Patellar Luxation in Dogs: Grades, Breeds at Risk, and Breeding Impact

Luxating patella affects millions of dogs worldwide and is one of the most common orthopedic conditions requiring surgical correction. Understanding grades and inheritance is essential for breeders in affected breeds.

What Is Patellar Luxation?

The patella (kneecap) normally rides in a groove at the end of the femur called the trochlear groove. In dogs with luxating patella, the kneecap slips (luxates) out of this groove — typically to the inside (medial luxation in small breeds) or outside (lateral luxation in large breeds).

When the patella luxates, the dog may intermittently skip, carry the leg, or show a characteristic "skip step" followed by sudden improvement when the patella pops back into place.

OFA Patella Grading Scale

The OFA grades patellar luxation from 0 to 4 using a physical examination:

Grade 0 (Normal): Patella sits in the trochlear groove normally. Does not luxate with manipulation.

Grade I: The patella can be manually luxated (pushed out of the groove) but returns to normal position when released. The dog rarely shows lameness.

Grade II: The patella luxates spontaneously during normal activity. The dog shows occasional lameness. The patella can be manually returned to the groove.

Grade III: The patella is luxated most of the time. Can be manually reduced but returns to luxated position quickly. The dog often shows persistent lameness.

Grade IV: The patella is permanently luxated and cannot be manually reduced. The trochlear groove is severely shallow or absent. Severe lameness is typical.

Breeds Most Commonly Affected

Small and toy breeds (medial luxation):

• Chihuahua (extremely high prevalence)
• Pomeranian
• Yorkshire Terrier
• Miniature and Toy Poodle
• Miniature Schnauzer
• Maltese
• Shih Tzu
• Bichon Frise

Large breeds (lateral luxation):

• Labrador Retriever
• Golden Retriever
• Great Dane

Inheritance

Patellar luxation has a significant hereditary component, though the genetics are complex (polygenic — multiple genes contribute). Dogs with Grade II or higher patellar luxation should not be bred. Grade I is a judgment call — many breeders exclude Grade I dogs from breeding programs entirely; others accept Grade I with disclosure and breeding to Grade 0 partners.

Surgical Treatment

Grades II–IV typically require surgical correction. The surgery involves:

• Deepening the trochlear groove
• Repositioning the tibial tuberosity (where the patellar tendon attaches)
• Tightening of the joint capsule

Surgery is highly successful in Grades II–III. Grade IV is more challenging. Post-operative recovery takes 8–12 weeks.

Dogs who have had surgical correction for patellar luxation should generally not be used in breeding programs — surgery corrects the effect, not the underlying structural cause.

Breeding Recommendations

• Grade 0: Acceptable for breeding with Grade 0 or Grade I partners
• Grade I: Breed only to Grade 0 dogs; disclose status to dam/stud owner
• Grade II or higher: Do not breed
• Surgically corrected dogs: Do not breed (surgery does not correct the genetic predisposition)

Summary

Patellar luxation ranges from Grade 0 (normal) to Grade IV (permanently displaced). Small breeds are most commonly affected via medial luxation. The OFA grades patellar status from physical examination. Grade II and above should be excluded from breeding programs. Grade I requires disclosure and Grade 0 pairing. Surgery corrects the condition but not the underlying genetic predisposition — operated dogs should not be bred.