Condition Breakdown: Luxating Patella

Skittles, a Norwich Terrier, with grade two medial luxating patella subscribes to a conditioning exercise program to help manage her condition. (Mary Young)

Have you noticed a funny little hitch in your dog’s movement or temporary or occasional lameness? Intermittent lameness can have many reasons for occurring but one of the most common cause of lameness is a condition known as luxating patella.

This condition can grow to be quite painful for your dog and puts them at greater risk of a CCL injury or developing arthritis later in life. While this is a lifelong condition there is much owners can do to manage luxating patella and help reduce their risk of further injury.

In this week's blog, we'll take a closer look at what luxating patella is, how to identify it, the common treatments for the condition, and how early intervention can slow the progression of the condition and reduce injury.

What is luxating patella? 

Holt (2017)

Sometimes referred to as a "trick knee" a luxating patella is a knee cap that moves out of its normal location.
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The patella slides in a groove on the lower end of the femur (the bone that runs between the hip and the knee). A ligament called the "patella ligament" which runs from the bottom of the patella to the tibia, (the bone just below the knee joint) keeps the patella in place. The thigh muscles are attached to the top of the patella. Most cases of luxating patella present as medial luxations, the patella moves towards the inside of the knee, but the patella can also move to the outside or laterally. Studies have shown that medial luxating patella occurs in 83% to 95% of all dogs diagnosed (Maddox, 2017). Small breed dogs were almost exclusively medial patellar luxations while lateral luxations were uncommon, but observed more often in larger-breed dogs.

When the thigh muscles contract, the force is passed through the patella and through the patella ligament, which results in straightening of the knee joint. The patella can luxate because the point where the patella ligament attaches to the tibia can sometimes be attached too far inward. As the thigh muscles contract, the force pulls the patella against the inner groove that it's sitting in.

As the dog moves, the inner groove of the knee can experience wear and the patella can move freely out of the groove or luxate. Minor grades of the condition can be hard to identify and is often first noticed in dogs around two years of age.  

Dogs with this condition can be at an increased risk of injury. Research shows that at least 15% to 20% of dogs with patellar luxation will eventually rupture their cranial cruciate ligament (Mayer 2020). This can occur for two reasons:

1. A luxating patella will change the biomechanics of the knee and cause the cranial cruciate ligament to experience more stress and strain.
2. If the luxating patella is chronic, the knee can become inflamed causing a breakdown of the ligaments (especially cruciate ligaments).

How to Determine if your Dog has Luxating Patella 

Often, I see clients who describe an abnormal gait in their dogs and it's after some closer inspection that we're able to determine that we're dealing with a luxating patella. The signs can range from mild to severe and include temporary or occasional lameness possibly accompanied by a 'hopping' or ’skipping’ motion.

In the video below you can see Fenris, a 4 year old Alaskan Klee Kai, with the tell tale hopping or hitch leg movement. I've slowed down the video and pointed out two instances of the hitch but he actually luxates three times in this short clip. Fenris was diagnosed with Grade 1 medial luxating patella to both his knees but it's his right knee that luxates more consistently.

Eventually, the dog may hold their leg permanently off the ground. If both legs are affected, the dog may adopt a crouched gait and posture, appear bow-legged and may even walk on the forelegs with the hind legs completely off the ground. The dog may also show reluctance to run and jump, have swelling around the stifle, or display signs of pain when the leg is manipulated.

The majority of luxating patella cases are congenital and hereditary, although a mode of inheritance has not been described. Research has show that heritability of patellar luxation is equal between purebred and mixed-breed dogs (Bellumori et al 2013). Occasionally, traumatic cases do occur when a blow is sustained to the retinacular structures, particularly on the lateral side of the stifle joint, however congenital malformations is a more common cause. Females have also been reported to be 1.5 times more likely to be affected than males (Harasen, 2006). Because luxating patella is generally considered an inherited condition it's recommended that dogs with this condition are not used for breeding. Even if only one dog of the breeding pair has the condition it can increase the prevalence of patellar luxation in their offspring by 45% compared to that with two unaffected parents (Lavrijsen 2013). 

Generally speaking, however, luxating patella is more common in small breeds, such as Papillons, Pomeranians, Chihuahuas, Boston Terriers, Jack Russel Terriers, Yorkies, and Miniature or Toy Poodles. Larger breeds have less genetic predisposition to problems with the kneecap but there have been cases of larger breeds also developing the condition (particularly the Akita, Labrador, Golden Retriever, Malamute, Boxer, and Husky). Large breeds can develop a secondary issues with their patella especially if they have an issue with their hips. If a joint above the kneecap like the hip joint, or one below the kneecap like the ankle develops a problem, it can change the ergonomics of your dog's body and cause a ripple effect throughout the leg.

Grading the Luxation 

The condition is usually diagnosed by feel and is assigned a grade based on severity. 

• Grade One (recurrent type): The knee cap can be manipulated out of its groove, but returns to its normal position spontaneously  
• Grade Two (recurrent type): the knee cap rides out of its groove occasionally and can be replaced in the groove by manipulation  
• Grade Three (permanent type): The knee cap rides out of its groove most of the time but can be replaced in the groove by manipulation  
• Grade Four (permanent type): The knee cap is out of its groove all the time and cannot be manipulated back into the groove.  

Depending on where your dog falls on this scale a conditioning program may be suitable as a form of treatment. Grades 3 and 4 are generally harder to manage conservatively as the patella doesn't stay in the the groove of the knee cap often enough. 

As the condition can worsen over time, a dog with an untreated grade 1 or 2 luxations could eventually degrade into a lower grade and may eventually require surgery. Surgical correction of patella luxation grades 1, 2, or 3 generally have a good clinical outcome, whereas surgical correction of grade 4 patella luxations comes with a more guarded prognosis. Not all dogs are good surgical candidates, however, as the breed, age and medical history could effect outcomes. If your dog has a high functioning grade 3 and 4, conservative manage can still have its place. Even with surgery, the treatment goals and approaches of conservative treatment are focused on building strength which will benefit a post-operative dog.  

Late Onset Luxating Patella

Generally speaking, most patients are under two years of age when they start presenting with luxating patella(s), however, aging patients can also show the condition later in life. Retired performance dogs may see a sudden occurrence of subluxation.  This could mean that the dog had a minor grade of luxation throughout the entirety of their life that went unnoticed when the dog was fit. As dogs age the muscles supporting the hind end and the knee may begin to decondition and decrease the stability of the knee and patella. 

Older dogs may also experience some rear end weakness that can place increased strain on the patella. So a late onset luxating patella may be a result of another area of weakness or compensation. 

A Conservative Approach to Treatment 

While dogs with a minor grade may be able to move through life relatively unencumbered over time the condition of the knee can worsen and your dog may begin to experience increased lameness and pain. Other conditions, such as osteoarthritis, may set in and reduce their quality of life. When it comes to treatment of the condition many owners prefer to avoid putting their dog through knee surgery and opt to take a more conservative approach. The conservative approach with regular conditioning exercises started when the dog is young can go a long way to reduce their risk of injury and prevent further degradation of the knee groove, reduce pain associated with luxating and increase their overall quality of life. 

The goal of a luxating patella conditioning program is to strengthen the neighbouring muscles of the knee joint. Conditioning exercises will help to increase the strength of the core, small stabilizer and hind end musculature.  

Some of the exercise that may be included are;

• Sit to Stands - This exercise will help work the flexor and extensor muscles in the rear limbs and mild weight-shifting to the front legs. The sit to stand can also be done on an incline to add greater challenge to the glut and hind end muscles. 
• 1 or 2 Leg/Paw Lifts - This exercise helps body awareness, core/spine strengthening, and small stabilizer strengthening.
• Backing Up - This exercise will target the hamstring muscles, rear end awareness, rear end and core strengthening and improve the dog's ability to weight shift.  
• Figure Eights - This exercise promotes spine range of motion, increases weight bearing and joint flexion (on the limbs closest to the cone), increases joint extension (the limbs opposite the cone), and limb awareness.
• Cavaletti training - This exercise will increase dog's stride length, body awareness and coordination and improves shoulder and hip flexibility. This exercise can also be used to help teach proper gait which may benefit a dog who has learned an improper gait due to the luxation.

Is my dog a surgical candidate? The goal of conservative treatment (e.g. canine physio) is to strengthen the surrounding muscles of the knee enough to provide functional stability and limit any pain or compensation issues. If this can not be achieved, a visit to your primary care veterinarian is likely warranted with a possible referral to an orthopaedic specialist.  ​

Other Conservative Strategies 

There are a number of other conservative strategies that can be employed to address luxating patella that a canine PT can provide. Manual therapy, such as myofascial release, can help ease the tension in the fascia and manage pain and inflammation, helping your dog to function normally. Mobilizations may also be used at various joints to improve range of motion and decrease pain.

Passive range of motion stretches will also help the flexibility and mobility of the joints and muscles. Stretches of the sartorius, hamstring and quadricep muscles 3x week for 30 seconds (1 rep of each) can greatly assist with maintaining proper muscle length (Davies, 2005).

Our goal in conditioning is to improve the strength of the surrounding muscles, limit pain and compensation issues,  and to improve the dog’s mobility. Other treatments that can reduce the risk of injury are:

• Supplements - E.g. 1-TDC, Tumeric, Green Lip Mussel
• Weekly conditioning exercises
• Laser therapy
• PEMF/ Assisi Loop
• Exercise modification (done more frequently for shorter duration)
• Owner education: management of condition, identifying and managing aggravating factors​
• Swimming
• Acupuncture
• Weight management to decrease strain on the joints, muscles, ligaments and tendons. 

If your dog has been diagnosed with luxating petalla reach out your canine PT and see about building a program and treatment plan to help your dog manage this lifelong condition!

Sources

Alam MR, Lee JI, Kang HS et al. Frequency and distribution of patellar luxation in dogs. 134 cases (2000 to 2005). Vet Cop Orthop Traumatol 20(1), 2007: 59 – 64.

Bellumori TP, Famula TR, Bannasch DL et al. Prevalence of inherited disorders among mixed-breed and purebred dogs: 27, 254 cases (1995 – 2010) J Am Vet Med Assoc 242(11), 2013: 1549-1555.

​Davis DS, Ashby PE, McCale KL, McQuain JA, Wine JM. The effectiveness of 3 stretching techniques on hamstring flexibility using consistent stretching parameters. J Strength Cond Res. 2005 Feb;19(1):27-32. doi: 10.1519/14273.1. PMID: 15705041.

Harasen, Greg. “Patellar Luxation” The Canadian Veterinary Journal (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1524842/) 
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Holt, Alexandria D., "Systematic review of patellar luxation in dogs," ​University of Tennessee at Chattanooga (2017) ​https://scholar.utc.edu/cgi/viewcontent.cgi?article=1108&context=honors-theses

Lavrijsen IC, Heuven HC, Breur GJ, et al. Phenotiypic and genetic trends of patellar luxation in Dutch Flat-Coated Retrievers. Anim Genet 44(6), 2013: 736-741.

Maddox, Maria., "Luxating patellas: pathology and treatment options," Today's Veterinary Nurse (2017) https://todaysveterinarynurse.com/articles/luxating-patellas-pathology-and-treatment-options/

Mayer, Julie., "Treatment options for your dog's luxating patella." Dog Naturally (2020) dogsnaturallymagazine.com/treatment-options-for-the-luxating-patella/​