Patella Luxation in Dogs and Cats
The kneecap that slips out of its groove, and how to stabilise the joint around it.
Patella luxation is when the kneecap slides out of its groove in the thigh bone. In most small dogs it goes inward, towards the other leg, and the hallmark sign is a brief skip: a few hops on three legs, then a sudden return to normal once the kneecap pops back. How much treatment it needs depends on the grade, and on whether it is causing pain, muscle loss, or both.
Most dogs with grade one or two patella luxation do well with physiotherapy and targeted strengthening to stabilise the joint without any surgery. Grades three and four almost always need surgical correction first, with rehab beginning once the knee has settled.
Reviewed by Doris Ho, our co-founder and primary physiotherapist, who has practised animal physiotherapy since 2013.
Quick facts
- What it is: the kneecap (patella) slips out of its groove on the thigh bone, usually inward in small dogs, usually outward in large breeds.
- Who tends to be affected: primarily small-breed dogs, Pomeranians, Maltese, Chihuahuas, Shih Tzus, French Bulldogs and Toy Poodles. Cats are affected less commonly, and large breeds tend toward the lateral variant.
- Signs to watch for: the three-legged skip for a few steps then back to normal; reluctance to jump or climb stairs; occasionally a click or catching feeling at the knee.
- Outlook with rehabilitation: grade one and many grade two cases remain comfortable for years with muscle-strengthening work. Grades three and four almost always need surgery first, then rehab to rebuild the leg.
- Why the quadriceps matters: the muscles around the knee are the joint's main stabiliser. A kneecap that slips when that muscle is weak can often be held in place once the muscle is strong.
What patella luxation is
The kneecap (patella) is a small bone embedded in the tendon that runs over the front of the knee. In a healthy knee it sits in a channel on the end of the thigh bone, the trochlear groove, and glides smoothly up and down as the joint bends and straightens. Patella luxation happens when that groove is too shallow, or the leg's alignment is slightly off, or both, so the kneecap rides over the ridge of the groove and slips to one side.
In small dogs the direction is almost always medial, inward towards the other leg. In larger breeds it goes lateral, outward. Either way, with the kneecap out of the groove, the quadriceps muscle can't extend the knee properly, so the dog drops onto three legs. After a few steps the kneecap usually finds its way back. The leg straightens, and the dog carries on as if nothing happened. That is the skip, and it is how most owners first notice the problem.
Grades one to four: what they mean
Vets grade patella luxation from one to four depending on how far out the kneecap goes and how easily it returns.
| Grade | What the kneecap does | What owners usually see |
|---|---|---|
| Grade 1 | Stays in place on its own; vet can push it out but it pops straight back. | Usually no lameness. Often found at a routine check. |
| Grade 2 | Pops out spontaneously, usually when the knee flexes; tends to pop back on its own or when the leg is straightened. | The characteristic skip: a few hops on three legs, then normal again. |
| Grade 3 | Sits dislocated most of the time; vet can push it back, but it slips straight out again. | Persistent lameness on the affected leg; muscle loss visible on the outer thigh. |
| Grade 4 | Permanently dislocated; cannot be repositioned manually. | A leg that has never worked properly, often with a bow-legged or crouched posture. |
Grade and symptoms don't always line up neatly. Some grade two dogs skip occasionally and show no distress at all between episodes. Others with the same anatomy find every walk uncomfortable. The grade describes the anatomy; what the dog can do comfortably day to day is what drives the treatment decision.
How patella luxation changes the knee over time
Left unmanaged, patella luxation tends to progress rather than stay the same. Repeated slipping wears the edges of the trochlear groove, making it shallower, which makes the kneecap slip more easily. At the same time, the quadriceps tendon and patellar ligament start pulling at a slight angle instead of straight over the knee, and over time that misalignment distorts the attachment of the tendon on the shinbone.
In young dogs the concern is bone shape: a growing bone that develops with a misaligned patella will remodel along those lines, and the longer it runs, the more bone surgery needs to correct. In older dogs the concern is cartilage wear. In both groups, building the muscle that holds the joint together buys time, and in grade one and many grade two cases it can keep a dog comfortable indefinitely without any operation.
How AURA helps
Whether we are managing a grade one or two conservatively, or rehabilitating a knee after surgical correction, the tools we reach for are the same. What changes is the sequence and how much load we ask the joint to take.
Wondering whether your dog needs surgery or physio?
Send us a short video of their walk. We'll say what grade the skip looks like and whether rehab alone is likely to be enough, or whether a surgical opinion is the next step.
What rehab does after patella surgery
Grades three and four almost always need surgical correction before rehab can meaningfully begin. The operation typically deepens the trochlear groove (trochleoplasty), sometimes moves the bony attachment of the patellar tendon on the shinbone (tibial crest transposition), and tightens the soft tissue on the side the kneecap was sliding toward. Surgery corrects the anatomy; it cannot restore the muscle the leg lost while the kneecap was slipping, retrain the movement pattern the joint has developed, or dissolve the scar tissue that builds during healing. That part is what rehab is for.
The question of whether surgery is necessary at all lies roughly at the boundary between grades two and three. A young dog with grade two luxation that skips daily and has visible quadriceps loss on the affected side is a reasonable surgical candidate. An older grade two dog that occasionally skips but is comfortable, active and carrying good muscle mass is often managed conservatively with very good results. Weight also matters: every kilogram of excess body weight increases the load through every step. Grade two dogs who reach and hold a healthy body weight and do consistent strengthening work frequently never need surgery.
What recovery looks like
The path through rehab differs depending on whether we are managing the condition conservatively or following surgery.
Conservative management (grade 1 to 2)
Physiotherapy starts immediately. The focus is quadriceps and gluteal strengthening, balance work, and avoiding slippery surfaces at home. No confinement, but no high-impact jumping or sudden twisting. The goal is the best possible muscular support for the joint as it is, and in many dogs that support is enough to keep the kneecap where it belongs.
Post-surgical rest (first two to four weeks)
Strict confinement, short leash-only toilet trips, and no weight-bearing exercise until the soft tissues have settled. Laser therapy to reduce post-operative swelling. Gentle passive range-of-motion to stop the knee stiffening during the rest period.
Controlled loading (four to eight weeks)
Once the surgeon gives clearance, we add the underwater treadmill at high water level (more buoyancy, less joint load), sit-to-stands, and short controlled leash walks. The knee gets stronger without being asked to do more than it can handle yet.
Strengthening (eight to twelve weeks and beyond)
Water level drops, land exercises become more demanding, and the emphasis shifts to rebuilding the full quadriceps and gluteal muscle mass the knee needs to stay stable. Working dogs and active dogs get a longer reconditioning runway before returning to full activity.
When to call your vet
Most patella luxation progresses slowly, but a few changes are worth acting on quickly rather than watching.
Call your vet today
- A leg that was managing suddenly stops bearing weight entirely.
- The knee swells markedly overnight, or feels hot compared to the other side.
- After surgery: the wound opens, or there is discharge, redness, or a bad smell.
- A sudden stumble or twist after which the dog will not put the leg down at all.
Book a recheck soon
- Skip frequency increasing week on week rather than staying stable.
- Visible muscle loss on the outer thigh compared to the other side.
- A reluctance to jump or use stairs that was not there before.
Cats tend to hide discomfort. A cat that has quietly stopped jumping to its usual perches, or is grooming one leg more than usual, is worth a vet check even without any obvious lameness.
What to ask your vet or specialist
Worth a screenshot before your next appointment:
- What grade is the luxation, and which direction does the kneecap go?
- Is it in one knee or both?
- What does the quadriceps muscle look like on the affected side?
- Does the tibial crest need to be moved, or is deepening the groove alone enough?
- Can we try physio first, and what change in symptoms would push us toward surgery?
- After surgery, how long before the underwater treadmill can start?
- What body weight should we be aiming for?
Outlook
Grade one cases rarely need surgery, and most dogs stay comfortable for life with consistent muscle conditioning and a healthy weight. Grade two varies: many do well with physio alone for years, some progress and eventually need surgical correction, and outcomes after surgery are generally very good. Grades three and four need surgical correction, and most dogs walk normally afterwards, with the best results in those whose surgery happens before the bone has significantly remodelled.
The variable that most owners underestimate is muscle. A strong quadriceps can hold a grade two patella in place for years. A weak one allows a grade one to become a grade two. Physiotherapy, and keeping a lean body weight, are the two things that most directly control how fast a luxating patella progresses, and they cost nothing compared to surgery.
Common questions about patella luxation
What is the skip my dog does?
The skip is the patella popping out of its groove. With the kneecap displaced, the quadriceps cannot straighten the knee, so the dog lifts the leg and hops for a few steps. Once the kneecap pops back into position, the leg works normally again and the dog puts it down as if nothing happened. The skip is the hallmark of grade two luxation.
Does patella luxation always need surgery?
No. Grade one rarely needs surgery. Grade two often does not, particularly in dogs with good muscle mass and a healthy body weight who respond well to physiotherapy. Grades three and four almost always do. The decision depends on grade, symptom frequency, muscle condition, and age, not on grade alone.
Can physio prevent surgery from ever being needed?
In grade one and some grade two cases, yes. Strengthening the quadriceps and surrounding muscles can hold the patella stable enough that the joint never progresses to needing an operation. It is not a guarantee, but it is a meaningful intervention, not just management.
Is patella luxation painful?
It varies. The moment the kneecap slips can be uncomfortable, but many dogs between episodes show no pain at all. Over time, repeated slipping wears the cartilage in the trochlear groove, and that wear causes ongoing discomfort. Grade three and four dogs are more consistently painful than grades one and two.
My dog has it in both knees. What happens then?
Bilateral patella luxation is common, particularly in small breeds. Both knees are assessed and graded independently; the rehab addresses both. When surgery is needed in both, vets typically do one knee at a time to allow the dog to bear weight on the other side during recovery, usually with a gap of six to twelve weeks between operations.
How long after surgery before my dog is back to normal?
Most dogs are comfortable and walking well by six to eight weeks after surgery. Full muscle recovery and return to normal activity, including running and jumping, takes closer to three to four months. Dogs who go through structured rehab after surgery typically recover faster and with better muscle balance than those who rest alone.
Sources and further reading
- Gibbons SE, et al. Patellar luxation in 70 large breed dogs. Journal of Small Animal Practice, 2006.
- Arthurs GI, Langley-Hobbs SJ. Complications associated with corrective surgery for patellar luxation in 109 dogs. Veterinary Surgery, 2006.
- Roush JK. Canine patellar luxation. Veterinary Clinics of North America: Small Animal Practice, 1993.
- MSD Veterinary Manual. Patellar Luxation in Dogs and Cats.
- Singleton WB. The diagnosis and surgical treatment of some abnormal stifle conditions in the dog. Veterinary Record, 1969.
- Kirkby Shaw K, et al. Fundamental principles of rehabilitation and musculoskeletal tissue healing. Veterinary Surgery, 2020.
- Levine D, Millis DL (eds). Canine Rehabilitation and Physical Therapy, 2nd ed. Saunders/Elsevier, 2013.
Worried about your animal?
Tell us what you've noticed and how it started. We'll say whether it sounds urgent, whether to come in, and what we'd do.