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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 305 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 6081

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old woman is 7 days postoperative from a total knee arthroplasty. She has been receiving unfractionated heparin for DVT prophylaxis. Her platelet count precipitously drops from 250,000 to 90,000. What is the underlying pathophysiology of this complication?

. Antibodies directed against platelet factor 4 (PF4)-heparin complexes
. Direct toxicity of unfractionated heparin to bone marrow megakaryocytes
. Depletion of Vitamin K-dependent clotting factors
. Autoimmune destruction of platelets via splenic macrophages (ITP mechanism)
. Systemic activation of coagulation leading to Disseminated Intravascular Coagulation

Correct Answer & Explanation

. Antibodies directed against platelet factor 4 (PF4)-heparin complexes

Explanation

Heparin-induced thrombocytopenia (HIT) Type II is a severe, immune-mediated complication of heparin therapy. It typically occurs 5-10 days after starting heparin and is caused by the formation of IgG antibodies against complexes of heparin and Platelet Factor 4 (PF4). These immune complexes activate platelets, leading to paradoxical widespread thrombosis and a consumptive drop in platelet count.

Question 6082

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced the incidence of wear and subsequent osteolysis. However, increasing the radiation dose to increase cross-linking has a known deleterious effect on the material. What is the primary disadvantage of increased cross-linking?

. Increased generation of reactive oxygen species in vivo
. Decreased yield strength, ductility, and fracture toughness
. Increased melting temperature requiring higher machining costs
. Increased biologic reactivity of the wear particles generated
. Decreased resistance to adhesive wear

Correct Answer & Explanation

. Decreased yield strength, ductility, and fracture toughness

Explanation

While high doses of irradiation (cross-linking) significantly decrease adhesive and abrasive wear, it alters the mechanical properties of the polyethylene, specifically decreasing its yield strength, ductility, and fracture toughness. This makes the material more brittle and susceptible to fatigue failure (e.g., rim cracking or catastrophic failure in thin poly liners).

Question 6083

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male presents with instability and swelling in his knee 2 years after a primary total knee arthroplasty (TKA). On examination, the knee is stable in full extension but exhibits significant anteroposterior laxity at 90 degrees of flexion. Which of the following technical errors during the index procedure most likely caused this complication?

. Excessive distal femoral resection
. Excessive resection of the posterior femoral condyles
. Oversizing of the femoral component
. Inadequate release of the posterior cruciate ligament
. Placing the femoral component in excessive flexion

Correct Answer & Explanation

. Excessive resection of the posterior femoral condyles

Explanation

Flexion instability (stable in extension, loose in flexion) is caused by a mismatched flexion gap relative to the extension gap. Excessive resection of the posterior femoral condyles directly enlarges the flexion space without altering the extension space, leading to this presentation.

Question 6084

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male presents with severe knee pain, erythema, and a draining sinus 3 weeks following a total knee arthroplasty. Radiographs show well-fixed implants. What is the standard of care surgical management?

. One-stage revision arthroplasty
. Two-stage revision arthroplasty with an antibiotic spacer
. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange
. Long-term suppressive intravenous antibiotics alone
. Immediate implant removal and knee arthrodesis

Correct Answer & Explanation

. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange

Explanation

For early acute periprosthetic joint infections (typically defined as <4 weeks postoperatively) with stable implants, DAIR with modular component exchange is the preferred treatment. This minimizes morbidity while addressing the immature biofilm.

Question 6085

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, osteolysis is primarily driven by a macrophage-mediated inflammatory response to wear debris. Which size range of polyethylene particles is most osteolytic?

. < 0.1 micrometers
. 0.1 to 1.0 micrometers
. 1.0 to 10 micrometers
. 10 to 50 micrometers
. > 50 micrometers

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Polyethylene particles in the submicron range (0.1 to 1.0 micrometers) are most readily phagocytosed by macrophages. This triggers the release of inflammatory cytokines (such as TNF-alpha, IL-1, and IL-6), leading to subsequent osteoclast activation and osteolysis.

Question 6086

Topic: 3. Adult Reconstruction (Hip & Knee)

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

. Resect more distal femur
. Resect more proximal tibia
. Upsize the femoral component
. Downsize the femoral component
. Release the posterior capsule

Correct Answer & Explanation

. Downsize the femoral component

Explanation

If a knee is balanced in extension but tight in flexion, the flexion gap needs to be increased without altering the extension gap. Downsizing the femoral component (utilizing the same posterior reference) decreases the posterior condylar offset, thereby specifically enlarging the flexion gap.

Question 6087

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active male undergoes a total hip arthroplasty using a ceramic-on-ceramic bearing surface. Which of the following complications is unique to this specific bearing combination compared to metal-on-polyethylene?

. Trunnionosis
. Squeaking
. Cold flow (creep)
. Galvanic corrosion
. High volumetric wear

Correct Answer & Explanation

. Squeaking

Explanation

Ceramic-on-ceramic bearings have the lowest volumetric wear rate among THA bearing surfaces but are uniquely associated with audible 'squeaking' (reported in up to 10% of cases) and the risk of catastrophic ceramic fracture. Cold flow (creep) is seen with polyethylene. Trunnionosis and galvanic corrosion are associated with metal components, particularly metal-on-metal or modular head-neck junctions.

Question 6088

Topic: 3. Adult Reconstruction (Hip & Knee)

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

. Decrease the AP size of the femoral component
. Recut the distal femur
. Release the posterior cruciate ligament
. Upsize the tibial polyethylene insert
. Recut the proximal tibia

Correct Answer & Explanation

. Decrease the 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 affecting the extension gap. Decreasing the AP size of the femoral component achieves this by translating the posterior condyles anteriorly.

Question 6089

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient undergoes a total hip arthroplasty using a ceramic-on-ceramic bearing surface. One year later, they complain of a high-pitched squeaking noise with walking, without pain. What is the most common cause of squeaking in this specific bearing couple?

. Polyethylene wear
. Galvanic corrosion
. Stripe wear from edge loading
. Trunnionosis
. Acetabular loosening

Correct Answer & Explanation

. Stripe wear from edge loading

Explanation

Squeaking is a well-described complication of ceramic-on-ceramic THA, often caused by edge loading and microseparation resulting in stripe wear. It is highly dependent on cup position, particularly excessive anteversion or vertical orientation.

Question 6090

Topic: 3. Adult Reconstruction (Hip & Knee)

Osteolysis following cementless total hip arthroplasty is primarily mediated by which of the following cell types in response to polyethylene wear debris?

. Osteoblasts
. T-lymphocytes
. Polymorphonuclear leukocytes
. Macrophages
. Fibroblasts

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose submicron polyethylene wear particles and subsequently release pro-inflammatory cytokines such as TNF-alpha and IL-1. This cascade stimulates osteoclastic bone resorption, leading to periprosthetic osteolysis.

Question 6091

Topic: 3. Adult Reconstruction (Hip & Knee)

In modern total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) compared to conventional polyethylene is associated with which of the following biomechanical property changes?

. Increased fatigue resistance and increased elasticity
. Increased ultimate tensile strength
. Decreased wear rate and decreased fracture toughness
. Decreased wear rate and increased yield strength
. Increased elongation to failure

Correct Answer & Explanation

. Decreased wear rate and decreased fracture toughness

Explanation

Highly cross-linked polyethylene (HXLPE) drastically reduces volumetric wear rates, thereby decreasing osteolysis and aseptic loosening. However, the cross-linking process and subsequent thermal treatments decrease the material's mechanical properties, including ultimate tensile strength, elongation to failure, and fracture toughness.

Question 6092

Topic: 3. Adult Reconstruction (Hip & Knee)

In modern cementless total hip arthroplasty, osteointegration of a porous-coated titanium femoral stem is highly dependent on initial rigid stability. What is the generally accepted maximum threshold of initial micromotion at the bone-implant interface that still allows for bony ingrowth rather than fibrous encapsulation?

. 50 micrometers
. 250 micrometers
. 500 micrometers
. 1 millimeter
. 2 millimeters

Correct Answer & Explanation

. 50 micrometers

Explanation

For reliable bone ingrowth into a porous surface, relative micromotion between the implant and host bone must be minimized. The generally accepted threshold is < 40 to 50 micrometers. Micromotion between 50 and 150 micrometers typically results in a combination of bone and fibrous ingrowth, whereas motion > 150 micrometers predictably leads to fibrous encapsulation and lack of osseointegration.

Question 6093

Topic: 3. Adult Reconstruction (Hip & Knee)

During the trialing phase of a posterior-stabilized total knee arthroplasty, the surgeon notes that the joint is excessively tight in full extension, but perfectly balanced in 90 degrees of flexion. Which of the following surgical interventions is the most appropriate next step to correct this specific mismatch?

. Release the posterior capsule or resect more distal femur
. Resect more proximal tibia
. Increase the size of the femoral component
. Decrease the thickness of the tibial polyethylene insert
. Translate the femoral component anteriorly

Correct Answer & Explanation

. Release the posterior capsule or resect more distal femur

Explanation

A gap mismatch characterized by a tight extension gap and a balanced flexion gap requires an intervention that alters the extension space without affecting the flexion space. Resecting more distal femur or releasing structures that are tight only in extension (like the posterior capsule) will open the extension gap without changing the flexion gap. Resecting more tibia or downsizing the poly would incorrectly loosen the already balanced flexion gap.

Question 6094

Topic: 3. Adult Reconstruction (Hip & Knee)

A new diagnostic test for periprosthetic joint infection is evaluated in a population with a very high disease prevalence. Compared to a population with low prevalence, how will the positive predictive value (PPV) and negative predictive value (NPV) change?

. PPV increases, NPV increases
. PPV decreases, NPV decreases
. PPV increases, NPV decreases
. PPV decreases, NPV increases
. PPV and NPV remain unchanged

Correct Answer & Explanation

. PPV increases, NPV decreases

Explanation

Predictive values are dependent on the disease prevalence within the tested population. As the prevalence of a disease increases, the Positive Predictive Value (PPV) increases and the Negative Predictive Value (NPV) decreases.

Question 6095

Topic: 3. Adult Reconstruction (Hip & Knee)
The primary mechanism of wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular liners that leads to periprosthetic osteolysis in total hip arthroplasty is:
. Adhesive wear
. Abrasive wear
. Fatigue wear
. Third-body wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the most common and clinically significant mode of wear in standard metal-on-polyethylene bearings. It generates billions of submicron polyethylene particles that trigger a macrophage-mediated foreign body response, ultimately leading to osteolysis.

Question 6096

Topic: 3. Adult Reconstruction (Hip & Knee)

The addition of Vitamin E (alpha-tocopherol) to highly cross-linked polyethylene (HXLPE) in total joint arthroplasty primarily serves which of the following functions?

. Increases the inherent crystallinity of the polyethylene
. Acts as a free radical scavenger to prevent in vivo oxidation
. Increases the overall macroscopic yield strength of the liner
. Promotes osteoblastic bone ingrowth directly into the bearing surface
. Eliminates the need for gamma irradiation during sterilization

Correct Answer & Explanation

. Acts as a free radical scavenger to prevent in vivo oxidation

Explanation

Vitamin E is doped or blended into HXLPE to act as an antioxidant that quenches free radicals generated during the cross-linking irradiation process. This prevents long-term in vivo oxidation, thereby preserving the material's mechanical integrity and wear resistance.

Question 6097

Topic: Total Hip Arthroplasty (THA)

During total hip arthroplasty, increasing the femoral offset without significantly altering the leg length yields which of the following biomechanical outcomes?

. Decreases the resting tension of the abductor musculature
. Increases the global joint reactive force acting across the hip
. Increases the moment arm of the hip abductor muscles
. Increases the inherent risk of bony impingement during abduction
. Decreases the bending stress placed upon the femoral stem

Correct Answer & Explanation

. Increases the moment arm of the hip abductor muscles

Explanation

Increasing femoral offset directly increases the lever arm (moment arm) of the abductor muscles, thereby optimizing their mechanical advantage. This reduces the required abductor force to stabilize the pelvis, which in turn effectively decreases the overall joint reactive force.

Question 6098

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active male undergoes total hip arthroplasty with a ceramic-on-ceramic bearing surface. What is the most common unique complication associated with this specific bearing choice?

. Massive osteolysis from submicron wear debris
. Trunnionosis with elevated blood metal ions
. Audible squeaking during gait
. Catastrophic linear wear after 5 years
. Adverse local tissue reaction (ALTR) formation

Correct Answer & Explanation

. Audible squeaking during gait

Explanation

Ceramic-on-ceramic bearings offer exceptionally low wear rates but are associated with the unique complication of audible squeaking. This phenomenon is often linked to component malposition, microseparation, or stripe wear.

Question 6099

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is tight in flexion but symmetric and perfectly balanced in extension. Which of the following adjustments is the most appropriate surgical solution?

. Recut the distal femur to remove more bone
. Upsize the femoral component
. Release the posterior cruciate ligament
. Downsize the femoral component with the same posterior referencing guide
. Increase the thickness of the tibial polyethylene insert

Correct Answer & Explanation

. Downsize the femoral component with the same posterior referencing guide

Explanation

A knee that is tight in flexion but balanced in extension implies a tight flexion gap. Downsizing the femoral component using the same posterior referencing guide shifts the posterior condyles anteriorly, thereby increasing the flexion gap without altering the extension gap.

Question 6100

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty using a posterior referencing system, the surgeon notes that the trial components result in a knee that is tight in flexion but perfectly balanced in extension. Which of the following is the most appropriate step to balance the knee?

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

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion but balanced in extension indicates a flexion gap that is too small relative to the extension gap. When using posterior referencing, downsizing the femoral component reduces the anterior-posterior dimension of the femur, increasing the flexion gap without altering the distal cut (which dictates the extension gap).

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