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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 134 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 2661

Topic: 3. Adult Reconstruction (Hip & Knee)
In the evolution of bearing surfaces for total hip arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) was introduced to improve long-term survivorship. The process of irradiating the polyethylene to induce cross-linking primarily improves which of the following material properties?
. Tensile strength
. Fatigue strength
. Resistance to adhesive and abrasive wear
. Resistance to in vivo oxidation
. Yield strength

Correct Answer & Explanation

. Resistance to adhesive and abrasive wear

Explanation

The primary purpose of irradiating UHMWPE is to break polymer chains and form cross-links, which vastly improves its resistance to adhesive and abrasive wear (thereby reducing osteolysis). However, this cross-linking comes at a mechanical cost: it actually decreases the material's tensile strength, yield strength, and fatigue resistance. To combat oxidation from free radicals generated during irradiation, the polyethylene is subsequently remelted, annealed, or doped with an antioxidant like Vitamin E.

Question 2662

Topic: 3. Adult Reconstruction (Hip & Knee)

To optimize stability and minimize the risk of posterior dislocation in primary total hip arthroplasty, the combined anteversion (McKhann's or Ranawat's concept) of the acetabular and femoral components should ideally fall into which range?

. 0 to 15 degrees
. 15 to 20 degrees
. 25 to 45 degrees
. 50 to 65 degrees
. Greater than 65 degrees

Correct Answer & Explanation

. 25 to 45 degrees

Explanation

The concept of combined anteversion (the sum of cup anteversion and femoral stem anteversion) helps prevent impingement and dislocation. For a posterior approach, the widely accepted safe zone for combined anteversion is between 25 and 45 degrees.

Question 2663

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the trial reduction reveals that the knee is excessively tight in flexion but symmetric and well-balanced in extension. Which of the following surgical steps is the most appropriate to correct this mismatch?

. Downsize the femoral component while utilizing an anterior referencing guide
. Resect more distal femur
. Upsize the femoral component
. Resect more proximal tibia
. Perform a larger posterior capsular release

Correct Answer & Explanation

. Downsize the femoral component while utilizing an anterior referencing guide

Explanation

When a knee is tight in flexion but balanced in extension, the flexion gap is too small relative to the extension gap. To increase the flexion gap without altering the extension gap, the surgeon must resect more posterior femoral condyle. Downsizing the femoral component (decreasing the AP size) and keeping the anterior flange flush (anterior referencing) will resect more posterior bone, enlarging the flexion gap.

Question 2664

Topic: 3. Adult Reconstruction (Hip & Knee)

In patients undergoing total hip arthroplasty (THA) with a ceramic-on-ceramic bearing surface, the phenomenon of 'squeaking' is a known complication. Which of the following factors is most strongly and consistently associated with the development of this noise?

. Use of a larger femoral head size (>36 mm)
. Decreased femoral offset
. Obesity (BMI > 40)
. Acetabular cup retroversion and steep inclination
. Use of an uncemented femoral stem

Correct Answer & Explanation

. Acetabular cup retroversion and steep inclination

Explanation

Squeaking in ceramic-on-ceramic THA is multifactorial but is most strongly correlated with component malposition, specifically acetabular cup retroversion or steep (excessive) inclination. This malposition leads to edge loading, disruption of fluid-film lubrication, stripe wear on the ceramic head, and subsequent micro-vibrations that produce the audible squeak.

Question 2665

Topic: 3. Adult Reconstruction (Hip & Knee)

What is the primary mechanical and chemical advantage of incorporating Vitamin E (alpha-tocopherol) into highly cross-linked polyethylene (HXLPE) in total joint arthroplasty?

. It increases the melting point of the polyethylene, allowing higher sterilization temperatures.
. It acts as a free radical scavenger, eliminating the need for post-irradiation remelting while preventing oxidation.
. It enhances the initial cross-linking density prior to gamma irradiation.
. It increases the elastic modulus of the bearing surface to match cortical bone.
. It promotes rapid osteointegration at the cement-bone interface.

Correct Answer & Explanation

. It acts as a free radical scavenger, eliminating the need for post-irradiation remelting while preventing oxidation.

Explanation

Vitamin E is an antioxidant that acts as a free radical scavenger. By adding Vitamin E to highly cross-linked polyethylene (HXLPE), manufacturers can avoid the post-irradiation remelting or annealing steps that decrease mechanical strength. This provides a bearing surface that maintains high mechanical strength and fatigue resistance while effectively preventing long-term oxidative degradation.

Question 2666

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty, the trial reduction reveals that the knee is excessively tight in both flexion and extension. Which of the following is the most appropriate surgical step to balance the knee?

. Recut the distal femur to remove more bone.
. Decrease the femoral component size.
. Downsize the thickness of the tibial polyethylene insert.
. Release the posterior cruciate ligament.
. Translate the femoral component anteriorly.

Correct Answer & Explanation

. Downsize the thickness of the tibial polyethylene insert.

Explanation

When a knee is symmetrically tight in both flexion and extension, the overall joint space (global gap) is too small. The easiest and most appropriate first step is to decrease the thickness of the tibial polyethylene insert. If the thinnest poly is already being used, the proximal tibia should be recut to increase both the flexion and extension gaps equally.

Question 2667

Topic: Total Hip Arthroplasty (THA)

A 68-year-old female experiences recurrent anterior dislocations following a right total hip arthroplasty performed via a posterior approach. Radiographs show the acetabular component has 55 degrees of inclination and 35 degrees of anteversion. The femoral stem is in neutral version. Which of the following is the most appropriate definitive management?

. Prescribe an abduction brace for 6 weeks.
. Revise the femoral stem to a retroverted position.
. Revise the acetabular component to decrease anteversion.
. Perform a greater trochanteric advancement.
. Exchange the femoral head to a larger diameter and add a constrained liner without changing the shell.

Correct Answer & Explanation

. Revise the acetabular component to decrease anteversion.

Explanation

The acetabular component is excessively anteverted (35 degrees) and over-inclined (55 degrees). The normal target (Lewinnek safe zone) is typically 15-20 degrees of anteversion and 40-45 degrees of inclination. Excessive anteversion strongly predisposes to anterior dislocation. The appropriate definitive treatment is revision of the malpositioned acetabular component to restore appropriate anteversion and inclination.

Question 2668

Topic: 3. Adult Reconstruction (Hip & Knee)

In modern metal-on-polyethylene total hip arthroplasty, the development of an adverse local tissue reaction (ALTR) often referred to as 'trunnionosis' is most commonly driven by which of the following mechanisms at the head-neck taper?

. Galvanic corrosion
. Fretting corrosion
. Mechanically assisted crevice corrosion
. Pitting corrosion
. Uniform corrosion

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

Trunnionosis in modern modular total hip arthroplasty is primarily caused by mechanically assisted crevice corrosion (MACC). The micromotion at the modular head-neck junction (fretting) destroys the protective passivation layer of the metal, and the local restricted fluid environment (crevice) becomes highly acidic, leading to accelerated localized corrosion and the release of metal ions that trigger an adverse local tissue reaction (ALTR).

Question 2669

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old patient sustains a periprosthetic femur fracture around a total hip arthroplasty following a mechanical fall. Radiographs demonstrate a fracture around the stem. The stem is radiographically loose, but there is adequate proximal bone stock. According to the Vancouver classification, what is the standard treatment for this injury?

. Open reduction and internal fixation with a locking plate alone
. Revision to a standard cemented short stem
. Revision to a cementless long bypass stem
. Impaction bone grafting with retention of the original stem
. Conservative management with traction

Correct Answer & Explanation

. Revision to a cementless long bypass stem

Explanation

This is a Vancouver B2 fracture (fracture around the stem, loose stem, adequate bone stock). The standard of care for a Vancouver B2 fracture is revision arthroplasty using a cementless long bypass stem (such as a fully porous-coated or fluted tapered modular stem) that bypasses the most distal fracture line by at least two cortical diameters. ORIF alone is contraindicated for a loose stem and is associated with high failure rates.

Question 2670

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old patient who underwent a primary posterior-stabilized (PS) total knee arthroplasty 18 months ago presents with anterior knee pain and a palpable 'catch' or 'clunk' in the knee. The classic patellar clunk syndrome occurs during which of the following phases of knee range of motion?

. Passive knee flexion beyond 90 degrees
. Active knee extension from approximately 45 degrees to 30 degrees
. Active knee flexion from 0 degrees to 10 degrees
. Passive extension at full terminal extension
. Deep weight-bearing squatting

Correct Answer & Explanation

. Active knee extension from approximately 45 degrees to 30 degrees

Explanation

Patellar clunk syndrome is a complication most commonly associated with posterior-stabilized (PS) total knee arthroplasty designs. A fibrosynovial nodule forms at the superior pole of the patella. As the knee is flexed, the nodule drops into the intercondylar box of the femoral component. As the knee is actively extended, typically between 45 and 30 degrees of flexion, the nodule catches on the superior edge of the intercondylar box and pops out, producing a painful 'clunk'.

Question 2671

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, after making the standard bony cuts, the surgeon uses spacer blocks and notes that the knee is tight in extension but balanced in flexion. Which of the following is the most appropriate next step to balance the knee?

. Resect additional posterior femoral condyle
. Downsize the femoral component
. Resect additional distal femur
. Resect additional proximal tibia
. Release the superficial medial collateral ligament

Correct Answer & Explanation

. Resect additional distal femur

Explanation

If a knee is tight in extension but balanced in flexion, the extension gap needs to be increased without affecting the flexion gap. Resecting more distal femur or releasing the posterior capsule will achieve this. Resecting additional proximal tibia would increase both gaps symmetrically.

Question 2672

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male with a metal-on-polyethylene total hip arthroplasty presents with new-onset groin pain 8 years postoperatively. Radiographs show a well-fixed stem and cup. Joint aspiration yields fluid with elevated cobalt levels but normal chromium levels. MRI with MARS sequencing shows a large cystic mass adjacent to the joint. What is the most likely diagnosis?

. Polyethylene wear-induced osteolysis
. Adverse local tissue reaction (ALTR) secondary to trunnionosis
. Infection by a low-virulence organism like C. acnes
. Periprosthetic joint infection with Staphylococcus aureus
. Primary soft tissue sarcoma

Correct Answer & Explanation

. Adverse local tissue reaction (ALTR) secondary to trunnionosis

Explanation

Elevated serum or synovial fluid cobalt levels out of proportion to chromium levels in the setting of a non-metal-on-metal THA strongly suggests mechanically assisted crevice corrosion (MACC) at the modular head-neck junction (trunnionosis). This causes an adverse local tissue reaction (ALTR), frequently presenting as a pseudotumor or cystic mass.

Question 2673

Topic: 3. Adult Reconstruction (Hip & Knee)

What is the primary mechanism of wear in a well-functioning metal-on-polyethylene total hip arthroplasty?

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

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary mechanism of wear in a well-functioning metal-on-polyethylene total hip arthroplasty. It occurs when microscopic asperities on the metal surface temporarily bond to the softer polyethylene. As the surfaces slide, these bonds break, tearing away submicron particles of polyethylene. Abrasive wear occurs when a rough, harder surface plows into a softer surface (e.g., a scratched femoral head). Third-body wear involves foreign particles (like bone or cement) acting as an abrasive between the two surfaces. Fatigue wear is due to cyclic loading leading to subsurface delamination.

Question 2674

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old patient underwent a total hip arthroplasty utilizing a ceramic-on-ceramic bearing. At a 2-year follow-up, the patient complains of a noticeable squeaking noise with certain hip movements. Which of the following factors is most strongly and mechanically associated with squeaking in this specific bearing surface?

. Excessive acetabular cup anteversion
. Excessive acetabular cup retroversion
. Edge loading due to component malposition
. The use of a small diameter femoral head (e.g., 28 mm)
. Patient body mass index (BMI) greater than 40

Correct Answer & Explanation

. Edge loading due to component malposition

Explanation

Squeaking is a well-documented complication specific to ceramic-on-ceramic (CoC) total hip arthroplasties. It is strongly associated with edge loading, which occurs when the femoral head loads against the rim of the acetabular liner rather than the center. This is most often caused by cup malposition (especially steep inclination or inadequate anteversion leading to microseparation or impingement). Edge loading disrupts the fluid film lubrication and causes stripe wear, eventually leading to the audible squeak.

Question 2675

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty for a severe, rigid varus deformity, the surgeon performs a standard medial release. After releasing the deep medial collateral ligament and excising all medial osteophytes, the knee remains excessively tight medially in both flexion and extension. What is the next most appropriate anatomical structure to release to balance the knee?

. Posterior cruciate ligament
. Posteromedial capsule
. Superficial medial collateral ligament
. Semimembranosus insertion
. Pes anserinus

Correct Answer & Explanation

. Superficial medial collateral ligament

Explanation

In varus knee balancing, the release sequence targets specific tight structures. The deep MCL and osteophytes are released first. If the knee is tight in both flexion and extension, the superficial medial collateral ligament (sMCL) is the primary structure restricting both gaps. Releasing the sMCL (often via subperiosteal stripping off the tibia) will increase both the flexion and extension gaps symmetrically. If the knee was tight ONLY in extension, the posteromedial capsule and semimembranosus would be the next structures to release.

Question 2676

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female with advanced Parkinson's disease suffers her third posterior dislocation following a primary total hip arthroplasty (THA). Evaluation reveals her acetabular and femoral components are well-fixed and in acceptable alignment. Abductor muscle function is intact. Which of the following is the most appropriate surgical option?

. Revision to a constrained acetabular liner
. Revision to a dual mobility articulation
. Revision of the femoral stem to increase anteversion
. Application of a hip spica cast for 6 weeks
. Trochanteric advancement to tension the abductors

Correct Answer & Explanation

. Revision to a dual mobility articulation

Explanation

Dual mobility cups are highly effective for managing or preventing recurrent instability in patients with neuromuscular disorders like Parkinson's disease. They provide a larger effective femoral head diameter, dramatically increasing the jump distance. Because her abductors are intact, dual mobility is preferred over a constrained liner, which has a higher risk of impingement, mechanical failure, and component loosening.

Question 2677

Topic: 3. Adult Reconstruction (Hip & Knee)

During a revision total knee arthroplasty, the surgeon notes that the medial collateral ligament (MCL) is severely attenuated and non-functional, resulting in gross, uncorrectable coronal plane instability. The extensor mechanism and posterior capsule remain structurally intact. Which of the following implant constraints is the most appropriate choice?

. Cruciate-retaining (CR) TKA
. Posterior-stabilized (PS) TKA
. Constrained Condylar Knee (CCK) TKA
. Rotating hinge TKA
. Unicompartmental knee arthroplasty

Correct Answer & Explanation

. Constrained Condylar Knee (CCK) TKA

Explanation

A Constrained Condylar Knee (CCK) is indicated when there is severe collateral ligament (MCL or LCL) deficiency causing coronal instability. The CCK design features a high and wide central post within a deep femoral box to provide varus/valgus constraint. A rotating hinge is typically reserved for global (multiligamentous) instability, massive bone loss, or combined collateral and extensor mechanism deficiencies.

Question 2678

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient presents 2 years after a posterior-stabilized (PS) total knee arthroplasty with anterior knee pain and a subjective feeling of the knee 'giving way' into recurvatum. Radiographs show no component loosening. Revision surgery is performed, and inspection of the polyethylene insert reveals advanced wear exclusively on the anterior aspect of the tibial post. Which of the following surgical errors most likely caused this specific wear pattern?

. Excessive posterior slope of the tibial component
. Excessive flexion of the femoral component
. Undersizing of the femoral component
. Internal rotation of the tibial component
. Anterior placement of the femoral component

Correct Answer & Explanation

. Excessive flexion of the femoral component

Explanation

Anterior post impingement in a PS total knee arthroplasty typically occurs in full extension or hyperextension. If the femoral component is placed in excessive flexion, the intercondylar box and cam mechanism can impinge on the anterior aspect of the tibial post as the knee reaches full extension. Other causes of anterior post impingement include inadequate posterior slope (or excessive anterior slope) of the tibial component and recurvatum deformity.

Question 2679

Topic: Total Hip Arthroplasty (THA)

A patient with a ceramic-on-ceramic total hip arthroplasty (THA) complains of a loud squeaking noise during gait. This phenomenon is strongly associated with 'edge loading' of the ceramic components. Which of the following acetabular component position errors most significantly increases the risk of edge loading?

. Decreased cup inclination and decreased cup anteversion
. Increased cup inclination and excessive cup anteversion
. Decreased cup inclination and increased femoral offset
. Increased femoral offset and decreased cup anteversion
. Decreased femoral offset and decreased cup inclination

Correct Answer & Explanation

. Increased cup inclination and excessive cup anteversion

Explanation

Edge loading in a ceramic-on-ceramic THA occurs when the femoral head contacts the rim of the acetabular liner rather than the articulating concavity, leading to stripe wear, loss of fluid film lubrication, and squeaking. The risk of edge loading is markedly increased with suboptimal cup positioning, specifically increased cup inclination (a steep cup) and excessive anteversion or retroversion.

Question 2680

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old man with advanced Paget's disease of the right hemipelvis and proximal femur is scheduled for a total hip arthroplasty (THA). Which of the following perioperative considerations is most accurate regarding THA in patients with Paget's disease?

. They have a substantially decreased risk of intraoperative hemorrhage
. Preoperative treatment with bisphosphonates increases the risk of excessive intraoperative bleeding
. Uncemented femoral stems have a higher rate of survival than cemented stems
. There is an increased risk of early aseptic loosening with uncemented components
. Prophylactic radiation is routinely required to prevent heterotopic ossification

Correct Answer & Explanation

. There is an increased risk of early aseptic loosening with uncemented components

Explanation

THA in Pagetic bone is challenging due to hypervascularity, altered bone mechanics, and deformity. Patients are at increased risk of bleeding, which can be mitigated by preoperative bisphosphonate therapy. Due to the poor structural quality and ongoing remodeling of Pagetic bone, uncemented stems have historically shown a higher risk of early aseptic loosening and subsidence compared to cemented stems, making cemented femoral fixation generally preferred, though modern highly porous components are closing this gap.

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