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Medial Patellar Luxation
 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. In my experience, 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)(Fig 1). 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 can be categorized from mild to severe and graded from 1-4 respectively. Grade one luxations only luxate under digital pressure. These patients are usually asymptomatic and usually do not require surgery. In grade 2 luxations the patellar spontaneously slips 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.
 The most common clinical signs with MPL include limping and skipping with the affected leg or legs. A popping/clicking sound or feel may be heard or felt by the owner when the pet flexes and extends the rear legs. Clinical signs usually begin around one year of age. Infrequently, some dogs live for years with a MPL without clear clinical signs only to develop lameness in later life. In this scenario many times a cranial cruciate ligament rupture or tear is responsible for the late onset of lameness. In some patients with late onset of signs the cartilage wears through to the underlying bone causing acute pain and lameness.
 The diagnosis of MPL is usually made on orthopedic examination although radiography (X-Rays) may also be helpful. The indications for surgery include presence of clinical signs, spontaneous luxation and the grade of luxation as mentioned above. Animals left untreated are prone to develop arthritis and may be predisposed to cranial cruciate tears (also known as ACL tears).
Typically, 5 surgical procedures are used to treat the majority of MPLs. A releasing incision is performed on the medial (inward side) of the joint to allow the patellar to move in a lateral (outward) direction. The lateral joint capsule is tightened by a procedure called lateral imbrication. The grove is deepened where the patellar normally glides. Several techniques are frequently utilized to accomplish this. Finally, the attachment point of the patellar tendon is aligned with the remainder of limb. Either a tibial crest transposition or de-rotational suture can be performed for patellar tendon alignment (Fig 2).
The prognosis for MPL repair is excellent in animals with grades 1-3. At Colorado Canine Orthopedics patients can be comfortably discharged from the hospital the day of surgery. Healing time depends on the age of the patient and procedures employed. In puppies healing usually takes about 1 month. During this convalescent period animals can go on short leash walks, do lots of lap sitting but should not be permitted to jump from furniture or stairs. Following healing the patient can return to a normal, fully active life style.
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Figure 1 Figure 2
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