Updated: 12/3/2019

Shoulder Periprosthetic Infection

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Introduction
  • Periprosthetic shoulder infection is the major cause for revision within the first 2 years after arthroplasty
  • Epidemiology
    • incidence
      • 3.9% for primary unconstrained arthroplasty
      • 3.3% - 4.0% for reverse shoulder arthroplasty
    • demographics
      • males more likely to be colonized with P. acnes
    • risk factors
      • coagulopathy, renal failure, diabetes, lupus, rheumatoid arthritis
      • intra-articular steroid injection within 3 months of surgery 
      • arthroplasty for fracture, cuff arthropathy, or radiation-induced osteonecrosis
      • previous shoulder surgery or arthroplasty
      • smoking has been found to be an independent risk factor for infection in reverse and anatomic total shoulder arthroplasty 
  • Pathophysiology
    • pathobiology
      • micro-organisms most commonly isolated:
        • Staphylococcus aureus
        • Staphylococcus epidermidis
        • Propionibacterium acnes (P. acnes)
          • characteristics
            • gram-positive, facultative, aerotolerant, anaerobic rod that ferments lactose to propionic acid
            • concentrated in the axilla
            • forms biofilm within 18-90h (found on implant surface and on synovial tissue) >> planktonic (explains why aspiration is only 17% sensitive)
            • infection more common in males
          • Mean duration of culture incubation between 7-21 days
  • Prophylaxis
    • antibiotic prophylaxis
      • administered within 30 minutes of incision
      • continued for 24 hours postoperatively
      • clindamycin for P. acnes
    • hair removal by electric clippers
    • preparation of the surgical site
Classification
  • Time of onset
    • acute infection
      • infection within 3-6 weeks from surgery
        • CDC definition < 90 days from date of joint replacement
      • biology
        • usually confined to joint space
        • no invasion into prosthetic-bone interface
        • less likely for biofilm production
    • chronic infection
      • infection more than 3-6 weeks from surgery
        • CDC definition > 90 days from date of joint replacement
      • biology
        • biofilm created by all bacteria forms on implant within four weeks
          • composition
            • 15% cells and 85% polysaccharide layer (glycocalyx) 
            • glycocalyx allows biofilm to adhere to prosthesis and  isolate infection and protect bacteria from host immune system
          • consequence
            • no method exists to safety remove biofilm and eradication is difficult
            • prosthetic explant indicated with infection >4 weeks due to biofilm production
          • infection has invaded prosthetic-bone interface
  • Source of infection
    • direct invasion
      • sinus tract into joint capsule
      • wound dehiscence
    • hematogenous infection
      • infection in a longstanding infection-free joint secondary to another infection (eg. dental work, infected gallbladder)
Presentation
  • History
    • may have had a systemic illness
    • skin penetration
  • Symptoms
    • common symptoms
      • persistent shoulder pain
      • systemic symptoms of infection
      • swelling and drainage
      • infection with P. acnes does not usually cause swelling, erythema, fever or purulent discharge
  • Physical exam
    • inspection
      • sinus tract to joint is diagnostic
      • warmth, erythema, edema
    • motion
      • limited by pain and edema
Imaging
  • Radiographs
    • findings 
      • normal with early infection
      • periosteal reaction 
      • osteopenia
      • lucencies around component
      • pseudosubluxation of the humeral head
  • Ultrasound
    • findings
      • may be helpful to identify loculated fluid collections away from the glenohumeral joint
  • MRI
    • findings
      • may be helpful to identify loculated fluid collections away from the glenohumeral joint
  • Positron emission tomography (PET)
    • indication
      • useful adjunct in screening
    • sensitivity and specificity
      • 98% sensitivity and 98% specificity
Studies
  • Labs
    • blood panel
      • WBC
        • not specific or sensitive
        • may be normal in P. acnes infection
    • ESR and CRP 
      • CRP
        • physiology
          • peaks 2-3 days after surgery
          • returns to normal at 14-21 days
          • may be normal in P. acnes infection
      • ESR 
        • physiology
          • peaks 5-7 days after surgery
          • returns to normal 90 days (3 months)
          • may be normal in P. acnes infection
  • Joint aspiration
    • should be considered in all cases of deep infection
    • lab order request
      • cell count and differential
        • WBC > 50,000 
      • crystals
        • presence does not exclude an infectious process
      • gram stain
        • may be negative in cases of infection
        • positive in approximately in 75% of cases
      • cultures and specificity
        • positive in approximately 80% of cases
        • hold cultures for at least 21 days to isolate P. acnes
        • fungal cultures held for 4 weeks
        • mycobacterial cultures held for 8 weeks
Treatment
  • Nonoperative
    • antibiotic suppression
      • indications
        • severely ill patients
        • those unwilling to go surgery
      • outcomes
        • failure rates of 60-75%
  • single-stage revision
    • indications
      • uncommonly performed
      • identified low virulence organism with good antibiotic sensitivity
      • healthy patient and soft tissue
    • advantages
      • reduced hospital stay
      • reduced cost
      • reduced period of antibiotic administration
  • 2-stage implant exchange
    • indications
      • gold standard
      • medically fit for multiple procedures
      • unknown micro-organism
      • requires adequate bone stock
      • requires microbial eradication prior to second stage
  • resection arthroplasty
    • indications
      • medically complex patients
      • frail patients who are poor surgical candidates
      • insufficient bone stock
      • recalcitrant infection
    • outcomes
      • poor functional results, but pain relief in over 50% of cases
  • arthrodesis
    • indications
      • rarely performed as bone stock is often compromised
  • Techniques
    • Debridement and prosthesis retention
      • approach
        • delto-pectoral approach
      • instrumentation
        • mobile parts of the prosthesis may be exchanged especially in reverse total shoulder (glenosphere, polyethylene liner)
      • complications specific to this treatment
        • inadequate clearance of organism
      • outcomes
        • 50% failure rate
    • Single stage revision
      • approach
        • delto-pectoral approach
      • soft tissue
        • debride all infected soft tissue
      • bone work
        • debride all infected bone
      • instrumentation
        • remove infected prosthesis and implant a new one
        • consider replacement with reverse total shoulder for re-implantation as soft tissue debridement may sacrifice rotator cuff
      • complications specific to this treatment
        • inadequate clearance of organism
      • outcomes
        • variable, as high as 90% success in some series
    • Staged implant exchange
      • approach
        • delto-pectoral approach
      • soft tissue
        • debride all infected soft tissues
      • bone work
        • debride all infected bone
      • instrumentation
        • antibiotic-impregnated cement spacer
          • permits local antibiotic delivery and induces formation of a pseudocapsule that can be mobilized with the cuff
          • benefits
            • maintains soft-tissue tension
            • decreases pain
            • improves functional status
            • allows patient to perform physical therapy
          • technique
            • mix antibiotics with PMMA and form cement by hand or with mold
            • humeral stem may be fabricated from Steinmann pin and chest tube
      • complications specific to this treatment
        • recurrent infection
      • outcomes
        • some remain satisfied and elect to leave the spacer
        • variable 60%-90% success rate
    • Resection arthroplasty
      • approach
        • delto-pectoral
      • soft tissue
        • debride all infected soft tissue
      • bone work
        • debride all infected bone
        • preservation of tuberosities is predictive for better results
      • instrumentation
        • all instrumentation is removed
      • complications specific to this treatment
        • poor functional outcome likely
        • antero-superior subluxation of humerus if tuberosities and cuff removed
      • outcomes
        • functional results are poor, but pain relief is achieved in more than 50%
    Complications
    • Failure to eradicate infection
     

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