Septic Arthritis

Any joint cavity contains synovial fluid, cellular matter and some white blood cells. Bacterial infection of this joint cavity is called Septic arthritis or Infectious arthritis. It is regarded as the most perilous type of acute arthritis. Amongst 100,000 general people, 2 to 10 have this disease. Also, in 100,000 rheumatoid arthritis patients, 30 to 70 are affected by it. About half of the cases are pertaining to knee joints. Wrists, hips and ankles are also involved.

Symptoms of Septic arthritis

• sedimentation rate more than 50 mm/hr - true for 60 to 80% cases
• feverish condition - true for 40 to 60% cases
• high leukocyte count - true for 25 to 60% cases

Generally, a single joint exhibits swelling and there is pain after active or passive movement. Those having rheumatoid arthritis, systemic connective tissue disorders and gout are more prone to this disease. In 10 to 19% patients, the disease appears as polyarticular arthritis.

Causes of Septic arthritis

• intravenous drug use
• record of sexually transmitted disease
• immunosuppressive states
• recent steroid injection
• joint disease

Diagnosis of Septic arthritis
The synovial fluid analysis should have the following parameters:

• gram stain
• culture
• leukocyte count
• differential and crystal examination

When a leukocyte count of more than 50,000 along with a polymorphonuclear leukocyte predominance is seen, Septic arthritis is generally inferred. The gram stain is found positive in 11 to 80% cases. Rarely, the precipitated mucin in the synovial fluid may lead to a false positive. In 90% of nongonococcal bacterial arthritides, the synovial fluid culture is positive.

Differential diagnosis

• Seronegative spondyloarthropathies like psoriatic arthritis, Reiter's syndrome, ankylosing spondylitis and arthritis pertaining to inflammatory bowel disease can show up as an acute inflamed joint
• 20% patients having untreated Lyme disease develop chronic persistent synovitis
• 15% of people with infective endocarditis are affected by this disease
• those having chronic joint disease are at a greater risk of septic arthritis as the delay in diagnosis and start of treatment may cause a severe flare-up of the disease

Treatment of Septic arthritis

1 - Antibiotic treatment
The choice of the antibiotic depends on following factors:

• age of the patient
• assumed source of infection
• infection profile of patient
• immunosuppression like the record of diabetes
• suspected pathogenic organism

The treatment is planned as follows:

• initially, parenteral antibiotics are used. Cephalosporin or semi-synthetic penicillin is advised. If there is allergy to penicillin, then clindamycin or vancomycin is prescribed
• third generation cephalosporins are recommended for gram-negative bacterial infection
• direct inoculation of antibiotics is not essential as it is not more useful than parenteral antibiotics

The duration of this treatment depends on response of the patient and the organism isolated during final culture.

2 - Draining infected joints
Needle aspiration is employed for simple cases. For complex ones like shoulder, hip or sacroiliac joints, an open arthrotomy is the initial option. After arthrotomy, the joints must be closed. Draining these joints with closed suction systems is done. Surgical treatment is considered for patients who do not respond to antibiotics or have diseases like diabetes, rheumatoid arthritis, immunosuppression or systemic symptoms. The objective of surgical method is the removal of nonviable tissue and purulent substance to finalize the need of synovectomy.

3 - Prosthetic joint infection
In a large number of cases, removing the prosthetic joint is essential. This is done by excision arthroplasty or reimplantation of the joint. There is a 4 to 6 week antibiotic therapy between the removal and reimplantation of a new prosthesis. If surgical removal is not practical, then long-term suppressive antibiotics is the choice.

It has been found that after the symptoms start if the patient starts treatment within a week, there is a good response. If treatment is started after a month, the response is poor.