Medial patellar luxation (MPL) is a common problem, especially in small and toy breed dogs. Poodles are the most common breed affected. Large breeds and cats infrequently develop MPLs. Akitas are the exception to this rule, developing patellar luxations almost as often as toy breeds.
As the name medial patellar luxation implies, the patellar (knee cap), luxates (slips out of position) medially (toward the inward side of the leg). The problem is believed to be congenital and occurs typically between 6 and 12 months of age. The disorder usually affects both rear legs (possibly to varying degrees).
Patellar luxations in dogs can be categorized from mild to severe and graded from 1-4 respectively.
- Grade 1 luxations only luxate under digital pressure. These patients are usually asymptomatic and usually do not require surgery.
- Grade 2 luxations are characterized by the patellar spontaneously slipping in and out of position. Most dogs with grade 2 luxations experience mild to moderate lameness and often skip with the leg up for several steps when the patellar is out. Then when the patellar slips back into position the skipping temporarily resolves. Grade 2 MPLs usually require surgical repair.
- Grade 3 luxations are always out of position but can be reduced by digital pressure. Patients with grade 3 luxations experience mild to severe lameness, skip sometimes and almost always require surgery.
- Grade 4 luxations are always out and cannot be reduced by digital pressure. Patients with grade 4 luxations usually experience severe lameness and require surgical repair.