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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 307 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 6121

Topic: 3. Adult Reconstruction (Hip & Knee)

In evaluating a randomized controlled trial comparing two total knee arthroplasty designs, the 'power' of the study represents which of the following statistical concepts?

. The probability of rejecting the null hypothesis when it is true
. The probability of accepting the null hypothesis when it is true
. 1 minus the probability of a Type I error
. 1 minus the probability of a Type II error
. The pre-determined alpha level

Correct Answer & Explanation

. 1 minus the probability of a Type II error

Explanation

Statistical power is the probability that a study will correctly reject a false null hypothesis (detecting a true difference). It is mathematically defined as 1 minus beta (the probability of a Type II error).

Question 6122

Topic: 3. Adult Reconstruction (Hip & Knee)
In the mechanism of aseptic loosening following total hip arthroplasty, which specific cell type orchestrates the initial inflammatory response to submicron ultra-high-molecular-weight polyethylene (UHMWPE) wear debris?
. Osteoblasts
. T-lymphocytes
. Macrophages
. Osteoclasts
. Fibroblasts

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages are the primary effector cells in periprosthetic osteolysis. They phagocytose polyethylene particles and release pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6), which ultimately stimulate osteoclastic bone resorption.

Question 6123

Topic: 3. Adult Reconstruction (Hip & Knee)

A new diagnostic test for periprosthetic joint infection correctly identifies 90 out of 100 infected joints and correctly rules out infection in 80 out of 100 non-infected joints. What is the sensitivity of this new diagnostic test?

. 10%
. 20%
. 80%
. 90%
. 100%

Correct Answer & Explanation

. 90%

Explanation

Sensitivity is the true positive rate, calculated as True Positives divided by the sum of True Positives and False Negatives. In this scenario, 90 / (90 + 10) equals 90%.

Question 6124

Topic: 3. Adult Reconstruction (Hip & Knee)

Which type of wear mechanism is most commonly responsible for the generation of submicron polyethylene particles that subsequently lead to macrophage-induced osteolysis in total hip arthroplasty?

. Abrasive wear
. Adhesive wear
. Third-body wear
. Fretting wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear occurs when micro-junctions form between opposing bearing surfaces and tear off, generating millions of submicron polyethylene particles. These particles are highly reactive and are phagocytosed by macrophages, initiating the osteolytic cascade.

Question 6125

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the introduction of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear and secondary osteolysis. However, the manufacturing process of highly cross-linking the polyethylene results in an important mechanical trade-off. What is the primary negative mechanical consequence of this process?

. Decreased fatigue strength and ductility
. Decreased adhesive wear resistance
. Increased oxidative degradation
. Increased abrasive wear
. Increased yield strength

Correct Answer & Explanation

. Decreased fatigue strength and ductility

Explanation

Highly cross-linking polyethylene significantly improves its resistance to adhesive and abrasive wear, dramatically lowering volumetric wear rates. However, the cross-linking process (and the subsequent remelting/annealing used to eliminate free radicals and prevent oxidation) fundamentally alters the polymer's mechanical properties, leading to decreased fatigue strength, reduced ductility (elongation to failure), and lower ultimate tensile strength. This makes HXLPE more susceptible to catastrophic failure/fracture, especially in thin liners or high-stress designs.

Question 6126

Topic: 3. Adult Reconstruction (Hip & Knee)
A 55-year-old male with a metal-on-metal total hip arthroplasty presents with groin pain and an expanding soft tissue mass. Aspiration yields sterile, cloudy fluid. Histology of the periprosthetic tissue reveals an Aseptic Lymphocyte-dominated Vasculitis-Associated Lesion (ALVAL). This pathological response is driven by which immunologic mechanism?
. Type I hypersensitivity
. Type II hypersensitivity
. Type III hypersensitivity
. Type IV hypersensitivity
. IgE-mediated mast cell degranulation

Correct Answer & Explanation

. Type IV hypersensitivity

Explanation

Adverse local tissue reactions (ALTR) or ALVAL in metal-on-metal implants are driven by a delayed hypersensitivity response to metal ions (specifically cobalt and chromium). This is a Type IV (cell-mediated) hypersensitivity reaction. It is characterized by perivascular lymphocytic infiltration, tissue necrosis, and the formation of pseudotumors, distinct from the innate macrophage-driven response seen in typical polyethylene wear osteolysis.

Question 6127

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon notes that the knee is well-balanced in extension but unacceptably tight in 90 degrees of flexion. Which of the following technical adjustments is the most appropriate next step to balance the knee?

. Decrease the anteroposterior (AP) size of the femoral component
. Recess or release the medial collateral ligament
. Increase the thickness of the polyethylene insert
. Resect more distal femur
. Increase the anteroposterior (AP) size of the femoral component

Correct Answer & Explanation

. Decrease the anteroposterior (AP) size of the femoral component

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without altering the extension gap. Decreasing the femoral component AP size, using anterior referencing to take more posterior condylar bone, effectively increases the flexion gap.

Question 6128

Topic: 3. Adult Reconstruction (Hip & Knee)

Highly cross-linked polyethylene (HXLPE) was developed to reduce wear rates in total hip arthroplasty. However, the cross-linking process introduces free radicals that can lead to long-term oxidation and material degradation. Which of the following manufacturing steps is used to eliminate or neutralize these free radicals?

. Gamma irradiation in an oxygen-rich environment
. Ethylene oxide gas sterilization
. Addition of Vitamin E or post-irradiation melt annealing
. Increasing the overall thickness of the polyethylene liner
. Reducing the molecular weight of the polyethylene chains

Correct Answer & Explanation

. Addition of Vitamin E or post-irradiation melt annealing

Explanation

Free radicals generated during the gamma irradiation process of HXLPE are eliminated either by thermal treatment (remelting or annealing) or by the addition of antioxidants such as Vitamin E. This prevents oxidative degradation while maintaining wear resistance.

Question 6129

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the Musculoskeletal Infection Society (MSIS) and International Consensus Meeting (ICM) criteria, which of the following is considered a "major" criterion, sufficient on its own to definitively diagnose a periprosthetic joint infection (PJI)?

. Elevated serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
. Positive leukocyte esterase on a synovial fluid strip
. Elevated synovial fluid polymorphonuclear (PMN) percentage
. Purulence observed in the affected joint during surgery
. A sinus tract directly communicating with the joint prosthesis

Correct Answer & Explanation

. A sinus tract directly communicating with the joint prosthesis

Explanation

The major criteria for diagnosing PJI include a sinus tract communicating with the joint or the isolation of the exact same organism from two separate tissue/fluid cultures. The other options listed are minor criteria.

Question 6130

Topic: 3. Adult Reconstruction (Hip & Knee)
Metal hypersensitivity after joint arthroplasty is most commonly mediated by which type of immune reaction?
. Type I (IgE-mediated)
. Type II (Cytotoxic)
. Type III (Immune complex)
. Type IV (Cell-mediated, delayed-type)
. Type V (Autoantibody-mediated)

Correct Answer & Explanation

. Type IV (Cell-mediated, delayed-type)

Explanation

Metal hypersensitivity is a Type IV, cell-mediated (delayed-type) hypersensitivity reaction. T-lymphocytes become sensitized to metal ions acting as haptens, subsequently releasing cytokines that recruit macrophages and cause tissue damage.

Question 6131

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) primarily reduces which type of wear compared to conventional polyethylene?

. Adhesive wear
. Abrasive wear
. Fatigue wear
. Third-body wear
. Corrosive wear

Correct Answer & Explanation

. Fatigue wear

Explanation

Highly cross-linked polyethylene significantly reduces adhesive wear at the articular bearing surface. However, cross-linking decreases the material's mechanical toughness, making it theoretically more susceptible to fatigue wear.

Question 6132

Topic: 3. Adult Reconstruction (Hip & Knee)

In a posterior approach to the hip for total hip arthroplasty, the "safe zone" for acetabular cup placement to minimize dislocation risk is traditionally described by Lewinnek. What are these target parameters?

. 40 degrees abduction, 15 degrees anteversion
. 30 degrees abduction, 10 degrees anteversion
. 50 degrees abduction, 25 degrees anteversion
. 45 degrees abduction, 0 degrees anteversion
. 35 degrees abduction, 30 degrees anteversion

Correct Answer & Explanation

. 40 degrees abduction, 15 degrees anteversion

Explanation

The Lewinnek safe zone for acetabular component positioning is historically defined as 40 degrees (± 10 degrees) of abduction (inclination) and 15 degrees (± 10 degrees) of anteversion. Deviation from this zone increases the risk of postoperative impingement and dislocation.

Question 6133

Topic: 3. Adult Reconstruction (Hip & Knee)

Following uncemented total hip arthroplasty with an extensively porous-coated cobalt-chromium femoral stem, a patient develops proximal femoral cortical osteopenia. Which biomechanical principle best explains this phenomenon?

. Wolff's Law
. Hooke's Law
. Young's Modulus
. Poisson's ratio
. Galvanic corrosion

Correct Answer & Explanation

. Wolff's Law

Explanation

Wolff's Law states that bone remodels in response to mechanical stress. A stiff femoral stem bears most of the load (stress shielding), bypassing the proximal femur and leading to adaptive bone resorption and osteopenia.

Question 6134

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male with a 5-year-old total hip arthroplasty presents with worsening hip pain. Aspiration of the hip joint yields fluid with a white blood cell count of 45,000 cells/mcL and 95% polymorphonuclear leukocytes. Culture grows Staphylococcus epidermidis. What is the most widely accepted definitive surgical management?

. One-stage revision arthroplasty
. Two-stage revision arthroplasty with an antibiotic spacer
. Suppressive oral antibiotics alone
. Irrigation and debridement with modular head/liner exchange
. Arthrodesis of the hip

Correct Answer & Explanation

. Two-stage revision arthroplasty with an antibiotic spacer

Explanation

The patient meets MSIS criteria for a chronic periprosthetic joint infection. In North America, the gold standard treatment for a chronic PJI (usually > 4 weeks post-op) is a two-stage revision arthroplasty utilizing an antibiotic-eluting spacer.

Question 6135

Topic: 3. Adult Reconstruction (Hip & Knee)
In total joint arthroplasty, the wear of ultra-high-molecular-weight polyethylene (UHMWPE) components generates particles that can lead to osteolysis. Which cell type is primarily responsible for phagocytosing these wear particles and initiating the inflammatory cascade?
. Osteoblasts
. Fibroblasts
. Macrophages
. Polymorphonuclear leukocytes
. T-lymphocytes

Correct Answer & Explanation

. Macrophages

Explanation

UHMWPE wear debris particles are primarily phagocytosed by tissue macrophages. This activates the macrophages to release pro-inflammatory cytokines such as TNF-α, IL-1, and IL-6, which subsequently stimulate osteoclast-mediated bone resorption (osteolysis), leading to aseptic loosening.

Question 6136

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the American College of Chest Physicians (ACCP) evidence-based clinical practice guidelines, what is the minimum recommended duration for pharmacologic thromboprophylaxis following a standard-risk total hip arthroplasty?

. 1 to 3 days
. 5 to 7 days
. 10 to 14 days
. 21 to 28 days
. 35 to 42 days

Correct Answer & Explanation

. 10 to 14 days

Explanation

The ACCP guidelines recommend pharmacologic thromboprophylaxis for a minimum of 10 to 14 days following major orthopedic surgery (total hip arthroplasty, total knee arthroplasty, and hip fracture surgery). Extended prophylaxis for up to 35 days is suggested for higher-risk patients.

Question 6137

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old patient who underwent an uncomplicated primary total hip arthroplasty (THA) 8 years ago presents with a first-time posterior dislocation. The patient denies trauma. Radiographs show eccentric position of the femoral head within the acetabular shell. What is the most likely primary cause of this late dislocation?

. Acetabular component aseptic loosening
. Polyethylene wear leading to loss of offset and component impingement
. Missed periprosthetic joint infection
. Subsidence of the femoral stem
. Neuromuscular decline due to aging

Correct Answer & Explanation

. Polyethylene wear leading to loss of offset and component impingement

Explanation

Dislocation occurring more than 5 years after primary THA is considered a 'late' dislocation. The most common cause is polyethylene wear, which leads to eccentric seating of the femoral head in the liner. This causes a decrease in offset, laxity of the soft tissues, and early impingement of the neck on the acetabular rim, collectively predisposing the hip to dislocation.

Question 6138

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old man presents with persistent groin pain one year after a primary total hip arthroplasty utilizing a metal-on-metal bearing surface. Joint aspiration yields no microbial growth, but serum metal ion levels are markedly elevated. Which histological finding is most characteristic of his presumed condition?

. Extensive neutrophilic infiltrate
. Abundant polymethylmethacrylate debris
. Perivascular lymphocytic infiltrate
. Mononucleated giant cells with foreign bodies
. Fibroblast proliferation with absent macrophages

Correct Answer & Explanation

. Perivascular lymphocytic infiltrate

Explanation

Adverse local tissue reaction (ALTR) or Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL) is characteristic of metal-on-metal implant failure. Histologically, it presents as a severe, delayed-type hypersensitivity reaction marked by a perivascular lymphocytic infiltrate.

Question 6139

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, which of the following combinations of bearing surfaces exhibits the lowest volumetric wear rate in vitro?

. Cobalt-chrome on highly cross-linked polyethylene
. Ceramic on standard ultra-high molecular weight polyethylene
. Ceramic on ceramic
. Cobalt-chrome on cobalt-chrome
. Oxinium on highly cross-linked polyethylene

Correct Answer & Explanation

. Ceramic on ceramic

Explanation

Ceramic-on-ceramic bearing surfaces are exceptionally hard, scratch-resistant, and hydrophilic, leading to the lowest volumetric wear rates in vitro (often <0.1 mm^3/million cycles). This is vastly superior to metal-on-polyethylene and even highly cross-linked polyethylene pairings.

Question 6140

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

. Elevated serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
. Elevated synovial fluid white blood cell (WBC) count
. Positive histological analysis showing >5 neutrophils per high-power field
. A sinus tract communicating with the prosthesis
. A single positive intraoperative tissue culture

Correct Answer & Explanation

. A sinus tract communicating with the prosthesis

Explanation

The MSIS major criteria for definitive PJI are: 1) A sinus tract communicating with the prosthesis, OR 2) A pathogen isolated by culture from at least two separate tissue or fluid samples obtained from the affected joint. Elevated inflammatory markers, elevated synovial WBCs, and a single positive culture are all considered minor criteria.

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