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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 308 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 6141

Topic: 3. Adult Reconstruction (Hip & Knee)

Low molecular weight heparin (LMWH) is frequently used for venous thromboembolism (VTE) prophylaxis following total joint arthroplasty. What is the primary molecular target through which LMWH exerts its anticoagulant effect?

. Direct inhibition of Thrombin (Factor IIa)
. Inhibition of Vitamin K epoxide reductase
. Antithrombin-mediated inhibition primarily of Factor Xa
. Direct inhibition of Factor Xa
. Activation of Plasminogen

Correct Answer & Explanation

. Antithrombin-mediated inhibition primarily of Factor Xa

Explanation

LMWH binds to antithrombin, inducing a conformational change that dramatically accelerates its ability to inactivate coagulation factors, primarily Factor Xa. Unlike unfractionated heparin, LMWH chains are too short to efficiently bridge antithrombin to thrombin (Factor IIa), giving it a much higher anti-Xa to anti-IIa activity ratio.

Question 6142

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient presents with an acutely swollen and painful prosthetic knee 4 years after index arthroplasty. Aspiration yields cloudy fluid. Which of the following synovial fluid analysis results most strongly suggests chronic prosthetic joint infection (PJI)?

. WBC 1,500 cells/mcL with 40% PMNs
. WBC 3,500 cells/mcL with 75% PMNs
. WBC 25,000 cells/mcL with 85% PMNs
. Presence of positively birefringent rhomboid crystals
. Glucose level equal to serum glucose

Correct Answer & Explanation

. WBC 25,000 cells/mcL with 85% PMNs

Explanation

In chronic prosthetic joint infections (more than 4-6 weeks out), the threshold for diagnosing PJI is generally lower than native joints (often >3,000 cells/mcL and >80% PMNs depending on criteria). A WBC of 25,000 with 85% PMNs is highly suggestive of PJI. Native septic arthritis typically requires a WBC > 50,000.

Question 6143

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates. However, what is a primary mechanical trade-off or disadvantage of increasing the degree of cross-linking in polyethylene?

. Increased susceptibility to rapid oxidative degradation in vivo without remelting
. Decreased ultimate tensile strength and fracture toughness
. Increased generation of very large-sized polyethylene wear debris
. Decreased biocompatibility leading to faster, more aggressive osteolysis
. Increased coefficient of friction when articulating against ceramic heads

Correct Answer & Explanation

. Decreased ultimate tensile strength and fracture toughness

Explanation

Highly cross-linking polyethylene decreases wear but negatively impacts its mechanical properties, including decreased ultimate tensile strength, fatigue strength, and fracture toughness. This can theoretically increase the risk of component fracture, particularly in thin liners or constrained designs.

Question 6144

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient presents with aseptic loosening of a total hip arthroplasty 15 years after the index surgery. Radiographs show extensive periprosthetic radiolucencies. The biological cascade leading to this osteolysis is primarily initiated by which of the following?

. T-cell mediated delayed hypersensitivity
. B-cell antibody production against metal ions
. Macrophage phagocytosis of polyethylene particulate debris
. Direct toxic effect of polymethylmethacrylate (PMMA) on osteoblasts
. Complement cascade activation by titanium wear particles

Correct Answer & Explanation

. Macrophage phagocytosis of polyethylene particulate debris

Explanation

Aseptic loosening in total joint arthroplasty is primarily driven by macrophage phagocytosis of sub-micron polyethylene wear debris. This activates macrophages to release inflammatory cytokines (IL-1, IL-6, TNF-alpha), which subsequently stimulate osteoclastic bone resorption.

Question 6145

Topic: 3. Adult Reconstruction (Hip & Knee)

The scaphoid receives its primary intraosseous blood supply from branches of the radial artery. At which precise anatomical location do the predominant nutrient vessels enter the scaphoid?

. Volar aspect of the proximal pole
. Dorsal ridge at the scaphoid waist
. Volar tubercle
. Dorsal aspect of the proximal pole
. Through the scapholunate interosseous ligament

Correct Answer & Explanation

. Dorsal aspect of the proximal pole

Explanation

The primary blood supply to the scaphoid enters through the dorsal ridge near the waist and flows in a retrograde fashion to the proximal pole. This retrograde blood flow is why proximal pole fractures have a high rate of avascular necrosis.

Question 6146

Topic: 3. Adult Reconstruction (Hip & Knee)

Increasing the femoral head offset during a total hip arthroplasty primarily has which of the following biomechanical effects on the hip joint?

. Increases the joint reaction force across the acetabulum
. Decreases the moment arm of the abductor musculature
. Increases the mechanical advantage and tension of the abductors
. Decreases the impingement-free range of motion
. Shifts the center of rotation medially

Correct Answer & Explanation

. Increases the mechanical advantage and tension of the abductors

Explanation

Increasing femoral offset directly increases the moment arm of the abductor muscles. This provides a greater mechanical advantage, restoring abductor tension and reducing the overall force required by the abductors to stabilize the pelvis. As a result, the net joint reaction force across the hip is decreased, and impingement-free motion is generally improved.

Question 6147

Topic: 3. Adult Reconstruction (Hip & Knee)

A biomechanical study evaluates the effect of a new total hip arthroplasty implant design on hip joint forces. Moving the center of rotation of the acetabulum medially and inferiorly accomplishes which of the following?

. Increases the joint reactive force
. Decreases the abductor moment arm
. Increases the abductor moment arm
. Increases the body weight lever arm
. Decreases the strain on the anterior cruciate ligament

Correct Answer & Explanation

. Increases the joint reactive force

Explanation

Moving the hip's center of rotation medially decreases the lever arm of body weight, while moving it inferiorly (assuming offset is maintained) effectively increases the abductor moment arm. Both changes optimize biomechanics by reducing the overall joint reactive force.

Question 6148

Topic: 3. Adult Reconstruction (Hip & Knee)
A patient is prescribed low-molecular-weight heparin (LMWH) for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the primary molecular target of this medication?
. Direct thrombin (Factor IIa) inhibition
. Vitamin K epoxide reductase inhibition
. Potentiation of antithrombin III primarily against Factor Xa
. Binding to the glycoprotein IIb/IIIa receptor
. Activation of tissue plasminogen activator

Correct Answer & Explanation

. Potentiation of antithrombin III primarily against Factor Xa

Explanation

LMWH exerts its anticoagulant effect by binding to antithrombin III, causing a conformational change that primarily accelerates its inhibition of Factor Xa. It has significantly less inhibitory effect on thrombin (Factor IIa) compared to unfractionated heparin.

Question 6149

Topic: Total Hip Arthroplasty (THA)

Fretting and crevice corrosion are most commonly observed at which specific interface in modern total hip arthroplasty?

. Between the acetabular shell and the polyethylene liner
. At the modular head-neck taper junction
. Between the femoral stem and the bone cement
. At the articulating surface of a ceramic-on-ceramic bearing
. Between the acetabular shell and the host bone

Correct Answer & Explanation

. At the modular head-neck taper junction

Explanation

Mechanically assisted crevice corrosion (MACC), also known as trunnionosis, occurs at modular junctions such as the head-neck taper of a femoral stem. Micro-motion (fretting) at this interface disrupts the protective passivation layer, leading to corrosion and adverse local tissue reactions.

Question 6150

Topic: 3. Adult Reconstruction (Hip & Knee)

In Total Hip Arthroplasty (THA), which of the following bearing surface combinations offers the lowest volumetric wear rate?

. Cobalt-chrome on highly cross-linked polyethylene
. Ceramic on highly cross-linked polyethylene
. Ceramic on ceramic
. Cobalt-chrome on conventional polyethylene
. Oxinium on highly cross-linked polyethylene

Correct Answer & Explanation

. Ceramic on ceramic

Explanation

Ceramic-on-ceramic bearing surfaces provide the lowest volumetric wear rate among all THA bearing couples. However, they carry specific risks, including squeaking and catastrophic ceramic fracture.

Question 6151

Topic: 3. Adult Reconstruction (Hip & Knee)

Aseptic loosening following total hip arthroplasty is primarily mediated by a biologic cascade initiated by particulate wear debris. Which size range of polyethylene particles is most biologically active in stimulating macrophage-induced osteolysis?

. Less than 0.1 micrometers
. 0.1 to 1.0 micrometers
. 1.0 to 10 micrometers
. 10 to 50 micrometers
. Greater than 50 micrometers

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Polyethylene particles in the 0.1 to 1.0 micrometer range are easily phagocytosed by macrophages. This phagocytosis triggers the release of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6) that activate osteoclasts and lead to periprosthetic osteolysis.

Question 6152

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old female presents with severe wrist pain after a fall. Radiographs show a displaced scaphoid waist fracture. The proximal pole is at highest risk for avascular necrosis due to a retrograde blood supply entering primarily through which surface?

. Volar surface
. Dorsal ridge
. Proximal articular surface
. Distal pole palmar surface
. Radial styloid articulation

Correct Answer & Explanation

. Dorsal ridge

Explanation

The scaphoid receives 70-80% of its blood supply from branches of the radial artery that enter distally at the dorsal ridge and course retrogradely. This places proximal pole fractures at a distinctively high risk for avascular necrosis.

Question 6153

Topic: Total Hip Arthroplasty (THA)

A patient undergoes a posterior-approach total hip arthroplasty. Postoperatively, the patient experiences recurrent posterior dislocations. Which of the following component malpositions is most likely responsible?

. Excessive anteversion of the acetabular cup
. Excessive retroversion of the acetabular cup
. Excessive valgus of the femoral stem
. Insufficient femoral offset
. Excessive anterior tilt of the pelvis

Correct Answer & Explanation

. Excessive retroversion of the acetabular cup

Explanation

Excessive retroversion of the acetabular component in a THA is a primary cause of posterior instability and dislocation. Proper anteversion (usually 15-20 degrees) and inclination (40-45 degrees) are crucial for dynamic stability.

Question 6154

Topic: 3. Adult Reconstruction (Hip & Knee)
In total hip arthroplasty, the biologic response to ultra-high molecular weight polyethylene (UHMWPE) wear debris is primarily mediated by the activation of which cell type?
. Osteoblasts
. Macrophages
. T-lymphocytes
. Neutrophils
. Mast cells

Correct Answer & Explanation

. Macrophages

Explanation

Polyethylene wear particles are phagocytosed by macrophages, which subsequently release pro-inflammatory cytokines such as TNF-alpha and IL-1. This cascade leads to osteoclast activation and periprosthetic osteolysis.

Question 6155

Topic: 3. Adult Reconstruction (Hip & Knee)
What is the primary biological mechanism driving particulate-induced osteolysis (aseptic loosening) in total joint arthroplasty?
. Direct mechanical wear of bone by the implant surface
. Macrophage phagocytosis of wear debris releasing TNF-alpha and IL-1
. Osteoblast apoptosis triggered by fretting metal ions
. T-cell mediated delayed hypersensitivity response
. Complement cascade activation by PMMA cement particles

Correct Answer & Explanation

. Macrophage phagocytosis of wear debris releasing TNF-alpha and IL-1

Explanation

Aseptic loosening is primarily driven by macrophages that phagocytose wear debris, notably ultra-high molecular weight polyethylene (UHMWPE). This triggers the release of pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6), which subsequently stimulate aggressive osteoclastic bone resorption.

Question 6156

Topic: 3. Adult Reconstruction (Hip & Knee)
In the setting of aseptic loosening of a total hip arthroplasty, the generation of ultra-high-molecular-weight polyethylene (UHMWPE) wear debris leads to periprosthetic osteolysis. Which cell type is primarily responsible for phagocytosing these particles and initiating the inflammatory cascade?
. Osteoblast
. Osteoclast
. Fibroblast
. Macrophage
. T-lymphocyte

Correct Answer & Explanation

. Macrophage

Explanation

Macrophages phagocytose polyethylene wear particles (specifically those 0.1 to 1.0 micrometers in size) and subsequently release inflammatory cytokines like TNF-alpha, IL-1, and IL-6. This cascade stimulates osteoclast differentiation and ultimately leads to periprosthetic osteolysis.

Question 6157

Topic: 3. Adult Reconstruction (Hip & Knee)

After a 90-minute complex total knee arthroplasty, the pneumatic tourniquet is finally deflated. Which of the following systemic physiological changes is most likely to occur immediately following deflation?

. Increased central venous pressure
. Increased systemic pH
. Increased core body temperature
. Decreased end-tidal carbon dioxide
. Decreased systemic blood pressure and increased end-tidal carbon dioxide

Correct Answer & Explanation

. Decreased systemic blood pressure and increased end-tidal carbon dioxide

Explanation

Tourniquet deflation releases ischemic and acidotic blood metabolites back into the systemic circulation. This transiently decreases systemic blood pressure, decreases systemic pH (acidosis), decreases core temperature, and sharply increases end-tidal CO2 as accumulated CO2 is exhaled.

Question 6158

Topic: Total Knee Arthroplasty (TKA)

In an orthopedic clinical trial comparing two types of total knee implants, the researchers want to ensure they have an 80% probability of detecting a true clinical difference if one actually exists. This probability represents which of the following statistical concepts?

. Type I error (alpha)
. Type II error (beta)
. Statistical power (1 - beta)
. Positive predictive value
. Confidence interval

Correct Answer & Explanation

. Statistical power (1 - beta)

Explanation

Statistical power is defined as 1 - beta, which is the probability of correctly rejecting the null hypothesis when it is false (i.e., finding a true difference). A power of 0.80 (80%) is generally considered the standard benchmark for a well-designed clinical trial.

Question 6159

Topic: 3. Adult Reconstruction (Hip & Knee)
Aseptic loosening secondary to periprosthetic osteolysis is a leading cause of late failure in total joint arthroplasty. Ultra-high-molecular-weight polyethylene (UHMWPE) wear debris is phagocytosed by macrophages, leading to the secretion of which primary cytokine that drives osteoclast activation?
. Interleukin-1 (IL-1)
. Interleukin-4 (IL-4)
. Interleukin-10 (IL-10)
. Transforming growth factor-beta (TGF-beta)
. Interferon-gamma (IFN-gamma)

Correct Answer & Explanation

. Interleukin-1 (IL-1)

Explanation

Phagocytosis of UHMWPE wear debris by macrophages leads to the secretion of pro-inflammatory cytokines, most notably IL-1, IL-6, and TNF-alpha. These cytokines upregulate RANKL expression, driving osteoclastogenesis and subsequent periprosthetic osteolysis.

Question 6160

Topic: 3. Adult Reconstruction (Hip & Knee)

Trunnionosis in total hip arthroplasty (THA) leads to adverse local tissue reactions (ALTR) due to mechanically assisted crevice corrosion. Which combination of THA components presents the highest risk for severe trunnionosis?

. Small ceramic head on a titanium alloy stem
. Large ceramic head on a cobalt-chromium stem
. Small cobalt-chromium head on a cobalt-chromium stem
. Large cobalt-chromium head on a titanium alloy stem
. Oxinium head on a titanium alloy stem

Correct Answer & Explanation

. Large cobalt-chromium head on a titanium alloy stem

Explanation

Trunnionosis is the wear and corrosion at the head-neck junction. Risk factors include larger head size (which increases the lever arm and frictional torque at the trunnion), and mixed-metal combinations (galvanic corrosion). A large cobalt-chromium (CoCr) head on a titanium (Ti) stem carries the highest risk for significant trunnionosis.

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