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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 310 of 326

This practice set contains high-yield board review questions covering key concepts in 3. Adult Reconstruction (Hip & Knee). Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 6181

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female undergoes knee aspiration for suspected periprosthetic joint infection (PJI). The synovial fluid is noticeably blood-tinged. How does this gross appearance affect the use of a leukocyte esterase (LE) test strip?

. The test will yield a false negative due to red blood cell competitive binding.
. Significant blood contamination can cause false-positive readings, necessitating centrifugation prior to testing.
. The test remains unaffected as long as the fluid is read within 60 seconds.
. The sensitivity decreases exponentially due to fluid dilution.
. Blood neutralizes the esterase enzyme, requiring the use of alpha-defensin instead.

Correct Answer & Explanation

. Significant blood contamination can cause false-positive readings, necessitating centrifugation prior to testing.

Explanation

Gross blood contamination can interfere with the colorimetric reading of a leukocyte esterase strip, leading to false-positive results. Centrifuging the sample and testing the clear supernatant mitigates this issue and restores test accuracy.

Question 6182

Topic: 3. Adult Reconstruction (Hip & Knee)

In the diagnostic algorithm for periprosthetic joint infection (PJI), which of the following scenarios is the most widely accepted indication for utilizing Next-Generation Sequencing (NGS) on synovial fluid?

. Routine screening of all painful arthroplasties prior to revision.
. Suspected culture-negative PJI, particularly in the setting of prior antibiotic exposure.
. Immediate post-operative fever within 24 hours of primary arthroplasty.
. Differentiating acute gouty arthropathy from bacterial septic arthritis.
. As a substitute for synovial fluid cell count when a "dry tap" occurs.

Correct Answer & Explanation

. Suspected culture-negative PJI, particularly in the setting of prior antibiotic exposure.

Explanation

Next-Generation Sequencing (NGS) detects microbial DNA and is highly sensitive. It is most beneficial in cases of culture-negative PJI where traditional cultures fail to grow an organism, often due to prior antibiotic administration.

Question 6183

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male presents with stiffness and vague pain 2 years following a total shoulder arthroplasty. A joint aspiration is performed to rule out infection. To optimize the detection of Cutibacterium acnes, what specific instruction must be given to the microbiology laboratory?

. Incubate aerobic cultures for 7 days.
. Incubate anaerobic cultures for at least 14 days.
. Perform a rapid nucleic acid amplification test immediately.
. Plate the specimen exclusively on MacConkey agar.
. Process the fluid using only acid-fast bacilli (AFB) stains.

Correct Answer & Explanation

. Incubate anaerobic cultures for at least 14 days.

Explanation

Cutibacterium acnes is a slow-growing anaerobic organism commonly responsible for shoulder PJIs. Cultures must be held in anaerobic conditions for a minimum of 14 days to prevent false-negative results.

Question 6184

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, what is the accepted threshold for synovial fluid white blood cell (WBC) count to meet criteria for an acute periprosthetic joint infection (within 90 days of surgery)?

. > 1,500 cells/uL
. > 3,000 cells/uL
. > 10,000 cells/uL
. > 25,000 cells/uL
. > 50,000 cells/uL

Correct Answer & Explanation

. > 10,000 cells/uL

Explanation

The 2018 ICM recognizes different thresholds for acute versus chronic PJI. For an acute PJI (within 90 days post-op), a synovial fluid WBC > 10,000 cells/uL or PMN > 90% is highly suggestive of infection.

Question 6185

Topic: 3. Adult Reconstruction (Hip & Knee)

You are attempting to aspirate a painful total hip arthroplasty for suspected PJI but obtain a "dry tap" despite fluoroscopic confirmation of intra-articular needle placement. What is the most appropriate next step to obtain fluid for microbiological analysis?

. Instill 10-20 cc of sterile normal saline without preservatives, aspirate, and send for culture.
. Perform a blind core needle biopsy of the anterior capsule.
. Inject 10 cc of local anesthetic, wait 5 minutes, and re-aspirate.
. Start empiric antibiotics and repeat the aspiration in 48 hours.
. Schedule the patient for a gallium radionucleotide scan.

Correct Answer & Explanation

. Instill 10-20 cc of sterile normal saline without preservatives, aspirate, and send for culture.

Explanation

In the event of a "dry tap" during joint aspiration, instilling sterile, non-bacteriostatic saline and re-aspirating the lavage fluid is the recommended technique to recover organisms for culture.

Question 6186

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a suspected chronic knee PJI has been taking oral amoxicillin for a recent dental infection. To maximize the diagnostic yield of synovial fluid cultures, what is the recommended minimum duration to withhold antibiotics prior to aspiration?

. 24 hours
. 3 days
. 7 days
. 14 days
. 6 weeks

Correct Answer & Explanation

. 14 days

Explanation

Current guidelines recommend an "antibiotic holiday" of at least 14 days prior to obtaining synovial fluid or tissue cultures to minimize the risk of false-negative culture results.

Question 6187

Topic: 3. Adult Reconstruction (Hip & Knee)

Serum D-dimer was incorporated into the 2018 ICM scoring system for periprosthetic joint infection (PJI). Which of the following statements regarding its role is most accurate?

. It serves as a definitive major criterion for diagnosing PJI.
. It is a minor criterion that carries an equal point value to serum CRP.
. It is highly specific for detecting Cutibacterium acnes infections.
. It maintains diagnostic utility only when drawn within 14 days postoperatively.
. It has replaced the need for synovial fluid cell count in modern algorithms.

Correct Answer & Explanation

. It is a minor criterion that carries an equal point value to serum CRP.

Explanation

In the 2018 ICM criteria, an elevated serum D-dimer (> 850 ng/mL) is considered a minor criterion and is awarded 2 points, which is the same weight given to an elevated serum CRP (> 10 mg/L).

Question 6188

Topic: 3. Adult Reconstruction (Hip & Knee)

During a revision total knee arthroplasty for presumed aseptic loosening, suspicious periprosthetic tissue is sent for intraoperative frozen section. According to the 2018 ICM criteria, which histological finding is considered a positive minor criterion for PJI?

. > 1 neutrophil per high-power field (HPF) in 3 separate fields
. > 5 neutrophils per HPF in 5 separate fields at 400x magnification
. The presence of any multinucleated giant cells
. > 20 lymphocytes per HPF in 5 separate fields
. Extensive perivascular eosinophilic infiltration

Correct Answer & Explanation

. > 5 neutrophils per HPF in 5 separate fields at 400x magnification

Explanation

Positive histology, defined as greater than 5 polymorphonuclear neutrophils (PMNs) per high-power field in at least 5 separate fields (at 400x magnification), is a minor criterion highly suggestive of PJI.

Question 6189

Topic: 3. Adult Reconstruction (Hip & Knee)

When analyzing synovial fluid from a painful total hip arthroplasty to evaluate for a chronic periprosthetic joint infection (PJI), which polymorphonuclear (PMN) cell percentage is the accepted minor criterion threshold in the 2018 ICM scoring system?

. > 20%
. > 45%
. > 65%
. > 80%
. > 95%

Correct Answer & Explanation

. > 80%

Explanation

For chronic PJI, the 2018 ICM utilizes a synovial fluid PMN percentage > 80% (or a synovial WBC > 3,000 cells/uL) as a minor criterion, awarding 3 points toward the diagnosis.

Question 6190

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a history of latent tuberculosis presents with chronic loosening of a hip prosthesis. Routine testing is negative. If mycobacterial periprosthetic joint infection is suspected, which of the following is true regarding diagnostic testing?

. Acid-fast bacilli (AFB) smears of synovial fluid have a sensitivity exceeding 90%.
. Synovial fluid and tissue cultures must be maintained for at least 6 to 8 weeks.
. Synovial fluid alpha-defensin testing is highly specific for mycobacteria.
. Synovial fluid WBC counts in mycobacterial PJI typically exceed 100,000 cells/uL.
. Next-generation sequencing cannot detect mycobacterial DNA.

Correct Answer & Explanation

. Synovial fluid and tissue cultures must be maintained for at least 6 to 8 weeks.

Explanation

Mycobacterium tuberculosis is a fastidious, slow-growing organism. Routine cultures will not detect it, and specific AFB cultures must be held for 6 to 8 weeks. AFB smears are notoriously insensitive.

Question 6191

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female presents with acute knee pain, swelling, and erythema 3 weeks following a primary total knee arthroplasty. Aspiration of the joint is performed. According to the 2018 International Consensus Meeting (ICM) criteria, which of the following synovial fluid white blood cell (WBC) thresholds supports a diagnosis of an acute postoperative periprosthetic joint infection?

. Greater than 1,500 cells/mcL
. Greater than 3,000 cells/mcL
. Greater than 10,000 cells/mcL
. Greater than 25,000 cells/mcL
. Greater than 50,000 cells/mcL

Correct Answer & Explanation

. Greater than 10,000 cells/mcL

Explanation

In the acute postoperative period (less than 90 days), the threshold for diagnosing PJI is higher due to expected postoperative inflammation. The 2018 ICM cutoff for acute PJI is a WBC count greater than 10,000 cells/mcL with greater than 90% PMNs.

Question 6192

Topic: 3. Adult Reconstruction (Hip & Knee)

What is the primary diagnostic advantage of utilizing next-generation sequencing (NGS) of synovial fluid in the evaluation of suspected periprosthetic joint infection (PJI)?

. It completely replaces the need for standard antimicrobial susceptibility testing.
. It has 100% specificity for differentiating active infection from contamination.
. It amplifies and sequences 16S ribosomal RNA to identify pathogens in culture-negative scenarios.
. It determines the precise minimum inhibitory concentration (MIC) of intra-articular antibiotics.
. It relies exclusively on identifying specific fungal elements in mixed infections.

Correct Answer & Explanation

. It amplifies and sequences 16S ribosomal RNA to identify pathogens in culture-negative scenarios.

Explanation

Next-generation sequencing (NGS) targets the 16S rRNA gene for bacteria, offering high sensitivity for detecting organisms in culture-negative PJI or when patients have received prior antibiotics. However, it does not currently replace traditional phenotypic susceptibility testing.

Question 6193

Topic: 3. Adult Reconstruction (Hip & Knee)

Aspiration of a persistently painful metal-on-metal total hip arthroplasty yields fluid with a WBC count of 4,500 cells/mcL and a polymorphonuclear (PMN) cell differential of 45%. Based on this synovial fluid profile, what is the most likely diagnosis?

. Acute periprosthetic joint infection
. Chronic periprosthetic joint infection
. Adverse local tissue reaction (ALTR)
. Acute gouty arthropathy
. Normal postoperative healing

Correct Answer & Explanation

. Adverse local tissue reaction (ALTR)

Explanation

Metal-on-metal arthroplasties with ALTR typically present with elevated synovial WBC counts (often 3,000 to 10,000) but a remarkably low PMN percentage (usually less than 50%). This macrophage predominance helps differentiate ALTR from a chronic PJI, which is PMN-predominant.

Question 6194

Topic: 3. Adult Reconstruction (Hip & Knee)

When evaluating a painful shoulder arthroplasty for a suspected Cutibacterium acnes infection, which of the following statements regarding the diagnostic workup is most accurate?

. Serum ESR and CRP are consistently elevated in over 80% of cases.
. The organism is an aerobic Gram-negative bacillus with rapid growth.
. Aspiration cultures should be incubated for a minimum of 14 days.
. Synovial alpha-defensin testing yields a zero percent false-negative rate.
. Synovial fluid WBC typically exceeds 50,000 cells/mcL in chronic cases.

Correct Answer & Explanation

. Aspiration cultures should be incubated for a minimum of 14 days.

Explanation

Cutibacterium acnes is a slow-growing, Gram-positive, anaerobic rod frequently responsible for shoulder PJI. Cultures must be held for at least 14 days to minimize false negatives, and systemic inflammatory markers (ESR/CRP) are frequently normal.

Question 6195

Topic: 3. Adult Reconstruction (Hip & Knee)

During the evaluation of a suspected periprosthetic joint infection, a point-of-care leukocyte esterase strip test is utilized. The aspirated synovial fluid is grossly bloody. What is the recommended technique to properly utilize the leukocyte esterase strip in this scenario?

. Discard the bloody sample and re-aspirate the joint after 48 hours.
. Read the strip immediately within 10 seconds before red blood cells coagulate.
. Centrifuge the synovial fluid and test the clear supernatant.
. Dilute the synovial fluid 1:1 with sterile normal saline prior to testing.
. Add potassium hydroxide (KOH) to lyse the red blood cells before applying the strip.

Correct Answer & Explanation

. Centrifuge the synovial fluid and test the clear supernatant.

Explanation

Grossly bloody synovial fluid visually obscures the colorimetric change on leukocyte esterase strips, rendering them uninterpretable. Centrifuging the sample and testing the clear supernatant effectively restores the diagnostic accuracy of the test.

Question 6196

Topic: 3. Adult Reconstruction (Hip & Knee)

Synovial fluid calprotectin has recently gained attention in the workup of periprosthetic joint infection (PJI). What is the primary clinical utility of this biomarker?

. It serves as a marker of osteoclast activation indicating aseptic loosening.
. It is an emerging point-of-care test with diagnostic accuracy comparable to alpha-defensin.
. It is a highly specific marker used exclusively for diagnosing fungal PJI.
. It replaces standard cultures as it provides antibiotic susceptibility profiles.
. It is heavily elevated only in metallosis and adverse local tissue reactions.

Correct Answer & Explanation

. It is an emerging point-of-care test with diagnostic accuracy comparable to alpha-defensin.

Explanation

Synovial fluid calprotectin is an antimicrobial peptide released by activated neutrophils. It has emerged as a rapid, inexpensive, and highly sensitive point-of-care biomarker for diagnosing PJI, performing comparably to alpha-defensin.

Question 6197

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a painful total knee arthroplasty has been taking oral cephalexin for a suspected urinary tract infection. You plan to aspirate the knee to rule out chronic PJI. According to major consensus guidelines, how long should antibiotics ideally be held prior to aspiration to optimize culture yield?

. Antibiotics do not need to be held if modern culture media are used.
. 48 hours
. 7 days
. 14 days
. 28 days

Correct Answer & Explanation

. 14 days

Explanation

Concurrent or recent antibiotic therapy suppresses bacterial growth and significantly increases the rate of culture-negative PJI. Systemic antibiotics should ideally be held for at least 14 days prior to obtaining diagnostic joint aspirations.

Question 6198

Topic: 3. Adult Reconstruction (Hip & Knee)

While attempting to aspirate a suspected chronically infected total hip arthroplasty, you obtain a 'dry tap'. You decide to inject 10 mL of sterile normal saline and re-aspirate the fluid. Which of the following tests remains the most reliable diagnostic option when performed on this lavage fluid?

. Synovial fluid WBC count
. Synovial fluid polymorphonuclear (PMN) percentage
. Synovial fluid microbiological culture
. Synovial fluid C-reactive protein (CRP) level
. Synovial fluid leukocyte esterase strip test

Correct Answer & Explanation

. Synovial fluid microbiological culture

Explanation

Injecting normal saline to lavage a dry joint significantly dilutes the returned fluid, rendering cell counts, PMN percentages, and biomarker concentrations inaccurate. However, microbiological culture of the lavage fluid remains valid and is a crucial diagnostic step.

Question 6199

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection, what is the role of the serum D-dimer test?

. It is a definitive major criterion that establishes a diagnosis independently.
. It replaces synovial fluid culture in culture-negative scenarios.
. It is a minor criterion that demonstrates improved sensitivity compared to serum ESR.
. Its primary utility is to exclude deep vein thrombosis prior to revision surgery.
. It is the sole marker used to diagnose acute postoperative PJI.

Correct Answer & Explanation

. It is a minor criterion that demonstrates improved sensitivity compared to serum ESR.

Explanation

The 2018 ICM criteria include serum D-dimer as a minor diagnostic biomarker for PJI. Evidence demonstrates that it offers better sensitivity and specificity than traditional markers like ESR for detecting chronic PJI.

Question 6200

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female is suspected of having a culture-negative periprosthetic joint infection (PJI) of the knee. Standard cultures are negative at 7 days. Which of the following represents the primary advantage of Next-Generation Sequencing (NGS) over standard culture in this scenario?

. It detects both viable and non-viable organisms, making it highly sensitive.
. It requires active bacterial replication to yield a positive result.
. It identifies antibiotic susceptibilities faster than standard cultures.
. It has a lower false-positive rate compared to standard tissue cultures.
. It eliminates the need for using other clinical criteria to establish PJI.

Correct Answer & Explanation

. It detects both viable and non-viable organisms, making it highly sensitive.

Explanation

Next-Generation Sequencing (NGS) detects the DNA of both viable and non-viable bacteria. This makes it highly sensitive for diagnosing culture-negative PJI, particularly when the patient has recently received antibiotics.

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