Osteomyelitis

Osteomyelitis is an infection within the bone and marrow. It can occur when bacteria enter a traumatic wound such as a bite or gunshot or secondary to penetration by a foreign object such as a nail, etc. More commonly however osteomyelitis arises as a complication of surgery on a bone usually following repair of a fracture with metal implants. Rarely osteomyelitis can develop as a result of infection being carried in the bloodstream and settling in the bone. Most cases of osteomyelitis are caused by bacterial infections but in warmer climates fungal infections can also affect the bones. Osteomyelitis is more common in dogs, but it can also affect cats with much less frequency.

©Douglas McCallum

Osteomyelitis can develop if infection is able to enter bones due to contamination during surgery or after an accident. The risk of infection entering the bone during surgery increases with the length of the operation, when there is a lot of tissue damage around the surgical site and in patients with poor immune systems. Deep wounds such as gun shot wounds or bites pose the most risk for bacteria entering the bone. Tooth root infections can also spread from the teeth into the bone of the jaw.

Young cats occasionally develop osteomyelitis due infection in the blood settling out in the bones. Young animals have growth plates at the end of each bone and since these have an increased blood supply, they are the areas most prone to infections.

Cats with infection will feel unwell, be off their food and may have a high temperature. The affected bone/limb will be very painful, so cats with osteomyelitis are likely to lame, stiff or unwilling to exercise. There may also be pain, redness and swelling at the site of a wound or a discharge from the wound. If any of these are noted, an examination with a veterinarian is required.

Your veterinarian would probably be suspicious that your pet may have an infection if they show any of the signs mentioned above. To confirm whether the infection is within the bone or just within the wound itself your veterinarian will want to take X-rays of the bones, or in some cases, an MRI or CT scan may be needed. The changes in the bone may not be visible on X-ray immediately and can take 7-14 days to develop after infection. Identification of the cause of infection is very important so samples may need to be taken from the wound or deeper tissues. A blood and urine sample is sometimes required in neonates (kittens under 4 weeks old) to check for infection within the body.

Osteomyelitis can be treated and in some cases cured. In other cases however osteomyelitis becomes chronic requiring ongoing medication. Early diagnosis and treatment is essential to ensure a good outcome. It is important that samples of any infection are collected to identify the causing agent so that correct treatment is prescribed the first time. If your pet is very unwell, they may have to be admitted to hospital initially for intensive treatment. Long courses of treatment are always required which may need to be continued for many weeks after all signs of infection have resolved. It is very easy for pockets of infection to hide away in the bones and if treatment is stopped too soon these may flare up again. Worse still, if the infection recurs it may then be resistant to the previous treatment.

Since bone infection is painful your pet will also need a long course of pain relief to keep them comfortable during the recovery period.

If an infection develops in any bone where there are plates or pins to repair a fracture these will probably have to be removed. Infection can hide away around these implants and it is very difficult to achieve a resolution if any implants are left in. In a few cases it can be very difficult to control infection and amputation may be recommended. Cats that have amputations make a full recovery and most lead happy normal lives.

In the case of osteomyelitis, prevention is the best option where possible. In most cases of fracture repair antibiotics are not needed after surgery. However if your veterinarian is concerned about the risk of infection after surgery, especially where the bone has broken through the skin or when a wound is present  they will prescribe antibiotics for your pet. You must make sure that you give these as directed and always complete the course – even when your pet seems well.

If osteomyelitis has developed, a long course of treatment will be required and your veterinarian will need to carry out regular monitoring of the affected area to make sure your pet is getting better. Regular X-rays will be taken to monitor bone healing. Repeated surgeries may also be required, either to take out plates or screws or to remove any dead or infected bone.

Some of the drugs used to treat osteomyelitis can have significant side effects and your pet will need to be monitored carefully in case any of these develop.