History and Epidemiology

Considered an orthopedic or rheumatologic emergency, septic arthritis is an inflammation of the joints caused by a bacterium, fungus, virus, or other pathogen.¹ Also referred to as infectious arthritis, septic arthritis is usually bacterial and typically develops when an infection elsewhere in the body spreads through the bloodstream to the joint.² There are about 2 to 6 cases per 100,000 people each year.¹

Septic arthritis is more common in children than in adults. The incidence of septic arthritis peaks when kids are aged 2 to 3. Septic arthritis tends to disproportionately affect males.

Staphylococcus aureus is the most common bacterial culprit in adults with bacterial arthritis.¹ Kingella kingae is the most common gram-negative bacterial cause in children younger than 2 to 3 years old. In addition, Group B Streptococcus, Staphylococcus aureus, Neisseria gonorrhea, and gram-negative bacilli are common among newborns. Neisseria gonorrhea is a concern in sexually active adolescents. By contrast, salmonella species infections are associated with sickle cell disease.

Risk factors for bacterial arthritis include¹:

Advancing age
Underlying diabetes mellitus
Underlying rheumatoid arthritis
Recent joint surgery
Joint prosthesis
History of intra-articular injection
History of skin infections or cutaneous ulcers
Underlying human immunodeficiency virus (HIV)
Underlying osteoarthritis
Sexual activity
Sepsis

Prolonged antibiotic therapy increases the risk for fungal infections, while puncture wounds and injection drug use can increase the risk for joint infection due to Pseudomonas aeruginosa.¹

Bacterial Arthritis Diagnosis & Presentation

It’s important to have a high index of suspicion when a patient presents with signs and symptoms of septic arthritis, especially if they have predisposing risk factors and/or comorbid conditions. Such early diagnosis and treatment can prevent lasting joint damage.

Patients with bacterial arthritis usually present with acute onset pain and swelling in one large joint.¹ The hip joint is most commonly affected in children, while the knee is most commonly affected in adults. Symptoms come on rapidly and can be local and/or systemic. The main symptoms of bacterial arthritis include fever, swelling, and trouble moving the affected joint.¹

Children with bacterial arthritis may present with local symptoms including pain, joint swelling, warmth and redness around the affected joint, limited range of motion, limp, and pseudoparalysis.¹ Systemic symptoms in pediatric patients with bacterial arthritis include fever, tachycardia, irritability, and decreased appetite.¹

Diagnosis includes arthrocentesis with synovial fluid analysis to determine what organism is causing the infection.³ Culturing the synovial fluid or tissue is the only definitive method for diagnosing septic arthritis. This can be done via culture, gram stain, crystals analysis, and/or white blood cell count with differential.

Synovial fluid with white blood cell counts greater than 50,000 and 90% neutrophil predominance points to a bacterial infection.¹ Low synovial fluid white blood cell count may occur in peripheral leukopenia, early infection, disseminated gonococcal arthritis, and joint prosthesis. A synovial fluid white blood cell count of 1100 in prosthetic joint infections with a neutrophil differential of 64% points to bacterial arthritis.

Obtain two sets of blood cultures to rule out bacteremia. If neisseria is believed to be the cause, take cultures from the cervix, rectum, and throat too.¹ Additional laboratory tests for diagnosing bacterial arthritis include:

Complete blood count
Erythrocyte sedimentation rate (ESR)
C-reactive protein (CRP)
Glucose, protein, and lactate analyses^1,3

Bear in mind that an elevated ESR and CRP support the diagnosis of bacterial arthritis but should not be considered definitive.

Bacterial Arthritis Imaging

Imaging studies of the affected joint(s) can assess and quantify any damage. Imaging tests may include ultrasonography, MRI, and bone scans.¹

Taking a thorough medical history and conducting a physical exam can also help identify risks and reveal effusions and limited range of motion. Staph infections are primarily monoarticular but neisseria tends to affect multiple joints.¹ Group B streptococci infection often involves the sternoclavicular and sacroiliac joints. There may be pain upon palpation.

Adults with potential gonococcal arthritis are usually young, healthy, and sexually active.¹ They may have dermatitis, tenosynovitis, nonerosive arthritis, and a migratory pattern of arthritis upon physical exam.

Differential Diagnosis

Differential diagnoses of bacterial arthritis may include:¹

Acute gout
Pseudogout
Osteoarthritis
Fracture
Meniscal tear
Osteonecrosis
Foreign body
Plant-thorn synovitis
Rheumatoid arthritis
Behcet syndrome
Ankylosing spondylitis
Psoriatic arthritis
Reactive arthritis
Inflammatory bowel disease-related arthritis
Sarcoidosis
Lupus
Still disease
Bacterial endocarditis
HIV
Lyme arthritis
Tumor
Hemarthrosis
Clotting disorders or anticoagulant therapy
Neuropathic arthropathy
Dialysis-related amyloidosis
Avascular necrosis

Bacterial Arthritis Management (Nonpharmacotherapy and Pharmacotherapy)

Typically, treatment of bacterial arthritis includes antibiotics, drainage of joint fluid, and physical therapy to maintain joint motion.^{1, 2} It is usually treated on an inpatient basis initially. Getting an orthopedic surgeon involved right away is critical.^{1, 3} Consider an infectious disease consult as well.

Joint drainage via joint aspiration, arthroscopy, or open joint surgery can relieve pain, reduce inflammation and prevent further joint damage.¹ Intravenous antimicrobial therapy directed against an anticipated and likely cause of infectious disease should be started after joint aspiration.

Empiric antistaphylococcal antibiotic coverage for all age and risk categories includes nafcillin, oxacillin, and vancomycin.¹ Empiric antibiotics for nongonococcal bacterial arthritis involves using intravenous vancomycin targeted at gram-positive organisms, particularly if MRSA is suspected.

The typical treatment for nongonococcal bacterial arthritis is intravenous antibiotics for two weeks followed by an additional 1 to 2 weeks of oral antibiotic therapy.¹ Longer antibiotic therapy may be reasonable for bacterial arthritis caused by P aeruginosa.

Gonococcal arthritis is very responsive to intravenous ceftriaxone which is continued for 24 to 48 hours after clinical improvement before starting oral therapy for the duration of the treatment.¹ If the patient doesn’t improve within 5 to 6 days, the joint should be re-aspirated and Lyme disease should be ruled out.¹

Blood and synovial fluid cultures and sensitivities should inform prolonged antimicrobial treatment.¹ Additional antibiotics may be warranted based on patient’s age, risk factors, and gram staining. For example, third-generation cephalosporin antibiotics like ceftriaxone, ceftazidime, or cefotaxime should be used for additional gram-negative coverage if the patient is immunocompromised, abuses intravenous drugs or the gram stain is negative.¹ The joint should be immobilized for up to three days maximum. Physical therapy may be indicated to restore joint function and prevent muscle atrophy.

Patients who develop bacterial arthritis in the prosthetic joint will likely need the joint replaced with a joint spacer that can be removed after several months and replaced with a new prosthetic.¹ Infectious arthritis caused by a virus usually goes away on its own with no specific treatment.² Fungal infections are treated with antifungal medication.

Monitoring and Follow-up

Antibiotic treatment can be continued at home. Patients must be on high alert for signs of infection or inflammation at the site of the IV line.¹Patients with bacterial arthritis should be followed after discharge to monitor for long-term complications.³ Potential complications may include osteomyelitis, chronic pain, osteonecrosis, leg length discrepancies, sepsis/septic shock, and death.¹

Despite the use of antibiotics for treatment, septic arthritis has a mortality rate of up to 15%. Mortality varies based on the bacterial strain. Infection with neisseria is rarely associated with death, but staph infections can carry a mortality rate of more than 50%.

The rate of complications is highest in newborns and patients with delayed diagnoses. Growth deformities in newborns may not be evident for years. Newborns with a history of septic arthritis should be followed through skeletal maturity.¹

References

Momodu I, Savaliya V. Septic arthritis. In: StatPearls. NCBI Bookshelf version StatPearls Publishing: 2022.
Infectious arthritis. Arthritis Foundation. Accessed Sept. 3, 2022
Gottlieb M, Holladay D, Rice M. Current approach to the evaluation and management of septic arthritis. Pediatr Emerg Care. 2019;35:509-515. doi: 10.1097/PEC.0000000000001874

About the Author

Denise Mann, MS, is a veteran freelance health writer in New York. Her work has appeared on HealthDay, among other outlets. She was awarded the 2004 and 2011 journalistic Achievement Awards from the American Society for Aesthetic Plastic Surgery. She was also named the 2011 National Newsmaker of the Year by the Community Anti-Drug Coalitions of America. She has also been awarded the Arthritis Foundation’s Northeast Region Prize for Online Journalism, the Excellence in Women’s Health Research Journalism Award, the Gold Award for Best Service Journalism from the Magazine Association of the Southeast, a Bronze Award from The American Society of Healthcare Publication Editors, and an honorable mention in the International Osteoporosis Foundation Journalism Awards. She was part of the writing team awarded a 2008 Sigma Delta Chi award for her part in a WebMD series on autism. Mann has a graduate degree from the Medill School of Journalism at Northwestern University in Evanston, Ill.