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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 128 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 2541

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, trial reduction reveals the knee is tight in flexion but well-balanced and stable in extension. What is the most appropriate surgical step to correct this mismatch?

. Resect more distal femur
. Downsize the femoral component
. Increase the thickness of the tibial polyethylene insert
. Upsize the femoral component
. Release the posterior capsule

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion but balanced in extension has an isolated narrow flexion gap. Downsizing the femoral component decreases the anteroposterior (AP) dimension of the femur, which selectively opens the flexion gap without altering the extension gap.

Question 2542

Topic: 3. Adult Reconstruction (Hip & Knee)

In fully porous-coated cementless femoral stems used in total hip arthroplasty, rigid biologic fixation depends on bone ingrowth. What is the optimal pore size range for the porous coating to promote maximum osteoconduction and rigid fixation?

. 10 to 50 micrometers
. 50 to 400 micrometers
. 500 to 800 micrometers
. 1 to 2 millimeters
. 3 to 4 millimeters

Correct Answer & Explanation

. 50 to 400 micrometers

Explanation

The optimal pore size for reliable bone ingrowth in cementless arthroplasty components is strictly between 50 and 400 micrometers. Pores smaller than 50 micrometers typically result in fibrous tissue ingrowth rather than true bone, while pores larger than 400 micrometers can compromise the structural integrity of the coating and fail to provide adequate initial mechanical stability.

Question 2543

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, the trial components are placed and joint kinematics are assessed. The knee is perfectly balanced in extension, but the flexion gap is excessively tight. Which of the following adjustments is most appropriate to correct this mismatch?

. Thicken the tibial polyethylene insert
. Resect more distal femur
. Increase the posterior slope of the tibial cut
. Upsize the femoral component
. Translate the femoral component posteriorly

Correct Answer & Explanation

. Increase the posterior slope of the tibial cut

Explanation

A knee that is balanced in extension but tight in flexion requires an intervention that specifically addresses the flexion gap without altering the extension gap. Increasing the posterior slope of the tibial cut removes more posterior tibial bone, effectively opening the flexion gap while having a negligible effect on the extension gap. Upsizing the femoral component or translating it posteriorly would further tighten the flexion gap. Resecting more distal femur would loosen the extension gap.

Question 2544

Topic: 3. Adult Reconstruction (Hip & Knee)

A 60-year-old woman presents with persistent groin pain 5 years following a primary total hip arthroplasty. Her implant is a metal-on-polyethylene bearing with a 36-mm cobalt-chromium head on a titanium stem. Radiographs show no loosening, but an MRI with MARS sequencing reveals a large cystic pseudotumor. Blood tests reveal significantly elevated serum cobalt levels with normal serum chromium levels. Which of the following is the most likely etiology?

. Polyethylene wear debris
. Acetabular component loosening
. Trunnionosis (mechanically assisted crevice corrosion)
. Deep prosthetic joint infection
. Metal hypersensitivity (Type IV)

Correct Answer & Explanation

. Trunnionosis (mechanically assisted crevice corrosion)

Explanation

The patient has Adverse Local Tissue Reaction (ALTR) secondary to trunnionosis (corrosion at the head-neck taper junction). This is classic in metal-on-polyethylene THAs (especially with large modular heads) where mechanically assisted crevice corrosion occurs at the trunnion. The hallmark laboratory finding is a disproportionately elevated serum cobalt level compared to chromium.

Question 2545

Topic: 3. Adult Reconstruction (Hip & Knee)

During a mechanically aligned posterior-stabilized total knee arthroplasty, using a measured resection technique, trial components are placed. The knee is perfectly balanced in full extension but is excessively tight in 90 degrees of flexion, preventing the surgeon from completing the flexion arc. Which of the following surgical adjustments is the most appropriate next step to achieve a balanced gap?

. Recut the distal femur to resect more bone
. Decrease the size of the femoral component
. Increase the size of the femoral component
. Release the posterior capsule
. Increase the thickness of the polyethylene insert

Correct Answer & Explanation

. Decrease the size of the femoral component

Explanation

A knee that is balanced in extension but tight in flexion requires an increase in the flexion gap without altering the extension gap. Decreasing the size of the femoral component (using anterior referencing) results in a thicker posterior condylar cut (resecting more posterior femoral bone), which effectively enlarges the flexion gap without changing the distal femoral cut (which controls the extension gap). Recutting the distal femur would affect the extension gap. Releasing the posterior capsule affects the extension gap primarily.

Question 2546

Topic: 3. Adult Reconstruction (Hip & Knee)

Highly cross-linked polyethylene (HXLPE) used in total hip arthroplasty reduces wear primarily by which of the following mechanisms?

. Decreasing free radicals through gamma irradiation in air
. Increasing the crystalline content of the polyethylene
. Decreasing the molecular weight of the polymer chains
. Decreasing the number of amorphous regions while increasing cross-linking between polymer chains
. Eliminating the need for terminal sterilization

Correct Answer & Explanation

. Decreasing the number of amorphous regions while increasing cross-linking between polymer chains

Explanation

HXLPE reduces wear by creating cross-links between polymer chains in the amorphous regions, restricting chain mobility and thereby increasing wear resistance. Free radicals are decreased by remelting or annealing, not irradiation in air (which causes oxidation).

Question 2547

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient who underwent a posterior-stabilized total knee arthroplasty 6 months ago presents with a painful catching sensation and a palpable 'clunk' as the knee extends from 45 degrees of flexion to full extension. What is the most common anatomic etiology of this complication?

. Overstuffing of the patellofemoral joint
. A prominent fibrotic nodule at the superior pole of the patella
. Impingement of the patellar component on the tibial post
. Lateral retinacular tightness causing patellar maltracking
. Undersized femoral component causing mid-flexion instability

Correct Answer & Explanation

. A prominent fibrotic nodule at the superior pole of the patella

Explanation

Patellar clunk syndrome occurs primarily in posterior-stabilized TKA designs. It is caused by the development of a fibrotic nodule in the suprapatellar synovium, just proximal to the superior pole of the patella. As the knee extends, this nodule catches in the intercondylar box of the femoral component and then 'clunks' out.

Question 2548

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient presents with groin pain 5 years after receiving a metal-on-polyethylene total hip arthroplasty utilizing a modular titanium femoral stem and a cobalt-chromium femoral head. Aspiration shows aseptic dark fluid. The most likely cause of failure is adverse local tissue reaction (ALTR) secondary to mechanically assisted crevice corrosion. Where is this corrosion occurring?

. Between the acetabular shell and the polyethylene liner
. At the femoral head-neck taper junction
. Between the femoral stem and the cement mantle
. Between the acetabular shell and the host bone
. At the articular interface of the head and liner

Correct Answer & Explanation

. At the femoral head-neck taper junction

Explanation

Trunnionosis is wear/corrosion at the modular junction between the femoral head and the stem neck (the trunnion). Mechanically assisted crevice corrosion at this titanium/cobalt-chromium interface can release metal ions leading to an adverse local tissue reaction (ALTR) or pseudotumor, even in metal-on-polyethylene bearings.

Question 2549

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty, after making the standard bone cuts, the surgeon evaluates the gaps. The extension gap is perfectly balanced, but the flexion gap is unacceptably tight. Which of the following adjustments will best correct this imbalance?

. Resect more distal femur
. Downsize the femoral component
. Increase the posterior slope of the tibial cut
. Release the posterior capsule
. Translate the femoral component anteriorly

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A tight flexion gap with a balanced extension gap can be corrected by downsizing the femoral component. This utilizes a smaller anteroposterior dimension and thus increases the flexion gap without affecting the extension gap. Releasing the posterior capsule or resecting more distal femur would affect the extension gap.

Question 2550

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old active male undergoes a total hip arthroplasty using a ceramic-on-ceramic bearing surface. At his 2-year follow-up, he complains of an audible squeaking sound during certain activities. Which of the following factors is most strongly associated with this complication?

. Edge loading due to acetabular component malposition
. Femoral stem subsidence
. Excessive anteversion of the femoral stem
. Delayed infection with Cutibacterium acnes
. Allergic reaction to the ceramic debris

Correct Answer & Explanation

. Edge loading due to acetabular component malposition

Explanation

Squeaking in ceramic-on-ceramic total hip arthroplasty is multifactorial but is most strongly associated with component malposition, specifically leading to edge loading or micro-separation, which results in loss of fluid film lubrication and stripe wear on the femoral head.

Question 2551

Topic: Total Hip Arthroplasty (THA)

A 55-year-old active male underwent a ceramic-on-ceramic total hip arthroplasty 2 years ago. He complains of a new-onset squeaking noise from his hip during certain movements. Evaluation reveals proper component fixation. Which factor is most strongly associated with squeaking in ceramic-on-ceramic THA?

. Use of an un-cemented femoral stem
. Smaller femoral head diameter
. Stripe wear from edge loading due to component malposition
. High patient BMI
. Excessive femoral anteversion

Correct Answer & Explanation

. Stripe wear from edge loading due to component malposition

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly correlated with edge loading, which leads to localized stripe wear, fluid film disruption, and vibration. This is typically related to component malposition, particularly acetabular cup anteversion or inclination outside the safe zone, or microseparation during swing phase.

Question 2552

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection (PJI), which of the following is considered a major criterion, sufficient to definitively diagnose PJI?

. Elevated serum CRP > 10 mg/L and ESR > 30 mm/hr
. Synovial fluid white blood cell count > 3,000 cells/uL
. A single positive intraoperative tissue culture
. A sinus tract communicating with the joint
. Positive alpha-defensin test

Correct Answer & Explanation

. A sinus tract communicating with the joint

Explanation

The 2018 ICM criteria establish two major criteria that are definitively diagnostic for PJI: 1) A sinus tract communicating with the joint, or 2) Two positive periprosthetic cultures with phenotypically identical organisms. The other choices represent minor criteria used in the scoring algorithm.

Question 2553

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, trial reduction reveals the knee is tight in full extension but perfectly balanced and symmetric in 90 degrees of flexion. Which of the following is the most appropriate next step in management?

. Recut the proximal tibia with more posterior slope
. Release the posterior cruciate ligament
. Resect more distal femur
. Decrease the size of the femoral component
. Translate the femoral component anteriorly

Correct Answer & Explanation

. Resect more distal femur

Explanation

A knee that is tight in extension but balanced in flexion implies an extension gap that is too small compared to the flexion gap. Resecting more distal femur will enlarge the extension gap without affecting the flexion gap. Changing the tibial cut affects both gaps equally. Downsizing the femur increases the flexion gap.

Question 2554

Topic: 3. Adult Reconstruction (Hip & Knee)

In metal-on-polyethylene total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) was introduced to reduce wear. However, standard cross-linking involves irradiation that produces free radicals. How are these free radicals most commonly eliminated to prevent long-term oxidative degradation?

. Sterilization with ethylene oxide
. Adding cobalt-chromium particulate debris
. Melting or remelting the polyethylene
. Increasing the radiation dose to 10 Mrad
. Implanting the components in a vacuum environment

Correct Answer & Explanation

. Melting or remelting the polyethylene

Explanation

Irradiation of polyethylene causes cross-linking (improving wear resistance) but also creates free radicals (causing oxidative degradation and embrittlement over time). To eliminate these free radicals, the polyethylene undergoes a thermal treatment, typically either melting (heating above the melting point) or annealing (heating below the melting point). Melting eliminates all free radicals but slightly reduces mechanical strength.

Question 2555

Topic: 3. Adult Reconstruction (Hip & Knee)

In modern total hip arthroplasty, the adoption of highly cross-linked polyethylene (HXLPE) has significantly reduced the rate of osteolysis and aseptic loosening. However, the cross-linking process alters the material's properties. Which of the following mechanical properties is typically decreased as a direct result of increased cross-linking?

. Ultimate tensile strength
. Wear resistance
. Oxidation resistance
. Young's modulus
. Creep resistance

Correct Answer & Explanation

. Wear resistance

Explanation

The irradiation process used to highly cross-link polyethylene drastically improves its wear resistance. However, this comes at the expense of several mechanical properties, including a decrease in ultimate tensile strength, yield strength, ductility, and fracture toughness. Subsequent thermal treatments (remelting or annealing) are used to eliminate free radicals and improve oxidation resistance, but remelting can further decrease mechanical strength.

Question 2556

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection (PJI), which of the following is considered a 'Major Criterion' that is definitive for the diagnosis of PJI?

. Synovial fluid white blood cell (WBC) count > 3,000 cells/uL
. Synovial fluid polymorphonuclear (PMN) percentage > 80%
. Two positive periprosthetic tissue cultures with phenotypically identical organisms
. A positive leukocyte esterase strip test (++ or greater)
. Elevated synovial alpha-defensin level

Correct Answer & Explanation

. Two positive periprosthetic tissue cultures with phenotypically identical organisms

Explanation

Under the ICM criteria for PJI, there are two major criteria; the presence of either one is definitive for infection. These are: 1) A sinus tract communicating with the joint/prosthesis, or 2) Two positive periprosthetic tissue or fluid cultures growing the same organism. The other options (WBC count, PMN %, leukocyte esterase, alpha-defensin, CRP/ESR) are minor criteria that contribute points toward a diagnostic score.

Question 2557

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old female presents with a painful popping sensation in her knee 18 months following a primary posterior-stabilized total knee arthroplasty (TKA). The symptom occurs consistently as her knee extends from 45 degrees of flexion to full extension. She is diagnosed with 'patellar clunk syndrome.' What is the precise anatomical etiology of this phenomenon?

. A hypertrophic fibrous nodule on the deep surface of the quadriceps tendon catching in the femoral intercondylar box
. Dynamic subluxation of the extensor mechanism laterally due to an unreleased tight lateral retinaculum
. Impingement of the popliteus tendon on an oversized posterolateral femoral condyle
. Asymmetric polyethylene wear leading to sudden mediolateral translational instability
. An oversized femoral component causing severe overstuffing of the anterior compartment

Correct Answer & Explanation

. A hypertrophic fibrous nodule on the deep surface of the quadriceps tendon catching in the femoral intercondylar box

Explanation

Patellar clunk syndrome is a known complication specific to posterior-stabilized total knee arthroplasty designs. It is caused by the formation of a hypertrophic fibrosynovial nodule on the undersurface of the quadriceps tendon, just proximal to the superior pole of the patella. As the knee extends from a flexed position, this nodule becomes incarcerated in the intercondylar box of the femoral component, popping out with a painful 'clunk' as extension continues.

Question 2558

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following is the most unique potential complication associated with ceramic-on-ceramic total hip arthroplasty bearing surfaces compared to highly cross-linked polyethylene bearing surfaces?

. Trunnionosis at the head-neck taper
. Osteolysis secondary to massive particulate debris
. Audible squeaking during range of motion
. Delayed-type metal hypersensitivity (ALVAL)
. Accelerated stress shielding of the proximal femur

Correct Answer & Explanation

. Audible squeaking during range of motion

Explanation

Squeaking is a unique, specific complication of ceramic-on-ceramic (CoC) bearing surfaces, occurring in up to 10% of patients. It is often related to component malposition (e.g., edge loading), stripe wear, or micro-separation. Osteolysis is more common with conventional polyethylene, and ALVAL/trunnionosis is typically associated with metal-on-metal or modular metallic junctions.

Question 2559

Topic: Total Knee Arthroplasty (TKA)

During the trial phase of a total knee arthroplasty (TKA) using a gap balancing technique, the surgeon finds that the knee is excessively tight in flexion but perfectly balanced and stable in extension. Which of the following component or bony adjustments is the most appropriate next step?

. Release the posterior cruciate ligament (PCL), increase the posterior slope of the tibial cut, or downsize the femoral component
. Resect an additional 2 millimeters of the distal femur
. Upsize the femoral component to increase the anteroposterior diameter
. Insert a thicker tibial polyethylene insert
. Release the posterior capsule and strip the posterior femur

Correct Answer & Explanation

. Release the posterior cruciate ligament (PCL), increase the posterior slope of the tibial cut, or downsize the femoral component

Explanation

A knee that is tight in flexion but balanced in extension requires addressing the flexion gap without altering the extension gap. Options include decreasing the anteroposterior dimension of the femur (downsizing the femoral component), increasing the posterior tibial slope, or releasing the posterior cruciate ligament (if a CR knee is being used). Resecting more distal femur or releasing the posterior capsule would inappropriately loosen the extension gap.

Question 2560

Topic: 3. Adult Reconstruction (Hip & Knee)

An 80-year-old female sustains a periprosthetic femur fracture around her cemented total hip arthroplasty stem after a fall. Radiographs demonstrate a fracture around the tip of the stem. The stem appears subsided and loose, but there is excellent diaphyseal bone stock remaining. According to the Vancouver classification, what is the most appropriate definitive management?

. Open reduction and internal fixation with cerclage cables only
. Open reduction and internal fixation with a lateral locking plate and cables, retaining the stem
. Revision of the femoral stem to a long, fully porous-coated cementless stem
. Revision of the femoral stem to a long cemented stem
. Impaction bone grafting with a standard length stem

Correct Answer & Explanation

. Revision of the femoral stem to a long, fully porous-coated cementless stem

Explanation

This is a Vancouver B2 periprosthetic fracture (fracture around the stem, loose stem, good bone stock). The standard of care for a Vancouver B2 fracture is revision of the loose component to a long cementless stem that bypasses the fracture site by at least two cortical diameters.

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