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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 322 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 6421

Topic: Total Knee Arthroplasty (TKA)

A 17-year-old female soccer player sustains a non-contact anterior cruciate ligament (ACL) tear. Compared to her male counterparts, she is at a substantially higher risk for this injury. Which of the following biomechanical or anatomic risk factors is most strongly associated with this increased risk in females?

. Increased intercondylar notch width
. Decreased Q angle
. Neuromuscular imbalances characterized by quadriceps dominance
. Decreased posterior tibial slope
. Hypertrophy of the semitendinosus muscle

Correct Answer & Explanation

. Neuromuscular imbalances characterized by quadriceps dominance

Explanation

Female athletes face a higher risk of non-contact ACL tears largely due to neuromuscular factors, particularly "quadriceps dominance" and weaker hamstring co-contraction. Additionally, females generally possess a narrower intercondylar notch, increased Q angle, and increased dynamic valgus loading.

Question 6422

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male presents to the emergency department with acute onset of severe left groin pain and inability to bear weight 2 weeks after a primary total hip arthroplasty (THA) performed via a posterior approach. Radiographs show well-fixed components with a posteriorly dislocated femoral head. Which of the following component positions most likely predisposed the patient to this specific direction of instability?

. Excessive femoral anteversion
. Excessive acetabular anteversion
. Increased femoral offset
. Acetabular retroversion
. Increased acetabular center-edge angle

Correct Answer & Explanation

. Acetabular retroversion

Explanation

Acetabular retroversion, as well as decreased femoral anteversion (retroversion), strongly predisposes a total hip arthroplasty to posterior dislocation. Excessive anteversion of either the acetabular or femoral component typically predisposes the joint to anterior dislocation.

Question 6423

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon medializes the acetabular component and increases the femoral offset. What is the combined effect on the hip joint reaction force (JRF) and abductor muscle force?

. Increased JRF, Increased abductor force
. Decreased JRF, Decreased abductor force
. Decreased JRF, Increased abductor force
. Increased JRF, Decreased abductor force

Correct Answer & Explanation

. Decreased JRF, Decreased abductor force

Explanation

Medializing the acetabulum decreases the body weight lever arm, and increasing offset increases the abductor lever arm. Both biomechanical alterations reduce the required abductor force and the total joint reaction force.

Question 6424

Topic: Total Hip Arthroplasty (THA)

A 4-year-old girl presents with a congenital short femur resulting in a 2.5 cm leg length discrepancy (LLD). Using the Paley multiplier method, if her age- and gender-specific multiplier is approximately 1.5, what is her predicted LLD at skeletal maturity assuming constant inhibition?

. 2.5 cm
. 3.75 cm
. 4.5 cm
. 5.0 cm

Correct Answer & Explanation

. 3.75 cm

Explanation

The multiplier method predicts the ultimate LLD at skeletal maturity by multiplying the current discrepancy by the age- and gender-specific multiplier. For this patient, 2.5 cm x 1.5 = 3.75 cm.

Question 6425

Topic: Total Hip Arthroplasty (THA)

A patient presents with symptomatic bilateral coxa valga. How does this specific proximal femoral deformity alter hip biomechanics compared to a normal neck-shaft angle?

. Increases the abductor lever arm and decreases joint reaction force
. Decreases the abductor lever arm and increases joint reaction force
. Increases the body weight lever arm and decreases joint reaction force
. Decreases both the abductor lever arm and joint reaction force

Correct Answer & Explanation

. Decreases the abductor lever arm and increases joint reaction force

Explanation

Coxa valga increases the neck-shaft angle, which decreases the femoral offset and shortens the abductor lever arm. This mechanical disadvantage requires increased abductor muscle force, thereby increasing the overall hip joint reaction force.

Question 6426

Topic: 3. Adult Reconstruction (Hip & Knee)

During revision total hip arthroplasty for severe acetabular bone loss, the surgeon accepts a "high hip center" (superior placement of the acetabular component without medialization). How does this position affect hip biomechanics?

. Increases the resting length of the abductors and decreases joint reaction force
. Decreases the abductor moment arm and increases the joint reaction force
. Decreases the body weight moment arm and decreases joint reaction force
. Increases femoral offset and improves abductor efficiency

Correct Answer & Explanation

. Decreases the abductor moment arm and increases the joint reaction force

Explanation

A high and lateral hip center displaces the center of rotation away from the abductor origin. This shortens the abductor muscles, decreases their moment arm, and drastically increases the force they must generate, thereby increasing total joint reaction force.

Question 6427

Topic: 3. Adult Reconstruction (Hip & Knee)

During a complex revision total hip arthroplasty, the surgeon places the acetabular component in a superior and medial position (high hip center). Assuming femoral lateralization is not altered, what is the expected biomechanical consequence on the hip joint?

. Increased abductor moment arm and decreased joint reaction force.
. Decreased abductor moment arm and increased joint reaction force.
. Decreased body weight moment arm and decreased joint reaction force.
. Increased abductor moment arm and increased joint reaction force.
. No net change in the overall joint reaction force.

Correct Answer & Explanation

. Decreased abductor moment arm and increased joint reaction force.

Explanation

A high hip center displaces the center of rotation superiorly and medially. Without increased femoral offset, this shortens the abductor moment arm and lengthens the body weight moment arm, leading to a significantly higher joint reaction force.

Question 6428

Topic: 3. Adult Reconstruction (Hip & Knee)

In a patient undergoing primary total hip arthroplasty, the surgeon uses a high-offset femoral stem instead of a standard stem. What is the primary biomechanical advantage of this decision?

. Decreases abductor tension and increases the joint reaction force.
. Increases the abductor moment arm and decreases the joint reaction force.
. Decreases the abductor moment arm and decreases the joint reaction force.
. Increases the body weight moment arm and increases the joint reaction force.
. Increases the overall leg length without altering the joint reaction force.

Correct Answer & Explanation

. Increases the abductor moment arm and decreases the joint reaction force.

Explanation

Increasing femoral offset lengthens the abductor moment arm, making the abductor muscles biomechanically more efficient. This reduces the muscle force required for pelvic stability, thereby significantly decreasing the joint reaction force.

Question 6429

Topic: 3. Adult Reconstruction (Hip & Knee)

Moving the hip center of rotation medially and inferiorly during total hip arthroplasty has what primary effect on hip biomechanics?

. Decreases abductor moment arm and increases joint reaction force.
. Increases abductor moment arm and decreases joint reaction force.
. Decreases abductor moment arm and decreases joint reaction force.
. Increases body weight moment arm and increases joint reaction force.
. Increases body weight moment arm and decreases joint reaction force.

Correct Answer & Explanation

. Increases abductor moment arm and decreases joint reaction force.

Explanation

Medializing and inferiorly translating the hip center of rotation increases the abductor moment arm and decreases the body weight moment arm. This significantly reduces the overall joint reaction force across the hip.

Question 6430

Topic: 3. Adult Reconstruction (Hip & Knee)

During total hip arthroplasty for developmental dysplasia of the hip (DDH), placing the acetabular component in a "high hip center" without adequate lateralization has what primary biomechanical consequence?

. Increases the abductor moment arm.
. Decreases the abductor moment arm and increases joint reaction forces.
. Maintains normal joint reaction forces while equalizing leg length.
. Eliminates the risk of hip dislocation.
. Increases the femoral offset significantly.

Correct Answer & Explanation

. Decreases the abductor moment arm and increases joint reaction forces.

Explanation

A high hip center inherently decreases the abductor moment arm and shortens the resting length of the abductor musculature. This reduces their mechanical efficiency, requiring a higher force output and thereby increasing the resultant joint reaction forces.

Question 6431

Topic: Total Hip Arthroplasty (THA)

A 10-year-old girl (skeletal age 10) presents with a predicted leg length discrepancy of 3.2 cm at maturity. Assuming growth follows the Menelaus rule, at what approximate skeletal age should a distal femoral epiphysiodesis be performed to equalize her limb lengths?

. Immediately at skeletal age 10
. At skeletal age 11
. At skeletal age 12
. At skeletal age 13
. At skeletal age 14

Correct Answer & Explanation

. At skeletal age 11

Explanation

Using the Menelaus rule, the distal femur grows approximately 10 mm (1 cm) per year, and girls cease growth at skeletal age 14. To correct a 3.2 cm discrepancy, approximately 3 years of growth arrest are needed, indicating the procedure should be performed at skeletal age 11.

Question 6432

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty for developmental dysplasia, the surgeon places the acetabular component in a 'high hip center' (superior and lateral) position. What is the primary biomechanical consequence of this placement?

. Increases the abductor moment arm and decreases joint reaction force.
. Decreases the abductor moment arm and increases joint reaction force.
. Decreases the abductor moment arm and decreases joint reaction force.
. Has no net effect on the joint reaction force.
. Shifts the center of rotation medially and inferiorly.

Correct Answer & Explanation

. Decreases the abductor moment arm and increases joint reaction force.

Explanation

Placing the hip center superiorly and laterally shortens the abductor moment arm. This requires the abductor muscles to generate significantly more force to stabilize the pelvis, which consequently increases the overall joint reaction force.

Question 6433

Topic: Total Hip Arthroplasty (THA)

The Paley Multiplier method is frequently used to predict leg length discrepancy at skeletal maturity for patients with congenital femoral deficiency. What is the fundamental assumption of this predictive model?

. The leg length discrepancy increases by a fixed absolute number of millimeters each year.
. The inhibition of growth (ratio of the short limb to the normal limb) remains constant throughout development.
. Bone age must always be used instead of chronological age for accurate prediction.
. It is only applicable for predictions after the age of 5 years.
. The contralateral normal leg grows at an exponentially decreasing rate.

Correct Answer & Explanation

. The inhibition of growth (ratio of the short limb to the normal limb) remains constant throughout development.

Explanation

The Multiplier method for congenital limb deficiencies assumes a constant percentage of growth inhibition. This means the affected limb grows at a consistently slower proportional rate compared to the normal limb throughout childhood.

Question 6434

Topic: 3. Adult Reconstruction (Hip & Knee)

A patient undergoes total hip arthroplasty. During templating, the surgeon plans to increase the femoral offset compared to the patient's native anatomy. How will this purely biomechanical change affect the required abductor muscle force and the total joint reaction force (JRF) during single-leg stance?

. Increases abductor force, increases JRF
. Decreases abductor force, increases JRF
. Decreases abductor force, decreases JRF
. Increases abductor force, decreases JRF
. No effect on abductor force, decreases JRF

Correct Answer & Explanation

. Decreases abductor force, decreases JRF

Explanation

Increasing femoral offset extends the abductor moment arm. A longer moment arm reduces the required abductor muscle force to balance the pelvis, which consequently decreases the overall joint reaction force across the hip.

Question 6435

Topic: Total Hip Arthroplasty (THA)

A non-ambulatory child with severe cerebral palsy develops bilateral spastic coxa valga. How does the pathophysiology of coxa valga alter the normal biomechanics of the hip joint?

. It increases femoral offset and increases abductor mechanical advantage.
. It decreases femoral offset and decreases abductor mechanical advantage.
. It increases femoral offset and decreases the joint reaction force.
. It decreases femoral offset and increases abductor mechanical advantage.
. It creates an excessive retroversion of the femoral neck without altering offset.

Correct Answer & Explanation

. It decreases femoral offset and decreases abductor mechanical advantage.

Explanation

Coxa valga is characterized by an increased neck-shaft angle, which anatomically decreases the horizontal femoral offset. This shortens the abductor moment arm, reducing the mechanical advantage of the abductors and increasing the joint reaction force.

Question 6436

Topic: Total Knee Arthroplasty (TKA)

In the standard evaluation of normal lower extremity mechanical alignment using a full-length standing anteroposterior radiograph, what are the normal ranges for the mechanical lateral distal femoral angle (mLDFA) and the mechanical medial proximal tibial angle (mMPTA)?

. mLDFA 80-84 degrees; mMPTA 90-95 degrees
. mLDFA 85-90 degrees; mMPTA 85-90 degrees
. mLDFA 90-95 degrees; mMPTA 80-84 degrees
. mLDFA 95-100 degrees; mMPTA 95-100 degrees
. mLDFA 85-90 degrees; mMPTA 95-100 degrees

Correct Answer & Explanation

. mLDFA 85-90 degrees; mMPTA 85-90 degrees

Explanation

The normal mLDFA is approximately 87 degrees (range 85-90), and the normal mMPTA is also approximately 87 degrees (range 85-90). This combined anatomy keeps the knee joint line horizontal to the ground during normal single-leg stance.

Question 6437

Topic: 3. Adult Reconstruction (Hip & Knee)

During a revision total hip arthroplasty, the hip center of rotation is inadvertently placed 2 cm superior and 2 cm lateral to its anatomic location. How does this altered hip center mechanically affect the required abductor muscle force and the resultant joint reaction force (JRF)?

. Decreases abductor force and decreases JRF
. Increases abductor force and increases JRF
. Decreases abductor force and increases JRF
. Increases abductor force and decreases JRF
. No change in abductor force but increases JRF

Correct Answer & Explanation

. Decreases abductor force and increases JRF

Explanation

Placing the hip center superiorly and laterally shortens the abductor moment arm and lengthens the body weight moment arm. This mechanical disadvantage requires much higher abductor muscle forces to maintain pelvic stability, which proportionally increases the joint reaction force.

Question 6438

Topic: Total Hip Arthroplasty (THA)

In a single-leg stance static free-body diagram of the hip, if the patient's effective body weight (W) is 600 N, the body weight moment arm is 10 cm, and the abductor moment arm is 5 cm, what is the approximate magnitude of the total hip joint reaction force (JRF)? (Assume all forces act in parallel).

. 600 N
. 1200 N
. 1800 N
. 2400 N
. 3000 N

Correct Answer & Explanation

. 1800 N

Explanation

The required abductor force (F_abd) is calculated by balancing moments: F_abd = (600 N * 10 cm) / 5 cm = 1200 N. The total joint reaction force is the sum of the effective body weight and the abductor force (JRF = 600 N + 1200 N = 1800 N).

Question 6439

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon opts for a high-offset stem without changing the vertical position of the hip center. Compared to a standard offset stem, what is the biomechanical effect on the abductor muscle force and the joint reaction force (JRF)?

. Increased abductor force, increased JRF
. Increased abductor force, decreased JRF
. Decreased abductor force, decreased JRF
. Decreased abductor force, increased JRF
. No change in either force

Correct Answer & Explanation

. Increased abductor force, decreased JRF

Explanation

Increasing the femoral offset lengthens the abductor lever arm. A longer abductor lever arm means less muscle force is required to counteract the body weight moment, which proportionally decreases the overall joint reaction force.

Question 6440

Topic: Total Hip Arthroplasty (THA)

The Paley multiplier method is highly accurate for predicting leg length discrepancy at skeletal maturity. What is the fundamental physiological assumption underlying the use of this method in congenital limb deficiencies?

. Growth inhibition increases exponentially with advancing age
. Growth inhibition remains a constant proportion of normal growth
. The leg length discrepancy remains a constant absolute value throughout childhood
. Growth velocity always peaks earlier in the congenitally affected limb
. The discrepancy spontaneously corrects during the pubertal growth spurt

Correct Answer & Explanation

. Growth inhibition remains a constant proportion of normal growth

Explanation

The multiplier method assumes that the relative growth inhibition of the affected bone remains constant over time. Because the ratio of the discrepancy to the total length is constant, simple multiplication can predict the discrepancy at skeletal maturity.

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