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Lower Extremity Trauma MCQs

Practice Set 23 of 34

This practice set contains high-yield board review questions covering key concepts in Lower Extremity Trauma. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 441

Topic: Lower Extremity Trauma

A surgeon decides to upsize a solid tibial intramedullary nail from 10 mm to 12 mm. What is the approximate proportional increase in the bending stiffness of the implant?

. 1.2 times
. 1.44 times
. 1.7 times
. 2.1 times
. 4.0 times

Correct Answer & Explanation

. 2.1 times

Explanation

The bending stiffness of a solid cylinder is proportional to the radius to the fourth power based on the area moment of inertia. Upsizing the nail from 10 mm to 12 mm increases the stiffness by (12/10)^4, which equals approximately 2.07.

Question 442

Topic: Lower Extremity Trauma

The torsional rigidity of a solid cylindrical intramedullary nail is proportional to its radius raised to which of the following powers?

. First power
. Second power
. Third power
. Fourth power
. Fifth power

Correct Answer & Explanation

. Fourth power

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar area moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, small increases in nail radius dramatically increase torsional stiffness.

Question 443

Topic: Lower Extremity Trauma

In the design of a solid intramedullary nail, doubling the radius of the nail will increase its bending stiffness by what factor?

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The bending stiffness of a solid cylinder is proportional to its area moment of inertia, which is calculated as (pi * r^4) / 4. Therefore, doubling the radius increases the bending stiffness by a factor of 16 (2^4 = 16).

Question 444

Topic: Lower Extremity Trauma

Regarding the gross anatomy and biomechanics of the knee menisci, the medial meniscus differs from the lateral meniscus in that the medial meniscus is:

. More mobile during terminal knee flexion
. C-shaped and covers less of the tibial plateau articular surface
. O-shaped and covers more of the tibial plateau articular surface
. Devoid of any direct attachment to the joint capsule
. Primarily composed of Type II collagen rather than Type I

Correct Answer & Explanation

. O-shaped and covers more of the tibial plateau articular surface

Explanation

The medial meniscus is C-shaped, larger in AP dimension, and firmly attached to the deep medial collateral ligament, making it less mobile than the O-shaped lateral meniscus. Both menisci are primarily composed of Type I collagen.

Question 445

Topic: Lower Extremity Trauma

If the radius of a solid cylindrical intramedullary nail is doubled, by what factor does its theoretical bending stiffness increase?

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The area moment of inertia for a solid cylinder, which dictates its bending stiffness, is proportional to the radius raised to the fourth power (r^4). Therefore, doubling the radius of a solid intramedullary nail increases its bending stiffness by a factor of 16 (2^4).

Question 446

Topic: Lower Extremity Trauma

The anterolateral ligament (ALL) of the knee has gained attention as an important secondary restraint to internal tibial rotation. From its femoral origin near the lateral epicondyle, where is its primary insertion site on the tibia?

. Gerdy's tubercle
. The fibular head
. Midway between Gerdy's tubercle and the fibular head
. The anterior tibial tuberosity
. The posteromedial tibial plateau

Correct Answer & Explanation

. Midway between Gerdy's tubercle and the fibular head

Explanation

The anterolateral ligament (ALL) originates on the lateral femoral epicondyle and inserts on the anterolateral tibia, specifically midway between Gerdy's tubercle and the fibular head. It is a distinct ligamentous structure of the anterolateral capsule.

Question 447

Topic: Lower Extremity Trauma

A 24-year-old hockey player sustains an external rotation injury to his ankle.

Radiographs demonstrate widening of the medial clear space. Which ligament is primarily ruptured first in this syndesmotic injury sequence?

. Anterior inferior tibiofibular ligament (AITFL)
. Posterior inferior tibiofibular ligament (PITFL)
. Interosseous ligament
. Deltoid ligament
. Calcaneofibular ligament

Correct Answer & Explanation

. Anterior inferior tibiofibular ligament (AITFL)

Explanation

In a syndesmotic (high ankle) sprain, the anterior inferior tibiofibular ligament (AITFL) is typically the first structure to tear. This is followed by the interosseous membrane and the PITFL as the deforming external rotation force continues.

Question 448

Topic: Lower Extremity Trauma

A 22-year-old soccer player sustains an acute knee injury. During physical examination, a positive pivot shift test is elicited. Which of the following structures is primarily responsible for the reduction of the lateral tibial plateau during the flexion phase of this clinical test?

. Iliotibial band
. Biceps femoris
. Popliteus
. Lateral collateral ligament
. Anterolateral ligament

Correct Answer & Explanation

. Iliotibial band

Explanation

The pivot shift test demonstrates anterior subluxation of the lateral tibial plateau in extension due to ACL deficiency. As the knee is flexed past 20 to 30 degrees, the iliotibial band transitions from an extensor to a flexor, pulling the tibia posteriorly and reducing the subluxation.

Question 449

Topic: Lower Extremity Trauma

A patient presents for total knee arthroplasty with an extra-articular diaphyseal femoral deformity consisting of 15 degrees of varus bowing. According to established alignment principles, what is the best intra-articular adjustment to achieve a neutral postoperative mechanical axis without performing a corrective femoral osteotomy?

. Increase the valgus cut angle of the distal femur
. Decrease the valgus cut angle of the distal femur
. Make a standard 5-degree valgus cut and use a thicker medial polyethylene
. Translate the femoral component laterally
. Under-resect the medial tibial plateau

Correct Answer & Explanation

. Increase the valgus cut angle of the distal femur

Explanation

For a varus extra-articular femoral bowing deformity, the mechanical axis drops medially. To compensate intra-articularly and restore a neutral mechanical axis perpendicular to the floor, the surgeon must increase the valgus angle of the distal femoral cut beyond the standard 5 to 7 degrees.

Question 450

Topic: Lower Extremity Trauma

During a TKA for a patient with a 30-degree flexion contracture, the surgeon balances the flexion gap appropriately but finds the knee remains tight in extension despite adequate posterior capsular release. What is the most appropriate next step?

. Resect additional proximal tibia
. Resect additional distal femur
. Downsize the femoral component
. Upsize the femoral component
. Recut the anterior femur

Correct Answer & Explanation

. Resect additional distal femur

Explanation

A knee that is tight in extension but balanced in flexion requires enlargement of the extension gap only. Resecting additional distal femur achieves this isolated increase without altering the flexion gap.

Question 451

Topic: Lower Extremity Trauma

The bending stiffness of a solid titanium intramedullary nail is proportional to its radius raised to which power?

. Second
. Third
. Fourth
. Fifth
. Sixth

Correct Answer & Explanation

. Fourth

Explanation

The area moment of inertia for a solid cylinder, which governs its resistance to bending (bending stiffness), is proportional to the radius to the fourth power (r^4). Therefore, even a small increase in nail diameter drastically increases its stiffness.

Question 452

Topic: Lower Extremity Trauma

According to biomechanical principles, the bending rigidity of a solid cylindrical intramedullary nail is directly proportional to which of the following?

. Radius squared
. Radius cubed
. Radius to the fourth power
. Cross-sectional area
. Length of the nail squared

Correct Answer & Explanation

. Radius to the fourth power

Explanation

The bending rigidity of a solid cylindrical structure is proportional to the area moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, a small increase in the nail's radius significantly increases its resistance to bending.

Question 453

Topic: Lower Extremity Trauma

When comparing a slotted (open-section) intramedullary nail to an unslotted (closed-section) intramedullary nail of the same diameter and wall thickness, what is the primary biomechanical consequence of the slot?

. Slotting increases torsional rigidity
. Slotting decreases bending rigidity but not torsional rigidity
. Slotting decreases torsional rigidity significantly
. Slotting has no effect on torsional rigidity
. Slotting increases both bending and torsional rigidity

Correct Answer & Explanation

. Slotting decreases torsional rigidity significantly

Explanation

A closed-section (unslotted) tube has a much higher polar moment of inertia compared to an open-section (slotted) tube. Therefore, slotting significantly decreases the torsional rigidity of an intramedullary nail.

Question 454

Topic: Lower Extremity Trauma

A solid cylindrical intramedullary nail's resistance to bending is proportional to its area moment of inertia. If the radius of the nail is doubled, its bending stiffness increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The area moment of inertia for a solid cylinder is proportional to the radius to the fourth power (r^4). Therefore, doubling the radius increases bending stiffness by a factor of 2^4 = 16.

Question 455

Topic: Lower Extremity Trauma

The meniscus relies on its unique structural composition to distribute axial loads in the knee. The primary function of the circumferentially oriented Type I collagen fibers in the menisci is to?

. Resist shear stresses during knee flexion
. Resist radial stresses during varus loading
. Resist hoop stresses generated by axial compression
. Provide nourishment to the avascular inner third
. Attach the meniscal horns to the tibial plateau

Correct Answer & Explanation

. Resist hoop stresses generated by axial compression

Explanation

Axial loading of the knee tends to extrude the meniscus peripherally. The robust circumferential Type I collagen fibers resist this outward expansion by converting compressive forces into tensile "hoop stresses," maintaining joint congruity.

Question 456

Topic: Lower Extremity Trauma

Placing a longitudinal slot in a cylindrical intramedullary nail significantly decreases which of its primary mechanical properties?

. Bending rigidity
. Torsional rigidity
. Tensile strength
. Compressive strength
. Fatigue life under compression

Correct Answer & Explanation

. Torsional rigidity

Explanation

Slotted nails have significantly less torsional rigidity compared to solid or closed-section nails. While this allows for easier insertion and some radial compressibility, it substantially reduces rotational stability.

Question 457

Topic: Lower Extremity Trauma

When evaluating an ankle mortise radiograph for a suspected syndesmotic injury, the medial clear space (MCS) is a critical parameter. Which of the following conditions definitively describes an abnormal medial clear space indicative of deep deltoid ligament disruption?

. MCS > 2 mm
. MCS > 4 mm, or greater than the superior clear space
. MCS > tibiofibular clear space
. MCS > 6 mm with external rotation stress only
. MCS > tibiofibular overlap

Correct Answer & Explanation

. MCS > 4 mm, or greater than the superior clear space

Explanation

A medial clear space of greater than 4 mm, or an MCS that is wider than the superior clear space between the talar dome and tibial plafond, is considered abnormal and highly suggestive of a deep deltoid ligament tear and syndesmotic instability.

Question 458

Topic: Lower Extremity Trauma

A 22-year-old skier presents with lateral ankle pain and a snapping sensation behind the lateral malleolus when circumducting the foot. Radiographs demonstrate a 'fleck sign' avulsed from the lateral malleolus. Which anatomic structure is compromised?

. Anterior talofibular ligament
. Calcaneofibular ligament
. Superior peroneal retinaculum
. Inferior peroneal retinaculum
. Peroneus brevis tendon

Correct Answer & Explanation

. Superior peroneal retinaculum

Explanation

The fleck sign represents a bony avulsion of the superior peroneal retinaculum from the posterolateral fibula. This injury commonly leads to peroneal tendon subluxation or dislocation.

Question 459

Topic: Lower Extremity Trauma

In orthopedic biomechanics, for a solid cylindrical intramedullary nail, the bending stiffness is proportional to the radius raised to which power?

. Second power
. Third power
. Fourth power
. Fifth power
. Inverse of the radius

Correct Answer & Explanation

. Second power

Explanation

The bending stiffness of a solid cylinder is directly proportional to its area moment of inertia. For a solid cylinder, the area moment of inertia is proportional to the radius to the fourth power (r^4).

Question 460

Topic: Lower Extremity Trauma

An orthopedic surgeon decides to change an intramedullary nail from a solid titanium rod with a radius of 'r' to a solid titanium rod with a radius of '2r'. Assuming identical material properties, by what factor does the bending rigidity of the nail increase?

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

The bending rigidity is proportional to the area moment of inertia, which for a solid cylinder is proportional to the radius to the fourth power (r^4). Therefore, doubling the radius (2r) increases the bending rigidity by a factor of 16 (2^4).

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