Luxating Patella: Why Your Dog’s Knee Is Popping
If you’ve answered “yes”, there’s a good chance your dog may have luxating patellas.
Let’s start with talking about the knee
The knee is an amazing, complex joint made up of three bones – the femur, the tibia, and the patella (the kneecap) – held together by tendons, ligaments, and muscle (Figure 1). Where the bones meet, cartilage covers the surface of the bone. The same cartilage provides a smooth surface for the patella to glide, allowing the knee to bend.
Figure 1: Anatomy of the knee (Washington State University (https://hospital.vetmed.wsu.edu/2022/01/04/cat-and-dog-anatomy/))
Figure 2: Medial vs Lateral patella luxation (Holt 2017, https://scholar.utc.edu/cgi/viewcontent.cgi?article=1108&context=honors-theses)
What does “luxating patella” mean?
When the patella is “luxated”, the kneecap is essentially displaced. Instead of just sliding up-and-down, it can move from side-to-side. Most kneecaps displace towards the animal’s body (i.e. medially/ inwards), this is more common in smaller breeds. In some cases, the kneecap displaces away from the body (i.e. laterally/ outwards), this is more common in larger breeds. About 50% of the dogs with patella luxation are affected in both legs.
What causes luxating patellas?
The cause of luxating patella is poorly understood. However, this condition is known to be associated with a genetic malformation or traumatic in origin. There are a number of skeletal abnormalities affecting the alignment of the hindlimb that can be the cause of luxating patellas. The most common causes are a shallow groove, abnormal bow-legged conformation and displacement of the attachment of the kneecap to the shin bone (tibia).
Some breeds are more predisposed to developing patella luxation, these include:
- Miniature Poodle
- Miniature Pinscher
- Bichon Frise
- Shar Pei
- Staffordshire Terrier
- French Bulldogs
Should I get it fixed?
Luxating patella in itself is not the most painful condition but rather uncomfortable. However, with each luxation, protective lining of cartilage is worn out and eventually, raw bone is exposed. This leads to the development of osteoarthritis, which is a chronic and painful condition. On top of that, instability of the knee resulting from the luxating patella may lead to other knee injuries such as “cranial cruciate ligament injury” – the same injury many football players suffer from. This causes permanent lameness and can affect their ability to walk normally. Cranial cruciate ligament can be partially or completely ruptured. The only treatment for cruciate ligament disease is surgery.
Indication for luxating patella surgery depends on the severity of the condition and the patient itself. First, your veterinarian will perform a thorough examination of the legs and grade the luxation.
Luxation of patella is graded from 1 to 4. Grade 1 is the least severe and grade 4 is the most severe luxation:
Grade 0: Normal
Grade 1: Knee cap can luxate with some effort but immediately pops back into the original position
Grade 2: Knee cap can luxate but spends most of the time in the normal position
Grade 3: Knee cap can be replaced into the normal position but spends most of the time luxated
Grade 4: Knee cap is luxated and cannot be replaced into the original position.
Depending on the severity of luxation, they may recommend monitoring, medical therapy or radiographic assessment of the joint with surgical intervention. Patients with grade 1 patella luxation are usually managed successfully without surgical intervention. However, many patients with Grade 1 luxating patellas will eventually move onto Grade 2 patients. 50% of the patients with grade 2 patients will eventually require surgery at some point in their lives.
How do we assess patella luxation?
Physical assessment and radiograph under general anaesthetic are super important! When they are completely relaxed, our assessment of the biomechanics of the knee is way more accurate than when they’re awake and stressed, where their muscles are tensed. While they are under anaesthetic, we also take the opportunity to radiograph their knees, so we can assess their knee for any arthritic changes.
How is patella luxation treated?
If detected early before 16 weeks of age, a soft tissue technique can be performed without involving any bone, hence, less invasive.
Beyond 16 weeks of age, a bone surgical technique is usually required. This may include one or all of the following surgical techniques
- Tibial tuberosity transposition (TTT)
- This procedure involves using a metal rod, wires and creating a bone fragment to create stability in the knee ligaments and tendons to hold the kneecap in its natural position (Figure 3).
Figure 3: Tibial tuberosity transposition diagram (Yeadon 2010, https://www.semanticscholar.org/paper/Tibial-tuberosity-transposition-advancement-for-of-Yeadon-Fitzpatrick/6d3b71278a5ebcc1d85fa99bafd91cacf10ed548)
- Deepening of the groove where the patella normally sits in to create stability using either a block recession sulcoplasty or wedge recession sulcoplasty (Figure 4 and 5).
Figure 4: Block recession sulcoplasty (Veterinary instrumentation 2019, https://www.petvetbiomed.com/html5/web/10200/36779ImageFile3.pdf)
- Femoral osteotomy
- In severely bow-legged dogs, the thigh bone (femur) has to be surgically cut and remodelled to create a normal straight leg (Figure 6).
Figure 6: Distal femoral osteotomy (Perry and Dejardin 2021).
It is important to perform surgery before arthritis develops as the long-term prognosis is much more promising. Once arthritis has developed, it is impossible to treat and we can only manage its progression. If x-rays do not show any arthritis, your dog should regain full use of its leg.
What to expect after the surgery?
Your furbaby will generally have to be on pain relief and antibiotics after the surgery. You should expect up to a 6-8 weeks recovery period. Throughout this period, your furbaby has to be strictly cage-rested with restricted activity. At day 14 post surgery, we will commence your furbaby on a course of joint supplement injection called Pentosan Sulphate for 4 weeks. This joint supplement improves joint fluid quality and production to help aid recovery and reduce the rate of osteoarthritis progression. This is also the time where we highly recommend your furbaby to commence physiotherapy to strengthen their muscles and to facilitate healing. At the end of the 6-8 weeks period, we will repeat radiographs to evaluate how well the bone is healing after their surgery.
If you have more questions than you do answers, talking to your vet is the best thing we can advise. While the patella popping in and out is largely pain-free (for now), the instability can cause issues in the future. Have a chat to see what you can do for your furbaby! Please do not hesitate to give us a call or chat via the My Vet AH app.