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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 311 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 6201

Topic: 3. Adult Reconstruction (Hip & Knee)

A surgeon uses a leukocyte esterase (LE) colorimetric strip to evaluate a knee aspirate for suspected PJI. The aspirate is grossly bloody. What is the most significant limitation of the LE strip test in this specific scenario?

. False-negative results due to LE degradation by hemoglobin.
. Inability to read the colorimetric change due to interference by red blood cells.
. False-positive results due to the lysis of red blood cells.
. Chemical cross-reactivity between the esterase reagent and serum albumin.
. Red blood cells actively absorbing and neutralizing leukocyte esterase.

Correct Answer & Explanation

. Inability to read the colorimetric change due to interference by red blood cells.

Explanation

High concentrations of red blood cells or tissue debris in synovial fluid obscure the colorimetric reading of the LE strip. Centrifugation of the fluid is often required prior to testing to obtain an interpretable result.

Question 6202

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient is referred with a painful total knee arthroplasty while currently taking oral cephalexin. To optimize the diagnostic yield of a synovial fluid culture, for what minimum duration should the antibiotics be discontinued prior to joint aspiration?

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

Correct Answer & Explanation

. 14 days

Explanation

The 2018 International Consensus Meeting (ICM) recommends an antibiotic holiday of at least 14 days prior to obtaining synovial cultures. This minimizes suppression of bacterial growth and maximizes the chances of identifying the causative organism.

Question 6203

Topic: 3. Adult Reconstruction (Hip & Knee)

A knee aspiration for a suspected PJI yields a grossly bloody sample. Synovial fluid analysis reports 50,000 RBCs/mcL and 3,500 WBCs/mcL. What is the approximate adjusted WBC count to account for peripheral blood contamination?

. 500 WBCs/mcL
. 1,500 WBCs/mcL
. 2,500 WBCs/mcL
. 3,400 WBCs/mcL
. 3,500 WBCs/mcL

Correct Answer & Explanation

. 3,400 WBCs/mcL

Explanation

The standard correction for a bloody aspirate is subtracting 1 WBC for every 500 RBCs to account for peripheral blood. Subtracting 100 WBCs (50,000 divided by 500) from the initial 3,500 yields an adjusted count of 3,400 WBCs/mcL.

Question 6204

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old male presents with a swollen, painful knee 3 weeks after an uncomplicated primary total knee arthroplasty. Which of the following synovial fluid WBC thresholds is most appropriate for diagnosing an acute PJI in this early postoperative period?

. > 1,500 cells/mcL
. > 3,000 cells/mcL
. > 10,000 cells/mcL
. > 27,800 cells/mcL
. > 50,000 cells/mcL

Correct Answer & Explanation

. > 10,000 cells/mcL

Explanation

In the acute postoperative period (within 6 weeks of surgery), normal postoperative inflammation is still present. Therefore, the threshold for diagnosing PJI is elevated to a synovial WBC count of > 10,000 cells/mcL.

Question 6205

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient is undergoing aspiration and tissue biopsy prior to revision of a reverse total shoulder arthroplasty for suspected Cutibacterium acnes infection. How many days should the cultures be held to ensure optimal detection of this specific organism?

. 3 days
. 5 days
. 7 days
. 14 days
. 21 days

Correct Answer & Explanation

. 14 days

Explanation

Cutibacterium acnes is a slow-growing, anaerobic Gram-positive bacillus common in shoulder PJI. Protocols recommend holding these cultures for 14 days to maximize detection of this indolent pathogen.

Question 6206

Topic: 3. Adult Reconstruction (Hip & Knee)

Alpha-defensin has emerged as a reliable synovial biomarker for PJI. Which of the following cells is the primary source of alpha-defensin in an infected joint space?

. Macrophages
. T-lymphocytes
. Neutrophils
. Synoviocytes
. Osteoblasts

Correct Answer & Explanation

. Neutrophils

Explanation

Alpha-defensin is a naturally occurring antimicrobial peptide released by activated neutrophils in response to pathogens. Its presence in synovial fluid strongly correlates with a neutrophil-driven response to infection.

Question 6207

Topic: 3. Adult Reconstruction (Hip & Knee)

During a fluoroscopy-guided aspiration of a painful total hip arthroplasty, no fluid is obtained initially (a "dry tap"). Which of the following is the most appropriate next step to evaluate for PJI?

. Re-attempt the aspiration in exactly 2 weeks.
. Inject 5-10 cc of sterile non-bacteriostatic normal saline and re-aspirate.
. Inject intra-articular radiopaque dye to confirm capsular distention, then stop.
. Inject a combination of local anesthetic and corticosteroid for pain relief.
. Proceed directly to a two-stage revision arthroplasty.

Correct Answer & Explanation

. Inject 5-10 cc of sterile non-bacteriostatic normal saline and re-aspirate.

Explanation

In the event of a "dry tap," instilling a small volume of sterile, non-bacteriostatic saline allows for fluid retrieval for culture. While cell counts will be diluted and unreliable, cultures and alpha-defensin assays may still be diagnostic.

Question 6208

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following systemic serum biomarkers has been identified as highly sensitive and specific for the diagnosis of PJI, performing comparably to or better than ESR and CRP in recent consensus literature?

. Fibrinogen
. D-dimer
. Serum amyloid A
. Procalcitonin
. Interleukin-10

Correct Answer & Explanation

. D-dimer

Explanation

Serum D-dimer has been validated as a highly promising biomarker for PJI. Multiple studies show it outperforms traditional inflammatory markers like ESR and CRP in both sensitivity and specificity for diagnosing periprosthetic joint infection.

Question 6209

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the ICM criteria, positive histological analysis of periprosthetic tissue is a minor criterion for PJI. What is the specific cellular threshold required to meet this criterion?

. > 1 neutrophil per high-power field in 5 fields
. > 5 neutrophils per high-power field in 5 fields
. > 10 neutrophils per high-power field in 10 fields
. > 50 neutrophils per high-power field in 5 fields
. The presence of any multinucleated giant cells

Correct Answer & Explanation

. > 5 neutrophils per high-power field in 5 fields

Explanation

The established histological criterion for PJI is the presence of greater than 5 polymorphonuclear neutrophils (PMNs) per high-power field in 5 distinct tissue fields at 400x magnification.

Question 6210

Topic: 3. Adult Reconstruction (Hip & Knee)

Synovial fluid C-reactive protein (CRP) has been increasingly utilized in the diagnostic workup for PJI. Which of the following statements is most accurate regarding synovial CRP?

. It is significantly less accurate than serum CRP in detecting indolent PJI.
. It strongly correlates with serum CRP but offers superior diagnostic accuracy for PJI.
. It is considered invalid if the patient is taking non-steroidal anti-inflammatory drugs.
. It has a negligible false-positive rate in the presence of acute crystalline arthropathy.
. It is falsely decreased in the setting of severe adverse local tissue reactions to metal.

Correct Answer & Explanation

. It strongly correlates with serum CRP but offers superior diagnostic accuracy for PJI.

Explanation

Synovial fluid CRP is an excellent localized marker for PJI that offers better sensitivity and specificity than systemic serum CRP. It is rapidly becoming a standard test when evaluating a painful arthroplasty.

Question 6211

Topic: 3. Adult Reconstruction (Hip & Knee)

Following an uncomplicated total joint arthroplasty, at what time point does the serum C-reactive protein (CRP) typically peak, and when does it generally return to its normal baseline?

. Peaks at 24 hours, returns to normal by 7 days
. Peaks at 2-3 days, returns to normal by 3 weeks
. Peaks at 7 days, returns to normal by 6 weeks
. Peaks at 14 days, returns to normal by 3 months
. Peaks at 2-3 days, returns to normal by 6 months

Correct Answer & Explanation

. Peaks at 2-3 days, returns to normal by 3 weeks

Explanation

The normal postoperative kinetic profile for serum CRP demonstrates a peak at day 2 or 3 postoperatively, followed by a steady decline to normal baseline levels within approximately 21 days.

Question 6212

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient is undergoing workup for an indolent, chronic total knee arthroplasty infection. Routine bacterial and fungal cultures are negative, and a mycobacterial infection is strongly suspected. What specific culture medium must be requested?

. MacConkey agar
. Sabouraud dextrose agar
. Lowenstein-Jensen medium
. Thayer-Martin agar
. Chocolate agar

Correct Answer & Explanation

. Lowenstein-Jensen medium

Explanation

Lowenstein-Jensen medium is the specialized solid lipid-based medium required for the isolation and growth of mycobacteria. Sabouraud dextrose is for fungi, and Thayer-Martin is for Neisseria.

Question 6213

Topic: 3. Adult Reconstruction (Hip & Knee)

Synovial fluid calprotectin has emerged as a rapid biomarker for PJI. Which of the following accurately describes its primary clinical utility?

. It reliably differentiates between gram-positive and gram-negative infections.
. It serves as a rapid point-of-care test reflecting localized neutrophil activation.
. It is highly specific for diagnosing fungal and atypical mycobacterial PJI.
. It is a definitive replacement for standard synovial fluid aerobic and anaerobic cultures.
. It has high sensitivity but extremely low specificity in chronic, late-onset PJI.

Correct Answer & Explanation

. It serves as a rapid point-of-care test reflecting localized neutrophil activation.

Explanation

Calprotectin is a major protein found in the cytosol of neutrophils. A rapid point-of-care calprotectin lateral flow assay strongly correlates with the synovial neutrophil count, providing a highly sensitive and specific immediate marker for PJI.

Question 6214

Topic: 3. Adult Reconstruction (Hip & Knee)

Although the synovial fluid alpha-defensin test is highly accurate for diagnosing PJI, false positives can occasionally occur. Which of the following non-infectious conditions is most likely to produce a false-positive alpha-defensin test?

. Avascular necrosis of the femoral head
. Metallosis from an adverse local tissue reaction
. An acute flare of primary osteoarthritis
. Systemic lupus erythematosus
. Concurrent administration of oral antibiotics

Correct Answer & Explanation

. Metallosis from an adverse local tissue reaction

Explanation

Severe adverse local tissue reactions (ALTR) or metallosis can cause an intense local inflammatory response that interferes with lateral flow assays. This is a recognized, albeit rare, cause of a false-positive alpha-defensin test.

Question 6215

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female with a painful total hip arthroplasty has a high clinical suspicion of periprosthetic joint infection (PJI). Standard cultures at 14 days are negative. What is the primary advantage of next-generation sequencing (NGS) of synovial fluid in this scenario?

. Detects antibiotic susceptibilities faster
. Higher specificity than standard culture
. Identifies organisms in culture-negative PJI
. Replaces alpha-defensin as a major criterion
. Has a lower false-positive rate than standard culture

Correct Answer & Explanation

. Identifies organisms in culture-negative PJI

Explanation

Next-generation sequencing (NGS) is highly sensitive and can identify pathogen DNA in culture-negative cases, especially when prior antibiotics were given. However, its specificity is lower due to potential contamination or the detection of non-viable organisms.

Question 6216

Topic: 3. Adult Reconstruction (Hip & Knee)

You attempt a knee aspiration for suspected PJI but obtain a "dry tap." What is the most appropriate next step to obtain a fluid sample for diagnostic testing?

. Inject 10-20 cc of bacteriostatic saline and re-aspirate
. Inject 10-20 cc of sterile normal saline without preservative and re-aspirate
. Proceed directly to two-stage revision
. Order a PET scan
. Perform an open arthrotomy for tissue biopsy

Correct Answer & Explanation

. Inject 10-20 cc of sterile normal saline without preservative and re-aspirate

Explanation

Injecting non-bacteriostatic sterile normal saline and re-aspirating (lavage) is recommended for a dry tap. Bacteriostatic saline contains preservatives that inhibit bacterial growth and can lead to false-negative cultures.

Question 6217

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following serum markers has been newly introduced as a minor criterion for diagnosing PJI?

. Procalcitonin
. Interleukin-6 (IL-6)
. D-dimer
. Tumor Necrosis Factor-alpha (TNF-alpha)
. Leukocyte esterase

Correct Answer & Explanation

. D-dimer

Explanation

Serum D-dimer was included in the 2018 ICM criteria as a valuable serum biomarker for PJI. It has shown comparable sensitivity and specificity to standard markers like ESR and CRP.

Question 6218

Topic: 3. Adult Reconstruction (Hip & Knee)

A synovial fluid sample from a symptomatic TKA is placed on a leukocyte esterase (LE) strip, which reads "++". What is the significance of this test in the context of PJI?

. It is a major criterion for PJI diagnosis.
. It detects the presence of alpha-defensin.
. It is a minor criterion that can be unreadable in grossly bloody aspirates.
. It has low specificity for PJI.
. It requires 48 hours for interpretation.

Correct Answer & Explanation

. It is a minor criterion that can be unreadable in grossly bloody aspirates.

Explanation

Leukocyte esterase is a rapid, inexpensive test that detects neutrophil activity and acts as a minor criterion for PJI. However, grossly bloody aspirates can obscure the color change on the test strip, limiting its utility in those instances.

Question 6219

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male presents with stiffness and vague pain 1 year after a total shoulder arthroplasty. Aspiration is performed. Given the most common indolent organism in this location, how long should the cultures be held?

. 5 days
. 7 days
. 10 days
. 14 days
. 28 days

Correct Answer & Explanation

. 14 days

Explanation

Cutibacterium acnes is a slow-growing anaerobe commonly responsible for shoulder PJI. Cultures should be held for a minimum of 14 days to minimize the risk of false-negative results.

Question 6220

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with suspected PJI was started on empiric oral antibiotics by their primary care provider. The antibiotics were stopped yesterday. To optimize the yield of a synovial fluid aspiration for culture, how long should you wait before performing the aspiration?

. 24 hours
. 3 days
. 7 days
. 14 days
. 28 days

Correct Answer & Explanation

. 14 days

Explanation

To reduce the risk of false-negative cultures, it is recommended to discontinue antibiotic therapy for at least 14 days prior to obtaining synovial fluid or tissue cultures for PJI diagnosis.

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