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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 236 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 4701

Topic: 3. Adult Reconstruction (Hip & Knee)

During total hip arthroplasty via a posterior approach, the surgeon utilizes the transverse acetabular ligament (TAL) to guide cup positioning. Aligning the opening of the trial cup parallel to the TAL provides a reliable intraoperative reference for which of the following parameters?

. Cup abduction angle
. Cup anteversion
. Leg length
. Femoral offset
. Center of rotation height

Correct Answer & Explanation

. Cup anteversion

Explanation

The transverse acetabular ligament (TAL) bridges the acetabular notch inferiorly. It is widely considered a reliable and patient-specific intraoperative anatomical landmark for determining the native version of the acetabulum. Placing the cup such that its face is parallel to the TAL helps the surgeon achieve appropriate cup anteversion.

Question 4702

Topic: 3. Adult Reconstruction (Hip & Knee)

What is the primary mechanism of polyethylene wear in a well-functioning, well-aligned total knee arthroplasty without third-body debris?

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

Correct Answer & Explanation

. Adhesive wear

Explanation

In a well-aligned, well-functioning TKA, the normal motion between the highly polished metal condyles and the polyethylene insert predominantly causes adhesive wear (also seen as burnishing). Delamination and fatigue wear are catastrophic wear modes associated with older sterilization techniques (gamma irradiation in air causing subsurface oxidation) or severe edge loading.

Question 4703

Topic: 3. Adult Reconstruction (Hip & Knee)

After a total hip arthroplasty, a patient has a noticeable Trendelenburg gait. Radiographic evaluation shows that the femoral offset of the prosthesis is significantly less than the contralateral native hip. How does decreased femoral offset contribute to this gait abnormality?

. It increases the resting tension on the abductor musculature, causing early fatigue.
. It decreases the lever arm of the abductor muscles, requiring higher force generation to maintain pelvic level.
. It increases the lever arm of the body weight relative to the center of rotation.
. It decreases the joint reaction force across the hip articulation.
. It causes direct mechanical impingement of the greater trochanter on the ilium during stance.

Correct Answer & Explanation

. It decreases the lever arm of the abductor muscles, requiring higher force generation to maintain pelvic level.

Explanation

Femoral offset is the perpendicular distance from the center of rotation of the femoral head to the anatomical axis of the femur. Decreasing the offset shortens the lever arm of the abductor muscles. To balance the moment created by body weight, the abductors must generate significantly more force. Inability to generate this excess force results in a Trendelenburg gait.

Question 4704

Topic: 3. Adult Reconstruction (Hip & Knee)

Following a high tibial osteotomy for varus gonarthrosis, a patient undergoes a total knee arthroplasty. The surgeon notes significant difficulty everting the patella and exposing the joint due to patella baja. Which step is most appropriate to manage the exposure difficulty without permanently compromising the extensor mechanism?

. Perform a V-Y quadricepsplasty
. Perform a tibial tubercle osteotomy
. Release the patellar tendon completely from the tibial tubercle
. Resect the lower pole of the patella
. Release the lateral retinaculum only

Correct Answer & Explanation

. Perform a tibial tubercle osteotomy

Explanation

Patella baja (infera) is common after HTO (especially if the tubercle is not altered or due to scarring) and severely limits patellar eversion during subsequent TKA. A tibial tubercle osteotomy (TTO) provides an excellent, extensile exposure that preserves the continuity of the extensor mechanism, allowing for secure repair and even proximal advancement of the tubercle if needed to correct the baja.

Question 4705

Topic: Total Knee Arthroplasty (TKA)

During femoral preparation in a TKA, a posterior referencing sizing guide is used. The femur measures between sizes, and the surgeon chooses the larger size. Assuming the posterior cuts remain constant, what is the most likely consequence of this decision?

. Notching of the anterior femoral cortex
. A loose flexion gap
. Overstuffing the patellofemoral joint
. A tight flexion gap
. Excessive femoral rollback

Correct Answer & Explanation

. Overstuffing the patellofemoral joint

Explanation

With a posterior referencing system, the posterior femoral resection is constant regardless of component size. If a larger size is chosen, the anterior resection line moves further anteriorly, meaning less anterior bone is removed. When the larger implant is placed, its anterior flange will protrude further anteriorly than the native bone, leading to overstuffing of the patellofemoral joint. Conversely, choosing the smaller size risks anterior cortical notching.

Question 4706

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old man presents with progressive groin pain 7 years after a primary metal-on-polyethylene THA. Radiographs show well-fixed components with normal alignment. A metal artifact reduction sequence (MARS) MRI reveals a solid and cystic mass surrounding the hip joint. Laboratory analysis shows elevated serum cobalt levels with normal chromium levels. What is the primary mechanism of failure?

. Polyethylene wear leading to macrophage activation
. Galvanic corrosion at the head-neck junction
. Mechanically assisted crevice corrosion at the modular head-neck junction
. Edge loading from cup malposition
. Type IV hypersensitivity to the titanium stem

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the modular head-neck junction

Explanation

The presentation of a pseudotumor (solid/cystic mass on MARS MRI) with elevated serum cobalt (and often normal or slightly elevated chromium, leading to a high Co:Cr ratio) in a metal-on-polyethylene THA is classic for trunnionosis. This is caused by mechanically assisted crevice corrosion (fretting and corrosion) at the modular head-neck junction.

Question 4707

Topic: Total Knee Arthroplasty (TKA)

A 70-year-old woman complains of a 'giving way' sensation in her knee, particularly when descending stairs, 18 months following a posterior-stabilized TKA. On physical examination, her knee is perfectly stable to varus and valgus stress at 0 degrees and 90 degrees of flexion, but demonstrates significant laxity at 45 degrees of flexion. Which of the following intraoperative technical errors most likely caused this complication?

. Undersizing the femoral component
. Excessive distal femoral resection compensated by a thicker polyethylene insert
. Internal rotation of the tibial component
. Downsizing the tibial component
. Excessive release of the posterior cruciate ligament

Correct Answer & Explanation

. Excessive distal femoral resection compensated by a thicker polyethylene insert

Explanation

Mid-flexion instability is characterized by stability at full extension and 90 degrees of flexion, but laxity in the mid-arc of motion (usually 30-60 degrees). This is classically caused by joint line elevation. If the surgeon resects too much distal femur, the extension gap becomes larger than the flexion gap. To balance the knee in extension, a thicker polyethylene insert is used, which over-stuffs the flexion gap (unless the posterior condyles are also augmented). This elevates the joint line, altering the kinematics of the collateral ligaments in mid-flexion and leading to laxity.

Question 4708

Topic: 3. Adult Reconstruction (Hip & Knee)

An 82-year-old woman with a history of a cemented THA placed 15 years ago sustains a fall. Radiographs demonstrate a displaced periprosthetic fracture around the femoral stem. The fracture extends to the mid-diaphysis. The femoral stem is loose, and there is severe proximal femoral bone loss (less than 2 cm of intact diaphyseal bone proximal to the fracture). According to the Vancouver classification, what is the most appropriate management?

. Open reduction and internal fixation with a locking plate
. Revision to a standard length cementless porous-coated stem
. Revision to a long cemented stem with impaction bone grafting
. Proximal femoral replacement (tumor prosthesis)
. Cortical strut allografts alone

Correct Answer & Explanation

. Proximal femoral replacement (tumor prosthesis)

Explanation

This is a Vancouver B3 periprosthetic fracture: fracture around the stem (B), loose implant (3 - poor bone stock). B1 = stable stem; B2 = loose stem, good bone stock; B3 = loose stem, poor bone stock. The standard of care for a Vancouver B3 fracture in an elderly, low-demand patient is a proximal femoral replacement (megaprosthesis) to allow for immediate weight-bearing and early mobilization.

Question 4709

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following findings alone is considered a definitive major criterion for diagnosing a periprosthetic joint infection?

. Synovial white blood cell count greater than 3,000 cells/ยตL
. Elevated serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
. Two positive periprosthetic tissue cultures with the same organism
. Positive leukocyte esterase on synovial fluid dipstick
. Positive alpha-defensin test

Correct Answer & Explanation

. Two positive periprosthetic tissue cultures with the same organism

Explanation

The 2018 ICM criteria for periprosthetic joint infection (PJI) identify two major criteria, either of which definitively establishes the diagnosis: 1) Two positive periprosthetic cultures with phenotypically identical organisms, or 2) A sinus tract communicating with the joint. The other options (synovial WBC, ESR/CRP, leukocyte esterase, alpha-defensin) are minor criteria that contribute to a scoring system but are not definitive on their own.

Question 4710

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old woman is undergoing revision THA for aseptic loosening. Preoperative radiographs and intraoperative findings reveal severe acetabular bone loss with complete separation of the superior and inferior halves of the hemipelvis. The remaining iliac bone is inadequate for biological fixation of a standard hemispherical cup. What is the most appropriate acetabular reconstruction option?

. Jumbo hemispherical cup with multiple screws
. Impaction bone grafting with a cemented cup
. Custom triflange acetabular component or a cup-cage construct
. High hip center using a standard cementless cup
. Bipolar hemiarthroplasty

Correct Answer & Explanation

. Custom triflange acetabular component or a cup-cage construct

Explanation

The scenario describes a pelvic discontinuity (Paprosky type 3B with poor remaining bone stock). The inferior and superior halves of the pelvis are mechanically disconnected. When remaining bone stock is insufficient for a highly porous metal cup to achieve biological fixation (less than 50% contact), a mechanically stable construct that bridges the discontinuity is required. A custom triflange acetabular component or a cup-cage construct provides mechanical stability across the discontinuity and allows for immediate fixation.

Question 4711

Topic: 3. Adult Reconstruction (Hip & Knee)

In a posterior-stabilized (PS) total knee arthroplasty, the cam and post mechanism is primarily designed to replicate the function of the posterior cruciate ligament (PCL). At what angle of knee flexion does the femoral cam typically engage the tibial post to initiate femoral rollback?

. 0 to 15 degrees
. 30 to 45 degrees
. 60 to 75 degrees
. 90 to 105 degrees
. 120 to 135 degrees

Correct Answer & Explanation

. 60 to 75 degrees

Explanation

In a standard posterior-stabilized (PS) TKA design, the femoral cam engages the tibial spine (post) at approximately 60 to 75 degrees of knee flexion. Upon engagement, the cam-post mechanism forces the femoral component to translate posteriorly on the tibial plateau (femoral rollback). This improves knee flexion by preventing posterior impingement of the femur on the posterior tibia and optimizes the extensor mechanism lever arm.

Question 4712

Topic: Total Knee Arthroplasty (TKA)

A 64-year-old man presents with a painful catching sensation in his right knee 14 months after a primary posterior-stabilized TKA. He notes a distinct 'clunk' when actively extending the knee from a flexed position, typically occurring between 30 and 45 degrees of flexion. Non-operative management has failed. What is the most appropriate surgical treatment?

. Revision of the femoral component
. Polyethylene liner exchange
. Arthroscopic or open excision of a suprapatellar fibrous nodule
. Lateral retinacular release
. Tibial tubercle osteotomy

Correct Answer & Explanation

. Arthroscopic or open excision of a suprapatellar fibrous nodule

Explanation

The clinical presentation is classic for Patellar Clunk Syndrome, a complication most commonly associated with posterior-stabilized (PS) TKA designs (especially older designs with a sharp, boxy intercondylar notch). A fibrous nodule develops on the posterior aspect of the quadriceps tendon just proximal to the superior pole of the patella. As the knee extends from flexion (usually around 30-45 degrees), this nodule catches in the intercondylar box of the femoral component and then pops out with a painful clunk. Treatment is excision of the nodule, often done arthroscopically.

Question 4713

Topic: Total Hip Arthroplasty (THA)

A 75-year-old patient with Parkinson's disease and a history of recurrent hip dislocations after a primary THA is undergoing revision surgery. The surgeon decides to use a dual mobility articulation. What is the primary biomechanical advantage of this bearing design in preventing dislocation?

. It restricts hip range of motion to prevent impingement.
. It increases the functional jump distance.
. It uses a constrained locking ring to hold the femoral head.
. It increases the coefficient of friction to stabilize the joint.
. It lateralizes the center of rotation to increase abductor tension.

Correct Answer & Explanation

. It increases the functional jump distance.

Explanation

A dual mobility bearing consists of a small metallic or ceramic femoral head that articulates within a large mobile polyethylene liner, which in turn articulates within a highly polished metal acetabular shell. This design effectively increases the functional head size. A larger head size directly increases the 'jump distance' (the distance the femoral head must travel to dislocate over the rim of the cup) and improves the impingement-free range of motion.

Question 4714

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old woman with a ceramic-on-ceramic total hip arthroplasty presents with a loud, audible squeaking noise coming from her hip during walking. She is otherwise asymptomatic. Radiographs show a well-fixed cementless stem and a cementless cup. Which of the following surgical factors is most strongly associated with this phenomenon?

. Acetabular component placed in excessive retroversion and high inclination
. Use of a large diameter femoral head
. Femoral stem placed in varus alignment
. Leg length discrepancy of greater than 1 cm
. Excessive offset of the femoral component

Correct Answer & Explanation

. Acetabular component placed in excessive retroversion and high inclination

Explanation

Squeaking in ceramic-on-ceramic (CoC) THA is a known complication. It is strongly associated with edge loading of the ceramic bearings. Edge loading occurs when the contact patch between the head and the liner extends over the rim of the liner. This is most commonly caused by malposition of the acetabular component, specifically excessive inclination (steep cup) and anteversion or retroversion mismatch.

Question 4715

Topic: Total Knee Arthroplasty (TKA)

During a complex revision total knee arthroplasty, the surgeon notes complete absence of the medial collateral ligament (MCL) after removal of the previous implants. The lateral collateral ligament (LCL) and extensor mechanism are intact. Which of the following implant constraints is most appropriate for this patient?

. Cruciate-retaining (CR) knee
. Posterior-stabilized (PS) knee
. Constrained condylar knee (CCK)
. Rotating hinge knee
. Unicompartmental knee

Correct Answer & Explanation

. Rotating hinge knee

Explanation

Implant constraint selection depends on ligamentous competency. A PS knee requires competent MCL and LCL. A constrained condylar knee (CCK) features a tall, wide post that substitutes for the LCL and MCL to some degree, making it suitable for collateral ligament attenuation or moderate laxity. However, a CCK cannot compensate for the complete absence or gross incompetence of a primary collateral ligament (like the MCL). When a collateral ligament is completely absent, a linked implant, such as a rotating hinge knee, is required to prevent coronal plane instability.

Question 4716

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old woman with a metal-on-metal hip resurfacing presents with unexplained pain and swelling 3 years postoperatively. Infection workup is negative. Histological analysis of the periprosthetic tissue obtained during revision surgery reveals a massive perivascular infiltrate of T-lymphocytes and plasma cells, with minimal macrophages. This histological picture is characteristic of:

. Aseptic loosening secondary to polyethylene wear
. Acute bacterial infection
. Aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL)
. Foreign body giant cell reaction to PMMA
. Gouty arthropathy

Correct Answer & Explanation

. Aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL)

Explanation

The histological findings of a perivascular infiltrate composed predominantly of lymphocytes (T-cells) and plasma cells, rather than macrophages, are the hallmark of an Aseptic Lymphocyte-dominated Vasculitis-Associated Lesion (ALVAL). This is a Type IV (delayed) hypersensitivity reaction to metal ions (usually cobalt and chromium) seen in metal-on-metal articulations or modular junctions (trunnionosis).

Question 4717

Topic: Total Knee Arthroplasty (TKA)

A 70-year-old patient with severe rheumatoid arthritis presents for a primary TKA. Examination reveals a fixed 20-degree valgus deformity. The surgeon plans a lateral parapatellar approach. Which of the following structures is typically the first to be released off the lateral femoral condyle to balance the extension gap in a fixed valgus knee?

. Popliteus tendon
. Lateral collateral ligament (LCL)
. Iliotibial (IT) band
. Posterolateral capsule
. Biceps femoris tendon

Correct Answer & Explanation

. Iliotibial (IT) band

Explanation

Balancing a severe fixed valgus knee often requires a stepwise release of lateral structures. While techniques vary, the classic sequence (e.g., Ranawat's 'inside-out' or standard outside-in release) typically begins with the release of the iliotibial (IT) band, as it is a major deforming force in extension. If the knee remains tight in extension, the LCL and popliteus are assessed and sequentially released.

Question 4718

Topic: 3. Adult Reconstruction (Hip & Knee)

Lewinnek's 'safe zone' for acetabular component positioning in total hip arthroplasty was historically described to minimize the risk of dislocation. What are the specific angular parameters defined by this safe zone?

. 30 ยฑ 10 degrees of inclination and 10 ยฑ 5 degrees of anteversion
. 40 ยฑ 10 degrees of inclination and 15 ยฑ 10 degrees of anteversion
. 45 ยฑ 5 degrees of inclination and 20 ยฑ 5 degrees of anteversion
. 50 ยฑ 10 degrees of inclination and 15 ยฑ 5 degrees of anteversion
. 35 ยฑ 10 degrees of inclination and 25 ยฑ 10 degrees of anteversion

Correct Answer & Explanation

. 40 ยฑ 10 degrees of inclination and 15 ยฑ 10 degrees of anteversion

Explanation

In 1978, Lewinnek et al. described an acetabular 'safe zone' of 40 ยฑ 10 degrees of inclination (abduction) and 15 ยฑ 10 degrees of anteversion. Cups placed outside this zone were historically associated with a higher rate of dislocation. While modern understanding emphasizes that functional pelvic position (spinopelvic mobility) plays a critical role, the Lewinnek safe zone remains a fundamental baseline.

Question 4719

Topic: 3. Adult Reconstruction (Hip & Knee)
In revision total hip arthroplasty for a patient with severe proximal femoral bone loss (Vancouver B3 or Paprosky IIIA), a modular fluted tapered titanium stem is chosen. What is the primary biomechanical mechanism by which this stem achieves initial rotational stability?
. Three-point bending in the proximal diaphysis
. Collar resting on the medial calcar
. Impaction of cancellous bone graft around the proximal body
. Engagement of the longitudinal flutes into the intact distal diaphyseal cortex
. Proximal porous coating for bone ingrowth

Correct Answer & Explanation

. Engagement of the longitudinal flutes into the intact distal diaphyseal cortex

Explanation

Modular fluted tapered titanium stems are designed to bypass deficient proximal bone and achieve initial fixation in the intact distal diaphysis. The 2 to 3-degree taper provides excellent axial stability via a 'wedge' effect, while the longitudinal flutes (splines) cut into the diaphyseal cortical bone to provide initial rotational stability.

Question 4720

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male with a metal-on-polyethylene THA 8 years ago presents with groin pain. Radiographs show a well-fixed stem and cup. MARS MRI demonstrates a mixed solid and cystic periarticular mass. Hip aspiration reveals low synovial white blood cells but significantly elevated levels of cobalt and chromium. What is the most likely underlying etiology?

. Polyethylene wear resulting in macrophage-mediated osteolysis
. Galvanic corrosion and fretting at the modular head-neck junction
. Impingement of the iliopsoas tendon on the anterior acetabular rim
. Latent Periprosthetic Joint Infection (PJI) with an atypical organism
. Acetabular component aseptic loosening

Correct Answer & Explanation

. Galvanic corrosion and fretting at the modular head-neck junction

Explanation

The clinical presentation describes an Adverse Local Tissue Reaction (ALTR) in the setting of a metal-on-polyethylene total hip arthroplasty. Because the bearing surface is not metal-on-metal, the source of the elevated cobalt and chromium ions is mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction.

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