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Orthopedic Board Prep: Interactive Viva Exam Practice for Trauma & Surgical Cases

Structured Oral Examination: Infected TKA Case Questions

23 Apr 2026 92 min read 156 Views
Illustration of oralexamination question infected - Dr. Mohammed Hutaif

Key Takeaway

We review everything you need to understand about Structured Oral Examination: Infected TKA Case Questions. An **oralexamination question infected** total knee arthroplasty (TKA) presents with increasing pain, stiffness, and recurrent swelling. Diagnosing this involves a detailed history, clinical examination, and key investigations. Initial tests include routine blood work like CRP and ESR; IL-6 assays offer higher sensitivity. Further steps may involve radioisotope bone scans, alignment checks, and joint aspiration to confirm the infection.

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Question 1

A 68-year-old male presents with acute onset knee pain, swelling, and warmth 3 weeks after a primary total knee arthroplasty (TKA). He is febrile (38.8°C) and unable to bear weight. Arthrocentesis reveals synovial fluid with 120,000 WBC/µL, 95% neutrophils, and a positive Gram stain for Gram-positive cocci in clusters. What is the most appropriate initial management strategy?





Explanation

This patient presents with an acute periprosthetic joint infection (PJI) within 3 months of primary TKA, high WBC count in synovial fluid, and positive Gram stain, suggesting bacterial infection (likely Staphylococcal). DAIR (Debridement, Antibiotics, and Implant Retention) is the preferred initial management for acute PJI, especially if symptoms are present for less than 3-6 weeks, the components are stable, and the soft tissues are healthy. Exchange of modular components (polyethylene liner) significantly improves DAIR success rates by removing the biofilm burden from these surfaces. Long-term suppressive antibiotics are for chronic, incurable cases or patients unsuitable for surgery. Single-stage revision is considered for acute PJI in selected cases, but DAIR is often preferred first given the short symptom duration. Two-stage revision is typically reserved for chronic PJI or failed DAIR. Arthrodesis is a salvage procedure for recurrent failed infections.

Question 2

A 72-year-old diabetic female undergoes a two-stage revision for chronic PJI due to MRSA. The first stage involves implant removal, extensive debridement, and placement of an articulating antibiotic-loaded cement spacer. After 6 weeks of targeted intravenous antibiotics, her ESR is 25 mm/hr (down from 80), CRP is 3 mg/L (down from 55), and repeat knee aspirations are negative for growth on multiple cultures. What is the most critical next step before proceeding to the second stage of reimplantation?





Explanation

The most critical step to confirm infection eradication before proceeding to the second stage of reimplantation is obtaining at least two, preferably three, consecutive negative synovial fluid cultures from the knee, ideally after a period off antibiotics (e.g., 2 weeks) to reduce false negatives. While inflammatory markers (ESR, CRP) can guide treatment, they are not definitive for eradication. Imaging (MRI, CT) may be useful for assessing bone stock or identifying occult infection but does not replace microbiological confirmation. Serum alpha-defensin is a diagnostic marker for PJI, not typically used for confirming eradication post-treatment. Empirically continuing antibiotics without microbiological clearance increases the risk of resistance and does not confirm eradication.

Question 3

Which of the following synovial fluid characteristics is most strongly indicative of a periprosthetic joint infection (PJI) in a patient with a painful TKA?





Explanation

According to the 2018 International Consensus Meeting (ICM) criteria for PJI, synovial fluid white blood cell (WBC) count >3,000 cells/µL and synovial fluid polymorphonuclear neutrophil (PMN) percentage >80% are major criteria for diagnosing PJI. While other thresholds exist (e.g., AAOS guidelines suggest >2,500 WBC/µL with >60% PMN for acute PJI, and >1,700 WBC/µL with >65% PMN for chronic PJI), a WBC count of 50,000 cells/µL with 80% neutrophils far exceeds all thresholds and is highly specific for PJI. The other options, while possibly elevated, are less definitively indicative of PJI, with some (like 1,500 WBC) potentially falling into indeterminate zones depending on the PMN%.

Question 4

A 55-year-old male with a history of intravenous drug use develops fever, chills, and painful left knee swelling 3 months after a primary TKA. Initial synovial fluid aspiration is negative for culture despite elevated inflammatory markers. Surgical debridement is performed, and multiple periprosthetic tissue samples are sent for culture. What is the optimal strategy for culturing these tissue samples to maximize yield?





Explanation

To maximize the yield for diagnosing PJI, especially in cases where synovial fluid culture is negative, it is crucial to send at least 5-6 periprosthetic tissue samples for both aerobic and anaerobic culture. Additionally, extending the incubation time to 10-14 days (or even longer for suspected fungal/mycobacterial infections) significantly increases the detection rate of slow-growing or fastidious organisms that may form biofilms. A single sample is insufficient due to sampling error and low bacterial load in biofilm. Fungal and mycobacterial cultures should be considered but not as the sole focus. Rapid PCR can be helpful but does not replace culture as the gold standard for guiding antibiotic therapy.

Question 5

Which of the following host factors is most strongly associated with an increased risk of periprosthetic joint infection (PJI) following total knee arthroplasty?





Explanation

Obesity (BMI >30 kg/m²) is a consistently recognized and significant independent risk factor for PJI following TKA, primarily due to factors like increased soft tissue bulk, compromised wound healing, altered immune response, and higher incidence of comorbidities. While rheumatoid arthritis, COPD, and psoriasis can contribute to overall surgical risk, obesity has a more direct and stronger epidemiological link to PJI. History of DVT is a thrombotic risk, not directly a PJI risk factor.

Question 6

A 65-year-old male presents with recurrent episodes of cellulitis around his 5-year-old TKA. He has a draining sinus tract with purulent discharge. His inflammatory markers are mildly elevated. Synovial fluid aspiration is not possible due to the sinus. What is the most appropriate initial management strategy?





Explanation

A draining sinus tract that communicates with a prosthetic joint is considered pathognomonic for a periprosthetic joint infection (PJI), even if inflammatory markers are only mildly elevated or aspirations are not possible. In such chronic cases, the biofilm is well established, and DAIR is typically ineffective. Therefore, a two-stage revision arthroplasty is the gold standard for managing chronic PJI with a sinus tract. This involves implant removal, debridement, spacer placement, and a subsequent reimplantation after infection eradication. DAIR is not appropriate here given the chronic nature and established sinus. Oral or topical antibiotics alone are insufficient.

Question 7

Which of the following is considered a major diagnostic criterion for periprosthetic joint infection (PJI) according to the 2018 International Consensus Meeting (ICM) criteria?





Explanation

According to the 2018 ICM criteria, a positive alpha-defensin test in synovial fluid is considered a major diagnostic criterion for PJI, with high sensitivity and specificity. Elevated ESR and CRP are minor criteria. Fever and localized pain are clinical signs but not major diagnostic criteria on their own. A history of wound dehiscence is a risk factor, not a diagnostic criterion.

Question 8

A 70-year-old male with a history of diabetes and rheumatoid arthritis undergoes TKA. On post-operative day 7, he develops a rapidly expanding hematoma around the incision. Surgical evacuation of the hematoma reveals extensive necrotic tissue. Intraoperative cultures are positive for Group A Streptococcus. What is the most appropriate course of action?





Explanation

Group A Streptococcus (GAS) causes rapidly progressive, highly virulent infections, often associated with significant soft tissue necrosis and systemic toxicity. In such cases, the infection is often fulminant, and the biofilm forms quickly and aggressively. While DAIR can be considered for very early acute PJI, the presence of extensive necrotic tissue and a highly virulent organism like GAS often warrants more aggressive treatment. Immediate implant removal and placement of an antibiotic-loaded cement spacer (first stage of a two-stage revision) is often necessary to adequately address the infection and necrotic burden, especially when the infection is aggressive and destructive. DAIR success rates are low for GAS infections with significant soft tissue involvement. Single-stage revision is generally not recommended for such aggressive acute infections where eradication is uncertain. Wound debridement and washout alone are insufficient. Antibiotics alone cannot penetrate a mature biofilm and necrotic tissue effectively.

Question 9

What is the primary mechanism by which antibiotic-loaded bone cement (ALBC) spacers help in eradicating infection during the first stage of a two-stage revision for PJI?





Explanation

The primary mechanism by which antibiotic-loaded bone cement (ALBC) spacers aid in infection eradication is by creating a very high local concentration of antibiotics at the infection site. This local delivery allows for concentrations far exceeding what can be achieved systemically, which is crucial for penetrating biofilms and effectively killing bacteria. While some structural support is offered, and they maintain the joint space, their main therapeutic benefit is antibiotic elution. They do not directly absorb cytokines, mechanically remove biofilm (though debridement does), or primarily stimulate local immune responses in this context.

Question 10

Regarding the duration of intravenous antibiotic therapy after a successful DAIR procedure for acute PJI, which of the following is generally recommended?





Explanation

Following a successful DAIR (Debridement, Antibiotics, and Implant Retention) for acute PJI, the typical recommendation is 2-4 weeks of targeted intravenous antibiotic therapy, followed by an extended course of oral antibiotics for several months (e.g., 3-6 months, sometimes longer, depending on the organism and patient factors). This prolonged systemic therapy is crucial to suppress residual bacteria and prevent recurrence. Shorter durations are insufficient for eradicating PJI. 6-12 weeks of IV antibiotics is typically reserved for two-stage revisions where the implant is removed, or for very complex cases.

Question 11

A patient undergoing two-stage revision for PJI has an articulating antibiotic-loaded cement spacer in place. Which type of antibiotic is generally preferred for incorporation into the cement spacer?





Explanation

The ideal antibiotic for incorporation into bone cement should be heat-stable (to withstand the exothermic polymerization process), broad-spectrum (to cover common PJI pathogens, at least initially), bactericidal (for definitive killing), and demonstrate good elution characteristics from the cement. Aminoglycosides (e.g., gentamicin, tobramycin) and vancomycin are commonly used because they meet these criteria. Bacteriostatic antibiotics are generally less preferred for severe infections. High systemic absorption is undesirable for local delivery, and short half-life would require higher loading. Focusing solely on Gram-negative organisms would miss Gram-positive cocci, which are the most common cause of PJI.

Question 12

Which of the following organisms is most commonly implicated in late chronic periprosthetic joint infections (PJI) (>1 year post-op)?





Explanation

Coagulase-negative Staphylococci (CoNS), particularly Staphylococcus epidermidis, are the most common organisms implicated in late chronic PJIs. These organisms are typically low-virulence and often present with indolent symptoms that manifest months to years after the initial surgery. While Staphylococcus aureus is also common, it tends to cause more acute and subacute infections. Pseudomonas and Enterobacteriaceae are less common but can cause severe infections, often associated with healthcare-associated exposures or immunocompromised hosts. Streptococcus pyogenes typically causes acute, aggressive infections.

Question 13

What is the typical success rate of a well-executed two-stage revision arthroplasty for chronic PJI?





Explanation

The typical success rate for eradicating infection with a well-executed two-stage revision arthroplasty for chronic PJI ranges from 85% to 95%. This is considered the gold standard for chronic PJI treatment due to its high efficacy in eliminating the infection while maintaining joint function. The other options represent significantly lower or impossibly high success rates for this complex surgical intervention. While a 100% success rate is not achievable, this method offers the best chance for infection eradication and functional restoration.

Question 14

A patient with a chronically infected TKA caused by methicillin-resistant Staphylococcus aureus (MRSA) is undergoing two-stage revision. During the first stage, extensive debridement is performed. What is the most appropriate empirical intravenous antibiotic regimen to initiate while awaiting definitive culture sensitivities?





Explanation

For known or suspected MRSA PJI, vancomycin is the cornerstone of empirical treatment because of its reliable activity against MRSA. Rifampin is a potent anti-biofilm agent and is often added as a synergistic agent, particularly for staphylococcal infections, but it should never be used as monotherapy due to rapid resistance development. Cefazolin is ineffective against MRSA. Ciprofloxacin, clindamycin, ampicillin/sulbactam, and piperacillin/tazobactam are generally not reliably effective against MRSA. The combination of Vancomycin and Rifampin provides excellent coverage for MRSA and biofilm activity while awaiting sensitivities, although rifampin should be used with caution due to drug interactions and resistance potential.

Question 15

Which of the following factors would most strongly contraindicate a DAIR (Debridement, Antibiotics, and Implant Retention) procedure for a periprosthetic joint infection?





Explanation

The presence of a draining sinus tract communicating with the joint prosthesis is an absolute contraindication to DAIR. A sinus tract indicates a chronic, well-established infection with significant biofilm formation, making implant retention highly unlikely to succeed. In such cases, a two-stage revision is typically required. Symptom duration of 4 weeks is at the upper limit but still potentially acceptable for DAIR. Positive Gram stain and systemic signs of infection are consistent with PJI and would prompt DAIR if other criteria are met. Patient age is not a contraindication to DAIR.

Question 16

In the setting of a two-stage revision for PJI, what is the recommended minimum 'antibiotic holiday' period before performing repeat aspirations to confirm infection eradication prior to the second stage?





Explanation

To accurately assess for infection eradication during a two-stage revision, it is recommended to have an 'antibiotic holiday' of at least 1-2 weeks (typically 2 weeks is preferred) before performing repeat aspirations. This period allows any residual bacteria to become metabolically active and increases the sensitivity of cultures by minimizing false negatives due to antibiotic suppression. Aspirating while on antibiotics significantly increases the risk of false-negative results, leading to premature reimplantation and high rates of recurrence.

Question 17

A patient develops a PJI after TKA caused by Cutibacterium acnes (formerly Propionibacterium acnes). This organism is typically associated with which type of PJI presentation?





Explanation

Cutibacterium acnes (formerly P. acnes) is a common skin commensal that can cause low-grade, indolent, late-onset periprosthetic joint infections. These infections are often characterized by subtle symptoms, delayed diagnosis, and may require extended culture incubation times (e.g., 10-14 days) to detect the organism. They typically do not cause fulminant acute infections or systemic sepsis. This organism is more commonly associated with shoulder PJI but can occur in the knee.

Question 18

What is the recommended range for the concentration of vancomycin often incorporated into antibiotic-loaded bone cement for spacers in PJI treatment?





Explanation

For antibiotic-loaded bone cement (ALBC) spacers, especially in a two-stage revision, high doses of antibiotics are typically incorporated to achieve maximal local elution. For vancomycin, a common concentration range is 4-8 grams per 40g cement pack. Some may use up to 10g depending on the situation, but going much higher can compromise the mechanical properties of the cement. The lower doses (0.1-2g) are more typical for prophylactic ALBC used in primary TKA, not for treating established infection.

Question 19

Which of the following is an advantage of using an articulating antibiotic-loaded cement spacer compared to a static spacer in a two-stage revision?





Explanation

Articulating antibiotic-loaded cement spacers offer several advantages over static spacers, primarily allowing for earlier and greater knee range of motion, which helps maintain the soft tissue envelope, prevent arthrofibrosis, and improve functional outcomes. While both spacer types elute antibiotics, articulating spacers are generally not superior in terms of elution concentration. Static spacers often provide more stability and are easier to mold. Neither eliminates the need for systemic antibiotics. Removing articulating spacers can sometimes be more challenging than static ones if they become ingrown or fractured.

Question 20

When considering a single-stage revision for chronic PJI, which of the following scenarios would be the most suitable indication?





Explanation

Single-stage revision for chronic PJI is a viable option in highly selected cases. The ideal candidate has a well-characterized, susceptible organism (e.g., sensitive Staph aureus, CoNS), good soft tissue envelope, healthy host (Cierny-Mader Type A), minimal bone loss, and no active draining sinus tract. Infections caused by multi-drug resistant organisms, extensive bone loss, active sinus tracts, or multiple prior failures typically necessitate a two-stage approach for higher success rates. A single-stage procedure requires meticulous debridement and confident eradication in one setting.

Question 21

A patient develops a PJI 2 years after TKA with Staphylococcus aureus. He undergoes a DAIR procedure with polyethylene exchange and receives appropriate IV and oral antibiotics. 6 months later, he presents with recurrent knee pain and elevated inflammatory markers. What is the most likely reason for the failure of DAIR in this case?





Explanation

The most likely reason for DAIR failure in this scenario, especially with a recurrence after a seemingly appropriate initial attempt, is the inherent limitation of antibiotics to fully eradicate established biofilm. Biofilm, a protective matrix produced by bacteria, significantly reduces antibiotic penetration and makes bacteria highly resistant to systemic therapy. While the other options could contribute to failure, biofilm resistance is a fundamental challenge to DAIR success in chronic or recurrent infections. DAIR is less effective for late-onset chronic PJI (>3 months) and is prone to failure in recurrent infections. Exchanging femoral and tibial components is part of a revision, not DAIR. Inadequate antibiotic duration is a possibility, but biofilm resistance is more fundamental.

Question 22

Which imaging modality is most sensitive for detecting early osteomyelitis or loosening in a periprosthetic infection setting when plain radiographs are inconclusive?





Explanation

While MRI offers good soft tissue and bone marrow assessment, it is severely limited by artifact from metal implants. Nuclear medicine scans (Technetium-99m bone scan combined with Gallium-67 scan or Indium-111 labeled leukocyte scan) are generally considered the most sensitive and specific imaging modalities for detecting early osteomyelitis, implant loosening, and differentiating between aseptic loosening and septic loosening in the presence of metallic implants. Plain radiographs are initial, but often inconclusive. CT is good for bone detail but less sensitive for early infection. Ultrasound is useful for fluid collections but not osteomyelitis or loosening.

Question 23

What is the primary role of rifampin in the treatment regimen for staphylococcal periprosthetic joint infections?





Explanation

Rifampin is highly effective in disrupting bacterial biofilms, particularly those formed by staphylococci. It is used synergistically with other antistaphylococcal agents (e.g., fluoroquinolones, vancomycin, beta-lactams) and should never be used as monotherapy due to the rapid development of resistance. It does not primarily cover Gram-negative organisms, and its main role is not bone penetration (though it has good penetration) but rather biofilm eradication. It does not directly reduce systemic inflammation as its primary action.

Question 24

In a patient presenting with suspected PJI, what is the most sensitive and specific test available for diagnosis before surgical intervention?





Explanation

Synovial fluid alpha-defensin has emerged as a highly sensitive and specific diagnostic marker for PJI, even in equivocal cases or when patients are on antibiotics. It is particularly useful for differentiating between aseptic loosening and PJI. ESR and CRP are useful inflammatory markers but lack the specificity of alpha-defensin and can be elevated in non-infectious conditions. Serum D-dimer is primarily for DVT exclusion. Plain radiographs are important for assessing hardware and bone but are not specific for infection.

Question 25

A 45-year-old active male develops chronic PJI secondary to a highly resistant Staphylococcus epidermidis. After multiple failed two-stage revisions, he desires a definitive solution, but a further revision is deemed too risky due to extensive bone loss and poor soft tissues. What is the most appropriate salvage procedure?





Explanation

Knee arthrodesis (fusion) is a recognized salvage procedure for failed periprosthetic joint infection, especially when eradication is difficult, and the patient has significant bone loss, poor soft tissues, or has failed multiple prior revisions. It provides a stable, pain-free limb, though function is compromised. Amputation is a last resort, usually for intractable, limb-threatening infections. Long-term suppressive antibiotics are for patients who cannot tolerate surgery or for whom infection cannot be eradicated, but fusion offers a more definitive mechanical solution. Excision arthroplasty (Girdlestone knee) typically results in a flail, painful, unstable knee. Further revisions might be considered but were stated as too risky in the prompt.

Question 26

Which type of periprosthetic joint infection is most commonly associated with a hematogenous spread from a distant source?





Explanation

Late chronic infections (>12 months post-op) are most commonly associated with hematogenous seeding from a distant source (e.g., urinary tract infection, dental abscess, skin infection). Bacteria travel through the bloodstream and colonize the implant surface. Acute post-operative infections and early acute infections are more commonly due to intraoperative contamination or early wound complications. Early chronic infections can be a mix of both but are often indolent intraoperative contaminants.

Question 27

What is the primary goal of extensive debridement during the first stage of a two-stage revision for PJI?





Explanation

The primary goal of extensive debridement during the first stage of a two-stage revision is to remove all infected and necrotic soft tissue, granulation tissue, and bacterial biofilm from the periprosthetic space and bone. This reduction of bacterial load is crucial for successful infection eradication. While preparing the bone for a spacer is a secondary outcome, the main focus is on meticulously cleaning the entire infected bed. Bone resection for lengthening is not a goal, and harvesting tissue is for closure, not debridement itself. Exposing vessels is not the primary goal.

Question 28

Which risk factor is considered the most modifiable patient-specific risk factor for reducing the incidence of PJI in patients undergoing TKA?





Explanation

Uncontrolled Type 2 Diabetes Mellitus, particularly with an elevated HbA1c (>7.5-8.0%), is a highly modifiable risk factor. Preoperative optimization of glycemic control has been shown to significantly reduce the risk of PJI. While obesity is also modifiable, achieving significant weight loss prior to surgery can be challenging. Advanced age and inflammatory arthritis are non-modifiable. Male gender is a less significant or inconsistent risk factor compared to diabetes or obesity.

Question 29

A patient with a TKA develops a Candida albicans PJI. Which of the following is the most appropriate management strategy?





Explanation

Fungal PJI, especially due to Candida, is challenging to treat. It requires aggressive surgical debridement and implant removal (two-stage revision is preferred) in conjunction with prolonged, targeted systemic antifungal therapy. Initial therapy often involves potent agents like amphotericin B or an echinocandin, followed by a prolonged course of fluconazole once sensitivity is confirmed and the patient is stable. DAIR is almost always ineffective for fungal PJI. Single-stage revision carries high failure rates. Arthrodesis is a salvage procedure, not first-line. Long-term suppressive therapy without implant removal is unlikely to eradicate the infection.

Question 30

What is the primary advantage of using a static antibiotic-loaded cement spacer over an articulating spacer in certain complex PJI cases?





Explanation

Static antibiotic-loaded cement spacers, while limiting joint motion, offer advantages in complex PJI cases, particularly those with severe bone loss, poor soft tissue coverage, or instability. They provide greater mechanical stability, can be custom-molded to fill large defects, allow for extensive debridement without concern for subsequent articulation, and are often simpler to fabricate. They also prevent bony overgrowth into the joint space. Articulating spacers are better for functional recovery and joint mechanics. Antibiotic elution concentrations are similar. Neither directly reduces the risk of aseptic loosening in the long term, as the goal is infection eradication.

Question 31

A 75-year-old male with a 10-year-old TKA presents with sudden onset excruciating knee pain, swelling, and fever. Synovial fluid analysis shows 80,000 WBC/µL, 92% neutrophils. Gram stain is negative. What is the most appropriate next step given the clinical scenario?





Explanation

Given the acute presentation, high fever, and highly inflammatory synovial fluid analysis (very high WBC and PMN%), this is an acute PJI until proven otherwise, even with a negative Gram stain. A negative Gram stain does not rule out infection, as its sensitivity is low. Urgent surgical debridement, washout, and collection of multiple periprosthetic tissue samples for aerobic, anaerobic, fungal, and mycobacterial cultures are crucial. Delaying surgery for further aspirations or imaging risks worsening infection and irreversible damage. Empirical oral antibiotics alone are insufficient for acute PJI.

Question 32

Which of the following describes the most common classification system used to stage infected total knee arthroplasties based on onset time?





Explanation

The Coventry Classification (also known as the classic classification system) categorizes PJI based on the time of onset: Type I (acute postoperative, within 3 months), Type II (delayed/early chronic, 3-24 months), and Type III (late/chronic hematogenous, >24 months). This helps guide treatment decisions. Cierny-Mader is for osteomyelitis, Gustilo-Anderson for open fractures. Frick and Masri are not standard PJI classifications.

Question 33

When is the use of long-term suppressive oral antibiotics (LTSA) most appropriate for a patient with a periprosthetic knee infection?





Explanation

Long-term suppressive oral antibiotics (LTSA) are generally reserved for patients with chronic PJI who are not surgical candidates due to severe comorbidities, or as a last resort after multiple failed definitive surgical treatments. The goal is to control the infection and symptoms rather than eradicate it, accepting the implant remains infected. It is not a primary treatment for acute PJI, nor for young, active patients who could benefit from revision. It is also not prophylactic or suitable as the sole treatment for recurrent acute episodes where surgical intervention is usually warranted.

Question 34

A 60-year-old male develops a PJI 1 year post-TKA due to coagulase-negative Staphylococcus. He undergoes a DAIR procedure. Which of the following oral antibiotics is most commonly used in combination with rifampin for suppressive or prolonged post-DAIR therapy for Staphylococcal PJI?





Explanation

For staphylococcal PJI (including coagulase-negative Staphylococci), a fluoroquinolone (like ciprofloxacin or levofloxacin) is often chosen to combine with rifampin for oral suppressive or prolonged post-DAIR therapy, due to its good bone penetration and synergy with rifampin against biofilm. However, given the options, Levofloxacin is the appropriate fluoroquinolone. Doxycycline can also be used but Levofloxacin is a more common and robust choice in this context. Cephalexin and clindamycin are typically less preferred for suppressive therapy with rifampin due to resistance profiles or less optimal synergy. Metronidazole has no activity against staphylococci.

Question 35

What is the recommended approach to managing PJI caused by culture-negative organisms, but with strong clinical and inflammatory marker evidence of infection?





Explanation

Culture-negative PJI is a diagnostic and therapeutic challenge. When there is strong clinical suspicion and inflammatory evidence of PJI despite negative conventional cultures, it necessitates aggressive surgical intervention. This involves implant removal, extensive debridement, and sending multiple periprosthetic tissue samples for extended incubation (10-14 days), specialized media (e.g., fungal, mycobacterial), and molecular techniques like broad-range PCR, to identify the causative organism. Empirical antibiotic treatment without definitive diagnosis is prone to failure. Managing as aseptic loosening ignores the clear signs of infection. Fusion is a salvage, not initial diagnostic, procedure. Serum alpha-defensin is a diagnostic aid but doesn't replace definitive culture for guiding therapy or ruling out unusual pathogens.

Question 36

Which of the following scenarios carries the highest risk of PJI for a TKA patient?





Explanation

A patient with an active, untreated infection at a distant site (e.g., infected foot ulcer in a diabetic) undergoing a total joint arthroplasty is at extremely high risk for hematogenous seeding and subsequent PJI. All active infections should be completely resolved and treated before elective joint replacement. Revision TKA also carries a higher risk than primary TKA, but an active infection elsewhere is generally considered a strong contraindication to elective arthroplasty until resolved.

Question 37

What percentage of surgical procedures for PJI eradication are typically considered successful with two-stage revision, allowing for reimplantation?





Explanation

The success rate for two-stage revision arthroplasty in eradicating infection, leading to successful reimplantation, is generally cited to be in the range of 85-95%. This makes it the gold standard for chronic PJI treatment. While not 100%, it offers the best chance of infection eradication and restoration of function compared to other methods.

Question 38

Which of the following statements regarding the role of C-reactive protein (CRP) in PJI management is most accurate?





Explanation

Serial CRP measurements are very useful for monitoring treatment response and trending infection resolution after surgical debridement (e.g., DAIR or first stage of two-stage revision). A declining CRP indicates effective treatment, while a persistently elevated or rising CRP suggests ongoing or recurrent infection. CRP is sensitive but not highly specific, as it can be elevated in many inflammatory conditions. No single cutoff is definitively diagnostic, although very high levels are highly suggestive. A normal CRP does not definitively rule out PJI, especially in low-grade or indolent infections.

Question 39

What is the recommended minimum duration of antibiotic therapy for a low-virulence PJI (e.g., CoNS) treated with DAIR and polyethylene exchange?





Explanation

For low-virulence organisms treated with DAIR, the typical recommendation is 2-4 weeks of targeted intravenous antibiotics, followed by a prolonged course of oral antibiotics for 3-6 months. This extended duration of oral suppressive therapy is crucial to prevent recurrence given the challenges of eradicating biofilm with implant retention. Shorter durations are associated with higher failure rates.

Question 40

What is the primary concern regarding the use of systemic fluoroquinolones (e.g., ciprofloxacin, levofloxacin) in combination with rifampin for Staphylococcal PJI?





Explanation

While fluoroquinolones are effective against many Staphylococci and have good bone penetration, the primary concern when used in combination with rifampin is the rapid development of resistance if the fluoroquinolone is used as monotherapy, or if rifampin is not introduced simultaneously with a companion drug. Also, rifampin is a potent inducer of cytochrome P450 enzymes, leading to numerous drug-drug interactions that must be carefully managed. Renal toxicity is more associated with aminoglycosides and vancomycin. Anaphylaxis is not a primary concern for fluoroquinolones. Lack of efficacy is incorrect as they are often used in this setting.

Question 41

Which of the following techniques is most effective in preventing PJI during TKA surgery?





Explanation

Strict adherence to sterile technique throughout the surgical procedure, combined with appropriate perioperative prophylactic intravenous antibiotics, is the cornerstone of PJI prevention. Preoperative MRSA screening and decolonization is also highly recommended and shown to reduce risk, but it's part of a broader protocol and not the single most effective. Laminar flow is beneficial but not universally available or proven to be more critical than core sterile technique. Postoperative prophylactic antibiotics beyond 24 hours are not generally recommended due to increased resistance risk without clear benefit. Routine use of ALBC for primary TKA is debated and not as universally effective as core sterile technique and appropriate single-dose prophylaxis.

Question 42

A patient with a chronically infected TKA caused by a sensitive Staphylococcus aureus is scheduled for a two-stage revision. What is the standard duration of antibiotic-free interval recommended before reimplantation to confirm eradication?





Explanation

To accurately assess for infection eradication during a two-stage revision, an antibiotic-free interval of at least 1 to 2 weeks (often 2 weeks is preferred) is recommended before performing repeat aspirations for culture. This 'antibiotic holiday' allows any remaining bacteria to regain metabolic activity, thus increasing the sensitivity of cultures and minimizing false negatives caused by antibiotic suppression. Less than 72 hours is too short, and longer periods may increase the risk of re-infection or spacer complications.

Question 43

What is the primary limitation of serum inflammatory markers (ESR, CRP) in diagnosing periprosthetic joint infection?





Explanation

The primary limitation of serum inflammatory markers like ESR and CRP in diagnosing PJI is their lack of specificity. They can be elevated in numerous non-infectious inflammatory conditions (e.g., rheumatoid arthritis flares, gout, trauma, other surgeries, obesity), leading to false positives. While sensitive, their non-specificity necessitates combining them with other diagnostic criteria. They are not specific to fungal infections, can be elevated in acute infections, are routine and inexpensive, and can be elevated locally without systemic sepsis.

Question 44

In the presence of an infected TKA, which finding on plain radiographs would be most concerning for established chronic PJI with significant bone involvement?





Explanation

Periprosthetic lucencies greater than 2mm, progressive, or circumferential are highly concerning for established chronic PJI with bone involvement, often indicating loosening or osteolysis due to infection. These findings suggest bone resorption around the implant, a common manifestation of chronic infection. Soft tissue swelling and mild malalignment are less specific. Heterotopic ossification is not directly indicative of infection. An increase in joint space is unlikely with PJI and more likely with component dissociation.

Question 45

For patients with an infected TKA who undergo a two-stage revision, what is generally the most important factor for maximizing patient satisfaction and functional outcomes after reimplantation?





Explanation

Aggressive physical therapy and rehabilitation to restore motion and strength are paramount for maximizing patient satisfaction and functional outcomes after reimplantation. While infection eradication is the primary goal, functional recovery depends heavily on regaining range of motion, strength, and confidence in the limb. Spacer choice (articulating), early mobilization, and dedicated rehab are critical. The latest components or prolonged antibiotics alone do not guarantee good function, and a low-impact lifestyle may be necessary but doesn't drive satisfaction as much as regained function.

Question 46

What is the recommended approach for managing a PJI caused by multiple organisms (polymicrobial infection) versus a monomicrobial infection?





Explanation

Polymicrobial infections are generally more challenging to treat than monomicrobial infections and are associated with a poorer prognosis. They often require a more aggressive surgical approach (typically two-stage revision) and broader, carefully selected antibiotic coverage to target all identified organisms. Their complexity makes them harder to eradicate. DAIR is less likely to succeed. Monomicrobial infections by virulent organisms can also necessitate implant removal. The choice of antibiotics is more complex, not simpler.

Question 47

Which of the following interventions has the strongest evidence for reducing the incidence of PJI in the immediate perioperative period?





Explanation

Single-dose intravenous prophylactic antibiotics administered within 60 minutes prior to surgical incision has the strongest and most consistent evidence for reducing the incidence of PJI. This ensures adequate tissue levels of antibiotics at the time of potential contamination. Extended postoperative antibiotics are generally not recommended due to increased resistance risk without clear benefit. Pulsatile lavage efficacy is debated, antibiotic-impregnated drapes have some evidence but not as strong as systemic antibiotics. Blood transfusions are for anemia, not direct PJI prevention.

Question 48

Which factor is most crucial in determining the type of antibiotic-loaded cement spacer (articulating vs. static) to be used during a two-stage revision for PJI?





Explanation

The quality of the remaining bone stock, the integrity of the extensor mechanism, and the status of the collateral ligaments are crucial in determining whether an articulating or static spacer can be used. Articulating spacers require sufficient bone and soft tissue integrity to maintain stability and allow motion. If there is significant bone loss or compromise to the extensor mechanism or ligaments, a static spacer may be necessary to provide stability and maintain the joint space. Patient's age or BMI are less direct determinants, and early weight-bearing preference is secondary to biomechanical stability.

Question 49

A 78-year-old male with multiple comorbidities is diagnosed with a chronic PJI of the knee. He is deemed too frail for a two-stage revision, but the infection is causing severe pain and intermittent draining. Which of the following is the most appropriate palliative option?





Explanation

Given that the patient is too frail for a definitive two-stage revision, long-term suppressive oral antibiotics with implant retention is the most appropriate palliative option. The goal is to manage symptoms, reduce pain, and control the infection without attempting complete eradication through surgery. DAIR is typically for acute infections or early chronic infections in healthier patients. Arthrodesis and amputation are definitive surgical solutions, which the patient is too frail for. Single-stage revision is also a definitive surgical procedure, not palliative.

Question 50

What is the recommended treatment for a TKA infection caused by Mycobacterium tuberculosis?





Explanation

Tuberculosis PJI is a rare but severe form of infection. It requires aggressive surgical management, typically a two-stage revision with complete implant removal and thorough debridement, combined with prolonged multi-drug anti-TB therapy, usually for 12-18 months. DAIR is generally ineffective for mycobacterial infections. Single-stage revision has a high failure rate. Long-term suppressive antibiotics are not curative. Arthrodesis is a salvage option, not the primary treatment.

Question 51

Which of the following is the most accurate statement regarding synovial fluid leukocyte esterase for PJI diagnosis?





Explanation

Synovial fluid leukocyte esterase (LE) is a rapid, point-of-care test that has a high negative predictive value (NPV) for PJI. This means a negative result makes PJI highly unlikely. While not as specific as alpha-defensin, its rapid nature and high NPV make it a valuable screening tool. Its accuracy can be affected by blood contamination or recent antibiotic use, but its high NPV is a key advantage. It does not differentiate between Gram-positive and Gram-negative bacteria and is not superior to alpha-defensin.

Question 52

What is the most appropriate management for a patient with a chronically infected TKA and significant knee pain who refuses any further surgical intervention?





Explanation

If a patient with chronic PJI refuses further surgical intervention, the most appropriate management is palliative. This typically involves initiating long-term suppressive oral antibiotics to control the infection and reduce symptoms, coupled with aggressive pain management, and functional bracing or orthoses if mechanical instability is an issue. This approach aims to maximize comfort and function while accepting the presence of the infection. Amputation is a surgical option and a last resort. Insisting on surgery is unethical if the patient has capacity and refuses. Physical therapy alone is insufficient for infection control.

Question 53

A 68-year-old male undergoes TKA. On post-operative day 5, he develops a fever of 39.5°C and severe pain. The wound is erythematous and draining purulent fluid. What is the most likely pathogen?





Explanation

An acute, virulent infection developing within days to a week post-operatively, presenting with high fever, severe pain, and purulent drainage, is most characteristic of Staphylococcus aureus. S. aureus is a highly virulent pathogen often associated with acute, rapidly progressing infections. S. epidermidis and Cutibacterium acnes typically cause more indolent, late-onset infections. Candida and E. coli are less common but can cause acute infections, though S. aureus is the most likely in this classic scenario.

Question 54

Which of the following describes a key principle for successful DAIR (Debridement, Antibiotics, Implant Retention) in PJI?





Explanation

DAIR is a treatment option for acute PJI, but its success depends on strict criteria: 1) short symptom duration (<3-6 weeks), 2) stable implants, 3) a sensitive, low-virulence organism (e.g., sensitive Staph aureus, streptococci), and 4) intact soft tissues. It relies on meticulous debridement, exchange of modular components (polyethylene liner), and prolonged targeted antibiotic therapy. It does not involve complete removal of all components and is not applicable to all PJI cases, especially chronic or those with virulent/resistant pathogens, or fungal/mycobacterial infections. Indefinite monotherapy is inappropriate.

Question 55

In the context of PJI diagnostics, what is the role of histopathological analysis of periprosthetic tissues?





Explanation

Histopathological analysis of periprosthetic tissues (e.g., frozen sections or permanent sections) is a valuable diagnostic tool. It can identify inflammatory infiltrates (e.g., >5 neutrophils per high-power field in 5 fields) that are highly suggestive of infection, even in culture-negative cases. It does not identify specific bacterial species or quantify antibiotic susceptibility (that's microbiology's role) but provides morphological evidence of an inflammatory response indicative of infection. While it helps differentiate between septic and aseptic loosening, it's not the sole criterion and can't replace culture for guiding antibiotic choice.

Question 56

What is the recommended approach for obtaining synovial fluid cultures to avoid contamination?





Explanation

To avoid contamination and obtain accurate synovial fluid cultures, aspiration must be performed using strict aseptic technique. It is also recommended to discard the first few milliliters of fluid collected, as this 'waste' fluid may contain skin contaminants introduced by the needle's passage. Aspirating through a sinus tract is highly prone to contamination. Non-sterile conditions or lack of skin prep are unacceptable. While fluid collected during surgery is valuable, preoperative aspiration is crucial for diagnosis and guiding initial empirical therapy.

Question 57

A patient with a chronically infected TKA has failed multiple surgical revisions. He develops persistent sepsis, severe soft tissue breakdown, and intractable pain. What is the definitive salvage procedure to consider?





Explanation

In cases of intractable, limb-threatening infection with persistent sepsis, severe soft tissue breakdown, and failed multiple surgical revisions, above-knee amputation becomes the definitive salvage procedure. While arthrodesis is also a salvage procedure for failed infection, amputation is considered when the limb is no longer salvageable and poses a threat to the patient's life or quality of life due to persistent infection. Excision arthroplasty (Girdlestone) provides a flail, unstable, painful limb, often requiring eventual amputation. Repeat revisions are not feasible if already failed multiple times with severe local complications. Long-term suppressive antibiotics are palliative, not curative, and insufficient for severe sepsis and tissue breakdown.

Question 58

Which of the following organisms is particularly challenging to culture in standard laboratory settings and may require extended incubation times (e.g., 10-14 days) for detection?





Explanation

Cutibacterium acnes (formerly Propionibacterium acnes) is a slow-growing, fastidious anaerobic organism that is a common cause of low-grade PJI, particularly in the shoulder, but also in the knee. Its detection often requires extended incubation times (10-14 days or longer) for cultures to become positive. The other listed organisms are typically identified within standard incubation periods (2-5 days).

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