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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 126 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 2501

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior-stabilized total knee arthroplasty (TKA), after making the initial bone cuts, the surgeon uses spacer blocks to assess the gaps. The knee is found to be balanced and symmetrical in extension, but it is unacceptably tight in flexion. Which of the following is the most appropriate surgical step to balance the knee?

. Recut the distal femur to remove more bone
. Downsize the femoral component and use a thicker polyethylene insert
. Decrease the posterior slope of the tibial cut
. Upsize the femoral component to increase the posterior offset
. Recut the posterior femur to remove more bone or use a smaller femoral component

Correct Answer & Explanation

. Recut the posterior femur to remove more bone or use a smaller femoral component

Explanation

If a TKA is balanced in extension but tight in flexion, the flexion gap needs to be increased without altering the extension gap. The flexion gap is primarily determined by the posterior femoral condyles and the tibial cut. Since the extension gap is fine, the tibial cut should not be altered (as it affects both gaps equally). Therefore, the solution is to remove more posterior femoral bone. This is accomplished by downsizing the femoral component (which shifts the posterior cut anteriorly) or recutting the posterior femur with an anterior referencing system.

Question 2502

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active man presents with a high-pitched 'squeaking' sound coming from his hip during ambulation. He underwent a primary total hip arthroplasty 3 years ago. What bearing surface combination is most classically associated with this specific phenomenon?

. Metal-on-polyethylene
. Ceramic-on-polyethylene
. Ceramic-on-ceramic
. Metal-on-metal
. Oxinium-on-highly cross-linked polyethylene

Correct Answer & Explanation

. Ceramic-on-ceramic

Explanation

Squeaking is a well-documented and specific complication associated with ceramic-on-ceramic bearing surfaces in total hip arthroplasty. It is thought to be caused by microseparation, stripe wear, component malposition (e.g., edge loading), or third-body debris altering the fluid film lubrication.

Question 2503

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old woman undergoes revision total hip arthroplasty for recurrent instability due to severe abductor deficiency. A constrained acetabular liner is placed to prevent further dislocations. Which of the following is the most frequent mode of failure associated with constrained liners?

. Aseptic loosening at the bone-implant interface of the acetabular shell
. Accelerated polyethylene wear leading to severe pelvic osteolysis
. Fatigue fracture of the modular femoral neck
. Dislocation of the femoral head from the constrained locking mechanism
. Dissociation of the constrained liner from the metal acetabular shell

Correct Answer & Explanation

. Aseptic loosening at the bone-implant interface of the acetabular shell

Explanation

While constrained liners prevent the femoral head from dislocating, they do so by transferring the impaction and impingement forces directly to the acetabular shell-bone interface. This increased stress most commonly leads to aseptic loosening of the acetabular component. Dislocation from the mechanism or liner dissociation are less common modes of failure.

Question 2504

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria for Periprosthetic Joint Infection (PJI), which of the following findings is considered a 'major' criterion, meaning it is diagnostic in itself of a PJI in a total knee arthroplasty?

. Elevated serum C-reactive protein (CRP) > 10 mg/L
. Synovial fluid white blood cell (WBC) count > 3,000 cells/µL
. Positive alpha-defensin test
. Two positive periprosthetic cultures with phenotypically identical organisms
. Elevated synovial fluid polymorphonuclear (PMN) percentage > 80%

Correct Answer & Explanation

. Two positive periprosthetic cultures with phenotypically identical organisms

Explanation

According to the ICM criteria, there are two major criteria that definitively diagnose a PJI: 1) A sinus tract communicating with the joint, or 2) Two positive periprosthetic tissue/fluid cultures with phenotypically identical organisms. The other options are considered 'minor' criteria that contribute points toward the diagnostic scoring system but are not independently diagnostic.

Question 2505

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active female undergoes a primary total hip arthroplasty using a ceramic-on-ceramic bearing surface. Two years later, she presents complaining of an audible 'squeaking' sound from the hip during walking, bending, and ascending stairs. There is no pain, and radiographs show well-fixed components. Which of the following factors is most strongly associated with the development of squeaking in ceramic-on-ceramic articulations?

. Use of a larger diameter femoral head (>36 mm)
. Acetabular component retroversion and low inclination
. Microseparation and edge-loading due to steep acetabular cup inclination
. Titanium taper corrosion (trunnionosis)
. Aseptic loosening of the femoral stem

Correct Answer & Explanation

. Microseparation and edge-loading due to steep acetabular cup inclination

Explanation

Squeaking is a specific complication associated with ceramic-on-ceramic (CoC) bearing surfaces, occurring in up to 10% of patients. The most consistent biomechanical factor linked to CoC squeaking is edge-loading, which typically results from malpositioning of the acetabular component—specifically high inclination (steep cup) and extreme anteversion or retroversion. Edge-loading disrupts the fluid film lubrication, leading to stripe wear and the subsequent squeaking phenomenon.

Question 2506

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty in a patient with a fixed varus deformity of 15 degrees, a step-wise medial soft tissue release is undertaken. Following the release of the deep medial collateral ligament and osteophytes, the joint remains excessively tight medially in extension, but is balanced in flexion. What is the most appropriate next step in the soft tissue release sequence?

. Release of the superficial medial collateral ligament from its tibial attachment
. Release of the pes anserinus tendons
. Release of the posterior oblique ligament and posteromedial capsule
. Epicondylar osteotomy of the medial femoral condyle
. Release of the anterior cruciate ligament

Correct Answer & Explanation

. Release of the posterior oblique ligament and posteromedial capsule

Explanation

In a varus knee undergoing TKA, medial releases should be targeted based on whether the knee is tight in flexion, extension, or both. The deep MCL affects both. If the knee remains tight specifically in extension (but balanced in flexion), the posteromedial corner structures must be released. This includes the posterior oblique ligament, the posteromedial capsule, and potentially the semimembranosus expansion. Releasing the superficial MCL (sMCL) predominantly affects the flexion gap more than the extension gap, and extensive release of the sMCL risks creating instability.

Question 2507

Topic: 3. Adult Reconstruction (Hip & Knee)

In modern total hip arthroplasty, the use of highly cross-linked ultra-high-molecular-weight polyethylene (HXLPE) has significantly reduced the rate of wear and subsequent osteolysis. However, the processes of cross-linking and subsequent thermal treatment (melting or annealing) primarily result in which of the following mechanical trade-offs?

. Increased susceptibility to oxidation and decreased yield strength
. Decreased fatigue strength and fracture toughness
. Increased sliding friction and higher torque forces
. Decreased resistance to adhesive wear
. Increased fluid absorption causing liner swelling

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

While highly cross-linked polyethylene substantially improves wear resistance (decreasing abrasive and adhesive wear), the higher cross-link density—along with thermal treatments to eliminate free radicals—makes the material more brittle. This results in decreased mechanical properties, specifically decreased fatigue strength, ultimate tensile strength, and fracture toughness, which can increase the risk of catastrophic liner fracture.

Question 2508

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female undergoes a primary total hip arthroplasty via a posterior approach. On post-operative day one, she is noted to have a profound foot drop and absent sensation over the dorsum of her foot, though sensation on the plantar aspect of the foot is intact. What structure was most likely injured during the procedure?

. Tibial division of the sciatic nerve
. Peroneal division of the sciatic nerve
. Sural nerve
. Saphenous nerve
. Femoral nerve

Correct Answer & Explanation

. Peroneal division of the sciatic nerve

Explanation

The sciatic nerve consists of the common peroneal and tibial divisions. During a posterior approach to the hip, the peroneal division is uniquely vulnerable to injury (often from excessive traction or retractor placement) because it is tethered at the fibular head and sits more laterally. Injury results in foot drop (loss of dorsiflexion) and numbness over the dorsum of the foot.

Question 2509

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty (TKA), the surgeon inserts the trial components and assesses the gaps. The knee is perfectly balanced and symmetrical in full extension, but it is too tight in flexion, preventing full range of motion. What is the most appropriate surgical modification to correct this specific mismatch?

. Resect more bone from the distal femur
. Downsize the femoral component (smaller AP dimension)
. Release the posterior capsule
. Resect more bone from the proximal tibia
. Upsize the tibial polyethylene insert

Correct Answer & Explanation

. Downsize the femoral component (smaller AP dimension)

Explanation

A knee that is tight in flexion but balanced in extension requires an isolated increase in the flexion gap. Downsizing the femoral component (smaller Anterior-Posterior dimension) shifts the posterior condyles anteriorly, effectively increasing the flexion gap without altering the extension gap. Resecting more distal femur or releasing the posterior capsule affects the extension gap. Resecting more tibia or changing the poly affects both gaps equally.

Question 2510

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, standard gamma irradiation and cross-linking of polyethylene can generate free radicals. Which post-irradiation process is most commonly used to completely eliminate these free radicals and prevent oxidation, despite slightly decreasing mechanical strength?

. Ethylene oxide sterilization
. Remelting (heating above the melting point)
. Annealing (heating below the melting point)
. Vitamin E infusion prior to irradiation
. Plasma gas sterilization

Correct Answer & Explanation

. Remelting (heating above the melting point)

Explanation

Remelting involves heating the polyethylene above its melting point. This completely eliminates free radicals, effectively reducing oxidation risk, but it decreases the crystallinity and mechanical properties (like yield and ultimate tensile strength) compared to annealing.

Question 2511

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male is evaluated for a painful total knee arthroplasty 3 years after the index surgery. According to the 2018 International Consensus Meeting (ICM) criteria for diagnosing Periprosthetic Joint Infection (PJI), which of the following minor criteria provides the highest number of points toward the diagnostic score?

. Elevated serum C-reactive protein (CRP)
. Positive synovial fluid alpha-defensin
. Elevated serum D-dimer
. Single positive tissue culture
. Elevated erythrocyte sedimentation rate (ESR)

Correct Answer & Explanation

. Positive synovial fluid alpha-defensin

Explanation

In the 2018 ICM criteria for PJI, a positive synovial fluid alpha-defensin test (or high leukocyte esterase) provides 3 points. Elevated serum CRP (>10 mg/L), elevated D-dimer (>860 ng/mL), and a single positive culture each provide 2 points. Elevated ESR provides 1 point. A total score of 6 or greater confirms PJI.

Question 2512

Topic: Total Knee Arthroplasty (TKA)

In a posterior-stabilized Total Knee Arthroplasty (TKA), the trial components demonstrate a knee that is perfectly balanced and symmetric in full extension but is excessively tight in flexion, causing liftoff and preventing flexion past 80 degrees. The joint line and patellar tracking are acceptable. Which of the following is the most appropriate intraoperative step to balance the knee?

. Use a thinner polyethylene insert
. Resect additional bone from the distal femur
. Release the posterior knee capsule
. Increase the posterior slope of the tibial cut
. Upsize the femoral component

Correct Answer & Explanation

. Increase the posterior slope of the tibial cut

Explanation

When a TKA is balanced in extension but tight in flexion, the flexion gap must be increased without significantly altering the extension gap. Increasing the posterior slope of the tibial cut effectively opens the flexion gap without changing the extension gap. Using a thinner insert or resecting more distal femur would loosen the knee in extension. Upsizing the femoral component would make the flexion space even tighter.

Question 2513

Topic: 3. Adult Reconstruction (Hip & Knee)

A 50-year-old active male underwent a total hip arthroplasty (THA) utilizing a ceramic-on-ceramic bearing surface. Two years postoperatively, he presents complaining of an audible 'squeaking' sound emanating from his hip during deep flexion activities. Which of the following component malpositions is most strongly associated with the development of this phenomenon?

. Acetabular cup retroversion
. Acetabular cup placed in excessive inclination and anteversion
. Femoral stem placed in varus
. Femoral stem placed in excessive anteversion
. Failure to restore native femoral offset

Correct Answer & Explanation

. Acetabular cup placed in excessive inclination and anteversion

Explanation

Squeaking in ceramic-on-ceramic (CoC) THA is strongly correlated with edge loading. Edge loading most commonly occurs when the acetabular component is placed in excessive inclination (abduction) and/or excessive anteversion, leading to unseating of the head and shifting of the contact stress to the rim of the liner, which disrupts the fluid lubrication film.

Question 2514

Topic: Total Hip Arthroplasty (THA)

When revising a total hip arthroplasty to reduce the risk of postoperative dislocation, increasing the femoral head size (e.g., from 28 mm to 36 mm) primarily improves stability by increasing the impingement-free range of motion and increasing which of the following parameters?

. Volumetric wear rate
. Jump distance
. Medialization of the center of rotation
. Risk of trunnionosis
. Acetabular component version

Correct Answer & Explanation

. Jump distance

Explanation

A larger femoral head enhances THA stability via two main mechanisms: 1) Increasing the head-neck ratio, which improves the impingement-free range of motion, and 2) Increasing the 'jump distance,' which is the vertical distance the femoral head must travel out of the acetabular socket before it dislocates. While a larger head may increase volumetric wear, that is an adverse effect, not a mechanism of stability.

Question 2515

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary Total Knee Arthroplasty utilizing measured resection, the surgeon notes that with the trial components in place, the knee is well-balanced and stable in extension but excessively tight in flexion. Which of the following maneuvers is the most appropriate next step to balance the knee?

. Recut the distal femur to remove more bone
. Increase the thickness of the polyethylene insert
. Downsize the femoral component
. Upsize the femoral component
. Release the posterior capsule

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is tight in flexion but well-balanced in extension implies that the flexion gap is too small relative to the extension gap. When using an anterior referencing system, downsizing the femoral component decreases the anteroposterior (AP) dimension of the femur by removing more posterior condylar bone. This specifically increases the flexion gap without affecting the extension gap.

Question 2516

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old female with a metal-on-metal total hip arthroplasty placed 8 years ago presents with new-onset groin pain. A MARS MRI reveals a solid pseudotumor and fluid collection around the hip joint. Laboratory tests show elevated serum cobalt and chromium. Aspiration yields clear fluid with 200 WBCs/uL and 10% PMNs. What is the definitive management?

. Two-stage revision arthroplasty for infection
. Revision of the acetabular and femoral components to a non-metal-on-metal bearing
. Isolated bearing exchange utilizing a larger metal head
. Observation and repeat MRI in 6 months
. Initiation of systemic chelation therapy

Correct Answer & Explanation

. Revision of the acetabular and femoral components to a non-metal-on-metal bearing

Explanation

The patient has an Adverse Local Tissue Reaction (ALTR) / Aseptic Lymphocyte-Dominated Vasculitis-Associated Lesion (ALVAL) secondary to a metal-on-metal bearing. This is confirmed by the pseudotumor on MRI, elevated metal ions, and negative infection workup (low WBC and PMNs on aspiration). The definitive treatment is revision arthroplasty to a different bearing surface (e.g., ceramic-on-polyethylene) to remove the source of metal wear debris.

Question 2517

Topic: Total Hip Arthroplasty (THA)

When comparing ceramic-on-ceramic (CoC) to metal-on-polyethylene (MoP) total hip arthroplasties, which of the following is an established advantage of the CoC articulation?

. Elimination of the risk of bearing fracture
. Increased resistance to third-body wear
. Complete absence of squeaking
. Higher tolerance for component malposition
. Lower rate of impingement at the extremes of motion

Correct Answer & Explanation

. Increased resistance to third-body wear

Explanation

Ceramic-on-ceramic bearings have very high scratch resistance and are highly resistant to third-body wear compared to MoP bearings. However, they carry a known risk of catastrophic component fracture, have a lower tolerance for malposition (which can lead to edge loading, stripe wear, and squeaking), and do not inherently lower the rate of mechanical impingement.

Question 2518

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female presents with a painful 'catch' and a palpable pop at 30 to 45 degrees of knee flexion as she actively extends her knee, one year following a posterior-stabilized (PS) total knee arthroplasty. What implant design factor is most heavily implicated in the pathogenesis of this condition?

. Excessive valgus alignment of the femoral component
. High box-to-cam ratio of the femoral component
. A thick anterior flange of the femoral component
. Medialization of the patellar button
. Use of an all-polyethylene tibial component

Correct Answer & Explanation

. High box-to-cam ratio of the femoral component

Explanation

The patient has patellar clunk syndrome, caused by a fibrosynovial nodule at the superior pole of the patella catching in the intercondylar box of a PS femoral component during extension. Risk factors include a high or sharp anterior intercondylar box (high box-to-cam ratio), patella baja, thick patellar buttons, and a flexed femoral component.

Question 2519

Topic: 3. Adult Reconstruction (Hip & Knee)

Seven years after undergoing a primary non-cemented total hip arthroplasty using a titanium stem, a cobalt-chromium head, and a highly cross-linked polyethylene liner, a 62-year-old man presents with progressive groin pain. Radiographs show a well-fixed stem and cup with no osteolysis. Metal ion testing reveals elevated cobalt levels that are disproportionately higher than chromium levels. MRI with metal artifact reduction shows a cystic fluid collection. What is the primary mechanism of failure?

. Polyethylene wear resulting in macrophage activation
. Mechanically assisted crevice corrosion at the head-neck taper
. Galvanic corrosion at the acetabular shell-screw interface
. Aseptic loosening of the femoral stem
. Chronic periprosthetic joint infection

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the head-neck taper

Explanation

The scenario describes adverse local tissue reaction (ALTR) or pseudotumor formation secondary to trunnionosis. This occurs via mechanically assisted crevice corrosion (MACC) at the head-neck taper (trunnion), particularly when a cobalt-chromium head is used on a titanium stem. The disproportionately high serum cobalt relative to chromium is a hallmark of taper corrosion, unlike bearing surface wear in metal-on-metal hips where the ratio is closer to 1:1.

Question 2520

Topic: 3. Adult Reconstruction (Hip & Knee)

A surgeon is performing a cruciate-retaining total knee arthroplasty (CR-TKA). With the trial components in place, the knee is found to be perfectly balanced in full extension, but abnormally tight in 90 degrees of flexion. Which of the following maneuvers is most appropriate to resolve this specific kinematic mismatch?

. Increase the thickness of the tibial polyethylene insert
. Recut the distal femur to remove more bone
. Release the posterior cruciate ligament (PCL)
. Upsize the femoral component
. Release the superficial medial collateral ligament

Correct Answer & Explanation

. Release the posterior cruciate ligament (PCL)

Explanation

A knee that is tight in flexion but balanced in extension in a CR-TKA indicates an isolated tight flexion gap. This can be caused by a tight PCL, insufficient posterior tibial slope, or an oversized anteroposterior femoral component. Releasing the PCL (or increasing posterior tibial slope, or downsizing the femoral component AP dimension) will increase the flexion gap without affecting the extension gap. Recutting the distal femur affects only the extension gap.

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