Your Chihuahua suddenly lifts a hind leg while running, hops a few steps, then continues as if nothing happened. Your Yorkshire starts limping after playing, but it passes in a few minutes. You think he stumbled or it's muscle fatigue. In reality, you're probably observing the most characteristic sign of patellar luxation (a condition often underestimated by small breed owners).

Patellar luxation (or dislocated kneecap) is one of the most common orthopedic conditions in dogs. Left untreated, patellar luxation may gradually lead to cartilage damage and osteoarthritis. The earlier it is recognised, the easier it is to manage.

The Patella: Anatomy and Luxation Mechanism

The patella is a small bone located at the front of the knee that glides in a groove of the femur called the trochlear groove. It plays an essential role in extending the leg and transmitting muscle forces.

• In a healthy joint, the patella remains centered in its groove with every movement. • In case of luxation, it moves out of its groove, most often towards the inside of the knee (medial luxation), more rarely outwards (lateral luxation, mostly recorded in large breeds).

• This displacement is not always permanent: the patella can spontaneously return to its place, which makes the condition deceptive and often detected late.

Important to understand

Patellar luxation is usually a developmental orthopaedic condition with a strong hereditary component. Rather than resulting from a single injury, it develops as the bones and soft tissues grow out of alignment.. It does not heal on its own and tends to worsen over time (even in the absence of apparent clinical signs).

A condition classified into four grades

Veterinarians assess the severity of the luxation according to four stages, based on clinical examination and knee manipulation:

• Grade I: The patella can be manually luxated but returns to place on its own. Few or no visible signs. Many dogs remain comfortable for years.

• Grade II: The patella luxates spontaneously during certain movements. The dog does the "frog leap" intermittently: it lifts a leg for a few steps, then resumes normally.

• Grade III: The patella is luxated most of the time. Lameness is more constant and the limb begins to deform. It can still be manually reduced but re-luxates immediately.

• Grade IV: The patella is permanently luxated and can no longer be replaced. The gait is crouched, major locomotor difficulties are present, and bone deformities are severe.

Important to remember

Grades I and II can remain asymptomatic for a long time, especially in small breeds. However, it is at these early stages that management is the simplest and most effective. Waiting for obvious lameness often means waiting for Grade III.

Why does luxation worsen?

Patellar luxation tends to worsen because each episode of instability gradually changes the mechanics of the knee.

• Repeated movements of the patella out of its groove wear down the articular cartilage.

• The trochlear groove flattens, making future luxation even easier.

• The ligaments and tendons that hold the patella become unbalanced, causing a progressive internal rotation of the tibia.

• Changes in limb alignment may gradually become visible, depending on the direction and severity of the luxation.

• Osteoarthritis sets in irremediably, even if the patella is eventually managed.

An untreated Grade II can thus become a Grade III or IV in a few years, especially in active or overweight dogs. Overweight is a direct mechanical aggravating factor: excess body weight increases the mechanical load on an already unstable joint and is recognised as an important aggravating factor.

Most affected breeds

Medial patellar luxation is up to 12 times more common in small breeds than in large ones (Di Dona et al., 2018). The predisposition is both genetic and morphological. Although small breeds account for the majority of cases, patellar luxation can occur in dogs of any size.

Sources: O'Neill et al., BMC Veterinary Research, 2016. Di Dona et al., Veterinary Medicine: Research and Reports, 2018.

Clinical signs to watch for

Beyond the intermittent "frog leap", other signs should alert you:

• Reluctance to jump, climb stairs, or sit normally

• Slight stiffness after rest, quickly passing with warm-up

• Discreet clicking noises in the knee upon flexion

• More constant lameness, visible muscle atrophy on the thigh

• Progressive limb deformity: "X-shaped" legs, low posture, swaying gait

Radiographs are commonly used to assess bone alignment, associated deformities and the presence of osteoarthritis, although the diagnosis itself is primarily clinical.

Management: when should surgery be performed?

The decision depends on the grade, breed, age, weight, and quality of life of the dog.

Conservative treatment (grades I and some II)

Reserved for dogs with few symptoms. It is based on strict weight management, adapted exercise, and physical therapy to strengthen the knee's stabilizing muscles. Regular monitoring is essential to detect any progression in grade.

Surgical treatment (symptomatic grades II, III and IV)

This is the reference treatment as soon as the quality of life is affected. Surgery usually combines several techniques tailored to the individual dog. These may include deepening the trochlear groove, realigning the patellar tendon and correcting bone deformities when necessary. Overall outcomes are generally very good, particularly for Grade II disease, with reported success rates exceeding 90% in many published series.

The link with the cruciate ligament

An untreated patellar luxation weakens the entire knee. Abnormal biomechanical stresses created by chronic instability significantly increase the risk of cranial cruciate ligament rupture. In the Swedish population studied by Engdahl et al. (2023), dogs with patellar luxation have a higher risk of cranial cruciate ligament rupture than the general canine population. The mechanisms that cause one often cause the other (hence the importance of not waiting).

What you can do now

Do not trivialise an intermittent, even fleeting, lifted paw. If your dog belongs to a predisposed breed, even without obvious lameness, ask your veterinarian for an orthopaedic examination. A grade I detected early can be managed well. A grade III discovered late involves more complex surgery and a less predictable prognosis...

Many owners wait until their dog starts limping every day before seeking advice. Yet the classic "skipping" gait is often the earliest warning sign. Recognising it early may help slow joint deterioration and preserve long-term mobility.

Maintaining an optimal weight remains your best daily lever to limit mechanical aggravation and slow the onset of osteoarthritis.

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Sources

1. O'Neill DG et al. (2016). Epidemiology of patellar luxation in dogs attended in general veterinary practice in England. BMC Veterinary Research. PMC4898461 • Di Dona F. et al. (2018). Patellar luxation in dogs. Veterinary Medicine: Research and Reports, 9: 23–32. PMC6055913
2. Engdahl K. et al. (2023). The epidemiology of patellar luxation in an insured Swedish canine population. Acta Veterinaria Scandinavica.
3. Lavrijsen IC et al. (2013). Phenotypic and genetic trends of patellar luxation in the Dutch Flat-Coated Retriever. Animal Genetics. PubMed 24033452