summary Shoulder Prosthetic Joint infections are serious complications of shoulder arthroplasty and a major cause for revision within the first 2 years. Diagnosis is multifaceted and involves a high index of suspicion given the indolent nature of the most common organism Cutibacterium acnes. Elevated inflammatory markers, radiographic changes around the prosthesis and aspiration results can all assist with diagnosis. Treatment generally involves prolonged IV antibiotics and two-stage revision arthroplasty. Epidemiology Incidence ~4% for primary TSA and RSA ~15% for revision TSA and RSA Demographics males more likely to be colonized with Cutibacterium acnes (formerly known as Propionibacterium acnes) Risk factors postoperative hematoma intra-articular steroid injection within 3 months of surgery smoking young age male gender arthroplasty for trauma revision surgery Etiology Pathophysiology pathobiology micro-organisms most commonly isolated: Staphylococcus aureus Staphylococcus epidermidis Cutibacterium acnes (most common) characteristics gram-positive, facultative, aerotolerant, anaerobic rod that ferments lactose to propionic acid concentrated in the axilla within the dermal sebaceous glands forms biofilm within 18-90h (found on implant surface and on synovial tissue) >> planktonic explains why aspiration is only 17% sensitive 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 C. acnes Routine MRSA screening Application of 5% povidone-iodine solution to each nostril for 10 seconds per nostril, 1 hour before surgery. Or pre-operative application of 2% mupirocin to the nares twice daily for 5 days hair removal by electric clippers preparation of the surgical site Classification Time of onset acute infection infection <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 >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 protect bacteria from host immune system consequence no method exists to safely remove biofilm and eradication is difficult prosthetic explant indicated for infection >4 weeks due to biofilm production infection has invaded prosthetic-bone interface Source of infection direct invasion sinus tract into joint capsule or 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 or skin penetration Symptoms common symptoms persistent shoulder pain (most common) persistent draining sinus (second most common) systemic symptoms of infection (fevers, chills, night sweats) stiffness infection with C. acnes does not usually cause swelling, erythema, fever or purulent discharge Physical exam inspection sinus tract to joint is diagnostic motion limited by pain and edema Imaging Radiographs essential to exclude other causes findings normal with early infection osteopenia periprosthetic lucencies pseudosubluxation of the humeral head effusion endosteal scalloping bony resorption Bone scan not routinely obtained as their efficacy has not been demonstrated Ultrasound findings helpful to identify loculated fluid collections away from the glenohumeral joint MRI findings helpful to identify fluid collections Positron emission tomography (PET) indication useful adjunct in screening sensitivity and specificity 98% sensitivity and 98% specificity Studies Labs serology WBC physiology not specific or sensitive may be normal in C. acnes infection ESR and CRP have not demonstrated sufficient sensitivity or specificity to suggest PJI CRP physiology peaks 2-3 days after surgery returns to normal at 14-21 days may be normal in C. acnes infection ESR physiology peaks 5-7 days after surgery returns to normal 90 days (3 months) may be normal in C. acnes alpha-defensin is investigational Joint aspiration no universal guidelines on when to aspirate should be considered in all cases of deep infection lab order request cell count and differential WBC > 50,000 (500 cells/uL) 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 synovial tissue cultures are the gold standard positive in approximately 80% of cases hold cultures for 14-28 days to isolate C. acnes cultures should be on aerobic, anaerobic, and broth media at least 4 specimens should be obtained at surgery fungal cultures held for 4 weeks mycobacterial cultures held for 8 weeks Treatment Nonoperative antibiotic suppression indications severely ill patients those unwilling to undergo surgery guided by culture results consultation with infectious disease antibiotic Penicillin is the antibiotic of choice for treatment of C.acnes outcomes failure rates of 60-75% Operative irrigation and debridement with component retention inidications acute infections (<4 weeks) 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 amputation indications rarely performed and reserved for life-threatening infection Techniques Antibiotic suppression antibiotic Aspiration cultures may direct antibiotic Penicillin is most common for C. acnes complication inadequate clearance of organism Irrigation and debridement and component retention approach delto-pectoral approach instrumentation mobile parts of the prosthesis may be exchanged especially in RSA (glenosphere, polyethylene liner and tray) complications inadequate clearance of organism outcomes 50% failure rate Single-stage revision approach delto-pectoral approach debridement debride all infected soft tissue and bone instrumentation remove infected prosthesis and implant a new one consider replacement with RSA for re-implantation as soft tissue debridement may sacrifice rotator cuff complications inadequate clearance of organism outcomes variable, as high as 90% success in some series 2-stage implant exchange approach delto-pectoral approach debridement debride all infected soft tissues and bone instrumentation removal of implants and implantation of an 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 recurrent infection outcomes some remain satisfied and elect to leave the spacer variable 60%-90% success rate Resection arthroplasty approach delto-pectoral debridement debride all infected soft tissue and bone preservation of tuberosities is predictive for better results instrumentation all instrumentation is removed complications poor functional outcome likely antero-superior subluxation of humerus if tuberosities and cuff removed outcomes functional results are poor pain relief is achieved in more than 50% Arthrodesis approach S-shaped incision beginning over the scapular spine, traversing anterior over the acromion, and extending down the anterolateral aspect of the arm debridement resect rotator cuff bicep tenodesis decorticate glenoid, humeral head, and undersurface of acromion instrumentation a 10-hole 4.5mm pelvic reconstruction plate is commonly used with a goal of 30-30-30 30 degrees of abduction 30 degrees of forward flexion 30 degrees of internal rotation compression screws placed across the glenohumeral joint complication infection nonunion malposition prominant hardware humeral shaft fracture outcomes improvement in pain with fusion Amputation approach dependent on the level of amputation or shoulder disarticulation debridement removal of soft tissue and bone to desired level of resection instrumentation removal of all implants complication infection neruomas Complications Failure to eradicate infection Humerus or glenoid fracture Poor bone stock