Septic until proven otherwise

Septic arthritis

Septic arthritis is defined as bacterial invasion of the synovial space. There are several routes by which this can occur. The most common causes are hematologic spread or direct invasion. The knee is the most commonly affected joint in adults, and the hip is the most frequently infected in children.1 Once inside the joint, bacterial growth and invasion can occur essentially unchecked.

There has been little change in the pathogens causing septic arthritis over the past 20 years.2 The top 3 pathogens cultured from adults remain Staphylococcus aureus, Streptococcus pneumoniae, and Gram-negative bacilli. Over the past 2 to 3 years, reports in the literature show an increased incidence of methicillin-resistant S aureus (MRSA) causing cellulitis. There is no clear consensus on whether or not MRSA is becoming an increasingly common cause of septic arthritis.

Neisseria gonorrhoeae is the most common cause of nontraumatic acute monoarthritis in young, sexually active people.3 Neisseria gonorrhoeae grows very poorly in cultured joint fluid. Obtain cultures from the oral pharynx, anus, and vagina of high-risk individuals.

Diagnosis

You cannot reliably diagnose or exclude a septic joint on history alone; however, you can facilitate your diagnosis by ascertaining the patient’s risk factors and determining the acuity of onset of symptoms, any associated trauma, associated systemic symptoms, recent surgery, and travel and sexual history.3

There are no specific physical findings that will enable you to make a definitive diagnosis. The classically taught symptoms of septic arthritis include fever, chills, and an acutely red, exquisitely tender, warm, swollen joint. However, these markers are not specific and cannot differentiate crystalline and infectious etiologies.1 Fever has been found to be a poor indicator of septic arthritis. The literature reports only 50% of patients who present with septic joints have fevers.1 The other frequently quoted diagnostic signs are decreased range of motion and severe pain with manual compression of the joint; however, well-designed studies have yet to show any correlation between these classically taught findings and the diagnosis of a septic joint.

There is no absolute white blood cell (WBC) count, erythrocyte sedimentation rate, or C-reactive protein value that is sensitive or specific enough to make the diagnosis of septic arthritis.1 This is a particularly important point, as we are frequently asked by consultants to order these tests to exclude underlying infection. You must not rely on these tests alone to exclude the diagnosis of a septic joint. Radiographs of the affected joint are not routinely warranted in the workup of acute monoarthritis.

Recommendations

The goal of treatment is to rapidly eradicate the infection and protect the joint. It is universally accepted that antibiotics should be promptly administered once the diagnosis is strongly suspected. The currently recommended choice of antibiotics is a third-generation cephalosporin or vancomycin if MRSA is a concern.7 For patients who are allergic to cephalosporins, a fluoroquinolone, such as levofloxacin or ciprofloxacin, is suggested.7

The literature is unclear as to how long intravenous antibiotics should be continued. Most protocols recommend an intravenous course of 2 to 4 weeks’ duration followed by an additional 2 to 6 weeks of oral antibiotics.

Septic arthritis is an orthopedic emergency. There continues to be controversy regarding medical versus surgical joint decompression. Medical management consists of needle aspiration of the joint. If pus reaccumulates, repeat aspiration is performed. Surgical drainage is accomplished by arthrotomy or arthroscopy and the possible placement of tubes to drain the joint. No randomized controlled studies have evaluated joint drainage procedures compared with no-drainage procedures.

Conclusion

Mortality from septic arthritis is reported to be between 8% and 15%.1 Unfortunately, this has not changed dramatically despite the advent of intravenous antibiotics. The patient’s outcome depends on a host of factors, such as previous joint damage, the virulence of the infecting organism, and the speed with which adequate treatment is begun.

This patient must be considered to have septic arthritis until proven otherwise. It is critical to promptly diagnose and treat the joint infection, which has a potentially devastating course. As laboratory tests are neither sensitive nor specific in diagnosing or excluding septic arthritis, arthrocentesis and synovial fluid analysis are mandatory. Give the patient broad-spectrum antibiotics immediately and consult an orthopedic surgeon.