Bacterial ArthritisDz

Synonyms: Septic arthritis, infectious arthritis, gonococcal arthritis.

ICD-9 Codes: Pyogenic arthritis, 711.0; gonococcal arthritis, 098.5; bacterial arthritis unspecified, 711.4.
Definition: Bacterial arthritis is a bacterial infection of the joint space that may affect any type of joint.

Etiology: Most cases of bacterial arthritis are hematogenously disseminated. Others may occur by direct invasion (e.g., trauma) or contiguous spread (e.g., osteomyelitis). Reasons for invasion of the joint space by bacteria are not known, but preexisting articular abnormalities (e.g., RA, OA) or previous surgery may contribute to entry of the infectious agent. Comorbid conditions such as diabetes mellitus or drugs (corticosteroids) that impair immune function may be contributing factors.

At-Risk Populations: Those at risk include the very young, elderly, or immunosuppressed (e.g., by cytotoxics or corticosteroids); those with chronic arthropathies (e.g., RA, OA), prosthetic joints, repeated joint aspiration or injection, or systemic illness (e.g., chronic liver disease, neoplasia, sickle cell); intravenous substance abusers; and those engaged in high-risk sexual activity or who have had recent trauma or surgery.

Pathology: Joint cultures are usually positive for the causative agent unless antibiotics have been previously given. An important exception is gonococcal arthritis, in which >90% of synovial fluid cultures are often negative, even with appropriate culture techniques. Common pathogens in septic arthritis include staphylococci (Staphylococcus aureus, Staphylococcus epidermidis), streptococci (Streptococcus pyogenes, Streptococcus pneumoniae), neisseriae (Neisseria gonorrhoeae, Neisseria meningitidis), Haemophilus influenzae, Salmonella, Proteus mirabilis, and Bacteroides fragilis.

Demographics: All age groups are susceptible. An increasing percentage of patients have a chronic underlying disease (e.g., RA, diabetes), but healthy individuals can also be affected. Septic arthritis in children is usually caused by S. aureus, group B streptococci, or H. influenzae. Young adults are likely to have gonococcal or staphylococcal infection. The elderly are commonly affected by bacterial arthritis owing to staphylococcal, streptococcal, gram-negative, and polymicrobic infections.

Cardinal Findings: The classic presentation is an acute monarticular arthritis with effusion, warmth, and erythema, often accompanied by fever. Polyarticular onset occurs in a minority of cases and carries a poorer prognosis.

—Gonococcal arthritis: Typically seen in young, sexually active (often menstruating) females. Gonococcal arthritis often affects the knees, ankles, wrists, or elbows as monarthritis or oligoarthritis. Tenosynovitis and migratory arthralgias are common, and characteristic pustular (often painful) lesions are found on the skin. Fever may be absent, and a minority will have genitourinary, pharyngeal, or rectal symptoms on presentation. If suspected, every orifice should be swabbed and cultured for gonococcus on Thayer- Martin culture medium. A small minority of patients have a positive synovial fluid culture.
—Staphylococcal arthritis: Usually monarticular (seldom polyarticular), staphy-lococcal arthritis affects the knee, hip, shoulder, elbow, wrist, or ankle, and
>90% of patients exhibit high fevers. Involvement of the sternoclavicular joint, shoulder, or sacroiliac joint should raise suspicion of a staphylococcal infection and, possibly, intravenous substance abuse. Patients with preexisting arthritis (e.g., RA) are prone to infection with S. aureus.
—Prosthetic joints: Fewer than 2% of those with joint replacements develop a septic joint. Those at greatest risk are patients with RA, with distant infections, or who use corticosteroid or are undergoing revision arthroplasty. When septic arthritis immediately follows the procedure, S. epidermidis, S. aureus, or skin anaerobes are the most common pathogens. High fevers and purulent effusions develop. Late prosthetic infection (>1 year postoperatively) is usually less symptomatic and is most likely to be caused by S. aureus, non–group A streptococci, and gram-negative organisms.
—Intravenous substance abuse: Common sites of infection include the shoulder, sternoclavicular, and sacroiliac joints. Infections in the sacroiliac joint may present as low back or buttock pain with only subtle suggestions of infection. These patients are commonly infected by S. aureus and gram-negative organisms (e.g., Pseudomonas aeruginosa).

Diagnostic Tests: Joint aspiration and culture of synovial fluid is usually diagnostic in those with nongonococcal septic arthritis (Table 5). Blood should also be cultured and is frequently positive in nongonococcal arthritis. Other measures, such as the synovial fluid WBC count and ESR or CRP elevations, are only suggestive. Joint aspiration and the interpretation of synovial fluid results are discussed on p. 17. Aspiration should be performed with a large-bore needle to remove as much purulent material as possible. Synovial fluid WBC counts should be >30,000 cells/mm3 with gonococcal arthritis and >50,000 cells/mm3 with nongonococcal septic arthritis. The percentage of neutrophils is as important as cell counts and usually exceeds 85% in septic arthritis. The presence of crystals in synovial fluid does not exclude a coexistent infection. Gram stains are useful in making initial antibiotic choices, but culture confirmation is required. Needle aspiration should not be performed through skin or soft tissues that show signs of infection. If the joint in question has been surgically replaced, orthopaedic consultation should be considered before any joint aspiration or injection.

Imaging: Radiographs are seldom revealing and may only show soft tissue swelling with acute septic arthritis. Radiographic changes may take 2 to 3 weeks to become apparent. Thus, an early diagnosis must be established on clinical grounds and synovial fluid culture. The presence of gas formation should suggest infection with Escherichia coli or anaerobes. Radiography and other modalities may be necessary to diagnose an infected prosthetic joint. Radiographs may show bone resorption and radiolucency at the implant-bone interface, with or without evidence of overlying periosteal reaction. Technetium bone scanning may suggest an infected prosthesis before changes on plain radiography. MRI and gallium- and indium-labeled WBC scanning have not been shown to be of value in such patients.

Keys to Diagnosis: Acute monarticular arthritis with fever is the most common presentation, but polyarticular and subacute afebrile presentations also occur. In patients with inflammatory types of arthritis (e.g., RA), activity in one joint that seems out of proportion to that in others should raise suspicion of septic arthritis. Acute inflammatory monarthritis in the setting of positive blood cultures should strongly suggest septic arthritis.

Differential Diagnosis: Bacterial arthritis may often be confused with other forms of infectious arthritis (viral, fungal, mycobacterial). The infectious arthropathies are compared in Table 6. Bacterial arthritis should also be distinguished from acute crystal-induced arthritis (e.g., gout, pseudogout), Reiter ’s syndrome, Lyme disease, septic bursitis, overlying cellulitis, osteomyelitis, foreign body reaction, fracture, or mechanical joint derangement.

Therapy: Parenteral antibiotics must be given as soon as possible after the initial joint aspiration. Although culture results are pending (usually 24–48 hours), the initial antibiotic should include coverage for S. aureus (Table 6). Parenteral therapy is recommended for at least 3 weeks for S. aureus and gram- negative organisms, 7 days for gonococcal infection, and 2 weeks for most other organisms (e.g., S. pyogenes, H. influenzae). Follow-up therapy with oral antibiotics is of unproven benefit. With the availability of long-lasting intravenous access lines and home care teams, prolonged hospitalization is not required. Before hospital discharge, serial joint taps must show a steady and marked decrease in synovial fluid WBCs and sterile synovial fluid culture. There is no role for intraarticular antibiotics.

Surgery: The role of surgical drainage is controversial except in inaccessible sites such as the hip, where a surgical approach (open drainage or fluoro- scopically-guided needle aspiration) is often required. In children, all septic hips require arthrotomy to reduce intraarticular pressure and allow adequate drainage. Most other joints can be treated by serial needle aspirations and do not require surgical drainage unless the leukocyte count does not drop as expected or cultures do not rapidly become sterile.

Prognosis: In general, mortality rates are below 5%. Prognosis is poorest in the elderly and those with gram-negative infections, polyarticular involvement, prosthetic joints, or delayed diagnosis. If less than 1 week elapses before initiation of therapy, the prospect for maintaining normal joint function is very good; if the time before treatment is 1 month or more, the outcome is usually poor. Infections of prosthetic joints present major surgical problems, usually requiring removal of the components, prolonged antibiotic treatment, and then revised reconstruction. Such cases should be referred to an orthopedist at the outset.

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