Luxating Patella in Dogs: Grades, Signs and Treatment

You have probably seen it: a small dog trotting along, suddenly hopping for a stride or two with one hind leg held up, then carrying on as if nothing happened. That skip is the classic sign of a luxating patella — a kneecap slipping out of its groove.

It is one of the most common orthopaedic conditions in dogs, and one of the most commonly shrugged off.

What is actually happening

The patella, or kneecap, normally sits in a groove at the bottom of the thigh bone and slides up and down as the leg bends. A tendon runs over it, connecting the thigh muscles to the shin bone.

For that system to work, three things have to line up: the groove needs to be deep enough, the attachment point on the shin needs to be correctly positioned, and the bones need to be straight.

In affected dogs one or more of these is off. Usually the groove is too shallow, and often the attachment point on the shin bone sits slightly to one side, pulling the kneecap off track. When it slips — usually inwards, towards the middle of the body, which is called medial luxation — the leg cannot extend properly. The dog holds it up, the quadriceps relaxes, the kneecap pops back, and the dog walks on.

Who gets it

Small and toy breeds overwhelmingly: Yorkshire Terriers, Pomeranians, Chihuahuas, Miniature Poodles, Bichons, Jack Russells, French Bulldogs, Cavaliers. Medial luxation is the usual pattern.

Larger breeds get it less often, and when they do it is more likely to be lateral — slipping outwards — and more often associated with other limb deformities.

It is largely developmental and heritable, which is why breeding stock should be examined. A minority of cases are traumatic.

The grades

Vets grade it one to four, based on examination.

Grade 1. The kneecap can be pushed out of the groove by hand but returns on its own immediately. The dog usually shows no signs at all. Often found incidentally.

Grade 2. The kneecap luxates occasionally on its own, and stays out until it pops back — either spontaneously or when the leg is straightened. This is the classic skipping dog.

Grade 3. The kneecap sits out of the groove most of the time. It can be pushed back in but slips out again. The dog often has an altered gait, crouching or bow-legged.

Grade 4. Permanently dislocated and cannot be replaced by hand. Significant deformity, and the dog may walk with a crouched posture or barely use the leg.

Grades can progress over time, particularly in young growing dogs, so a grade 1 at six months is worth rechecking.

Why it matters even when mild

The skipping looks harmless, and in grade 1 it often is. But a kneecap tracking incorrectly wears cartilage, and the abnormal mechanics load the rest of the leg differently.

Dogs with patellar luxation have a substantially increased risk of rupturing the cranial cruciate ligament in the same leg. That is the complication worth avoiding, because it is far more serious and far more expensive.

Diagnosis

Physical examination is the main tool. Your vet will flex and extend the knee while applying pressure to the kneecap to see how easily it displaces and how it returns.

X-rays are used to assess bone alignment, look for arthritis, and plan surgery. They also help rule out hip problems, which can produce similar-looking lameness.

Treatment

Conservative management

Appropriate for grade 1 and many grade 2 dogs who are not bothered day to day.

• Weight control. Every extra gram loads the joint. This is the single most effective thing you can do.
• Muscle maintenance. Good quadriceps tone helps hold the kneecap in place. Controlled lead walking, gentle hill work and hydrotherapy all help; erratic sprinting and jumping do not.
• Reduce jumping. Off furniture, out of cars, up stairs. Ramps and steps genuinely help.
• Non-slip flooring. Small dogs skidding on laminate are repeatedly stressing exactly the wrong structures.
• Pain relief when needed, prescribed by your vet.
• Joint supplements, which have modest evidence but are widely used.

Surgery

Recommended for dogs with grade 3 or 4, for grade 2 dogs with persistent pain or lameness, and where cruciate damage is developing.

Surgery usually combines several procedures in one operation:

• Trochleoplasty — deepening the groove so the kneecap sits securely
• Tibial tuberosity transposition — moving the attachment point on the shin bone so the pull is straight
• Soft tissue release and imbrication — loosening the tight side of the joint capsule and tightening the slack side

Success rates are generally good, with most dogs returning to normal or near-normal function. Recurrence happens in a minority, more often in higher grades.

Recovery involves six to eight weeks of restricted activity: lead-only toilet breaks, no stairs, no jumping, no slippery floors, and a graded return under veterinary guidance. Physiotherapy improves outcomes.

Keeping a rested dog occupied

Nose work, lick mats, stuffed toys and lying-down training exercises all fill a confined day without loading the leg.

Prevention

You cannot change a dog’s conformation, but you can:

• Buy from breeders who have their dogs’ knees examined and graded
• Keep dogs lean from puppyhood
• Fit non-slip runners before there is a problem
• Discourage jumping off furniture in at-risk breeds from the start

When to see the vet

Any recurrent skipping step warrants an examination, even if the dog seems fine. Knowing the grade tells you whether to simply manage weight and monitor, or whether to plan ahead. The dogs that do worst are the ones whose owners waited until the leg stopped working.