by Dr Willem van Wyk Mammals
Mammals have evolved some idiosyncratic body parts, but of all the joints, the knee wins the prize for the worst design in the entire body. The hip has a ball and socket that fit snugly into one another, and the elbow has a beautiful interlocking design, but the knee is essentially two bones that need to balance on top of one another. It is no wonder then, that the knee is the most common cause for lameness in younger dogs. Of all the conditions that occur in the knees, patella luxation is one of the most common.
What is patella luxation?
The big thigh muscles are responsible for extending (straightening) the knee. These muscles are very strong, as they provide a lot of the power when an animal runs or jumps. They attache to the lower leg through a common tendon that implants on the top of the tibia, or shin bone. In order to keep this tendon in place, it attaches to the kneecap or patella, which slides inside a groove on the lower end of the thigh bone. The patella is further held in place by two small attachments, called the collateral patella ligaments, that attach to either side of the lower end of the femur. If everything works as it should, the patella can slide effortlessly up and down the groove as the knee bends. Unfortunately, this is not always the case, and there are three main problems that cause things to go awry. In some dogs, the groove that the patella slides in, is very shallow, which allows it to jump out of the track that it is supposed to stay on. The two collateral ligaments are sometimes rather flimsy, and can stretch or tear when the patella is pulled to either side. Thirdly, the attachment to the lower leg might not be centred, which causes the patella to be pulled to one side when the knee is bent. In many small breed dogs, all three of these problems are often present, particularly if the dog has bowed hind legs, which causes the patella to slip to the inside of the leg quite easily. Once this has happened once, the collateral ligaments and other stabilising tissues in the knee stretch or tear, which makes it easier for the offending patella to go walkabout again. Some dogs may develop patella luxation without any of the usual risk factors being present. This usually only happens in a traumatic patella luxation, where the dog is involved in some kind of accident where an unnaturally large force is applied to the knee.
Luxating Patella in Dogs Signs and Symptoms
I often have clients who describe how their dog’s knee sometimes pops or clicks out. An observant vet might notice this as well when examining the dog for other things. I have diagnosed countless luxating patellas while I express anal glands or take temperatures on dogs. Sometimes the owner notices that the dog gets their leg stuck in a locked position for a few moments whilst running. The first time a knee “pops out” like this, it can be very painful, and the dog might yelp in pain as the collateral ligaments tear with the first big luxation. After this initial painful luxation, some dogs may show very little pain with the patella popping in and out of its groove freely. Over months and years however, the malalignment in the knee causes an accelerated process of arthritis to develop. Everyone gets arthritis if you are lucky enough to grow old, but with a luxating patella, a knee can become horribly arthritic long before its time. If an owner does not notice the patella popping in and out, they might notice that a painful knee starts interfering with exercise, or when the dog gets up in the mornings.
Diagnosis: How can I tell if my dog has a Luxating patella?
A vet can usually diagnose patella luxation with a simple hands-on examination. X-rays or other imaging techniques might also incidentally diagnose patella luxation, but the first diagnosis is often made long before the x-ray machine has warmed up. Patella luxations are graded for severity on a scale of one to four:
Grade 1: The patella can be pushed out of alignment, but pops back in spontaneously.
Grade 2: The patella luxates spontaneously, and can spend time either in its little groove, or out of position next to the knee.
Grade 3: The patella is luxated most of the time, but can be returned to its normal position by pushing on it.
Grade 4: The patella is permanently luxated, and cannot be reduced to its normal position. It is important that a vet examines a dog with potential patella luxation, even if the dog may have had the condition for years. The instability caused by patella luxation will result in arthritis developing, and the dog may be predisposed to other injuries to the knee once the patella is luxating.
Breeds at risk of Patella Luxation
Almost all small breed dogs are at risk, but the prevalence of patella luxation has increased in some large breed dogs in recent years. Female dogs are slightly more prone to the condition than males. In male dogs, there is no difference in risk for intact or desexed dogs, but interestingly, spayed females are less likely to be affected than intact females.
The following dogs often develop luxating patellas:
Small breed dogs:
• Boston terrier • Yorkshire terrier
• Miniature poodle
Large breed dogs:
• Chinese Shar Pei
• Flat-Coated Retriever
• Great Pyrenees
Prognosis: Can a dog live with Luxating patella?
Patella luxation is luckily one of the most successfully treated orthopaedic diseases in veterinary science. Many people are afraid to have their dogs undergo surgery for this condition, but it is one of the diseases where surgery is usually highly effective.
A good prognosis is only possible with proper rehabilitation and care after surgery however, so speak to a hydro-therapist or rehabilitation expert before surgery to put a recovery plan in place.
Treatment and Rehabilitation for Patella Luxation in dogs.
Three main surgeries have been developed to treat the condition.
The first surgery is called a tibial crest transposition, and involves loosening the ligament that attaches the patella to the lower leg, and repositioning it in line with the centre of the leg.
The second surgery is called a trochleoplasty, and is performed by excavating the groove that the patella slides in.
The third surgery is called lateral imbrication and is performed by cutting out a small slice of the connective tissues over the outside of the knee, which results in increased tension on the patella back towards the middle of the knee. Surgeons would often combine these techniques for the best results.
With proper confinement and rehabilitation therapy, these patients make full recoveries and run around on their new knees for many years. It is extremely important to do proper rehabilitation, however, as I have witnessed many perfect surgeries being ruined by neglectful aftercare. It is also important to do exercises on the other leg, as most dogs develop the disease in both legs.
Hydrotherapy is a crucial part of this and is aimed at strengthening all the muscles of the hind leg so that the entire joint is stabilised. It is also important to mobilise the joint, to allow for a full range of motion post-surgery. Proper rehabilitation will make recovery faster, and minimise long term complications.
We can supply you with a rehabilitation book to assist you after your dog has had surgery, this includes our Medial Patellar Luxation home therapy guide – Which gives you full week by week instructions on how to rehabilitate your dog after surgery.
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