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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 252 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 5021

Topic: Total Knee Arthroplasty (TKA)

In kinematic alignment (KA) for total knee arthroplasty, the primary surgical goal differs significantly from mechanical alignment (MA). Which of the following best describes the core principle of kinematic alignment?

. Creating a neutral mechanical axis perpendicular to the floor
. Resecting the distal femur at 5 degrees of valgus to the anatomical axis
. Co-aligning the components with the three kinematic axes of the normal knee to restore the pre-arthritic joint lines
. Releasing the medial collateral ligament to balance a varus deformity
. Ensuring the tibial component is strictly perpendicular to the tibial mechanical axis

Correct Answer & Explanation

. Creating a neutral mechanical axis perpendicular to the floor

Explanation

Kinematic alignment aims to restore the patient's pre-arthritic anatomy and native joint lines by aligning the implants with the natural kinematic axes of the knee. This minimizes the need for soft tissue releases, unlike traditional mechanical alignment.

Question 5022

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon inadvertently places the femoral component in excessive internal rotation. Which of the following is the most likely consequence of this error?

. Medial patellar subluxation
. Lateral patellar maltracking and tilt
. Excessive tightness in the lateral flexion gap
. Increased femoral rollback during deep flexion
. Genu recurvatum

Correct Answer & Explanation

. Medial patellar subluxation

Explanation

Internal rotation of the femoral component translates the trochlear groove medially, relatively lateralizing the tibial tubercle and increasing the Q-angle. This commonly results in lateral patellar maltracking, tilt, and potential subluxation.

Question 5023

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female presents with groin pain two years after an uncomplicated total hip arthroplasty using a metal-on-polyethylene bearing with a titanium stem and a large diameter cobalt-chrome head. Inflammatory markers are normal, but metal artifact reduction sequence (MARS) MRI shows a pseudotumor. What is the most likely source of the pathology?

. Aseptic loosening of the acetabular component
. Polyethylene wear debris
. Corrosion at the head-neck junction (trunnionosis)
. Metallosis from the porous coating of the stem
. Missed low-grade periprosthetic joint infection

Correct Answer & Explanation

. Aseptic loosening of the acetabular component

Explanation

Adverse local tissue reactions (ALTR) can occur in metal-on-polyethylene THAs due to mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction. This risk is elevated with large-diameter, heavy cobalt-chrome heads on titanium stems.

Question 5024

Topic: 3. Adult Reconstruction (Hip & Knee)

In evaluating a patient with a stiff spine (lumbar fusion from L2 to pelvis) planned for a total hip arthroplasty, understanding spinopelvic kinematics is crucial. Because the pelvis fails to retrovert when the patient transitions from standing to sitting, what dislocation risk is significantly increased?

. Anterior dislocation during standing
. Posterior dislocation during sitting
. Anterior dislocation during sitting
. Posterior dislocation during standing
. Superior dislocation during gait

Correct Answer & Explanation

. Anterior dislocation during standing

Explanation

In a patient with a fused or stiff lumbopelvic junction, the pelvis cannot retrovert during sitting to naturally increase functional acetabular anteversion. This leads to anterior bony impingement and a high risk of posterior dislocation when seated.

Question 5025

Topic: 3. Adult Reconstruction (Hip & Knee)

A surgeon is performing a total hip arthroplasty using the direct lateral (Hardinge) approach. To prevent an iatrogenic Trendelenburg gait, the proximal split of the gluteus medius should not extend more than 3 to 5 cm proximal to the tip of the greater trochanter. Which structure is protected by this limitation?

. Sciatic nerve
. Inferior gluteal nerve
. Superior gluteal nerve
. Pudendal nerve
. Femoral nerve

Correct Answer & Explanation

. Sciatic nerve

Explanation

The superior gluteal nerve innervates the gluteus medius and minimus, passing approximately 3 to 5 cm proximal to the tip of the greater trochanter. Extending the muscular split beyond this point risks denervating the abductors, resulting in a postoperative Trendelenburg lurch.

Question 5026

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following synovial fluid profiles is most consistent with a chronic periprosthetic joint infection in a knee arthroplasty?

. WBC count of 1,500 cells/µL with 50% neutrophils
. WBC count of 2,000 cells/µL with 60% neutrophils
. WBC count of 4,500 cells/µL with 85% neutrophils
. WBC count of 8,000 cells/µL with 65% neutrophils
. WBC count of 25,000 cells/µL with 40% neutrophils

Correct Answer & Explanation

. WBC count of 1,500 cells/µL with 50% neutrophils

Explanation

For chronic PJI (>6 weeks post-op), a synovial fluid WBC count greater than 3,000 cells/µL and a polymorphonuclear (PMN) percentage > 80% are highly suggestive of infection according to MSIS criteria.

Question 5027

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with osteoarthritis presents with a fixed varus deformity of 15 degrees and a flexion contracture of 20 degrees. Why is a medial unicompartmental knee arthroplasty (UKA) contraindicated in this patient?

. UKA cannot adequately correct severe fixed deformities and contractures
. The ACL is always deficient in patients with >10 degrees of varus
. Medial UKA will accelerate lateral compartment arthritis in all varus knees
. The patellofemoral joint will automatically subluxate
. UKA components are not available for patients with varus deformities

Correct Answer & Explanation

. UKA cannot adequately correct severe fixed deformities and contractures

Explanation

Absolute contraindications for unicompartmental knee arthroplasty include a fixed varus deformity >10 degrees and a flexion contracture >15 degrees. UKA is a resurfacing procedure that cannot effectively release or balance severe, fixed soft tissue contractures without early failure.

Question 5028

Topic: 3. Adult Reconstruction (Hip & Knee)

When placing screws in the acetabular component during a total hip arthroplasty, the posterior-superior quadrant is generally considered the 'safe zone'. Which major vascular structure is at greatest risk if a screw penetrates the anterior-superior quadrant?

. Obturator artery
. External iliac artery
. Internal pudendal artery
. Superior gluteal artery
. Sciatic nerve

Correct Answer & Explanation

. Obturator artery

Explanation

The anterior-superior quadrant is considered a danger zone due to the proximity of the external iliac vessels. Screws in the anterior-inferior quadrant risk the obturator nerve and vessels.

Question 5029

Topic: Total Hip Arthroplasty (THA)

A 55-year-old male with a history of severe slipped capital femoral epiphysis (SCFE) undergoes a total hip arthroplasty. During the operation, the surgeon finds it difficult to restore femoral offset without excessively lengthening the limb. Sinking the femoral stem deeper is not possible due to a narrow diaphysis. What is the most appropriate next step?

. Use a standard offset stem with a longer head
. Use a high-offset stem with the appropriate neck length
. Perform a subtrochanteric shortening osteotomy
. Use a constrained acetabular liner to allow laxity
. Accept the limb lengthening to ensure stability

Correct Answer & Explanation

. Use a standard offset stem with a longer head

Explanation

A high-offset femoral stem increases the abductor lever arm (offset) without increasing vertical height (leg length). This is ideal when offset must be increased, but leg length is already equal or slightly long.

Question 5030

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient complains of a stiff knee six months after a primary total knee arthroplasty. Range of motion is 10 to 80 degrees. Radiographs show the femoral component is oversized and placed in excessive flexion. Which of the following kinematics best explains the limited flexion?

. Tightness in the extension gap
. Overstuffing of the anterior compartment and tight flexion gap
. Laxity in the medial flexion gap
. Patella baja preventing extension
. Excessive posterior condylar offset causing laxity

Correct Answer & Explanation

. Tightness in the extension gap

Explanation

An oversized femoral component, particularly one placed in excessive flexion, increases the anteroposterior diameter of the femur, tightening the flexion gap and overstuffing the patellofemoral joint. This physically blocks deep flexion.

Question 5031

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following modifications in total hip arthroplasty bearing surfaces utilizes a free radical scavenger to minimize in vivo oxidation while maintaining mechanical strength?

. Addition of calcium hydroxyapatite to polyethylene
. Annealing polyethylene below its melting point
. Infusing highly cross-linked polyethylene with Vitamin E
. Using a ceramic-on-ceramic coupling
. Using oxidized zirconium (Oxinium) heads

Correct Answer & Explanation

. Addition of calcium hydroxyapatite to polyethylene

Explanation

Vitamin E (alpha-tocopherol) acts as a powerful antioxidant and free radical scavenger. Infusing highly cross-linked polyethylene with Vitamin E prevents oxidation without the need for post-irradiation melting, thereby preserving mechanical and fatigue strength.

Question 5032

Topic: 3. Adult Reconstruction (Hip & Knee)
During pre-operative templating for a complex revision total hip arthroplasty, the surgeon classifies the acetabular defect as Paprosky Type IIIB. Which of the following radiographic findings defines this defect?
. Superior migration of the hip center < 3 cm with an intact Kohler line
. Superior migration of the hip center > 3 cm with medial migration beyond Kohler line
. Ischial osteolysis with an intact superior rim
. Isolated anterior column defect with intact posterior wall
. A contained cavitary defect with an intact peripheral rim

Correct Answer & Explanation

. Superior migration of the hip center > 3 cm with medial migration beyond Kohler line

Explanation

Paprosky Type IIIB acetabular defects are characterized by severe bone loss with superior migration > 3 cm and violation of Kohler's line (medial migration/pelvic discontinuity). Type IIIA involves superior migration > 3 cm but with an intact Kohler's line.

Question 5033

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty (TKA), the surgeon checks the gap kinematics with spacer blocks. The extension gap is symmetric and perfectly balanced, but the flexion gap is unacceptably tight symmetrically. What is the most appropriate surgical step to balance the knee?

. Recut the proximal tibia with more posterior slope
. Downsize the femoral component
. Release the posterior cruciate ligament (PCL)
. Mill an additional 2mm from the distal femur
. Perform a fractional lengthening of the medial collateral ligament

Correct Answer & Explanation

. Recut the proximal tibia with more posterior slope

Explanation

A symmetrically tight flexion gap with a balanced extension gap is best treated by downsizing the femoral component. This increases the anteroposterior dimension of the flexion space without altering the extension gap.

Question 5034

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old male with a metal-on-polyethylene total hip arthroplasty utilizing a large-diameter cobalt-chromium head on a titanium stem presents with groin pain and a large cystic mass. Aspiration yields sterile, thick, dark fluid. What is the primary pathophysiologic mechanism responsible for this presentation?

. Type IV delayed hypersensitivity to polymethylmethacrylate
. Volumetric wear of the polyethylene liner
. Mechanically assisted crevice corrosion at the head-neck taper
. Galvanic corrosion exclusively due to mixed metal usage
. Atypical periprosthetic joint infection due to Cutibacterium acnes

Correct Answer & Explanation

. Type IV delayed hypersensitivity to polymethylmethacrylate

Explanation

This patient has trunnionosis (mechanically assisted crevice corrosion), exacerbated by the use of a large-diameter cobalt-chromium head on a titanium stem. Fretting at the modular head-neck junction disrupts the passivation layer, leading to localized corrosion, adverse local tissue reactions, and pseudotumor formation.

Question 5035

Topic: 3. Adult Reconstruction (Hip & Knee)

A 78-year-old female presents to the emergency department after a mechanical fall. She has a painful, shortened right leg. Radiographs demonstrate a fracture around her cemented femoral stem.

Assuming the radiograph shows a fracture at the tip of the stem with evidence of a loose implant but adequate distal bone stock, what is the most appropriate definitive management?

. Open reduction and internal fixation with a lateral locking plate and cables
. Revision total hip arthroplasty using a standard-length cemented stem
. Revision total hip arthroplasty using a long, diaphyseal-engaging, fully porous-coated stem
. Nonoperative management in a long-leg cast
. Cortical strut allografting alone

Correct Answer & Explanation

. Open reduction and internal fixation with a lateral locking plate and cables

Explanation

A periprosthetic fracture at the tip of the stem with a loose component and adequate distal bone stock is classified as a Vancouver B2 fracture. The gold standard treatment is revision arthroplasty utilizing a long, cementless, diaphyseal-engaging stem that bypasses the fracture site by at least two cortical diameters.

Question 5036

Topic: 3. Adult Reconstruction (Hip & Knee)

In the diagnostic algorithm for a suspected periprosthetic joint infection (PJI), a synovial fluid alpha-defensin test is ordered. What is the specific biological origin and function of alpha-defensin in this clinical context?

. An acute phase reactant produced by the liver in response to IL-6
. An antimicrobial peptide released by activated neutrophils
. A cytokine secreted by macrophages to recruit osteoclasts
. A degradation product of bacterial cell walls
. A biomarker of osteoblast apoptosis

Correct Answer & Explanation

. An acute phase reactant produced by the liver in response to IL-6

Explanation

Alpha-defensin is a highly specific antimicrobial peptide released by neutrophils in response to pathogens. Its presence in synovial fluid is a major criterion for diagnosing periprosthetic joint infection due to its high sensitivity and specificity.

Question 5037

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient who underwent a posterior-stabilized (PS) total knee arthroplasty two years ago complains of an audible and painful 'pop' at the anterior knee when extending from a flexed position. What is the anatomical basis of this specific complication?

. Subluxation of the patellar component over the medial femoral condyle
. Impingement of the popliteus tendon on the posterolateral femoral condyle
. A fibrous nodule forming in the superior patellar pole catching in the intercondylar box
. Aseptic loosening of the tibial baseplate causing toggle during extension
. Overhang of the femoral component irritating the iliotibial band

Correct Answer & Explanation

. Subluxation of the patellar component over the medial femoral condyle

Explanation

Patellar clunk syndrome is uniquely associated with posterior-stabilized TKA designs. It occurs when a fibrous nodule develops at the superior pole of the patella and gets caught in the intercondylar box of the femoral component during active extension.

Question 5038

Topic: 3. Adult Reconstruction (Hip & Knee)

During preoperative templating for a primary total hip arthroplasty, the surgeon plans to place the acetabular component medial to the anatomic center of rotation. What is the primary biomechanical effect of this medialization?

. Increases the body weight lever arm
. Decreases the joint reaction force
. Decreases the abductor muscle lever arm
. Increases the risk of sciatic nerve palsy
. Increases the rate of polyethylene wear

Correct Answer & Explanation

. Increases the body weight lever arm

Explanation

Medializing the center of rotation of the hip decreases the lever arm of the body weight. According to static hip biomechanics, this significantly decreases the overall joint reaction force on the hip.

Question 5039

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient presents with persistent anterior knee pain and lateral patellar subluxation 6 months following a primary total knee arthroplasty. CT imaging is ordered to assess component rotation. Which of the following component malrotations is the most likely cause of this patellofemoral tracking issue?

. External rotation of the femoral component
. Internal rotation of the tibial component
. Excessive posterior slope of the tibial tray
. External rotation of the tibial component
. Internal rotation of the patellar button

Correct Answer & Explanation

. External rotation of the femoral component

Explanation

Internal rotation of the tibial component or the femoral component lateralizes the tibial tubercle relative to the trochlear groove. This increases the Q-angle, leading to lateral patellar maltracking and anterior knee pain.

Question 5040

Topic: 3. Adult Reconstruction (Hip & Knee)

When performing a direct lateral (Hardinge) approach for a total hip arthroplasty, the surgeon must split the gluteus medius. To prevent denervation of the anterior portion of the gluteus medius and the tensor fasciae latae, the proximal split must not exceed what safe distance from the tip of the greater trochanter?

. 1 cm
. 3 cm
. 5 cm
. 8 cm
. 10 cm

Correct Answer & Explanation

. 1 cm

Explanation

The superior gluteal nerve crosses approximately 5 cm proximal to the tip of the greater trochanter. Extending the gluteus medius split beyond this 5 cm 'safe zone' risks denervating the anterior gluteus medius, gluteus minimus, and tensor fasciae latae.

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