Dislocation of the patella: what is it?
The patella (or patella) is a small bone placed in front of the femur, buried in the tendon of the quadriceps muscle which is used to extend the thigh. Normally, the patella slides in a bony pit formed in the femur during flexion and extension movements of the knee. It then remains well aligned with the quadriceps and the patellar tendon which attaches it to the tibia, the bone located just below the knee joint.
Read also: Anatomy of the dog's pawsWe speak of patellar luxation (or patellar luxation) when the kneecap comes out of its housing during flexion and extension movements of the knee.When the patella is displaced inside the knee, it is called medial patellar dislocation and when it is displaced outside the groove of the femur, then it is called lateral patellar dislocation.
Dislocated patella is the most common orthopedic condition in dogs.
What causes patellar luxation in dogs?
In dogs, patella luxation can occur as a result of knee trauma.
When it is not of traumatic origin, this orthopedic condition could also result from a misalignment of the knee extensor apparatus linked to a developmental anomaly that occurred during the dog's growth linked to :
- a defect in the depth of the trochlea of the femur, this bony groove in which the patella slides,
- a malformation of the hip, femur and/or tibia,
- an abnormally long patellar tendon.
Small dogs, and in particular Boston Terriers, Chihuahuas, Pomeranians, Yorkshires and Miniature Poodles, are racially predisposed to patella luxation.
But, in recent years, the disease has also been affecting larger dogs such as the Shar Pei, Pyrenean Mountain, Akita Inu, Labrador, and Golden Retriever, among other breeds.
This condition is bilateral (affects both kneecaps) in 50% of cases and affects females more predominantly than males.
Dislocation of the patella in dogs: signs and symptoms
In dogs, the signs of patella luxation vary greatly depending on the severity of the condition and its grade.
Dislocation of the patella can give rise to no symptoms, be associated with a weak and intermittent lameness of the hindquarters up to a more severe, frequent or permanent lameness, with suppression of the supports.
Puppies with bilateral patellar dislocation may exhibit bowed hind legs that become more curvature as they grow.
Over time, the dislocation can eventually erode the cartilage and lead to osteoarthritis, causing significant joint pain.
How is patella luxation diagnosed in dogs?
The diagnosis of patella dislocation is made during an orthopedic examination by the veterinarian. During this examination, the veterinarian will try to feel your pet's knee and mobilize its patella to check its stability and determine its grade of dislocation.
The 4 grades of patella luxation
Grade 1: the patella can be placed out of its groove manually but spontaneously returns to its normal position,
Grade 2: the patella moves on its own from its groove occasionally and can be replaced by manipulation or spontaneously repositioned,
Grade 3: the ball joint comes out of its groove most or all of the time. It can be relocated manually but reluxes immediately,
Grade 4: The patella remains dislocated, permanently out of its groove and cannot be replaced manually. It is associated with limb deformities.
The veterinarian may also need to check the integrity of the cranial cruciate ligament by other mobility tests which may require tranquilization or even general anesthesia of the animal.
Finally, the veterinarian may also use additional examinations such as X-rays of the pelvis, knee and/or shins or a three-dimensional CT scan.
Patellar dislocation in dogs: what treatment?
The treatment of patella luxation is a surgical treatment. It is generally indicated for grade 2 and above dislocations and may consist of:
- an intervention on the soft tissues surrounding the patella,
- an increase in the depth of the femoral groove,
- a realignment of the knee extensor apparatus by transposition of the tibial crest,
- a correction of bone deformities of the femur.
Following the surgery, a rest period of 6 to 8 weeks during which games, jumps, races, walking on slippery surfaces and going up and down stairs should be avoided . The dog's outings must then be done only on a leash for hygienic needs.
Your veterinarian may also prescribe anti-inflammatories and painkillers for your dog.
Physiotherapy sessions that can be performed at home or in a physiotherapy center may be necessary to improve joint ankylosis and promote good recovery for your pet.