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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 301 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 6001

Topic: 3. Adult Reconstruction (Hip & Knee)

According to current consensus guidelines, chronic suppressive antibiotic therapy for a periprosthetic joint infection is most appropriate for a patient meeting which of the following criteria?

. Acute postoperative infection within 2 weeks of surgery
. Unstable implant with severe bone loss
. Retained implant with a highly virulent organism (e.g., MRSA)
. Retained well-fixed implant in a medically compromised patient with a susceptible organism
. Patient with a chronically draining sinus tract

Correct Answer & Explanation

. Retained well-fixed implant in a medically compromised patient with a susceptible organism

Explanation

Chronic suppressive antibiotics are indicated for patients with a retained, well-fixed prosthesis who are unfit for revision surgery. The pathogen must be of low virulence, highly susceptible to an oral antibiotic, and there should be no loosening or draining sinus.

Question 6002

Topic: 3. Adult Reconstruction (Hip & Knee)

In a patient undergoing a primary total hip arthroplasty with a highly cross-linked polyethylene liner and a cobalt-chrome femoral head, which type of wear mechanism is predominantly responsible for the generation of submicron particulate debris?

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

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary mechanism of normal articulation wear in metal-on-polyethylene bearings. This microscopic transfer of material generates submicron particles that can be phagocytosed by macrophages, initiating the osteolysis cascade.

Question 6003

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female presents with persistent knee pain 14 months after a primary total knee arthroplasty (TKA). Radiographs show no obvious signs of component loosening. Which of the following is statistically the most common cause for revision TKA within the first 2 years after the index procedure?

. Aseptic loosening
. Periprosthetic joint infection
. Polyethylene wear and osteolysis
. Periprosthetic fracture
. Patellar maltracking

Correct Answer & Explanation

. Periprosthetic joint infection

Explanation

Periprosthetic joint infection is the most common reason for early revision (within the first 2 years) following total knee arthroplasty. Aseptic loosening and polyethylene wear are the most common causes for late revisions.

Question 6004

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male presents with a painful right total hip arthroplasty 3 years after the index procedure. Inflammatory markers are elevated, and hip aspiration reveals a synovial fluid white blood cell count of 45,000 cells/uL with 90% polymorphonuclear leukocytes. What is the most appropriate definitive management?

. One-stage exchange arthroplasty
. Two-stage exchange arthroplasty
. Debridement, antibiotics, and implant retention (DAIR)
. Chronic suppressive antibiotic therapy
. Hip disarticulation

Correct Answer & Explanation

. Two-stage exchange arthroplasty

Explanation

A chronic periprosthetic joint infection presenting years after the index procedure with high WBCs and PMNs is definitively treated with a two-stage exchange arthroplasty in North America. DAIR is reserved for acute postoperative or acute hematogenous infections with stable implants.

Question 6005

Topic: 3. Adult Reconstruction (Hip & Knee)

During trial reduction of a posterior-stabilized total knee arthroplasty, the knee is found to be tight in flexion but stable and well-balanced in extension. Which of the following adjustments is most appropriate to achieve a balanced gap?

. Resect more proximal tibia
. Decrease the posterior slope of the tibial cut
. Downsize the femoral component
. Release the posterior capsule
. Upsize the femoral component

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion but balanced in extension has a tight flexion gap. Downsizing the femoral component (which removes more posterior condylar bone) or increasing the posterior tibial slope will specifically enlarge the flexion gap without affecting the extension gap.

Question 6006

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old woman underwent a posterior-stabilized total knee arthroplasty (TKA) 8 months ago. She now complains of a painful catching sensation and an audible "clunk" when her knee extends from 40 degrees of flexion. What is the most likely etiology of her symptoms?

. Aseptic loosening of the tibial component
. Patellar clunk syndrome
. Polyethylene wear
. Pes anserine bursitis
. Popliteus tendon impingement

Correct Answer & Explanation

. Patellar clunk syndrome

Explanation

Patellar clunk syndrome is a known complication of posterior-stabilized TKA, characterized by a fibrotic nodule forming at the superior pole of the patella. As the knee extends, this nodule catches in the intercondylar box of the femoral component and pops out with an audible clunk.

Question 6007

Topic: 3. Adult Reconstruction (Hip & Knee)

The introduction of highly cross-linked polyethylene (HXLPE) in modern total hip arthroplasty has primarily reduced implant wear rates through which of the following mechanisms?

. Decreasing the crystallinity of the polymer matrix
. Increasing the oxidation potential of the material
. Limiting plastic deformation and molecular chain sliding
. Increasing the overall elasticity modulus of the bearing
. Enhancing fluid film lubrication between surfaces

Correct Answer & Explanation

. Limiting plastic deformation and molecular chain sliding

Explanation

Cross-linking of polyethylene is achieved via irradiation, which creates covalent bonds between adjacent polymer chains. This restricts the mobility of the molecular chains, limiting plastic deformation and chain sliding, which significantly decreases adhesive and abrasive wear. Post-irradiation melting or annealing (or adding Vitamin E) is used to quench free radicals and prevent oxidation.

Question 6008

Topic: 3. Adult Reconstruction (Hip & Knee)

When comparing bearing surfaces in total hip arthroplasty (THA), which of the following represents the primary advantage of a ceramic-on-ceramic articulation compared to metal-on-highly crosslinked polyethylene?

. Lowest volumetric wear rate
. Elimination of fracture risk
. Increased tolerance to impingement
. Lower rate of postoperative squeaking
. Increased ease of revision for component loosening

Correct Answer & Explanation

. Lowest volumetric wear rate

Explanation

Ceramic-on-ceramic bearings have the lowest volumetric wear rate of all bearing combinations. However, they carry unique risks including catastrophic component fracture and audible squeaking.

Question 6009

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following isolated findings serves as a definitive major criterion for diagnosing a periprosthetic joint infection?

. Elevated serum C-reactive protein (CRP)
. Gross purulence observed in the joint space
. A single positive intraoperative tissue culture
. A sinus tract communicating directly with the prosthesis
. Elevated synovial fluid polymorphonuclear (PMN) percentage

Correct Answer & Explanation

. A sinus tract communicating directly with the prosthesis

Explanation

The major criteria for definitive periprosthetic joint infection are a sinus tract communicating with the joint/prosthesis OR two positive periprosthetic cultures with phenotypically identical organisms. Purulence alone is no longer considered a definitive major criterion.

Question 6010

Topic: 3. Adult Reconstruction (Hip & Knee)

When comparing bearing surfaces in total hip arthroplasty, which of the following is the primary long-term advantage of a ceramic-on-ceramic articulation compared to a metal-on-polyethylene articulation?

. Higher resistance to catastrophic fracture
. Lower volumetric wear rate
. Increased impingement tolerance without edge loading
. Greater forgiveness of acetabular component malposition
. Elimination of the risk for stripe wear

Correct Answer & Explanation

. Lower volumetric wear rate

Explanation

Ceramic-on-ceramic bearings exhibit the lowest volumetric wear rate of any bearing surface, generating exceptionally small and biologically inert wear particles. However, they remain susceptible to catastrophic fracture and squeaking, particularly if placed in malposition.

Question 6011

Topic: 3. Adult Reconstruction (Hip & Knee)

In a patient undergoing total hip arthroplasty, the use of a large-diameter cobalt-chromium femoral head on a titanium alloy femoral stem most significantly increases the risk of which of the following complications?

. Aseptic loosening due to stress shielding
. Mechanically assisted crevice corrosion
. Polyethylene wear due to decreased contact area
. Head-neck dissociation during reduction
. Ceramic squeaking during ambulation

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

The combination of a cobalt-chromium head on a titanium stem, particularly with large diameter heads that increase torque at the modular junction, predisposes the implant to mechanically assisted crevice corrosion (trunnionosis). This galvanic and mechanical wear process can lead to the release of metal ions and subsequent adverse local tissue reactions (ALTR).

Question 6012

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, the surgeon notes that the knee is tight in flexion but symmetric and balanced in extension. Which of the following is the most appropriate surgical step to balance the knee?

. Release the posterior cruciate ligament
. Decrease the distal femoral resection
. Resect more proximal tibia
. Downsize the femoral component
. Increase the distal femoral resection

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion but balanced in extension has an isolated tight flexion gap. Downsizing the femoral component (using a smaller AP size) and shifting the component anteriorly effectively increases the flexion gap without altering the extension gap. Resecting more tibia would open both gaps equally. Releasing the PCL is not relevant here as it is already sacrificed in a posterior-stabilized TKA.

Question 6013

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, utilizing a femoral component with an increased lateral offset will have which of the following primary biomechanical effects?

. Decreases the abductor moment arm
. Increases the resultant joint reaction force
. Increases the abductor moment arm
. Decreases the risk of greater trochanteric bursitis
. Increases the patient's overall leg length

Correct Answer & Explanation

. Increases the abductor moment arm

Explanation

Increasing the femoral offset increases the distance from the center of rotation of the femoral head to the anatomical axis of the femur. This effectively increases the abductor moment arm, which subsequently reduces the amount of abductor muscle force required to stabilize the pelvis, thereby decreasing the resultant joint reaction force across the hip.

Question 6014

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, trial components are inserted. The surgeon notes that the joint space is perfectly balanced in full extension but is excessively tight in 90 degrees of flexion. Which of the following isolated maneuvers is the most appropriate next step to correct this specific mismatch?

. Downsize the femoral component
. Upsize the femoral component
. Recut the proximal tibia with a thicker resection
. Release the posterior capsule
. Insert a thicker polyethylene insert

Correct Answer & Explanation

. Downsize 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. Downsizing the femoral component (using standard posterior referencing) reduces the posterior condylar offset, thereby increasing the flexion gap exclusively. Recutting the tibia or changing the poly thickness would affect both gaps.

Question 6015

Topic: 3. Adult Reconstruction (Hip & Knee)

Following a posterior-stabilized total knee arthroplasty, a patient experiences recurrent knee instability, specifically feeling a 'clunk' when extending the knee from a flexed position. Exam reveals catching in the patellofemoral joint. What is the primary cause and the most appropriate management?

. Oversized femoral component; revision to a smaller size
. Fibrotic nodule at the superior pole of the patella; arthroscopic or open excision
. Polyethylene wear; revision of the tibial insert
. Patellar maltracking; lateral retinacular release
. Quadriceps weakness; physical therapy focusing on VMO strengthening

Correct Answer & Explanation

. Fibrotic nodule at the superior pole of the patella; arthroscopic or open excision

Explanation

Patellar clunk syndrome is a known complication specific to posterior-stabilized TKA. It is caused by a fibrotic nodule forming at the superior pole of the patella that catches in the intercondylar box of the femoral component during extension from a flexed position. Treatment consists of arthroscopic or open excision of the fibrotic nodule.

Question 6016

Topic: 3. Adult Reconstruction (Hip & Knee)

When selecting bearing surfaces for a total hip arthroplasty in a young, active patient, which of the following combinations demonstrates the lowest in vitro volumetric wear rate?

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

Correct Answer & Explanation

. Ceramic on ceramic

Explanation

Ceramic-on-ceramic (CoC) bearing surfaces exhibit the lowest volumetric wear rates of all currently used combinations, making them appealing for very young, active patients. However, they carry unique risks such as component fracture and audible squeaking. Highly cross-linked polyethylene drastically reduces wear compared to conventional polyethylene but still wears more than a CoC construct.

Question 6017

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female presents with groin pain and swelling three years after a primary metal-on-polyethylene total hip arthroplasty (THA). Serum cobalt and chromium levels are significantly elevated. Joint aspiration yields sterile, dark fluid. The components appear well-fixed on radiographs, but MRI shows a large cystic pseudotumor. What is the primary mechanism of failure in this scenario?

. Aseptic loosening secondary to polyethylene wear debris
. Mechanically assisted crevice corrosion at the modular head-neck junction
. Type IV delayed hypersensitivity to bone cement
. Galvanic corrosion between the titanium stem and cobalt-chrome screws
. Undetected indolent periprosthetic joint infection

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the modular head-neck junction

Explanation

The patient is experiencing an adverse local tissue reaction (ALTR) or metallosis (trunnionosis) in a metal-on-polyethylene THA. This is primarily caused by mechanically assisted crevice corrosion (fretting and corrosion) at the modular junction between the femoral head and the trunnion of the stem. This generates metal ions (cobalt and chromium) leading to a localized inflammatory response and pseudotumor formation.

Question 6018

Topic: 3. Adult Reconstruction (Hip & Knee)
In the pathogenesis of periprosthetic osteolysis following total joint arthroplasty, which of the following characteristics of ultra-high-molecular-weight polyethylene (UHMWPE) wear particles most aggressively stimulates the macrophage-mediated inflammatory cascade?
. Particles sized between 10 to 50 micrometers
. Particles sized between 0.1 to 1.0 micrometers
. Particles with a highly smooth and spherical morphology
. Particles that remain strongly bound to the titanium stem
. Particles that are exclusively generated by backside wear

Correct Answer & Explanation

. Particles sized between 0.1 to 1.0 micrometers

Explanation

The biological response to wear debris in arthroplasty is highly dependent on particle size. Macrophages are most actively stimulated to phagocytose polyethylene particles that are in the submicron to low-micron range, specifically 0.1 to 1.0 micrometers. Once phagocytosed, the macrophages release pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6), leading to RANKL activation and subsequent osteoclastic bone resorption.

Question 6019

Topic: 3. Adult Reconstruction (Hip & Knee)

In aseptic loosening of a total hip arthroplasty, which of the following cell types is primarily responsible for internalizing particulate wear debris and initiating the osteolytic cascade?

. Osteoblasts
. Osteoclasts
. Macrophages
. T-lymphocytes
. Chondrocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages are the primary effector cells in the pathogenesis of aseptic loosening (particle disease). They phagocytize wear debris (such as polyethylene particles) and subsequently release pro-inflammatory cytokines (e.g., TNF-alpha, IL-1, IL-6), which stimulate osteoclastic bone resorption.

Question 6020

Topic: 3. Adult Reconstruction (Hip & Knee)

According to Lewinnek's 'safe zone' for acetabular cup placement in total hip arthroplasty, which of the following parameters is associated with the lowest risk of dislocation?

. 30 degrees of inclination and 10 degrees of anteversion
. 40 degrees of inclination and 15 degrees of anteversion
. 50 degrees of inclination and 20 degrees of anteversion
. 40 degrees of inclination and 30 degrees of anteversion
. 45 degrees of inclination and 0 degrees of anteversion

Correct Answer & Explanation

. 40 degrees of inclination and 15 degrees of anteversion

Explanation

Lewinnek described a safe zone for acetabular component positioning to minimize the risk of dislocation. This zone is classically defined as 40 degrees +/- 10 degrees of abduction (inclination) and 15 degrees +/- 10 degrees of anteversion. Option B (40 degrees inclination, 15 degrees anteversion) falls squarely in the middle of this safe zone.

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