates occasionally during normal activity (this is your classic intermittent skipper) but returns to the groove by itself or with a stretch of the leg. This is the most common grade I see in the consulting room.
- Grade III: The kneecap is out of the groove most of the time. It can be pushed back manually, but it slips out again readily. These dogs usually have a more persistent, visible gait abnormality and often some bony deformity.
- Grade IV: The kneecap is permanently dislocated and cannot be manually replaced. The leg is usually noticeably bowed and the dog significantly impaired.
The principle is straightforward. Low grades with no real signs are managed conservatively. Higher grades, and any grade causing genuine lameness or pain, are surgical conversations. A Grade I in an otherwise sound dog generally needs nothing more than awareness and weight control. A Grade III or IV is usually heading for surgery, because the joint will not function properly and the arthritis will only worsen.
Why “Just a Skip” Is Worth Taking Seriously
Here is the part owners underestimate. Every time that kneecap rides out of its groove, it grinds against the ridge of the femur. Over months and years, that abrasion wears the cartilage and accelerates osteoarthritis in a young joint. A dog with an untreated Grade II or III luxation is laying down arthritic change long before you would otherwise expect it — which is why a five-year-old can present with a knee that looks a decade older on X-ray.
There is also an important interaction with the other big knee problem: cruciate ligament disease. A knee that is poorly aligned and repeatedly luxating is mechanically unstable, and that instability puts abnormal load on the cruciate ligaments. Dogs with chronic patellar luxation are at increased risk of cruciate rupture, and when both go at once the surgical reconstruction is considerably more involved. Catching and correcting a problematic luxating patella early can spare the dog a second, worse injury down the line.
Management and Surgery, Realistically
For the dogs that do not need surgery — the mild, low-grade, comfortable ones — management is about protecting the joint. Keep the dog lean, because every extra kilo loads a knee that is already working at a mechanical disadvantage; this is one of the clearest cases where careful weight management directly changes the outcome. Maintain good thigh muscle through sensible, consistent exercise, avoid the repetitive high-impact twisting that aggravates the knee, and monitor for any worsening of the skip.
When surgery is warranted, the aim is to fix the underlying mechanics rather than just tidy the soft tissue. Depending on what is wrong, a surgeon may deepen the groove so the patella sits more securely, move the bony attachment point of the patellar ligament to straighten the line of pull, and tighten or release the surrounding tissues. Done well, outcomes are good, and most dogs return to full, sound function.
The message I want to leave you with is simple: an intermittent skipping hindlimb is not a personality trait. Have your vet feel the knee. If it is a quiet Grade I, you can relax with a plan. If it is more than that, knowing now — while the cartilage is still healthy — is worth far more than discovering it later as advanced arthritis.