What is Patella Luxation?

Patella luxation (also called "luxating patella" or "slipping kneecap") occurs when the patella (kneecap) moves out of its normal groove in the femur (thighbone). The patella normally sits in a groove called the trochlear groove and slides up and down smoothly as the leg bends and straightens. In patella luxation, the kneecap shifts to one side, disrupting normal movement and causing varying degrees of lameness and discomfort.

Patella luxation is one of the most common orthopedic conditions in small and toy dog breeds and is also seen in cats. It can be medial (shifting inward, most common) or lateral (shifting outward, more common in large breeds).

Grading

Patella luxation is graded on a scale of 1–4 based on severity:

Grade 1

  • Patella can be manually luxated but returns to its groove spontaneously
  • Rarely causes lameness
  • Dog may occasionally skip a step

Grade 2

  • Patella luxates during normal movement and may stay out of place until manually repositioned or the animal extends the leg
  • Intermittent lameness — the classic "skipping" gait
  • Most common grade seen in practice

Grade 3

  • Patella is out of position most of the time but can be manually repositioned
  • Persistent lameness and abnormal gait
  • Progressive joint changes

Grade 4

  • Patella is permanently luxated and cannot be repositioned
  • Severe lameness and an inability to fully extend the leg
  • Significant skeletal deformities often present
  • Crouched posture and bowlegged or knock-kneed stance

Commonly Affected Breeds

Dogs (Medial Luxation)

  • Chihuahua
  • Pomeranian
  • Yorkshire Terrier
  • Miniature and Toy Poodle
  • Maltese
  • Papillon
  • French Bulldog
  • Boston Terrier
  • Cavalier King Charles Spaniel

Dogs (Lateral Luxation)

  • Large breeds: Great Dane, Saint Bernard, Irish Wolfhound
  • Flat-coated Retriever

Cats

  • Devon Rex
  • Abyssinian
  • Domestic Shorthair

Causes

  • Genetics: The primary cause; the condition is heritable
  • Congenital malformation: Shallow trochlear groove, misaligned tibial crest, or abnormal limb angles
  • Trauma: Less common; a direct injury to the knee can cause luxation in an otherwise normal joint

Symptoms

  • Intermittent or persistent lameness
  • Skipping or hopping (holding the affected leg up for a few steps, then using it normally again)
  • Sudden yelping or signs of pain
  • Difficulty jumping
  • Crouching gait
  • Progressive stiffness
  • In severe cases, inability to fully straighten the leg

Screening

  • Physical examination: A veterinarian can diagnose and grade patella luxation through palpation
  • X-rays: Assess bony anatomy, alignment, and secondary arthritic changes
  • Screening is recommended at routine wellness visits, especially in predisposed breeds

For Breeders

  • OFA offers patella evaluation certification
  • Dogs should be evaluated at 12 months of age or older
  • Only dogs with normal patellas should be used for breeding
  • Breeding affected animals perpetuates the condition in the breed

Treatment

Conservative Management (Grade 1, mild Grade 2)

  • Weight management
  • Controlled exercise and physical therapy
  • Joint supplements
  • Anti-inflammatory medications as needed
  • Monitoring for progression

Surgery (Grade 2–4, or any grade causing significant lameness)

Several surgical techniques may be used, often in combination:

  • Trochleoplasty: Deepening the trochlear groove so the patella sits properly
  • Tibial crest transposition: Moving the attachment point of the patellar ligament for better alignment
  • Soft tissue reconstruction: Tightening or releasing tissues around the knee to help keep the patella in place
  • Corrective osteotomy: For severe cases with significant bone deformity

Surgical success rates are high (approximately 90% for Grades 2–3), and most animals return to normal or near-normal function.

Canada Flag