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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 309 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 6161

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient is scheduled for an elective total hip arthroplasty. According to recent AAOS guidelines, which of the following is an appropriate venous thromboembolism (VTE) prophylaxis for a patient with standard risk and no history of bleeding disorders?

. Aspirin monotherapy
. Low-molecular-weight heparin (LMWH) for exactly 14 days
. Warfarin with an INR target of 2.5-3.5
. Prophylactic inferior vena cava filter placement
. Unfractionated heparin continuous infusion

Correct Answer & Explanation

. Aspirin monotherapy

Explanation

Current AAOS guidelines support the use of aspirin for VTE prophylaxis in standard-risk patients undergoing total joint arthroplasty, balancing effective prevention with lower bleeding risks.

Question 6162

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the International Consensus Meeting (ICM) criteria, which of the following is considered a 'major criterion' for the definitive diagnosis of a periprosthetic joint infection (PJI)?

. Elevated serum CRP > 10 mg/L and ESR > 30 mm/hr
. Purulence in the affected joint observed intraoperatively
. Elevated synovial fluid leukocyte count greater than 3,000 cells/uL
. Two positive periprosthetic tissue cultures yielding identical organisms
. Elevated synovial fluid alpha-defensin

Correct Answer & Explanation

. Two positive periprosthetic tissue cultures yielding identical organisms

Explanation

The two major criteria for PJI are a sinus tract communicating with the prosthesis and two positive periprosthetic cultures with phenotypically identical organisms. The others are minor criteria.

Question 6163

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male with a metal-on-metal total hip arthroplasty presents with groin pain and an enlarging pseudotumor. Histological analysis of the periprosthetic tissue will most likely demonstrate which of the following distinct features?

. Massive neutrophil infiltration indicating acute infection
. Aseptic lymphocytic vasculitis-associated lesion (ALVAL)
. Abundant foreign-body giant cells containing highly birefringent polymeric particles
. Malignant spindle cells with osteoid production
. Acellular fibrinous exudate without macrophages

Correct Answer & Explanation

. Aseptic lymphocytic vasculitis-associated lesion (ALVAL)

Explanation

Adverse local tissue reactions (ALTR) associated with metal-on-metal implants are characterized histologically by ALVAL (aseptic lymphocytic vasculitis-associated lesion). This features a dense perivascular lymphocytic infiltrate indicative of a delayed-type hypersensitivity response.

Question 6164

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient presents with aseptic loosening 15 years after a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following cells is the primary mediator of the osteolysis observed in this condition?

. Osteoblasts
. T-lymphocytes
. Macrophages
. Polymorphonuclear leukocytes
. B-lymphocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages are the primary cells responsible for recognizing particulate wear debris. Upon phagocytosing polyethylene particles, they release pro-inflammatory cytokines like TNF-alpha and IL-1, which upregulate RANKL and stimulate osteoclast-mediated bone resorption.

Question 6165

Topic: Total Hip Arthroplasty (THA)

A 58-year-old male with a ceramic-on-ceramic total hip arthroplasty presents with an audible squeaking noise from his hip during certain movements. There is no pain, and radiographs show well-fixed components. Which of the following technical factors during the index surgery most likely contributed to this issue?

. Increased femoral offset
. Excessive anteversion of the femoral stem
. Excessive cup inclination
. Use of a large diameter femoral head
. Placement of a constrained liner

Correct Answer & Explanation

. Excessive cup inclination

Explanation

Squeaking in ceramic-on-ceramic THA is often associated with component malposition, specifically excessive acetabular cup inclination or anteversion. This malpositioning leads to edge loading, disrupting the fluid film lubrication and causing the audible squeak.

Question 6166

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is well-balanced in extension but unacceptably tight in flexion. Which of the following intraoperative adjustments is most appropriate to balance the knee?

. Recut the distal femur to remove more bone
. Release the posterior capsule
. Downsize the femoral component using an anterior referencing guide
. Decrease the posterior slope of the tibial cut
. Increase the size of the polyethylene insert

Correct Answer & Explanation

. Downsize the femoral component using an anterior referencing guide

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap. Downsizing the femoral component using an anterior referencing system will resect more posterior femoral condyle, thereby selectively increasing the flexion gap.

Question 6167

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection (PJI), which of the following is considered a definitive major criterion for diagnosing PJI?

. A single positive intraoperative tissue culture yielding a highly virulent organism.
. A synovial fluid white blood cell (WBC) count greater than 3,000 cells/microliter.
. A positive synovial fluid alpha-defensin immunoassay.
. Purulence in the affected joint observed directly during the surgical procedure.
. A sinus tract communicating directly with the prosthesis.

Correct Answer & Explanation

. A sinus tract communicating directly with the prosthesis.

Explanation

Under the 2018 ICM criteria, there are only two major criteria that definitively confirm a PJI: 1) Two positive periprosthetic cultures with phenotypically identical organisms, or 2) A sinus tract communicating with the joint. All other findings (including elevated WBC, positive alpha-defensin, single positive culture, and purulence) are considered minor criteria that contribute to an aggregate diagnostic score.

Question 6168

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following statements regarding the synovial fluid alpha-defensin test for periprosthetic joint infection (PJI) is most accurate?

. It is an acute-phase reactant synthesized primarily by the liver in response to IL-6.
. Its accuracy is significantly compromised by concurrent systemic inflammatory diseases such as rheumatoid arthritis.
. It maintains high diagnostic accuracy and is largely unaffected by prior antibiotic administration.
. It is highly sensitive for fungal pathogens but lacks specificity for bacterial PJI.
. It must be analyzed manually because automated cell counters falsely elevate its levels in the presence of blood.

Correct Answer & Explanation

. It maintains high diagnostic accuracy and is largely unaffected by prior antibiotic administration.

Explanation

Alpha-defensin is an antimicrobial peptide released by human neutrophils in response to pathogens. A major clinical advantage of the alpha-defensin test is that it maintains its high sensitivity and specificity for diagnosing PJI even when patients have been previously treated with antibiotics. It is also unaffected by concurrent systemic inflammatory conditions like rheumatoid arthritis.

Question 6169

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male presents with chronic knee pain and stiffness 3 years after a total knee arthroplasty (TKA). Aspiration of the joint yields 3 cc of clear synovial fluid. Which of the following synovial fluid analysis thresholds most strongly supports a diagnosis of chronic PJI?

. WBC > 50,000 cells/uL with > 90% polymorphonuclear cells (PMNs)
. WBC > 3,000 cells/uL with > 80% polymorphonuclear cells (PMNs)
. WBC > 1,500 cells/uL with > 65% polymorphonuclear cells (PMNs)
. WBC > 10,000 cells/uL with > 90% polymorphonuclear cells (PMNs)

Correct Answer & Explanation

. WBC > 3,000 cells/uL with > 80% polymorphonuclear cells (PMNs)

Explanation

For chronic PJI (typically defined as occurring >90 days postoperatively), the generally accepted threshold is a synovial fluid WBC count > 3,000 cells/uL and/or a PMN percentage > 80%. This is significantly lower than the threshold for a native septic joint (WBC > 50,000 cells/uL) because biofilm formation in PJI attenuates the typical robust leukocytic response. Acute post-op PJI (<90 days) utilizes a higher threshold of approximately > 10,000 cells/uL and > 90% PMNs.

Question 6170

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a painful metal-on-metal (MoM) total hip arthroplasty undergoes diagnostic joint aspiration to rule out infection. Which of the following is a critical modification required during the synovial fluid analysis?

. The fluid must be tested immediately for leukocyte esterase before centrifugation.
. A manual hemocytometer count must be utilized because automated cell counters falsely elevate the WBC count by counting metal debris.
. Alpha-defensin testing is contraindicated due to cross-reactivity with cobalt and chromium ions.
. The sample must be incubated exclusively in strictly anaerobic environments to prevent metal oxidation.

Correct Answer & Explanation

. A manual hemocytometer count must be utilized because automated cell counters falsely elevate the WBC count by counting metal debris.

Explanation

In metal-on-metal bearings or cases with severe metallosis, suspended metal debris in the synovial fluid is often misread by automated cell counters as leukocytes, leading to falsely elevated WBC counts. Therefore, a manual count using a hemocytometer is required to obtain an accurate WBC count.

Question 6171

Topic: 3. Adult Reconstruction (Hip & Knee)

You are following the postoperative inflammatory markers of a patient who underwent an uncomplicated primary total hip arthroplasty (THA). Assuming a normal recovery without infection, at what postoperative timeframes do C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR) typically peak?

. CRP peaks at day 2; ESR peaks at days 5 to 7.
. CRP peaks at day 5 to 7; ESR peaks at day 2.
. Both CRP and ESR peak simultaneously at day 14.
. CRP peaks at day 14; ESR peaks at day 21.

Correct Answer & Explanation

. CRP peaks at day 2; ESR peaks at days 5 to 7.

Explanation

In normal, uncomplicated postoperative recovery after total joint arthroplasty, CRP is an acute responder that peaks rapidly around postoperative day 2 and typically returns to baseline within 3 weeks. ESR is a slower responder, peaking around postoperative days 5 to 7, and can take up to 6 to 12 weeks to normalize.

Question 6172

Topic: 3. Adult Reconstruction (Hip & Knee)

During a diagnostic aspiration of a suspected infected total knee arthroplasty, the surgeon encounters a 'dry tap'. The surgeon injects 10 mL of sterile, non-bacteriostatic normal saline, ranges the knee, and re-aspirates the fluid. Which of the following synovial fluid parameters remains the most diagnostically reliable despite the saline dilution?

. Absolute synovial WBC count
. Synovial fluid polymorphonuclear (PMN) percentage
. Synovial fluid leukocyte esterase
. Synovial fluid protein concentration

Correct Answer & Explanation

. Synovial fluid polymorphonuclear (PMN) percentage

Explanation

When a saline lavage is performed during a 'dry tap', parameters relying on absolute concentrations (such as the absolute WBC count, leukocyte esterase, and protein) become artificially lowered due to dilution and lose their established diagnostic thresholds. However, the PMN percentage represents a ratio of cell types and remains largely reliable and unaffected by the dilution.

Question 6173

Topic: 3. Adult Reconstruction (Hip & Knee)
A 72-year-old female presents 4 weeks post-total knee arthroplasty with an acute onset of severe pain, erythema, and a large effusion. She undergoes a joint aspiration. What is the accepted synovial WBC threshold indicating acute periprosthetic joint infection (<90 days post-op)?
. > 1,500 cells/uL
. > 3,000 cells/uL
. > 10,000 cells/uL
. > 50,000 cells/uL

Correct Answer & Explanation

. > 10,000 cells/uL

Explanation

For acute periprosthetic joint infections (defined typically as within the first 6-12 weeks or <90 days postoperatively), the diagnostic threshold is higher than for chronic PJI due to expected postoperative inflammation. The accepted threshold for acute PJI is > 10,000 cells/uL and a PMN percentage of > 90%.

Question 6174

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male complains of insidious, progressive shoulder pain and stiffness 14 months after a primary anatomic total shoulder arthroplasty. Serum ESR and CRP are normal. An ultrasound-guided aspiration is performed. To accurately diagnose Cutibacterium acnes (formerly Propionibacterium acnes), which specific microbiological protocol must be requested?

. Aerobic incubation on chocolate agar for 5 days.
. Culture on MacConkey agar to isolate lactose-fermenting colonies.
. Standard anaerobic culture for a maximum of 3 to 5 days.
. Extended anaerobic culture monitoring for up to 14 days.

Correct Answer & Explanation

. Extended anaerobic culture monitoring for up to 14 days.

Explanation

Cutibacterium acnes is an indolent, slow-growing anaerobic Gram-positive bacillus that is a leading cause of shoulder periprosthetic joint infections. It frequently presents with normal serum inflammatory markers and no frank purulence. Because of its slow growth rate, routine 3-5 day cultures will often yield false negatives; standard protocol requires holding anaerobic cultures for up to 14 days.

Question 6175

Topic: 3. Adult Reconstruction (Hip & Knee)

The leukocyte esterase (LE) colorimetric strip test is an effective, rapid diagnostic tool for PJI. However, false or unreadable results frequently occur in the setting of hemarthrosis. To obtain a valid LE strip reading in heavily blood-stained synovial fluid, what preparatory step must be taken?

. Adding ethylenediaminetetraacetic acid (EDTA) to the fluid prior to testing.
. Diluting the synovial fluid 1:1 with sterile saline.
. Centrifuging the sample to precipitate red blood cells and testing the clear supernatant.
. Warming the sample to 37 degrees Celsius for 30 minutes before dipping the strip.

Correct Answer & Explanation

. Centrifuging the sample to precipitate red blood cells and testing the clear supernatant.

Explanation

Leukocyte esterase strips rely on a color change to indicate the presence of neutrophil esterase. Gross blood in the synovial fluid heavily obscures this color change, making the strip unreadable. The validated method to overcome this is centrifuging the sample to pellet the red blood cells and then testing the clear supernatant.

Question 6176

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with suspected chronic PJI of the hip has been empirically placed on oral antibiotics by their primary care physician. To maximize the diagnostic yield of pre-operative joint aspiration cultures, what is the minimum recommended 'antibiotic holiday' (duration to withhold antibiotics) prior to obtaining the aspiration?

. 3 days
. 7 days
. 14 days
. 28 days

Correct Answer & Explanation

. 14 days

Explanation

According to the American Academy of Orthopaedic Surgeons (AAOS) guidelines and the International Consensus Meeting (ICM) on PJI, an 'antibiotic holiday' of at least 14 days (2 weeks) is recommended prior to obtaining diagnostic cultures to minimize the risk of false-negative culture results.

Question 6177

Topic: 3. Adult Reconstruction (Hip & Knee)

During a revision total knee arthroplasty for suspected culture-negative PJI, the surgeon extracts the femoral and tibial components and sends them for sonication. What is the primary mechanism by which sonication improves the microbiological yield in PJI?

. It utilizes low-frequency ultrasound waves to physically dislodge and disrupt bacterial biofilm from the implant surface.
. It introduces targeted bacteriophages that selectively lyse persister cells into the culture medium.
. It denatures local antibiotics clinging to the implant, preventing them from inhibiting in vitro bacterial growth.
. It amplifies traces of bacterial DNA to levels detectable by standard real-time PCR.

Correct Answer & Explanation

. It utilizes low-frequency ultrasound waves to physically dislodge and disrupt bacterial biofilm from the implant surface.

Explanation

Sonication involves submersing explanted hardware in a fluid bath and applying low-frequency ultrasound. The acoustic cavitation physically dislodges and disrupts the protective extracellular polymeric substance (EPS) of the biofilm, releasing viable sessile bacteria into the planktonic state, which significantly increases the sensitivity of subsequent cultures.

Question 6178

Topic: 3. Adult Reconstruction (Hip & Knee)

Under the 2018 International Consensus Meeting (ICM) minor criteria scoring system for PJI, which of the following synovial fluid or serum findings is assigned a weight of exactly 3 points?

. Elevated serum D-dimer (>860 ng/mL)
. Elevated synovial fluid PMN percentage (>80%)
. Elevated serum ESR (>30 mm/hr)
. Positive synovial fluid leukocyte esterase (++ strip test)

Correct Answer & Explanation

. Positive synovial fluid leukocyte esterase (++ strip test)

Explanation

In the 2018 ICM scoring algorithm for PJI, a positive synovial fluid leukocyte esterase (++) OR an elevated synovial WBC count (>3000) yields 3 points. Positive Alpha-defensin also yields 3 points. Serum D-dimer (>860 ng/mL) or CRP (>10 mg/L) yields 2 points. Synovial PMN percentage (>80%) yields 2 points, and elevated ESR (>30) yields 1 point. A total score of 6 or more confirms PJI.

Question 6179

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following is considered the primary advantage of utilizing Next-Generation Sequencing (NGS) over standard culture techniques in the diagnosis of periprosthetic joint infections?

. It allows for the rapid determination of exact Minimum Inhibitory Concentrations (MIC) for antibiotic therapy.
. It can identify pathogen DNA regardless of organism viability, making it highly useful in culture-negative PJI.
. It requires significantly less laboratory processing time and is currently cheaper than standard automated culture systems.
. It exclusively detects viable, actively replicating bacteria, thereby eliminating the risk of false positives from contaminants.

Correct Answer & Explanation

. It can identify pathogen DNA regardless of organism viability, making it highly useful in culture-negative PJI.

Explanation

Next-Generation Sequencing (NGS) is highly sensitive as it sequences all microbial DNA present in a sample. Its primary advantage is the ability to identify the precise causative organism in culture-negative PJI scenarios (e.g., when the patient is on active antibiotics or when the bacteria are dead or non-culturable). It cannot directly determine standard MICs and has a risk of detecting clinically irrelevant contaminant DNA.

Question 6180

Topic: 3. Adult Reconstruction (Hip & Knee)

The 2018 International Consensus Meeting (ICM) introduced a novel serum biomarker to the diagnostic criteria for PJI. This marker is valued for its high sensitivity and comparable performance to serum CRP. Which biomarker is this?

. Serum D-dimer
. Serum Interleukin-6 (IL-6)
. Serum Procalcitonin
. Serum Alpha-defensin

Correct Answer & Explanation

. Serum D-dimer

Explanation

Serum D-dimer was formally introduced as a minor criterion in the 2018 ICM diagnostic algorithm for PJI. It was established as an equivalent alternative to serum CRP, where an elevated D-dimer (>860 ng/mL) or an elevated CRP (>10 mg/L) equally contributes 2 points to the aggregate PJI score.

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