Septic arthritis (MSK) Flashcards
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
What is an empirical Abx agent used in septic arthritis?
IV vancomycin
What Abx can be used in septic arthritis with sickle cell anaemia?
IV ceftriaxone
How do we manage septic arthritis in a prosthetic joint?
Do not aspirate - refer to orthopaedic surgeon and aspirate in theatre
How do we manage septic arthritis with systemic involvement?
Follow local protocol for suspected sepsis
How is viral septic arthritis managed?
Typically self-limiting, no antiviral required
When is physiotherapy done for septic arthritis?
As early as possible
What are some complications of septic arthritis? (4)
- antibiotic-associated allergic reaction
- osteomyelitis
- joint destruction
- septicaemia
Describe the prognosis of septic arthritis.
Delayed treatment can lead to irreversible joint destruction and subsequent disability
