Luxating Patella

Patellar luxations (knee cap dislocations) occur frequently in dogs and occasionally in cats.  It occurs when the patient's kneecap (patella) is dislocated from its normal anatomic position in the groove of the thigh bone (femur). It is for this reason that most dogs with the condition will hold up their hind legs for a few minutes. Commonly, we see this condition in toy or small breed dogs such as the Yorkshire Terrier, Pomeranian, Pekingese, Chihuahua, and Boston Terrier. Female dogs are 1 1/2 times more likely to acquire the condition. It can also occur in large or giant breed dogs and occasionally in cats.  Most animals have intermittent patella luxations causing occasional lameness.  Other times, the luxation may be frequent or permanent and the dog or cat may be constantly limping on the leg or not using the leg at all. 

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Symptoms and Types

The specific symptoms of a dislocated kneecap will depend on the severity and persistence of the condition, as well as the amount of arthritis that is involved. Typically, a dog with a dislocated kneecap will exhibit prolonged abnormal hindlimb movement, occasional skipping or hindlimb lameness, and sudden lameness. The dog will rarely feel pain or discomfort once the kneecap is out of position, only feeling pain at the moment the kneecap slides out of the thigh bone's ridges. You can view a medical diagram of patellar luxation in a dog here

Causes

A dislocated kneecap is usually caused by a genetic malformation or trauma. The clinical signs of the genetic condition will normally start showing approximately four months after birth. Medial patellar luxations are associated with a “bow-legged” confirmation while lateral patellar luxations are associated with a “knock-kneed” posture.

Diagnosis

Diagnosis is via a physical examination and radiographs (x-rays).  Patellar luxations are typically graded in an effort to better track the progression of the luxation over the animal's life.  The grading system ranks the animal between 1 and 4. See below for detail. A dislocated kneecap is diagnosed through a variety of means. Radiographs are taken to determine if other disease processes are evident. It is also necessary for the veterinarian to perform an examination by touch to feel for kneecap freedom. A definitive diagnosis is generally very straightforward for dogs with patellar luxation. This is especially true if the lameness has been present since your dog was a puppy. If your dog is older, and the severity of lameness has recently worsened, other causes of lameness should be evaluated. Other problems of the knee such as rupture of the cranial cruciate ligament, knee infection, joint cancer or immune diseases such as polyarthrtitis can complicate therapy for patellar luxations. Other potential diagnoses include hip dysplasia, herniated intervertebral disc or problems with the femur or tibia (i.e. bone cancer or fungal infection).

Grade 1: The patella can be luxated with hand manipulation, but returns to its normal location without assistance and is almost always in an appropriate position. Grade 1 luxations are infrequently associated with any lameness.

Grade 2: The patella will luxate spontaneously, but is most often in its normal position. Significant lameness can be associated with grade 2 luxations.

Grade 3: The patella will luxate spontaneously and is most often located out of its normal position. It can however be returned to its normal location with hand manipulation. Significant lameness is often associated with grade 3 luxations.

Grade 4: The patella is always located out of its normal position and cannot be returned to normal with hand manipulations. This grade is often associated with a severe “bow-legged” or “knock-kneed” limb appearance, and often causes severe lameness. Grade 4 luxations can cause debilitating lameness especially in large dogs.

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Management

Most mild to moderate cases of patellar luxation can be treated with pain management and physical therapy as needed.  In the severe cases, surgery may be necessary in order to keep the patella in the correct position and bring pain relief to the animal.

Physical Therapy

The goal of physical therapy is to strengthen the muscles that support normal patellar motion, and improve flexibility of the surrounding joints and muscles. Because the joints 'above' the knee and 'below' the knee can affect the knee joint itself, care must be taken to address any issues in those areas as well. If the patient lacks flexibility in his hips, or if the quadricepts muscles are more overdeveloped than the hamstring and glute muscles, addressing these imbalances will  improve the stability of the kneecap.


Physical Therapy Exercises For Your Dog (always follow your veterinarian's advice when planning a physical therapy protocol for your pet) :

  • Have your dog move from 'sit' to a 'stand' several times in a row. Make sure he sits squarely, not 'camping over' to one side
  • If you have carpeted stairs, have your dog ascend and descend three to 5 times. You can also find a steep hill and have him walk up (slowly - patients moving too fast or trotting can 'cheat' and hold up the affected limb) and down or zig-zag across the face of the hill.
  • Teach your pet to army crawl by having him in a down position and slowly lure him forward - encourage him to keep his rear end down
  • Walking over cavalettis will encourage flexion and extension of the stifles
  • Underwater treadmills or swimming are excellent ways to strenghten the surrounding knee structures. Have your pet wear a lifevest if you cannot see the bottom of any body of water, or if the water depth covers the topline of your pet!

Sometimes, chronic cases can lead to erosion of the cartilage on the femur from the constant friction, and eventually, to osteoarthritis. In this case, pain is usually involved and lameness is more constant and severe. Occasionally, a luxating patella can lead to a ruptured cranial cruciate ligament. The literature states that at least 15% to 20% of dogs with patellar luxation will eventually rupture their cranial cruciate ligament. Two main reasons why this scenario may follow are that the luxating patella will change the biomechanics of the knee and subject the cranial cruciate ligament to more stress and strain, and the inflamed environment inside an arthritic joint will cause a breakdown of the ligaments (especially cruciate ligaments).

Surgical Correction

Surgery is recommended for animals with grades 2, 3 and 4 luxations that have significant lameness. Dogs with grade 3 or 4 patellar luxation generally will have significant lameness and therefore surgical correction is recommended. The goal of surgery is to keep the patella in its appropriate location at all times. Because every situation is different, the surgeons' approach may be different even in similar cases. There are generally three main surgical maneuvers:

(1) Trochleoplasty – The trochlear groove, located at the end of the femur, is abnormally shallow in dogs with patellar luxations. If abnormally shallow, then the groove is deepened in a surgery called a trochleoplasty.

(2) Tibial Tuberosity Transposition – The tibial tuberosity, which attaches the patellar ligament to the tibia, 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, and typically heals during the next 8 weeks.

(3) Lateral Imbrication and Medial Release – 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  opposite is performed in dogs with lateral patellar luxation.

 

 

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