Patellar Luxation in Chihuahuas: What You Should Know

Does your Chihuahua hold up or “favor” one of his hind legs when walking? While bodily injury can cause Chihuahuas to hop rather than walk on all fours, another possible explanation is patellar luxation. It’s a common orthopedic condition in Chihuahuas. A study conducted by researchers in Sweden found that 23% of Chihuahuas were affected by it.

What Is Patellar Luxation?

Patellar luxation is an orthopedic condition that’s characterized by the kneecap slipping out of the femoral groove. It’s a risk factor for osteoarthritis. As the kneecap constantly slips in and out of the femoral groove, the cartilage in this groove will wear down.

The kneecap is also known as the patella. It’s a mostly flat and round bone. The kneecap supports the surrounding muscles, tendons and ligaments while simultaneously protecting the knee joint from trauma.

The kneecap normally sits in a shallow cartilage-lined groove at the bottom of the femur. Even when Chihuahuas stretch their legs, all of their kneecaps will typically remain within the groove of the respective femur. Patellar luxation, however, involves the kneecap sleeping out of this groove. The term “luxation” refers to the dislocation of an anatomical feature. In patellar luxation, the kneecap becomes dislocated by sipping out of the femoral groove.

Patellar luxation can occur in all dogs, but it’s particularly common in toy breeds. In addition to the Chihuahua, other breeds at risk for patellar luxation include:

• Affenpinscher
• Australian Terrier
• Bichon Frise
• Boston Terrier
• Cavalier King Charles Spaniel
• Cocker Spaniel
• Dachshund
• English Bulldog
• French Bulldog
• Havanese
• Lhasa Apso
• Maltese
• Miniature Pinscher
• Miniature Poodle
• Pomeranian
• Pug
• Shih Tzu
• Silky Terrier
• Toy Poodle
• Yorkshire Terrier

Medial vs Lateral Luxation: What’s the Difference?

Patellar luxation can be classified as medial or lateral depending on the direction in which the kneecap slips. When the kneecap slips inward toward the Chihuahua’s body, it’s classified as medial luxation. When the kneecap slips outward away from the Chihuahua’s body, it’s classified as lateral luxation.

As shown in the illustration below, the kneecap is connected to the patellar ligament. Contraction of the thigh muscles will create a pulling force on the patellar ligament, which in turn moves the kneecap. In a normal knee, the kneecap will continue to move up and down in the femoral groove as the Chihuahua contracts and relaxes his thigh muscles. In a knee with patellar luxation, it will move medially or laterally.

Most cases of patellar luxation in Chihuahuas involve medial slippage. The Chihuahua’s kneecap slips medially toward his body. But some cases of patellar luxation involve lateral slippage, and there are Chihuahuas with patellar luxation that experience both medial and lateral slippage (bilateral).

The 4 Grades of Patellar Luxation

There are four Grades of patellar luxation depending on the severity. Grade 1 patellar luxation is the least severe, whereas Grade 4 is the most severe.

• Grade 1: The kneecap only slips out of the femoral groove when manual pressure is applied. It’s accompanied by minor rotation of the tibia. The kneecap returns to its original position in the femoral groove when the pressure is released.
• Grade 2: The most common type of patellar luxation, Grade 2 involves the kneecap occasionally slipping out of the femoral groove as the Chihuahua walks or otherwise contracts his thigh muscles. It’s accompanied by up to 30 degrees of tibial crest torsion.
• Grade 3: The kneecap has become permanently dislocated. It no longer stays in the femoral groove. Instead, the kneecap remains luxated. It’s accompanied by 30 to 50 degrees of tibial crest torsion. The femoral groove has typically flattened to the point where it no longer supports the kneecap. If the kneecap is manually manipulated back into the femoral groove, it will slip out on its own.
• Grade 4: The most severe — and fortunately the rarest — type of patellar luxation, Grade 4 involves the permanent and extreme dislocation of the kneecap. It’s accompanied by 50 to 90 degrees of tibial crest torsion. The femoral groove has either flattened or developed a convex shape. The kneecap won’t return to the formal groove, nor can it be manually manipulated back into this groove.

Which Legs Are Affected?

Only the hind legs are affected by patellar luxation. Some Chihuahuas experience patellar luxation in a single hind leg, whereas others experience this mobility-restricting condition in both of their hind legs. Regardless, their forelegs should continue to function normally by retaining their kneecaps to their femoral grooves; the kneecap will only slip out of place in one or both of their hind legs.

Signs and Symptoms of Patellar Luxation

Like with other medical conditions, the signs and symptoms of patellar luxation will vary depending on the severity. Chihuahuas with Grade 1 patellar luxation may not exhibit any visible signs or symptoms. They are typically asymptomatic, though some of them may occasionally skip while walking.

In more severe cases of patellar luxation, you may notice the following signs and symptoms:

• Walking while holding up a hind leg
• Shaking the affected hind leg before placing pressure on it again
• A “knock-knee” posture in which both hind legs tilt inward at the knees
• A “bow-legged” posture in which the knees of the hind legs are spaced apart but the paws are close together
• Reluctance to jump
• Unable to bend the affected knee
• Lower energy levels
• Whelping, whimpering or other signs of pain
• In Grade 4 and Grade 5 patellar luxation, complete lameness of a hind leg when walking

Causes of Patellar Luxation

Most cases of patellar luxation in Chihuahuas involve genetic abnormalities. When compared to larger breeds, Chihuahuas and other toy breeds are more likely to be born with abnormalities that predispose them to this orthopedic condition.

Chihuahuas may be born with an abnormally shallow femoral groove, for instance. There must be a certain amount of depth to the femoral groove for it to hold the kneecap. If it’s too shallow, the kneecap will easily slip out.

Misalignment of the patellar ligament and the femoral groove is a common cause of patellar luxation in Chihuahuas. The patellar ligament should be center to the tibia and femur. Some Chihuahuas are born with a misaligned patellar ligament that’s off-center to the tibia and femur. Other Chihuahuas may develop this same type of misalignment as their bodies grow.

Injury to the knee can cause patellar luxation in Chihuahuas. Any form of blunt-force trauma to the knee may damage the patellar ligament. If the patellar ligament becomes torn or loose, it may not keep the kneecap in the femoral groove. It’s not as common as generic abnormalities like a shallow femoral groove or misalignment of the patellar ligament, but injury to the knee can still cause patellar luxation.

Diagnosis for Patellar Luxation

Veterinarians may use a variety of methods to diagnose patellar luxation in Chihuahuas. An orthopedic examination can provide insight into knee function. During an orthopedic examination, the veterinarian will examine the Chihuahua’s walking gait, range of motion and joint extensions. 

In addition to an orthopedic examination, veterinarians may use medical imaging as part of the diagnosis process. X-rays and computed tomography (CT) scans can reveal images of the Chihuahua’s knee structure. Veterinarians may use X-rays or CT scans to look for abnormalities of the tibia, femoral groove or other parts of the knee.

In recent years, veterinarians have begun to use ultrasound to diagnose patellar luxation in Chihuahuas. Ultrasound is an imaging technique that involves the use of sound waves. Sound waves with an ultrasonic frequency are used to create images of the inside of a person’s or animal’s body.

When diagnosing patellar luxation, veterinarians may use ultrasound to look for cartilage damage. The femoral groove is lined with cartilage. There’s essentially a layer of soft cartilage to prevent the knee cap from directly touching the femur. Chihuahuas with patellar luxation may have little or no cartilage remaining in the femoral groove, which is something veterinarians can check by performing an ultrasound.

Treatment for Patellar Luxation

Treatment for patellar luxation may include any combination of physiotherapy, medication, lifestyle changes and surgery. Physiotherapy is designed to strengthen the muscles in the hind legs. As patellar luxation becomes progressively worse, Chihuahuas may no longer place their body weight on one or both of their hind legs. This can lead to muscle loss.

Physiotherapy can strengthen the Chihuahua’s leg muscles so that he can better control the affected hind leg or legs. Because it involves physical activity, such as stretching and flexing, physiotherapy should only be performed under the guidance of a veterinary professional. Veterinary professionals can closely monitor the Chihuahua during the physiotherapy regimen to promote a positive prognosis.

Nonsteroidal anti-inflammatory drugs (NSAIDs) like carprofen and firocoxib are commonly used to treat patellar luxation. Patellar luxation is almost always accompanied by inflammation. The femoral groove contains cartilage to prevent bone-on-bone contact. Rather than touching the femur, the kneecap will move up and down in this cartilage-lined groove.

With patellar luxation, the kneecap will slip medially or laterally. It will essentially “pop out” of the femoral groove, which can cause the cartilage to wear down. The kneecap will then rub against the femur. The bone-on-bone contact between the kneecap and the femur can cause inflammation. NSAIDs are a class of medications that suppress the body’s inflammation response and, thus, reduce swelling.

Veterinarians may prescribe analgesics in conjunction with NSAIDs. Analgesics are designed to reduce pain. They can ease the symptoms of patellar luxation and improve the Chihuahua’s quality of life.

Some veterinarians may recommend lifestyle changes as part of their treatment strategy. If the Chihuahua is overweight, veterinarians may recommend reducing his caloric intake and/or switching to a different type of food. Veterinarians may also recommend joint supplements like chondroitin and glucosamine as part of their treatment strategy.

Surgery for Patellar Luxation

Chihuahuas suffering from Grade 3 or Grade 4 patellar luxation may be candidates for surgery. There are different surgical procedures used to treat patellar luxation, but nearly all of them have the same primary objective: to keep the kneecap in the femoral groove at all times.

One of the most common surgical procedures for patellar luxation is trochleoplasty. It involves deepening the femoral or “trochlear” groove. An abnormally shallow femoral groove may not retain the kneecap. A veterinary surgeon, though, can deepen this groove with trochleoplasty.

Patellar luxation may occur if the femur is abnormally shaped, which may be treated with corrective surgery on the femur. The veterinary surgeon may cut and reshape the femur during this procedure.

Tissue reconstruction is a surgical procedure for patellar luxation. If the soft tissue connected to a Chihuahua’s kneecap is too loose or too tight, it may allow the kneecap to slip out of place. During a tissue reconstruction surgery, the veterinary surgeon can correct the problematic tissue.

Some cases of patellar luxation are treated by surgically moving the attachment point of the patellar ligament. In a normal knee, the attachment point is center to the tibia. In cases of patellar luxation, the attachment point is often located to the side of the tibia. Tibial tubercle transposition is a surgical procedure that involves moving the attachment point of the patellar ligament so that it’s aligned with the tibia.

Video of 3-Pound Chihuahua With Patellar Luxation

Tips for Managing Your Chihuahua’s Patellar Luxation

Following the veterinarian’s recommendations is essential to a positive prognosis. A licensed veterinarian can properly diagnose patellar luxation, and he or she can recommend a treatment strategy to alleviate this orthopedic condition. In addition to this professional advice, however, you should consider the following tips to better manage your Chihuahua’s patellar luxation.

• Invest in an orthopedic bed to reduce pressure on his knees and joints.
• Provide your Chihuahua with doggy ramps so that he can access furniture and other elevated surfaces without jumping.
• When picking up your Chihuahua, hold him underneath the torso without placing pressure on his knees.
• Consider an orthopedic knee brace. Orthopedic knee braces are semi-elastic sleeves that are designed to support and stabilize the knees.
• Encourage your Chihuahua to walk. Forcing him to lie in a bed all day long can worsen his patellar luxation by contributing to muscle loss. Short, gentle walks, on the other hand, will promote stronger leg muscles.
• Place rugs or mats on hard flooring surfaces so that your Chihuahua has better traction.
• Monitor your Chihuahua during walks and playtime while taking note of any changes in his gait. If his gait worsens — he always skips, can longer place pressure on a hind leg, whelps in pain, etc. — inform the veterinarian.

In Conclusion

Patellar luxation is an orthopedic condition that involves the kneecap slipping out of the femoral groove. It can affect a single hind leg or both hind legs. Regardless, the Chihuahua’s forelegs should continue to function normally.

References:

https://www.acvs.org/small-animal/patellar-luxations

https://www.dovepress.com/patellar-luxation-in-dogs-peer-reviewed-fulltext-article-VMRR