LUXATING PATELLA OR DISLOCATED KNEECAP IN CATS

Luxating patella (kneecap dislocation) is a condition where the kneecap does not remain in its normal location and slides into either the inside or outside of the thigh bone joint groove. This abnormality can cause intermittent or permanent pain, limping and walking difficulty. It most commonly occurs in dogs; however, it also occurs in cats due to congenital (born with) developmental anomalies of the hind leg bones.

The kneecap usually sits in a smooth groove that moves up and down as the knee joint bends and straightens. In cats with luxating patella, the kneecap slips to the inside or outside of the joint when it is supposed to be in the center, therefore restricting normal function. The severity will vary from mild intermittent dislocations to complete frequent dislocations.

Causes

In cats, luxating patella is often caused by structural defects in the bones and soft tissues of the hind leg. In most cases, it is a congenital defect, meaning the cat is born with a pre existing defect in the joint alignment.

Genetics play a large role in all breeds, but especially in certain breeds that have been known to transmit their joint alignment issues throughout generations. Abnormal development of the femur, tibia or patellar ligament may result in incorrect alignment of the kneecap.

Trauma or injury is a less common cause of luxating patella. A fall or accident that damages the joint or a sudden twisting movement of the knee joint may cause dislocation of the kneecap. Obesity may aggravate the symptoms of luxating patella by additional stress on the joint.

Symptoms

Early and Mild Signs

• Skipping or hopping on one back leg
• Limping for a short period of time before it goes away
• Avoiding jumping up high or climbing
• Having some stiffness in the legs upon rising from lying down

More Advanced Signs

• Lameness is present for long periods of time
• Abnormal gait (walking) of the hind legs
• Cat appears uncomfortable with movement
• Reduced energy level
• Muscle loss in the affected limb over time

Risks

Untreated luxating patella can contribute to chronic discomfort, joint instability, cartilage damage and the development of arthritis over time. Repeated episodes of patellar displacement may increase stress on the knee joint and contribute to inflammation, cartilage damage and osteoarthritis.

Recurring dislocations create chronic discomfort, which results in decreased physical exercise and potentially muscle atrophy, creating increased joint instability. It could lead to a reduction in overall quality of life with significant reductions in activities that require jumping or ambulation.

Long term secondary effects include cartilage damage from repeated trauma and the development of degenerative joint disease due to the continued progression of luxation.

Diagnosis

Diagnosis is typically made by a veterinarian through an orthopedic examination and a physical assessment of the pet.

A veterinarian will perform a manual manipulation of the pet’s knee to assess if the patella can move from its natural position. The veterinarian will also grade the degree of luxation (the frequency and ease with which the kneecap comes out of place) when determining what treatments to use.

Diagnostic Methods

• Orthopedic examination
• X-ray for structural integrity and alignment of bones within the joint
• Motion analysis (to examine movement patterns)
• Evaluation of joints for potential degenerative or arthritic changes

This data will assist in developing a plan of care to treat the degree of luxation and develop a treatment plan.

Treatment

The treatment method used will depend on the severity of the condition and the amount of effect it has on the pet’s ability to comfortably move around.

Conservative Management

Pet owners may opt to treat mild conditions without using surgical intervention. Treatment options include managing their pets weight, controlling high impact activities while encouraging safe, controlled exercise to maintain muscle strength.

In addition to these methods veterinarians may prescribe physiotherapeutic techniques and controlled exercises that are designed to increase strength in muscle groups adjacent to the affected area and promote stability in the affected joint.

Surgical Treatment

Cats with moderate to severe luxation, frequent dislocations, pain or significant mobility problems may benefit from surgical correction. There are several types of surgeries available, some involve deepening the femoral groove, others involve adjusting the location of the patellar ligament, while other procedures correct the malformation of the bones. The purpose of surgery is to align the patella properly so that future dislocations do not occur.

Post-Treatment Care

• Limited activity during recovery
• Medications for pain management
• Slow, gradual return to normal movement
• Follow up veterinary checkups

Prevention

Since many cases of luxating patellae are congenital, it may not always be possible to completely prevent them.

• Maintain your cat at a healthy body weight to reduce unnecessary stress on the joints.
• Try not to let at-risk cats jump excessively.
• Keep your environment safe from trauma or injury
• Have regular vet visits for the earliest signs of lameness or loss of mobility
• Since the longer you wait, the worse the potential damage to the affected joints, have your veterinarian treat your cat’s symptoms promptly.