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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 182 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 3621

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with acute onset of knee pain, swelling, and wound drainage 3 weeks after a primary TKA. Inflammatory markers are elevated. Knee aspiration yields 65,000 WBC/µL with 92% neutrophils. Cultures subsequently grow Staphylococcus aureus. Radiographs confirm the implants are well-fixed. What is the most appropriate surgical treatment?

. Intravenous antibiotics for 6 weeks without surgery
. One-stage exchange arthroplasty
. Two-stage exchange arthroplasty
. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange
. Suppressive oral antibiotics

Correct Answer & Explanation

. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange

Explanation

The patient has an acute post-operative periprosthetic joint infection (typically defined as occurring within 4 weeks of surgery). For acute post-operative infections with well-fixed implants and appropriate soft tissue coverage, Debridement, Antibiotics, and Implant Retention (DAIR) with modular polyethylene exchange is the standard of care.

Question 3622

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old male undergoes a primary total knee arthroplasty. Intraoperatively, the surgeon notes that the patella tracks laterally and tends to subluxate during flexion. Which of the following intraoperative technical errors is the most likely cause of this finding?

. External rotation of the tibial component
. External rotation of the femoral component
. Internal rotation of the femoral component
. Medialization of the patellar component
. Lateralization of the tibial tray

Correct Answer & Explanation

. Internal rotation of the femoral component

Explanation

Internal rotation of the femoral component and/or internal rotation of the tibial component increases the Q-angle, leading to lateral patellar tracking and potential subluxation. Internal rotation of the femoral component displaces the trochlear groove medially, exacerbating lateral tracking. To improve patellar tracking, the surgeon can externally rotate the femoral or tibial components, medialize the patellar component, or lateralize the femoral/tibial components.

Question 3623

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female presents with a painful catching sensation when actively extending her knee from a flexed position, 1 year after undergoing a total knee arthroplasty (TKA). Operative reports indicate she received a posterior-stabilized implant. Which of the following is the most likely cause of her symptoms?

. A fibrous nodule at the superior pole of the patella engaging the intercondylar notch
. Hypertrophy of the infrapatellar fat pad
. An undersized femoral component
. Internal rotation of the tibial tray
. Asymmetric polyethylene wear

Correct Answer & Explanation

. A fibrous nodule at the superior pole of the patella engaging the intercondylar notch

Explanation

Patellar clunk syndrome is a known complication most commonly associated with posterior-stabilized (PS) TKA designs. It is caused by the formation of a fibrous nodule at the superior pole of the patella or within the quadriceps tendon. During active extension from a flexed position (usually around 30-45 degrees), this nodule catches in the femoral intercondylar box and then 'clunks' out, causing pain and a catching sensation.

Question 3624

Topic: 3. Adult Reconstruction (Hip & Knee)

In the manufacturing of highly cross-linked polyethylene (HXLPE) for total hip arthroplasty, the material is subjected to irradiation followed by thermal treatment (remelting or annealing). Compared to annealing, the remelting process has which of the following effects on the polyethylene?

. Increases the amount of residual free radicals
. Decreases the oxidation resistance of the polyethylene
. Decreases the fatigue crack propagation resistance
. Increases the ultimate tensile strength
. Decreases the risk of long-term component fracture

Correct Answer & Explanation

. Decreases the fatigue crack propagation resistance

Explanation

Remelting HXLPE (heating it above its melting point) effectively eliminates residual free radicals created during irradiation, significantly improving oxidation resistance compared to annealing (heating below the melting point). However, the remelting process permanently decreases the crystallinity of the polyethylene. This loss of crystallinity leads to a reduction in its mechanical properties, including decreased yield strength, ultimate tensile strength, and fatigue crack propagation resistance.

Question 3625

Topic: Total Knee Arthroplasty (TKA)

A 68-year-old female undergoes a right TKA for severe valgus osteoarthritis with a 20-degree valgus deformity and a 15-degree flexion contracture. Postoperatively in the recovery room, she is noted to have a dense foot drop and numbness over the dorsum of her right foot. Which of the following is the most appropriate initial management?

. Immediate surgical exploration of the peroneal nerve
. Magnetic resonance imaging (MRI) of the lumbar spine
. Removal of all compressive dressings and slight flexion of the knee
. Application of an ankle-foot orthosis and routine discharge
. Electromyography (EMG) of the lower extremity

Correct Answer & Explanation

. Removal of all compressive dressings and slight flexion of the knee

Explanation

Peroneal nerve palsy is a dreaded complication following TKA for severe valgus and flexion deformities. It occurs due to traction/stretching of the nerve as the contracted lateral structures are corrected into extension and neutral alignment. The most critical initial step is to remove all compressive dressings (e.g., ACE wraps, continuous passive motion straps) and slightly flex the knee to relieve mechanical tension on the nerve. Immediate exploration is rarely indicated. EMG is useful only after 3 to 6 weeks if symptoms do not improve.

Question 3626

Topic: Total Knee Arthroplasty (TKA)

During a total knee arthroplasty, the surgeon inadvertently places the femoral component in excessive internal rotation relative to the epicondylar axis. Which of the following biomechanical consequences is most likely to occur?

. Lateral patellar tracking and medial compartment tightness in flexion
. Lateral patellar tracking and lateral compartment tightness in flexion
. Medial patellar tracking and medial compartment tightness in flexion
. Medial patellar tracking and lateral compartment tightness in flexion
. Global symmetrical instability in both flexion and extension

Correct Answer & Explanation

. Lateral patellar tracking and lateral compartment tightness in flexion

Explanation

Internal rotation of the femoral component in a TKA has two primary negative effects. First, it medializes the femoral trochlear groove, which effectively increases the Q-angle and leads to lateral patellar maltracking. Second, it shifts the posterior medial condyle distally/posteriorly relative to the lateral condyle, resulting in a tight medial flexion gap and a loose lateral flexion gap.

Question 3627

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active male who underwent a total hip arthroplasty with a ceramic-on-ceramic bearing 3 years ago presents with an audible squeaking noise from his hip during deep flexion activities. He reports no pain, and serial radiographs show well-fixed components with no signs of osteolysis. Which of the following is the most significant biomechanical risk factor for this squeaking phenomenon?

. Acetabular component retroversion
. Edge loading due to cup malposition
. Use of a 32-mm instead of a 36-mm femoral head
. A body mass index (BMI) of less than 25
. A history of developmental dysplasia of the hip

Correct Answer & Explanation

. Edge loading due to cup malposition

Explanation

Squeaking is a well-documented phenomenon unique to hard-on-hard bearings, particularly ceramic-on-ceramic THA. The most significant biomechanical risk factor is edge loading, which often occurs secondary to acetabular component malposition (such as excessive inclination or inappropriate anteversion causing impingement and lift-off). Edge loading disrupts the critical fluid-film lubrication, causing the ceramic surfaces to rub directly against each other, creating a stripe of wear and a high-frequency squeaking sound.

Question 3628

Topic: Total Hip Arthroplasty (THA)

The direct anterior approach (DAA) for total hip arthroplasty has gained popularity due to its use of a true internervous and intermuscular plane. When compared to the posterior approach, the DAA is associated with a higher incidence of which of the following complications?

. Postoperative posterior dislocation
. Greater trochanteric fracture
. Injury to the lateral femoral cutaneous nerve
. Sciatic nerve palsy
. Deep vein thrombosis

Correct Answer & Explanation

. Injury to the lateral femoral cutaneous nerve

Explanation

The direct anterior approach utilizes the Hueter interval between the tensor fasciae latae (innervated by the superior gluteal nerve) and the sartorius (innervated by the femoral nerve). The lateral femoral cutaneous nerve (LFCN) courses superficially over the anterior aspect of the thigh and is at high risk of stretch or transection during this approach, leading to meralgia paresthetica. The posterior approach is historically associated with a higher risk of posterior dislocation, while the DAA has higher rates of LFCN injury and intraoperative proximal femoral fractures.

Question 3629

Topic: 3. Adult Reconstruction (Hip & Knee)
A 70-year-old male presents with chronic pain and swelling in his left knee 2 years after a primary TKA. Joint aspiration yields synovial fluid with a white blood cell (WBC) count of 4,500 cells/μL and 85% polymorphonuclear leukocytes (PMNs). According to the 2018 International Consensus Meeting (ICM) criteria, which of the following additional findings would definitively confirm the diagnosis of a periprosthetic joint infection (PJI) without requiring further minor criteria?
. Elevated serum C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR)
. Positive leukocyte esterase strip test of the synovial fluid
. Two positive periprosthetic cultures of phenotypically identical organisms
. A single positive culture of Staphylococcus epidermidis from synovial fluid
. A positive synovial Alpha-defensin immunoassay

Correct Answer & Explanation

. Two positive periprosthetic cultures of phenotypically identical organisms

Explanation

According to the 2018 ICM criteria for Periprosthetic Joint Infection (PJI), the presence of one of two major criteria is definitively diagnostic of PJI: 1) Two positive periprosthetic cultures with phenotypically identical organisms, or 2) A sinus tract communicating with the joint. The other options (elevated serum CRP/ESR, positive leukocyte esterase, positive alpha-defensin, elevated synovial WBC count/PMN %) are minor criteria, which must be tallied to reach a score of 6 or greater to confirm the diagnosis when a major criterion is absent.

Question 3630

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old female presents with groin pain and a feeling of fullness in her hip 6 years after a THA utilizing a metal-on-polyethylene bearing with a large (36 mm) cobalt-chromium femoral head on a titanium alloy stem. Laboratory testing reveals elevated serum cobalt levels, while chromium levels are normal. MRI with metal artifact reduction sequence (MARS) shows a thick-walled cystic mass adjacent to the greater trochanter. What is the most likely diagnosis?

. Aseptic loosening of the acetabular component
. Polyethylene wear-induced osteolysis
. Adverse local tissue reaction (ALTR) secondary to mechanically assisted crevice corrosion
. Chronic periprosthetic joint infection
. Iliopsoas tendinitis with secondary bursitis

Correct Answer & Explanation

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

Explanation

The clinical scenario is classic for mechanically assisted crevice corrosion (MACC), also known as trunnionosis, occurring at the modular head-neck junction. This complication is particularly prevalent when utilizing large diameter cobalt-chromium heads on titanium stems. The corrosion releases cobalt ions (resulting in elevated serum cobalt disproportionate to chromium) and triggers an adverse local tissue reaction (ALTR) or pseudotumor, visible on MARS MRI as a cystic or solid periarticular mass.

Question 3631

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon inadvertently elevates the joint line by 6 mm while balancing the flexion and extension gaps. How does this intraoperative error affect the knee's extensor mechanism and postoperative kinematics?

. It decreases strain on the patellar tendon, reducing the risk of anterior knee pain.
. It creates a relative patella baja, increasing patellofemoral contact forces and limiting maximal flexion.
. It creates patella alta, leading to late engagement of the patella in the trochlear groove.
. It increases the moment arm of the quadriceps, significantly improving extensor mechanism efficiency.
. It moves the instant center of rotation distally, increasing mid-flexion instability.

Correct Answer & Explanation

. It creates a relative patella baja, increasing patellofemoral contact forces and limiting maximal flexion.

Explanation

Elevating the joint line in TKA results in a condition known as pseudo-patella baja (or relative patella baja). Because the distance from the patella to the tibial tubercle is fixed by the length of the patellar tendon, raising the articular surface of the femur and tibia effectively lowers the patella relative to the new joint line. This mismatch increases patellofemoral contact forces, can cause anterior knee pain, limits postoperative range of motion (reduced flexion), and may cause impingement of the patella against the anterior tibial polyethylene tray.

Question 3632

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female presents 4 weeks after primary TKA with increasing knee pain, swelling, and erythema. Synovial fluid aspiration shows 45,000 WBCs/mcL with 92% PMNs. Cultures grow methicillin-sensitive Staphylococcus aureus (MSSA). Which of the following surgical interventions is most appropriate for this acute periprosthetic joint infection?

. Single-stage revision arthroplasty
. Two-stage revision arthroplasty with an articulating spacer
. Two-stage revision arthroplasty with a static spacer
. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange
. Suppressive oral antibiotics and observation

Correct Answer & Explanation

. Debridement, antibiotics, and implant retention (DAIR) with polyethylene exchange

Explanation

This patient presents with an acute early periprosthetic joint infection (<90 days postoperatively, often defined as <4 weeks in classic literature). According to standard guidelines, DAIR with modular component (polyethylene) exchange is indicated for acute infections with a known, susceptible organism, stable implants, and an adequate soft tissue envelope.

Question 3633

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with groin pain 6 years after a primary THA using a metal-on-polyethylene bearing. Aspiration is negative for infection. MRI with metal artifact reduction sequence (MARS) shows a large solid pseudotumor adjacent to the hip joint. Cobalt levels are markedly elevated, while chromium levels are minimally elevated. What is the most likely diagnosis?

. Adverse local tissue reaction due to bearing surface wear
. Trunnionosis (mechanically assisted crevice corrosion)
. Polyethylene wear with osteolysis
. Unrecognized low-grade periprosthetic joint infection
. Psoas impingement on an overhanging acetabular component

Correct Answer & Explanation

. Trunnionosis (mechanically assisted crevice corrosion)

Explanation

An elevated cobalt level that is disproportionately higher than the chromium level (often > 3:1 ratio), along with a pseudotumor (ALTR) in the setting of a metal-on-polyethylene bearing, is classic for trunnionosis. This occurs due to mechanically assisted crevice corrosion at the modular head-neck junction. Metal-on-metal bearing wear typically produces more equal elevations of cobalt and chromium.

Question 3634

Topic: 3. Adult Reconstruction (Hip & Knee)

During total hip arthroplasty performed through a posterior approach, the surgeon aims to place the acetabular component in the classic "Lewinnek safe zone." What are the target angles for inclination and anteversion?

. 30° +/- 10° inclination, 10° +/- 10° anteversion
. 40° +/- 10° inclination, 15° +/- 10° anteversion
. 45° +/- 10° inclination, 20° +/- 10° anteversion
. 50° +/- 10° inclination, 25° +/- 10° anteversion
. 55° +/- 10° inclination, 30° +/- 10° anteversion

Correct Answer & Explanation

. 40° +/- 10° inclination, 15° +/- 10° anteversion

Explanation

The classic Lewinnek safe zone for acetabular component positioning is 40° +/- 10° of inclination (abduction) and 15° +/- 10° of anteversion. Placement outside this zone has historically been associated with an increased risk of dislocation, though recent literature emphasizes the importance of spinopelvic mobility in functional component positioning.

Question 3635

Topic: Total Knee Arthroplasty (TKA)

Following the implantation of trial components during a TKA, the surgeon notices that the patella tends to tilt and subluxate laterally during knee flexion. Which of the following adjustments to the components would exacerbate this problem?

. Internal rotation of the tibial component
. External rotation of the femoral component
. Medialization of the patellar button
. Lateralization of the tibial tray
. External rotation of the tibial component

Correct Answer & Explanation

. Internal rotation of the tibial component

Explanation

Lateral patellar subluxation is caused by an increased Q-angle or component malrotation. Internal rotation of the tibial component lateralizes the tibial tubercle relative to the femur, increasing the Q-angle and exacerbating lateral patellar tracking. External rotation of the femoral and tibial components, and medialization of the patellar button generally improve patellar tracking.

Question 3636

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old active male underwent a metal-on-metal hip resurfacing 6 weeks ago. He now complains of sudden onset groin pain and inability to bear weight. Radiographs show a femoral neck fracture. Which of the following is the most significant intraoperative risk factor for this complication?

. Valgus placement of the femoral component
. Varus placement of the femoral component
. Use of a posterolateral approach
. Uncemented femoral component fixation
. Excessive component anteversion

Correct Answer & Explanation

. Varus placement of the femoral component

Explanation

Femoral neck fracture is a well-known early complication of hip resurfacing arthroplasty. The most significant surgical risk factor is varus malalignment of the femoral component, which significantly increases sheer stress on the femoral neck. Other risk factors include superior femoral neck notching, female gender, poor bone quality, and unrecognized osteonecrosis.

Question 3637

Topic: 3. Adult Reconstruction (Hip & Knee)

When performing a total knee arthroplasty using an extramedullary (EM) femoral alignment guide, which anatomic landmark is essential for determining the proximal point of the mechanical axis of the femur?

. Greater trochanter
. Piriformis fossa
. Center of the femoral head
. Anterior superior iliac spine (ASIS)
. Lateral epicondyle

Correct Answer & Explanation

. Center of the femoral head

Explanation

The mechanical axis of the femur is defined as a line drawn from the center of the femoral head to the center of the knee joint. When using an extramedullary guide or computer navigation without intramedullary access, identifying the center of the femoral head is critical to accurately reproduce the mechanical axis and ensure proper coronal alignment of the femoral component.

Question 3638

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active man underwent a total hip arthroplasty (THA) with a ceramic-on-ceramic bearing 3 years ago. He presents with a new onset of audible squeaking from the hip during activity, without significant pain. Radiographs demonstrate a well-fixed implant with cup anteversion of 10 degrees and an abduction angle of 55 degrees. What is the most likely pathophysiologic cause of the squeaking?

. Acetabular component malposition leading to edge loading
. Head-neck taper corrosion
. Ceramic liner fracture
. Impingement of the femoral neck on the anterior capsule
. Polyethylene wear

Correct Answer & Explanation

. Acetabular component malposition leading to edge loading

Explanation

Ceramic-on-ceramic bearings have very low wear rates but can be associated with audible squeaking. Squeaking is strongly correlated with component malposition, specifically high abduction angles (vertical cups) and extremes of anteversion, which lead to edge loading, stripe wear, and microseparation.

Question 3639

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old woman presents 1 year after a primary posterior-stabilized total knee arthroplasty (TKA) with complaints of the knee 'giving way' when going down stairs and rising from a low chair. On examination, the knee has a range of motion of 0 to 130 degrees. The knee is stable to varus and valgus stress at 0 degrees but has marked anteroposterior translation at 90 degrees of flexion. Radiographs show a well-fixed prosthesis. What is the most likely surgical error that caused her symptoms?

. Undersized femoral component leading to an increased flexion gap
. Oversized femoral component leading to a tight flexion gap
. Excessive distal femoral resection leading to a loose extension gap
. Inadequate tibial slope leading to a tight flexion gap
. Excessive polyethylene thickness leading to a tight extension gap

Correct Answer & Explanation

. Undersized femoral component leading to an increased flexion gap

Explanation

Flexion instability is characterized by a stable knee in extension but gross instability in flexion. This typically results from an oversized flexion gap relative to the extension gap. Common causes include undersizing the femoral component (leading to excessive posterior femoral resection) or an excessive posterior tibial slope.

Question 3640

Topic: Total Knee Arthroplasty (TKA)

A 62-year-old man who underwent a posterior-stabilized TKA 9 months ago presents with an anterior knee catch and an audible 'clunk' when extending his knee actively from 45 degrees of flexion to full extension. What is the primary pathophysiologic mechanism of this complication?

. Patellar component loosening
. Oversized patellar button
. Fibrous nodule entrapment in the femoral intercondylar notch
. Impingement of the patella on the anterior tibial post
. Over-resection of the anterior femoral condyle

Correct Answer & Explanation

. Fibrous nodule entrapment in the femoral intercondylar notch

Explanation

Patellar clunk syndrome typically occurs after posterior-stabilized TKA and is caused by the formation of a fibrosynovial nodule at the superior pole of the patella. During knee flexion, the nodule engages the intercondylar box of the femoral component. As the knee extends, the nodule forcibly pops out of the box (typically between 30 to 45 degrees of flexion), producing a palpable and audible clunk.

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