Patella Luxation

Patella Luxation (Dislocating Knee Cap)

Patellar luxation is one of the more common causes of lameness we see in our practice. The condition primarily affects smaller dogs such as Pugs, Yorkshire Terriers and Miniature Poodles. However we also see the problem in some larger breeds such as Staffordshire Bull Terriers and Labradors.

Often the problem affects both knees. One of the greatest concerns we have is that although initially the lameness may not be severe, the arthritis produced by patella luxation as the dog ages can be extremely severe and debilitating. Consequently, we believe early diagnosis and treatment is so important to prevent these chronic changes.

Signs

Depending on when first noted signs can vary greatly with the severity of the disease. In the early stages it may be noticed as a popping of the knee cap in an inward direction either by the owner or at a routine examination with us. This might often be as early as the first or second puppy vaccination.

Many patients present with a skipping, hopping gait where they will suddenly carry the leg up for a few steps.

Some patients become increasingly reluctant to jump up. As the disease progresses the duration and severity of this skipping, then lameness becomes worse.

Causes

Patella luxation or the potential to develop luxation is congenital, i.e. they are born with this potential. Oddly the initiating problem often stems from the hip joint where the angle the femur attaches to the pelvis causes the femur to deviate in an outward direction. As the puppy grows this causes a bowing of the femur and subsequent torsion of the femur and tibia.

It is this misalignment of the femur and tibia that produces the knee cap to dislocate. There then follow a series of consequences.

Femoral groove is shallow – as the patella flicks over the side of the femoral groove this is worn down. The patella doesn’t sit firmly in the groove so there is a lack of stimulation for the groove to form well. The result is a rather dished or flat shape where there should be a deep groove. As the patella moves in and out of the groove it wears the cartilage. This causes pain and triggers a cascade of progressive arthritic changes.

Quadriceps muscles pull at an abnormal angle causing further bowing of the leg, pain and muscle tightness.

Abnormal stresses within the knee then make other knee conditions more likely such as cruciate ligament failure.

Muscles on the inside thigh become tight and shortened pulling the patella out more frequently and further.

It is because of the progressively degenerative nature of this condition that makes early diagnosis and treatment imperative to ensure a pain free dog in the short and often more significantly longer term.

Diagnosis

Lameness is the most frequent presenting symptom that alerts us to a problem with the patella. This may only be infrequent with occasional skipping or hopping.

When we examine your dog and find the patella is either fully luxated or can be popped back and forth, a full assessment of the dog is made to consider any other orthopaedic problems, body condition, muscle tone and symmetry.

At this stage we will probably advise a radiographic assessment of your dog, generally looking at knees, hips and lumbar spine. Once we have this information then we can discuss the best way forward to help your dog.

Treatment

Although surgery is the cornerstone of treatment we also need to take careful consideration of pain relief before during and after surgery. Body condition is an important factor in how well these patients do. We need good muscle bulk and good weight control.

An exercise programme especially immediately post-surgery is also an important consideration. We are lucky enough to have our own water treadmill and a vet who practices acupuncture which may be relevant for your dog.

The following surgical options will be considered often in combination:

Tibial Tuberosity Transposition

This is the most important part of surgical treatment for patellar luxation. It involves cutting the bone the patella ligament attaches to and reattaching this crest with pins and wires to realign the pull of the patella.

The image above shows the reattached tibial crest fixed in place with 2 fine pins and a figure of 8 tension band wire.

Medial Muscle Release

If the patella has been allowed to sit on the inside of the knee for a period then the muscles on the outside of the thigh become stretched and muscles on the inside of the thigh become shortened. If this is not addressed when the tibial tuberosity is moved laterally there is a lot of muscle tension from these medial thigh muscles. Careful dissection allows us to free up the muscle groups and reduce the medial pull post-operatively.

Conversely the lateral joint capsule is often stretched and saggy once the knee cap is repositioned. This will be tightened up or imbricated as part of the surgical closure.

Recession Sulcoplasty

We create a deeper groove in the femur for the patella to sit in. A wedge is cut in the femur and removed. The cut sides of the femur are carefully cut again to widen the gap. The wedge is then replaced. This deepens the groove but maintains the cartilage that the patella glides on.

Ridge Stop

This is an implant that as its name suggests increases the height of the medial ridge of the groove. The ridgestop implant is made of high density polyurethane and fixed in position with screws.

Post-Operative Home Care

When you go home the nurse will go through all the medication and care plan. Please anything you are unsure about just ask.

Antibiotics are normally given for 5 days post op.

For Pain Relief, we tend to start with a combination of a non-steroidal analgesic which should be given every day. We will also send your dog home with additional pain relief for you to use if your dog still feels sore. If in doubt, giving too much pain relief is better than not enough!

If your dog will let you, apply an ice pack wrapped in a tea towel around the stifle three times daily for about seven minutes each day.

Exercise

When you take your dog home, especially in the first couple of weeks we need to keep him / her restricted. Avoid all slippery surfaces (laminate floors etc.), stairs and any form of jumping.

When you are with your dog, they can potter about freely as long as they are on carpets/non slip floors and not able to jump up onto chairs etc.

When unsupervised your dog must be left in either a collapsible kennel or a small room max 3m x 3m.

We do like to start controlled exercise fairly soon after the surgery to keep muscle bulk and good joint movement.

For the first couple of days you can take your dog out to the garden on a lead to go to the toilet then straight back in.

From day 3 onwards slow, controlled steady lead walks initially in the garden then outside are recommended. Initially 5 minutes twice daily ideally with your dog on your right if it was the right leg operated on or left if it was the left.

Exercise can gradually be increased if your dog seems comfortable. Add 5 minutes to the time of each walk. Increasing by this amount every 5 days or so. After week 2 you can also increase the frequency of walks going out 3-4 times. 3-4 shorter walks are more beneficial than one long walk.

We normally check your dog 4-5 days after the surgery then a week later. We then normally have you back in for a post-op X-ray at 4 weeks. Once we can see the implants are stable and things are healing as expected we will get you to increase the amount of exercise.

Physiotherapy

In the early stages we will show you how to do passive range of motion exercises. The important thing with these is they are passive! They involve gentle extension and flexion of the knee. This should be done 2-3 times a day with about 10 slow gentle repetitions. Again if your dog is happy to allow it gentle massage of the quadriceps muscles above the knee for 5 minutes before these passive movements is helpful.

After 3-4 weeks we might suggest some hydrotherapy in our water treadmill. This allows us to build muscle bulk and improve range of motion and gait in a controlled manner.

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