Chest bone deformity in cats typically refers to a common deformity known as “funnel chest,” which is known by the medical term "pectus excavatum". Pectus excavatum is a condition in which the chest bone (sternum) and the ribs to which it is connected grow abnormally. The result is a chest that has a sunken or concave look; ideally it should look slightly convex.

The definitive manifestation of pectus excavatum is the aforementioned sunken appearance of the chest bone. The deformity compresses the lungs and the heart, thus hampering their ability to function normally. As a result, the affected cat has difficulty breathing, and when it does, there’s an increased depth to the breathing. Also, it can be quite a struggle for the cat to move around, let alone do routine exercise. 

Other symptoms of chest bone deformity include:

Currently, there is no known cause of chest bone deformity in cats. Although some researchers believe that some cat breeds are genetically predisposed to develop pectus excavatum, no cat breed is spared from the condition. Indeed, chest bone deformity can occur in cats that are less likely than others to develop it. However, researchers theorize that the deformity occurs when the costal cartilages—which constitute connective tissue that join the ribs to the chest bone—grow in an irregular fashion. This causes the chest bone to move inward. Also, chest bone deformity is linked to other conditions, such as Marfan syndrome, which is a connective tissue disorder.

To make a diagnosis of pectus excavatum, the veterinarian to which you take your cat needs a full and complete history of its health. Informing him or her of the cat’s breed, parentage, genetic background, and onset of signs and symptoms would be extremely helpful. The veterinarian will get x-rays of the thorax to check for any abnormalities. Usually, veterinarians stick with just x-rays. In some instances, however, he or she might be required to go further to determine a diagnosis. This includes using echocardiography to take pictures of the heart to see if it has shifted from its normal position, or whether it has any functional defects. Some questionable findings, such as a heart murmur, may warrant ultrasound. Also, there may be reason to conduct a urinalysis or a series of blood tests.

Once a diagnosis of pectus excavatum has been made, the veterinarian determines the best course of treatment for the condition. In some cases, the condition is mild enough to skip treatment altogether. Depending on the mildness of the deformity, the veterinarian will guide you in compressing the chest in a way that brings the chest bone and costal cartilages to the normal convex shape, or he or she might introduce a splint to do so. However, if the cat has symptoms or the chest is compromised based on the captured radiographs, the deformity is severe enough to deserve treatment. Currently, surgery is the only mode of treatment for chest bone deformity in cats. This usually involves one of the following:

The method of treatment that the veterinarian chooses depends on how bad the condition is and how old the cat is. During surgery, there’s always the risk of the cat succumbing to air leaking in the chest (pneumothorax) or bleeding into it due to needle penetration. The first few weeks after treatment is crucial, since there’s a strong chance of complications occurring. Sores tend to develop on the underside of the cast, so make sure you rub them when it’s time to remove them as advised by the veterinarian. 

Watch out for breathing difficulties, especially during the first two days after surgery. If you detect any issues with the cat’s behavior, breathing, or chest movement, call your veterinarian immediately. The cat is prescribed antibiotics for two weeks, in addition to a short course of painkillers. You should give it manual lateral chest compressions to help decrease the sunken appearance. If the cat gets the fiberglass cast treatment, the cast is kept in place for the next six weeks. Ensure that the cat limits exercise or moving around when the cast is on, especially considering that it may feel sore. It should be kept away from other animals, as well as active children; the best way to ensure this might be to keep it in a cage. Also, change the cat’s bandage material every two weeks.