Septic Arthritis
Understanding Your Pet's Medical Diagnosis
What is septic arthritis?
An animal has septic arthritis if germs (pathogenic microorganisms) are found inside one or more joints.
What causes septic arthritis?
In most patients, septic arthritis is caused by germs that are carried by the blood from an infection elsewhere in the body, or from contamination due to a traumatic injury such as bite or gunshot wounds. Septic arthritis can also develop from the spread of a bone infection located near the involved joint, or from germ contamination following surgery. Common sources of blood-borne infection include dental disease and infection of the skin, gastrointestinal tract, prostate gland, and anal sacs.
What are the signs of septic arthritis?
Most often you will note a sudden onset of a severe lameness. Your pet may be depressed and show a loss of appetite. Occasionally, your pet will have a mild degree of lameness that has been slowly progressive. Previous trauma incidents such as a dog bite or penetrating injury may have occurred.
Physical examination findings include:
How is septic arthritis diagnosed?
Your veterinarian may suspect septic arthritis following a thorough physical examination, but will probably perform several tests to confirm the diagnosis and underlying cause. Blood tests may reveal the body's response to an infection. Commonly, the white blood cells will have a "left shift" (increased proportion of young cells). Radiographs (X-rays) are performed to demonstrate the presence of joint changes, and to check for evidence of bone destruction. It is important to obtain fluid from the affected joint (joint tap) so that can be checked under the microscope to confirm the presence of infection, and so that it can be cultured to identify the type of offending germs present (although cultures of the fluid are not always successful in providing germ identification). A joint tap is usually performed under heavy sedation or general anesthesia to ensure accurate placement of a needle into the joint so that appropriate fluid samples can be withdrawn.
How is septic arthritis treated?
Treatment of septic arthritis requires long-term antibiotic therapy. It is recommended that antibiotic therapy be given for 4 to 8 weeks to ensure adequate clearing of this type of infection. Antibiotics are chosen based on the results of joint fluid cultures. Once identification of the offending germ is made, tests can be performed to determine which antibiotics are most effective against that particular germ. Your veterinarian can then select an effective antibiotic. If the joint fluid culture does not grow the offending germ, your veterinarian must use professional judgement to select an antibiotic that is very effective against a wide range of germs. In selected cases, surgery is also sometimes required. During surgery, a catheter is sometimes placed in the joint order to flush (lavage) the joint for a short time.
What is the prognosis for animals with septic arthritis?
Patients that receive treatment early in the course of the condition will respond well to appropriate antibiotic treatment. Those patients who have treatment delayed, or those affected by certain types of germs, will have a guarded to poor prognosis. The development of permanent bony changes (arthritis) may affect normal range of motion in the joint even after the infection is controlled.
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