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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 127 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 2521

Topic: Total Knee Arthroplasty (TKA)

During the final trial phase of a total knee arthroplasty (TKA), the surgeon observes lateral subluxation of the patella during knee flexion. The 'no thumb' test shows the patella popping out of the trochlear groove laterally. Which of the following iatrogenic component malrotations is the most likely cause of this abnormal patellar tracking?

. Internal rotation of the femoral component
. External rotation of the femoral component
. External rotation of the tibial component
. Medialization of the femoral component
. Lateralization of the tibial component

Correct Answer & Explanation

. Internal rotation of the femoral component

Explanation

Lateral patellar maltracking in TKA is often related to malrotation of the components. Internal rotation of the femoral component effectively medializes the trochlear groove relative to the extensor mechanism, increasing the Q-angle and causing the patella to track laterally. Internal rotation of the tibial component (relative to the tibial tubercle) essentially lateralizes the tibial tubercle, also increasing the Q-angle and causing lateral tracking. Therefore, internal rotation of the femoral component is correct.

Question 2522

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following is the recognized threshold of linear wear rate for conventional polyethylene in total hip arthroplasty above which the risk of pelvic osteolysis significantly increases?

. 0.05 mm/year
. 0.1 mm/year
. 0.2 mm/year
. 0.5 mm/year
. 1.0 mm/year

Correct Answer & Explanation

. 0.1 mm/year

Explanation

Osteolysis risk in THA is strongly correlated with polyethylene wear. A linear wear rate greater than 0.1 mm/year is the widely accepted threshold for the development of clinically significant periprosthetic osteolysis. Highly cross-linked polyethylene was developed to reduce wear rates below this critical threshold.

Question 2523

Topic: 3. Adult Reconstruction (Hip & Knee)

In total knee arthroplasty, excessive internal rotation of the femoral component will most likely lead to which of the following complications?

. Patellar maltracking and lateral patellar tilt
. Tightness in flexion laterally
. Increased Q-angle with medial patellar subluxation
. Extension gap instability
. Premature polyethylene wear on the medial condyle

Correct Answer & Explanation

. Patellar maltracking and lateral patellar tilt

Explanation

Internal rotation of the femoral component in TKA medializes the trochlear groove, increasing the Q-angle and leading to lateral patellar maltracking, lateral patellar tilt, and potential lateral patellar dislocation. It also creates a tight medial flexion gap and loose lateral flexion gap.

Question 2524

Topic: 3. Adult Reconstruction (Hip & Knee)
A 60-year-old male who underwent a metal-on-metal total hip arthroplasty 8 years ago presents with groin pain and a palpable mass. Serum cobalt and chromium levels are elevated. MRI with MARS sequencing shows a cystic pseudotumor. Which type of hypersensitivity reaction is considered the primary mechanism for Adverse Local Tissue Reaction (ALTR) in metal-on-metal hips?
. Type I (IgE mediated)
. Type II (Cytotoxic)
. Type III (Immune complex)
. Type IV (Delayed-type hypersensitivity)
. Type V (Stimulatory)

Correct Answer & Explanation

. Type IV (Delayed-type hypersensitivity)

Explanation

ALTR or ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion) in metal-on-metal hip arthroplasty is primarily driven by a Type IV delayed-type hypersensitivity reaction to metal wear debris (specifically cobalt and chromium ions). This is a T-cell mediated response.

Question 2525

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, after making all initial bony cuts, the surgeon uses spacer blocks and notes that the joint is excessively tight in flexion but well-balanced in extension. Which of the following is the most appropriate intraoperative adjustment to balance the knee?

. Resect 2 mm more of the distal femur
. Upsize the femoral component to increase the anteroposterior dimension
. Downsize the femoral component and augment the posterior condyles
. Downsize the femoral component and translate it slightly anteriorly
. Resect 2 mm more of the proximal tibia

Correct Answer & Explanation

. Downsize the femoral component and translate it slightly anteriorly

Explanation

A tight flexion gap with a balanced extension gap indicates that the posterior condylar offset is too large. Downsizing the femoral component decreases its anteroposterior dimension, effectively reducing posterior condylar thickness and opening the flexion gap. It often must be translated anteriorly to avoid notching the anterior femur.

Question 2526

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following best describes the primary biomechanical mechanism by which Zirconia-toughened Alumina (ZTA) ceramics resist crack propagation in modern total hip arthroplasty?

. Cross-linking of the polymer chains under thermal stress
. A stress-induced phase transformation from a tetragonal to a monoclinic crystal structure
. A stress-induced phase transformation from a monoclinic to a tetragonal crystal structure
. The addition of vitamin E to prevent oxidative degradation at the grain boundaries
. Metallic lattice deformation and strain hardening at the crack tip

Correct Answer & Explanation

. A stress-induced phase transformation from a tetragonal to a monoclinic crystal structure

Explanation

Zirconia in ZTA undergoes a phase transformation from a metastable tetragonal phase to a stable monoclinic phase when subjected to local stress (such as an advancing crack tip). This transformation is accompanied by a localized volume expansion (approximately 4%), which induces compressive stresses that close the crack tip and stop propagation. This is known as transformation toughening.

Question 2527

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized (PS) total knee arthroplasty, the surgeon evaluates the gaps and notices that the knee is tight in flexion but balanced in extension. Assuming an anterior referencing system was used, which of the following intraoperative adjustments is the most appropriate next step to balance the knee?

. Release the posterior cruciate ligament
. Upsize the femoral component
. Downsize the femoral component
. Resect more distal femur
. Thicken the polyethylene insert

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion and balanced in extension indicates an unequal gap where the flexion gap is smaller than the extension gap. To increase the flexion gap without affecting the extension gap, the posterior condylar offset must be reduced. In an anterior referencing system, downsizing the femoral component decreases the posterior condylar dimension, thus effectively opening the flexion gap. Resecting more distal femur would increase the extension gap. Releasing the PCL is not applicable here as a PS knee implies the PCL is already resected.

Question 2528

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male presents with a 'squeaking' sound coming from his total hip arthroplasty, which was performed 3 years ago. He is otherwise asymptomatic and radiographs are pristine. Which of the following bearing surfaces is most strongly associated with this phenomenon?

. Metal-on-polyethylene
. Ceramic-on-ceramic
. Metal-on-metal
. Ceramic-on-polyethylene
. Oxinium-on-polyethylene

Correct Answer & Explanation

. Ceramic-on-ceramic

Explanation

Squeaking is a known complication almost exclusively associated with ceramic-on-ceramic (CoC) bearing surfaces in total hip arthroplasty. It is reported in up to 1-10% of cases and is thought to be multifactorial (e.g., stripe wear, edge loading from component malposition, or third-body debris). As long as the patient is asymptomatic, no surgical intervention is required.

Question 2529

Topic: 3. Adult Reconstruction (Hip & Knee)

A 60-year-old female presents with groin pain and swelling three years following a metal-on-metal total hip arthroplasty. Aspiration is negative for infection, but MRI demonstrates a cystic pseudotumor. Histological examination of the periprosthetic tissue is most likely to reveal which of the following?

. Sheets of neutrophils and bacteria
. Birefringent polymeric wear debris under polarized light
. Diffuse perivascular lymphocytic infiltrates
. Abundant giant cells containing polyethylene particles
. Monosodium urate crystals

Correct Answer & Explanation

. Diffuse perivascular lymphocytic infiltrates

Explanation

The clinical presentation is highly indicative of an adverse local tissue reaction (ALTR) or aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL), commonly seen with metal-on-metal implants. Histologically, ALVAL is characterized by a delayed type IV hypersensitivity reaction, demonstrating prominent diffuse perivascular lymphocytic infiltrates (predominantly T-cells and macrophages). Polyethylene debris produces macrophage-mediated osteolysis without massive lymphocytic infiltrates.

Question 2530

Topic: 3. Adult Reconstruction (Hip & Knee)

Based on classic indications for a medial unicompartmental knee arthroplasty (UKA), which of the following is considered an absolute contraindication to the procedure?

. Patient age greater than 60 years
. A 10-degree flexion contracture
. Inflammatory arthropathy (e.g., Rheumatoid arthritis)
. Isolated medial compartment bone-on-bone osteoarthritis
. Grade II chondromalacia of the patellofemoral joint

Correct Answer & Explanation

. Inflammatory arthropathy (e.g., Rheumatoid arthritis)

Explanation

Inflammatory arthropathy (such as rheumatoid arthritis) is considered an absolute contraindication to unicompartmental knee arthroplasty (UKA) because the systemic, pan-articular nature of the disease will eventually destroy the unresurfaced compartments. Classic Kozinn and Scott indications include non-inflammatory OA, intact ACL, correctable deformity (<15 deg flexion contracture, <5-10 deg varus/valgus), and no significant anterior knee pain.

Question 2531

Topic: 3. Adult Reconstruction (Hip & Knee)

Highly cross-linked polyethylene (HXLPE) is utilized in total hip arthroplasty to reduce volumetric wear. The manufacturing process involves irradiation followed by thermal treatment (remelting or annealing). What is the primary purpose of this thermal treatment step?

. To increase the ultimate tensile strength of the polyethylene
. To eliminate free radicals and improve oxidation resistance
. To increase the crystallinity of the polyethylene
. To directly increase the cross-link density
. To sterilize the component prior to packaging

Correct Answer & Explanation

. To eliminate free radicals and improve oxidation resistance

Explanation

Irradiation generates free radicals that cross-link the polyethylene chains (improving wear resistance) but leaves residual free radicals. Thermal treatment (remelting or annealing) extinguishes these residual free radicals, which prevents subsequent in vivo oxidation and embrittlement.

Question 2532

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, trial components are placed. The knee is found to be perfectly balanced and stable in full extension, but it is excessively tight in flexion, preventing range of motion beyond 70 degrees. Which of the following is the most appropriate intraoperative step to balance the knee?

. Decrease the distal femoral resection
. Increase the distal femoral resection
. Downsize the femoral component using a posterior referencing guide
. Increase the posterior slope of the tibial cut
. Release the posterior capsule

Correct Answer & Explanation

. Increase the posterior slope of the tibial cut

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without affecting the extension gap. This can be achieved by increasing the posterior slope of the tibial cut, or by using a smaller femoral component with an anterior referencing guide (which moves the posterior condyles anteriorly). Downsizing with a posterior referencing guide does not increase the flexion gap. Since this is a PS knee, releasing the PCL is not an option as it is already resected.

Question 2533

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with groin pain 5 years after a primary total hip arthroplasty. Serum metal ion testing reveals elevated cobalt levels that are disproportionately higher than chromium levels. Radiographs demonstrate well-fixed components. MRI with metal artifact reduction sequence (MARS) shows a solid pseudotumor surrounding the joint. What is the most likely cause of failure in this patient?

. Polyethylene wear and osteolysis
. Corrosion at the modular head-neck junction (Trunnionosis)
. Low-grade periprosthetic joint infection
. Ceramic liner fracture
. Iliopsoas impingement

Correct Answer & Explanation

. Corrosion at the modular head-neck junction (Trunnionosis)

Explanation

Trunnionosis (mechanically assisted crevice corrosion) occurs at the modular head-neck junction of total hip implants. It classically presents with elevated cobalt levels (often disproportionately higher than chromium) and adverse local tissue reactions (ALVAL/pseudotumor formation), even when the bearing surfaces are intact and components are well-fixed.

Question 2534

Topic: 3. Adult Reconstruction (Hip & Knee)

Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty to reduce wear rates. What is the primary molecular mechanism by which irradiation improves the wear resistance of polyethylene?

. Decreasing the crystallinity of the polymer matrix
. Increasing the generation of unreacted free radicals
. Decreasing plastic deformation under sustained load
. Increasing the number of covalent bonds between adjacent polymer chains
. Integrating Vitamin E directly into the polymer backbone

Correct Answer & Explanation

. Increasing the number of covalent bonds between adjacent polymer chains

Explanation

Cross-linking uses gamma or electron-beam irradiation to cleave carbon-hydrogen bonds, creating free radicals that subsequently combine to form covalent bonds between adjacent polyethylene chains. This dense three-dimensional network significantly reduces abrasive and adhesive wear, although it decreases certain mechanical properties such as ductility and fatigue crack propagation resistance.

Question 2535

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary Total Knee Arthroplasty (TKA), placing the femoral component in excessive internal rotation relative to the transepicondylar axis will most likely lead to which of the following patellofemoral complications?

. Patellar maltracking and lateral subluxation
. Increased flexion gap on the medial side
. Patella baja (infera)
. Medial compartment tightness primarily in extension
. Anterior knee pain due to medial patellar subluxation

Correct Answer & Explanation

. Patellar maltracking and lateral subluxation

Explanation

Internal rotation of the femoral component relative to the surgical transepicondylar axis shifts the trochlear groove medially. This effectively increases the Q-angle and relative lateral pull on the patella, resulting in lateral patellar maltracking, tilt, lateral subluxation, and an increased risk of patellar component wear or failure.

Question 2536

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon evaluates the gaps after initial bone cuts. The knee is balanced and symmetric in extension, but it is tight symmetrically in flexion. Which of the following is the most appropriate next step to balance the knee?

. Recut the distal femur to remove more bone
. Downsize the femoral component and use a thicker tibial polyethylene insert
. Increase the posterior slope of the tibial cut
. Release the posterior cruciate ligament or decrease the anterior-posterior size of the femoral component
. Release the posterior capsule

Correct Answer & Explanation

. Release the posterior cruciate ligament or decrease the anterior-posterior size of the femoral component

Explanation

A knee that is tight in flexion but symmetric and balanced in extension requires an increase in the flexion gap without altering the extension gap. This can be achieved by downsizing the femoral component (which removes more posterior condylar bone) or by releasing the posterior cruciate ligament (PCL) if a cruciate-retaining technique is being used. Recutting the distal femur would affect the extension gap, and increasing the posterior slope of the tibia alters both gaps but risks altering joint biomechanics excessively.

Question 2537

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with groin pain and a palpable mass three years after undergoing a primary total hip arthroplasty using a metal-on-polyethylene bearing with a large-diameter cobalt-chromium femoral head. Aspiration is negative for infection, but MRI shows a fluid collection with a thick pseudocapsule. Blood tests reveal elevated serum cobalt levels with normal chromium levels. Which of the following is the most likely etiology of his symptoms?

. Bearing surface wear
. Trunnionosis (mechanically assisted crevice corrosion)
. Periprosthetic joint infection
. Aseptic loosening of the acetabular component
. Hypersensitivity to polyethylene debris

Correct Answer & Explanation

. Trunnionosis (mechanically assisted crevice corrosion)

Explanation

Elevated cobalt levels out of proportion to chromium levels, combined with an adverse local tissue reaction (ALTR) in a metal-on-polyethylene total hip arthroplasty, strongly suggests trunnionosis. This is mechanically assisted crevice corrosion occurring at the modular head-neck junction. Bearing surface wear in MoP would not cause significantly elevated serum metal ions.

Question 2538

Topic: Total Knee Arthroplasty (TKA)

During a cruciate-retaining total knee arthroplasty (CR-TKA), the surgeon uses spacer blocks to check gap balancing. The extension gap is perfectly balanced, but the knee is significantly too tight in flexion. Which of the following is the most appropriate next step to balance the knee?

. Resect more distal femur
. Downsize the femoral component to resect more posterior condyle
. Decrease the posterior tibial slope
. Upsize the femoral component
. Release the superficial medial collateral ligament

Correct Answer & Explanation

. Downsize the femoral component to resect more posterior condyle

Explanation

If a knee is tight in flexion but balanced in extension, the flexion gap must be increased without affecting the extension gap. Options to specifically increase the flexion gap include downsizing the femoral component (which resects more posterior femoral condylar bone), increasing the posterior tibial slope, or recessing the PCL. Resecting more distal femur would inappropriately increase the extension gap.

Question 2539

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old male who underwent a total hip arthroplasty with a ceramic-on-ceramic (CoC) bearing two years ago presents with a loud, audible 'squeaking' sound coming from his hip during certain movements. Which of the following is considered the primary risk factor for this squeaking?

. Use of an undersized uncemented femoral stem
. Component malposition leading to edge loading and stripe wear
. Unrecognized subacute periprosthetic joint infection
. Formation of a large intra-articular metal-induced pseudotumor
. Subclinical dislocation of the femoral head

Correct Answer & Explanation

. Component malposition leading to edge loading and stripe wear

Explanation

Squeaking in ceramic-on-ceramic (CoC) total hip arthroplasty is overwhelmingly associated with acetabular component malposition (e.g., excessively vertical or retroverted cup). This malposition leads to loss of the fluid lubrication film, edge loading of the femoral head against the ceramic rim, and subsequent 'stripe wear', which generates the acoustic squeak.

Question 2540

Topic: 3. Adult Reconstruction (Hip & Knee)

When comparing bearing surfaces in total hip arthroplasty, which of the following combinations demonstrates the lowest volumetric wear rate in laboratory simulations?

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

Correct Answer & Explanation

. Ceramic on ceramic

Explanation

Ceramic-on-ceramic bearings exhibit the lowest volumetric wear rates of all available bearing couples (less than 1 cubic millimeter per year). However, they carry unique risks such as squeaking and catastrophic component fracture.

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