Septic arthritis (MSK) Flashcards
(32 cards)
What is septic arthritis.
The infection of 1 or more joints caused by pathogenic inoculation of microbes
What are the two routes of spread for septic arthritis?
- direct inoculation - iatrogenic from arthrocentesis or trauma leading to open wounds around joints
- haematogenous spread - spread from a distant site e.g. abscess, wound infection, septicaemia
What is the most common causative organism of septic arthritis in adults and children >2 years?
Staphylococcus aureus (gram +ve)
What is the most common causative organism of septic arthritis in young adults who are sexually active?
Neisseria gonorrhoeae (gram -ve diplococci)
What is the most common causative organism of septic arthritis in children <4 years?
Streptococcus pneumoniae
What is the most common causative organism of septic arthritis in a prosthetic joint?
Staphylococcus epidermis
Describe the mechanism of septic arthritis. (Low yield)
- pathogen enters joint via bloodstream from nearby infection, or directly (e.g. via open fracture)/skin surface during trauma
- infection of joint –> endotoxin production –> damage of articular cartilage –> cytokine release –> neutrophil attraction –> inflammation + damage
- inflammatory response –> increase in intra-articular pressure –> compresses BVs supplying joint –> necrosis + joint destruction
What are the two types of septic arthritis?
- non-gonococcal arthritis - majority, includes all other pathogens mainly S. aureus –> often a single joint affected (knee)
- gonococcal arthritis - caused by N. gonorrhoeae, usually affects sexually active adolescents, spreads from infection of cervix, urethra or pharynx –> affects multiple joints and causes multiple skin lesions + tenosynovitis
What are the clinical features of septic arthritis? (4)
- red, hot, swollen, painful, restricted joint
- acute presentation (symptoms <2 weeks)
- fever
- usually single joint - most commonly knee joint (followed by hip, wrist, shoulder, ankle)
When can multiple joints (polyarthritis) be affected in septic arthritis? (2)
- immunosuppressed
- gonococcal arthritis
What is the triad of clinical features in septic arthritis?
- fever
- joint pain
- restricted ROM
What might you see on examination of septic arthritis? (6)
- red, hot, swollen, painful
- immobile
- severe pain on passive movement
- pyrexic
- signs for aetiology - trauma, injury, recent infection
- erythema migrans
What are some risk factors for septic arthritis? (6)
- underlying joint disease (OA/RA)
- prosthetic joint
- age>80
- immunosuppression
- diabetes
- IV drug use
- (HIV)
- (exposure to ticks –> Lyme disease)
What is the 1st line investigation for septic arthritis?
- urgent joint aspiration & culture
- aspirate will be grossly purulent
- send synovial fluid for MC&S, gram staining, WCC
- rule out crystal arthritis
- PCR if viral cause
What is arthrocentesis?
Joint aspiration - procedure in which synovial fluid is aspirated from a joint using a sterile needle (done before prescribing Abx)
What does synovial fluid analysis show in septic arthritis? (3)
- appearance often yellow-green and turbid
- increased WCC (>90% neutrophils)
- gram stain: S. aureus –> gram +ve diplococci, coagulase +ve
What other investigations can be done for septic arthritis? (7)
- FBC - high WCC & neutrophils
- CRP & ESR - high
- blood cultures
- viral serology
- LFTs - may affect Abx choice, end-organ damage
- MRI - osteomyelitis, oedema around synovium, spread of infection outside joint
- plain joint radiographs - may appear normal, increased fluid in synovial part of joint, narrowing of joint space, destruction of bone adjacent to cartilage
What are some differential diagnoses for septic arthritis?
- osteoarthritis
- psoriatic arthritis
- rheumatoid arthritis
- gout - synovial fluid polarising microscopy reveals urate crystals
- pseudogout - pyrophosphate
- haemarthrosis - blood
- trauma
- bursitis
- cellulitis
- TB - positive mycobacterial smears/cultures
- Lyme disease - Lyme titre +ve
- transient synovitis - normal aspirate
What is the diagnostic criteria for septic arthritis based on?
Joint aspirate:
- positive for bacteria/virus
- high WCC
- purulent aspirate
What is the most important aspect of septic arthritis treatment?
Antibiotics + joint washout (therapeutic arthrocentesis)
How do we manage emergency septic arthritis?
- temporary joint immobilisation - use a splint
- analgesia
- immediate joint aspiration –> empirical antibiotic therapy
- aspiration also provides symptomatic relief
- empirical Abx initially, then tailor to patient demographics and clinical factors, narrow choice after MC&S
- high dose IV Abx for 2 weeks –> switch to oral for up to 4 weeks
- commonly flucloxacillin/clindamycin –> cefuroxime/gentamicin, cefuroxime+vancomycin
What IV Abx is used in septic arthritis that covers gram +ve cocci?
Flucloxacillin
What IV Abx is used in septic arthritis if patient is penicillin allergic?
Clindamycin
How long should the Abx course be given for in septic arthritis?
- 4-6 weeks
- high dose IV Abx for 2 weeks –> up to 4 weeks oral Abx
