Medial Patellar Luxation

Client Handout

WHAT IS MEDIAL PATELLAR LUXATION?

Medial patellar luxation is a common condition in small and toy breed dogs, although it can occur in large breeds as well. The patella (knee cap) is a small bone that sits underneath the patellar tendon that connects the quadriceps (thigh) muscles to the front of the tibia (shin bone).  During flexion and extension of the knee, the patella slides up and down a groove in the bottom of the femur (trochlea) to keep the tendon in position in the centre of the bone.

In some dogs, the patella can slip sideways or “dislocate” out of the trochlea, usually to the inside (medial) side of the knee. This is called medial patellar luxation. This usually happen due to developmental issues with the femur and tibia bones, contributing to a bow-legged appearance, and the trochlea can also be shallower than normal. The tibial crest will often be more medial (towards the inside of the knee) than normal, which causes the patella to be pulled out of the normal groove during flexion of the knee.

Commonly affected breeds include Chihuahuas, Miniature Poodles (and their crosses), Bichon Frise, Maltese and French bulldogs.

SIGNS OF PATELLAR LUXATION

Dogs with a luxating patella can show intermittent lameness, and they may “hop” or “skip” when running where they will hold a back leg up for a few strides before putting it down and continuing to walk or run normally.

Over time, the patella moving in and out of position will wear down the cartilage and bone on the inner ridge of bone and osteoarthritis will develop, causing chronic pain and lameness.

Approximately 50% of dogs with patellar luxation will be affected in both legs. Affected dogs will be more likely to damage their cranial cruciate ligament as well.

DIAGNOSIS

A luxating patella can be diagnosed by feeling the knee and the position of the patella during a clinical examination. Sometimes x-rays are needed to look at the conformation of the bones.

There are different grades based on increasing severity of the condition:

Grade 1 – the patella can be luxated during manipulation, but goes back into position on its own.

Grade 2 – the patella will luxate spontaneously, and won’t go back until the stifle is extended and rotated.

Grade 3 – the patella is permanently luxated, but can be pushed back into position manually.

Grade 4 – the patella is permanently luxated and can’t be pushed back into a normal position.

Surgery is normally indicated for grades 2-4.

TREATMENT

Surgery is a very effective treatment for patellar luxation, and is most successful when done early in the disease process before irreversible osteoarthritis has developed.

Depending on the individual animal, a combination of techniques is normally used to improve knee function. These include:

Deepening of the trochear groove – this is done by cutting a block or wedge shaped segment of bone out of the trochlea, and removing some bone underneath to deepen the groove. This prevents the patella from popping out of position as easily.

Tibial crest transposition – this involves cutting the small segment of bone where the patellar tendon attaches on the tibia, and moving it sideways into a better position that is aligned with the pull of the quadriceps muscle. This prevents the sideways pull on the patella that causes it to pop out of position. The bone is then anchored in its new position with small pins, and sometimes wire.

Lateral imbrication and medial release – the joint capsule and other soft tissues on the lateral side that are stretched from repeated luxation are tightened with overlapping sutures to prevent medial movement of the patella. Sometimes it is also necessary to make a cut in the tissues on the medial side that are too tight, to allow the patella to move back into a normal position.

Prognosis after surgery is excellent if surgery is done before significant secondary changes and arthritis develop.

Image: Post operative xray

RECOVERY

After surgery your dog will be kept in hospital overnight. Once home, you will need to restrict your dog’s activity for 6-8 weeks after surgery to allow the bone to heal.

To aid in healing and rapid return to function, post operative care will include:

  • a series of six therapeutic laser sessions (two sessions per week for three weeks),
  • a series of four injections of Synovan® to help with joint health and mobility, (one injection a week for four weeks)
  • one treatment session with a rehab-focussed veterinarian at our North Nowra practice. This is normally arranged for 1-2 weeks after surgery. Further rehab sessions can be organised if you wish to continue this.