Like cruciate disease, patella luxation is another relatively common cause of a hind leg lameness in dogs that we see regularly at AlphaPet.
It is caused by the patella (knee cap) slipping onto either the outside (lateral) or inside (medial) side of the stifle (knee joint) when an animal is moving. This is uncomfortable, and sometimes will cause animals to do a hop- skip- jump sort of movement, or to kick the leg out, in order to get the patella to go back in line.
Anatomically, the patella (knee cap) sits in a groove at the bottom of the femur (thigh bone). It is held straight in between the big quadriceps muscle on the front of the thigh of the dog, and the patella tendon, an attachment between the patella and the tibial crest (a bony prominence on the front of the tibia/ shin bone). If any of these elements are not completely in line, if they point, even slightly, towards the inside or outside of the leg, then they will make the patella slip out of its groove onto the inside or the outside of the leg. Additionally, the groove that the patella sits in can be too shallow, without high enough sides, which makes it very easy for the patella to slip out of line.
We often see this problem in small or toy breed dogs, that have been born with these anatomical differences predisposing them to having a luxating patella. For example, Chihuahuas, Miniature Poodles, Boston and Yorkshire Terriers commonly have this problem. Also, some large breed dogs can be lame due to a luxating patella, the most common larger breeds are the Shar Pei and Flat Coat Retriever. It is often a problem that affects both of the hindlimbs, but often one more so than the other.
When a vet examines an animal for a luxating patella, as well as watching how they are walking, they will grade the extent of the luxation from 1 to 4. A grade 1 luxation is the mildest form, where we can push the knee cap out of its groove, but when we let it go, it goes straight back to where it should be again. At the other end of the spectrum, a grade 4 luxation is where the patella is constantly sitting outside of the groove on either the medial or lateral side of the leg, and it cannot be replaced to where it should be even with some pressure.
If a dog is lame because of a low grade luxating patella, sometimes at first the Vet will prescribe some pain killer anti-inflammatory medication, in case the dog has sprained the knee which is what is exacerbating a mild patella problem. However, if the problem continues, and if the animal is quite young (which is commonly the case) it is best to consider surgical treatment to prevent the problem from getting worse, and to limit the amount of eventual arthritis within the joint.
We will always take some X-rays of the animal's stifle (knee) joints under sedation prior to surgery. This enables us to check there is nothing else wrong with the joint (for example cruciate ligament problems, as they can occur simultaneously) and helps us to plan the surgery.
The way of treating the luxation surgically, is a tailor-made to each individual dog's leg depending on what exact anatomical abnormalities they have causing the luxation to occur.
The joint is fully opened. Firstly a trochleoplasty is usually performed. This is to deepen the groove that the patella sits in, so it is more stable and less likely to slip out of line. This is usually done by lifting out a block of the smooth joint cartilage at the base of the femur, deepening the bony groove, then replacing the smooth cartilage into the groove again for the patella to sit in. Then an assessment is made as to whether the tibial crest (a bony prominence on the front of the tibia/ shin bone) is perfectly in line with the quadriceps muscle above it, or whether it's position is pulling the patella to one side. If it is not in the right location, a tibial crest transposition is performed. This means that the tibial crest is cut, relocated to a better location, and then held in place with pin(s) and possibly a wire. Then as the knee is closed, the soft tissue problems are addressed, sometimes by leaving one side of the joint partially open, and tightly closing the other side to keep the patella in the right location. If there is a lot of excess soft tissue, some may be removed, or it may be stitched closed overlapping each other.
Generally we bandage the leg for the first 24hrs after the surgery to help with swelling and bruising, while the animal spends the night after the surgery in our West Meads Hospital being monitored and given further pain relief by our Twilight nurses. Beyond this, the dressing is removed and the animal is discharged. Generally they recover very well from the surgery and are often walking on the leg in the few days after the surgery itself.
As with any other orthopaedic surgery, the animal needs to be very strictly rested for 6 weeks following the surgery. At that point we will perform X Rays again at this point to check that the bone has fully healed (if a tibial crest transposition was performed). If there has been any irritation with the pin implants, then these may be removed at this point, but otherwise they can be left in situ for the rest of the dog's life. Occasionally, with a severe, grade 4, luxation, the surgery may not 100% cure the problem, but will usually make it a much lower grade than it was pre-surgery. If the results are still not adequate though, very occasionally, a second surgery is required.