Multisystem Processes & Disorders

Prosthetic joint infection: workup and management

Clinical Overview and When to Suspect Prosthetic Joint Infection

— Occurs in ~1–2% of primary hip/knee arthroplasties; up to 5–10% of revisions

— Lifetime risk rises with each revision; leading cause of revision TKA

— Bacteria adhere to prosthesis, form biofilm that resists antibiotics and host defenses

— Explains why source control (hardware removal/debridement) is usually required alongside antibiotics

— Early (<3 months): virulent organisms — S. aureus, GNRs, often perioperative inoculation

— Delayed (3–12 months): low-virulence — coag-negative staph, Cutibacterium acnes (shoulder), Enterococcus

— Late (>12 months): hematogenous seeding — skin, dental, GU, GI sources

— Persistent or new joint pain after arthroplasty, especially pain at rest or pain that never resolved postoperatively

— Wound drainage >5–7 days, dehiscence, sinus tract

— Early loosening of a well-fixed implant on imaging

— Acute monoarticular pain/swelling in a prosthetic joint with fever or bacteremia

— Diabetes (especially HbA1c >7.5–8%), obesity, RA, immunosuppression, prior PJI, MRSA colonization, smoking, malnutrition (albumin <3.5)

Definition: Prosthetic joint infection (PJI) is infection involving the implant, adjacent bone, or periprosthetic soft tissue after arthroplasty (hip, knee, shoulder most common).

Epidemiology:

Pathogenesis — biofilm matters:

Classification by timing (post-implantation):

When to suspect PJI:

High-risk hosts:

Board pearl: A draining sinus tract communicating with the prosthesis is itself diagnostic of PJI — no further confirmatory test required per MSIS/IDSA criteria.

Step 3 management: In the ambulatory clinic, a patient with a prior TKA presenting with new knee pain >6 months postop should not be labeled "mechanical loosening" until PJI has been actively excluded with ESR/CRP and joint aspiration referral.

Presentation Patterns and Key History

— Fever, erythema, warmth, wound drainage, purulence

— Acute onset severe joint pain in a previously well-functioning prosthesis

— Often associated bacteremia: dental work, UTI/pyelo, cellulitis, IVDU, endocarditis

— Persistent low-grade pain since surgery that "never felt right"

— Pain at rest and with weight-bearing (mechanical loosening pain is typically only with activity)

— Stiffness, mild swelling, low-grade or absent fever

— Sinus tract or recurrent superficial drainage

— Date of arthroplasty, number of prior revisions, intraoperative complications

— Postop course: wound healing, prolonged drainage, hematoma, antibiotics given

— Interval bacteremic events: dental procedures without prophylaxis (high-risk patients), urosepsis, skin infections, line infections

— Comorbidities: DM control, immunosuppressants (TNF inhibitors, steroids, methotrexate), HIV, malignancy

— Prior MRSA/MSSA colonization or decolonization

— Constant rest pain, night pain

— Any sinus or drainage

— Systemic symptoms (fevers, chills, sweats, weight loss)

— Early failure (<2 years) of well-implanted hardware

— Pain only with activity, relieved by rest

— Years of pain-free function followed by gradual mechanical symptoms

Acute presentation (early postop or acute hematogenous):

Chronic indolent presentation (more common, more missed):

Key history to elicit:

Symptoms that argue FOR infection over aseptic loosening:

Symptoms that argue AGAINST infection:

Key distinction: Aseptic loosening pain = activity-related, relieved with rest. PJI pain = present at rest and at night, often constant. This single history point reframes the entire workup.

Step 3 management: On a Step 3 vignette, "well-functioning TKA for 8 years, now fevers after a dental cleaning with new knee pain" = late hematogenous PJI — order blood cultures and arrange joint aspiration; do not start empiric antibiotics before aspiration unless septic/unstable.

Physical Exam Findings and Hemodynamic Assessment

— Inspect for erythema, induration, healed vs. dehisced incision, sinus tract (probe gently to check for communication with prosthesis)

— Palpable warmth, effusion, fluctuance

— Restricted painful range of motion; pain with axial loading or rotation

— Compare with contralateral joint

— Regional lymphadenopathy (inguinal for hip/knee, axillary for shoulder)

— Distal neurovascular check — rule out compartment compromise, especially in acute swelling

— Skin survey for portals of entry: tinea pedis, ulcers, eczema, IV sites

— Vital signs: fever, tachycardia, hypotension, tachypnea — qSOFA/SIRS

— Oral cavity and dentition (abscess, poor dentition)

— Cardiac auscultation for new murmur (concurrent endocarditis — especially S. aureus PJI)

— Skin/IV sites; GU exam if indicated; spine for vertebral osteo if back pain

— Most chronic PJI patients are hemodynamically stable

— Acute hematogenous or postoperative PJI can present with sepsis or septic shock — manage per Surviving Sepsis: 30 mL/kg crystalloid, broad-spectrum antibiotics within 1 hour, lactate, blood cultures x2 before antibiotics if feasible

— Deep PJI may have minimal overlying findings — absence of erythema does not exclude infection

— Obese patients and deep hip prostheses are particularly easy to miss

— A non-tender, well-healed scar with persistent pain still warrants workup

Local exam — the operated joint:

Regional exam:

Systemic exam — assess for hematogenous source and sepsis:

Hemodynamic assessment:

Pitfalls on exam:

Board pearl: Always probe a sinus near a prosthesis — if the probe reaches metal/bone, PJI is established and warrants surgical referral, not just topical wound care.

CCS pearl: On a CCS case with fever + prosthetic joint, order vitals, blood cultures x2, CBC, CMP, ESR, CRP, and orthopedic consult on the first screen — then advance the clock.

Diagnostic Workup — Initial Labs, Imaging, and Joint Aspiration

— ESR and CRP together — sensitivity ~95% when both elevated; normal values argue strongly against chronic PJI (NPV high)

— Thresholds (chronic PJI, >6 weeks postop): ESR >30 mm/h, CRP >10 mg/L

— Acute postop (<6 weeks): CRP can be normally elevated; use higher cutoffs (CRP >100 mg/L) and trend

— D-dimer and IL-6 are emerging adjuncts (MSIS criteria) but not first-line on Step 3

— WBC often normal in chronic PJI; leukocytosis suggests acute/hematogenous

— Blood cultures x2 before antibiotics if febrile or acute presentation

— Look for periprosthetic lucency >2 mm, focal osteolysis, hardware loosening, subperiosteal reaction, gas

— Early imaging may be normal — does not exclude PJI

— Indicated when ESR/CRP elevated, or high clinical suspicion regardless of labs

— Hold antibiotics ≥2 weeks before aspiration if patient is stable, to maximize culture yield

— Send: cell count with differential, Gram stain, aerobic + anaerobic cultures, crystals (rule out gout), and alpha-defensin if available

— WBC >3,000/µL and/or PMN >80% — highly suggestive

— Acute postop thresholds higher: WBC >10,000, PMN >90%

— Positive alpha-defensin = strong evidence of PJI

Serum inflammatory markers (screening):

CBC, BMP, blood cultures:

Plain radiographs (always first imaging):

Joint aspiration (synovial fluid analysis) — the key test:

Synovial fluid PJI thresholds (chronic, >6 weeks postop):

Key distinction: Native septic arthritis cutoff is WBC >50,000 with PMN >90% — PJI thresholds are far lower (>3,000). Applying native-joint cutoffs to a prosthetic joint will miss most PJIs.

Step 3 management: Order ESR + CRP + plain films first; if either marker elevated or suspicion remains, refer for arthrocentesis under sterile/fluoro guidance — do not aspirate through cellulitic skin.

Diagnostic Workup — Advanced and Confirmatory Studies

— If first tap is dry or equivocal and suspicion persists, repeat aspiration with fluoroscopic or US guidance

— Avoid saline lavage for culture (dilutes yield)

— MRI with metal-artifact reduction — assess soft tissue abscess, osteomyelitis, sinus tract

— CT — periprosthetic lucency, sequestra, abscess; useful when MRI artifact limits

— Three-phase bone scan — sensitive but not specific; remains positive up to 1 year postop, less useful early

— Tagged WBC scan + sulfur colloid marrow scan — improves specificity, useful when MRI inconclusive

— FDG-PET — emerging, not yet standard first-line

— Multiple periprosthetic tissue cultures (≥3, ideally 5–6) — single positive may be contaminant; ≥2 with same organism = PJI

— Histopathology of periprosthetic tissue — >5 neutrophils per HPF in ≥5 HPFs supports PJI

— Sonication of explanted hardware — dislodges biofilm bacteria; increases culture yield, especially after recent antibiotics

— 16S rRNA PCR, next-generation sequencing — useful for culture-negative PJI or fastidious organisms (Cutibacterium, Mycoplasma, Brucella)

— Sinus tract communicating with prosthesis, OR

— Two positive cultures with same organism, OR

— Combination of minor criteria (elevated ESR/CRP, elevated synovial WBC/PMN, positive alpha-defensin, positive histology, single positive culture)

— Causes: prior antibiotics, fastidious organisms, fungi, mycobacteria

— Hold antibiotics ≥2 weeks before resampling whenever clinically safe

Repeat aspiration:

Advanced imaging:

Intraoperative diagnosis (gold standard tier):

Molecular diagnostics:

MSIS/IDSA diagnostic criteria — PJI is confirmed by:

Culture-negative PJI (~5–15%):

Board pearl: Sonication fluid culture from explanted hardware is the highest-yield test for biofilm organisms — particularly valuable when preop cultures were negative.

Step 3 management: Always document why empiric antibiotics were (or were not) held before sampling — this is a frequent quality-of-care question and a frequent exam point.

Risk Stratification and First-Line Management Logic

— (1) Is the prosthesis salvageable?

— (2) Acute vs. chronic infection?

— (3) Host fitness for major surgery?

— Indicated when all are true:

— Symptoms <3–4 weeks duration

— Implant is well-fixed, no sinus tract

— Soft tissue envelope intact

— Susceptible organism (avoid in resistant GNR, fungi, atypical mycobacteria when possible)

— Procedure: open debridement, exchange of modular components (polyethylene liner, femoral head), retain stem/cup

— Followed by 6 weeks IV/oral antibiotics + chronic suppression in many cases

— Stage 1: Remove all hardware + cement, place antibiotic-impregnated spacer, 4–6 weeks IV antibiotics

— Antibiotic holiday and reassess (ESR/CRP trend, aspiration)

— Stage 2: Reimplant new prosthesis once infection controlled

— Best success rates (~85–90%) for difficult-to-treat organisms

— Single operation: remove infected hardware + reimplant during same procedure

— Reserved for select patients: known susceptible organism, healthy soft tissue, no sinus, immunocompetent host

— Common in Europe; growing US use

— Salvage for failed multiple revisions, poor soft tissue, non-ambulatory patients, severe comorbidity

— Patients unfit for surgery, well-fixed implant, oral susceptible organism, tolerable antibiotic

Three core management decisions:

DAIR (Debridement, Antibiotics, Implant Retention):

Two-stage exchange (gold standard for chronic PJI in US):

One-stage exchange:

Resection arthroplasty / arthrodesis / amputation:

Chronic suppression alone (no surgery):

Key distinction: <3–4 weeks of symptoms + well-fixed prosthesis = DAIR candidate. >4 weeks or loose implant = staged exchange. This duration threshold drives the algorithm.

Step 3 management: Always involve orthopedic surgery AND infectious disease early — co-management is standard of care and a frequent right answer.

Pharmacotherapy — Empiric and Pathogen-Directed Regimens

— Vancomycin (covers MRSA, CoNS) + cefepime or piperacillin-tazobactam (covers GNRs including Pseudomonas)

— Add anaerobic coverage if abdominopelvic source suspected

— MSSA: nafcillin or cefazolin IV; add rifampin if hardware retained (DAIR) — rifampin penetrates biofilm

— MRSA: vancomycin or daptomycin; add rifampin if retained hardware

— Coag-negative staph: vancomycin ± rifampin

— Streptococci: penicillin G or ceftriaxone

— Enterococcus (susceptible): ampicillin ± ceftriaxone or aminoglycoside; vancomycin if PCN allergic; VRE → daptomycin/linezolid

— Enterobacterales: ceftriaxone or ertapenem based on susceptibilities; fluoroquinolone PO if susceptible (excellent bone penetration)

— Pseudomonas: cefepime, ceftazidime, or pip-tazo + consideration of ciprofloxacin PO transition

— Cutibacterium acnes (shoulder): penicillin G or ceftriaxone, then amoxicillin

— Fungal (Candida): fluconazole if susceptible, echinocandin initial, long suppression

— Always add to a companion drug to prevent resistance (never monotherapy)

— Use only with retained hardware (DAIR) or stage-1 spacer

— Major interactions: warfarin, DOACs, statins, OCPs, antiretrovirals (CYP3A4 inducer)

— Common regimens: cephalexin, amoxicillin, doxycycline, TMP-SMX, levofloxacin, linezolid (short courses due to toxicity)

— Duration: 3–6 months minimum after DAIR; lifelong suppression often if hardware retained and high reinfection risk

Empiric antibiotics — only after cultures obtained (unless septic):

Pathogen-directed therapy (typical 6-week IV/highly bioavailable PO course):

Rifampin — the biofilm drug:

Oral step-down / chronic suppression:

Board pearl: Rifampin + fluoroquinolone is the canonical oral combination for staphylococcal PJI with retained hardware — high biofilm penetration, excellent bioavailability.

Step 3 management: Check baseline LFTs before rifampin; counsel patients about orange discoloration of tears, urine, sweat and contact-lens staining — a classic safety/counseling question.

Surgical Management — DAIR, One-Stage, and Two-Stage Exchange

— Open arthrotomy (arthroscopic debridement is inferior and discouraged)

— Thorough synovectomy, copious lavage (9+ liters), exchange modular parts (poly liner, femoral head)

— Multiple intraoperative cultures and tissue for path

— Success: ~50–70% overall; better with MSSA + rifampin, worse with MRSA, S. aureus bacteremia, sinus, or symptoms >3 weeks

— Remove all components, cement, infected bone

— Place antibiotic-loaded cement spacer (vancomycin + tobramycin/gentamicin typical); articulating vs. static spacer

— 4–6 weeks IV pathogen-directed antibiotics

— Antibiotic-free interval (2–8 weeks), monitor ESR/CRP trend and clinical exam

— Repeat aspiration before stage 2 if any concern

— Confirm infection cleared (cultures, frozen section)

— Implant new prosthesis with antibiotic-loaded cement

— Brief postop antibiotic course (often until intraop cultures return)

— Same-session removal, debridement, and reimplantation

— Strict selection: identified susceptible organism preop, intact soft tissues, no sinus, immunocompetent

— Outcomes increasingly comparable to two-stage in selected cohorts

— Resection arthroplasty (Girdlestone for hip): functional but shortened limb

— Arthrodesis (knee): stable but rigid

— Above-knee amputation: last resort for life-threatening or unreconstructable cases

— Optimize HbA1c <7.5–8%, smoking cessation ≥4 weeks pre-op, nutrition (albumin >3.5), MRSA decolonization (mupirocin + chlorhexidine), staged dental clearance

— Hold biologics per ACR/AAHKS guidelines preop

DAIR procedure details:

Two-stage exchange — Stage 1 (resection):

Two-stage — Stage 2 (reimplantation):

One-stage exchange:

Salvage options:

Perioperative optimization (Step 3 favorite):

Key distinction: DAIR = early/acute, well-fixed. Two-stage = chronic, loose, or failed DAIR. One-stage = highly selected, known susceptible organism.

CCS pearl: On a CCS case, "consult orthopedic surgery" and "consult infectious disease" early earn points; delaying surgical source control while cycling antibiotics is penalized.

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher prevalence of PJI due to comorbidity and longer prosthesis dwell time

— Frailty, dementia, and functional status drive whether two-stage exchange is feasible — many elders better served by DAIR + chronic suppression or resection arthroplasty

— Goals-of-care discussions essential before committing to multi-stage surgery

— Polypharmacy: rifampin drug interactions are a major issue (warfarin, DOACs, statins, antihypertensives)

— Vancomycin: trough-based or AUC-based dosing (target AUC 400–600); renal dose adjustment essential, monitor SCr 2–3x/week

— Aminoglycosides: avoid if possible; ototoxic and nephrotoxic; monitor levels

— Daptomycin: dose-adjust for CrCl <30; monitor CK weekly (myopathy risk, esp. with statins — hold statin)

— Beta-lactams: dose-adjust (cefepime — neurotoxicity/myoclonus in renal failure is a classic Step 3 pitfall)

— TMP-SMX: hyperkalemia, AKI risk; avoid with ACEi/ARB in elderly when possible

— Antibiotic-loaded cement spacers can release nephrotoxic doses of aminoglycosides — monitor renal function postop

— Rifampin: hepatotoxic; check LFTs at baseline and every 2–4 weeks; avoid in active hepatitis or transaminases >3x ULN

— Linezolid: lactic acidosis and cytopenias; weekly CBC if >2 weeks

— Fluoroquinolones: QT prolongation, tendinopathy (worse in elderly, on steroids, post-transplant), C. diff risk

— PICC complications: line infection, thrombosis (DVT prophylaxis considerations)

— Weekly labs: CBC, BMP, LFTs; vancomycin levels; CK for daptomycin

— Coordination with home health, ID clinic follow-up — a classic transitions-of-care item

Elderly considerations:

Renal impairment:

Hepatic impairment:

OPAT (outpatient parenteral antibiotic therapy) safety:

Board pearl: Cefepime neurotoxicity (myoclonus, encephalopathy, non-convulsive status) is dose- and renal-function-dependent — recognize it on the CCS as an iatrogenic complication, not "worsening sepsis."

Step 3 management: When choosing between DAIR + suppression vs. two-stage exchange in a frail 85-year-old, patient functional status and goals outweigh the "gold standard" — document a goals-of-care conversation.

Special Populations — Pregnancy, Pediatrics, and Immunocompromised

— PJI is rare in pregnancy (prostheses uncommon in this age group); usually post-traumatic or congenital hip arthroplasty patients

— Imaging: prefer MRI without gadolinium and ultrasound; minimize CT/fluoroscopy

— Safe antibiotics: penicillins, cephalosporins, vancomycin (category B-equivalent)

— Avoid: fluoroquinolones (cartilage in animal studies — relative), tetracyclines (after 1st trimester — fetal teeth/bone), TMP-SMX in 1st (folate antagonism) and 3rd trimester (kernicterus), rifampin near term (neonatal hemorrhage — give vitamin K)

— Aminoglycosides — fetal ototoxicity

— Defer elective surgical exchange when feasible; manage with IV beta-lactam + ortho/ID/MFM co-management

— Higher infection rates than adult arthroplasty

— S. aureus and S. epidermidis predominate

— Consider Kingella in young children

— Long-term consequences: limb-length discrepancy, repeated revisions

— Solid organ transplant, hematologic malignancy, chronic steroids, biologics (TNF-α inhibitors, JAK inhibitors)

— Atypical organisms: fungi (Candida, Aspergillus), mycobacteria (TB, NTM), nocardia

— Lower threshold to send mycobacterial and fungal cultures, 16S/ITS PCR if culture-negative

— Hold biologics perioperatively per ACR guidance (TNFi: 1 dosing interval; methotrexate may often be continued)

— Reinstate immunosuppression only after wound healed and infection controlled

— Risk for hematogenous PJI and concurrent endocarditis — always echo if S. aureus bacteremia

— Address SUD with MAT (buprenorphine/methadone), harm reduction; OPAT may require alternative models (long-acting agents like dalbavancin/oritavancin)

Pregnancy:

Pediatric prosthetic joints (oncologic/limb-salvage endoprostheses):

Immunocompromised hosts:

People who inject drugs:

Key distinction: In immunocompromised patients with culture-negative PJI, escalate to fungal, mycobacterial, and molecular diagnostics — do not assume contamination.

Step 3 management: For S. aureus PJI, always obtain TTE (and TEE if high pretest probability) — concurrent endocarditis changes duration and intensity of therapy and disqualifies many DAIR candidates.

Complications and Adverse Outcomes

— Bacteremia and sepsis — particularly S. aureus; consider endocarditis, vertebral osteomyelitis, epidural abscess

— Metastatic infection: psoas abscess, septic emboli, secondary septic arthritis of other joints

— Sinus tract formation and chronic drainage — increases reinfection at exchange

— Periprosthetic osteomyelitis with sequestrum — may necessitate larger bone resection

— Wound dehiscence, hematoma, periprosthetic fracture

— Spacer-related: dislocation, fracture, bone loss between stages, spacer subsidence

— Heterotopic ossification, stiffness, arthrofibrosis

— Nerve injury (peroneal, sciatic, femoral)

— DVT/PE — extended VTE prophylaxis is standard (aspirin or DOAC per protocol)

— Vancomycin: AKI, infusion reaction (red-man), DRESS, ototoxicity

— Daptomycin: myopathy, eosinophilic pneumonia

— Linezolid: thrombocytopenia, peripheral/optic neuropathy, serotonin syndrome with SSRIs, lactic acidosis

— Rifampin: hepatitis, drug interactions, GI upset, orange secretions

— Fluoroquinolones: tendinopathy/rupture, aortic aneurysm/dissection, QT, dysglycemia, C. diff

— C. difficile colitis — high risk with prolonged broad-spectrum therapy

— Line-associated bloodstream infection and PICC-associated DVT

— Persistent pain, decreased ROM, gait abnormality even after eradication

— Higher re-revision rates and shorter prosthesis lifespan

— Psychological burden, depression, opioid dependence — screen and address

— 1-year mortality after PJI approaches 5–10%, comparable to many cancers

— Higher with S. aureus, polymicrobial, multiple revisions, frailty

— 10–20% after two-stage exchange; higher after DAIR

— Same organism (relapse) or new organism (reinfection)

Infection-related complications:

Surgical complications:

Antibiotic-related complications:

Functional outcomes:

Mortality:

Reinfection:

Board pearl: PJI carries a 5-year mortality comparable to many solid tumors — treat it as the serious systemic illness it is, not a local hardware problem.

Step 3 management: Screen and treat depression, control pain with multimodal (acetaminophen, NSAIDs if safe, neuropathic agents) and minimize chronic opioids during prolonged convalescence.

When to Escalate — ICU, Consults, and Inpatient Triage

— Septic shock, vasopressor requirement, lactic acidosis

— Respiratory failure (septic emboli, ARDS, eosinophilic pneumonia from daptomycin)

— Severe metabolic derangement, AKI requiring CRRT

— Acute systemic infection, hemodynamic instability, bacteremia

— Need for urgent surgical debridement (DAIR or resection)

— Inability to tolerate oral intake, need for IV antibiotic initiation/titration

— Comorbidity decompensation (DKA, decompensated HF) driven by infection

— Orthopedic surgery: every confirmed or strongly suspected PJI — they own source control

— Infectious diseases: drug selection, duration, suppression, atypical organisms, antibiotic toxicity

— Plastic surgery: soft tissue defect, flap coverage planning

— Cardiology / TEE: S. aureus bacteremia, suspected endocarditis

— Vascular surgery: mycotic aneurysm or vascular involvement

— Pharmacy: OPAT planning, drug interactions (rifampin), TDM

— Anesthesia / pre-op clinic: optimization for staged surgery

— Palliative care: non-reconstructable disease, goals-of-care

— Social work / case management: OPAT logistics, home health, SNF placement

— Psychiatry / addiction medicine: if SUD present

— Stable, chronic indolent presentation with reliable follow-up → outpatient workup with prompt aspiration and ortho/ID referral

— Acute, febrile, or systemically ill → admit

— Coordinated discharge with OPAT, ID follow-up within 1–2 weeks, ortho follow-up at 2 weeks, lab monitoring schedule explicit on discharge summary

— Closed-loop communication with PCP — a frequent Step 3 patient-safety theme

Immediate ICU triage:

Inpatient admission criteria:

Consult triggers — assemble the team early:

Outpatient vs. inpatient decision:

Transitions of care:

CCS pearl: On CCS, after stabilizing the patient and obtaining cultures, consult orthopedic surgery and infectious diseases on the same screen — both teams are required for standard-of-care management; consulting only one is incomplete.

Step 3 management: Document a clear escalation plan ("return precautions: fever, worsening pain, drainage") and ensure follow-up appointments are scheduled before discharge — failure here is a classic safety-event vignette.

Key Differentials — Same-Category (Joint/Bone) Causes

— Most common cause of arthroplasty pain >2 years out

— Activity-related pain, relieved by rest; no systemic symptoms

— Radiographs: progressive radiolucency >2 mm at bone-cement or bone-implant interface, component migration

— ESR/CRP usually normal; synovial WBC <3,000

— Acute pain after fall or low-energy trauma in osteopenic bone

— Radiograph diagnostic; Vancouver classification (hip), Rorabeck (knee)

— Surgical fixation vs. revision based on stability and bone stock

— Polyethylene wear, osteolysis from particle disease — chronic, mechanical pain, classic radiographs

— Component malposition (impingement, instability, recurrent dislocation)

— Trunnionosis (metal-on-metal corrosion at modular junction) — adverse local tissue reaction, pseudotumor; elevated serum cobalt/chromium

— Gout or pseudogout can affect prosthetic joints, especially when surrounding native tissue or remaining cartilage exists

— Synovial fluid: crystals, cell count may overlap with PJI; always send cultures — coexistence with infection possible

— Anticoagulated patient, sudden swelling without infection; aspirate shows bloody fluid, no organisms

— Diagnosis of exclusion; patch testing limited utility

— Eosinophilic infiltrate on histology

— Easily missed; MRI or bone scan diagnostic

— Stiffness and pain post-arthroplasty (hips especially); radiographs show ectopic bone

— Iliopsoas tendinitis after THA, pes anserine bursitis after TKA

— Point tenderness, no effusion, normal markers

Aseptic loosening:

Periprosthetic fracture:

Hardware-related mechanical issues:

Crystal arthropathy in a prosthetic joint:

Hemarthrosis:

Reactive synovitis / metal hypersensitivity:

Stress fracture / insufficiency fracture of adjacent bone (pubic ramus, sacrum after THA):

Heterotopic ossification:

Tendinopathy / bursitis:

Key distinction: PJI vs. aseptic loosening is the single highest-yield discrimination — infection = pain at rest, elevated ESR/CRP, synovial WBC >3,000; loosening = activity pain, normal markers, lucent lines on imaging.

Board pearl: Always send synovial fluid for both crystals and culture — gout in a prosthetic joint does not exclude superimposed infection.

Key Differentials — Other-Category Causes

— Lumbar radiculopathy (L4–L5) → anterior thigh/knee pain mimicking TKA/THA pain; positive straight leg raise, dermatomal, neurogenic

— Hip pathology referring to knee — classic in pediatrics and adults: groin/thigh pain perceived at the ipsilateral knee

— Spinal stenosis with neurogenic claudication mimics post-arthroplasty walking pain

— Peripheral arterial disease — calf/thigh pain with exertion, decreased pulses, ABI <0.9

— DVT of the operated extremity — calf swelling, Homan's sign poor — get Doppler US

— Mycotic pseudoaneurysm near hip prosthesis — rare but catastrophic

— Cellulitis, superficial wound infection (above fascia) — treated with antibiotics alone, does not require hardware exchange — but be sure deep infection is excluded

— Necrotizing fasciitis — surgical emergency, rapid progression, pain out of proportion

— Polymyalgia rheumatica in older adults — proximal stiffness, elevated ESR; responds dramatically to low-dose steroids

— Rheumatoid arthritis flare in prosthetic joint patient — symmetric polyarticular involvement, elevated RF/anti-CCP

— Psoriatic / reactive arthritis — dactylitis, enthesitis, skin/eye findings

— Periprosthetic sarcoma, lymphoma, or metastasis — rare; bony lesion not explained by infection or wear

— Complex regional pain syndrome (CRPS) — allodynia, color/temperature changes, swelling out of proportion

— Neuropathic pain from surgical nerve injury (saphenous, lateral femoral cutaneous)

— Hematogenous S. aureus may seed both endocardium and prosthesis simultaneously — always evaluate the heart with bacteremia

Referred pain to a prosthetic joint — the great mimic:

Vascular causes:

Soft tissue infection without prosthetic involvement:

Systemic / metabolic mimics:

Tumor:

Pain syndromes:

Endocarditis presenting as PJI:

Key distinction: A patient with knee pain after TKA + back pain + positive SLR → think lumbar radiculopathy first, not PJI — but still check ESR/CRP if any doubt.

Step 3 management: A "negative" superficial wound infection still warrants vigilant follow-up — track ESR/CRP and have a low threshold to re-image and aspirate if symptoms recur.

Secondary Prevention, Discharge Medications, and Long-Term Plan

— Pathogen-directed antibiotics — typically 6 weeks IV or highly bioavailable oral (fluoroquinolone-based for GNRs, rifampin-combination for staph with retained hardware)

— Chronic oral suppression for selected DAIR patients or unfit-for-revision patients (cephalexin, doxycycline, TMP-SMX, amoxicillin) — duration months to lifelong

— VTE prophylaxis per protocol (aspirin 81 mg or DOAC) — extended duration post-arthroplasty

— Pain control: acetaminophen scheduled, NSAIDs if safe, taper opioids; consider neuropathic agents

— HbA1c <7.5–8% before elective stage-2 reimplantation

— Smoking cessation — pharmacotherapy (nicotine replacement, varenicline, bupropion) + counseling

— Nutrition: albumin >3.5 g/dL, prealbumin trend, dietitian referral

— Weight optimization; address obesity (lifestyle, GLP-1 agonists where indicated)

— MRSA decolonization before stage 2: mupirocin intranasal + chlorhexidine bathing

— Dental clearance — treat active dental disease

— Routine prophylaxis NOT recommended for most arthroplasty patients per AAOS/ADA

— Consider in high-risk patients: prior PJI, immunocompromise, type 1 DM, recent (<2 yr) arthroplasty undergoing high-risk dental work

— Amoxicillin 2 g PO 30–60 min pre-procedure when indicated; clindamycin no longer first-line for PCN allergy (use cephalexin or azithromycin)

— Treat UTIs promptly; screen and treat skin infections; podiatry care for diabetic feet

— Coordinate with rheumatology/transplant; reinstate biologics only after wound healed and infection controlled, lowest effective dose

— Influenza, pneumococcal, COVID-19, RSV (age-appropriate), shingles, Tdap — reduce systemic infection sources

Post-treatment discharge regimen:

Optimize host factors to prevent recurrence:

Long-term dental/procedural antibiotic prophylaxis:

Address bacteremic seeding sources:

Long-term immunosuppression management:

Vaccination:

Board pearl: Routine dental antibiotic prophylaxis is NOT indicated for most arthroplasty patients — a frequently tested misconception. Reserve for high-risk patients with high-risk procedures.

Step 3 management: Build a written long-term plan at discharge: antibiotic stop date, lab monitoring schedule, follow-up appointments, return precautions, and explicit dental prophylaxis guidance.

Follow-Up, Monitoring, and Rehabilitation

— Ortho: 2 weeks post-discharge (wound check), 6 weeks, 3 months, 6 months, then annually

— ID clinic: 1–2 weeks post-discharge, every 2–4 weeks during IV therapy, then 3 and 6 months after completing treatment

— PCP: 1 week post-discharge for medication reconciliation and chronic disease management

— Weekly CBC, BMP, LFTs for most regimens

— Vancomycin: trough/AUC twice weekly, SCr 2–3x/week

— Daptomycin: weekly CK; hold concurrent statins

— Linezolid: weekly CBC; monitor for neuropathy if >2 weeks

— Rifampin: LFTs at baseline, 2 weeks, then monthly

— Aminoglycoside-eluting spacer: SCr 2–3x/week initially

— ESR and CRP at baseline, every 2–4 weeks; CRP should normalize within 4–6 weeks, ESR slower (3 months)

— Persistent or rising markers → recurrence concern → re-evaluate

— Plain radiographs at 6 weeks, 3, 6, 12 months — look for spacer position, bone reaction, lucency

— Advanced imaging only for symptom recurrence

— PT focused on ROM, strengthening, gait training — protocol depends on surgical approach and weight-bearing restrictions

— Avoid aggressive ROM if spacer in place — risk of fracture/dislocation

— Assistive devices, home safety evaluation (especially elderly)

— OT for ADL adaptation

— Warn that pain may persist for months even after eradication

— Explain reinfection risk and warning signs

— Discuss sexual activity, return to work, driving timelines

— Mental health screening (PHQ-9, GAD-7) — depression common during prolonged convalescence

— New fever, increasing pain, new drainage, wound separation → contact ID/ortho immediately

— Dental and minor procedure plans — pre-coordinate

Follow-up cadence after PJI treatment:

Laboratory monitoring during IV therapy:

Trend inflammatory markers:

Imaging surveillance:

Rehabilitation:

Counseling:

Patient education on return precautions:

Board pearl: CRP normalizes faster than ESR — a falling CRP at 4 weeks is reassuring, but persistently elevated ESR alone may simply reflect slow kinetics.

Step 3 management: Build a "single-page" follow-up roadmap and confirm patient and PCP both receive it — this transitions-of-care detail is a frequently tested patient-safety practice.

Ethical, Legal, and Patient Safety Considerations

— Patients must understand realistic outcomes: success rates (~85% for two-stage, ~50–70% for DAIR), risk of reinfection, possible need for resection arthroplasty or amputation, prolonged antibiotic course with toxicities, months of impaired function

— Document specific discussion of alternatives, including chronic suppression alone for poor surgical candidates

— Capacity assessment in elderly/demented patients; involve surrogate decision-makers via advance directives or POA

— Frail elderly or terminally ill patients may decline staged exchange; palliative suppression + comfort-focused care is ethically appropriate

— Avoid surgical "rescue" that prolongs morbidity without meaningful functional benefit

— OPAT discharge requires confirmed home infusion provider, PICC line care plan, weekly lab draws, ID follow-up — gaps here drive readmissions

— Medication reconciliation: rifampin's interactions can cause subtherapeutic INR with warfarin (clot risk) or failed contraception — explicit counseling required

— Use teach-back at discharge to verify understanding

— Avoid empiric antibiotics before cultures whenever the patient is hemodynamically stable — early antibiotic exposure causes culture-negative PJI and prolongs definitive management

— MRSA outbreaks, surgical site infection rates reported to NHSN — surgical site infection within 90 days of arthroplasty is a reportable HAI

— Hospital-acquired conditions affect CMS reimbursement (value-based care relevance)

— If retained surgical material or breach of sterile technique contributed to PJI, ethical and legal obligation to disclose the error to the patient transparently per AMA and hospital risk management guidance

— Two-stage exchange and OPAT are resource-intensive — engage social work/case management early; some patients require SNF placement or home health authorization

Informed consent for staged surgery:

Goals-of-care conversations:

Transitions-of-care safety (high-yield Step 3 theme):

Antibiotic stewardship:

Mandatory reporting and public health:

Disclosure of harm:

Insurance and access:

Step 3 management: Before discharging a patient on rifampin who is also on warfarin, explicitly counsel on tighter INR monitoring and contraceptive failure risk — missing this is the canonical safety-error question.

Board pearl: A draining post-arthroplasty wound being managed with serial dressing changes without aspiration or specialist referral is a sentinel patient-safety failure — escalate to ortho/ID immediately.

High-Yield Associations and Rapid-Fire Clinical Facts

— S. aureus (MSSA/MRSA): early/acute, hematogenous; check echo

— Coagulase-negative staph: chronic, indolent, low-grade pain

— Cutibacterium acnes: shoulder arthroplasty, indolent; requires extended (14-day) anaerobic culture

— Streptococcus spp.: hematogenous (dental, GI, GU)

— Enterococcus: GI/GU source; biliary or urinary

— Gram-negatives (E. coli, Pseudomonas): urinary source, postoperative wound

— Polymicrobial: sinus tract, fecal contamination, decubitus proximity

— Candida: immunocompromised, parenteral nutrition, prior broad-spectrum antibiotics

— Mycobacteria (TB, NTM): immunocompromised, endemic regions, water/instrument contamination

— Symptoms <3 weeks + well-fixed implant = DAIR candidate

— Symptoms >4 weeks or loose implant = two-stage exchange

— Only with retained hardware; always with a companion drug; CYP3A4 inducer; orange secretions; LFT monitoring

Organism-host associations:

Timing rules:

Synovial fluid PJI cutoffs: WBC >3,000/µL, PMN >80% (chronic, >6 wks postop)

MSIS major criteria: sinus tract communicating with prosthesis OR two positive cultures with same organism = definite PJI

Rifampin pearls:

Dental prophylaxis: NOT routine; high-risk patients only

Endocarditis association: S. aureus bacteremia + PJI → always echo

Mortality: 1-year ~5–10%; 5-year similar to many cancers

DAIR success: ~50–70%; two-stage success: ~85–90%

MRSA decolonization: mupirocin + chlorhexidine before stage-2 reimplantation

Optimization: HbA1c <7.5–8%, smoking cessation, nutrition (albumin >3.5)

Imaging: plain films first; MRI with metal-artifact reduction; tagged WBC + sulfur colloid for ambiguous cases

Sonication fluid culture: highest yield for biofilm organisms

OPAT toxicities: vanc → AKI; dapto → CK rise; linezolid → cytopenias/neuropathy; ceftriaxone → biliary sludge

Cefepime + renal failure: neurotoxicity, myoclonus

Daptomycin is inactivated by surfactant — do not use for pneumonia

Board pearl: Shoulder arthroplasty pain + negative routine cultures = think Cutibacterium acnes — request prolonged (14-day) anaerobic incubation.

Step 3 management: Always pair the timing rule, the implant-stability question, and the host fitness question to pick DAIR vs. exchange — these three drive nearly every PJI vignette.

Board Question Stem Patterns

— "70-year-old with TKA 8 years ago, well functioning, develops fever and knee pain after dental cleaning. Exam: warm, swollen knee."

— Answer: Blood cultures + joint aspiration + ortho/ID consult. Do not start empiric antibiotics first (if stable).

— "62-year-old, THA 14 months ago, persistent groin pain that never resolved. Afebrile. ESR 60, CRP 35."

— Answer: Arthrocentesis with cell count, Gram stain, cultures, crystals. Cutoffs WBC >3,000, PMN >80%.

— "Postop day 10 TKA, persistent serosanguineous drainage, low-grade fever."

— Answer: Open debridement (DAIR) with poly liner exchange + IV antibiotics + tissue cultures.

— "Persistent shoulder pain post-arthroplasty, routine cultures negative."

— Answer: Cutibacterium acnes — extend anaerobic culture to 14 days.

— Stem gives duration and implant stability. Symptoms <3 weeks + well-fixed = DAIR; chronic or loose = two-stage exchange.

— Patient on warfarin started on rifampin → INR drops → monitor more frequently, expect higher warfarin doses; OCP user → use backup contraception.

— Order echocardiogram (TTE → TEE if high suspicion) — concurrent endocarditis.

— Routine TKA, asks about antibiotic prophylaxis for routine cleaning → not indicated for most patients.

— Elderly patient on cefepime for PJI develops myoclonus and confusion → hold cefepime, adjust for renal function.

— Activity-related pain, normal ESR/CRP, lucent lines on radiograph — favors loosening, not PJI.

— Frail 88-year-old with PJI declining multi-stage surgery → chronic oral suppression is ethically appropriate.

— Visible sinus communicating with prosthesis = definitive PJI; no further diagnostic test required to confirm.

Pattern 1 — Late hematogenous PJI:

Pattern 2 — Chronic indolent PJI:

Pattern 3 — Early postop wound drainage:

Pattern 4 — Shoulder arthroplasty + culture-negative:

Pattern 5 — DAIR vs. two-stage:

Pattern 6 — Rifampin counseling:

Pattern 7 — S. aureus PJI + new murmur:

Pattern 8 — Dental prophylaxis question:

Pattern 9 — Cefepime neurotoxicity:

Pattern 10 — Aseptic loosening mimic:

Pattern 11 — Goals of care:

Pattern 12 — Sinus tract:

Board pearl: When the stem gives both acute onset and a bacteremic source (dental, UTI, IVDU), think late hematogenous PJI — and always evaluate for endocarditis if S. aureus.

Step 3 management: The most common wrong answer is "start broad-spectrum antibiotics" before obtaining cultures in a stable patient — the right move is aspirate, culture, then treat.

One-Line Recap

— Diagnose: ESR + CRP screen, then arthrocentesis with cell count (WBC >3,000, PMN >80%), Gram stain, culture, and crystals; sinus tract communicating with prosthesis or two matching cultures = definitive PJI; hold antibiotics ≥2 weeks before sampling when safe.

— Decide surgery: <3–4 weeks symptoms + well-fixed implant + susceptible organism = DAIR; chronic, loose, or sinus tract = two-stage exchange; salvage with resection arthroplasty or chronic suppression for poor surgical candidates.

— Treat: Pathogen-directed 6-week IV/high-bioavailability oral therapy; add rifampin to a companion drug for staphylococcal PJI with retained hardware; pursue chronic oral suppression in DAIR; monitor for drug toxicities (vanc/AKI, dapto/CK, linezolid/cytopenias, cefepime/neurotoxicity).

— Optimize and follow: HbA1c <7.5–8%, smoking cessation, nutrition, MRSA decolonization before reimplantation; ID and ortho co-management; trend CRP (normalizes 4–6 wks) and ESR; routine dental antibiotic prophylaxis is NOT indicated for most patients — reserve for high-risk hosts and procedures.

Core teaching point: Prosthetic joint infection is a biofilm-driven, surgically-managed disease defined by synovial fluid analysis and culture, treated by combined orthopedic source control (DAIR for acute well-fixed implants, two-stage exchange for chronic or loose ones) plus pathogen-directed antibiotics (with rifampin combinations when hardware is retained), supported by host optimization and meticulous longitudinal follow-up.

High-yield recap bullets:

Step 3 management: Always pair early orthopedic surgery and infectious diseases consultation, coordinate OPAT and transitions of care, document goals-of-care for frail patients, and counsel explicitly on rifampin interactions — these high-yield management moves convert a complex multi-month illness into a structured, exam-ready algorithm.