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Lower Extremity Trauma MCQs

Practice Set 25 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 481

Topic: Lower Extremity Trauma

When applying a lateral locking plate for a depressed Schatzker II tibial plateau fracture, what is the primary biomechanical rationale for ensuring the proximal row of screws is placed in a subchondral position?

. To prevent screw cut-out into the knee joint
. To avoid iatrogenic injury to the lateral meniscus
. To mechanically support the elevated articular surface and prevent subsidence
. To allow clearance for a concurrent intramedullary nail
. To maximize diaphyseal pull-out strength

Correct Answer & Explanation

. To prevent screw cut-out into the knee joint

Explanation

Proximal locking screws in a tibial plateau plate act as a fixed-angle scaffold or "raft." Placing them immediately subchondral supports the newly elevated articular fragments, preventing post-operative subsidence and loss of reduction.

Question 482

Topic: Lower Extremity Trauma

A 38-year-old man undergoes open reduction and internal fixation of a Schatzker IV (medial) tibial plateau fracture.

Which surgical approach is most appropriate for direct visualization and buttress plating of the posteromedial fragment?

. Anterolateral approach
. Direct anterior approach
. Posteromedial approach between the pes anserinus and medial gastrocnemius
. Posterolateral approach
. Midline longitudinal approach

Correct Answer & Explanation

. Anterolateral approach

Explanation

The posteromedial approach allows direct visualization and application of an anti-glide or buttress plate to the apex of the posteromedial fragment, effectively resisting the shear forces.

Question 483

Topic: Lower Extremity Trauma

A 40-year-old man sustains a bicondylar tibial plateau fracture (Schatzker VI) with a displaced posteromedial coronal split fragment. Standard anterolateral plating alone is planned. What is the most likely consequence of failing to specifically address the posteromedial fragment?

. Varus collapse of the knee
. Valgus collapse of the knee
. Anterior subluxation of the tibia
. Peroneal nerve palsy
. Rupture of the medial collateral ligament

Correct Answer & Explanation

. Varus collapse of the knee

Explanation

The posteromedial fragment involves the medial articular surface and supports the medial femoral condyle. Failure to anatomically buttress this fragment typically leads to varus collapse and posterior subluxation of the tibia.

Question 484

Topic: Lower Extremity Trauma

A 6-year-old girl presents with torticollis following an upper respiratory infection. A dynamic CT scan reveals atlantoaxial rotatory subluxation with an anterior displacement of the atlas of 4 mm on the axis. According to the Fielding and Hawkins classification, what type of injury is this?

. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type I

Explanation

Fielding and Hawkins Type II describes a rotatory subluxation with 3-5 mm of anterior displacement, indicating deficiency of the transverse ligament. Type I has no anterior displacement (<3 mm), and Type III has >5 mm of displacement.

Question 485

Topic: Lower Extremity Trauma

During the radiographic evaluation of a suspected syndesmotic injury, external rotation stress views are obtained. Which of the following radiographic measurements on an AP or mortise view is the most reliable indicator of deep deltoid ligament incompetence and syndesmotic instability?

. Tibiofibular clear space > 6 mm
. Tibiofibular overlap < 10 mm
. Medial clear space > 4 mm
. Talar tilt > 2 degrees
. Lateral clear space > 5 mm

Correct Answer & Explanation

. Tibiofibular clear space > 6 mm

Explanation

A medial clear space of >4 mm (or >5 mm depending on specific literature criteria) on an AP, mortise, or stress radiograph is a highly reliable indicator of lateral talar shift and underlying deep deltoid ligament rupture.

Question 486

Topic: Lower Extremity Trauma

A 24-year-old athlete sustains a twisting injury to the ankle. Anteroposterior (AP) and mortise radiographs are obtained to evaluate for a syndesmotic injury. Which of the following radiographic parameters is considered abnormal and highly suggestive of a syndesmotic disruption on a standard mortise view?

. Tibiofibular clear space of 4 mm
. Tibiofibular overlap of 2 mm
. Talar tilt of 1 degree
. Medial clear space of 3 mm
. Tibiofibular clear space greater than 6 mm

Correct Answer & Explanation

. Tibiofibular clear space of 4 mm

Explanation

On both AP and mortise views, a tibiofibular clear space greater than 5-6 mm measured 1 cm above the joint line is abnormal and strongly indicates a syndesmotic injury. A normal mortise view should also typically demonstrate a medial clear space of 4 mm or less.

Question 487

Topic: Lower Extremity Trauma

Which of the following radiographic parameters is the most accurate and reliable indicator of a syndesmotic injury on standard weight-bearing ankle radiographs?

. Tibiofibular overlap less than 1 mm on the AP view
. Tibiofibular clear space greater than 5 mm on the AP view
. Medial clear space greater than 4 mm on the Mortise view
. Tibiofibular overlap greater than 2 mm on the Mortise view
. Talar tilt greater than 2 degrees on the stress view

Correct Answer & Explanation

. Tibiofibular overlap less than 1 mm on the AP view

Explanation

A tibiofibular clear space greater than 5 mm measured 1 cm above the joint line on an AP or mortise radiograph is the most reliable plain radiographic sign of syndesmotic widening. Medial clear space widening represents deltoid ligament insufficiency.

Question 488

Topic: Lower Extremity Trauma

A 22-year-old football player sustains a hyperplantarflexion injury to his midfoot. Weight-bearing radiographs demonstrate a 2 mm diastasis between the base of the first and second metatarsals, with a 'fleck sign' present. What is the most appropriate management?

. Non-weight-bearing cast for 6 weeks
. Closed reduction and percutaneous pinning
. Corticosteroid injection and immediate return to play
. Open reduction and internal fixation or primary arthrodesis
. Orthotic management with a rigid carbon-fiber plate

Correct Answer & Explanation

. Non-weight-bearing cast for 6 weeks

Explanation

The presence of a 'fleck sign' (avulsion of the Lisfranc ligament from the base of the 2nd metatarsal) and diastasis greater than 2 mm indicates an unstable Lisfranc injury. Operative management with ORIF or primary arthrodesis is required to restore stable midfoot anatomy.

Question 489

Topic: Lower Extremity Trauma

A solid cylindrical intramedullary nail has a radius of 'r'. If the radius is doubled to '2r', the bending stiffness of the solid nail increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

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

Question 490

Topic: Lower Extremity Trauma

If the diameter of a solid intramedullary nail is increased from 10 mm to 12 mm, what is the approximate percentage increase in its bending stiffness?

. 20%
. 44%
. 73%
. 107%
. 150%

Correct Answer & Explanation

. 20%

Explanation

The bending stiffness of a solid cylinder is proportional to the radius to the fourth power (r^4). Increasing the diameter from 10 mm to 12 mm yields a ratio of 1.2^4, which equals 2.0736, representing an approximate 107% increase in bending stiffness.

Question 491

Topic: Lower Extremity Trauma



An orthopedic surgeon decides to over-ream a tibial diaphysis to insert a larger diameter intramedullary nail. By increasing the solid nail's radius by a factor of 2, the torsional rigidity of the nail increases by what factor?

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

The torsional rigidity of a solid cylindrical intramedullary nail is proportional to the polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, doubling the radius increases the torsional rigidity by a factor of 16 (2^4).

Question 492

Topic: Lower Extremity Trauma

A solid titanium intramedullary nail's resistance to bending (bending rigidity) is directly proportional to its radius raised to what power?

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

Correct Answer & Explanation

. First power

Explanation

The bending rigidity of a solid cylindrical implant is proportional to its area moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, small increases in nail diameter drastically increase bending stiffness.

Question 493

Topic: Lower Extremity Trauma

An orthopedic surgeon decides to over-ream the femoral canal to insert a solid intramedullary nail with a 12-mm outer diameter rather than a 10-mm outer diameter. Assuming the material is identical, the bending rigidity of the nail increases by approximately what factor?

. 1.2
. 1.4
. 2.1
. 1.7
. 2.5

Correct Answer & Explanation

. 1.2

Explanation

The bending rigidity of a solid cylinder is proportional to its area moment of inertia, which is calculated based on the radius to the fourth power (r^4). Increasing the diameter from 10 mm to 12 mm (a 1.2-fold increase) increases the bending rigidity by a factor of 1.2^4, which is approximately 2.1.

Question 494

Topic: Lower Extremity Trauma

According to the principles of biomechanics, the bending rigidity of a solid cylindrical intramedullary nail is proportional to its radius raised to which power?

. 1
. 2
. 3
. 4
. 5

Correct Answer & Explanation

. 1

Explanation

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

Question 495

Topic: Lower Extremity Trauma

The lateral meniscus is structurally and kinematically distinct from the medial meniscus. Which of the following is a defining anatomical feature of the lateral meniscus?

. It is firmly attached to the lateral collateral ligament
. It has a larger radius of curvature than the medial meniscus
. It is more rigidly fixed to the tibial plateau than the medial meniscus
. It receives attachments from the meniscofemoral ligaments of Humphrey and Wrisberg
. Its posterior horn acts as the primary wedge against anterior tibial translation

Correct Answer & Explanation

. It is firmly attached to the lateral collateral ligament

Explanation

The lateral meniscus is highly mobile, O-shaped, and is physically separated from the LCL by the popliteus tendon. It receives capsular attachments from the anterior (Humphrey) and posterior (Wrisberg) meniscofemoral ligaments.

Question 496

Topic: Lower Extremity Trauma

Histological analysis of articular cartilage from a patient with early osteoarthritis reveals duplication of a specific boundary layer. What is the normal functional significance of the tidemark in articular cartilage?

. It represents the primary vascular supply to the chondrocytes
. It is the boundary separating the superficial and middle zones of uncalcified cartilage
. It divides the uncalcified articular cartilage from the calcified cartilage
. It anchors the menisci to the tibial plateau
. It provides the primary source of stem cells for cartilage repair

Correct Answer & Explanation

. It represents the primary vascular supply to the chondrocytes

Explanation

The tidemark is a distinct histological line that demarcates the transition between the deep zone of uncalcified articular cartilage and the underlying calcified cartilage. Duplication or advancement of the tidemark is a hallmark of osteoarthritis.

Question 497

Topic: Lower Extremity Trauma

A 24-year-old soccer player presents with lateral ankle pain and a popping sensation behind the fibula when circumducting the foot. Radiographs reveal a cortical avulsion off the lateral ridge of the distal fibula. This "fleck sign" indicates an injury to which of the following structures?

. Anterior talofibular ligament
. Calcaneofibular ligament
. Superior peroneal retinaculum
. Inferior extensor retinaculum
. Cervical ligament

Correct Answer & Explanation

. Anterior talofibular ligament

Explanation

The "fleck sign" on a mortise or AP radiograph represents an osseous avulsion of the superior peroneal retinaculum from the posterolateral fibula. It is pathognomonic for peroneal tendon dislocation or subluxation.

Question 498

Topic: Lower Extremity Trauma

If a surgeon increases the diameter of a solid titanium intramedullary nail from 10 mm to 12 mm, the bending rigidity of the nail increases by a factor of approximately:

. 1.2
. 1.4
. 1.7
. 2.1
. 2.5

Correct Answer & Explanation

. 1.2

Explanation

The bending rigidity of a solid cylindrical object is proportional to its area moment of inertia, which is calculated as I = (π * r^4) / 4. Therefore, bending rigidity is proportional to the radius (or diameter) to the fourth power. Increasing the diameter from 10 to 12 mm represents a 1.2-fold increase. The new bending rigidity is (1.2)^4, which is 2.0736, or approximately a 2.1-fold increase.

Question 499

Topic: Lower Extremity Trauma

During a posterolateral approach to the tibial plateau, the surgeon must identify the common peroneal nerve. Immediately distal to the fibular head, which muscle does the common peroneal nerve dive beneath?

. Tibialis anterior
. Extensor digitorum longus
. Peroneus longus
. Soleus
. Gastrocnemius lateral head

Correct Answer & Explanation

. Peroneus longus

Explanation

After coursing distally and wrapping around the fibular neck, the common peroneal nerve dives deep to the origin of the peroneus longus muscle before bifurcating.

Question 500

Topic: Lower Extremity Trauma

A 45-year-old male sustains an acute posterior root tear of the medial meniscus while performing a deep squat.

Biomechanical studies have demonstrated that if this lesion is left untreated, the resultant changes in knee contact pressures are most equivalent to which of the following?

. Isolated anterior cruciate ligament rupture.
. Total medial meniscectomy.
. Partial medial meniscectomy.
. Posterior cruciate ligament rupture.
. Chondral delamination of the medial femoral condyle.

Correct Answer & Explanation

. Total medial meniscectomy.

Explanation

The posterior root of the medial meniscus anchors the meniscus to the tibial plateau, allowing it to convert axial loads into hoop stresses. A complete radial tear at or near the root disrupts these hoop stresses entirely, leading to meniscal extrusion. Biomechanical studies have shown that the peak contact pressures and contact areas in a knee with a medial meniscus root tear are biomechanically equivalent to those in a knee that has undergone a total medial meniscectomy.

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