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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 107 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 2121

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old man with a well-functioning TKA placed 4 years ago presents with acute onset of severe knee pain, swelling, and fever 5 days after a dental procedure. Synovial aspiration shows 65,000 WBC/mcL with 95% neutrophils, and Gram stain reveals Gram-positive cocci. Radiographs demonstrate well-fixed components. What is the most appropriate surgical management?

. Intravenous antibiotics alone for 6 weeks
. Arthroscopic joint lavage
. Debridement, antibiotics, and implant retention (DAIR) with modular exchange
. Single-stage revision arthroplasty
. Two-stage revision arthroplasty

Correct Answer & Explanation

. Debridement, antibiotics, and implant retention (DAIR) with modular exchange

Explanation

DAIR with polyethylene exchange is indicated for acute hematogenous periprosthetic joint infections (symptoms less than 3 weeks) with stable components. Two-stage revision is reserved for chronic infections or loose components.

Question 2122

Topic: Total Hip Arthroplasty (THA)

During templating for a primary THA, the surgeon plans to use a high-offset femoral stem instead of a standard-offset stem of the same neck length. How will this change affect the hip biomechanics?

. Increases abductor moment arm and increases leg length
. Increases abductor moment arm without changing leg length
. Decreases abductor tension and decreases leg length
. Increases leg length without changing the abductor moment arm
. Decreases joint reaction force and increases leg length

Correct Answer & Explanation

. Increases abductor moment arm without changing leg length

Explanation

Using a high-offset stem increases femoral offset and the abductor moment arm, which improves abductor mechanical advantage and reduces joint reaction forces. High offset options generally do not affect leg length compared to a standard stem.

Question 2123

Topic: Total Knee Arthroplasty (TKA)

During a primary TKA utilizing measured resection techniques, the surgeon evaluates the trial components. The knee is perfectly balanced and stable in extension but demonstrates severe laxity in flexion. What is the most appropriate step to balance the knee?

. Increase the thickness of the tibial polyethylene insert
. Downsize the femoral component and use a thicker polyethylene insert
. Upsize the femoral component
. Recut the distal femur to remove more bone
. Release the posterior cruciate ligament

Correct Answer & Explanation

. Upsize the femoral component

Explanation

A knee that is balanced in extension but loose in flexion has an isolated wide flexion gap. Upsizing the femoral component increases the AP dimension, tightening the flexion gap without affecting the extension gap.

Question 2124

Topic: 3. Adult Reconstruction (Hip & Knee)

A 78-year-old woman sustains a closed supracondylar femur fracture above a posterior-stabilized TKA. Radiographs show a displaced fracture (Su/Rorabeck Type II), but the femoral component remains perfectly aligned and well-fixed. What is the optimal surgical treatment?

. Nonoperative management with a hinged knee brace
. Open reduction and internal fixation with a lateral locking plate
. Distal femoral replacement
. Revision to a hinged total knee arthroplasty
. External fixation

Correct Answer & Explanation

. Open reduction and internal fixation with a lateral locking plate

Explanation

For periprosthetic distal femur fractures with a well-fixed TKA component and adequate bone stock, open reduction and internal fixation (e.g., lateral locking plate or retrograde nail) is the standard of care. Distal femoral replacement is reserved for loose components or non-reconstructable bone.

Question 2125

Topic: 3. Adult Reconstruction (Hip & Knee)

To minimize the risk of dislocation after a primary total hip arthroplasty, the acetabular component should ideally be placed within the Lewinnek safe zone. Which of the following target ranges defines this historical safe zone?

. Inclination of 30 to 50 degrees and anteversion of 5 to 25 degrees
. Inclination of 20 to 40 degrees and anteversion of 10 to 30 degrees
. Inclination of 40 to 60 degrees and anteversion of 0 to 15 degrees
. Inclination of 35 to 55 degrees and retroversion of 5 to 15 degrees
. Inclination of 15 to 35 degrees and anteversion of 20 to 40 degrees

Correct Answer & Explanation

. Inclination of 30 to 50 degrees and anteversion of 5 to 25 degrees

Explanation

The Lewinnek safe zone historically describes an optimal acetabular component position of 40° ± 10° for inclination and 15° ± 10° for anteversion to minimize the risk of postoperative dislocation.

Question 2126

Topic: Total Hip Arthroplasty (THA)

A 74-year-old woman undergoes a revision THA. Intraoperatively, she is found to have complete absence of the abductor musculature with severe fatty atrophy. Following placement of the revision components, the hip demonstrates significant instability and dislocates with minimal adduction. Which of the following is the most appropriate management?

. Placement of a dual-mobility articulation
. Use of an elevated rim (lipped) polyethylene liner
. Placement of a constrained acetabular liner
. Revision to a larger femoral head size only
. Application of an abduction brace postoperatively

Correct Answer & Explanation

. Placement of a constrained acetabular liner

Explanation

In the setting of severe or complete abductor deficiency causing intraoperative instability, a constrained acetabular liner is indicated to prevent dislocation. Dual mobility relies on dynamic soft-tissue stabilizers and may still fail in the complete absence of abductors.

Question 2127

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male with a metal-on-metal total hip arthroplasty (THA) presents with a new onset of groin pain and swelling. Blood tests reveal elevated serum cobalt and chromium ions. A joint aspiration is performed, and synovial fluid analysis shows a positive alpha-defensin test but negative bacterial cultures. Which of the following is the most likely cause of a false-positive alpha-defensin result in this clinical scenario?

. Rheumatoid arthritis flare
. Acute gouty arthropathy
. Metallosis / Adverse Local Tissue Reaction (ALTR)
. Systemic bacteremia
. Concurrent administration of oral antibiotics

Correct Answer & Explanation

. Metallosis / Adverse Local Tissue Reaction (ALTR)

Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils and is a highly sensitive and specific biomarker for periprosthetic joint infection (PJI). However, false-positive results can occur in the setting of metallosis or adverse local tissue reaction (ALTR) associated with metal-on-metal implants or mechanically failing components. The severe local inflammatory response and extensive tissue necrosis in ALTR can lead to neutrophil recruitment and subsequent alpha-defensin release in the absence of an infectious organism.

Question 2128

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for Periprosthetic Joint Infection, which of the following is considered a 'Major Criterion' that definitively diagnoses a PJI without the need for further scoring?

. A single positive intraoperative tissue culture for a highly virulent organism
. Elevated synovial fluid C-reactive protein (CRP) > 6.9 mg/L
. Synovial fluid white blood cell (WBC) count > 3,000 cells/µL
. Presence of a sinus tract communicating with the joint
. Positive leukocyte esterase (++ on a urine dipstick) of synovial fluid

Correct Answer & Explanation

. Presence of a sinus tract communicating with the joint

Explanation

Under the 2018 ICM criteria for PJI, there are two major criteria that definitively establish the diagnosis of infection: 1) Two positive periprosthetic cultures with phenotypically identical organisms, and 2) A sinus tract communicating with the joint. The other options (elevated synovial WBC, elevated synovial CRP, positive leukocyte esterase, and a single positive culture) are considered minor criteria that contribute points toward an aggregate diagnostic score.

Question 2129

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old male undergoes revision of a total shoulder arthroplasty for presumed aseptic loosening. Intraoperative tissue cultures are obtained. On postoperative day 12, the microbiology lab reports growth of Cutibacterium acnes. Which of the following best describes this organism and its management?

. It is an aerobic gram-negative bacillus requiring prolonged multidrug therapy
. It is an anaerobic gram-positive rod that typically causes indolent, late-onset infections
. It produces rapid, fulminant sepsis within 48 hours of surgery
. It is intrinsically resistant to Penicillin and requires intravenous Vancomycin
. It rarely forms a biofilm, making it highly susceptible to oral antibiotics alone

Correct Answer & Explanation

. It is an anaerobic gram-positive rod that typically causes indolent, late-onset infections

Explanation

Cutibacterium acnes (formerly Propionibacterium acnes) is a slow-growing, anaerobic to microaerophilic gram-positive rod commonly found on the skin, particularly around the shoulder and chest. It is a frequent cause of indolent, low-grade periprosthetic joint infections, especially in shoulder arthroplasty. Because of its slow growth, cultures must often be held for up to 14 days. It is generally highly susceptible to Penicillin and Ceftriaxone, but its ability to form biofilms on implants makes surgical intervention (such as revision) necessary.

Question 2130

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old female is diagnosed with an Enterococcus faecalis periprosthetic joint infection of her total hip arthroplasty. Which of the following is a hallmark characteristic of this organism that complicates systemic antibiotic therapy?

. Intrinsic resistance to all broad-spectrum cephalosporins
. Strict obligate anaerobic metabolism limiting tissue penetration
. Production of extended-spectrum beta-lactamases (ESBL)
. Inability to be cultured on standard sheep blood agar
. Dependence on intracellular replication within macrophages

Correct Answer & Explanation

. Intrinsic resistance to all broad-spectrum cephalosporins

Explanation

Enterococci, including E. faecalis, have intrinsic resistance to all cephalosporins, as well as relatively low susceptibility to many other beta-lactams due to the expression of low-affinity penicillin-binding proteins (PBPs). They are notoriously difficult to treat in PJI and often require combination therapy (such as Ampicillin + Ceftriaxone or an aminoglycoside) to achieve synergistic bactericidal activity, or agents like Linezolid or Daptomycin. They are facultative anaerobes and grow readily on standard media.

Question 2131

Topic: 3. Adult Reconstruction (Hip & Knee)

A surgeon is considering a single-stage (one-stage) exchange arthroplasty for a patient with an infected total knee arthroplasty. According to international consensus guidelines, which of the following is a strict contraindication to proceeding with a one-stage exchange?

. The infecting organism is known pre-operatively
. The organism is highly sensitive to available oral antibiotics
. Presence of a sinus tract with severely compromised local soft tissue
. Infection with a Gram-positive organism
. The patient has a history of well-controlled diabetes mellitus

Correct Answer & Explanation

. Presence of a sinus tract with severely compromised local soft tissue

Explanation

A single-stage exchange relies on a meticulous debridement and immediate reimplantation. Contraindications include unknown or culture-negative infections (where targeted antibiotic therapy cannot be planned), highly resistant organisms (where no effective oral/IV suppressive or targeted therapy exists), and severely compromised soft tissues or a sinus tract that precludes adequate primary closure and healthy tissue coverage. Well-controlled comorbidities and known susceptible organisms are prerequisites for a successful one-stage procedure.

Question 2132

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male is 3 weeks status post primary total knee arthroplasty and presents with increased pain, swelling, and erythema. A joint aspiration is performed. According to recent literature and consensus guidelines, which of the following synovial fluid white blood cell (WBC) thresholds is most appropriate to suggest an acute periprosthetic joint infection in this early post-operative period?

. > 1,500 cells/µL
. > 3,000 cells/µL
. > 5,000 cells/µL
. > 10,000 cells/µL
. > 50,000 cells/µL

Correct Answer & Explanation

. > 10,000 cells/µL

Explanation

In the acute post-operative period (typically defined as within the first 6 weeks following surgery), the baseline synovial fluid WBC count is naturally elevated due to surgical trauma and hematoma. The traditional threshold used to diagnose a chronic PJI (>3,000 cells/µL) is inadequate in this setting. Literature has established that a cutoff of >10,000 cells/µL (with >90% PMNs) is highly suggestive of an acute PJI in the early post-operative period. Some newer studies suggest a threshold as high as 27,800 cells/µL, but >10,000 is the classic threshold to distinguish from normal post-op inflammation.

Question 2133

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a culture-proven Candida albicans periprosthetic joint infection is planned for a two-stage exchange arthroplasty. Which of the following antifungal agents is most appropriate to incorporate into the polymethylmethacrylate (PMMA) cement spacer due to its thermal stability and proven elution properties?

. Fluconazole
. Caspofungin
. Amphotericin B
. Terbinafine
. Itraconazole

Correct Answer & Explanation

. Amphotericin B

Explanation

Amphotericin B (particularly in its liposomal or deoxycholate forms) and Voriconazole are the antifungal agents most commonly added to PMMA cement spacers for fungal PJIs. They possess the necessary thermal stability to withstand the exothermic reaction of PMMA polymerization and have demonstrated effective elution profiles. Fluconazole, while systemically effective, has poor thermal stability and highly variable elution from PMMA.

Question 2134

Topic: 3. Adult Reconstruction (Hip & Knee)

During pre-operative nutritional optimization for a patient scheduled for revision arthroplasty, the surgeon orders serum biomarkers to assess acute changes in nutritional status. Which of the following markers has the shortest half-life (approximately 2 to 3 days) and is best suited for monitoring short-term nutritional improvements?

. Serum Albumin
. Serum Transferrin
. Prealbumin (Transthyretin)
. Total Lymphocyte Count
. C-Reactive Protein

Correct Answer & Explanation

. Prealbumin (Transthyretin)

Explanation

Prealbumin (also known as transthyretin) has a half-life of approximately 2 to 3 days, making it a highly sensitive marker for assessing acute changes in nutritional status and the efficacy of nutritional supplementation. In contrast, serum albumin has a half-life of about 21 days and transferrin has a half-life of about 8 days, making them better indicators of chronic malnutrition but poor markers for short-term recovery.

Question 2135

Topic: Total Knee Arthroplasty (TKA)

During the second stage of a revision total knee arthroplasty for a prior infection, the surgeon evaluates the joint spaces using trial spacer blocks. The knee is noted to be unacceptably tight in flexion but excessively loose in extension. Which of the following surgical adjustments is most appropriate to balance the gaps?

. Downsize the femoral component and increase the thickness of the distal femoral augments
. Upsize the femoral component and decrease the thickness of the distal femoral augments
. Decrease the tibial polyethylene thickness and increase the posterior tibial slope
. Increase the tibial polyethylene thickness and distalize the joint line
. Release the posterior cruciate ligament and upsize the femoral component

Correct Answer & Explanation

. Downsize the femoral component and increase the thickness of the distal femoral augments

Explanation

Gap balancing in revision TKA is critical. If the knee is tight in flexion, the flexion gap must be increased. This is done by downsizing the femoral component, which translates the posterior condyles anteriorly. If the knee is loose in extension, the extension gap must be decreased. This is achieved by adding distal femoral augments, which translates the femoral component distally. Therefore, downsizing the femur and adding distal augments addresses both imbalances simultaneously.

Question 2136

Topic: 3. Adult Reconstruction (Hip & Knee)

A 40-year-old female presents with a chronic, culture-negative periprosthetic joint infection. Synovial fluid is sent for Next-Generation Sequencing (NGS). Which of the following molecular targets is primarily utilized by NGS to identify bacterial species in this setting?

. The 18S ribosomal RNA gene
. The mecA resistance gene
. The 16S ribosomal RNA gene
. The rpoB gene
. The vanA resistance gene

Correct Answer & Explanation

. The 16S ribosomal RNA gene

Explanation

Next-Generation Sequencing (NGS) for bacterial identification in culture-negative PJI primarily targets the 16S ribosomal RNA (rRNA) gene. The 16S rRNA gene is highly conserved among all bacteria but contains hypervariable regions that are species-specific, allowing for precise identification. The 18S rRNA gene is targeted for fungal identification. The mecA and vanA genes are markers of antibiotic resistance (MRSA and VRE, respectively), not broad species identification.

Question 2137

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male undergoes the second stage of a two-stage exchange arthroplasty for a previously infected total knee. Post-operative cultures remain negative, and the patient recovers well. Based on recent multi-center randomized controlled trials (such as the POET trial), what is the recommended duration of extended oral antibiotic prophylaxis to minimize the risk of reinfection?

. No oral antibiotics are indicated if intraoperative cultures are negative
. 14 days of targeted oral antibiotics
. 90 days (3 months) of targeted oral antibiotics
. 6 months of targeted oral antibiotics
. Lifelong suppressive oral antibiotics

Correct Answer & Explanation

. 90 days (3 months) of targeted oral antibiotics

Explanation

Recent evidence, prominently including the Prophylactic Oral Antibiotics in Two-Stage Exchange (POET) trial, has demonstrated that 90 days (3 months) of extended oral antibiotic prophylaxis following the reimplantation stage of a two-stage exchange arthroplasty significantly reduces the rate of reinfection compared to patients who receive only standard immediate postoperative IV antibiotics. Lifelong suppression is reserved for retained implants in medically unfit patients.

Question 2138

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following intraoperative factors is most strongly associated with the failure of a Debridement, Antibiotics, and Implant Retention (DAIR) procedure for an acute periprosthetic joint infection of a total knee arthroplasty?

. Failure to exchange the modular polyethylene liner
. Use of pulsatile lavage rather than bulb syringe irrigation
. Initiation of symptoms 10 days prior to presentation
. A synovial fluid WBC count > 50,000 cells/µL
. The use of regional anesthesia instead of general anesthesia

Correct Answer & Explanation

. Failure to exchange the modular polyethylene liner

Explanation

In a DAIR procedure, retention of the modular components (such as failing to exchange the polyethylene liner in a TKA) is a well-established, independent risk factor for failure. The modular interfaces harbor biofilm that cannot be adequately debrided unless the components are disassembled and exchanged. Therefore, exchanging the modular liner and thoroughly cleaning the baseplate is a critical step in maximizing the success of a DAIR.

Question 2139

Topic: 3. Adult Reconstruction (Hip & Knee)

A 79-year-old male with severe cardiopulmonary comorbidities presents with a chronic periprosthetic joint infection of his total hip arthroplasty. The organism is identified as a multi-drug susceptible Staphylococcus epidermidis. The implant is radiographically well-fixed, and the patient is deemed medically unfit for revision surgery. He is placed on chronic suppressive oral antibiotic therapy. What is the primary clinical endpoint of this treatment strategy?

. Complete eradication of the bacterial biofilm from the implant surface
. Sterilization of the periprosthetic soft tissues and synovial fluid
. Control of local symptoms and prevention of systemic sepsis or implant loosening
. Reversal of local osteolysis to promote secondary bone ingrowth
. Prevention of horizontal gene transfer leading to MRSA conversion

Correct Answer & Explanation

. Control of local symptoms and prevention of systemic sepsis or implant loosening

Explanation

Chronic suppressive antibiotic therapy is a palliative strategy used when curative surgery (like a 2-stage exchange) is contraindicated due to unacceptable surgical risk. The goal of suppressive therapy is NOT the eradication of the infection or biofilm, which is biologically impossible without removing the hardware. Rather, the goal is to control clinical symptoms (pain, swelling), prevent systemic dissemination (sepsis), and halt progressive periprosthetic osteolysis and implant loosening.

Question 2140

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a culture-negative PJI is found to have acid-fast bacilli on a specialized synovial fluid smear. Cultures eventually grow Mycobacterium fortuitum. Which of the following statements most accurately characterizes this infection?

. It is a highly destructive fungus requiring Amphotericin B
. It is a rapid-growing atypical mycobacterium that generally necessitates a two-stage exchange and prolonged multidrug therapy
. It is a fastidious gram-negative rod successfully treated with a single 6-week course of oral Ciprofloxacin
. It is universally sensitive to first-line anti-tuberculosis drugs such as Isoniazid and Pyrazinamide
. It presents exclusively in patients with advanced HIV/AIDS and CD4 counts < 50

Correct Answer & Explanation

. It is a rapid-growing atypical mycobacterium that generally necessitates a two-stage exchange and prolonged multidrug therapy

Explanation

Mycobacterium fortuitum is a non-tuberculous, 'rapid-growing' mycobacterium. Despite being termed 'rapid-growing' (colonies appear in < 7 days on specialized media, unlike M. tuberculosis which takes weeks), it is notoriously difficult to eradicate from prosthetic joints. It typically requires removal of the implants (two-stage exchange) combined with prolonged, tailored multidrug antimicrobial therapy. It is generally resistant to standard first-line anti-TB drugs like Isoniazid and Pyrazinamide, and can occur in immunocompetent hosts.

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