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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 233 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 4641

Topic: 3. Adult Reconstruction (Hip & Knee)
A 30-year-old male sustains a high-energy motor vehicle collision resulting in an open talar neck fracture with complete extrusion of the talar body. What is the expected rate of avascular necrosis (AVN) for this Hawkins Type III injury?
. 0-10%
. 20-30%
. 40-50%
. 75-100%
. 15-25%

Correct Answer & Explanation

. 75-100%

Explanation

Hawkins Type III talar neck fractures involve complete displacement of the talar body from both the subtalar and tibiotalar joints. The risk of avascular necrosis in Type III fractures is historically reported as 75-100%.

Question 4642

Topic: 3. Adult Reconstruction (Hip & Knee)

Which bearing surface combination in Total Hip Arthroplasty (THA) is uniquely associated with the phenomenon of 'stripe wear'?

. Ceramic-on-polyethylene
. Metal-on-metal
. Ceramic-on-ceramic
. Metal-on-polyethylene
. Oxidized zirconium-on-polyethylene

Correct Answer & Explanation

. Ceramic-on-ceramic

Explanation

Stripe wear is uniquely characteristic of ceramic-on-ceramic articulations. It occurs as a result of microseparation of the joint during the swing phase of gait, causing the edge of the socket to contact the femoral head, leading to a linear stripe of wear.

Question 4643

Topic: 3. Adult Reconstruction (Hip & Knee)

Patellar clunk syndrome, characterized by a painful catch or 'clunk' as the knee is extended from a flexed position, is most commonly associated with which type of total knee arthroplasty (TKA) design?

. Cruciate-retaining (CR)
. Posterior-stabilized (PS)
. Constrained non-hinged
. Rotating hinged
. Unicompartmental knee arthroplasty (UKA)

Correct Answer & Explanation

. Posterior-stabilized (PS)

Explanation

Patellar clunk syndrome is most classically associated with posterior-stabilized (PS) TKA designs. It is caused by the formation of a fibrous nodule at the superior pole of the patella that drops into the intercondylar box of the femoral component in deep flexion, snapping out as the knee extends.

Question 4644

Topic: 3. Adult Reconstruction (Hip & Knee)
Periprosthetic osteolysis in total hip arthroplasty is primarily mediated by the activation of which of the following cell types in response to ultra-high-molecular-weight polyethylene (UHMWPE) wear debris?
. Osteoblasts
. Chondrocytes
. Macrophages
. T-lymphocytes
. Neutrophils

Correct Answer & Explanation

. Macrophages

Explanation

UHMWPE wear debris particles are phagocytosed by tissue macrophages. These activated macrophages then release inflammatory cytokines like TNF-alpha and IL-1, stimulating osteoclastic bone resorption.

Question 4645

Topic: 3. Adult Reconstruction (Hip & Knee)
Hyaline articular cartilage provides a low-friction, load-bearing surface for synovial joints. Which of the following collagen types makes up the vast majority of the collagenous framework in normal adult articular cartilage?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type II

Explanation

Type II collagen constitutes 90 to 95 percent of the collagen found in normal articular cartilage. It provides the crucial tensile strength and serves as the structural framework to trap water-retaining proteoglycans.

Question 4646

Topic: 3. Adult Reconstruction (Hip & Knee)

During total hip arthroplasty using a standard posterior approach, what is the primary kinematic mechanism that most often precipitates a posterior dislocation in the early postoperative period?

. Excessive hip extension and external rotation
. Excessive hip flexion, adduction, and internal rotation
. Excessive hip abduction and external rotation
. Pure hip extension combined with abduction
. Pure hip internal rotation in full extension

Correct Answer & Explanation

. Excessive hip flexion, adduction, and internal rotation

Explanation

Following a posterior approach to the hip, the posterior soft tissue envelope is compromised. The classic position of instability leading to posterior dislocation is a combination of hip flexion, adduction, and internal rotation.

Question 4647

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following bearing surface combinations in total hip arthroplasty has the lowest documented volumetric wear rate?

. Metal-on-highly crosslinked polyethylene
. Ceramic-on-highly crosslinked polyethylene
. Ceramic-on-ceramic
. Metal-on-conventional polyethylene
. Metal-on-metal

Correct Answer & Explanation

. Ceramic-on-ceramic

Explanation

Ceramic-on-ceramic bearing surfaces exhibit the lowest volumetric wear rates of all modern bearing combinations. However, they carry unique risks, including squeaking and catastrophic ceramic fracture.

Question 4648

Topic: 3. Adult Reconstruction (Hip & Knee)
In the setting of total knee arthroplasty, which of the following mechanisms is primarily responsible for the catastrophic delamination of ultra-high-molecular-weight polyethylene (UHMWPE)?
. Adhesive wear
. Abrasive wear
. Third-body wear
. Subsurface fatigue wear
. Corrosive wear

Correct Answer & Explanation

. Subsurface fatigue wear

Explanation

Subsurface fatigue wear results from cyclic loading that creates peak shear stresses below the polyethylene surface. This leads to crack propagation and catastrophic delamination, a process historically accelerated by oxidation from gamma irradiation in air.

Question 4649

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, utilizing a larger diameter femoral head (e.g., 36 mm vs. 28 mm) utilizing conventional non-highly cross-linked polyethylene has which of the following effects on wear mechanics?

. Decreases both volumetric and linear wear.
. Increases volumetric wear and decreases linear wear.
. Decreases volumetric wear and increases linear wear.
. Increases both volumetric and linear wear.
. Has no effect on volumetric wear but increases linear wear.

Correct Answer & Explanation

. Increases volumetric wear and decreases linear wear.

Explanation

For conventional (non-highly cross-linked) polyethylene, increasing the size of the femoral head decreases the linear wear (due to increased surface area distributing the load), but it increases the volumetric wear (because the sliding distance per step is greater). This principle is described by Archard's Law. Highly cross-linked polyethylene drastically reduces wear, allowing larger heads to be used to decrease dislocation risk without significant osteolysis from volumetric wear.

Question 4650

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the Musculoskeletal Infection Society (MSIS) criteria, an elevated level of Alpha-defensin in synovial fluid is utilized as a diagnostic marker for periprosthetic joint infection (PJI). Alpha-defensin is primarily secreted by which of the following cell types in response to pathogens?

. Osteoblasts
. Macrophages
. T-lymphocytes
. Neutrophils
. Fibroblasts

Correct Answer & Explanation

. Neutrophils

Explanation

Alpha-defensin is a highly specific antimicrobial peptide that is released by activated neutrophils in response to the presence of pathogens. The synovial fluid alpha-defensin test has been validated as a highly sensitive and specific minor criterion (or standalone test in recent algorithms) for diagnosing periprosthetic joint infection (PJI).

Question 4651

Topic: 3. Adult Reconstruction (Hip & Knee)

A synovial fluid aspirate is obtained to evaluate a painful total knee arthroplasty. The alpha-defensin immunoassay returns positive. In the context of periprosthetic joint infection, which of the following cells is the primary source of alpha-defensin?

. Synovial fibroblasts
. Macrophages
. Neutrophils
. Osteoblasts
. T-lymphocytes

Correct Answer & Explanation

. Neutrophils

Explanation

Alpha-defensin is an antimicrobial peptide released predominantly by activated neutrophils in response to infection. It is a highly sensitive and specific biomarker for diagnosing periprosthetic joint infections.

Question 4652

Topic: Total Knee Arthroplasty (TKA)

A 68-year-old female presents with anterior knee pain and a painful 'clunk' when extending her knee from a flexed position, one year after a total knee arthroplasty (TKA). This complication is most classically associated with which TKA design?

. Cruciate-retaining
. Posterior-stabilized
. Mobile-bearing
. Hinged
. Unicompartmental

Correct Answer & Explanation

. Posterior-stabilized

Explanation

Patellar clunk syndrome is caused by a fibrous nodule forming at the superior pole of the patella that catches in the intercondylar notch of the femoral component. It is classically associated with posterior-stabilized TKA designs.

Question 4653

Topic: Total Knee Arthroplasty (TKA)

During a primary total knee arthroplasty (TKA), the surgeon places the trial components. The evaluation reveals a symmetric tight extension gap and a symmetric, well-balanced flexion gap. Which of the following is the most appropriate surgical step to correct this mismatch?

. Resect additional distal femur
. Resect additional proximal tibia
. Upsize the femoral component
. Downsize the femoral component
. Release the posterior cruciate ligament

Correct Answer & Explanation

. Resect additional distal femur

Explanation

In gap balancing for TKA, a tight extension gap with a normal flexion gap indicates that the distal femur is 'too long' (under-resected). The correct intervention is to resect additional distal femur. Resecting additional tibia would loosen both the extension and flexion gaps.

Question 4654

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon opts to use a high-offset femoral stem to lateralize the greater trochanter. According to standard hip biomechanics, how does this modification primarily affect the abductor mechanism and the joint reaction force?

. Increases the abductor moment arm and increases joint reaction forces
. Decreases the abductor moment arm and increases joint reaction forces
. Increases the abductor moment arm and decreases joint reaction forces
. Decreases the abductor moment arm and decreases joint reaction forces
. Does not alter the moment arm but decreases joint reaction forces

Correct Answer & Explanation

. Increases the abductor moment arm and decreases joint reaction forces

Explanation

Increasing the femoral offset lateralizes the greater trochanter, which increases the abductor moment arm. With a longer lever arm, the abductor muscles must generate less force to balance the pelvis during single-leg stance. Consequently, the overall joint reaction force across the hip is decreased, reducing wear on the bearing surfaces.

Question 4655

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with severe groin pain 5 years after undergoing a total hip arthroplasty with a large-diameter metal-on-polyethylene bearing. Aspiration is negative for infection. Serum cobalt levels are significantly elevated, while chromium levels are normal. MRI reveals a large solid pseudotumor. Which of the following is the most likely source of the elevated metal ions?

. Bearing surface wear
. Impingement of the femoral neck on the acetabular cup
. Taper corrosion at the head-neck junction
. Galvanic corrosion between the stem and a proximal cable
. Delamination of the polyethylene liner

Correct Answer & Explanation

. Taper corrosion at the head-neck junction

Explanation

Elevated serum cobalt levels with normal or only mildly elevated chromium levels in the setting of a metal head on a polyethylene liner indicate mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper junction. Unlike metal-on-metal bearings where both Co and Cr are elevated, trunnionosis typically presents with a disproportionately high Co/Cr ratio.

Question 4656

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female undergoes a total hip arthroplasty via a posterior approach. Postoperatively, she is unable to actively dorsiflex her ankle or extend her great toe, and has numbness over the dorsum of her foot. Which division of the sciatic nerve was most likely injured, and what is its anatomic position relative to the main nerve bundle?

. Tibial division; located medial and anterior
. Tibial division; located lateral and posterior
. Peroneal division; located medial and anterior
. Peroneal division; located lateral and posterior
. Femoral nerve; located anteriorly

Correct Answer & Explanation

. Peroneal division; located lateral and posterior

Explanation

The patient has a foot drop, indicating injury to the peroneal (fibular) division of the sciatic nerve. The peroneal division is more susceptible to injury during hip surgery because it is located laterally and posteriorly, with less protective connective tissue.

Question 4657

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active female undergoes a total hip arthroplasty with a ceramic-on-ceramic bearing surface. Two years later, she complains of a loud squeaking noise from her hip with deep flexion and pivoting. What is the most likely biomechanical cause of this phenomenon?

. Third-body wear from retained bone cement
. Trunnionosis at the head-neck junction
. Galvanic corrosion between the shell and liner
. Stripe wear due to edge loading and microseparation
. Polyethylene delamination from oxidation

Correct Answer & Explanation

. Stripe wear due to edge loading and microseparation

Explanation

Squeaking is a specific complication associated with ceramic-on-ceramic total hip arthroplasties. It is primarily caused by edge loading and microseparation of the femoral head from the liner, which leads to 'stripe wear' on the ceramic head and alters the fluid lubrication film.

Question 4658

Topic: 3. Adult Reconstruction (Hip & Knee)
To reduce polyethylene wear in total hip arthroplasty, manufacturers utilize highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE). While cross-linking successfully decreases abrasive and adhesive and abrasive and adhesive wear, it negatively alters which mechanical property of the polyethylene?
. It increases the elastic modulus significantly
. It decreases the coefficient of friction
. It increases resistance to oxidation
. It decreases ultimate tensile strength and fatigue crack propagation resistance
. It decreases the melting temperature making it unsuitable for sterilization

Correct Answer & Explanation

. It decreases ultimate tensile strength and fatigue crack propagation resistance

Explanation

Irradiation to create highly cross-linked polyethylene significantly reduces adhesive and abrasive wear. However, it compromises the material's mechanical properties, specifically reducing its ultimate tensile strength, fatigue resistance, and fracture toughness.

Question 4659

Topic: Total Hip Arthroplasty (THA)

A 65-year-old man presents with groin pain 5 years after a metal-on-polyethylene total hip arthroplasty. Aspiration yields fluid with numerous macrophages containing metallic debris. Which of the following implant factors most significantly increases the risk of mechanically assisted crevice corrosion (trunnionosis)?

. Increased femoral head size
. Decreased femoral offset
. Use of a ceramic femoral head
. Shorter femoral neck length
. Use of a highly cross-linked polyethylene liner

Correct Answer & Explanation

. Increased femoral head size

Explanation

Increased femoral head size increases the frictional torque and toggling forces at the head-neck junction (trunnion). This excess mechanical stress disrupts the passivation layer of the metal, leading to mechanically assisted crevice corrosion.

Question 4660

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old woman undergoes a posterior-approach total hip arthroplasty. Six weeks postoperatively, she dislocates her hip posteriorly while bending forward to tie her shoes in a low chair. On reduction, the components are well-fixed. Which technical error during cup placement most likely predisposed her to this specific dislocation?

. Excessive anteversion
. Inadequate anteversion (retroversion)
. Excessive abduction (inclination)
. Inadequate offset
. Excessive limb lengthening

Correct Answer & Explanation

. Inadequate anteversion (retroversion)

Explanation

Posterior dislocation typically occurs when the hip is flexed, adducted, and internally rotated. Inadequate anteversion (or relative retroversion) of the acetabular component fails to cover the anterior femoral head during flexion, leading to posterior impingement and subsequent posterior dislocation. Excessive anteversion predisposes to anterior dislocation.

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