Bone and Joint Infections Flashcards
Describe the presentation and differential diagnoses for septic arthritis
Presentation - New onset joint pain, red, hot, swollen joint, reduced range of movement and sepsis.
Differentials - Rheumatoid arthritis, psoriatic arthritis, crystal induced arthritis, trauma, haemarthrosis, or extra-articular infections (cellulitis/bursitis)
How can septic arthritis arise?
80% haematogenous - IE, skin infection, RTI, UTI, dental infections.
Direct inoculation - following arthroscopy, intra-articular injection, trauma or bite.
Contiguous spread (only 5%) - osteomyelitis, bursitis etc
What are the diagnostic tests involved in the diagnosis of septic arthritis?
-
Blood cultures (aseptic technique, do prior to other blood tests, aerobic (do first) and anaerobic bottles, 10mls per bottle prior to Abx therapy)
-** FBC, CRP, ESR, U&Es, LFTs & urate.** - Joint aspirate prior to abx - Minimum 1ml of synovial fluids. Synovial fluid WCC, synovial fluid microscopy and culture, synovial fluid examination under polarised light for crystals (urate/calcium pyophosphate)
Briefly explain the gram staining procedure
- Application of crystal violet which will stain gram positives,
- Application of iodine to lock in crystal violent stain.
- Alcohol wash
- Application of safranin
What are the causative microorganisms for septic arthritis
- Staphylococcus aureus,
- Streptococci,
- Coliforms
- Mycobacterium tuberculosis,
- Neisseria gonorrhoea (sexually active patients)
- Streptococcus pneumoniae (children)
What are the additional investigations required in septic arthritis
Goal - Investigate the source so if:
S. aureus - Blood culture/ECHO (source may be skin/soft tissue infections/IE).
Viridans strep - Blood culture and ECHO (source may be mouth/IE)
Enterococci/coliforms - Urine culture and abdominal imaging (source may be abdomen/UTI).
Gonococcal - STI screen (first pass urine and swabs in men, swabs in women).
Mycobacterium TB/fungal - synovial biopsy
Lyme arthritis - Diagnose by serum antibody testing
What is the treatment for septic arthritis?
- Start IV, bactericidal antibiotics
- May require washout
- MSSA - IV flucloxacillin.
- MRSA - IV Vancomycin,
- Streptococcus - IV benzylpenicillin,
- Enterococcus - IV amoxicillin/vancomycin.
- Enterobacteriaceae (gram neg) - IV ceftriaxone or IV meropenem if ESBL.
- Pseudomonas Aeruginosa - IV piperacillin/tazobactam
- N.gonorrhoea - IV ceftriaxone
Describe features of periprosthetic joint infections and the role of biofilms
It is an uncommon complication of arthroplasty but can cause pain, reduce mobility, prolong hospital stays.
- In the presence of prosthetic material, small numbers of microorganisms can cause an infection. Adhere to the surface and secrete extracellular substances to form complex glycocalyx structures. Organisms within biofilm communicate via quorum censoring, and are more resistant to antibiotic therapy
Explain the classification of periprosthetic joint infection
- Acute infections occur with immature biofilms. They present with a red, hot painful joint with fever/sepsis. May have prolonged leaking wound post of (7-10 days).
- Chronic infections have a mature biofilm. They present with stiff, painful joint and loosening of prosthesis on x-ray. Inflammatory markers may be mildly raised
What are some of the causative organisms in periprosthetic joint infections
Early (within 4 weeks) - caused by virulant pathogens, eg, S.aureus.
Delayed (3 months -3 years) - low virulence organisms eg, coagulase negative straph.
- In either early or delayed, organisms commonly come from endogenous skin flora or exogenous from theatre, and spread of bacteria from distant site to prosthesis can occur at any point.
Explain the diagnosis of periprosthetic joint infections
Acute - Joint aspirate for synovial WWC and microscopy/culture and blood cultures.
Chronic - Pre-operative joint aspirate for WWC and culture. Gram staining not sensitive in chronic. Finally do biomarkers.
For both - intraoperative samples for microbiology and histopathology. Must send multiple samples of pus, fluid, synovium, membrane and bone. No swabs/snus samples
What are the methods of biofilm disruption and other laboratory tests carried out with samples from periprosthetic joint infections
- Beadmill processing - shacking sample with glass bead to disrupt biofilm and dissociate bacteria from biofilm.
- Sonication of explanted prosthesis - Low intensity ultrasound to disintegrate biofilm.
- Lab tests - Direct and enrichment culture, culture for beta/non-haemolytic colonies and antibiotic sensitivity testing using antibiotic impregnated discs.
What are the surgical strategies for the treatment of periprosthetic joint infection
- DAIR. Debridement, antibiotics and implant retention.
- Complete removal of prosthesis either one or two stage exchange.
- Resection without reimplantation
- Amputation
What is the antimicrobial management of periprosthetic joint infections
- Delay unless septic. Empirical therapy using IV vancomycin and IV gentamicin. Once the causative pathogen is identified can do pathogen directed IV therapy or oral therapy. Same as septic arthritis: for anaerobes can give IV benzylpenicillin or IV metronidazole
- Give for 6 weeks following prosthesis removal and 3-6 months for DAIR/single stage revision.
What are the different classification systems for osteomyelitis and what do they use in the system?
- Cierny-mader classification - Anatomical type and host physiology. Limitations - does not take duration of symptoms into account.
- Waldvogel Classification - Duration of symptoms, pathogenesis (source) and presence of absence of vascular insufficiency
What are the virulence factors of S.aureus?
- Production of bacterial adhesions (promotes attachment to ECM proteins).
- Protein A, toxins and capsular polysaccharide which evades host defences.
- Invades tissue due to exotoxins, degrades components of ECM via hydrolase.
- Can form biofilms
What is the clinical presentation of osteomyelitis
- Severe pain,
- Fever,
- Swelling and erythema
- Wound over open fracture,
- Draining sinus/fistula,
- Probe to bone test (probe can touch bone through wound)
- Bone tenderness,
- Rigors or sepsis
Explain how osteomyelitis is diagnosed
- Blood cultures,
- Image guided bone biopsy: Aerobic and anaerobic cultures to microbiology. Sample may have 5 or more neutrophils per high power feild in histopathology.
- MRI: high diagnostic accuracy.
What are the potential causes of acute contiguous osteomyelitis
Spread from adjacent infection.
- Patient without vascular insufficiency then think potential puncture wounds through footwear, bites or dental infections.
- Patient with vascular insufficiency think diabetic foot infection
Acute infections are usually monomicrobial but chronic infections are normally polymicrobial
What are the common sites of acute haematogenous osteomyelitis and the common causative organisms
Adults - vertebral bodies, commonly S.aureus.
Children - growing ends of long bones (metaphyses), Commonly S. aureus but consider group A streptococcus.
Sickle cell disease - salmonella
IVDU - P. aeurginosa
Describe the clinical presentation of native vertebral osteomyelitis and the common causative microorganism
- Back pain, fever and raised inflammatory markers.
May present with a bloodstream infection or infective endocarditis or fever and new neurological symptoms.
Commonly caused by haematogenous seeding from adjacent disk space and most commonly caused by S aureus. In elderly patients UTI may be the source of gram -ve rods
What is the diagnosis and management of native vertebral osteomyelitis
Diagnosis - MRI spine, blood cultures or biopsy if BC negative. Withhold Abx until source confirmed unless septic.
- Use empirical Abx which cover gram +ve and -ve eg, flucloxacillin and gentamicin/ciprofloxacin.
- Surgery is indicated in patients with progressive neurological deficit, progressive deformity or spinal instability
Describe the presentation of diabetic foot infections
Can present with:
- Sepsis/fever,
- Superficial infection - Pus from ulcer bed, the surrounding skin can be red, hot, swollen with pain. Send swabs from infected ulcers prior to Abx.
- Osteomyelitis - Detected by serial plain X ray/MRI, probe to bone or percutaneous biopsy.
What is the antibiotic management for diabetic foot infections
- required MDT approach. The antibiotic choice depends on: Clinical severity of infection, local guidelines, MRSA status, comorbidities, allergies and drug-drug interactions. Requires 6 week duration of Abx
What is Potts Disease
Infection of vertebral body by mycobacterium tuberculosis.
