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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 185 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 3681

Topic: 3. Adult Reconstruction (Hip & Knee)

A surgeon is reviewing bearing surfaces for total hip arthroplasty. To reduce oxidation and improve wear resistance without sacrificing fatigue strength, vitamin E (alpha-tocopherol) is increasingly added to highly cross-linked polyethylene (HXLPE). What is the primary mechanism by which Vitamin E achieves this effect?

. Scavenging free radicals generated during the irradiation process
. Increasing the crystallinity of the polyethylene chains
. Promoting additional cross-linking during the sterilization phase
. Preventing third-body wear by increasing surface hardness
. Enhancing fluid-film lubrication at the articular interface

Correct Answer & Explanation

. Scavenging free radicals generated during the irradiation process

Explanation

Vitamin E acts as a powerful antioxidant by scavenging free radicals produced during the gamma irradiation process of HXLPE. This prevents long-term oxidation in vivo, eliminating the need for post-irradiation thermal treatments (like remelting), which are known to decrease the mechanical and fatigue strength of the polyethylene.

Question 3682

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male undergoes a revision total hip arthroplasty due to an adverse local tissue reaction (ALTR). The primary surgery utilized a titanium alloy stem with a cobalt-chromium modular head. Intraoperatively, significant black tissue debris is noted around the head-neck taper junction. Which of the following best describes the primary mechanism of wear and corrosion at this specific interface?

. Pure galvanic corrosion driven solely by the use of dissimilar metals
. Mechanically assisted crevice corrosion driven by micromotion and an oxygen-depleted environment
. Pitting corrosion due to systemic chloride ion attack on the passivating oxide layer
. Abrasive wear from third-body polymethylmethacrylate debris entering the taper
. Adhesive wear resulting from the micro-welding of articular bearing surfaces

Correct Answer & Explanation

. Mechanically assisted crevice corrosion driven by micromotion and an oxygen-depleted environment

Explanation

Trunnionosis at the modular head-neck taper of a total hip arthroplasty is primarily caused by mechanically assisted crevice corrosion (MACC). Micromotion (fretting) at the modular junction mechanically disrupts the protective passivating oxide layer of the metals. This disruption, combined with an oxygen-depleted environment within the crevice (which prevents the spontaneous repassivation of the oxide layer), leads to accelerated corrosive dissolution of metal ions and subsequent adverse local tissue reaction.

Question 3683

Topic: 3. Adult Reconstruction (Hip & Knee)
A 72-year-old man requires revision of a cemented total knee arthroplasty due to extensive aseptic loosening and osteolysis. Histologic analysis of the periprosthetic tissue demonstrates a dense macrophage infiltrate. Which of the following ultra-high-molecular-weight polyethylene (UHMWPE) particle sizes is most highly reactive and responsible for maximizing macrophage activation and subsequent osteolysis?
. Less than 0.1 micrometers
. 0.1 to 1.0 micrometers
. 5 to 10 micrometers
. 15 to 25 micrometers
. Greater than 50 micrometers

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Polyethylene wear particles are the primary initiators of aseptic loosening in joint arthroplasty. Local macrophages phagocytose these particles and subsequently release pro-inflammatory cytokines (such as TNF-alpha, IL-1, and IL-6) that stimulate osteoclastogenesis via the RANK/RANKL pathway. The most biologically active particles that maximize this macrophage activation are in the submicron range, specifically between 0.1 and 1.0 micrometers. Particles larger than 10 micrometers are generally too large for individual macrophages to ingest and typically elicit a foreign-body giant cell response instead.

Question 3684

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with severe groin pain 5 years after undergoing a total hip arthroplasty with a cobalt-chromium (CoCr) head on a titanium (Ti) alloy stem. Joint aspiration is negative for infection, but a metal artifact reduction sequence (MARS) MRI reveals a large cystic pseudotumor around the hip. What is the primary mechanism of corrosion occurring at the head-neck junction?

. Mechanically assisted crevice corrosion
. Pure galvanic corrosion
. Pitting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

Trunnionosis in total hip arthroplasty with mixed metal components (e.g., CoCr head on Ti stem) is primarily driven by mechanically assisted crevice corrosion (MACC). Micromotion (fretting) at the modular head-neck junction disrupts the passive protective oxide layer of the metals. This allows crevice corrosion to occur in the secluded, low-oxygen space of the Morse taper, leading to the release of metal ions and subsequent adverse local tissue reactions (ALTR).

Question 3685

Topic: 3. Adult Reconstruction (Hip & Knee)
In total joint arthroplasty, different mechanisms of polyethylene wear dictate implant longevity. Which of the following best describes the primary mechanism of ultra-high-molecular-weight polyethylene (UHMWPE) failure historically seen in total knee arthroplasty compared to total hip arthroplasty?
. Abrasive wear secondary to third-body debris
. Adhesive wear from micro-welds forming between the articular surfaces
. Subsurface delamination due to high contact stresses and fatigue
. Volumetric wear directly proportional to the size of the femoral head
. Galvanic corrosion at the modular junctions

Correct Answer & Explanation

. Subsurface delamination due to high contact stresses and fatigue

Explanation

Historically, the primary mode of UHMWPE failure in total knee arthroplasty (TKA) is subsurface delamination and fatigue wear. This occurs due to the relatively non-conforming nature of the tibiofemoral joint, leading to high cyclical, non-uniform contact stresses that exceed the fatigue strength of the polyethylene, particularly if it has undergone oxidative degradation (e.g., gamma-irradiated in air). In contrast, a total hip arthroplasty (THA) is a highly conforming ball-and-socket joint, and its primary wear mechanism is a combination of adhesive and abrasive wear, which generates millions of submicron volumetric wear particles that drive osteolysis.

Question 3686

Topic: 3. Adult Reconstruction (Hip & Knee)
A 68-year-old male presents with groin pain 15 years after an uncomplicated primary total hip arthroplasty. Radiographs demonstrate significant eccentric wear of the polyethylene liner and substantial periprosthetic acetabular osteolysis. What is the primary cellular mediator responsible for initiating the biological cascade leading to this osteolysis?
. Neutrophils
. T-lymphocytes
. Macrophages
. Osteoblasts
. Multinucleated giant cells

Correct Answer & Explanation

. Macrophages

Explanation

Aseptic loosening and periprosthetic osteolysis in joint arthroplasty are primarily driven by the generation of ultra-high-molecular-weight polyethylene (UHMWPE) wear debris. The debris particles (specifically those 0.1 to 1.0 micrometers in size) are phagocytosed by macrophages. This triggers the macrophages to release a cascade of pro-inflammatory cytokines (e.g., TNF-alpha, IL-1, IL-6), which subsequently stimulate osteoclastic bone resorption.

Question 3687

Topic: 3. Adult Reconstruction (Hip & Knee)
In total hip arthroplasty, the primary initiator of aseptic loosening and periprosthetic osteolysis is the biological response to wear debris. Which cell type phagocytoses these particles and subsequently secretes cytokines that stimulate osteoclastogenesis?
. Osteoblasts
. Fibroblasts
. Macrophages
. T-lymphocytes
. Neutrophils

Correct Answer & Explanation

. Macrophages

Explanation

Periprosthetic osteolysis is primarily initiated by macrophages that phagocytose ultra-high-molecular-weight polyethylene (UHMWPE) wear particles. These activated macrophages secrete inflammatory cytokines (such as TNF-alpha, IL-1, IL-6, and PGE2), which increase RANKL expression. This cascade ultimately drives osteoclast activation and subsequent periprosthetic bone resorption.

Question 3688

Topic: 3. Adult Reconstruction (Hip & Knee)
In total hip arthroplasty, the use of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) compared to conventional UHMWPE results in which of the following mechanical trade-offs?
. Decreased volumetric wear, decreased fatigue strength
. Decreased volumetric wear, increased fatigue strength
. Increased volumetric wear, decreased yield strength
. Increased volumetric wear, increased fatigue strength
. No change in volumetric wear, decreased oxidative degradation

Correct Answer & Explanation

. Decreased volumetric wear, decreased fatigue strength

Explanation

Highly cross-linked UHMWPE significantly decreases volumetric wear, which is highly beneficial for reducing particle-induced osteolysis and improving the longevity of the joint replacement. However, the cross-linking process (via irradiation) and subsequent thermal treatment (to eliminate free radicals) alter the material's mechanical properties, generally resulting in decreased fatigue strength, ultimate tensile strength, and ductility compared to conventional UHMWPE.

Question 3689

Topic: 3. Adult Reconstruction (Hip & Knee)

A 78-year-old woman with a history of a cemented left total hip arthroplasty performed 15 years ago falls from standing. Radiographs reveal a spiral periprosthetic femur fracture originating at the tip of the femoral stem and extending distally. The cement mantle is cracked, and the stem has subsided 1.5 cm into the canal, demonstrating gross radiographic loosening. However, the proximal femoral bone stock remains robust and circumferentially intact. According to the Vancouver classification, what is the classification of this fracture and the standard accepted treatment?

. Vancouver B1; Open reduction and internal fixation with a locking plate and cables
. Vancouver B2; Revision arthroplasty with a long-stem prosthesis
. Vancouver B3; Revision arthroplasty with a proximal femoral replacement (megaprosthesis)
. Vancouver C; Open reduction and internal fixation with an overlapping plate
. Vancouver A; Nonoperative management with toe-touch weight bearing

Correct Answer & Explanation

. Vancouver B2; Revision arthroplasty with a long-stem prosthesis

Explanation

The Vancouver classification for periprosthetic proximal femur fractures is highly tested. Type A is in the trochanteric region. Type B is around or just distal to the stem tip. Type C is well below the stem tip. Type B is subdivided by stem stability and bone stock: B1 (stable stem, good bone) treated with ORIF; B2 (loose stem, good bone) treated with revision arthroplasty bypassing the fracture; B3 (loose stem, poor bone) treated with revision and proximal femoral replacement or allograft. This patient has a fracture at the stem tip (Type B) with a loose stem (subsided 1.5 cm) but good proximal bone stock, classifying it as a Vancouver B2. The standard of care is revision arthroplasty using a long-stem prosthesis that bypasses the fracture by at least two cortical diameters.

Question 3690

Topic: 3. Adult Reconstruction (Hip & Knee)

A 78-year-old woman with a history of a cemented total hip arthroplasty performed 10 years ago falls and sustains a periprosthetic femur fracture. Radiographs demonstrate a fracture around the tip of the stem. The stem appears to be well-fixed with no evidence of cement mantle fracture or subsidence. According to the Vancouver classification, what is the most appropriate management for this injury?

. Protected weight-bearing and a fracture brace
. Open reduction and internal fixation with a lateral plate and cables
. Revision total hip arthroplasty with a long fully porous-coated stem
. Revision total hip arthroplasty with a long cemented stem
. Proximal femoral replacement

Correct Answer & Explanation

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

Explanation

This is a Vancouver B1 periprosthetic fracture, defined as a fracture around or just distal to a well-fixed femoral stem. The standard treatment for a Vancouver B1 fracture is open reduction and internal fixation (ORIF), typically utilizing a locked lateral plate with cables or unicortical screws proximally around the stem and bicortical screws distally. Revision arthroplasty is indicated for Vancouver B2 fractures (loose stem with adequate bone stock) or B3 fractures (loose stem with poor bone stock).

Question 3691

Topic: 3. Adult Reconstruction (Hip & Knee)
An 82-year-old woman presents with severe knee pain and inability to bear weight after a mechanical fall. She underwent a total knee arthroplasty 10 years ago. Radiographs demonstrate a displaced supracondylar distal femur fracture. Careful radiographic evaluation shows no evidence of osteolysis, and the femoral component remains rigidly fixed to the bone. What is the most appropriate surgical management?
. Revision to a distal femoral replacement (tumor prosthesis)
. Nonoperative management in a hinged knee brace locked in extension
. Open reduction and internal fixation with a lateral distal femur locking plate
. Revision of the femoral component with a long cemented diaphyseal engaging stem
. Primary above-knee amputation

Correct Answer & Explanation

. Open reduction and internal fixation with a lateral distal femur locking plate

Explanation

This patient has a Lewis-Rorabeck type II periprosthetic fracture, defined as a displaced fracture around a well-fixed prosthesis. The standard of care for a displaced periprosthetic distal femur fracture above a well-fixed total knee arthroplasty component is internal fixation. This is typically achieved with a lateral locking plate or a retrograde intramedullary nail (if the intercondylar box of the prosthesis is open and accommodates a nail). Revision arthroplasty to a distal femoral replacement is reserved for loose components (Lewis-Rorabeck type III) or profoundly deficient bone stock not amenable to any fixation.

Question 3692

Topic: 3. Adult Reconstruction (Hip & Knee)

A 50-year-old male presents with a posterior hip dislocation and an associated posterior wall acetabular fracture after a dashboard injury. The hip is reduced in the emergency department. Post-reduction CT scan reveals a single, large posterior wall fragment comprising 45% of the posterior wall, with 3 mm of displacement and evidence of marginal impaction. What is the most appropriate definitive management?

. Skeletal traction for 6 weeks followed by progressive weight-bearing
. Immediate total hip arthroplasty
. Open reduction and internal fixation of the posterior wall
. Closed treatment with touch-down weight-bearing for 12 weeks
. Arthroscopic debridement of the hip joint

Correct Answer & Explanation

. Open reduction and internal fixation of the posterior wall

Explanation

Posterior wall acetabular fractures require open reduction and internal fixation (ORIF) if the fragment constitutes greater than 40% of the posterior wall (invariably causing instability), if there is clinical or radiographic hip instability, or if there is associated marginal impaction. In this scenario, the presence of a large fragment (45%) combined with marginal impaction mandates surgical intervention to elevate and graft the impacted articular segment and rigidly fix the wall, thereby minimizing the risk of early post-traumatic osteoarthritis and instability.

Question 3693

Topic: 3. Adult Reconstruction (Hip & Knee)

An 82-year-old community-ambulating woman sustains a displaced femoral neck fracture after a mechanical fall. She has a history of controlled hypertension and diet-controlled type 2 diabetes. What is the primary clinical benefit of performing surgical management (hemiarthroplasty) within 24 to 48 hours of her presentation?

. Decreased 30-day and 1-year mortality rates
. Reduced incidence of avascular necrosis of the femoral head
. Lower risk of post-operative prosthetic dislocation
. Increased rate of fracture union
. Decreased need for post-operative blood transfusions

Correct Answer & Explanation

. Decreased 30-day and 1-year mortality rates

Explanation

Early surgical intervention (typically defined as within 24 to 48 hours of admission) for geriatric hip fractures is heavily supported by the literature to decrease 30-day and 1-year mortality rates, reduce the incidence of pressure ulcers, and shorten hospital lengths of stay. The rate of avascular necrosis and nonunion are not primarily mitigated by timing in the context of arthroplasty, and dislocation risk is largely dependent on the surgical approach and implant positioning.

Question 3694

Topic: 3. Adult Reconstruction (Hip & Knee)

A 78-year-old independent community-ambulating female sustains an anterior column and posterior hemitransverse acetabular fracture after a mechanical fall. Radiographs and CT demonstrate medial displacement of the femoral head, significant superomedial dome impaction ('gull sign'), and profound osteopenia. Which of the following represents the most appropriate surgical management to minimize prolonged morbidity and allow early mobilization?

. Percutaneous placement of an anterior and posterior column screw
. Open reduction and internal fixation (ORIF) via an ilioinguinal approach followed by non-weight-bearing for 12 weeks
. Acute total hip arthroplasty (THA) with concomitant stabilization of the anterior column
. Skeletal traction for 6 weeks followed by delayed THA
. Open reduction and internal fixation (ORIF) via a Kocher-Langenbeck approach

Correct Answer & Explanation

. Acute total hip arthroplasty (THA) with concomitant stabilization of the anterior column

Explanation

In elderly patients with osteopenic bone, acetabular fractures that present with poor prognostic factors for ORIFโ€”such as significant medial displacement, superomedial dome impaction ('gull sign'), comminution, and femoral head damageโ€”are at high risk of rapid post-traumatic arthrosis and fixation failure. Acute total hip arthroplasty (THA) supported by simultaneous column stabilization (e.g., cup-cage construct or internal fixation) is the treatment of choice. It allows immediate weight-bearing and avoids the complications of prolonged immobilization or multiple surgeries.

Question 3695

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following conditions is considered an absolute contraindication to total ankle arthroplasty (TAA)?

. Age over 70 years.
. End-stage osteoarthritis.
. Rheumatoid arthritis.
. Preoperative varus deformity of 5 degrees.
. Active deep infection or Charcot neuroarthropathy.

Correct Answer & Explanation

. Active deep infection or Charcot neuroarthropathy.

Explanation

Active deep infection, profound neuropathy (such as Charcot neuroarthropathy), and an inadequate soft tissue envelope are absolute contraindications to TAA. These conditions carry unacceptably high failure rates and risks of catastrophic complications.

Question 3696

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient with end-stage post-traumatic ankle osteoarthritis undergoes a total ankle arthroplasty using the standard anterior approach. During the superficial dissection and placement of retractors, which of the following nerves is at greatest risk of iatrogenic injury?

. Sural nerve
. Deep peroneal nerve
. Superficial peroneal nerve
. Saphenous nerve
. Medial plantar nerve

Correct Answer & Explanation

. Superficial peroneal nerve

Explanation

The standard anterior approach to the ankle utilizes an internervous plane between the superficial peroneal nerve (SPN) and the deep peroneal nerve. The SPN, particularly its medial dorsal cutaneous branch, crosses the operative field from lateral to medial and is at high risk of injury during superficial dissection and anterior retraction.

Question 3697

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old male with end-stage post-traumatic ankle osteoarthritis is being evaluated in the clinic to discuss surgical options, including total ankle arthroplasty (TAA) versus ankle arthrodesis. Which of the following is widely considered an absolute contraindication to Total Ankle Arthroplasty (TAA)?

. Avascular necrosis involving greater than 50% of the talar body
. Patient age greater than 60 years
. Concomitant end-stage subtalar joint osteoarthritis
. Body Mass Index (BMI) of 32 kg/m2
. A coronal plane deformity of 5 degrees in the hindfoot

Correct Answer & Explanation

. Avascular necrosis involving greater than 50% of the talar body

Explanation

Severe avascular necrosis (AVN) of the talar body (typically defined as >50% involvement) is an absolute contraindication for Total Ankle Arthroplasty due to the lack of viable bone stock needed to support the talar component, leading to early subsidence and catastrophic failure. Advanced age is not a contraindication (TAA is often preferred in older, lower-demand patients). Subtalar arthritis is actually an indication for TAA over fusion to preserve remaining hindfoot kinematics. Mild coronal deformity and a BMI of 32 are relative considerations, not absolute contraindications.

Question 3698

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female undergoes a reverse total shoulder arthroplasty (RTSA) for a comminuted 4-part proximal humerus fracture. Six months postoperatively, she presents with severe shoulder aching and stiffness, though she lacks systemic symptoms. Laboratory results show a normal ESR and CRP. Joint aspiration cultures grow Cutibacterium acnes after 10 days. Which of the following is true regarding this infection in the setting of shoulder arthroplasty?

. C. acnes is a gram-negative aerobic bacillus commonly found in the axilla.
. Preoperative skin preparation with chlorhexidine gluconate and alcohol is less effective than povidone-iodine against C. acnes.
. C. acnes is known for its fastidious, slow-growing nature, often requiring up to 14 days of anaerobic culture for detection.
. Single-stage revision is uniformly contraindicated in C. acnes periprosthetic joint infection (PJI).
. C. acnes infections typically present with high fever, marked leukocytosis, and elevated CRP within 2 weeks of surgery.

Correct Answer & Explanation

. C. acnes is known for its fastidious, slow-growing nature, often requiring up to 14 days of anaerobic culture for detection.

Explanation

Cutibacterium acnes (formerly Propionibacterium acnes) is a gram-positive anaerobic rod that is part of the normal skin flora, particularly in the shoulder region. It is a slow-growing, fastidious organism, and cultures should be held for at least 14 days in anaerobic environments to avoid false-negative results. Preoperative preparation with chlorhexidine/alcohol or hydrogen peroxide is more effective than povidone-iodine in reducing the burden of C. acnes. These infections often present indolently without systemic signs such as fever or significantly elevated inflammatory markers.

Question 3699

Topic: 3. Adult Reconstruction (Hip & Knee)

A 74-year-old female sustains a displaced 3-part proximal humerus fracture with varus impaction of the head. Bone density testing indicates significant osteoporosis. If the surgeon decides to proceed with open reduction and internal fixation (ORIF) using a locked plate rather than arthroplasty, what is the most common complication she is at risk for postoperatively?

. Glenoid erosion
. Rotator cuff tear arthropathy
. Intra-articular screw penetration (screw cut-out)
. Aseptic loosening of the diaphyseal screws
. Heterotopic ossification

Correct Answer & Explanation

. Intra-articular screw penetration (screw cut-out)

Explanation

Intra-articular screw penetration (screw cut-out) is the most frequent complication following locked plating of proximal humerus fractures, particularly in elderly patients with osteoporotic bone and varus-pattern fractures. It occurs due to varus collapse of the humeral head fragment, causing the screws to breach the articular surface. Medial calcar support is critical to minimize this risk.

Question 3700

Topic: 3. Adult Reconstruction (Hip & Knee)

A 19-year-old male presents to the emergency department with severe chest pain, shortness of breath, and dysphagia after being tackled during a rugby match. Examination reveals a depression at the right sternoclavicular joint. A CT scan confirms a posterior sternoclavicular dislocation. What is the most appropriate initial management?

. Immediate open reduction in the emergency department
. Observation and sling immobilization
. Closed reduction in the operating room with cardiothoracic surgery available
. Figure-of-eight brace application
. Resection arthroplasty of the medial clavicle

Correct Answer & Explanation

. Closed reduction in the operating room with cardiothoracic surgery available

Explanation

Posterior sternoclavicular dislocations are orthopedic emergencies due to the risk of compression of mediastinal structures (trachea, esophagus, major vessels). Attempts at closed reduction should be performed in the operating room with a cardiothoracic surgeon readily available on standby due to the life-threatening risk of major vascular injury during the reduction maneuver.

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