Patellar luxation in dogs

Content by Dr Nicole Olewinski – BVSc MRCVS

Patellar luxation is when the kneecap (patella) slips out of its normal position. Unlike joints such as the hip, the knee mainly works as a hinge, directing muscle power into running and jumping. The kneecap plays an important role in this by gliding up and down in a groove at the bottom of the thigh bone (femur), helping transfer force smoothly through the leg.

When the kneecap doesn’t stay within this groove and slips to one side, it’s called patellar luxation.

• A common condition that can lead to arthritis
• Small dogs more often have medial luxation (inwards)
• Large dogs more often have lateral luxation (outwards)
• Symptoms range from barely noticeable to difficulty walking
• Surgery is recommended for more severe case

The kneecap normally stays in place because it sits within a groove in the thigh bone and is stabilised by muscle tension. The force travels from the thigh muscles through the kneecap to the shin bone (tibia), where the patellar tendon attaches, helping to anchor the patella within the groove. If the groove is too shallow, or the bones of the leg have developed slightly out of alignment, the kneecap can drift or be pulled out of position.

In most cases, this is a developmental problem. And while both legs can be affected, one is often worse than the other. Less commonly, trauma or injury can cause the kneecap to luxate.

Patellar luxation is a common finding in practice. Small breed dogs are particularly prone to medial luxation (where the kneecap slips inwards), and many popular breeds and their crosses are affected:

• Bichons
• Cairn Terriers
• Chihuahuas
• Cavalier King Charles Spaniels
• Pugs
• Pomeranians
• Toy Poodles

In larger breeds, lateral luxation (where the kneecap slips outwards) is less common but well recognised, particularly in breeds such as:

• Flat-coated Retrievers
• Great Danes
• Irish Wolfhounds
• Saint Bernards

Signs vary depending on how often the kneecap moves out of place. In milder cases (Grade I and II), where the kneecap only slips briefly and returns to position on its own, the only sign may be an occasional skipped step.

In more severe cases (Grade III and IV), where the kneecap is out of place most or all of the time, lameness becomes more obvious. Dogs may even struggle with walking and getting up from lying down. If both legs are affected, they may develop a bow-legged or knock-kneed stance.

Diagnosis

In many cases, a vet can feel the kneecap moving out of position during an examination. To understand why this is happening and plan treatment, further imaging such as X-rays or – in more complex cases – CT scans may be recommended.

Treatment depends on the severity of the condition. Low-grade or mild patella luxation is often managed conservatively with weight control, physiotherapy, joint supplements and – where needed – anti-inflammatory medication.

In more severe cases, where the mechanics of the joint are significantly affected, surgery is usually recommended to improve mobility, comfort and long-term joint health. Surgery may involve deepening the groove, tightening soft tissues, and correcting bone alignment to prevent the kneecap from being pulled out of position.

Prognosis

Arthritis is a common long-term outcome of patellar luxation. In mild cases, many dogs live long, active lives with minimal impact, especially with early diagnosis and management.

For more severe cases, surgery can significantly improve comfort and joint function as well as delay the onset of arthritis. Without treatment, however, quality of life can be impacted by rapid onset of arthritis and difficulties with basic mobility.

“It may seem like a lot of fuss over a small bone, but the patella sits right in the middle of a powerful system. If that system isn’t aligned properly, it’s a bit like a tug of war between the top and bottom of the leg, putting real strain on the joint.

“In milder cases, you may not even realise there’s a problem until your vet picks it up. But no symptoms now doesn’t mean it’s something to ignore. By the time limping appears, there may already be wear and tear in the joint.

“I see this with my own elderly rescue dog, nicknamed the ‘Hairy Hippo’. She loves food and lounging on the sofa, which both pose risks. What feels like a small treat to us makes a big difference to a 5kg dog. Jumping onto furniture is another hazard… Those explosive movements can pop the patella out of place and increase inflammation. She also isn’t as strong as she used to be, and falls can add injury to an already arthritic joint.

“So if you notice your young dog skipping the odd step, or worse, get it checked out. Surgery is a big step – but if it’s appropriate, it can dramatically improve mobility and protect the joint from rapid decline.”

Dr Nicole Olewinski – BVSc MRCVS

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