Wednesday, February 23, 2011

Tracheal Collapse

Tracheal collapse is a chronic, progressive disease of the trachea, or windpipe. The trachea is a flexible tube and, similar to a vacuum cleaner hose, it has small rings of cartilage that help keep the airway open when the dog is breathing, moving, or coughing. The rings of cartilage are C-shaped, with the open part of the C facing upward. Between the two ends of the C is a long band of tissue- the dorsal membrane- that runs the length of the airway. In some dogs, the C-shaped cartilage becomes weak and begins to flatten out. Initially it becomes U shaped but, as the dorsal membrane stretches, the cartilage rings get flatter and flatter until the trachea collapses (Figure 1). The collapse can extend all the way into the bronchi- the tubes that feed air into the lungs, resulting in severe airway compromise in the animal.

Figure 1. Diagram of tracheal collapse. Tracheal collapse is graded mild (Grade 1 = 25% collapse) to severe (Grade 4 =100% collapse). The trachea in dogs most often collapses at the thoracic inlet (green arrows) where the trachea bends to enter the chest.

Initially dogs may present with a harsh dry cough that sounds like a goose honking. Coughing may occur when the dog is picked up or if someone pulls on its collar, since either may put pressure on the airway. As the disease progresses, the dogs may develop exercise intolerance or even turn blue with excitement. The strain of breathing may cause secondary heart disease. Some dogs may also have laryngeal paralysis along with tracheal collapse; the cartilages at the entrance to the windpipe will not open properly and the dogs will develop a wheezy noise when they breathe inward.

Small breed dogs are most commonly affected with the disease, particularly Yorkshire terriers, Pomeranians, poodles, and Chihuahuas. Affected dogs are often middle aged or older, though it can be seen in some young dogs as well. Dogs that are overweight or that live in household with smokers may be more at risk or at least more likely to show clinical signs.

Medical management includes weight loss, cough suppressants, antispasmodics or bronchodilators to reduce airway spasms, and sedation to reduce coughing and anxiety. Some dogs may require heavy doses of sedation to break the coughing cycle, since coughing will irritate the airway and lead to more coughing. Additionally dogs should be kept away from smoke and other environmental pollution (coughing may be even stimulated by smoke or other irritants brought in on clothing and hair). Dogs with infections are treated with antibiotics.

Medical management may work for up to 70% of dogs, particularly those that have mild collapse. Some animals do not respond to medical management, however, and require surgical or interventional treatment. Collapse of the trachea in the neck or thoracic inlet- the front part of the chest where the trachea bends- is treated by surgical placement of plastic rings (Figure 6, 7) or spirals around the outside of the trachea. If the collapse is deep within the chest, it can sometimes be corrected by placing a stent- a spring like device- inside of the airway to hold the trachea open (Figure 8). Most dogs that receive stents will require ring placement in the neck or thoracic inlet region as well.

Medical management is continued after the surgery, and most dogs are placed on a course of steroids to reduce swelling and irritation from the ring or stent placement. Owners must continue to keep their dogs thin and avoid exposing them to smoke or other airway pollutants. Also, they should use a harness that is specially made to fit low on the chest so that no pressure is put on the neck area when the dog is being walked. In winter months, a humidifier may help relieve irritation from dry, heated air.

At this time there is no known prevention for tracheal collapse, although reducing weight or exposure to airway irritants such as smoke may help. About 70% of dogs that are treated with medical management alone will show some improvement. About 20% of dogs that undergo tracheal ring placement will require a tracheostomy- a temporary or permanent breathing hole in the neck. About 75% of dogs improve after surgical placement of rings. Dogs that are older than 6 years of age or that have laryngeal or bronchial disease have more complications and a poorer long-term outcome. Of dogs that receive stents, 95% are immediately improved and 90% are markedly improved at the time of recheck. Control of coughing is important for a good outcome, and dogs with bronchial collapse (and therefore continued coughing) are much more likely to have problems after stent or ring placement.

This information on Tracheal Collapse and much more can be found on the American College of Veterinary Surgery's website!

Wednesday, February 16, 2011

Patellar luxation

The patella, or knee cap, is a small bone buried in the tendon of the extensor muscles (the quadriceps muscles) of the thigh. The patella normally rides in a femoral groove within the stifle. The patellar tendon attaches on the tibial crest, a bony prominence located on the tibia, just below the knee. The quadriceps muscle, the patella and its tendon form the “extensor mechanism” and are normally well-aligned with each other. Patellar luxation is a condition where the knee cap rides outside the femoral groove when the stifle is flexed. It can be further characterized as medial or lateral, depending on whether the knee cap rides on the inner or on the outer aspect of the stifle.

Patellar luxation is one of the most common congenital anomalies in dogs, diagnosed in 7% of puppies. The condition affects primarily small dogs, especially breeds such as Boston terrier, Chihuahua, Pomeranian, miniature poodle and Yorkshire terrier. The incidence in large breed dogs has been on the rise over the past ten years, and breeds such as Chinese shar pei, flat-coated retriever, Akita and Great Pyrenees are now considered predisposed to this disease. Patellar luxation affects both knees in 50% of all cases, resulting in discomfort and loss of function.

Patellar luxation occasionally results from a traumatic injury to the knee, causing sudden non-weight-bearing lameness of the limb. It may also develop subsequent to cranial cruciate deficiency in dogs that will typically have a chronic history of lameness. However, the cause remains unclear in the majority of dogs. Congenital patellar luxation is no longer considered an isolated disease of the knee, but rather a component/consequence of a complex skeletal anomaly affecting the overall alignment of the limb, including:
  • Abnormal conformation of the hip joint, such as hip dysplasia
  • Malformation of the femur, with angulation and torsion
  • Malformation of the tibia
  • Deviation of the tibial crest, the bony prominence onto which the patella tendon attaches below the knee
  • Tightness/atrophy of the quadriceps muscles, acting as a bowstring
  • A patellar ligament that may be too long
You should seek veterinary surgical advice if you have any concern about the gait of your pet or if your primary veterinarian advises you to do so. The severity of patellar luxation has been graded on a scale of 0 to 4, based on orthopedic examination of the knee. Surgical treatment is typically considered in grades 2 and over:

Grade I

Knee cap can be manipulated out of its groove, but returns to its normal position spontaneously

Grade II

Knee cap rides out of its groove occasionally and can be replaced in the groove by manipulation

Grade III

Knee cap rides out of its groove most of the time but can be replaced in the groove via manipulation

Grade IV

Knee cap rides out of its groove all the time and cannot be replaced inside the groove

Thank you American College of Veterinary Surgery for making this information available for all who are interested!