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Lower Extremity Trauma MCQs

Practice Set 29 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 561

Topic: Lower Extremity Trauma

A 60-year-old female undergoes an MRI of her knee for a suspected meniscal tear. An incidental intramedullary distal femur lesion is identified. Which of the following MRI findings best distinguishes a bone infarct from an enchondroma?

. Lobulated, bright high-signal intensity on T2-weighted images
. A serpiginous border with a 'double-line' sign
. Endosteal scalloping greater than two-thirds of cortical thickness
. Enhancement of the central matrix after gadolinium administration
. Presence of soft tissue extension

Correct Answer & Explanation

. A serpiginous border with a 'double-line' sign

Explanation

Bone infarcts are distinguished on MRI by a serpiginous, well-defined border frequently demonstrating the 'double-line' sign (hyperintense inner ring, hypointense outer ring on T2). Enchondromas typically show characteristic lobulated T2 hyperintensity.

Question 562

Topic: Lower Extremity Trauma

What is the primary function of the menisci in the knee joint?

. Initiate knee flexion
. Provide varus and valgus stability
. Increase articular congruence and distribute loads
. Synthesize synovial fluid
. Act as a direct attachment point for the quadriceps

Correct Answer & Explanation

. Increase articular congruence and distribute loads

Explanation

The menisci (medial and lateral) are C-shaped fibrocartilaginous structures that primarily increase the contact area between the femoral condyles and tibial plateau, thereby improving articular congruence and distributing compressive loads across the knee joint. They also play a role in shock absorption, joint lubrication, and stability, but load distribution and congruence are their main biomechanical functions. They do not initiate flexion, provide primary collateral stability (that's ligaments), synthesize synovial fluid (that's the synovium), or act as direct attachment points for the quadriceps (that's the patella and patellar tendon).

Question 563

Topic: Lower Extremity Trauma

According to the mechanical principles of intramedullary fixation, the bending stiffness of a solid cylindrical titanium intramedullary nail is proportional to its radius raised to which power?

. Radius (r^1)
. Radius squared (r^2)
. Radius cubed (r^3)
. Radius to the fourth power (r^4)
. Radius to the fifth power (r^5)

Correct Answer & Explanation

. Radius to the fourth power (r^4)

Explanation

The bending stiffness (area moment of inertia) of a solid cylinder is proportional to the radius to the fourth power (r^4). Torsional stiffness (polar moment of inertia) is also proportional to r^4. This means that even a small increase in the diameter of an intramedullary nail significantly increases its stiffness.

Question 564

Topic: Lower Extremity Trauma

What is the primary function of the menisci in the knee joint?

. To lubricate the joint surfaces
. To increase the stability of the joint by deepening the articular surface of the tibia for the femoral condyles
. To produce synovial fluid
. To act as a primary shock absorber
. To prevent hyperextension of the knee

Correct Answer & Explanation

. To increase the stability of the joint by deepening the articular surface of the tibia for the femoral condyles

Explanation

The menisci serve multiple functions, but their primary role is to improve the congruence between the incongruent femoral condyles and tibial plateau, thereby increasing the stability of the knee joint. They also act as secondary shock absorbers and play a role in load transmission and joint lubrication. While they contribute to shock absorption and load transmission, 'increasing stability by deepening the articular surface' is their fundamental anatomical contribution to joint mechanics.

Question 565

Topic: Lower Extremity Trauma

A patient sustains a Schatzker type II tibial plateau fracture (split-depression). Which surgical approach is generally most appropriate for direct visualization and internal fixation of this specific injury pattern?

. Medial approach
. Posteromedial approach
. Anterolateral approach
. Direct posterior approach
. Ilioinguinal approach

Correct Answer & Explanation

. Anterolateral approach

Explanation

Schatzker type II fractures involve a split and depression of the lateral tibial plateau. The standard anterolateral approach provides excellent visualization of the lateral articular surface and allows for appropriate application of a lateral buttress plate.

Question 566

Topic: Lower Extremity Trauma

During a primary total knee arthroplasty, the surgeon evaluates the gaps and finds the knee is tight in extension and symmetrical in flexion. Which of the following is the most appropriate next step in management?

. Recut the proximal tibia with more posterior slope
. Resect more distal femur
. Upsize the femoral component
. Release the posterior cruciate ligament
. Recut the distal femur with more valgus

Correct Answer & Explanation

. Resect more distal femur

Explanation

A tight extension gap with a balanced flexion gap is treated by resecting more distal femur. This increases the extension gap without affecting the flexion gap. Recutting the tibia would affect both gaps simultaneously. Upsizing the femoral component would decrease the flexion gap. Releasing the PCL primarily affects the flexion gap (increases it).

Question 567

Topic: Lower Extremity Trauma
An anterolateral approach to the proximal tibia is performed for a Schatzker type III tibial plateau fracture. Dissection is carried out between the tibialis anterior and extensor digitorum longus. Which neurovascular bundle supplies this compartment and courses on the anterior surface of the interosseous membrane?
. Superficial peroneal nerve and peroneal artery
. Deep peroneal nerve and anterior tibial artery
. Tibial nerve and posterior tibial artery
. Saphenous nerve and descending genicular artery
. Sural nerve and lesser saphenous vein

Correct Answer & Explanation

. Deep peroneal nerve and anterior tibial artery

Explanation

The anterior compartment of the leg is supplied by the deep peroneal nerve and the anterior tibial artery. These structures run together distally on the anterior surface of the interosseous membrane.

Question 568

Topic: Lower Extremity Trauma
This is a CT scan at the level of the distal femur and femoral component. What is the orientation of the femoral component in the CT scan?
. Properly rotated
. Internally rotated
. Externally rotated
. Excessive flexion

Correct Answer & Explanation

. Internally rotated

Explanation

A CT scan with metal artifact reduction is a useful study to evaluate femoral component rotation. Proper rotation would show that the transepicondylar line and posterior condylar line are parallel. The femoral component is internally rotated compared to the femoral epicondylar axis.

Question 569

Topic: Lower Extremity Trauma

A 42-year-old male is undergoing open reduction and internal fixation of a bicondylar tibial plateau fracture (Schatzker VI). The surgeon plans a standard posteromedial approach to directly reduce and buttress a displaced posteromedial fragment. The surgical interval for this approach involves mobilizing and retracting which two structures?

. Medial head of the gastrocnemius and the pes anserinus
. Semimembranosus and the medial head of the gastrocnemius
. Tibialis posterior and the flexor digitorum longus
. Medial head of the gastrocnemius and the soleus
. Tibialis anterior and the extensor hallucis longus

Correct Answer & Explanation

. Medial head of the gastrocnemius and the pes anserinus

Explanation

The standard posteromedial approach to the proximal tibia exploits the interval between the medial head of the gastrocnemius (which is retracted posteriorly/laterally to protect the neurovascular bundle) and the pes anserinus tendons (which are retracted anteriorly/medially). This provides excellent exposure of the posteromedial tibial plateau.

Question 570

Topic: Lower Extremity Trauma

A football player sustains a syndesmotic ankle sprain. Which ligament is typically the first to tear in a syndesmotic injury?

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

Correct Answer & Explanation

. Posterior inferior tibiofibular ligament (PITFL)

Explanation

In a syndesmotic injury (high ankle sprain), the progression of tearing typically begins anteriorly with the anterior inferior tibiofibular ligament (AITFL), followed by the interosseous ligament/membrane, and finally the posterior inferior tibiofibular ligament (PITFL).

Question 571

Topic: Lower Extremity Trauma

The anterolateral ligament (ALL) of the knee is an important secondary stabilizer against anterolateral rotatory instability. Where does the ALL typically insert on the tibia?

. Midway between Gerdy's tubercle and the fibular head
. Directly on Gerdy's tubercle
. At the tip of the fibular head
. Posterior to the fibular head
. The medial tibial plateau

Correct Answer & Explanation

. Midway between Gerdy's tubercle and the fibular head

Explanation

The ALL originates near the lateral epicondyle and inserts on the anterolateral tibia, approximately midway between Gerdy's tubercle and the fibular head. It acts as a secondary restraint to internal tibial rotation.

Question 572

Topic: Lower Extremity Trauma

An orthopedic manufacturer creates two solid circular intramedullary nails. If the radius of the second nail is increased by 10% compared to the first, approximately how much does its bending rigidity increase?

. 10%
. 21%
. 46%
. 100%
. 400%

Correct Answer & Explanation

. 10%

Explanation

The bending rigidity (area moment of inertia) of a solid cylinder is proportional to the radius to the fourth power (r^4). Increasing the radius by 10% (1.1x) increases the rigidity by 1.1^4 = 1.4641, representing a roughly 46% increase.

Question 573

Topic: Lower Extremity Trauma
An 8-year-old boy presents with a painful clunking sensation in his left knee when walking. MRI confirms a discoid lateral meniscus. During arthroscopic evaluation, the meniscus is found to be hypermobile due to an absent posterior meniscotibial attachment, tethered only by the meniscofemoral ligament. Which Watanabe type does this represent?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type III

Explanation

The Watanabe classification of discoid meniscus describes three types: Type I (Complete) covers the entire tibial plateau and has normal attachments; Type II (Incomplete) partially covers the plateau and has normal attachments; Type III (Wrisberg variant) lacks the normal posterior meniscotibial attachment (coronary ligament), relying solely on the meniscofemoral ligament of Wrisberg. This leads to a hypermobile meniscus and the classic 'snapping knee' syndrome.

Question 574

Topic: Lower Extremity Trauma

During the radiographic evaluation of a suspected midfoot injury, what finding is considered pathognomonic for a Lisfranc injury?

. Widening of the 1st and 2nd intermetatarsal space > 2mm
. A small bony avulsion fragment in the 1st intermetatarsal space (fleck sign)
. Dorsal displacement of the 1st metatarsal base on the medial cuneiform
. Plantar gapping of the 1st TMT joint
. Compression fracture of the cuboid

Correct Answer & Explanation

. Widening of the 1st and 2nd intermetatarsal space > 2mm

Explanation

The "fleck sign" represents a bony avulsion of the Lisfranc ligament from the base of the second metatarsal. When present on an AP or oblique radiograph, it is considered pathognomonic for a Lisfranc ligament injury.

Question 575

Topic: Lower Extremity Trauma

A competitive skier presents with lateral ankle pain and a snapping sensation behind the lateral malleolus after a sudden dorsiflexion and inversion injury. Radiographs show a small "fleck sign" avulsed from the posterolateral fibula. What is the primary stabilizing structure injured in this condition?

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

Correct Answer & Explanation

. Inferior extensor retinaculum

Explanation

The scenario describes peroneal tendon subluxation or dislocation. The mechanism typically causes attenuation or avulsion (fleck sign) of the superior peroneal retinaculum, which is the primary restraint to peroneal tendon displacement from the fibular groove.

Question 576

Topic: Lower Extremity Trauma
The bending rigidity of an intramedullary nail is mathematically dependent on its material properties and its cross-sectional geometry, specifically the area moment of inertia. For a solid circular intramedullary nail, if the radius is increased by a factor of 2, the bending rigidity increases by a factor of:
. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

For a solid cylinder, the area moment of inertia (I) is proportional to the radius raised to the fourth power (I = π * r^4 / 4). Therefore, doubling the radius (2r) increases the area moment of inertia, and thus the bending rigidity, by a factor of 2^4 = 16.

Question 577

Topic: Lower Extremity Trauma



According to the fundamental biomechanical principles of intramedullary nailing, if the working length of a solid intramedullary nail is doubled, its torsional rigidity is mathematically altered by what factor?

. Decreased by a factor of 2
. Decreased by a factor of 4
. Increased by a factor of 2
. Increased by a factor of 4
. Increased by a factor of 16

Correct Answer & Explanation

. Decreased by a factor of 2

Explanation

The torsional stiffness (rigidity) of a solid cylinder (like an intramedullary nail) is inversely proportional to its working length (L) and directly proportional to the polar moment of inertia, which relies on the fourth power of its radius (r^4). Because torsional rigidity = (G * J) / L, doubling the working length (L) decreases the overall torsional rigidity by half (a factor of 2).

Question 578

Topic: Lower Extremity Trauma

When replacing a solid intramedullary nail with a hollow intramedullary nail of the identical outer diameter, how is the torsional rigidity of the implant mathematically affected?

. It increases significantly
. It remains unchanged
. It decreases proportional to the inner radius to the fourth power
. It decreases proportional to the inner radius squared
. It decreases proportional to the length of the nail

Correct Answer & Explanation

. It increases significantly

Explanation

Torsional rigidity is proportional to the polar moment of inertia. For a hollow cylinder, it is proportional to (outer radius^4 - inner radius^4). Thus, hollowing the nail decreases its rigidity by a factor proportional to the inner radius^4.

Question 579

Topic: Lower Extremity Trauma

Meniscal tears are a common knee pathology. In basic science review of meniscal anatomy, which of the following statements is true regarding the medial meniscus compared to the lateral meniscus?

. The medial meniscus is more circular in shape
. The medial meniscus is more mobile
. The medial meniscus covers a larger percentage of its respective tibial plateau
. The medial meniscus is firmly attached to the deep medial collateral ligament
. The lateral meniscus lacks an attachment to the joint capsule

Correct Answer & Explanation

. The medial meniscus is more circular in shape

Explanation

The medial meniscus is larger, more 'C'-shaped (semilunar), less mobile, and covers less of the medial tibial plateau surface area compared to the lateral meniscus (which is more 'O'-shaped and covers more of the lateral plateau). The medial meniscus is firmly anchored to the joint capsule and the deep medial collateral ligament, restricting its mobility and making it more prone to injury.

Question 580

Topic: Lower Extremity Trauma

An orthopedic surgeon is performing a posterolateral approach to the tibial plateau. To adequately expose the joint, the fibular collateral ligament may need to be visualized. What nerve is most at risk during the distal extent of this exposure, and where does it typically cross the fibula?

. Common peroneal nerve; posterior to the fibular head
. Common peroneal nerve; wraps anteriorly around the fibular neck
. Deep peroneal nerve; pierces the anterior intermuscular septum
. Tibial nerve; passes deep to the soleus bridge
. Superficial peroneal nerve; runs along the lateral border of the fibula

Correct Answer & Explanation

. Common peroneal nerve; posterior to the fibular head

Explanation

The common peroneal nerve travels posterior to the biceps femoris and wraps around the fibular neck, placing it at high risk during posterolateral knee approaches.

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