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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 130 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 2581

Topic: 3. Adult Reconstruction (Hip & Knee)

During pre-operative planning for a total hip arthroplasty (THA) in a patient with severe protrusio acetabuli, the surgeon considers the effects of acetabular component positioning. Normalizing the center of rotation by lateralizing the acetabular cup out of the protrusio defect will have what direct effect on the biomechanics of the hip joint?

. Decreases the abductor lever arm
. Decreases the joint reaction force by decreasing the body weight lever arm
. Increases the joint reaction force by increasing the body weight lever arm
. Increases the incidence of anterior dislocation by increasing offset
. Decreases the tension on the iliopsoas tendon

Correct Answer & Explanation

. Increases the joint reaction force by increasing the body weight lever arm

Explanation

The joint reaction force (JRF) across the hip is a function of the body weight lever arm and the abductor lever arm. The center of rotation in a normal hip is located relatively medially. In protrusio, the center of rotation is excessively medialized, which abnormally decreases the body weight lever arm. When the surgeon lateralizes the cup to restore standard anatomic positioning, the distance from the center of gravity (body weight) to the center of rotation is increased. This increases the body weight lever arm, which subsequently increases the overall joint reaction force compared to the protrusio state. (However, restoring anatomy optimizes abductor mechanics and overall gait).

Question 2582

Topic: 3. Adult Reconstruction (Hip & Knee)
In the setting of metal-on-polyethylene total joint arthroplasty, the generation of ultra-high-molecular-weight polyethylene (UHMWPE) wear debris is a primary driver of macrophage activation and subsequent periprosthetic osteolysis. Which specific mode of wear is primarily responsible for generating the millions of submicron-sized particles that lead to this cascade?
. Abrasive wear
. Adhesive wear
. Fatigue wear
. Third-body wear
. Fretting wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear occurs when the bearing surfaces come into direct contact, creating microscopic transient chemical bonds or "micro-welds" between the polymer and the metal surface. As the surfaces continue to slide, these micro-welds are sheared off, pulling microscopic fragments of polyethylene away from the bulk material. This process continuously produces millions of tiny, submicron-sized wear particles. It is these submicron particles that are phagocytosed by macrophages, triggering the inflammatory cascade (release of TNF-alpha, IL-1, IL-6) that results in osteolysis. Abrasive wear creates larger scratches (ploughing), and fatigue wear leads to macroscopic delamination or pitting.

Question 2583

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the historical use of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic heads was associated with a specific mode of failure in vivo. Which of the following best describes this phenomenon?

. Catastrophic brittle fracture due to edge loading
. Phase transformation from tetragonal to monoclinic leading to surface roughening
. Galvanic corrosion at the trunnion interface
. Polyethylene oxidation induced by zirconium ions
. Adhesive wear due to third-body abrasive particles

Correct Answer & Explanation

. Phase transformation from tetragonal to monoclinic leading to surface roughening

Explanation

Y-TZP ceramics are prone to low-temperature degradation in the aqueous environment of the human body, a process known as phase transformation. The ceramic transforms from a tetragonal phase to a weaker monoclinic phase with a volumetric expansion, leading to microcracking, increased surface roughness, and subsequent massive polyethylene wear or ceramic fracture.

Question 2584

Topic: 3. Adult Reconstruction (Hip & Knee)

Patellar clunk syndrome is a recognized complication following total knee arthroplasty (TKA). Which of the following prosthesis designs and surgical factors is most strongly associated with the development of this complication?

. Cruciate-retaining design with a highly cross-linked polyethylene liner
. Posterior-stabilized design with a prominent femoral box and patella alta
. Anterior-stabilized design with a low-contact stress mobile bearing
. Unicompartmental knee arthroplasty in a patient with patella baja
. Cruciate-retaining design with a domed patellar button

Correct Answer & Explanation

. Posterior-stabilized design with a prominent femoral box and patella alta

Explanation

Patellar clunk syndrome is a complication primarily seen in posterior-stabilized (PS) TKA designs. It results from the formation of a fibrous nodule at the superior pole of the patella that catches within the intercondylar notch (femoral box) during active knee extension from a flexed position. Older PS designs with a sharp, prominent anterior intercondylar box, as well as joint line elevation leading to relative patella alta, significantly increase the risk.

Question 2585

Topic: 3. Adult Reconstruction (Hip & Knee)

In the context of total hip arthroplasty (THA), osteolysis is a primary cause of aseptic loosening. Which mechanism of polyethylene wear is the primary generator of the submicron, highly reactive particles that incite the macrophage-mediated osteolytic cascade?

. Abrasive wear
. Adhesive wear
. Third-body wear
. Fretting wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear occurs when microscopic asperities on the bearing surfaces bond and then break off. In metal-on-polyethylene THA bearings, adhesive wear is the primary source of the billions of submicron-sized polyethylene particles generated annually, which are phagocytosed by macrophages, initiating the release of cytokines (TNF-alpha, IL-1, IL-6) and leading to osteolysis.

Question 2586

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is symmetric and balanced in extension, but symmetrically tight in 90 degrees of flexion. Which of the following technical adjustments is the most appropriate next step to balance the knee?

. Resect more bone from the distal femur
. Downsize the femoral component and use anterior referencing
. Upsize the femoral component and use a thicker polyethylene insert
. Resect more bone from the proximal tibia
. Perform a release of the posterior capsule

Correct Answer & Explanation

. Downsize the femoral component and use anterior referencing

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without altering the extension gap. Downsizing the femoral component (using an anterior referencing system) translates the posterior condyles anteriorly, thereby resecting more posterior condylar bone and selectively increasing the flexion gap.

Question 2587

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female undergoes a primary total hip arthroplasty via a posterior approach. Six weeks postoperatively, she sustains a posterior dislocation while picking up an object from the floor. Closed reduction is successful. Plain radiographs demonstrate appropriate cup inclination (45 degrees) and anteversion (20 degrees). What is the most appropriate next step in management?

. Revision of the acetabular component to increase anteversion
. Revision to a constrained liner
. Application of a hip abduction brace for 6-12 weeks
. Revision of the femoral head to increase offset
. Observation with physical therapy and hip precautions

Correct Answer & Explanation

. Application of a hip abduction brace for 6-12 weeks

Explanation

For a first-time postoperative posterior dislocation occurring within the first few weeks following THA, with radiographically well-positioned components, the initial management is closed reduction followed by non-operative measures. The most appropriate step is the application of a hip abduction brace to restrict provocative positioning (flexion/adduction/internal rotation) while allowing the posterior soft tissues and capsule to heal. Early revision is not indicated unless there is a clear mechanical cause or recurrent instability.

Question 2588

Topic: 3. Adult Reconstruction (Hip & Knee)
Which of the following bearing surfaces in total hip arthroplasty exhibits the lowest volumetric wear rate in laboratory simulator testing?
. Cobalt-chrome on ultra-high-molecular-weight polyethylene (UHMWPE)
. Cobalt-chrome on highly cross-linked polyethylene (HXLPE)
. Ceramic on ultra-high-molecular-weight polyethylene (UHMWPE)
. Ceramic on ceramic
. Metal on metal

Correct Answer & Explanation

. Ceramic on ceramic

Explanation

Ceramic-on-ceramic bearing surfaces exhibit the lowest volumetric wear rates of all currently available bearing couples in total hip arthroplasty. This is due to their extreme hardness, scratch resistance, and excellent lubrication properties (fluid film lubrication). Despite the low wear rate, they carry distinct risks such as squeaking and catastrophic component fracture.

Question 2589

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for periprosthetic joint infection (PJI), which of the following represents a major criterion that is definitive for the diagnosis of PJI?

. Elevated serum C-reactive protein (CRP) and D-dimer
. Single positive tissue culture for Staphylococcus epidermidis
. Purulence in the affected joint
. Two positive periprosthetic cultures with phenotypically identical organisms
. Elevated synovial fluid leukocyte esterase

Correct Answer & Explanation

. Two positive periprosthetic cultures with phenotypically identical organisms

Explanation

According to the 2018 ICM criteria, the two major criteria (either of which definitively establishes the diagnosis of PJI) are: 1) Two positive periprosthetic cultures with phenotypically identical organisms, or 2) A sinus tract communicating with the joint. Purulence in the joint was downgraded to a minor criterion in modern scoring systems due to subjectivity and false positives in metal-on-metal or highly inflammatory conditions.

Question 2590

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following is considered a 'major criterion' for the definitive diagnosis of a Periprosthetic Joint Infection (PJI)?

. Elevated serum C-reactive protein (CRP) and D-dimer
. Elevated synovial white blood cell count > 3,000 cells/ยตL
. A single positive intraoperative tissue culture
. A sinus tract communicating directly with the joint
. A positive synovial fluid alpha-defensin immunoassay

Correct Answer & Explanation

. A sinus tract communicating directly with the joint

Explanation

The 2018 ICM criteria define two major criteria for definitive PJI: 1) Two positive periprosthetic cultures with phenotypically identical organisms, or 2) A sinus tract communicating with the joint. The other options are considered minor criteria that contribute to a scoring system but do not singularly confirm PJI.

Question 2591

Topic: 3. Adult Reconstruction (Hip & Knee)

In a well-functioning conventional metal-on-polyethylene Total Hip Arthroplasty (THA), what is the primary mode of wear that generates the majority of clinically significant submicron polyethylene debris, ultimately leading to macrophage-mediated osteolysis?

. Abrasive wear
. Adhesive wear
. Fatigue wear
. Third-body wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary continuous wear mechanism between two smooth bearing surfaces (such as the metal femoral head and the polyethylene liner). It occurs when microscopic asperities on the softer material (polyethylene) adhere to the harder surface and are then torn away during sliding motion. This process generates millions of submicron particles that provoke the biologic cascade leading to osteolysis.

Question 2592

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary posterior-stabilized total knee arthroplasty, the surgeon assesses the gap kinematics with trial components in place. The knee demonstrates a symmetric and well-balanced extension gap, but the flexion gap is unacceptably tight. Which of the following is the most appropriate technical adjustment to correct this imbalance?

. Resect more distal femur
. Increase the thickness of the polyethylene insert
. Downsize the femoral component
. Release the posterior capsule
. Release the superficial medial collateral ligament

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion but balanced in extension has an isolated tight flexion gap. To selectively loosen the flexion gap without altering the extension gap, the surgeon should decrease the anteroposterior dimension of the femoral component by downsizing it (using a smaller femoral component with the same anterior reference to decrease the posterior condylar offset). Increasing the posterior tibial slope (within safe limits) is another option. Resecting more distal femur or releasing the posterior capsule would inappropriately affect the extension gap.

Question 2593

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, which bearing surface combination exhibits the lowest linear wear rate but carries the unique risk of stripe wear and squeaking?

. Cobalt-chrome on highly cross-linked polyethylene
. Ceramic on ceramic
. Ceramic on highly cross-linked polyethylene
. Cobalt-chrome on cobalt-chrome
. Oxidized zirconium on highly cross-linked polyethylene

Correct Answer & Explanation

. Ceramic on ceramic

Explanation

Ceramic-on-ceramic bearings have the lowest linear and volumetric wear rates of all combinations. However, they are uniquely associated with audible 'squeaking' and can exhibit stripe wear during edge loading due to micro-separation.

Question 2594

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following is considered a 'major' criterion (definitive evidence) for the diagnosis of a periprosthetic joint infection?

. Elevated serum CRP > 10 mg/L
. Elevated synovial WBC > 3000 cells/uL
. Presence of a sinus tract communicating with the prosthesis
. A single positive intraoperative tissue culture
. Elevated synovial PMN percentage > 80%

Correct Answer & Explanation

. Presence of a sinus tract communicating with the prosthesis

Explanation

Under the MSIS criteria for periprosthetic joint infection, a major criterion is either: 1) a sinus tract communicating with the prosthesis, or 2) a pathogen isolated by culture from at least two separate tissue or fluid samples. The other options are considered minor criteria.

Question 2595

Topic: Total Hip Arthroplasty (THA)

A 68-year-old male undergoes a primary Total Hip Arthroplasty via a posterior approach. Postoperatively, he exhibits a complete foot drop and inability to extend his toes. Which specific neural structure is most commonly injured to produce this deficit during THA?

. Tibial division of the sciatic nerve
. Common peroneal division of the sciatic nerve
. Femoral nerve
. Deep peroneal nerve
. Superior gluteal nerve

Correct Answer & Explanation

. Common peroneal division of the sciatic nerve

Explanation

The common peroneal division of the sciatic nerve is the most frequently injured nerve during a THA (most commonly from stretch during leg lengthening or retractor placement). It is more susceptible than the tibial division because it is tethered at the fibular head, is positioned more laterally, and has less connective tissue support within the sciatic sheath.

Question 2596

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty, the surgeon trials the components and notes that the knee is perfectly balanced and stable in full extension, but feels excessively tight in 90 degrees of flexion. What is the most appropriate surgical step to correct this specific mismatch?

. Resect more bone from the distal femur
. Resect more bone from the proximal tibia
. Downsize the femoral component and use a thicker polyethylene insert
. Downsize the femoral component with an anterior referencing system
. Perform a posterior capsular release

Correct Answer & Explanation

. Downsize the femoral component with an anterior referencing system

Explanation

A knee that is balanced in extension but tight in flexion has an isolated tight flexion gap. With an anterior referencing system, downsizing the femoral component will decrease the anteroposterior dimension by resecting more posterior condylar bone, thereby enlarging the flexion gap without altering the distal femoral cut (which controls the extension gap).

Question 2597

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old highly active male is undergoing an elective Total Hip Arthroplasty. The surgeon opts for a ceramic-on-ceramic (CoC) bearing surface. Which of the following represents the primary biomechanical advantage of CoC compared to conventional metal-on-polyethylene bearings?

. Absolute elimination of component squeaking
. Highest resistance to catastrophic component fracture
. Lowest overall volumetric wear rate
. Greatest ease of modular component extraction during revision
. Best tribological tolerance for component malposition and edge loading

Correct Answer & Explanation

. Lowest overall volumetric wear rate

Explanation

Ceramic-on-ceramic (CoC) bearings provide the lowest volumetric wear rate of any current bearing couple due to their extreme hardness, wettability, and smoothness. This makes them highly desirable for young, active patients. However, they carry a risk of catastrophic fracture, can produce squeaking, and are highly intolerant of component malpositioning (which leads to edge loading and stripe wear).

Question 2598

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old man undergoes a right total hip arthroplasty via a posterior approach. Six weeks postoperatively, he experiences an anterior dislocation of the prosthesis while getting out of a low chair. Which of the following combinations of component positioning is most likely responsible for an anterior dislocation?

. Excessive acetabular anteversion and excessive femoral anteversion
. Acetabular retroversion and femoral retroversion
. Excessive acetabular anteversion and femoral retroversion
. Acetabular retroversion and excessive femoral anteversion
. Excessive acetabular inclination and femoral retroversion

Correct Answer & Explanation

. Excessive acetabular anteversion and excessive femoral anteversion

Explanation

Anterior dislocation in total hip arthroplasty typically occurs when the hip is placed in extension and external rotation, and is strongly associated with excessive combined anteversion (excessive acetabular anteversion and excessive femoral anteversion). Conversely, posterior dislocations are associated with inadequate anteversion or excessive retroversion.

Question 2599

Topic: 3. Adult Reconstruction (Hip & Knee)

The primary blood supply to the scaphoid bone is tenuous, predisposing the proximal pole to avascular necrosis after a fracture. This critical blood supply originates from branches of the radial artery and enters the bone at which specific anatomical location?

. Volar surface, distal to the waist
. Volar surface, proximal to the waist
. Dorsal ridge, distal to the waist
. Dorsal ridge, proximal to the waist
. Scapholunate interosseous ligament

Correct Answer & Explanation

. Dorsal ridge, distal to the waist

Explanation

The primary blood supply to the scaphoid (accounting for 70-80% of its vascularity) comes from dorsal branches of the radial artery that enter the bone along the dorsal ridge distal to the waist. This intraosseous blood flow is retrograde, explaining the high rate of avascular necrosis in proximal pole fractures.

Question 2600

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old man presents with a painful, swollen left hip 5 years after undergoing a primary total hip arthroplasty (THA) with a metal-on-polyethylene bearing. Radiographs reveal no evidence of loosening or osteolysis. Aspiration yields cloudy, non-purulent fluid with a normal white blood cell count. Laboratory evaluation reveals a significantly elevated serum cobalt level with a relatively normal serum chromium level. What is the most likely diagnosis?

. Periprosthetic joint infection
. Polyethylene wear-induced osteolysis
. Adverse local tissue reaction (ALTR) due to mechanically assisted crevice corrosion
. Recurrent occult dislocation
. Aseptic loosening due to stress shielding

Correct Answer & Explanation

. Adverse local tissue reaction (ALTR) due to mechanically assisted crevice corrosion

Explanation

The clinical presentation is classic for 'trunnionosis', which involves mechanically assisted crevice corrosion (MACC) at the head-neck junction of a total hip arthroplasty. This occurs even with metal-on-polyethylene bearings, specifically at the modular junction. It characteristically produces elevated serum cobalt levels that are out of proportion to chromium levels, leading to an adverse local tissue reaction (ALTR). Infection would typically show an elevated WBC count in the aspirate. Polyethylene wear typically causes osteolysis, which is not seen here.

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