Menu

1. General Principles & Basic Science MCQs

Practice Set 71 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1401

Topic: Biology, Genetics & Bone Healing

Which cell type is primarily responsible for the resorption of both the initial fracture hematoma and any necrotic bone fragments during the early stages of fracture healing?

. Osteoblasts
. Chondrocytes
. Fibroblasts
. Osteoclasts
. Mesenchymal stem cells

Correct Answer & Explanation

. Osteoclasts

Explanation

Correct Answer: DOsteoclasts are multinucleated cells derived from hematopoietic stem cells that are responsible for bone resorption. During fracture healing, they are crucial for removing necrotic bone fragments and remodeling the bone at the fracture site. Macrophages also play a role in clearing the hematoma and debris, but osteoclasts are specific to bone resorption. Osteoblasts form bone, chondrocytes form cartilage, fibroblasts form fibrous tissue, and mesenchymal stem cells differentiate into these cell types.

Question 1402

Topic: Biomechanics & Biomaterials

A titanium intramedullary nail is selected over a stainless steel nail of identical dimensions for a tibia fracture. Based on material properties, how does the titanium nail influence the biomechanical environment?

. It provides higher bending stiffness and absolute stability.
. It has a higher modulus of elasticity, increasing stress shielding.
. It has a lower modulus of elasticity, reducing bending stiffness and decreasing stress shielding.
. It prevents endochondral ossification by minimizing interfragmentary strain.
. It drastically increases the torsional rigidity compared to stainless steel.

Correct Answer & Explanation

. It has a lower modulus of elasticity, reducing bending stiffness and decreasing stress shielding.

Explanation

Titanium has a lower modulus of elasticity than stainless steel, making it less stiff and biomechanically closer to cortical bone. This allows more load-sharing, reduces stress shielding, and promotes callus formation.

Question 1403

Topic: Biology, Genetics & Bone Healing

During fracture healing after intramedullary nailing, the soft callus primarily consists of which of the following tissues, and how is it subsequently replaced?

. Woven bone, replaced by lamellar bone through primary healing
. Cartilage, replaced by bone through endochondral ossification
. Fibrous tissue, replaced by bone through intramembranous ossification
. Lamellar bone, replaced by Haversian systems through cutting cones
. Hyaline cartilage, replaced by fibrocartilage through creeping substitution

Correct Answer & Explanation

. Cartilage, replaced by bone through endochondral ossification

Explanation

Intramedullary nailing provides relative stability, initiating secondary fracture healing. The initial soft callus is composed primarily of cartilage, which is subsequently mineralized and replaced by woven bone via endochondral ossification.

Question 1404

Topic: Biomechanics & Biomaterials

Compared to stainless steel, titanium alloy intramedullary nails exhibit which of the following biomechanical characteristics?

. Higher modulus of elasticity
. Increased stiffness in bending
. Closer modulus of elasticity to cortical bone
. Greater risk of galvanic corrosion
. Higher notch sensitivity resulting in sudden catastrophic failure

Correct Answer & Explanation

. Closer modulus of elasticity to cortical bone

Explanation

Titanium alloy has a lower modulus of elasticity than stainless steel, making it biomechanically closer to that of cortical bone. This relative flexibility decreases stress shielding and allows for more favorable load sharing during fracture healing.

Question 1405

Topic: Biomechanics & Biomaterials

According to the polar area moment of inertia, the torsional rigidity of a solid cylindrical intramedullary nail is proportional to its radius raised to which power?

. First
. Second
. Third
. Fourth
. Fifth

Correct Answer & Explanation

. Fourth

Explanation

The torsional rigidity of a solid cylinder is determined by its polar moment of inertia, which is proportional to the fourth power of its radius (r^4). Therefore, even small increases in nail diameter exponentially increase its torsional stability.

Question 1406

Topic: Biomechanics & Biomaterials

The primary biomechanical consequence of utilizing a slotted (open-section) intramedullary nail compared to a solid (closed-section) nail of identical diameter and material is:

. Increased torsional rigidity
. Significantly decreased torsional rigidity
. Increased bending stiffness in the coronal plane
. Enhanced endosteal revascularization
. Promotion of primary rather than secondary bone healing

Correct Answer & Explanation

. Significantly decreased torsional rigidity

Explanation

Slotted nails have a significantly lower polar moment of inertia compared to solid nails, resulting in substantially decreased torsional rigidity. This makes them more prone to torsional deformation and failure under rotational loads.

Question 1407

Topic: 1. General Principles & Basic Science

To minimize the risk of thermal necrosis of cortical bone during intramedullary reaming, which of the following techniques is most effective?

. Using dull reamers at high speed to clear debris
. Using sharp reamers with a slow, cautious advancement rate
. Using sharp reamers with a rapid advancement rate to minimize duration of friction
. Applying continuous suction to the medullary canal without clearing the flutes
. Maintaining a pressurized tourniquet to reduce heated marrow embolization

Correct Answer & Explanation

. Using sharp reamers with a rapid advancement rate to minimize duration of friction

Explanation

Thermal necrosis is highly dependent on the duration of friction generated between the reamer and bone. Using sharp reamers with a rapid advancement rate (pushing firmly) minimizes the contact time and thereby reduces heat generation.

Question 1408

Topic: Biomechanics & Biomaterials

An initially statically locked intramedullary nail used to treat a 4-cm segmental tibial defect presents at 6 months with broken distal interlocking screws. What is the primary biomechanical cause of this failure?

. Galvanic corrosion between a titanium nail and stainless steel screws
. Cyclic loading over a large working length without bony support leading to fatigue failure
. Stress shielding caused by an oversized nail diameter
. Premature dynamization of the proximal segment
. Excessive torsional rigidity of the intramedullary nail

Correct Answer & Explanation

. Cyclic loading over a large working length without bony support leading to fatigue failure

Explanation

In cases of segmental defects or severe comminution, the nail and screws bear all physiological loads because there is no cortical bone contact to share the load. This large working length concentrates cyclic stresses on the screws, eventually causing fatigue failure prior to union.

Question 1409

Topic: Biology, Genetics & Bone Healing

Intramedullary nailing of a diaphyseal femur fracture predominantly promotes which type of bone healing, and through what stabilization mechanism?

. Primary bone healing via absolute stability
. Secondary bone healing via relative stability
. Primary bone healing via relative stability
. Secondary bone healing via absolute stability
. Membranous ossification via rigid compression

Correct Answer & Explanation

. Secondary bone healing via relative stability

Explanation

Intramedullary nails act as internal, load-sharing splints that provide relative stability. This permits controlled micromotion at the fracture site, which biologically stimulates secondary bone healing through enchondral ossification and callus formation.

Question 1410

Topic: Biomechanics & Biomaterials

A solid intramedullary nail is upgraded from a 10 mm diameter to a 12 mm diameter. Assuming identical material properties and working length, by what approximate factor does the torsional rigidity of the nail increase?

. 1.2
. 1.4
. 2.1
. 3.0
. 4.0

Correct Answer & Explanation

. 2.1

Explanation

The torsional rigidity of a solid cylindrical device is proportional to the polar moment of inertia, which scales with the radius to the fourth power (r^4). Increasing the diameter from 10 mm to 12 mm increases rigidity by a factor of (1.2)^4, which is approximately 2.1.

Question 1411

Topic: Biomechanics & Biomaterials

When comparing a titanium alloy intramedullary nail to a stainless steel nail of identical dimensions and design, the titanium nail biomechanically exhibits:

. Higher modulus of elasticity and increased bending stiffness
. Higher modulus of elasticity and decreased bending stiffness
. Lower modulus of elasticity and decreased bending stiffness
. Lower modulus of elasticity and increased bending stiffness
. Identical modulus of elasticity and decreased fatigue strength

Correct Answer & Explanation

. Lower modulus of elasticity and decreased bending stiffness

Explanation

Titanium alloy has a lower modulus of elasticity compared to stainless steel, making it less stiff and more flexible. This lower modulus allows the nail to more closely approximate the stiffness of cortical bone, potentially improving load sharing and reducing stress shielding.

Question 1412

Topic: Biology, Genetics & Bone Healing

A diaphyseal tibia fracture is treated with a statically locked intramedullary nail. According to Perren's strain theory, what range of interfragmentary strain is expected to promote the predominant mode of bone healing in this scenario?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 100%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Intramedullary nailing provides relative stability, resulting in interfragmentary strain typically between 2% and 10%. This strain environment promotes secondary bone healing through enchondral ossification and robust callus formation.

Question 1413

Topic: Biomechanics & Biomaterials

An intramedullary nail is manufactured from a titanium alloy rather than 316L stainless steel. What is the primary biomechanical difference regarding the material properties of the titanium nail?

. Higher modulus of elasticity leading to increased stiffness
. Lower modulus of elasticity resulting in stiffness closer to cortical bone
. Higher ultimate tensile strength preventing fatigue failure
. Lower notch sensitivity compared to stainless steel
. Higher galvanic corrosion potential in vivo

Correct Answer & Explanation

. Lower modulus of elasticity resulting in stiffness closer to cortical bone

Explanation

Titanium alloys possess a lower modulus of elasticity compared to stainless steel, making them less rigid and closer to the natural stiffness of cortical bone. However, they tend to be more notch sensitive.

Question 1414

Topic: Biomechanics & Biomaterials

Regarding the biomechanical footprint of intramedullary implants, which of the following characteristics best minimizes the 'stress shielding' effect on the surrounding diaphyseal bone?

. High area moment of inertia
. Use of 316L stainless steel rather than titanium
. Matching the modulus of elasticity of the implant to that of cortical bone
. Maximal interference fit at the isthmus without locking screws
. Increasing the wall thickness of a hollow nail

Correct Answer & Explanation

. Matching the modulus of elasticity of the implant to that of cortical bone

Explanation

Stress shielding occurs when a rigid implant bears too large a share of physiological loads, causing disuse osteopenia in adjacent bone. Using materials with a lower modulus of elasticity closer to cortical bone, like titanium, promotes healthier load sharing.

Question 1415

Topic: Biology, Genetics & Bone Healing

According to the principles of fracture healing, which tissue is the first to bridge a fracture gap undergoing secondary healing following stabilization with an intramedullary nail, due to its exceptionally high strain tolerance?

. Woven bone
. Lamellar bone
. Hyaline cartilage
. Granulation tissue
. Fibrocartilage

Correct Answer & Explanation

. Granulation tissue

Explanation

Granulation tissue is the first reparative tissue to form in a fracture gap. It can tolerate up to 100% strain without rupturing, effectively stabilizing the gap enough for stiffer tissues with lower strain tolerances to eventually form.

Question 1416

Topic: Biomechanics & Biomaterials

What is the primary effect of over-reaming the medullary canal by 2 mm beyond the native isthmus diameter on the inherent torsional strength of the diaphyseal bone itself?

. It increases torsional strength due to the resulting thermal hyperemic response
. It has no measurable effect on torsional strength as long as the periosteum is intact
. It decreases torsional strength by reducing the bone mass at the outer radius
. It significantly decreases torsional strength by removing bone from the inner radius
. It shifts the neutral axis of the bone, increasing its overall bending strength

Correct Answer & Explanation

. It decreases torsional strength by reducing the bone mass at the outer radius

Explanation

The torsional strength of a tubular bone depends heavily on its geometry, specifically the polar moment of inertia. Reaming removes cortical bone from the inner radius, which measurably reduces the remaining diaphyseal bone's inherent resistance to torsion.

Question 1417

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a high-energy midshaft tibia fracture treated with reamed intramedullary nailing is 8 weeks post-operative. Radiographs show early callus formation, and she has good pain control. According to the post-operative rehabilitation protocols, what is the most appropriate progression for her weight-bearing status at this stage?

. Continue strict non-weight bearing (NWB) until full cortical bridging is evident.
. Initiate full weight bearing as tolerated (FWBAT) immediately to promote bone healing.
. Progress from non-weight bearing (NWB) or touch-down weight bearing (TDWB) to protected weight bearing (PWB) or weight bearing as tolerated (WBAT).
. Begin plyometric exercises to strengthen the quadriceps and calf muscles.
. Remove all assistive devices and encourage independent ambulation.

Correct Answer & Explanation

. Progress from non-weight bearing (NWB) or touch-down weight bearing (TDWB) to protected weight bearing (PWB) or weight bearing as tolerated (WBAT).

Explanation

Correct Answer: CExplanation:The case's 'Phase 2 Early Mobilization & Progressive Loading (Weeks 6-12)' section states, 'Weight Bearing: Progress from NWB/TDWB to PWB/WBAT as radiological signs of healing (early callus formation) become evident and pain allows. Regular follow-up radiographs (every 4-6 weeks) guide progression.' The patient is 8 weeks post-op with early callus, fitting this phase.Option A is incorrect:Continuing strict NWB until full cortical bridging is too conservative for this stage, especially with early callus formation and good pain control.Option B is incorrect:Initiating FWBAT immediately is too aggressive. FWBAT is typically achieved later, once clinical and radiographic union are confirmed (Phase 3).Option D is incorrect:Plyometric exercises are part of 'Phase 3 Advanced Strengthening & Return to Activity (Weeks 12+)' and are too aggressive for 8 weeks post-op.Option E is incorrect:Removing all assistive devices and encouraging independent ambulation is part of later stages of rehabilitation (Phase 3), after significant progression in strength and confidence.

Question 1418

Topic: Infection, Pharmacology & VTE

The patient's proximal tibial diaphyseal fracture exhibits significant apex anterior (procurvatum) and apex lateral (valgus) angulation.

Which of the following anatomical structures is primarily responsible for the apex anterior (procurvatum) deformity observed in proximal third tibial fractures?

. Gastrocnemius muscle
. Soleus muscle
. Extensor mechanism (quadriceps via patellar tendon)
. Pes anserinus
. Iliotibial band

Correct Answer & Explanation

. Extensor mechanism (quadriceps via patellar tendon)

Explanation

Correct Answer: CThe case specifically addresses the deforming forces in proximal third tibial fractures: 'This specific deformity pattern is classic for proximal third tibial fractures and is driven by the unopposed pull of the extensor mechanism (quadriceps via the patellar tendon) on the proximal fragment, drawing it into extension, while the pes anserinus and iliotibial band exert variable varus/valgus and rotational forces.' The extensor mechanism, primarily through the patellar tendon, pulls the proximal fragment anteriorly, creating the apex anterior (procurvatum) deformity. The other options are either not the primary deforming force for procurvatum or contribute more to other deformities (e.g., pes anserinus and iliotibial band for varus/valgus).

Question 1419

Topic: 1. General Principles & Basic Science

To minimize the risk of thermal necrosis to the diaphyseal bone during reamed intramedullary nailing of a dense tibia, which of the following surgical techniques is most appropriate?

. Use dull reamers to minimize cutting friction
. Ream with continuous forward pressure without pausing to save time
. Use sharp reamers with slow advancement and frequent withdrawals
. Inflate a tourniquet to 300 mmHg to decrease blood flow and cool the bone
. Increase the reamer size in 2.0 mm increments

Correct Answer & Explanation

. Use sharp reamers with slow advancement and frequent withdrawals

Explanation

Thermal necrosis is prevented by using sharp, flute-clearing reamers, advancing slowly, and withdrawing frequently to clear bone debris. Tourniquet use should be avoided if possible as it eliminates cortical perfusion, increasing thermal damage risk.

Question 1420

Topic: Biomechanics & Biomaterials

Modern conventional antegrade tibial intramedullary nails are manufactured with a distinct proximal bend, known as the Herzog curve. What is the primary biomechanical purpose of this design feature?

. To increase the ultimate tensile strength of the titanium alloy
. To accommodate the extra-articular anterior starting point while aligning the nail with the straight diaphyseal canal
. To prevent rotation of the proximal fragment without the need for locking screws
. To avoid injury to the deep peroneal nerve during insertion
. To facilitate a completely intra-articular entry portal

Correct Answer & Explanation

. To accommodate the extra-articular anterior starting point while aligning the nail with the straight diaphyseal canal

Explanation

The Herzog curve allows the nail to enter via the proximal, slightly anterior extra-articular starting portal and then smoothly transition into the straight mechanical axis of the tibial diaphysis.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page