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Lower Extremity Trauma MCQs

Practice Set 4 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 61

Topic: Lower Extremity Trauma

Mr. J.S. undergoes serial debridements and successful vascular reconstruction. Five days post-injury, a clean, granulating wound bed is achieved over the extensive anteromedial defect. Given the exposed bone and large soft tissue defect, what is the most appropriate next step for definitive soft tissue coverage?

. Primary closure of the wound with sutures.
. Application of a split-thickness skin graft directly over the exposed bone.
. Delayed primary closure after another week of VAC therapy.
. Free tissue transfer (e.g., latissimus dorsi free flap).
. Local rotational flap from the contralateral leg.

Correct Answer & Explanation

. Free tissue transfer (e.g., latissimus dorsi free flap).

Explanation

Correct Answer: DThe case describes an extensive, irregular open wound (15 x 8 cm) with exposed, comminuted distal tibial shaft and metaphyseal fragments. When there is exposed bone, tendon, or hardware, and the defect is too large for primary closure or local flaps, a free tissue transfer (free flap) is the gold standard for definitive soft tissue coverage. A free flap, such as a latissimus dorsi flap, brings its own blood supply, providing well-vascularized tissue to cover the defect, promote healing, and protect the underlying structures.Option A is incorrect:Primary closure is not possible for such a large defect with significant soft tissue loss and exposed bone. Attempting primary closure would lead to excessive tension, wound dehiscence, and potential flap necrosis.Option B is incorrect:A split-thickness skin graft requires a well-vascularized, granulating wound bed for successful take. It cannot be applied directly over exposed bone, as bone lacks the necessary blood supply for graft survival.Option C is incorrect:While VAC therapy helps prepare the wound bed, a defect of this size with exposed bone will not be amenable to delayed primary closure. The tissue loss is too extensive.Option E is incorrect:Local rotational flaps are typically used for smaller defects or defects where adjacent healthy tissue is available. For a large anteromedial tibial defect with significant soft tissue avulsion, a local flap from the same leg is often insufficient or would compromise already traumatized tissue. A flap from the contralateral leg is not a 'local' flap and would be a complex procedure with significant donor site morbidity for a local flap.

Question 62

Topic: Lower Extremity Trauma

An orthopedic implant manufacturer is developing a new intramedullary nail. If they increase the nail's outer diameter by 15%, assuming identical material and inner diameter (if cannulated), by approximately what factor would its bending stiffness increase?

. 1.15
. 1.32
. 1.52
. 1.75
. 2.00

Correct Answer & Explanation

. 1.75

Explanation

Correct Answer: DRationale:The bending stiffness (EI) of an intramedullary nail is directly proportional to its Area Moment of Inertia (I). For a circular cross-section, the Area Moment of Inertia is proportional to the fourth power of its outer diameter (I ~ d4).If the diameter (d) increases by 15%, the new diameter (d') will be 1.15d.The new Area Moment of Inertia (I') will be proportional to (1.15d)4.I' ~ (1.15)4* d4I' ~ 1.74900625 * d4Therefore, the bending stiffness would increase by a factor of approximately 1.75.A) 1.15:This would be a linear increase, not considering the d4relationship.B) 1.32:This is approximately 1.152, which would be relevant for area, not MOI.C) 1.52:This is approximately 1.153.E) 2.00:This would require a larger increase in diameter.

Question 63

Topic: Lower Extremity Trauma

Regarding intramedullary nail design, increasing the nail's diameter primarily enhances its resistance to what type of biomechanical force?

. Axial compression.
. Torsional loads.
. Bending moments.
. Shear stress.
. Distraction forces.

Correct Answer & Explanation

. Bending moments.

Explanation

Correct Answer: CIncreasing the diameter of an intramedullary nail significantly enhances its moment of inertia, which is the key determinant of a structure's resistance to bending. The resistance to bending is proportional to the fourth power of the radius (or diameter), making diameter a critical factor for bending stiffness. While diameter also affects torsional stiffness, its most dramatic effect is on bending resistance. Axial compression resistance is primarily determined by the cross-sectional area, and shear stress resistance is also influenced by diameter but not as profoundly as bending.

Question 64

Topic: Lower Extremity Trauma

When performing retrograde intramedullary nailing for a distal femur fracture, what is the most critical anatomical consideration to prevent iatrogenic knee injury?

. A. Avoiding injury to the superior genicular artery.
. B. Ensuring proper entry point to prevent damage to the intercondylar notch and articular cartilage.
. C. Protecting the common peroneal nerve laterally.
. D. Preventing disruption of the posterior cruciate ligament attachment.
. E. Minimizing periosteal stripping during exposure.

Correct Answer & Explanation

. B. Ensuring proper entry point to prevent damage to the intercondylar notch and articular cartilage.

Explanation

Correct Answer: BThe most critical anatomical consideration when performing retrograde intramedullary nailing of the distal femur is ensuring the correct entry point to prevent damage to the intercondylar notch, articular cartilage, and potential compromise of the anterior cruciate ligament (ACL) insertion site. An incorrect entry point can lead to chondral damage, knee pain, and functional impairment. While protecting nerves (C) and minimizing soft tissue stripping (E) are important general principles, the specific challenge with retrograde nailing is the intra-articular entry. The genicular arteries (A) are less of a concern than articular damage. PCL attachment (D) is posterior and generally not at risk with standard entry.

Question 65

Topic: Lower Extremity Trauma

Following reamed intramedullary nailing of a tibial shaft fracture, a patient develops anterior knee pain. What is the most common cause of this complication?

. A. Osteoarthritis of the patellofemoral joint.
. B. Impingement of the proximal locking screws on the patellar tendon.
. C. Patellar tendon irritation from the nail entry portal.
. D. Neuroma formation in the infrapatellar branch of the saphenous nerve.
. E. Avascular necrosis of the patella.

Correct Answer & Explanation

. C. Patellar tendon irritation from the nail entry portal.

Explanation

Correct Answer: CAnterior knee pain is a well-known complication of tibial intramedullary nailing. The most common cause is irritation or impingement of the patellar tendon by the proximal end of the nail, or by prominent proximal locking screws. While infrapatellar nerve injury (D) can cause numbness and sometimes pain, and osteoarthritis (A) can be a pre-existing condition, the direct mechanical irritation by the hardware is the most frequent cause of post-operative anterior knee pain related to the nailing procedure itself. Avascular necrosis of the patella (E) is exceedingly rare.

Question 66

Topic: Lower Extremity Trauma

What is the most common cause of malrotation following intramedullary nailing of a femoral shaft fracture?

. A. Incorrect entry portal for the nail.
. B. Failure to restore the anatomical anteversion of the proximal femur during reduction.
. C. Distal locking screws placed inaccurately.
. D. Lack of intraoperative fluoroscopy.
. E. Post-operative muscle spasm.

Correct Answer & Explanation

. B. Failure to restore the anatomical anteversion of the proximal femur during reduction.

Explanation

Correct Answer: BMalrotation, particularly internal rotation deformity, is a common and often functionally significant complication after femoral intramedullary nailing. The most common cause is the failure to restore the anatomical anteversion of the proximal and distal femur during reduction and fixation. Intraoperative assessment of rotation (e.g., foot position, lesser trochanter profile, cortical step sign, C-arm techniques) is crucial. Incorrect entry portal (A) can cause malalignment, but not primarily malrotation. Distal locking (C) affects length and angulation more directly. While fluoroscopy (D) aids in visualization, it's theinterpretation and useof that information for rotational assessment that is key.

Question 67

Topic: Lower Extremity Trauma

What is the primary objective of obtaining an 'axial view' or 'ski tip view' of the distal femur during retrograde intramedullary nailing?

. A. To assess the entry point in the intercondylar notch.
. B. To confirm the rotational alignment of the distal fragment.
. C. To visualize and protect the popliteal neurovascular bundle.
. D. To ensure adequate distal locking screw placement.
. E. To assess for fracture propagation into the articular surface.

Correct Answer & Explanation

. D. To ensure adequate distal locking screw placement.

Explanation

Correct Answer: DThe 'axial view' or 'ski tip view' of the distal femur is crucial during retrograde intramedullary nailing to ensure proper distal locking screw placement (D). This view provides an orthogonal projection to the standard AP and lateral, allowing the surgeon to confirm that the screws are fully engaging the distal cortex and are within the bone, without exiting into soft tissues or the knee joint. It also helps to prevent nerve and vessel injury. While entry point (A) and articular surface assessment (E) are important, the ski tip view is specifically for confirming the distal locking.

Question 68

Topic: Lower Extremity Trauma

When comparing an unslotted to a slotted intramedullary nail of the same material and outer diameter, the unslotted nail provides a significant biomechanical advantage in resisting which of the following forces?

. Axial compression
. Bending
. Torsion
. Tension
. Shear

Correct Answer & Explanation

. Torsion

Explanation

Unslotted (closed-section) nails have significantly greater torsional rigidity compared to slotted (open-section) nails. While bending rigidity is also slightly increased, the most dramatic biomechanical difference is the resistance to torsional deformation.

Question 69

Topic: Lower Extremity Trauma

An intramedullary nail with a 1.5-meter radius of curvature (ROC) is inserted into a femur with a 1.2-meter ROC. This geometric mismatch most commonly increases the risk of which intraoperative complication?

. Posterior cortical blowout of the proximal femur
. Anterior cortical perforation of the distal femur
. Medial malleolar fracture
. Varus malalignment
. Lateral wall blowout of the greater trochanter

Correct Answer & Explanation

. Anterior cortical perforation of the distal femur

Explanation

A femur with a 1.2m ROC is more bowed than a nail with a 1.5m ROC (which is straighter). Forcing a straighter nail into a more bowed femur risks anterior cortical penetration or frank perforation in the distal femur.

Question 70

Topic: Lower Extremity Trauma

Which of the following design modifications of an intramedullary nail will most dramatically increase its torsional stiffness?

. Increasing the wall thickness of a slotted nail
. Changing from a slotted to a solid, unslotted design
. Increasing the number of interlocking screws from two to three
. Decreasing the working length of the nail
. Applying a pre-bent curvature to the nail

Correct Answer & Explanation

. Changing from a slotted to a solid, unslotted design

Explanation

Changing an intramedullary nail from a slotted to a closed-section (unslotted) design exponentially increases torsional stiffness. While increasing the radius also increases stiffness, closing the cross-section has the most massive impact on torsional rigidity.

Question 71

Topic: Lower Extremity Trauma

A surgeon evaluates a slotted versus a solid intramedullary nail of identical outer diameter and material. What is the most significant biomechanical consequence of the longitudinal slot?

. Significantly decreased bending rigidity
. Significantly decreased torsional rigidity
. Increased risk of thermal necrosis during insertion
. Increased axial stiffness
. Decreased resistance to shear forces

Correct Answer & Explanation

. Significantly decreased torsional rigidity

Explanation

The primary biomechanical difference between a solid and a slotted nail is that the slotted nail has significantly decreased torsional rigidity. While bending rigidity is only slightly affected by the slot, the open section dramatically reduces the construct's ability to resist twisting forces.

Question 72

Topic: Lower Extremity Trauma

How does increasing the working length of an intramedullary nail (defined as the distance between the most proximal and distal points of fixation) affect its biomechanical behavior?

. Increases torsional stiffness
. Increases bending stiffness
. Decreases both torsional and bending stiffness
. Increases axial stiffness while decreasing bending stiffness
. Has no effect on stiffness, only on fatigue life

Correct Answer & Explanation

. Decreases both torsional and bending stiffness

Explanation

The working length of an IM nail is inversely proportional to its stiffness. Increasing the distance between the locking screws effectively increases the span over which the nail must bear loads, thereby decreasing both torsional and bending stiffness.

Question 73

Topic: Lower Extremity Trauma

An elderly patient with an exaggerated anterior bow of the femur sustains a midshaft fracture. The surgeon inserts an intramedullary nail with a larger radius of curvature (less bowed) than the patient's native anatomy. This mismatch most significantly increases the risk of which intraoperative complication?

. Anterior cortical perforation of the distal femur
. Posterior cortical perforation of the distal femur
. Proximal lateral cortex blowout
. Delayed union due to excessive dynamization
. Rotational malalignment of the distal fragment

Correct Answer & Explanation

. Anterior cortical perforation of the distal femur

Explanation

A nail with a larger radius of curvature is straighter than a highly bowed femur. Upon insertion, the straight distal tip of the nail will tend to impinge upon and potentially perforate the anterior cortex of the distal femur.

Question 74

Topic: Lower Extremity Trauma

A manufacturer designs a new intramedullary nail with a longitudinal slot to allow for easier insertion and radial compression during placement. Compared to a closed-section (unslotted) nail of identical outer diameter, wall thickness, and material, the slotted nail primarily exhibits a significant reduction in:

. Bending rigidity in the anteroposterior plane.
. Bending rigidity in the coronal plane.
. Axial stiffness.
. Torsional rigidity.
. Tensile strength.

Correct Answer & Explanation

. Torsional rigidity.

Explanation

Slotted (open-section) intramedullary nails have significantly lower torsional rigidity compared to closed-section nails due to a lower polar moment of inertia. Bending rigidity is also affected but to a much lesser degree than the dramatic loss in torsional stability.

Question 75

Topic: Lower Extremity Trauma

During the insertion of an intramedullary nail for a transverse midshaft femur fracture, the surgeon notes impending perforation of the anterior cortex of the distal femur. Biomechanically, this complication is most commonly related to the use of an intramedullary nail possessing a:

. Radius of curvature greater than that of the native femur.
. Radius of curvature less than that of the native femur.
. Significantly shorter working length.
. Smaller outer diameter.
. Higher polar moment of inertia.

Correct Answer & Explanation

. Radius of curvature greater than that of the native femur.

Explanation

The native femur has an anterior bow with a radius of curvature of approximately 1.2 meters. A nail with a greater radius of curvature is 'straighter' than the femur, causing a mismatch that frequently leads to anterior cortical impingement or perforation distally.

Question 76

Topic: Lower Extremity Trauma

A 45-year-old male marathon runner complains of isolated medial knee pain. Radiographs demonstrate medial compartment osteoarthritis with a mechanical axis passing through the medial compartment. He is scheduled for a medial opening-wedge high tibial osteotomy (HTO). What is the optimal target for the postoperative mechanical axis?

. Exactly through the center of the knee joint (50% of the tibial plateau)
. Through the center of the medial compartment (25% of the tibial plateau)
. At the Fujisawa point (62% of the tibial plateau from medial to lateral)
. At the extreme lateral articular margin (100% of the tibial plateau)
. Anterior to the center of rotation to decrease patellofemoral pressure

Correct Answer & Explanation

. At the Fujisawa point (62% of the tibial plateau from medial to lateral)

Explanation

The goal of an HTO for medial compartment OA is to slightly overcorrect the mechanical axis into valgus to offload the medial side. The classic target is the Fujisawa point, located at 62-62.5% of the tibial plateau width from the medial edge.

Question 77

Topic: Lower Extremity Trauma

When evaluating a patient for patella alta, the Caton-Deschamps index is measured using which of the following radiographic landmarks on a true lateral radiograph?

. Ratio of the patellar tendon length to the longest diagonal length of the patella
. Ratio of the distance from the lower articular margin of the patella to the anterior tibial angle to the articular length of the patella
. Ratio of the distance from the lower pole of the patella to the tibial tubercle to the articular length of the patella
. Ratio of the perpendicular distance from the tibial plateau to the lower pole of the patella to the patellar articular length
. Ratio of the distance from the Blumensaat line to the superior pole of the patella

Correct Answer & Explanation

. Ratio of the distance from the lower articular margin of the patella to the anterior tibial angle to the articular length of the patella

Explanation

The Caton-Deschamps index relies on articular margins, making it useful even if the patellar poles are morphologically abnormal. It is the ratio of the distance from the inferior articular margin of the patella to the anterior angle of the tibial plateau, divided by the patellar articular length.

Question 78

Topic: Lower Extremity Trauma

A meta-analysis comparing intramedullary nailing (IMN) versus dynamic compression plating (DCP) for humeral shaft fractures shows similar rates of union. However, intramedullary nailing is associated with a significantly higher incidence of which complication?

. Radial nerve palsy
. Deep infection
. Shoulder pain and impingement
. Elbow stiffness
. Refracture after hardware removal

Correct Answer & Explanation

. Shoulder pain and impingement

Explanation

Intramedullary nailing of the humerus, particularly with antegrade insertion, is associated with a significantly higher rate of shoulder morbidity, including pain, stiffness, and rotator cuff pathology, compared to plate fixation.

Question 79

Topic: Lower Extremity Trauma

A 48-year-old highly active female presents with isolated lateral compartment knee osteoarthritis and a fixed 15-degree valgus deformity. She has failed all non-operative measures. What is the most appropriate joint-preserving surgical intervention?

. Medial opening wedge high tibial osteotomy
. Lateral closing wedge high tibial osteotomy
. Medial closing wedge distal femoral osteotomy
. Tibial tubercle anteriorization osteotomy
. Proximal fibular osteotomy

Correct Answer & Explanation

. Medial closing wedge distal femoral osteotomy

Explanation

For a young, active patient with isolated lateral compartment knee osteoarthritis and a significant valgus deformity, the deformity typically originates in the distal femur. A distal femoral osteotomy (such as a medial closing wedge) is the procedure of choice, as correcting large valgus deformities via the tibia creates an unacceptable, non-physiologic joint line obliquity.

Question 80

Topic: Lower Extremity Trauma

A 28-year-old athlete sustains a meniscal tear in his knee. Understanding the normal function of the menisci, which of the following is considered their primary biomechanical role in the knee joint?

. Limit hyperextension of the knee.
. Increase the congruity between the femoral condyles and tibial plateau.
. Provide intrinsic stability against varus and valgus stress.
. Lubricate the articular surfaces.
. House proprioceptive nerve endings for joint position sense.

Correct Answer & Explanation

. Increase the congruity between the femoral condyles and tibial plateau.

Explanation

Correct Answer: BThe menisci are C-shaped fibrocartilaginous structures that sit on the tibial plateau. Their primary biomechanical roles include increasing the contact area between the femoral condyles and tibial plateau, which significantly reduces contact stress on the articular cartilage. They also contribute to joint stability, shock absorption, and some lubrication, but increasing congruity and reducing stress are their most critical functions. Ligaments limit hyperextension and provide varus/valgus stability.

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