Patella Luxation (slipping kneecaps)

Patella luxation is the dislocation (slipping) of the patella (kneecap). In dogs the patella is a small bone that shields the front of the stifle joint. This bone is held in place by ligaments. As the knee joint is moved, the patella slides in a groove in the femur (leg thigh bone) called the trochlear groove.

What are the signs of luxating patella?

Indications of patella luxation are; difficulty in straightening the knee, pain in the stifle, limping, or the tip of the hock joint points outward while the toes point inward.

Causes of patella luxation

• Congenital, that is present at birth - common, and usually bilateral (both knees affected)
• Deformity of other structures (structures of the knee are all dependent on each other, biomechanical forces exerted on them will alter their shape & form)
• Following trauma to the stifle - uncommon & usually unilateral (only one knee affected). Injury causes tearing/stretching of the ligaments (cruciate & collateral) and other soft tissues around the joint resulting in instability which can allow the patella to slip out of the trochlear groove in which it sits.

The most common occurrence of luxating patella is the medial presentation in small or miniature dog breeds. Shallow femoral groove, weak ligaments and malalignment of the tendons and muscles that straighten the joint are all conditions that will predispose a dog toward luxating patella.

Shallow femoral groove, weak ligaments & malalignment of the tendons and muscles that straighten the joint are all conditions that will predispose a dog toward luxating patella.

Diagnosis

The diagnosis of this condition can usually be confirmed (by a vet) by manipulating the stifle joint and pushing the patella in and out of position.

Patella luxations fall into several categories:

1. Medial luxation; toy, miniature, and large breeds.
2. Lateral luxation; toy and miniature breeds.
3. Lateral luxation; large and giant breeds.
4. Trauma induced luxation; various breeds

Beyond the categorization of patella luxation there are 4 grades of deviation for this condition:

Grade 1: Intermittent patella luxation - occasional carrying of the affected limb. The patella can easily be manually luxated at full extension of the stifle, but returns to proper position when pressure is released.

Grade 2: Frequent patella luxation - in some cases luxation is more or less permanent. The affected limb is sometimes carried, although the dog may walk with the stifle slightly flexed.

Grade 3: Permanent patella luxation - even though the patella is luxated; many animals will walk with the limb in a semi-flexed position.

Grade 4: Permanent patella luxation - the affected limb is either carried or the animal walks in a crouched position, with the limb partially flexed.

Categories 1, 2, and 3 are either hereditary or strongly suspected of being inheritable.

Treatment

There are several different forms of treatment depending upon the severity of the condition:

• No treatment may be required for mild cases especially in small and toy breeds - grades 1 & 2
• Pain killers can be given when necessary
• Surgery to deepen a shallow trochlear groove - called trochleoplasty
• Surgery to stabilise the joint - e.g. repair of ruptured ligaments or tightening of the soft tissues around the joint
• Surgery to change the relationship of the patella to the adjacent bone - e.g. transplantation of the tibial crest