When an infective agent enters the joint, it can create septic or infective arthritis. The joint fluid becomes contaminated with microbes which usually produce exotoxins. These can damage the joint capsule and articular cartilage, initiating an inflammatory response. This is where the immune system launches an attack on the invading organisms resulting in a hot, swollen, painful joint.
Septic arthritis is an urgent situation which needs equally urgent treatment. Antimicrobial drugs are usually administered which reach the affected joint through the blood.
During the inflammatory response, the blood flow to the area increases as does the permeability of the capillaries. Anything being carried in the blood is thus delivered to the relevant area and the toxins removed in the blood at a more rapid rate than would be the case in the uninflamed joint.
The commonest cause of this relatively unusual type of arthritis is a penetrating foreign body like a thorn entering the joint capsule, taking with it a collection of microorganisms.
Infective agents can also enter the joint from the teeth of another dog or any animal that bites your dog on a joint.
Infection during or after joint surgery is also possible, although one would hope that such procedures would only be undertaken in the most sterile of operating theatres with highly skilled surgeons who understand that sterility is imperative.
Under normal circumstances, with a healthy dog living a healthy lifestyle with a good, strong immune system, this disease process is likely to be self-limiting. In a wonderfully healthy dog, white blood cells will enter the joint and remove the invading pathogen.
But if the immune system is overloaded, or suppressed by medication, or weak because of an unhealthy lifestyle, or if a huge quantity of infective pathogenic microorganisms is introduced into the joint, a full blown septic arthritis is likely to develop.
It will probably be necessary for the joint fluid to be aspirated by syringe and analysed under a microscope by a laboratory. The infective agent will be identified, its sensitivity to medication will be determined and appropriate antimicrobial medication can then be prescribed.
It may also be necessary for the affected joint to be opened, the pus drained and the whole joint capsule flushed clean.
Septic polyarthritis is the result of a whole body infection where the infective agent hones in on the joints. Once there, it damages the joint capsule and articular cartilage, causing inflammation and pain.
Affected dogs will be systemically unwell. They will have a high fever, be unwilling to move, want to sleep all the time and not be interested in food at all. In addition to the prescribed medical treatments, you can help your dog through this serious illness by keeping him comfortable, with a nice, thick, soft bed that he can easily access.
Give him filtered water to drink. If he doesn’t want to drink, it is worth gently syringing it into his mouth to keep him hydrated. Give him space, peace and quiet with plenty of love and kindness, completely respecting his needs.