What is patella luxation?
Patella luxation in dogs is a condition where the patella (knee cap) slips in and out of the groove. The patella can dislocate out of this groove, and therefore prevents the knee from extending properly.
It is a genetic condition that can affect any dog breed but more commonly toy and miniature breed dogs such as Poodles, Chihuahuas, Yorkshire Terriers and Pomeranians. The condition will sometimes only affect one leg but can be seen in both knees in around 50% of dogs. The condition can also affect some cats.
What are the symptoms of patella luxation in dogs?
Patella luxation is usually characterised by a ‘skipping’ or ‘hopping’ lameness, where the dog or cat will hold their leg up for several steps whilst running and then return to normal.
When both legs are affected, you may see ‘bunny hopping’ or dragging of the legs for short periods as well as a stiff and awkward gait. This is not usually painful but can lead to a more painful condition of (osteoarthritis) over time.
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What causes patella luxation?
In the majority of cases, the patella will luxate medially (towards the inside of the leg). This is caused by a combination of several factors which add together to cause a misalignment of the patella.
- Shallow trochlear groove. This is the groove on the femur in which the patella should sit and slide up and down smoothly as the knee joint bends and straightens. Dogs suffering from patella luxation often have a very shallow groove so that the patella will slip in and out easily.
- Medially placed tibial crest. The patella sits within the patella tendon which attaches the quadriceps muscles to the tibia (lower leg bone) via a prominent piece of the bone known as the tibial crest. In dogs with patella luxation, the tibial crest is often situated on the medial (inside) part of the bone, meaning the patella is pulled slightly medially rather than straight up and down through the trochlear groove.
- Bowed femur. In some dogs, a bowing (curvature) of the femur (the upper leg bone) can contribute to patella luxation.
How is patella luxation diagnosed?
Patella luxation is diagnosed by your vet who will carry out a physical examination on the dog during a consultation. During the examination, the vet will be able to manipulate the patella out of place to confirm the diagnosis. In some cases, X-rays may be required to assess the knee joint.
The grading system for patella luxation
Medial luxating patella is graded 1 – 4 based on severity.
- Grade 1. Patella can be manipulated out of position manually but doesn’t occur spontaneously and causes no clinical symptoms — usually an incidental finding.
- Grade 2. Patella can be manipulated in and out of position but remains within the trochlear groove for the majority of the time and will return to its normal position without manipulation. This can occur spontaneously with varying frequency.
- Grade 3. Patella is out of position most of the time, can be manipulated back into place but will luxate again quickly.
- Grade 4. Patella is permanently out of position and cannot be manipulated into the trochlear groove at all.
How is patella luxation treated?
Treatment for patella luxation is usually dependant on the severity of the patella’s condition. Grade 1 luxating patellas should be left and monitored as they rarely cause any problems. With grade 2, surgery should be considered and is dependant on the frequency of the signs.
Over time grade 2 medial locating patellas can deteriorate into higher grades. Surgery is always the recommended treatment for grades 3 and 4, as these will erode cartilage and cause the development of osteoarthritis over time.
Surgery usually involves several steps:
- Deepening the trochlear groove
- Transposition of the tibial crest to a more lateralised position (moving it sideways to straighten up the patella mechanism) — this is held in place with one or two small pins and a piece of wire to hold the tension
- Release of medial tissue — cutting/loosening tissues on the inside of the leg to reduce sideways tension on the patella and patella tendon
- In some extreme cases, surgery to correct the bowing of the femur may be required
Recovery from treatment
Total recovery time from patella luxation is normally 8 – 10 weeks. Following the surgery, your dog may be non-weight bearing on the leg for several days. Swelling and bruising are common and so anti-inflammatories and pain relief are dispensed. After two weeks of very strict rest, your dog will be able to start walking, gradually increasing the duration of lead walks, however, your dog will not be allowed off lead exercise for at least 8 weeks.
When both legs need to be operated on, we suggest a gap of about 6 weeks between surgeries to allow time for the initial surgery to heal.
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Whilst in the majority of dogs the implanted pins and wire will cause no issues, occasionally they will cause irritation or infection and may need to be removed once the bones have healed.
If your pet is showing any symptoms of patella luxation, get in touch with your local Animal Trust surgery and book a free consultation.