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Emergency and Acute Medicine – Septic Arthritis
Clinical Overview
Septic arthritis is an acute, destructive joint infection most commonly caused by bacterial seeding of the synovial space through hematogenous spread, though direct inoculation, invasive procedures, or contiguous spread from adjacent infection may also occur. The inflammatory response leads to rapid leukocyte migration into the joint, synovial proliferation, cartilage destruction, and purulent effusion. Permanent loss of joint function occurs in a substantial proportion of patients, and reported mortality remains significant. Early recognition and intervention are therefore critical.
In children, the hip is the most frequently involved joint, often following upper respiratory or ear infections or femoral venipuncture. Infants may present nonspecifically with irritability, fever, and poor feeding, whereas older children more commonly present with fever, limp, or refusal to bear weight. Pediatric hip infections carry a high risk of serious complications including avascular necrosis, epiphyseal separation, pathologic dislocation, and early degenerative arthritis.
Predisposing Factors And Microbiology
Risk is increased at the extremes of age, in patients with underlying joint disease such as rheumatoid or degenerative arthritis, intravenous drug use, endocarditis, immunosuppression, diabetes, malignancy, chronic steroid use, recent joint injections, trauma, prosthetic joints, or overlying skin infection. No organism is identified in a minority of cases.
Staphylococcus aureus remains the most common pathogen overall, particularly in adults, hip infections, and patients with rheumatoid arthritis or diabetes. Community-acquired MRSA is increasingly prevalent in some regions. Neisseria gonorrhoeae is the leading cause in young, sexually active individuals, often presenting with disseminated disease. Other causative organisms include streptococcal species, gram-negative rods such as Pseudomonas and Escherichia coli, Neisseria meningitidis, anaerobes, and, less commonly, mycobacteria or fungi in immunocompromised hosts.
Clinical Presentation
Septic arthritis typically presents with abrupt onset of severe joint pain, swelling, warmth, and marked tenderness, with pain on both active and passive movement. Fever is common but may be absent, particularly in older adults or those with rheumatoid arthritis. Joint effusion may be subtle in deep joints such as the hip, shoulder, or sacroiliac joint. Although any joint may be involved, the knee is most common, followed by the hip, shoulder, and ankle. Intravenous drug users frequently develop infections in atypical sites including the sacroiliac, sternoclavicular, and costochondral joints.
Polyarticular involvement occurs in a minority of cases and is more frequent in patients with rheumatoid arthritis, often leading to delayed diagnosis due to less dramatic presentations. Gonococcal septic arthritis may be monoarticular or migratory and is frequently associated with tenosynovitis, dermatitis, and subtle genitourinary symptoms.
Diagnostic Strategy
Prompt arthrocentesis is essential in all suspected cases and should not be delayed. Synovial fluid should be analyzed for cell count, differential, Gram stain, culture, glucose, and protein. Typical findings include turbid or purulent fluid with very high leukocyte counts and neutrophil predominance. Reduced synovial glucose and elevated protein further support infection. The presence of crystals does not exclude septic arthritis. Blood cultures are frequently positive and should be obtained, along with cultures from suspected primary infection sites when appropriate.
Serum inflammatory markers such as CRP and ESR are usually elevated and may assist in monitoring response to therapy. Procalcitonin may be useful as a supportive diagnostic marker. Imaging with plain radiographs helps assess baseline joint status and detect effusions, osteomyelitis, or foreign bodies. Ultrasound is valuable for detecting effusions and guiding aspiration, particularly in the hip. CT or MRI may be necessary for deep or difficult-to-access joints.
Management Principles
Patients may present septic and require immediate resuscitation. Joint aspiration should be performed promptly, but in toxic patients antibiotics should not be delayed while awaiting results. Empiric intravenous antibiotics should be initiated based on patient age, risk factors, and local resistance patterns, with coverage for staphylococci, streptococci, and gram-negative organisms as indicated. MRSA coverage should be included when risk factors are present. Suspected gonococcal infection should be treated with appropriate cephalosporins. Intra-articular antibiotics are contraindicated.
Early orthopedic consultation is essential to determine the need for surgical drainage, which may involve repeated aspirations, arthroscopy, or open arthrotomy. Pediatric hip infections typically require open surgical drainage. Adequate pain control and joint positioning to minimize further damage are important supportive measures.
Disposition And Follow-Up
All patients with suspected septic arthritis should be admitted until the diagnosis is confidently excluded. Most require prolonged intravenous antibiotic therapy and possible surgical intervention. Discharge is appropriate only when infection has been reliably ruled out. Close follow-up is required to monitor clinical response and prevent long-term complications.
Key Clinical Lessons And Common Errors
Inflammatory markers such as CRP and ESR are useful for tracking treatment response but should not replace synovial fluid analysis for diagnosis. Distinguishing septic arthritis from crystal arthropathy or transient synovitis can be challenging; when in doubt, joint aspiration is mandatory. A low threshold for arthrocentesis is essential to avoid delayed diagnosis and irreversible joint damage.
Clinical Overview
Septic arthritis is an acute, destructive joint infection most commonly caused by bacterial seeding of the synovial space through hematogenous spread, though direct inoculation, invasive procedures, or contiguous spread from adjacent infection may also occur. The inflammatory response leads to rapid leukocyte migration into the joint, synovial proliferation, cartilage destruction, and purulent effusion. Permanent loss of joint function occurs in a substantial proportion of patients, and reported mortality remains significant. Early recognition and intervention are therefore critical.
In children, the hip is the most frequently involved joint, often following upper respiratory or ear infections or femoral venipuncture. Infants may present nonspecifically with irritability, fever, and poor feeding, whereas older children more commonly present with fever, limp, or refusal to bear weight. Pediatric hip infections carry a high risk of serious complications including avascular necrosis, epiphyseal separation, pathologic dislocation, and early degenerative arthritis.
Predisposing Factors And Microbiology
Risk is increased at the extremes of age, in patients with underlying joint disease such as rheumatoid or degenerative arthritis, intravenous drug use, endocarditis, immunosuppression, diabetes, malignancy, chronic steroid use, recent joint injections, trauma, prosthetic joints, or overlying skin infection. No organism is identified in a minority of cases.
Staphylococcus aureus remains the most common pathogen overall, particularly in adults, hip infections, and patients with rheumatoid arthritis or diabetes. Community-acquired MRSA is increasingly prevalent in some regions. Neisseria gonorrhoeae is the leading cause in young, sexually active individuals, often presenting with disseminated disease. Other causative organisms include streptococcal species, gram-negative rods such as Pseudomonas and Escherichia coli, Neisseria meningitidis, anaerobes, and, less commonly, mycobacteria or fungi in immunocompromised hosts.
Clinical Presentation
Septic arthritis typically presents with abrupt onset of severe joint pain, swelling, warmth, and marked tenderness, with pain on both active and passive movement. Fever is common but may be absent, particularly in older adults or those with rheumatoid arthritis. Joint effusion may be subtle in deep joints such as the hip, shoulder, or sacroiliac joint. Although any joint may be involved, the knee is most common, followed by the hip, shoulder, and ankle. Intravenous drug users frequently develop infections in atypical sites including the sacroiliac, sternoclavicular, and costochondral joints.
Polyarticular involvement occurs in a minority of cases and is more frequent in patients with rheumatoid arthritis, often leading to delayed diagnosis due to less dramatic presentations. Gonococcal septic arthritis may be monoarticular or migratory and is frequently associated with tenosynovitis, dermatitis, and subtle genitourinary symptoms.
Diagnostic Strategy
Prompt arthrocentesis is essential in all suspected cases and should not be delayed. Synovial fluid should be analyzed for cell count, differential, Gram stain, culture, glucose, and protein. Typical findings include turbid or purulent fluid with very high leukocyte counts and neutrophil predominance. Reduced synovial glucose and elevated protein further support infection. The presence of crystals does not exclude septic arthritis. Blood cultures are frequently positive and should be obtained, along with cultures from suspected primary infection sites when appropriate.
Serum inflammatory markers such as CRP and ESR are usually elevated and may assist in monitoring response to therapy. Procalcitonin may be useful as a supportive diagnostic marker. Imaging with plain radiographs helps assess baseline joint status and detect effusions, osteomyelitis, or foreign bodies. Ultrasound is valuable for detecting effusions and guiding aspiration, particularly in the hip. CT or MRI may be necessary for deep or difficult-to-access joints.
Management Principles
Patients may present septic and require immediate resuscitation. Joint aspiration should be performed promptly, but in toxic patients antibiotics should not be delayed while awaiting results. Empiric intravenous antibiotics should be initiated based on patient age, risk factors, and local resistance patterns, with coverage for staphylococci, streptococci, and gram-negative organisms as indicated. MRSA coverage should be included when risk factors are present. Suspected gonococcal infection should be treated with appropriate cephalosporins. Intra-articular antibiotics are contraindicated.
Early orthopedic consultation is essential to determine the need for surgical drainage, which may involve repeated aspirations, arthroscopy, or open arthrotomy. Pediatric hip infections typically require open surgical drainage. Adequate pain control and joint positioning to minimize further damage are important supportive measures.
Disposition And Follow-Up
All patients with suspected septic arthritis should be admitted until the diagnosis is confidently excluded. Most require prolonged intravenous antibiotic therapy and possible surgical intervention. Discharge is appropriate only when infection has been reliably ruled out. Close follow-up is required to monitor clinical response and prevent long-term complications.
Key Clinical Lessons And Common Errors
Inflammatory markers such as CRP and ESR are useful for tracking treatment response but should not replace synovial fluid analysis for diagnosis. Distinguishing septic arthritis from crystal arthropathy or transient synovitis can be challenging; when in doubt, joint aspiration is mandatory. A low threshold for arthrocentesis is essential to avoid delayed diagnosis and irreversible joint damage.
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