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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 245 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 4881

Topic: Total Knee Arthroplasty (TKA)

During a mechanically aligned primary TKA, the surgeon uses an intramedullary guide for the distal femoral cut. To achieve a neutral mechanical axis, the valgus cut angle set on the distal femoral cutting block is typically based on the angle between which two axes?

. The femoral mechanical axis and the tibial mechanical axis
. The femoral anatomical axis and the clinical epicondylar axis
. The femoral anatomical axis and the femoral mechanical axis
. The tibial anatomical axis and the tibial mechanical axis
. The trans-epicondylar axis and the posterior condylar axis

Correct Answer & Explanation

. The femoral anatomical axis and the femoral mechanical axis

Explanation

In mechanical alignment, the goal is a femoral cut perpendicular to the mechanical axis. Because the intramedullary guide follows the femoral anatomical axis, the valgus cut angle (usually 5-7 degrees) compensates for the natural divergence between the anatomical and mechanical axes of the femur.

Question 4882

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female presents for revision THA. Radiographs demonstrate severe acetabular osteolysis with a fracture line separating the superior and inferior halves of the hemipelvis, indicating pelvic discontinuity.

What is the most appropriate reconstructive option to achieve long-term stability?

. Jumbo hemispherical multi-hole cup
. Cemented all-polyethylene cup
. Cup-cage construct or custom triflange acetabular component
. Standard uncemented cup with minimum 2 screws
. Bipolar hemiarthroplasty

Correct Answer & Explanation

. Cup-cage construct or custom triflange acetabular component

Explanation

Pelvic discontinuity occurs when there is a complete dissociation between the ilium and the ischium/pubis. Stable fixation requires bridging the defect, best achieved with a cup-cage construct, custom triflange, or an ilioischial plate combined with a trabecular metal shell.

Question 4883

Topic: Total Knee Arthroplasty (TKA)

During a TKA, a surgeon inadvertently uses a patellar button that is significantly thicker than the native resected patella, leading to an 'overstuffed' anterior compartment. What is the most likely clinical consequence of this error?

. Increased maximum knee flexion
. Decreased strain on the extensor mechanism
. Recurrent patellar subluxation due to medial retinacular laxity
. Reduced post-operative range of motion and anterior knee pain
. Increased risk of patellar clunk syndrome

Correct Answer & Explanation

. Reduced post-operative range of motion and anterior knee pain

Explanation

Overstuffing the patellofemoral joint increases tension on the extensor mechanism. This leads to increased retropatellar contact forces, resulting in anterior knee pain, and a mechanical block that reduces terminal knee flexion.

Question 4884

Topic: 3. Adult Reconstruction (Hip & Knee)

Highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates in THA. What is the primary biological and mechanical advantage of doping HXLPE with Vitamin E rather than performing post-irradiation remelting?

. It eliminates the need for initial gamma irradiation
. It prevents in vivo oxidation while preserving ultimate tensile strength and fatigue resistance
. It entirely stops the generation of polyethylene wear particles
. It increases the crystalline structure of the polyethylene to 100%
. It allows for the use of completely unconstrained liners without dislocation risk

Correct Answer & Explanation

. It prevents in vivo oxidation while preserving ultimate tensile strength and fatigue resistance

Explanation

Remelting HXLPE eliminates free radicals but decreases its mechanical properties (fatigue strength). Blending with Vitamin E (an antioxidant) neutralizes free radicals without the need for remelting, thereby maintaining the material's structural fatigue resistance while preventing oxidation.

Question 4885

Topic: Total Knee Arthroplasty (TKA)

A surgeon is performing a primary TKA on a patient with a severe fixed valgus deformity (Krackow Type II). After bone cuts, the lateral compartment remains excessively tight in extension but is adequately balanced in flexion. Which structure should be selectively released to correct this specific imbalance?

. Popliteus tendon
. Iliotibial band (ITB)
. Lateral collateral ligament (LCL)
. Posterior cruciate ligament (PCL)
. Medial collateral ligament (MCL)

Correct Answer & Explanation

. Iliotibial band (ITB)

Explanation

The iliotibial band (ITB) acts as a primary lateral tether in extension but relaxes in flexion. Therefore, a tight extension gap with a balanced flexion gap on the lateral side dictates selective release of the ITB or lateral capsule.

Question 4886

Topic: Total Hip Arthroplasty (THA)

During acetabular component fixation in THA, screw placement is targeted to specific anatomic zones to avoid neurovascular injury. According to Wasielewski's quadrant system, which quadrant is considered the 'safe zone' for placing screws?

. Anterosuperior quadrant
. Anteroinferior quadrant
. Posterosuperior quadrant
. Posteroinferior quadrant
. Central (cotyloid fossa) region

Correct Answer & Explanation

. Posterosuperior quadrant

Explanation

The posterosuperior quadrant is the safe zone for screw placement, providing excellent bone stock (ilium) while avoiding major neurovascular structures. The anterosuperior/anteroinferior quadrants risk injury to the external iliac vessels and obturator nerve.

Question 4887

Topic: 3. Adult Reconstruction (Hip & Knee)

Increasing femoral offset during a total hip arthroplasty has what primary biomechanical effect on the hip joint?

. Increases joint reaction force
. Decreases abductor muscle tension requirement
. Decreases the moment arm of the abductors
. Decreases global leg length
. Increases the risk of bony impingement

Correct Answer & Explanation

. Decreases abductor muscle tension requirement

Explanation

Increasing femoral offset increases the abductor moment arm. This mechanically reduces the required force generated by the abductor muscles to maintain pelvic stability, thereby decreasing the overall joint reaction force.

Question 4888

Topic: 3. Adult Reconstruction (Hip & Knee)

Review the provided imaging.

During a total knee arthroplasty, the surgeon notes that the extension gap is perfectly balanced, but the flexion gap is excessively tight. Which of the following is the most appropriate step to balance the knee?

. Resect more distal femur
. Downsize the tibial polyethylene insert
. Release the posterior capsule
. Increase the posterior slope of the proximal tibial resection
. Recut the femur in more extension

Correct Answer & Explanation

. Increase the posterior slope of the proximal tibial resection

Explanation

A tight flexion gap with a balanced extension gap can be addressed by increasing the posterior tibial slope, downsizing the femoral component, or recessing the PCL (in CR knees). Resecting more distal femur only loosens the extension gap.

Question 4889

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old male presents with persistent groin pain 4 years after a metal-on-polyethylene total hip arthroplasty. Aspiration is negative for infection, but serum cobalt levels are significantly elevated while chromium levels are normal. What is the most likely diagnosis?

. Adverse local tissue reaction due to bearing wear
. Mechanically assisted crevice corrosion (trunnionosis)
. Polyethylene wear-induced osteolysis
. Infection with a slow-growing atypical organism
. Unrecognized periprosthetic fracture

Correct Answer & Explanation

. Mechanically assisted crevice corrosion (trunnionosis)

Explanation

Elevated cobalt with normal or mildly elevated chromium in a metal-on-polyethylene THA is classic for mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper. Metal-on-metal bearing wear typically presents with elevations of both ions.

Question 4890

Topic: 3. Adult Reconstruction (Hip & Knee)

Review the radiograph.

A 72-year-old female sustains a periprosthetic femur fracture around a cemented total hip arthroplasty. Radiographs reveal a fracture at the tip of the stem. The stem is loose, but there is adequate proximal femoral bone stock. What is the appropriate Vancouver classification and standard management?

. Vancouver B1; Open reduction internal fixation
. Vancouver B2; Open reduction internal fixation
. Vancouver B2; Revision to a longer diaphyseal-engaging stem
. Vancouver B3; Revision with a proximal femoral replacement
. Vancouver C; Open reduction internal fixation

Correct Answer & Explanation

. Vancouver B2; Revision to a longer diaphyseal-engaging stem

Explanation

A periprosthetic fracture around the stem with a loose implant but adequate bone stock is a Vancouver B2 fracture. The gold standard treatment is revision to a longer stem (usually uncemented, diaphyseal-engaging) that bypasses the fracture by at least two cortical diameters.

Question 4891

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient presents with a palpable and audible clunk at 30 to 40 degrees of knee extension 1 year after a posterior-stabilized total knee arthroplasty. What is the primary etiology of this complication?

. Oversized tibial baseplate impinging on the popliteus
. Fibrous nodule formation at the superior pole of the patella
. Subclinical patellar tendon rupture
. Polyethylene wear of the central tibial post
. Asymmetric medial collateral ligament tightness

Correct Answer & Explanation

. Fibrous nodule formation at the superior pole of the patella

Explanation

Patellar clunk syndrome is caused by the formation of a fibrous nodule at the superior pole of the patella. During active extension, this nodule catches in the intercondylar notch/box of a posterior-stabilized femoral component and then pops out, producing a clunk.

Question 4892

Topic: 3. Adult Reconstruction (Hip & Knee)

In a posterior-stabilized total knee arthroplasty, the interaction between the femoral cam and the tibial post is designed to replicate the function of the posterior cruciate ligament (PCL). What specific kinematic function does this mechanism provide?

. Induces anterior femoral translation during flexion
. Induces posterior femoral rollback during deep flexion
. Prevents valgus instability in full extension
. Controls isolated internal rotation of the tibia
. Prevents anterior tibial translation in extension

Correct Answer & Explanation

. Induces posterior femoral rollback during deep flexion

Explanation

The cam-post mechanism in a posterior-stabilized TKA forces posterior femoral rollback during deep flexion. This mimics the native PCL, preventing posterior impingement of the tibia on the femur and thereby optimizing knee flexion.

Question 4893

Topic: 3. Adult Reconstruction (Hip & Knee)

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

. Elevated serum CRP and ESR
. Purulent fluid observed within the joint by the surgeon
. A single positive intraoperative tissue culture
. A sinus tract communicating with the prosthesis
. Elevated synovial fluid polymorphonuclear percentage

Correct Answer & Explanation

. A sinus tract communicating with the prosthesis

Explanation

A sinus tract communicating directly with the prosthesis is one of the major absolute criteria for periprosthetic joint infection. The other major criterion is two positive periprosthetic cultures with phenotypically identical organisms.

Question 4894

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active male with a ceramic-on-ceramic total hip arthroplasty reports an audible squeaking sound during certain activities. Which of the following component factors is most strongly associated with this phenomenon?

. Excessive femoral component retroversion
. Insufficient acetabular inclination
. Edge loading due to excessive acetabular cup anteversion or inclination
. Medialization of the acetabular component
. Use of a larger diameter femoral head

Correct Answer & Explanation

. Edge loading due to excessive acetabular cup anteversion or inclination

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly associated with edge loading. This phenomenon typically results from component malposition, specifically excessive cup inclination or anteversion, as well as microseparation during the swing phase of gait.

Question 4895

Topic: 3. Adult Reconstruction (Hip & Knee)

Review the radiograph.

A patient experiences recurrent posterior dislocations of their total hip arthroplasty. On radiographic evaluation, the acetabular component is found to have 5 degrees of anteversion and 30 degrees of inclination. What is the most appropriate acetabular revision strategy?

. Decrease anteversion and increase inclination
. Increase anteversion and increase inclination
. Decrease anteversion and decrease inclination
. Increase anteversion and maintain inclination
. Maintain anteversion and decrease inclination

Correct Answer & Explanation

. Increase anteversion and increase inclination

Explanation

The Lewinnek safe zone for an acetabular cup is 15 +/- 10 degrees of anteversion and 40 +/- 10 degrees of inclination. This patient's cup is under-anteverted and under-inclined, predisposing to posterior instability; therefore, both should be increased.

Question 4896

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following is considered an absolute contraindication for a medial unicompartmental knee arthroplasty (UKA)?

. Patient age greater than 80 years
. Body Mass Index of 32
. An intact anterior cruciate ligament
. Inflammatory arthritis such as Rheumatoid Arthritis
. Mild patellofemoral joint osteoarthritis

Correct Answer & Explanation

. Inflammatory arthritis such as Rheumatoid Arthritis

Explanation

Inflammatory arthropathies like rheumatoid arthritis involve the entire synovial lining and typically progress to pan-compartmental disease, making them absolute contraindications for UKA. An intact ACL is a strict prerequisite for UKA.

Question 4897

Topic: 3. Adult Reconstruction (Hip & Knee)

Following total hip arthroplasty, a patient at high risk for heterotopic ossification (HO) is prescribed prophylactic radiation therapy. To be maximally effective, within what timeframe relative to the surgery should the radiation be administered?

. 7 days before surgery
. 24 hours preoperatively to 72 hours postoperatively
. 7 to 10 days postoperatively
. 14 days postoperatively
. At the first radiographic sign of ossification

Correct Answer & Explanation

. 24 hours preoperatively to 72 hours postoperatively

Explanation

Prophylactic radiation for heterotopic ossification is most effective when administered within 24 hours preoperatively or up to 72 hours postoperatively. It works by inhibiting the differentiation of mesenchymal stem cells into osteoblasts.

Question 4898

Topic: 3. Adult Reconstruction (Hip & Knee)

Review the intraoperative image.

During a revision total knee arthroplasty, restoring the native joint line is critical for optimal outcome. What is the most reliable bony landmark to determine the native joint line level?

. 10 mm distal to the inferior pole of the patella
. 15 mm proximal to the fibular head
. 3 cm distal to the adductor tubercle
. 1 cm proximal to the tibial tubercle
. 2.5 to 3 cm distal to the medial epicondyle

Correct Answer & Explanation

. 2.5 to 3 cm distal to the medial epicondyle

Explanation

The native knee joint line is typically located 2.5 to 3 cm distal to the medial epicondyle and approximately 1.5 cm proximal to the fibular head. Restoring this level is essential for optimizing patellofemoral tracking and mid-flexion kinematics.

Question 4899

Topic: Total Hip Arthroplasty (THA)

Intraoperatively during a THA, the surgeon tests the hip and notes it is stable in all positions, but the leg is 15 mm longer than the contralateral side, and the surrounding soft tissues are extremely tight. What is the most appropriate surgical adjustment?

. Increase the acetabular offset
. Increase the neck length of the femoral head
. Change to a high-offset femoral stem
. Recut the femoral neck more distally and advance the stem
. Release the iliopsoas tendon completely

Correct Answer & Explanation

. Recut the femoral neck more distally and advance the stem

Explanation

If the hip is stable but the leg is too long with tight soft tissues, the center of rotation has been elevated too far superiorly. The appropriate step is to lower the stem by recutting the femoral neck more distally, decreasing leg length while maintaining stability.

Question 4900

Topic: 3. Adult Reconstruction (Hip & Knee)

In total knee arthroplasty, which of the following design characteristics of the polyethylene insert most significantly increases the risk of accelerated wear and osteolysis?

. Highly cross-linked polyethylene composition
. Thickness greater than 10 mm
. High conformity of the articular surface
. Flat (unconstrained) articular surface design with low contact area
. Convexity of the tibial articular surface matching the femur

Correct Answer & Explanation

. Flat (unconstrained) articular surface design with low contact area

Explanation

Flat or low-conformity polyethylene designs lead to point contact rather than surface contact, drastically increasing focal contact stresses. This predisposes the polyethylene to accelerated subsurface damage, delamination, wear, and subsequent osteolysis.

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