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Lower Extremity Trauma MCQs

Practice Set 2 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 21

Topic: Lower Extremity Trauma

A 40-year-old man sustains a Schatzker VI tibial plateau fracture. Which of the following neurovascular structures is at the highest risk of injury during a posteromedial surgical approach to the proximal tibia?

. Common peroneal nerve
. Anterior tibial artery
. Great saphenous vein and saphenous nerve
. Popliteal artery
. Sural nerve

Correct Answer & Explanation

. Great saphenous vein and saphenous nerve

Explanation

The posteromedial approach to the proximal tibia exploits the interval between the medial gastrocnemius and the pes anserinus. The great saphenous vein and saphenous nerve lie in the superficial fascia of this region and are highly susceptible to injury.

Question 22

Topic: Lower Extremity Trauma

A 35-year-old man sustains a high-energy Schatzker IV tibial plateau fracture with a large posteromedial shear fragment. Which of the following surgical approaches is most appropriate for direct visualization and buttress plating of this specific fragment?

. Anterolateral approach
. Direct medial approach
. Posteromedial approach utilizing the interval between the medial head of the gastrocnemius and the pes anserinus
. Posterior approach with a classic S-shaped incision
. Lateral approach with a fibular neck osteotomy

Correct Answer & Explanation

. Posteromedial approach utilizing the interval between the medial head of the gastrocnemius and the pes anserinus

Explanation

The posteromedial approach uses the interval between the medial head of the gastrocnemius (retracted laterally) and the pes anserinus (retracted medially). This allows direct, orthogonal access to the posteromedial shear fragment for optimal application of an anti-glide or buttress plate.

Question 23

Topic: Lower Extremity Trauma

A 10-year-old Jewish boy presents with right hip pain. Radiographs show an Erlenmeyer flask deformity of the distal femurs and avascular necrosis of the right femoral head. A defect in which of the following enzymes is responsible?

. Sphingomyelinase
. Hexosaminidase A
. Glucocerebrosidase
. Alpha-L-iduronidase
. Arylsulfatase B

Correct Answer & Explanation

. Glucocerebrosidase

Explanation

Gaucher disease is a lysosomal storage disorder caused by a deficiency in glucocerebrosidase. Classic orthopedic manifestations include the Erlenmeyer flask deformity of the distal femur, bone pain crises, and avascular necrosis of the femoral head.

Question 24

Topic: Lower Extremity Trauma

Osteochondral defects occur bilaterally in the distal femur in approximately:

. 10% to 20% of patients.
. 20% to 30% of patients.
. 30% to 40% of patients.
. 60% to 70% of patients.
. 80% to 90% of patients

Correct Answer & Explanation

. 20% to 30% of patients.

Explanation

Osteochondral defects occur bilaterally in the distal femur for approximately 20% to 30% of patients. The fact that 20% to 30% of patients with an osteochondral lesion in the distal femur have bilateral involvement suggests that there is a predisposition to the development of a lesion at this location, either genetic or secondary to repetitive microtrauma.

Question 25

Topic: Lower Extremity Trauma

An 11-year-old girl is observed for legs that have been bowed for the past 5 years. She has a mechanical axis that is in 26° of varus, a medial tibial plateau slope of 8°, a tibial joint angle of 15° varus, and a femoral joint angle of 10° varus. Her physis appears open. Recommended treatment is:

. Tibial valgus osteotomy
. Femoral valgus osteotomy
. Tibial and femoral valgus osteotomy
. Medial tibial plateau elevation
. Brace treatment

Correct Answer & Explanation

. Tibial and femoral valgus osteotomy

Explanation

Both a tibial and a femoral valgus osteotomy are necessary to correct significant deformities in these areas. A tibial valgus osteotomy is necessary but not sufficient. The femoral joint angle is off by 13° from the normal angle. A femoral valgus osteotomy is necessary but not sufficient. The tibial joint angle is off by 15° of varus. A tibial plateau elevation is not necessary for this mild degree of plateau depression. Brace treatment is not recommended for patients older than 3 years of age.

Question 26

Topic: Lower Extremity Trauma

When utilizing a posteromedial approach for open reduction and internal fixation of a Schatzker IV tibial plateau fracture, the surgical interval is developed between the medial head of the gastrocnemius and which of the following structures?

. Soleus
. Pes anserinus
. Semimembranosus
. Popliteus
. Tibialis posterior

Correct Answer & Explanation

. Pes anserinus

Explanation

The posteromedial approach to the proximal tibia utilizes the interval between the pes anserinus tendons anteriorly and the medial head of the gastrocnemius posteriorly. Retracting the gastrocnemius laterally safely protects the neurovascular bundle in the popliteal fossa.

Question 27

Topic: Lower Extremity Trauma

During the radiographic evaluation of an acute ankle injury, which of the following findings on standard plain radiographs is considered the most reliable indicator of a distal tibiofibular syndesmotic disruption?

. Tibiofibular clear space greater than 6 mm on both AP and mortise views
. Tibiofibular overlap greater than 10 mm on the AP view
. Medial clear space of 2 mm on the mortise view
. Talar tilt angle of 5 degrees
. Complete obliteration of the lateral gutter

Correct Answer & Explanation

. Tibiofibular clear space greater than 6 mm on both AP and mortise views

Explanation

A tibiofibular clear space greater than 5-6 mm on either the AP or mortise radiograph is the most reliable radiographic indicator of syndesmotic injury. Normal tibiofibular overlap should be >1 mm on the mortise view and >6 mm on the AP view.

Question 28

Topic: Lower Extremity Trauma

A 45-year-old man presents with a Schatzker type II tibial plateau fracture. Which of the following surgical approaches is most commonly utilized for open reduction and internal fixation of this injury?

. Posteromedial approach
. Anterolateral approach
. Direct medial approach
. Posterior approach

Correct Answer & Explanation

. Anterolateral approach

Explanation

A Schatzker type II fracture is a split-depression of the lateral tibial plateau. The anterolateral approach provides optimal visualization for elevating the depressed articular segment and applying a lateral buttress plate.

Question 29

Topic: Lower Extremity Trauma

A 23-year-old skier sustains a twisting injury to his knee. MRI demonstrates the bone bruise pattern shown.

What is the primary mechanism of injury associated with this classic bone bruise pattern?

. Direct anterior blow to the proximal tibia
. Hyperextension with varus stress
. Valgus stress with internal tibial rotation
. Pure hyperflexion injury
. Direct lateral blow to the knee

Correct Answer & Explanation

. Valgus stress with internal tibial rotation

Explanation

This bone bruise pattern on the lateral femoral condyle and posterolateral tibial plateau is pathognomonic for an anterior cruciate ligament (ACL) tear. It occurs due to the pivot-shift mechanism, which involves valgus stress coupled with internal rotation of the tibia.

Question 30

Topic: Lower Extremity Trauma
Review the provided sagittal MRI. In the setting of an acute non-contact pivoting injury resulting in an ACL rupture, which specific pattern of secondary trabecular microfractures (bone bruises) is classically observed on MRI?
. Medial femoral condyle and medial tibial plateau
. Lateral femoral condyle and posterolateral tibial plateau
. Anterior tibia and posterior patella
. Medial femoral condyle and lateral tibial plateau
. Lateral femoral condyle and anteromedial tibial plateau

Correct Answer & Explanation

. Lateral femoral condyle and posterolateral tibial plateau

Explanation

The classic mechanism for an ACL tear is a pivot shift (valgus and internal rotation). This mechanism causes the lateral femoral condyle to impact the posterolateral tibial plateau, resulting in the pathognomonic 'kissing' bone bruises seen in these locations on MRI.

Question 31

Topic: Lower Extremity Trauma

A 55-year-old male sustains a severe Schatzker VI bicondylar tibial plateau fracture. An external fixator is placed initially. Three weeks later, definitive fixation is planned. What is the optimal surgical approach to directly address and buttress a displaced posteromedial shear fragment?

. Anterolateral approach
. Direct posterior approach through the popliteal fossa
. Posteromedial approach
. Medial parapatellar approach
. Anteromedial approach

Correct Answer & Explanation

. Posteromedial approach

Explanation

The posteromedial approach utilizes the interval between the medial head of the gastrocnemius and the pes anserinus. It allows for direct visualization and optimal placement of a buttress plate to prevent varus collapse of a posteromedial shear fragment.

Question 32

Topic: Lower Extremity Trauma

Which of the following geometric modifications to a solid intramedullary nail will most dramatically increase its bending stiffness?

. Increasing the length of the nail by 10%
. Decreasing the working length by 50%
. Increasing the radius of the nail by 20%
. Changing the material from titanium to stainless steel
. Adding an anterior slot to the nail

Correct Answer & Explanation

. Increasing the radius of the nail by 20%

Explanation

The bending stiffness of a solid cylinder is proportional to the radius to the fourth power (r^4). Therefore, even a small increase in the nail's radius provides the most exponential increase in bending stiffness.

Question 33

Topic: Lower Extremity Trauma

When comparing a slotted hollow intramedullary nail to a non-slotted hollow intramedullary nail of the same diameter and wall thickness, the slotted nail exhibits a marked reduction primarily in which of the following mechanical properties?

. Axial stiffness
. Torsional stiffness
. Bending stiffness
. Tensile strength
. Yield strength

Correct Answer & Explanation

. Torsional stiffness

Explanation

A longitudinal slot in an intramedullary nail drastically reduces its torsional stiffness (often by more than 90% compared to a closed section). While bending stiffness is also slightly reduced, the torsional deficit is the most profound mechanical consequence.

Question 34

Topic: Lower Extremity Trauma

The formula for the area moment of inertia for a hollow tubular implant like an intramedullary nail relies heavily on the inner and outer radii. If the outer radius of a hollow nail is increased, the bending stiffness increases proportionally to which mathematical function?

. (Outer Radius)^2 - (Inner Radius)^2
. (Outer Radius)^3 - (Inner Radius)^3
. (Outer Radius)^4 - (Inner Radius)^4
. Pi * (Outer Radius - Inner Radius)
. The natural logarithm of the Outer Radius

Correct Answer & Explanation

. (Outer Radius)^4 - (Inner Radius)^4

Explanation

The bending stiffness of a hollow cylindrical implant is proportional to its area moment of inertia, calculated by the formula involving the difference of the outer and inner radii to the fourth power (r_out^4 - r_in^4).

Question 35

Topic: Lower Extremity Trauma

If the diameter of a solid cylindrical intramedullary nail is increased by 50% (e.g., from 10 mm to 15 mm), the bending stiffness of the implant increases by a factor of approximately:

. 1.50
. 2.25
. 3.37
. 5.06
. 16.0

Correct Answer & Explanation

. 5.06

Explanation

The bending stiffness of a solid cylinder is proportional to the area moment of inertia, which scales with the radius to the fourth power (r^4). Increasing the diameter by 1.5 times results in a stiffness increase of 1.5^4, which equals 5.06.

Question 36

Topic: Lower Extremity Trauma

A patient sustains an anterior cortical perforation of the distal femur during insertion of an antegrade femoral intramedullary nail. Which of the following geometric mismatches is the most likely culprit?

. The nail has a smaller radius of curvature than the femur
. The nail has a larger radius of curvature than the femur
. The nail has a smaller area moment of inertia than the femur
. The femur has a larger radius of curvature than the nail
. The femur has a greater polar moment of inertia than the nail

Correct Answer & Explanation

. The nail has a larger radius of curvature than the femur

Explanation

A larger radius of curvature denotes a mathematically straighter object. Because the natural femur has an anterior bow (smaller radius of curvature), driving a straighter nail (larger radius of curvature) can result in impingement and perforation of the anterior distal cortex.

Question 37

Topic: Lower Extremity Trauma

Which of the following biomechanical characteristics is most significantly and disproportionately reduced when utilizing a slotted (open-section) intramedullary nail compared to a solid (closed-section) nail of the exact same outer diameter?

. Area moment of inertia
. Bending stiffness
. Torsional rigidity
. Axial compression resistance
. Modulus of elasticity

Correct Answer & Explanation

. Torsional rigidity

Explanation

While slotting an intramedullary nail reduces both bending stiffness and torsional rigidity, its effect on torsional rigidity is much more profound. Slotted (open-section) nails demonstrate drastically lower resistance to rotational forces compared to closed-section cylinders.

Question 38

Topic: Lower Extremity Trauma

When comparing a closed-section (solid or continuous tube) intramedullary nail to a slotted (open-section) intramedullary nail of identical outer diameter and material, the closed-section nail possesses significantly greater:

. Axial compressibility
. Working length
. Bending stiffness
. Torsional stiffness
. Notch sensitivity

Correct Answer & Explanation

. Torsional stiffness

Explanation

A closed-section intramedullary nail has a vastly higher torsional stiffness compared to an open-section (slotted) nail of the same dimensions. While bending stiffness is also higher, the most dramatic biomechanical difference is in its resistance to torsion.

Question 39

Topic: Lower Extremity Trauma

Which of the following best describes the formula relationship for the bending stiffness (area moment of inertia) of a solid cylindrical intramedullary nail of radius (r)?

. Proportional to r squared
. Proportional to r cubed
. Proportional to r to the fourth power
. Proportional to r to the fifth power
. Inversely proportional to r to the fourth power

Correct Answer & Explanation

. Proportional to r to the fourth power

Explanation

The bending stiffness of a solid cylinder is determined by its area moment of inertia. This value is mathematically proportional to the radius raised to the fourth power.

Question 40

Topic: Lower Extremity Trauma

The anterior bow of a standard adult femur has an average radius of curvature of approximately 120 cm. If an intramedullary nail with a 200 cm radius of curvature is inserted into a femur with a 120 cm bow, what complication is most likely to occur?

. Anterior perforation of the distal femur
. Posterior perforation of the distal femur
. Anterior perforation of the proximal femur
. Medial cortical blowout at the isthmus
. Inability to pass the guide wire

Correct Answer & Explanation

. Anterior perforation of the distal femur

Explanation

A nail with a larger radius of curvature (e.g., 200 cm) is physically straighter than the native anterior bow of the femur (120 cm). During insertion, the mismatch tends to drive the distal tip of the nail anteriorly, risking anterior cortical perforation.

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