What you need to know about luxating patella
Updated: May 23
Hello! This blog post I intend to cover information about luxating patella. This is a fairly common ailment that effects predominately smaller breeds. Breeds most commonly affected would be your: Boston terriers, Pomeranians, chihuahuas, pekingese, rat terriers, and so on.
Luxating is a fancy word for dislocation and patella is the medical term for knee cap , so put the two together and the condition you have is knee caps that won't stay where they are supposed to. The knee cap seems like a trivial little bone, why is it so important that it stays in the right place?
Why do pets have knee caps?
This is a great video to illustrate why knee caps are so important. Physics at work! Patellas are uniquely shaped circular bones that fit in the groove between the big thigh bone, the femur, and the shin bone, the tibia. It's primary function is to act as a fulcrum for the patellar tendon as a class one lever system. This is big fancy talk for it makes the motion of the knee MORE EFFICIENT and able to BEAR HEAVIER LOADS. However, often times there are malformations of the tendon and/or the patella that cause this delicate anatomical system to go awry.
Anatomy of the dysfunctional knee:
There are several common culprits (that may happen alone, or together) when a dog is diagnosed with luxating patella.
1. The groove for the patella (known as the trochlear groove) is malformed or TOO SHALLOW.
2. The tibial tuberosity (the attachment for the patellar tendon) is not formed correctly or is OFF CENTERED.
3. The patellar tendon is TOO TIGHT or TOO LOOSE therefore causing a tracking disorder.
4. A sudden INJURY causes the patella to dislocate.
5. Bad breeding has led to postural changes (aka BOW LEGGEDNESS) which predisposes the knee to further strain
The patella can move several ways. The most predictable is MEDIAL displacement, also known as, towards the inside. The second most common is LATERAL displacement, also known as towards the outside.
The patella can also move SUPERIOR (upwards) also known as patella alta and INFERIOR (downwards) also known as patella baja. Alta is the 3rd most common, but patella baja is rare (in people and pets.)
How to grade a patellar luxation:
Assessing medial VS lateral
Figure A: How your vet will stress the knee to see if there is any lateral translation of the patella
Figure B: How your vet will stress the knee joint to see if there is any medial translation of the patella
When performing a physical exam of your animal, your vet will use the following scale to grade the severity of your dog's patellar issue:
1: Can push on the kneecap but it stays in the groove.
2: Can easily be pushed out, but mostly stays in the groove.
3: Kneecap mostly stays out, but can be pushed back in.
4: Mostly out of the groove, cannot be pushed back in.
Obviously, the higher the grade, the worse off your dog is. A grade 1-2 is easily managed with conservative measures, a grade 3 requires bracing at all times and is most likely surgical, and a grade 4 immediately needs surgery to correct.
What will it look like if my dog has luxated their patella?
Often dogs with patellar problems will "walk funny," puppy sit and/or sit unevenly, or be 3 legged lame like the one in the video.
I often find that they have difficulty going up/down stairs, will bunny hop, and will often yelp after suddenly starting to run after something.
Every dog is different, of course, but it's important to have your veterinarian to evaluate your pet and grade the dysfunction of the knee so you can know how to proceed.
(1) Trochleoplasty – As previously mentioned, the trochlear groove, located at the end of the femur, is abnormally shallow in dogs with patellar luxation. The groove is therefore evaluated in all dogs at the time of surgery. If it is abnormally shallow, then the groove is surgically deepened. Here are 3 different "bone shaving" techniques.
(2) Tibial Tuberosity Transposition – The attachment of the patellar ligament to the tibia, the tibial tuberosity, is detached and moved towards the outside of the joint in dogs with medial patellar luxation. In dogs with lateral luxation, the tibial tuberosity is moved towards the inside of the knee. The tuberosity is then stabilized in its new location with small pins.
(3) Lateral Imbrication and Medial Release – This procedure focuses on bringing bones closer together or further apart. The tissues that surround the patella are loosened or released on the inside of the knee and tightened or imbricated on the outside of the knee in dogs with medial patellar luxation. The exact opposite is performed in dogs with lateral patellar luxation.
(4) Desmotomy – Instead of correcting the bony abnormality, this surgery is focuses at correcting soft tissues surrounding the knee. Sometimes the ligaments are too lax (also known as loose) and this makes it hard for the knee cap to stay in proper position. The tissues that surround the patella are cut to loosen or tighten in specific areas. For example, if the patellar tendon is too loose, often it will be cut and shortened to better hold the patella in position. These procedures are often unsuccessful for long term correction if conducted in isolation. A desmotomy will often be performed in conjunction with another procedure.
(5) Knee replacement -- Similar to a human replacement, this completely corrects the bony abnormalities and replaces it with a surgical implant(s). This is not a widely used option.
MANUAL THERAPY (Adjustments/Massage) !!
I cannot stress this enough. Proper alignment of the hips, pelvis, and lower back are critical to the success of your pet's patellar issue. A gentle adjustment can correct the motion of the joints so the tracking issues are minimized and a massage can correct the tone of the muscles surrounding the knee (not too tight, not too loose). You'd be surprised at how many compensation patterns will arise in a chronic knee problem.
Important note: I can see dogs PRE-SURGICAL and POST-SURGICAL for patellar problems. If there is a surgical correction made, I would shift my focus at working on stabilizing structures away from the knee joint itself.
A dog with a grade 3 luxating patella needs to immediately be put in a brace. There are several braces available, but ultimately you want a brace that is going to keep the knee cap snug in the trochlear groove. I am partial to hard braces over soft ones. Sometimes kinesiology taping will suffice as a short term solution, but ultimately, owners need to invest in a long term bracing solution.
Here's a great video encapsulating what we've already talked about. In this video, he also discussed some proactive exercises to help your dog rehabilitate the knee
1. Sit to stand exercises
2. Going up down stairs
Some others he did not discuss ("high tech" options):
3. Wobble board
4. Underwater treadmill
5. Canine cavalettis