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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 257 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 5121

Topic: 3. Adult Reconstruction (Hip & Knee)

In a Posterior Stabilized (PS) total knee arthroplasty, what is the primary biomechanical function of the femoral cam and tibial post mechanism?

. To substitute for the anterior cruciate ligament (ACL)
. To provide varus-valgus stability in extension
. To induce paradoxical anterior femoral translation during deep flexion
. To force femoral rollback on the tibia during flexion
. To resist joint line elevation and maintain the patellar height

Correct Answer & Explanation

. To substitute for the anterior cruciate ligament (ACL)

Explanation

The cam-post mechanism in a PS knee substitutes for the posterior cruciate ligament (PCL). Its primary function is to engage during flexion and force the femur to roll backward on the tibia (femoral rollback), which optimizes clearance and allows for deeper flexion.

Question 5122

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total hip arthroplasty, the surgeon opts to increase the femoral offset compared to the patient's native anatomy. Assuming the leg length is kept constant, which of the following biomechanical effects is most likely to result from this change?

. Increased joint reaction force and decreased abductor muscle force
. Decreased joint reaction force and decreased abductor muscle force
. Increased joint reaction force and increased abductor muscle force
. Decreased joint reaction force and increased abductor muscle force
. No change in joint reaction force but increased risk of anterior dislocation

Correct Answer & Explanation

. Increased joint reaction force and decreased abductor muscle force

Explanation

Increasing the femoral offset increases the lever arm of the abductor musculature. This mechanical advantage means less abductor force is required to stabilize the pelvis during single-leg stance, which consequently decreases the overall joint reaction force.

Question 5123

Topic: 3. Adult Reconstruction (Hip & Knee)

A 52-year-old male with isolated medial compartment osteoarthritis is evaluated for a unicompartmental knee arthroplasty (UKA).

Which of the following conditions is considered a strict contraindication to a traditional mobile-bearing UKA?

. Age less than 55 years
. Body Mass Index (BMI) greater than 30
. Deficient anterior cruciate ligament (ACL)
. Patellofemoral chondromalacia without anterior knee pain
. Preoperative flexion arc of 110 degrees

Correct Answer & Explanation

. Age less than 55 years

Explanation

An intact ACL is critical for the success of traditional mobile-bearing UKA. ACL deficiency leads to altered kinematics, posterior tibial subluxation, and rapid eccentric wear or bearing dislocation.

Question 5124

Topic: Total Hip Arthroplasty (THA)

A dual mobility cup is often used in revision THA to reduce the risk of dislocation. Which of the following best describes the primary biomechanical principle of a dual mobility construct?

. It relies on a constrained rigid liner that locks the femoral head in place.
. It increases the 'jumping distance' by utilizing a large effective head size.
. It features an eccentric center of rotation to lateralize the femur.
. It increases the abductor lever arm through a specialized offset liner.
. It prevents impingement by utilizing a truncated femoral neck geometry.

Correct Answer & Explanation

. It relies on a constrained rigid liner that locks the femoral head in place.

Explanation

Dual mobility constructs feature a smaller inner head articulated within a large mobile polyethylene liner, which articulates with the metal shell. This mechanism essentially creates a very large effective head size, vastly increasing the 'jumping distance' required for dislocation.

Question 5125

Topic: Total Knee Arthroplasty (TKA)

During TKA, joint line restoration is critical for proper biomechanics. Which of the following is a direct consequence of inadvertently elevating the joint line by more than 8 mm?

. Patella alta
. Excessive tightness in full extension
. Looseness in full extension
. Decreased patellofemoral contact forces
. Mid-flexion instability and acquired patella baja

Correct Answer & Explanation

. Patella alta

Explanation

Joint line elevation shifts the relative position of the patella distally, resulting in acquired patella baja and increased patellofemoral contact stresses. It also alters the isometry of the collateral ligaments, leading to mid-flexion instability.

Question 5126

Topic: 3. Adult Reconstruction (Hip & Knee)
A 62-year-old female presents with a persistently painful, stiff, and swollen knee 1 year after a primary TKA. Inflammatory markers are normal, and aspiration yields fluid with <500 WBCs. She reports a history of a severe skin rash when wearing cheap jewelry. If metal hypersensitivity is suspected, which immunological mechanism is primarily responsible?
. Type I (IgE-mediated)
. Type II (Cytotoxic)
. Type III (Immune complex)
. Type IV (Delayed-type, T-cell mediated)
. Type V (Receptor-mediated)

Correct Answer & Explanation

. Type IV (Delayed-type, T-cell mediated)

Explanation

Metal hypersensitivity (such as to nickel, cobalt, or chromium) in joint arthroplasty acts as a Type IV delayed-type hypersensitivity reaction, which is a T-cell mediated immune response.

Question 5127

Topic: Total Knee Arthroplasty (TKA)

Patellar maltracking is a significant complication following TKA. Which of the following component malpositions is most likely to cause lateral patellar maltracking?

. External rotation of the femoral component
. Internal rotation of the tibial component
. Medialization of the femoral component
. Lateralization of the tibial component
. Decreased posterior tibial slope

Correct Answer & Explanation

. External rotation of the femoral component

Explanation

Internal rotation of the tibial component effectively lateralizes the tibial tubercle relative to the trochlear groove, increasing the Q angle and leading to lateral patellar maltracking. Internal rotation of the femoral component has a similar detrimental effect.

Question 5128

Topic: Total Hip Arthroplasty (THA)

When planning a primary THA, the surgeon uses the AP pelvis radiograph to assess leg length discrepancy.

Which of the following radiographic landmarks is most reliable for establishing a horizontal reference line for leg length measurement?

. Lesser trochanters
. Ischial tuberosities
. Superior aspect of the obturator foramina
. Radiographic teardrops
. Anterior superior iliac spines

Correct Answer & Explanation

. Lesser trochanters

Explanation

The inter-teardrop line is the most consistent and reliable horizontal reference line on an AP pelvis radiograph. It represents the inferior margin of the true acetabulum and is much less affected by pelvic tilt and rotation than the obturator foramina or ischial tuberosities.

Question 5129

Topic: 3. Adult Reconstruction (Hip & Knee)

During a measured-resection total knee arthroplasty, the trial components are placed. The knee is found to have a symmetric tight extension gap and a symmetric perfectly balanced flexion gap. Which of the following is the most appropriate next step to balance the knee?

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

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A symmetric tight extension gap with a balanced flexion gap is treated by resecting more distal femur. Altering the tibial cut would affect both the flexion and extension gaps simultaneously.

Question 5130

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following is traditionally considered an absolute contraindication to a fixed-bearing medial unicompartmental knee arthroplasty (UKA)?

. Patient age greater than 80 years
. Asymptomatic mild patellofemoral osteoarthritis
. Body Mass Index greater than 35
. Fixed varus deformity of 5 degrees
. Anterior cruciate ligament deficiency

Correct Answer & Explanation

. Patient age greater than 80 years

Explanation

ACL deficiency is a traditional strict contraindication to a fixed-bearing medial UKA due to altered kinematics leading to early aseptic loosening and polyethylene wear. Age and mild asymptomatic patellofemoral arthritis are no longer considered absolute contraindications.

Question 5131

Topic: 3. Adult Reconstruction (Hip & Knee)

In total knee arthroplasty, which of the following femoral component malpositions is most likely to lead to lateral patellar maltracking?

. Excessive external rotation
. Internal rotation
. Excessive valgus alignment
. Anterior translation
. Distal translation

Correct Answer & Explanation

. Excessive external rotation

Explanation

Internal rotation of the femoral component medializes the trochlear groove relative to the extensor mechanism. This increases the Q-angle and biomechanically drives the patella laterally, leading to maltracking.

Question 5132

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female with a metal-on-polyethylene THA presents with groin pain 5 years post-op. Radiographs show well-fixed components. Aspiration yields sterile fluid with a normal cell count. Serum metal ion testing shows heavily elevated Cobalt with normal Chromium levels. What is the most likely etiology?

. Ceramic head fracture
. Polyethylene wear
. Trunnionosis
. Acetabular loosening
. Metallosis from a loose porous coating

Correct Answer & Explanation

. Ceramic head fracture

Explanation

Trunnionosis involves mechanically assisted crevice corrosion at the modular head-neck junction. In a metal-on-polyethylene implant, an isolated disproportionate elevation in serum cobalt relative to chromium strongly suggests wear at the trunnion.

Question 5133

Topic: 3. Adult Reconstruction (Hip & Knee)

During a cruciate-retaining (CR) total knee arthroplasty trial, the knee is well-balanced in extension, but the anterior tibia lifts off the trial baseplate in deep flexion. What is the most likely cause?

. Loose posterior cruciate ligament
. Tight posterior cruciate ligament
. Oversized femoral component
. Excessive posterior tibial slope
. Medial collateral ligament tightness

Correct Answer & Explanation

. Loose posterior cruciate ligament

Explanation

A tight PCL causes excessive femoral rollback during flexion, which forcibly tilts the tibia and leads to anterior tibial lift-off. Management involves selectively releasing (recessing) the PCL or converting to a posterior-stabilized design.

Question 5134

Topic: 3. Adult Reconstruction (Hip & Knee)

A 75-year-old female sustains a periprosthetic femur fracture around a cemented polished taper slip stem. Radiographs demonstrate a fracture around the tip of the stem. The stem is radiographically loose, but the proximal bone stock is excellent (Vancouver B2).

What is the gold standard surgical management?

. ORIF with a lateral locking plate and cerclage cables
. Revision to a fully porous-coated cylindrical or fluted tapered cementless stem
. Revision to a standard length cemented stem
. Nonoperative management with skeletal traction
. Impaction bone grafting with a short primary stem

Correct Answer & Explanation

. ORIF with a lateral locking plate and cerclage cables

Explanation

Vancouver B2 fractures are defined by a loose stem in the setting of adequate proximal bone stock. The standard of care is revision arthroplasty using a long cementless stem (fluted tapered or fully porous-coated) that bypasses the most distal fracture line by at least two cortical diameters.

Question 5135

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient presents 3 weeks after an uncomplicated primary TKA with acute severe knee pain, erythema, and a large effusion. Synovial fluid analysis reveals a WBC of 45,000 cells/uL with 92% polymorphonuclear neutrophils. Radiographs show perfectly aligned, well-fixed components. What is the best definitive management?

. Intravenous antibiotics alone for 6 weeks
. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange
. Single-stage revision arthroplasty
. Two-stage revision arthroplasty with an antibiotic spacer
. Knee arthrodesis

Correct Answer & Explanation

. Intravenous antibiotics alone for 6 weeks

Explanation

For an acute early postoperative periprosthetic joint infection (less than 4 weeks from index surgery) with well-fixed components, DAIR with a modular polyethylene exchange is the standard of care to eradicate the infection while preserving bone stock.

Question 5136

Topic: 3. Adult Reconstruction (Hip & Knee)

Pre-operative templating for a primary total hip arthroplasty aims to restore native femoral offset. Failure to restore femoral offset (leaving it decreased) leads to which of the following biomechanical consequences?

. Increased abductor mechanical advantage
. Decreased joint reaction forces across the hip
. Decreased polyethylene wear secondary to impingement
. Abductor weakness and increased joint reaction forces
. Excessive leg lengthening

Correct Answer & Explanation

. Increased abductor mechanical advantage

Explanation

Decreasing the femoral offset shortens the abductor lever arm. This results in abductor weakness (manifesting as a Trendelenburg lurch) and forces the abductors to generate more tension to balance the pelvis, paradoxically increasing the total joint reaction force.

Question 5137

Topic: 3. Adult Reconstruction (Hip & Knee)

In the manufacturing of modern highly cross-linked polyethylene (HXLPE) for total hip arthroplasty, increasing the radiation dose improves wear resistance but is known to adversely decrease which of the following mechanical properties?

. Oxidation resistance
. Melting temperature
. Fatigue strength and fracture toughness
. Biocompatibility
. Adhesive wear

Correct Answer & Explanation

. Oxidation resistance

Explanation

High-dose gamma or electron beam irradiation creates cross-links that vastly improve wear resistance. However, this process alters the polymer's structural integrity, leading to a reduction in ultimate tensile strength, fatigue strength, and fracture toughness.

Question 5138

Topic: Total Knee Arthroplasty (TKA)

A patient with a severe 20-degree valgus knee deformity undergoes a primary posterior-stabilized TKA. On post-operative day 1, the patient exhibits a new-onset foot drop and numbness over the first dorsal web space. What is the most appropriate initial step in management?

. Immediate surgical exploration and neurolysis of the common peroneal nerve
. Order emergent Electromyography (EMG)
. Remove all compressive dressings and flex the knee to 20-30 degrees
. Immediate revision TKA to a constrained condylar knee to reduce the gap
. Administration of high-dose intravenous corticosteroids

Correct Answer & Explanation

. Immediate surgical exploration and neurolysis of the common peroneal nerve

Explanation

Peroneal nerve palsy following correction of a severe valgus knee is typically due to traction or compression. Initial management requires immediate removal of all compressive dressings and flexing the knee to relax the nerve; surgical exploration is reserved for refractory cases or known transection.

Question 5139

Topic: 3. Adult Reconstruction (Hip & Knee)

Six months following an uncemented total hip arthroplasty, a patient complains of severe sharp groin pain when actively lifting their leg to get into a car. Radiographs reveal an acetabular component that is prominent anteriorly. Which of the following is the most likely diagnosis?

. Iliopsoas impingement
. Heterotopic ossification
. Aseptic loosening of the femoral stem
. Gluteus medius tear
. Polyethylene osteolysis

Correct Answer & Explanation

. Iliopsoas impingement

Explanation

Iliopsoas impingement occurs when the tendon rubs against a prominent, overhanging anterior acetabular rim. It typically presents with reproducible groin pain during active hip flexion against gravity, such as lifting the leg into a vehicle.

Question 5140

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty, which of the following surgical steps carries the highest risk of iatrogenic injury to the popliteal artery?

. Distal femoral resection
. Proximal tibial resection
. Posterior femoral chamfer cut
. Anterior femoral rough cut
. Preparation of the patellar dome

Correct Answer & Explanation

. Distal femoral resection

Explanation

The popliteal artery is tethered firmly by the soleus arch just distal to the joint line, making it highly susceptible to injury during the flat proximal tibial bone cut if posterior retractors are not placed carefully.

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