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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 184 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 3661

Topic: Total Hip Arthroplasty (THA)

A 62-year-old woman is evaluated for persistent hip pain 8 years after receiving a metal-on-metal total hip arthroplasty. Radiographs reveal an acetabular inclination angle of 58 degrees. Laboratory testing demonstrates significantly elevated serum cobalt and chromium levels. Which of the following systemic conditions is a known, severe manifestation of cobalt toxicity (cobaltism) stemming from a failing metal-on-metal implant?

. Restrictive pulmonary disease
. Cardiomyopathy
. Acute tubular necrosis
. Aplastic anemia
. Hepatocellular carcinoma

Correct Answer & Explanation

. Cardiomyopathy

Explanation

Elevated serum cobalt levels from failing metal-on-metal implants can lead to systemic cobalt toxicity, or 'cobaltism.' This syndrome is characterized by a constellation of systemic effects, most notably a dilated cardiomyopathy, which can be fatal if the source is not removed. Other systemic manifestations of cobaltism include neuro-ocular toxicity (visual and hearing impairment), peripheral neuropathy, and thyroid dysfunction (hypothyroidism).

Question 3662

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old man presents with progressive groin pain and swelling in his left hip 6 years after a primary total hip arthroplasty utilizing a titanium stem, a modular cobalt-chromium (CoCr) femoral head, and a highly cross-linked polyethylene liner. An MRI with metal artifact reduction sequence (MARS) reveals a thick-walled cystic mass communicating with the joint space. Aspiration yields cloudy, sterile fluid. What is the primary pathophysiologic mechanism responsible for this presentation?

. Mechanically induced third-body wear of the polyethylene liner
. Type IV delayed hypersensitivity reaction to fretting and corrosion products at the head-neck junction
. Low-grade indolent infection caused by Cutibacterium acnes
. Polyethylene oxidation leading to catastrophic bearing failure
. Aseptic loosening secondary to classic macrophage-induced osteolysis

Correct Answer & Explanation

. Type IV delayed hypersensitivity reaction to fretting and corrosion products at the head-neck junction

Explanation

The clinical scenario describes an adverse local tissue reaction (ALTR) or aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) occurring in a metal-on-polyethylene total hip arthroplasty. In the absence of a metal-on-metal bearing surface, this reaction is typically triggered by mechanically assisted crevice corrosion (MACC) and fretting at the modular head-neck junction (trunnionosis) between the titanium stem and CoCr head. The release of metal ions and wear debris incites a Type IV delayed hypersensitivity reaction, leading to pseudotumor formation and tissue necrosis.

Question 3663

Topic: Total Hip Arthroplasty (THA)

A 45-year-old active male undergoes a primary total hip arthroplasty (THA). A ceramic-on-ceramic bearing is chosen. At 2-year follow-up, he complains of a squeaking noise from his hip during deep bending and walking. What is the most significant surgeon-controlled risk factor for this complication?

. Use of a 36-mm femoral head
. Cup anteversion of 15 degrees
. Cup inclination greater than 50 degrees
. Use of a highly cross-linked polyethylene liner
. Use of an uncemented femoral stem

Correct Answer & Explanation

. Cup inclination greater than 50 degrees

Explanation

Squeaking is a specific complication associated with ceramic-on-ceramic bearings. Risk factors include component malposition, specifically high acetabular cup inclination and/or version that leads to edge loading, loss of fluid film lubrication, and stripe wear. While patient factors (like high BMI or young age) play a role, surgeon-controlled factors primarily revolve around avoiding excessive inclination (>50 degrees) and malversion.

Question 3664

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female presents with a painful catching sensation in her left knee 14 months after a posterior-stabilized total knee arthroplasty (TKA). She reports a 'clunk' that is both heard and felt when extending her knee from a flexed position, typically occurring between 30 and 45 degrees of flexion. Which of the following is the most likely etiology of her symptoms?

. Undersized femoral component
. Fibrovascular nodule formation at the superior pole of the patella
. Overstuffing of the patellofemoral joint
. Use of a high-flexion polyethylene insert
. Internal rotation of the tibial component

Correct Answer & Explanation

. Fibrovascular nodule formation at the superior pole of the patella

Explanation

Patellar clunk syndrome is characterized by a painful catch or clunk when extending the knee from a flexed position. It occurs in posterior-stabilized (PS) knee designs when a fibrovascular nodule develops at the superior pole of the patella and catches in the intercondylar notch of the femoral component. Treatment typically involves arthroscopic resection of the nodule.

Question 3665

Topic: Total Knee Arthroplasty (TKA)

A 68-year-old male presents with a feeling of 'giving way' when descending stairs 1 year after a primary TKA. On examination, the knee is well-aligned, fully extends, and flexes to 125 degrees. There is a 2 mm symmetric opening to varus and valgus stress in extension. However, at 90 degrees of flexion, there is marked anterior-posterior translation and 6 mm of opening to varus and valgus stress. Which of the following surgical errors most likely contributed to this presentation?

. Undersizing the femoral component in the anteroposterior dimension
. Excessive distal femoral resection
. Excessive posterior tibial slope
. Oversizing the femoral component
. Inadequate posterior condylar offset restoration

Correct Answer & Explanation

. Undersizing the femoral component in the anteroposterior dimension

Explanation

The patient is experiencing flexion instability, characterized by a balanced extension gap but a loose flexion gap. Undersizing the femoral component in the anteroposterior (AP) dimension (especially when using anterior referencing, which resects more posterior condyle) increases the flexion gap without affecting the extension gap, leading to isolated flexion instability.

Question 3666

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following findings serves as a definitive major criterion that firmly establishes the diagnosis of a periprosthetic joint infection (PJI)?

. Elevated serum CRP, elevated serum ESR, and one positive intraoperative culture
. A sinus tract communicating with the joint
. Purulence in the joint with an elevated synovial fluid WBC count
. Positive leukocyte esterase on synovial fluid dipstick and elevated serum D-dimer
. Elevated alpha-defensin level and a positive synovial fluid Gram stain

Correct Answer & Explanation

. A sinus tract communicating with the joint

Explanation

According to the 2018 ICM criteria for PJI, the presence of a sinus tract communicating with the joint OR two positive periprosthetic cultures with phenotypically identical organisms are considered major criteria. Either of these is definitive evidence of PJI on its own. The other listed options represent minor criteria that must be scored cumulatively to reach a diagnosis.

Question 3667

Topic: 3. Adult Reconstruction (Hip & Knee)

An 82-year-old female falls and sustains a periprosthetic fracture of the right femur around her cemented THA, which was placed 15 years ago. Radiographs reveal a spiral fracture around the tip of the stem. The stem appears subsided and loose, but there is adequate bone stock proximally and distally. According to the Vancouver classification, what is the most appropriate management?

. Open reduction and internal fixation with a lateral locking plate and cerclage wires
. Revision total hip arthroplasty with a fully porous-coated long uncemented stem bypassing the fracture
. Revision total hip arthroplasty with a cemented long stem and impaction bone grafting
. Nonoperative management in a hip spica cast
. Excision arthroplasty (Girdlestone procedure)

Correct Answer & Explanation

. Revision total hip arthroplasty with a fully porous-coated long uncemented stem bypassing the fracture

Explanation

This is a Vancouver B2 periprosthetic femur fracture (fracture around the stem, loose stem, good bone stock). The gold standard treatment for a Vancouver B2 fracture is revision arthroplasty using a long uncemented, extensively porous-coated, or fluted tapered modular stem to bypass the fracture by at least two cortical diameters, combined with appropriate fracture fixation (e.g., cerclage cables) if necessary. ORIF alone is reserved for Vancouver B1 fractures (well-fixed stem).

Question 3668

Topic: 3. Adult Reconstruction (Hip & Knee)

In a posterior-stabilized (PS) total knee arthroplasty, the interaction between the femoral cam and the tibial post is designed to substitute for a native ligamentous structure. What is the primary biomechanical function of this cam-post engagement?

. To prevent anterior translation of the tibia during flexion
. To enforce posterior femoral rollback during deep flexion
. To provide valgus stability in extension
. To prevent posterior subluxation of the tibia in extension
. To assist in the screw-home mechanism during terminal extension

Correct Answer & Explanation

. To enforce posterior femoral rollback during deep flexion

Explanation

In a posterior-stabilized (PS) TKA, the cam on the femoral component engages the post on the tibial polyethylene insert during knee flexion. This mechanism substitutes for the resected posterior cruciate ligament (PCL). Its primary function is to enforce posterior femoral rollback (preventing anterior translation of the femur on the tibia) during deep flexion, which improves maximal flexion and optimizes the quadriceps lever arm.

Question 3669

Topic: 3. Adult Reconstruction (Hip & Knee)

Elevation of the joint line during a revision total knee arthroplasty, which often occurs due to the use of an oversized femoral component and a thick tibial polyethylene insert to fill gaps, is most likely to result in which of the following specific complications?

. Mid-flexion instability
. Relative (pseudo) patella baja and secondary impingement
. Excessive posterior femoral rollback
. Medial collateral ligament attenuation
. Patella alta and subluxation

Correct Answer & Explanation

. Relative (pseudo) patella baja and secondary impingement

Explanation

Elevating the joint line during TKA alters the kinematics of the knee. The distance from the tibial tubercle to the joint line decreases, leading to relative or 'pseudo' patella baja. This can result in impingement of the patella against the anterior tibial polyethylene or tibial tray, decreased range of motion, altered patellofemoral mechanics, and anterior knee pain.

Question 3670

Topic: Total Hip Arthroplasty (THA)

During preoperative templating for a total hip arthroplasty, the surgeon plans to increase the femoral offset by 10 mm compared to the contralateral normal hip, without changing the leg length. What is an expected biomechanical consequence of this planned alteration?

. Increased joint reaction force across the hip
. Decreased tension on the abductor musculature
. Increased risk of trochanteric bursitis and iliotibial band tension
. Decreased bending moment on the femoral stem
. Increased risk of bony impingement during abduction

Correct Answer & Explanation

. Increased risk of trochanteric bursitis and iliotibial band tension

Explanation

Increasing femoral offset increases the lever arm of the abductor muscles, which decreases the force required by the abductors to maintain a level pelvis and decreases the overall joint reaction force (making A and B incorrect). However, excessive offset lateralizes the greater trochanter, increasing tension on the iliotibial band, which dramatically increases the risk of trochanteric bursitis. It also increases the bending moment (stress) on the femoral stem.

Question 3671

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old male presents with new-onset right groin pain and a sensation of fullness 6 years after undergoing a primary total hip arthroplasty. The implant utilizes a titanium stem, a cobalt-chromium modular head, and a highly cross-linked polyethylene liner. Radiographs show a well-fixed stem and cup with no evidence of osteolysis. Laboratory evaluation reveals a normal ESR and CRP, but serum cobalt levels are markedly elevated at 14 mcg/L, while serum chromium is normal at 1.5 mcg/L. What is the most likely diagnosis?

. Polyethylene wear with secondary osteolysis
. Mechanically assisted crevice corrosion
. Metallosis secondary to acetabular component loosening
. Low-virulence periprosthetic joint infection
. Iliopsoas impingement on the anterior acetabular rim

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

The clinical scenario of a metal-on-polyethylene total hip arthroplasty with an elevated serum cobalt out of proportion to serum chromium is the hallmark of mechanically assisted crevice corrosion (MACC), also known as trunnionosis. This occurs at the modular head-neck junction. Metallosis from an adverse local tissue reaction (ALTR) can result, leading to groin pain and a cystic mass (pseudotumor) causing a sensation of fullness. Unlike metal-on-metal bearing wear, which typically presents with elevated levels of both cobalt and chromium, trunnionosis heavily favors cobalt elevation.

Question 3672

Topic: 3. Adult Reconstruction (Hip & Knee)

In evaluating the kinematics of a cruciate-retaining (CR) total knee arthroplasty (TKA) compared to a native knee, which of the following kinematic patterns is most frequently observed during deep flexion?

. Increased posterior femoral rollback
. Paradoxical anterior femoral translation
. Excessive internal rotation of the tibia
. Complete preservation of the 'screw-home' mechanism
. Lateral pivot pattern rather than medial pivot

Correct Answer & Explanation

. Paradoxical anterior femoral translation

Explanation

In a native knee, the femur undergoes posterior rollback during flexion, which is largely driven by the anterior cruciate ligament (ACL) and the geometry of the condyles. In a cruciate-retaining (CR) TKA, the ACL is sacrificed, and the posterior cruciate ligament (PCL) is retained. Because the intricate balance of the native ACL and joint geometry is altered, the femur commonly undergoes paradoxical anterior translation during mid-to-deep flexion instead of the native posterior rollback. This can lead to decreased maximal flexion and increased polyethylene wear.

Question 3673

Topic: 3. Adult Reconstruction (Hip & Knee)

During a direct anterior approach (DAA) for a primary total hip arthroplasty, the surgeon utilizes the Hueter interval to access the hip joint. Which of the following statements accurately describes the neurologic risk during the superficial dissection of this approach?

. The superior gluteal nerve is at high risk due to its course through the substance of the sartorius muscle.
. The obturator nerve is directly exposed when retracting the tensor fasciae latae laterally.
. The lateral femoral cutaneous nerve is highly susceptible to injury if dissection strays too far anteriorly or medially over the sartorius.
. The sciatic nerve is routinely encountered and must be retracted posteriorly before capsulotomy.
. The femoral nerve provides direct innervation to the tensor fasciae latae and must be mobilized.

Correct Answer & Explanation

. The lateral femoral cutaneous nerve is highly susceptible to injury if dissection strays too far anteriorly or medially over the sartorius.

Explanation

The direct anterior approach (DAA) utilizes the true internervous Hueter interval between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The lateral femoral cutaneous nerve (LFCN) typically courses over the sartorius or in the fascial layer just medial to the tensor fasciae latae. It is at significant risk of iatrogenic injury (stretching or transection) during the superficial dissection and retractor placement. Surgeons must stay carefully within the fascial sleeve of the TFL to minimize LFCN injury.

Question 3674

Topic: 3. Adult Reconstruction (Hip & Knee)
In the pathophysiology of aseptic loosening following total hip arthroplasty, the most robust inflammatory macrophage response and subsequent osteolysis is triggered by ultra-high molecular weight polyethylene (UHMWPE) wear particles of which specific size range?
. Less than 0.1 micrometers
. 0.1 to 1.0 micrometers
. 5 to 10 micrometers
. 10 to 50 micrometers
. Greater than 50 micrometers

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Macrophage activation and the subsequent inflammatory cascade (release of TNF-alpha, IL-1, IL-6) leading to osteolysis is most efficiently triggered by submicron polyethylene particles, specifically those in the 0.1 to 1.0 micrometer range. Particles in this size range are easily phagocytosed by macrophages, initiating an intracellular cascade that fails to digest the particle, keeping the macrophage continually activated. Particles larger than 10 micrometers are typically surrounded by foreign-body giant cells rather than individually phagocytosed.

Question 3675

Topic: 3. Adult Reconstruction (Hip & Knee)
Aseptic loosening secondary to periprosthetic osteolysis is a leading cause of total hip arthroplasty failure. This process is primarily mediated by a macrophage response to ultra-high-molecular-weight polyethylene (UHMWPE) wear debris. What is the optimal particle size range that most effectively stimulates macrophages to release pro-inflammatory cytokines?
. Less than 0.1 micrometers
. 0.1 to 1.0 micrometers
. 5.0 to 10.0 micrometers
. 10.0 to 50.0 micrometers
. Greater than 50.0 micrometers

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Macrophage-induced osteolysis is a particle-size-dependent phenomenon. The most biologically active UHMWPE wear particles are in the submicron range, specifically between 0.1 and 1.0 micrometers (often cited as 0.1-0.5 ยตm). These particles are easily phagocytosed by macrophages, which subsequently fail to digest them and instead release osteolytic cytokines like TNF-alpha, IL-1, and IL-6. Particles larger than 10 micrometers are typically engulfed by multinucleated giant cells but are less efficient at stimulating the massive cytokine cascade seen with submicron debris.

Question 3676

Topic: 3. Adult Reconstruction (Hip & Knee)

During the pathogenesis of a periprosthetic joint infection (PJI), Staphylococcus epidermidis transitions from a planktonic state to form a robust mature biofilm on the implant surface. Which of the following components is the primary structural constituent of the extracellular polymeric substance (EPS) matrix synthesized by these bacteria during the accumulation phase?

. Peptidoglycan
. Polysaccharide intercellular adhesin (PIA)
. Lipopolysaccharide (LPS)
. Fibronectin-binding protein (FnBP)
. Teichoic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Biofilm formation in Staphylococcus epidermidis (and many S. aureus strains) heavily relies on the production of Polysaccharide Intercellular Adhesin (PIA), which is synthesized by the gene products of the icaADBC operon. PIA forms the main bulk of the extracellular polymeric substance (EPS) matrix during the accumulation phase, encasing the bacteria and protecting them from host immune responses and antimicrobial agents. Fibronectin-binding proteins (Option D) are critical for the initial adhesion phase to host proteins coating the implant, rather than forming the bulk of the mature matrix.

Question 3677

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient undergoes revision total hip arthroplasty for aseptic loosening. Intraoperative tissue samples are obtained. The histologic analysis demonstrates a predominantly macrophage-driven inflammatory response. Which of the following cytokines is most directly responsible for the subsequent osteoclast activation and periprosthetic osteolysis seen in this condition?

. Interleukin-4 (IL-4)
. Interleukin-10 (IL-10)
. Tumor necrosis factor-alpha (TNF-alpha)
. Transforming growth factor-beta (TGF-beta)
. Interferon-gamma (IFN-gamma)

Correct Answer & Explanation

. Tumor necrosis factor-alpha (TNF-alpha)

Explanation

The biologic response to particulate wear debris (such as polyethylene) is mediated primarily by macrophages. Upon phagocytosis of wear debris, macrophages release pro-inflammatory cytokines, including TNF-alpha, IL-1, and IL-6. These cytokines directly stimulate osteoclastogenesis via the RANK/RANKL pathway, ultimately leading to periprosthetic osteolysis. IL-4, IL-10, and IFN-gamma typically exert inhibitory effects on osteoclastogenesis.

Question 3678

Topic: 3. Adult Reconstruction (Hip & Knee)
A 68-year-old man presents with aseptic loosening of his total hip arthroplasty 15 years after the index procedure. Radiographs show significant periprosthetic osteolysis. Which of the following particulate sizes and characteristics is most effectively phagocytosed by macrophages, subsequently triggering the greatest release of tumor necrosis factor-alpha (TNF-alpha) and RANKL?
. 0.1 to 1.0 micrometers
. 5.0 to 10.0 micrometers
. 10 to 50 micrometers
. Greater than 50 micrometers
. Soluble metallic ions

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Macrophages are most efficiently activated by ultra-high molecular weight polyethylene (UHMWPE) wear particles in the submicron size range of 0.1 to 1.0 micrometers. Particles larger than 10 micrometers are typically not phagocytosed by single macrophages and instead become surrounded by foreign body giant cells. The macrophage activation by submicron particles leads to the release of TNF-alpha, IL-1, IL-6, and PGE2, upregulating RANKL and driving osteoclastic bone resorption (osteolysis).

Question 3679

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old man presents with a chronic periprosthetic joint infection (PJI) 2 years after a total knee arthroplasty. Intraoperative cultures eventually grow Staphylococcus epidermidis. The pathogenesis of this infection involves the formation of a biofilm. Which phase of biofilm formation is characterized primarily by van der Waals forces and hydrophobic interactions without the production of an extracellular polymeric substance?

. Maturation phase
. Dispersion phase
. Quorum sensing phase
. Primary attachment phase
. Irreversible adhesion phase

Correct Answer & Explanation

. Primary attachment phase

Explanation

Biofilm formation occurs in several distinct phases: 1) Primary (reversible) attachment, mediated by weak non-specific forces such as van der Waals forces and hydrophobic interactions. 2) Irreversible adhesion, mediated by specific cell surface adhesins (e.g., MSCRAMMs). 3) Maturation, involving the production of the extracellular polymeric substance (EPS) matrix and cellular multiplication. 4) Dispersion/Detachment, where planktonic bacteria are released to spread the infection.

Question 3680

Topic: 3. Adult Reconstruction (Hip & Knee)

A histological slide from a revised total hip arthroplasty shows sheets of macrophages surrounding the implant interface. Polyethylene wear debris leads to aseptic loosening primarily through macrophage activation. Which of the following particulate sizes is most readily phagocytosed by macrophages, eliciting the strongest biological response for osteolysis?

. 0.1 to 1.0 micrometers
. 5.0 to 10.0 micrometers
. 15.0 to 50.0 micrometers
. 100 to 500 micrometers
. Greater than 1 millimeter

Correct Answer & Explanation

. 0.1 to 1.0 micrometers

Explanation

Macrophages preferentially phagocytose particles in the submicron range, typically 0.1 to 1.0 micrometers. Particles of this specific size elicit the most robust inflammatory response, causing macrophages to release pro-inflammatory cytokines such as TNF-alpha, IL-1, and IL-6. These cytokines stimulate osteoclastogenesis via the RANK/RANKL pathway, ultimately leading to periprosthetic osteolysis and aseptic loosening. Larger particles are typically surrounded by foreign body giant cells rather than individually phagocytosed by macrophages.

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