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2. Trauma MCQs

Practice Set 470 of 640

This practice set contains high-yield board review questions covering key concepts in 2. Trauma. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 9381

Topic: 2. Trauma

What is the biomechanical consequence of using a nail that is too short for a long diaphyseal fracture?

. Increased risk of rotational instability.
. Increased stress shielding of the fracture site.
. Higher probability of nail breakage at the fracture site.
. Stress concentrations at the nail tips leading to potential periprosthetic fractures.
. Promotion of hypertrophic non-union due to excessive motion.

Correct Answer & Explanation

. Stress concentrations at the nail tips leading to potential periprosthetic fractures.

Explanation

A nail that is too short does not extend sufficiently into the wide metaphysis, causing the ends of the nail to terminate in the narrower diaphysis. This creates stress risers at the tips of the nail and significantly increases the risk of periprosthetic fractures occurring at these points due to the abrupt change in stiffness between the stiff nail and the less stiff bone, concentrating stress at the nail tips. While rotational instability can occur with inadequate fixation, a short nail specifically predisposes to tip fractures.

Question 9382

Topic: 2. Trauma

Which type of intramedullary nail locking provides the strongest resistance to axial rotation at a comminuted diaphyseal fracture site?

. Static locking with two screws at each end.
. Dynamic locking with one screw at each end.
. Multiplanar locking with divergent screws.
. Unicortical locking screws.
. Reamed versus unreamed technique.

Correct Answer & Explanation

. Multiplanar locking with divergent screws.

Explanation

Multiplanar locking, where screws are placed at different angles and planes, significantly increases the rotational stability of the nail-bone construct, especially in comminuted fractures where the bone itself provides minimal intrinsic stability. This is superior to simply using more screws in a single plane. Static locking with two screws offers good rotational control, but multiplanar divergent screws provide an even greater 'grip' on the bone, distributing forces over a wider area and resisting rotation more effectively.

Question 9383

Topic: 2. Trauma

In a transverse femoral shaft fracture, what is the primary role of the locking screws in an intramedullary nail construct?

. To provide direct compression across the fracture.
. To transfer axial load from the nail to the bone.
. To prevent shortening and rotational instability.
. To provide absolute stability for primary bone healing.
. To increase the bending stiffness of the entire construct.

Correct Answer & Explanation

. To prevent shortening and rotational instability.

Explanation

In a transverse fracture, especially after reaming and insertion of an appropriately sized nail, the nail itself often provides good intrinsic stability against bending and some axial compression due to close bone-nail fit. The primary role of locking screws is to prevent shortening (axial collapse) and rotational instability by linking the nail to the bone fragments. They do not provide direct compression in the way a lag screw would, nor do they confer absolute stability for primary healing. Axial load is primarily transferred via bone-nail contact, but locking screws ensure this contact is maintained without excessive shortening or rotation.

Question 9384

Topic: 2. Trauma

A non-union develops after IM nailing of a femoral shaft fracture. Biomechanically, if the non-union is hypertrophic, what is the most likely contributing factor related to the implant construct?

. Excessive stiffness of the nail leading to stress shielding.
. Inadequate working length of the nail.
. Too much interfragmentary motion.
. Lack of reaming, resulting in a smaller diameter nail.
. Presence of a significant bone gap.

Correct Answer & Explanation

. Too much interfragmentary motion.

Explanation

A hypertrophic non-union is characterized by abundant callus formation that fails to bridge the fracture gap, often described as an 'elephant's foot' appearance. This pattern indicates a biological potential for healing (blood supply is adequate) but too much interfragmentary motion, preventing the callus from maturing and bridging. The implant construct (e.g., inadequate number of locking screws, screw loosening, or inappropriate dynamization) can contribute to this excessive motion. An atrophic non-union, conversely, is associated with poor biology and/or severe stress shielding.

Question 9385

Topic: 2. Trauma

What is the biomechanical significance of the 'cannulated' design in many modern intramedullary nails?

. Allows for controlled axial dynamization.
. Enhances resistance to torsional forces.
. Facilitates easier insertion over a guidewire, improving accuracy and reducing soft tissue trauma.
. Increases the bending stiffness of the nail.
. Reduces the risk of thermal necrosis during reaming.

Correct Answer & Explanation

. Facilitates easier insertion over a guidewire, improving accuracy and reducing soft tissue trauma.

Explanation

The cannulated design allows the nail to be inserted over a guidewire. This significantly aids in maintaining reduction, guides the reaming process, and facilitates accurate nail placement. It's a technical/surgical advantage that improves precision and reduces surgical morbidity rather than a direct enhancement of the biomechanical properties of the nail itself (e.g., stiffness or strength). While a cannulated nail has a slightly lower moment of inertia than a solid nail of the same outer diameter, the practical advantage of guidewire insertion outweighs this theoretical reduction in stiffness for most applications.

Question 9386

Topic: 2. Trauma

Which biomechanical characteristic best describes the primary advantage of reamed over unreamed intramedullary nailing for a diaphyseal fracture?

. Preservation of endosteal blood supply.
. Ability to use a larger diameter, stronger nail.
. Reduced risk of fat embolism.
. Faster insertion time.
. Lower incidence of infection.

Correct Answer & Explanation

. Ability to use a larger diameter, stronger nail.

Explanation

Reamed nailing allows for the insertion of a larger diameter nail, which has significantly greater stiffness and strength (especially in bending, proportional to r^4) compared to an unreamed nail. This stronger construct can provide more rigid fixation, better fill the medullary canal for improved load sharing, and allow for earlier weight-bearing. While reaming does cause temporary damage to the endosteal blood supply, the biomechanical advantage of a stronger implant often outweighs this in appropriate fracture patterns (e.g., stable transverse or short oblique fractures).

Question 9387

Topic: 2. Trauma

When managing a highly comminuted diaphyseal fracture with an intramedullary nail, which biomechanical strategy is most crucial for optimal healing?

. Achieving absolute stability through lag screw fixation.
. Minimizing the working length of the construct.
. Promoting controlled micromotion (relative stability) and load sharing.
. Using a nail with a very high modulus of elasticity.
. Ensuring primary cortical contact for torsional stability.

Correct Answer & Explanation

. Promoting controlled micromotion (relative stability) and load sharing.

Explanation

Highly comminuted fractures are best treated with relative stability. The goal is to allow controlled micromotion and load sharing, which stimulates secondary bone healing via callus formation. Absolute stability (as achieved with lag screws) is difficult to achieve and maintain in comminuted fractures and is not the primary goal of IM nailing in these cases. A longer working length and a nail with an elastic modulus closer to bone (not very high) are generally preferred to promote healing in comminuted fractures.

Question 9388

Topic: 2. Trauma

A 60-year-old female with osteoporosis sustains a subtrochanteric femoral fracture. An intramedullary nail is selected. What is a key biomechanical consideration for the proximal locking mechanism in this scenario?

. The use of unicortical screws to minimize stress risers.
. Maximizing the number of locking screws in a single plane.
. Employing multiplanar, divergent screws to enhance angular stability.
. Prioritizing dynamic locking to allow early axial micromotion.
. Selecting smaller diameter screws to reduce bone removal.

Correct Answer & Explanation

. Employing multiplanar, divergent screws to enhance angular stability.

Explanation

In osteoporotic subtrochanteric fractures, bone quality is poor, and the proximal fragment is often very short, making fixation challenging. Multiplanar, divergent screws (e.g., a lag screw combined with anti-rotation screws) are crucial to enhance angular stability and prevent cutout or collapse in the osteoporotic bone. This maximizes the 'grip' on the bone, resisting rotation, varus collapse, and pull-out, which are common failure modes in this fracture type and bone quality.

Question 9389

Topic: 2. Trauma

What is the main biomechanical advantage of an intramedullary nail's position directly within the bone's medullary canal?

. It makes the implant easier to remove post-healing.
. It minimizes soft tissue irritation compared to plates.
. It places the nail closer to the neutral mechanical axis, making it highly effective against bending forces.
. It allows for direct visualization of the fracture site during insertion.
. It facilitates revascularization of the bone fragments.

Correct Answer & Explanation

. It places the nail closer to the neutral mechanical axis, making it highly effective against bending forces.

Explanation

By being placed within the medullary canal, an IM nail is very close to the mechanical axis of the bone. This central placement makes it exceptionally effective at resisting bending forces (which are often the most significant forces acting on long bones) compared to plates placed eccentrically on the surface. Being close to the neutral axis means the bending moments are resisted more efficiently. While soft tissue irritation is reduced, this is more of a surgical/biological advantage than a pure biomechanical one related to its position within the canal's force resistance.

Question 9390

Topic: 2. Trauma

A surgeon opts for a smaller diameter intramedullary nail in an unreamed technique for a highly comminuted open tibial fracture. What is the primary biomechanical rationale for this choice?

. To maximize the bending stiffness of the construct.
. To promote absolute stability at the fracture site.
. To preserve the periosteal and endosteal blood supply, enhancing biological healing.
. To facilitate earlier weight-bearing compared to reamed nailing.
. To increase the implant's resistance to torsional forces.

Correct Answer & Explanation

. To preserve the periosteal and endosteal blood supply, enhancing biological healing.

Explanation

In the setting of a highly comminuted open tibial fracture, preserving the remaining blood supply (both endosteal by not reaming, and periosteal which might be compromised by the open nature and comminution) is paramount for healing. Unreamed nailing with a smaller nail minimizes disruption to the endosteal circulation, prioritizing biological healing over maximum mechanical stiffness. The goal is relative stability, promoting secondary healing.

Question 9391

Topic: 2. Trauma

What biomechanical concept explains why a dynamically locked IM nail might be chosen over a statically locked one for a healing transverse fracture?

. To increase rotational stability.
. To prevent shear forces at the fracture site.
. To allow controlled axial compression and load transfer, stimulating healing.
. To maximize the working length of the construct.
. To achieve absolute stability.

Correct Answer & Explanation

. To allow controlled axial compression and load transfer, stimulating healing.

Explanation

Dynamically locked IM nails allow for controlled axial compression at the fracture site by removing one set of locking screws. This axial micromotion and load transfer are biomechanically beneficial for stimulating secondary bone healing in a transverse fracture that has begun to unite. It prevents stress shielding and encourages bone consolidation. Static locking provides maximal stability in all planes, preventing shortening, while dynamic locking specifically allows for axial loading. Absolute stability is not the goal of IM nailing.

Question 9392

Topic: 2. Trauma

Which of the following fracture patterns is most likely to experience implant failure (e.g., nail bending or breakage) if treated with an IM nail that has insufficient bending stiffness?

. A stable transverse diaphyseal fracture.
. A minimally displaced short oblique fracture.
. A long spiral fracture with significant interfragmentary contact.
. A highly comminuted fracture with a large bone gap.
. An ipsilateral distal femoral and proximal tibial fracture.

Correct Answer & Explanation

. A highly comminuted fracture with a large bone gap.

Explanation

A highly comminuted fracture with a large bone gap implies that the bone fragments themselves cannot provide significant load sharing or stability, placing nearly the entire load on the intramedullary nail. If the nail has insufficient bending stiffness (e.g., too small a diameter, or poor material properties), it will be prone to fatigue failure, bending, or breakage due to high stress concentrations over the unsupported gap. Stable transverse or oblique fractures, and even long spiral fractures with good contact, allow for better load sharing and stress distribution between the bone and nail, reducing the demands on the implant.

Question 9393

Topic: 2. Trauma

What is the primary biomechanical advantage of using an intramedullary nail with an anatomical bow (e.g., for the femur or tibia)?

. To facilitate easier insertion without reaming.
. To better resist torsional forces.
. To optimize nail-bone contact, resisting bending and preventing stress risers.
. To provide greater ultimate tensile strength.
. To allow for multiplanar locking in the metaphysis.

Correct Answer & Explanation

. To optimize nail-bone contact, resisting bending and preventing stress risers.

Explanation

The anatomical bow of an IM nail (matching the natural curvature of the bone) is crucial for optimizing nail-bone contact along the entire length of the nail. This close fit minimizes stress concentrations, reduces toggling within the canal, and maximizes the load-sharing capacity, thereby enhancing the construct's resistance to bending forces and preventing potential stress risers at areas of poor contact. Nails that do not match the anatomical bow can create point contact, leading to stress shielding and potential fracture at the points of impingement.

Question 9394

Topic: 2. Trauma

A periprosthetic fracture occurs at the distal tip of a previously placed intramedullary femoral nail. Biomechanically, what is the most likely contributing factor?

. Excessive reaming during initial nail insertion.
. Inadequate locking screw length.
. Stress concentration at the junction of the stiff nail and more flexible bone.
. Failure of the proximal locking screws.
. Biological factors leading to hypertrophic non-union.

Correct Answer & Explanation

. Stress concentration at the junction of the stiff nail and more flexible bone.

Explanation

Periprosthetic fractures at the tips of an intramedullary nail are a classic complication related to stress concentration. The rigid implant abruptly ends within the bone, creating a sudden change in stiffness. This localized stress riser makes the bone susceptible to fracture under physiological loading, especially during falls or high-energy trauma. The concept is similar to a 'notch effect' where stress is concentrated at an abrupt change in geometry.

Question 9395

Topic: 2. Trauma

In the treatment of a proximal humeral fracture with a locked intramedullary nail, what is a critical biomechanical design feature to ensure adequate stability?

. A long working length to promote relative stability.
. Proximal locking screws that engage multiple planes and angles within the humeral head.
. A smaller diameter nail to minimize stress shielding.
. Cannulation for guidewire insertion only.
. Dynamization capabilities for early weight-bearing.

Correct Answer & Explanation

. Proximal locking screws that engage multiple planes and angles within the humeral head.

Explanation

Proximal humeral fractures, particularly those involving the head, require robust fixation against rotational and varus forces. Proximal locking screws that are multiplanar and divergent (e.g., aiming into the humeral head and greater tuberosity at different angles) provide superior purchase in the cancellous bone of the humeral head and resist both rotation and pull-out, which are common failure modes in this region. This enhances angular stability, critical for maintaining reduction. A long working length is less critical than proximal fixation in these metaphyseal fractures.

Question 9396

Topic: 2. Trauma

A surgeon chooses to perform primary static interlocking for a comminuted femoral shaft fracture with an IM nail. What is the main biomechanical rationale for this initial approach?

. To allow for immediate full weight-bearing.
. To provide maximal initial stability against shortening and rotation.
. To promote direct cortical apposition and primary bone healing.
. To minimize surgical time and blood loss.
. To facilitate early dynamization.

Correct Answer & Explanation

. To provide maximal initial stability against shortening and rotation.

Explanation

Primary static interlocking provides maximal initial stability against both shortening and rotational forces across a comminuted fracture. This prevents collapse and maintains anatomical alignment during the early healing phase, which is crucial where the bone itself offers little intrinsic stability. While immediate full weight-bearing might be a goal, maintaining initial reduction and stability against displacement is the fundamental biomechanical reason for static locking in unstable fractures. It does not typically promote primary bone healing in comminuted fractures, but rather secondary healing with adequate micromotion.

Question 9397

Topic: 2. Trauma

Which biomechanical factor is most likely to lead to delayed union or non-union in an IM nailed femoral fracture if the fracture gap is excessively large?

. Increased risk of implant infection.
. Failure to achieve absolute stability.
. Excessive interfragmentary strain leading to fibrous tissue formation.
. Stress shielding of the fracture fragments.
. Premature dynamization of the nail.

Correct Answer & Explanation

. Excessive interfragmentary strain leading to fibrous tissue formation.

Explanation

An excessively large fracture gap fundamentally alters the biomechanics of healing. Even with a well-fixed IM nail, a large gap means the interfragmentary strain will be too high, even with controlled micromotion. When strain exceeds the biological tolerance of reparative tissues (e.g., >10-15%), fibrous tissue or non-union results instead of bone formation. While stress shielding can contribute to delayed healing, an excessive gap primarily leads to excessive strain that inhibits osteogenesis.

Question 9398

Topic: 2. Trauma

What is the biomechanical significance of choosing an intramedullary nail with appropriate curvature for a femoral fracture?

. It allows for easier removal of the implant post-healing.
. It matches the natural femoral anterior bow, reducing stress at the nail-bone interface.
. It minimizes the risk of post-operative infection.
. It increases the torsional stiffness of the overall construct.
. It facilitates accurate placement of distal locking screws.

Correct Answer & Explanation

. It matches the natural femoral anterior bow, reducing stress at the nail-bone interface.

Explanation

The femur has a natural anterior bow. An IM nail with an appropriate matching curvature ensures that the nail conforms to the bone's anatomy, providing optimal contact along its length. This reduces stress concentrations at the nail-bone interface, minimizing the risk of anterior cortical impingement during insertion (which can lead to iatrogenic fracture) and subsequent stress risers, enhancing the construct's resistance to bending and overall load sharing efficiency. Mismatch can lead to point loading and potential complications.

Question 9399

Topic: 2. Trauma

In the context of IM nailing, what is the 'load sharing' principle, and why is it important for fracture healing?

. The nail carries 100% of the load, protecting the bone.
. The locking screws distribute load evenly between bone and nail.
. The bone and nail share the load, allowing physiological stress on the bone to stimulate healing.
. The external fixator shares load with the IM nail.
. It refers to the ability of the nail to distribute stress across multiple locking screws.

Correct Answer & Explanation

. The bone and nail share the load, allowing physiological stress on the bone to stimulate healing.

Explanation

Load sharing is a fundamental biomechanical advantage of intramedullary nails. Unlike load-bearing plates that initially carry almost all the load, IM nails, by being centrally located within the bone, share the physiological loads with the surrounding bone. This allows the bone to experience controlled stress and strain, which is crucial for stimulating biological processes like callus formation and remodeling, leading to robust secondary bone healing. Excessive stress shielding (where the implant bears too much load) can inhibit healing.

Question 9400

Topic: 2. Trauma

For a long spiral tibial fracture, which characteristic of the IM nail locking screws is most important for preventing post-operative shortening?

. The number of locking screws.
. The diameter of the locking screws.
. The material of the locking screws.
. The position of the locking screws in relation to the fracture site.
. The torque applied during screw insertion.

Correct Answer & Explanation

. The number of locking screws.

Explanation

In a long spiral fracture, especially if it's unstable or comminuted, the primary mechanism of failure is often shortening and rotation. An adequate number of locking screws (typically at least two proximally and two distally for static locking) is crucial to prevent axial collapse (shortening) and rotational instability. While screw diameter and position are important, ensuring sufficient points of fixation (number of screws) at both ends of the nail is fundamental to mechanically resist axial and rotational forces. If only one screw is used, it acts as a pivot, allowing collapse or rotation.

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