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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 324 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 6461

Topic: Total Hip Arthroplasty (THA)

A surgeon performs a total hip arthroplasty and intentionally decreases the femoral offset compared to the patient's native anatomy. What is the most significant biomechanical consequence of this change?

. Decreased joint reactive force across the hip
. Increased abductor muscle force required for pelvic stability
. Increased tension on the sciatic nerve
. Increased abductor moment arm length
. Increased bending moment on the femoral stem

Correct Answer & Explanation

. Increased abductor muscle force required for pelvic stability

Explanation

Decreasing femoral offset shortens the abductor moment arm. To maintain pelvic equilibrium against body weight, the abductor muscles must generate significantly more force, which concurrently increases the overall joint reactive force.

Question 6462

Topic: Total Hip Arthroplasty (THA)

According to Paley's rules of deformity correction, if an osteotomy is performed at a level outside the Center of Rotation of Angulation (CORA) and the hinge is placed at the osteotomy site, what is the geometric result of the correction?

. Collinear realignment with expected translation at the osteotomy
. Correction of angulation but creation of an iatrogenic translational deformity
. Translation of the mechanical axis without any change in angular deformity
. Perfect restoration of the anatomical axis with no translation
. Creation of an iatrogenic leg length discrepancy without changing the axis

Correct Answer & Explanation

. Correction of angulation but creation of an iatrogenic translational deformity

Explanation

Paley's Rule 3 dictates that when both the osteotomy and the hinge are located at a level distinct from the CORA, correcting the angular deformity will inadvertently cause the mechanical axis to translate, creating a secondary translational deformity.

Question 6463

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon inadvertently places the acetabular component in a high and lateral position relative to the true anatomic center of rotation. Biomechanically, what is the consequence of this cup placement?

. Increased abductor lever arm and decreased hip joint reaction force.
. Decreased abductor lever arm and increased hip joint reaction force.
. Increased abductor lever arm and increased hip joint reaction force.
. Decreased abductor lever arm and decreased hip joint reaction force.
. No change in the abductor lever arm, but increased shear force on the femoral component.

Correct Answer & Explanation

. Decreased abductor lever arm and increased hip joint reaction force.

Explanation

A high and lateral hip center decreases the offset (lever arm) of the abductor mechanism. To compensate and keep the pelvis level during single-leg stance, the abductors must fire with much greater force, substantially increasing the overall joint reaction force.

Question 6464

Topic: Total Hip Arthroplasty (THA)

In a patient undergoing total hip arthroplasty, the surgeon increases the femoral offset by 10 mm compared to the native anatomy. Which of the following biomechanical effects is most likely to occur as a direct result of this modification?

. Decreased strain on the abductor musculature and decreased joint reaction force
. Decreased strain on the abductor musculature and increased joint reaction force
. Increased joint reaction force and decreased torque on the femoral stem
. Decreased bending moment on the femoral component and increased abductor tension
. Increased bony impingement during hip abduction

Correct Answer & Explanation

. Decreased strain on the abductor musculature and increased joint reaction force

Explanation

Increasing femoral offset lengthens the abductor moment arm, which reduces the required abductor muscle force to maintain pelvic stability. Consequently, this leads to a decrease in the overall hip joint reaction force.

Question 6465

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon opts to use a femoral stem with an increased offset. Compared to a standard offset stem, what is the primary biomechanical effect of this decision on the hip joint?

. Decreases the abductor moment arm and increases joint reaction force
. Increases the abductor moment arm and decreases joint reaction force
. Increases the body weight moment arm and increases joint reaction force
. Medializes the femoral shaft and increases abductor tension

Correct Answer & Explanation

. Increases the abductor moment arm and decreases joint reaction force

Explanation

Increasing the femoral offset lateralizes the greater trochanter, which increases the abductor moment arm. A longer abductor moment arm means less abductor force is required to maintain a level pelvis, thus decreasing the overall joint reaction force.

Question 6466

Topic: Total Hip Arthroplasty (THA)

According to the principles of deformity correction (Osteotomy Rule 2), if the osteotomy is made at a level different from the CORA, but the axis of rotation is placed perfectly at the CORA, what is the geometric result?

. The bone corrects with pure angulation.
. The bone corrects with angulation and translation, restoring the mechanical axis.
. The mechanical axis is intentionally translated away from the joint center.
. The correction results in an inevitable leg length discrepancy.

Correct Answer & Explanation

. The bone corrects with angulation and translation, restoring the mechanical axis.

Explanation

Under Rule 2, placing the hinge at the CORA but making the osteotomy elsewhere allows for simultaneous angulation and translation. This restores the colinearity of the proximal and distal mechanical axes.

Question 6467

Topic: 3. Adult Reconstruction (Hip & Knee)

During a complex revision total hip arthroplasty, the surgeon places the acetabular component in a 'high hip center' (superiorly translated) without restoring the native lateral offset. What is the most significant negative biomechanical consequence of this placement?

. It excessively lengthens the limb.
. It shortens the abductor moment arm, leading to increased joint reaction forces.
. It decreases the body weight moment arm, leading to abductor fatigue.
. It retroverts the acetabulum, predisposing to anterior dislocation.

Correct Answer & Explanation

. It shortens the abductor moment arm, leading to increased joint reaction forces.

Explanation

A high, non-lateralized hip center brings the center of rotation closer to the line of action of the abductors. This significantly shortens the abductor moment arm, requiring much higher muscle forces to stabilize the pelvis and dramatically increasing joint reaction forces.

Question 6468

Topic: 3. Adult Reconstruction (Hip & Knee)

Medializing the hip center of rotation during a total hip arthroplasty for severe developmental dysplasia of the hip has what primary biomechanical effect?

. Increases the abductor moment arm
. Decreases the abductor moment arm
. Increases the body weight moment arm
. Decreases the body weight moment arm
. Increases the resultant joint reaction force

Correct Answer & Explanation

. Decreases the body weight moment arm

Explanation

Medializing the acetabulum decreases the lever arm of the body weight relative to the center of rotation. This reduces the mechanical advantage of the body weight, decreasing the required abductor force and lowering the joint reaction force.

Question 6469

Topic: 3. Adult Reconstruction (Hip & Knee)

Placing the acetabular component in a 'high and lateral' position during a complex total hip arthroplasty alters hip biomechanics in which of the following ways?

. Increases abductor moment arm and decreases joint reaction force
. Decreases abductor moment arm and increases joint reaction force
. Increases body weight moment arm and decreases joint reaction force
. Decreases both abductor and body weight moment arms proportionately
. Does not significantly alter the joint reaction force

Correct Answer & Explanation

. Decreases abductor moment arm and increases joint reaction force

Explanation

A high and lateral hip center decreases the abductor moment arm and increases the body weight moment arm. This requires greater force from the abductors, thereby increasing the overall joint reaction force and predisposing the patient to an antalgic limp.

Question 6470

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, utilizing a femoral component with an appropriately increased offset (while strictly maintaining leg length) has which of the following biomechanical effects?

. Decreases the abductor moment arm
. Increases the required abductor muscle force
. Increases the overall joint reaction force
. Decreases the overall joint reaction force
. Increases the body weight moment arm

Correct Answer & Explanation

. Decreases the overall joint reaction force

Explanation

Increasing femoral offset lengthens the abductor moment arm without changing leg length. This increased mechanical advantage requires less force from the abductors to stabilize the pelvis, thus significantly decreasing the overall joint reaction force.

Question 6471

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon medializes the acetabular cup to the level of the true floor of the acetabulum (cotyloid fossa). What is the primary biomechanical effect of this maneuver during single-leg stance?

. Decreases the abductor lever arm
. Increases the abductor lever arm
. Decreases the body weight lever arm
. Increases the body weight lever arm
. Increases the overall joint reaction force

Correct Answer & Explanation

. Decreases the body weight lever arm

Explanation

Medializing the acetabular center of rotation moves the hip joint closer to the body's center of gravity. This decreases the body weight lever arm, thereby reducing the required abductor muscle force and the overall hip joint reaction force.

Question 6472

Topic: 3. Adult Reconstruction (Hip & Knee)

During a revision total hip arthroplasty with severe acetabular bone loss, the surgeon places the new acetabular component in a superior and lateral "high hip center" position. What is the most significant biomechanical consequence of this placement?

. Decreased hip joint reaction force
. Increased abductor lever arm
. Decreased body weight lever arm
. Increased hip joint reaction force
. Improved resting tension of the iliopsoas

Correct Answer & Explanation

. Increased hip joint reaction force

Explanation

A superior and lateral center of rotation shortens the abductor lever arm and lengthens the body weight lever arm. This biomechanical disadvantage requires a massive increase in abductor force to maintain a level pelvis, dramatically increasing the hip joint reaction force.

Question 6473

Topic: Total Hip Arthroplasty (THA)

During templating for a total hip arthroplasty, the surgeon plans to use a high-offset femoral stem to increase global femoral offset without altering leg length. What is the expected effect of this choice on hip biomechanics and stability?

. Decreases abductor tension and decreases impingement risk
. Increases abductor tension and decreases impingement risk
. Increases abductor tension and increases impingement risk
. Decreases abductor tension and increases impingement risk
. Has no effect on abductor tension but decreases impingement risk

Correct Answer & Explanation

. Increases abductor tension and decreases impingement risk

Explanation

Increasing femoral offset shifts the femur laterally, which restores or increases the abductor lever arm (increasing resting abductor tension and mechanical advantage). It also distances the proximal femur from the pelvis, reducing the risk of bony impingement and improving stability.

Question 6474

Topic: Total Knee Arthroplasty (TKA)

A patient with a remote midshaft femur fracture malunion presents for TKA. Preoperative planning reveals a coronal plane extra-articular deformity. What is the generally accepted threshold for femoral extra-articular coronal deformity beyond which a concurrent osteotomy should be considered rather than an intra-articular compensatory resection?

. 5 degrees
. 10 degrees
. 20 degrees
. 30 degrees
. Intra-articular correction is always preferred regardless of angle

Correct Answer & Explanation

. 20 degrees

Explanation

Intra-articular compensatory bone cuts in TKA are generally safe for extra-articular femoral deformities up to 20 degrees in the coronal plane. Deformities exceeding this typically require concurrent or staged extra-articular osteotomy to avoid excessive ligamentous imbalance.

Question 6475

Topic: Total Knee Arthroplasty (TKA)

Elevation of the joint line during a revision TKA most commonly leads to which of the following postoperative complications?

. Mid-flexion instability
. Patella alta
. Hyperextension recurvatum
. Excessive femoral rollback
. Medial collateral ligament attenuation

Correct Answer & Explanation

. Mid-flexion instability

Explanation

Elevating the joint line alters the kinematics of the knee by moving the femoral origin of the collateral ligaments distally relative to the joint line. This mismatch often results in laxity in mid-flexion (mid-flexion instability) and can cause an apparent patella baja.

Question 6476

Topic: 3. Adult Reconstruction (Hip & Knee)

In a total knee arthroplasty, excessive internal rotation of the femoral component will most likely result in which of the following specific kinematic alterations?

. Medial patellar subluxation
. Lateral patellar subluxation
. Increased flexion gap symmetry
. External rotation of the tibia during gait
. Excessive gap tightness in extension

Correct Answer & Explanation

. Lateral patellar subluxation

Explanation

Internal rotation of the femoral component medializes the trochlear groove relative to the extensor mechanism. This increases the Q-angle vector and reliably leads to lateral patellar maltracking or subluxation.

Question 6477

Topic: Total Knee Arthroplasty (TKA)

Which of the following design modifications in a posterior-stabilized TKA helps substitute for the function of the resected posterior cruciate ligament (PCL)?

. Highly cross-linked polyethylene
. An anterior cam on the tibial polyethylene insert
. A femoral cam and tibial post mechanism
. Symmetric condylar geometry
. Increased anterior flange height

Correct Answer & Explanation

. A femoral cam and tibial post mechanism

Explanation

In a posterior-stabilized TKA, the PCL is excised. A central post on the tibial polyethylene insert engages a cam on the femoral component during flexion, physically forcing femoral rollback and preventing anterior subluxation of the femur.

Question 6478

Topic: Total Knee Arthroplasty (TKA)

When planning a primary TKA for a patient with an extra-articular valgus tibial deformity, intra-articular resection is typically considered acceptable if the deformity is within what angular limit in the coronal plane?

. 5 degrees
. 10 degrees
. 20 degrees
. 30 degrees
. 45 degrees

Correct Answer & Explanation

. 10 degrees

Explanation

Intra-articular bone cuts can safely compensate for up to 10 to 15 degrees of extra-articular coronal plane deformity in the tibia. Deformities greater than 10-15 degrees risk compromising the tibial attachment of the collateral ligaments, usually necessitating an extra-articular osteotomy.

Question 6479

Topic: Total Knee Arthroplasty (TKA)

During trial reduction in a cruciate-retaining TKA, the knee is perfectly balanced in full extension but significantly tight in flexion. Which of the following is the most appropriate surgical step to balance the knee?

. Resect more distal femur
. Downsize the femoral component
. Upsize the femoral component
. Use a thicker polyethylene insert
. Decrease the posterior tibial slope

Correct Answer & Explanation

. Downsize the femoral component

Explanation

A knee that is balanced in extension but tight in flexion has an isolated tight flexion gap. Downsizing the femoral component (using an anterior referencing system) reduces the posterior condylar offset, increasing the flexion gap without altering the extension gap.

Question 6480

Topic: 3. Adult Reconstruction (Hip & Knee)

During a cruciate-retaining total knee arthroplasty, trial reduction reveals a tight extension gap and a perfectly balanced flexion gap. What is the most appropriate next step to achieve a balanced knee?

. Resect additional posterior femoral condyle
. Downsize the femoral component
. Recut the proximal tibia
. Release the posterior capsule
. Increase the tibial polyethylene thickness

Correct Answer & Explanation

. Resect additional posterior femoral condyle

Explanation

A tight extension gap with a balanced flexion gap requires increasing the extension space without altering the flexion space. This is best accomplished by releasing the posterior capsule or resecting additional distal femur.

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