Septic Arthritis - Adult - Trauma

Introduction
Epidemiology body location most commonly affected joints in descending order knee (~ 50% of cases) > hip > shoulder > elbow > ankle > sternoclavicular joint found in IV drug users pseudomonas aeruginosa was most common pathogen in 1980's staphylococcus aureus is now the most common pathogen in all patients, including IV drug users risk factors age > 80 years medical conditions diabetes rheumatoid arthritis cirrhosis HIV history of crystal arthropathy endocarditis or recent bacteremia IV drug user recent joint surgery Pathophysiology pathoanatomy 3 etiologies of bacterial seeding of joint bacteremia direct inoculation from trauma or surgery contiguous spread from adjacent osteomyelitis cellular biology septic arthritis causes irreversible cartilage destruction in an involved joint cartilage injury can occur by 8 hours caused by release of proteolytic enzymes from inflammatory cells (PMNs) microbiology most common pathogens is staphylococcus aureus (accounts for >50% of cases) see Classification below Associated conditions prosthetic implant infection Prognosis delayed diagnosis can lead to profound, extensive cartilage damage within hours
Classification
By organism staphylococcus species staphylococcus aureus most common and accounts for >50% of cases MRSA staphylococcus epidermis neisseria gonorrhea account for ~20% of cases most common organism in otherwise healthy sexually active adolescents and young adults manifests as a bacteremic infection arthritis-dermatitis syndrome in ~60% of cases localized septic arthritis in ~40% cases gram-negative bacilli account for 10-20% of cases pathogens include E coli, proteus klebsiella enterobacter risk factors neonates IV drug users elderly immunocompromised patients with diabetes streptococcus streptococcus pyogenes (Group A) most common Group B streptococcus (e.g., agalactiae) predilection for infants, elderly and diabetic patients propionibacterium acnes associated with shoulder surgery salmonella or streptococcus pneumoniae seen in patients with sickle cell disease bartonella henselae seen in patients with HIV pseudomonas aeruginosa seen in patients with history of IV drug abuse pasteurella multocida seen in patients after dog or cat bite eikenella corrodens seen in patients after human bite fungal/candida found in immunocompromised host
Presentation
Symptoms pain in affected joint fevers (only present in 60% of cases) may appear toxic Physical exam inspection erythema effusion extremity tends to be in position of maximum joint volume hip would be in FABER position (flexed, abducted, externally rotated) palpation warmth tender motion inability to bear weight inability to tolerate PROM
Imaging
Radiographs recommended views AP and lateral of the joint in question findings may show joint space widening or effusion periarticular osteopenia Ultrasound indications may help in confirming joint effusion in large joint such as hip can be used in guiding aspirations MRI indications detects joint effusion, and may detect adjacent bone involvement such as osteomyelitis
Studies
Serum labs WBC >10K with left shift ESR >30 ESR is often elevated but may be normal early in process rises within 2 days of infection and can rise 3-5 days after initiation of appropriate antibiotics, and returns to normal 3-4 weeks CRP >5 most helpful best way to judge efficacy of treatment, as CRP rises within few hours of infection, and may normalize within 1 week of treatment Joint fluid aspirate gold standard for treatment and allows directed antibiotic treatment should be analyzed for cell count with differential gram stain culture glucose level crystal analysis septic arthritis occurs concurrently with gout or pseudogout in < 5% of cases characteristic findings joint fluid appears cloudy or purulent cell count with WBC > 50,000 is considered diagnostic for septic arthritis, however lower counts may still indicate infection gram stains only identifies infective organism 1/3 of time glucose less than 60% of serum level negative "string" sign septic synovial fluid has low viscosity compared to normal synovial fluid (high viscosity) Saline load test utilized to determine if wound near a joint communicates with the joint for the knee 155 mL of saline is needed to reach 95% sensitivity 175 mL of saline is needed to reach 99% sensitivity
Differential
Crystal arthropathy gout pseudogout Cellulitis Bursitis prepatellar bursitis
Treatment
Operative IV abx, operative irrigation and drainage of the joint indications considered an orthopaedic surgical emergency IV antibiotic therapy initiate empiric therapy prior to definitive cultures based on patient age and or risk factors young, healthy adults staphylococcus aureus and neisseria gonorrhea immunocompromised patients staphylococcus aureus and pseudomonas aeruginosa transition to organism-specific antibiotic therapy based once obtain culture sensitivities outcomes treatment can be monitored by following serum WBC, ESR, and CRP levels during treatment
Technique
Operative irrigation and drainage of the joint approach can be performed open or arthroscopically (depending on joint) irrigation remove all purulent fluid and irrigate joint debridement synovectomy can be performed as needed cultures obtain joint fluid and tissue for culture
Complications
Arthritis Fibrous ankylosis Osteomyelitis