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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 27 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 521

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old female presents with groin pain 4 years after a metal-on-metal hip resurfacing. Blood work shows a cobalt level of 12 ppb. MARS MRI shows a solid pseudotumor destroying the abductor musculature. What is the recommended definitive management?

. Observation and repeat MRI in 6 months
. Open debridement with retention of implants
. Revision to a total hip arthroplasty utilizing a dual-mobility bearing
. Administration of oral chelating agents
. Radiotherapy to the hip

Correct Answer & Explanation

. Revision to a total hip arthroplasty utilizing a dual-mobility bearing

Explanation

Symptomatic pseudotumors with elevated ions and tissue destruction require revision to a non-metal-on-metal THA. A dual-mobility bearing is often chosen due to the high risk of postoperative instability from abductor deficiency.

Question 522

Topic: Total Hip Arthroplasty (THA)

Which of the following patients is considered the ideal candidate for a metal-on-metal hip resurfacing?

. A 35-year-old female with developmental dysplasia of the hip
. A 45-year-old male with primary osteoarthritis and a 54mm femoral head size
. A 60-year-old female with osteoporosis
. A 50-year-old male with chronic kidney disease
. A 55-year-old female with rheumatoid arthritis

Correct Answer & Explanation

. A 45-year-old male with primary osteoarthritis and a 54mm femoral head size

Explanation

The most favorable outcomes and lowest failure rates for hip resurfacing occur in young, active males with large femoral head diameters (>50mm) and primary osteoarthritis.

Question 523

Topic: 3. Adult Reconstruction (Hip & Knee)

A 48-year-old male with a metal-on-metal hip resurfacing sustains a displaced, comminuted subtrochanteric femur fracture. The acetabular component is well-fixed. What is the most appropriate surgical treatment?

. Open reduction and internal fixation with a cephalomedullary nail
. Conversion to a total hip arthroplasty using a diaphyseal engaging stem
. Nonoperative management with skeletal traction
. Open reduction and internal fixation with a dynamic hip screw
. Conversion to a hemiarthroplasty

Correct Answer & Explanation

. Conversion to a total hip arthroplasty using a diaphyseal engaging stem

Explanation

Fixation of a subtrochanteric fracture around a resurfacing implant is biomechanically challenging and prone to failure. Conversion to a total hip arthroplasty with a long, diaphyseal engaging stem provides the most reliable outcome.

Question 524

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following implant design features in metal-on-metal hip arthroplasty most strongly contributes to decreased wear rates under optimal conditions?

. Increased clearance (gap) between the head and the cup
. Fluid film lubrication facilitated by large head diameters
. High surface roughness
. Low carbon content in the CoCr alloy
. High acetabular component anteversion

Correct Answer & Explanation

. Fluid film lubrication facilitated by large head diameters

Explanation

Under ideal conditions, large head diameters in metal-on-metal bearings promote effective fluid film lubrication. This fluid film separates the bearing surfaces, significantly reducing friction and wear.

Question 525

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following is considered an absolute contraindication to metal-on-metal (MOM) hip resurfacing?

. Chronic kidney disease
. Rheumatoid arthritis
. Osteoarthritis with large cysts
. Prior ipsilateral knee arthroscopy
. Avascular necrosis of the femoral head with less than 30% involvement

Correct Answer & Explanation

. Chronic kidney disease

Explanation

Metal ions (cobalt and chromium) generated by MOM bearings are primarily excreted through the kidneys. Chronic renal failure is an absolute contraindication due to the inability to clear these ions, leading to systemic metal toxicity.

Question 526

Topic: Total Hip Arthroplasty (THA)

What is the primary fluid lubrication regime under which a properly positioned metal-on-metal hip resurfacing bearing ideally operates during the steady-state phase?

. Boundary lubrication
. Fluid-film lubrication
. Mixed lubrication
. Elastohydrodynamic lubrication
. Hydrostatic lubrication

Correct Answer & Explanation

. Fluid-film lubrication

Explanation

MOM bearings are designed to operate under fluid-film lubrication, where a continuous layer of synovial fluid separates the articular surfaces. Disruption of this film, often due to edge loading or poor positioning, leads to boundary lubrication and accelerated wear.

Question 527

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a MOM hip resurfacing presents with groin pain. MARS MRI demonstrates a fluid collection. Biopsy of the tissue reveals a prominent perivascular lymphocytic infiltrate. Which of the following is the most likely diagnosis?

. Acute periprosthetic joint infection
. Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL)
. Foreign body granuloma reacting to polyethylene
. Metallosis due to massive abrasive wear
. Synovial chondromatosis

Correct Answer & Explanation

. Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL)

Explanation

ALVAL is an adverse local tissue reaction (ALTR) characteristic of metal hypersensitivity. It is driven by a type IV delayed hypersensitivity reaction, histologically presenting with perivascular T-lymphocyte infiltrates.

Question 528

Topic: Total Hip Arthroplasty (THA)

Which surgical technical error is most highly associated with an early femoral neck fracture following a metal-on-metal hip resurfacing?

. Varus component positioning and superior femoral neck notching
. Valgus component positioning and inferior femoral neck notching
. Excessive retroversion of the acetabular component
. Oversizing the femoral component by 4 mm
. Undersizing the acetabular component

Correct Answer & Explanation

. Varus component positioning and superior femoral neck notching

Explanation

Superior femoral neck notching and varus positioning of the femoral component create significant stress risers. These errors greatly increase the biomechanical risk of early postoperative femoral neck fractures.

Question 529

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following combinations of patient characteristics and implant features represents the highest risk for developing a pseudotumor and experiencing early failure in metal-on-metal hip resurfacing?

. Male gender and a femoral component size of 54 mm
. Female gender and a femoral component size of 44 mm
. Male gender with a BMI of 35 and a component size of 50 mm
. Female gender with a BMI of 22 and a component size of 52 mm
. Male gender with prior avascular necrosis and a component size of 48 mm

Correct Answer & Explanation

. Female gender and a femoral component size of 44 mm

Explanation

Female gender and small femoral component sizes (typically less than 48 mm) are major risk factors for failure. Smaller heads provide less clearance and are more prone to edge loading and increased wear rates.

Question 530

Topic: 3. Adult Reconstruction (Hip & Knee)

A 58-year-old man with a metal-on-metal total hip arthroplasty presents with visual changes, progressive hearing loss, and new-onset cardiomyopathy. Elevated serum levels of which element are most directly responsible for these systemic symptoms?

. Titanium
. Chromium
. Cobalt
. Molybdenum
. Aluminum

Correct Answer & Explanation

. Cobalt

Explanation

Systemic cobalt toxicity from a failing MOM implant can present with classic 'arthroprosthetic cobaltism'. Symptoms include cardiomyopathy, hypothyroidism, peripheral neuropathy, and visual or hearing impairment.

Question 531

Topic: 3. Adult Reconstruction (Hip & Knee)

When performing a primary total hip arthroplasty on a patient with advanced Paget's disease, what anatomical challenge is most frequently encountered on the acetabular side?

. Severe acetabular dysplasia with a lateralized center of rotation
. Protrusio acetabuli
. Avascular necrosis of the superior weight-bearing dome
. Complete congenital absence of the transverse acetabular ligament
. Hypertrophy of the pulvinar causing lateral subluxation

Correct Answer & Explanation

. Protrusio acetabuli

Explanation

Bone softening that occurs during the lytic and mixed phases of Paget's disease commonly leads to protrusio acetabuli. This requires careful reaming and often the use of bone graft or specialized supportive components.

Question 532

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient with a MOM hip resurfacing presents with a large, symptomatic pseudotumor compressing the femoral vein and serum cobalt levels of 22 ppb. Which of the following is the most definitive management?

. Aspiration of the pseudotumor and intra-articular corticosteroid injection
. Exchange of the femoral head to a larger MOM resurfacing component
. Revision to a total hip arthroplasty utilizing a non-metal-on-metal bearing
. Intravenous chelation therapy to reduce serum cobalt levels
. Observation with repeat MARS MRI in 6 months

Correct Answer & Explanation

. Revision to a total hip arthroplasty utilizing a non-metal-on-metal bearing

Explanation

Symptomatic pseudotumors with highly elevated metal ions indicate failure of the MOM bearing. The standard of care is surgical revision to a conventional THA using a different bearing surface (e.g., ceramic or polyethylene) to halt further metal wear.

Question 533

Topic: Total Hip Arthroplasty (THA)

Which design feature of a metal-on-metal hip resurfacing relies on establishing an 'equatorial bearing' and is critical for generating optimal fluid-film lubrication?

. Surface roughness profile
. Diametrical clearance
. Acetabular cup thickness
. Trunnion taper angle
. Stem flexibility

Correct Answer & Explanation

. Diametrical clearance

Explanation

Diametrical clearance is the specific difference between the outer diameter of the femoral head and the inner diameter of the acetabular cup. Precise clearance is essential to trap synovial fluid and maintain fluid-film lubrication.

Question 534

Topic: Total Hip Arthroplasty (THA)

A 55-year-old man presents with groin pain 4 years after a metal-on-metal (MOM) hip resurfacing. Blood work reveals elevated serum metal ions. According to major regulatory guidelines, serum cobalt levels above which of the following thresholds strongly indicate a poorly functioning bearing and warrant advanced imaging?

. 1 ppb (mcg/L)
. 3 ppb (mcg/L)
. 7 ppb (mcg/L)
. 15 ppb (mcg/L)
. 25 ppb (mcg/L)

Correct Answer & Explanation

. 7 ppb (mcg/L)

Explanation

Serum cobalt or chromium levels greater than 7 ppb (mcg/L) are widely considered the threshold for concern in MOM hip replacements. Levels above this suggest increased wear, such as from edge loading, and warrant a Metal Artifact Reduction Sequence (MARS) MRI to evaluate for adverse local tissue reactions.

Question 535

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following combinations of patient and implant characteristics confers the highest risk for early failure and pseudotumor formation following a metal-on-metal hip resurfacing?

. Male sex and femoral head diameter of 54 mm
. Female sex and femoral head diameter of 44 mm
. Male sex and acetabular inclination of 40 degrees
. Female sex and femoral head diameter of 50 mm
. Male sex and high body mass index

Correct Answer & Explanation

. Female sex and femoral head diameter of 44 mm

Explanation

Female sex and small component size (femoral head diameter less than 48 mm) are major risk factors for failure and pseudotumor formation in MOM hip resurfacing. Smaller head sizes have reduced clearance and are significantly more prone to edge loading, which accelerates wear.

Question 536

Topic: 3. Adult Reconstruction (Hip & Knee)



A 50-year-old woman undergoes revision of a painful metal-on-metal hip resurfacing. Intraoperatively, a large cystic mass containing thick, necrotic fluid is found. Histopathological examination of the periprosthetic tissue is most likely to reveal which of the following?

. Abundant sheets of neutrophils and intracellular bacteria
. A dense perivascular infiltrate of lymphocytes and plasma cells
. Birefringent needle-shaped crystals under polarized light
. Non-caseating granulomas with Langhans giant cells
. Extensive woven bone formation with hyperactive osteoblasts

Correct Answer & Explanation

. A dense perivascular infiltrate of lymphocytes and plasma cells

Explanation

The findings describe ALVAL (aseptic lymphocytic vasculitis-associated lesion) or a pseudotumor. Histologically, ALVAL is characterized by a dense, perivascular infiltrate of T-lymphocytes and macrophages, indicating a delayed-type hypersensitivity reaction to metal wear debris.

Question 537

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old active male underwent an uncomplicated metal-on-metal hip resurfacing 4 weeks ago. He now presents to the emergency department with severe acute groin pain and inability to bear weight after a minor twisting injury. His leg is shortened and externally rotated. What is the most common early major complication of this specific procedure?

. Acetabular component aseptic loosening
. Femoral neck fracture
. Sciatic nerve palsy
. Pseudotumor formation
. Systemic cobalt toxicity

Correct Answer & Explanation

. Femoral neck fracture

Explanation

Femoral neck fracture is the most common early major complication following metal-on-metal hip resurfacing, typically occurring within the first few weeks to months. Risk factors include superior notching of the femoral neck during preparation, varus component positioning, and unrecognized osteonecrosis.

Question 538

Topic: 3. Adult Reconstruction (Hip & Knee)



A patient presents with persistent groin pain 3 years following a metal-on-metal hip resurfacing. Radiographs show well-fixed components without signs of loosening. Serum cobalt is 9.5 ppb. Which of the following is the most appropriate next step in the diagnostic workup?

. Technetium-99m bone scan
. Ultrasound-guided hip aspiration for cell count and culture
. Metal artifact reduction sequence (MARS) MRI
. Immediate revision to a total hip arthroplasty
. Empiric trial of oral antibiotics

Correct Answer & Explanation

. Metal artifact reduction sequence (MARS) MRI

Explanation

In a patient with a painful MOM hip replacement and elevated metal ions (>7 ppb), a Metal Artifact Reduction Sequence (MARS) MRI is the diagnostic imaging modality of choice. It is highly sensitive for detecting adverse local tissue reactions (ALTR) and pseudotumors.

Question 539

Topic: Total Hip Arthroplasty (THA)

Metal-on-metal (MOM) hip resurfacing is considered for young, active patients with osteoarthritis, but stringent patient selection is required. Which of the following conditions is considered an absolute contraindication for a MOM hip resurfacing?

. Patient age less than 40 years
. Male gender
. End-stage renal disease
. Previous arthroscopic labral repair
. Body mass index of 28

Correct Answer & Explanation

. End-stage renal disease

Explanation

Renal failure is an absolute contraindication to MOM hip resurfacing. Metal ions (cobalt and chromium) are primarily excreted by the kidneys, and impaired renal clearance rapidly leads to systemic accumulation and severe metal toxicity.

Question 540

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old man with Paget's disease affecting his left pelvis and proximal femur undergoes a primary total hip arthroplasty (THA). Compared to a patient undergoing THA for primary osteoarthritis, this patient is at an increased risk for which of the following perioperative complications?

. Heterotopic ossification
. Sciatic nerve palsy
. Deep vein thrombosis
. Intraoperative hemorrhage
. Ceramic liner fracture

Correct Answer & Explanation

. Intraoperative hemorrhage

Explanation

Active Paget's disease features highly vascular, hyperemic bone resulting from increased osteoclastic and osteoblastic activity. Consequently, patients are at a significantly increased risk for excessive intraoperative hemorrhage during major orthopedic procedures.

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