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1. General Principles & Basic Science MCQs

Practice Set 91 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 1801

Topic: 1. General Principles & Basic Science

What is the main difference between a self-tapping screw and a conventional tapping screw in terms of surgical technique?

. Self-tapping screws always require a larger pilot hole than tapping screws.
. Conventional tapping screws necessitate a separate tapping step after drilling.
. Self-tapping screws are exclusively used for cancellous bone.
. Conventional tapping screws provide less pull-out strength.
. Self-tapping screws have a blunt tip, while tapping screws have a sharp tip.

Correct Answer & Explanation

. Conventional tapping screws necessitate a separate tapping step after drilling.

Explanation

Correct Answer: BA conventional (non-self-tapping) screw requires that a pilot hole be drilled and then a tap (a separate instrument that cuts threads into the bone) be used before the screw is inserted. A self-tapping screw has cutting flutes at its tip that create the threads in the bone as the screw is inserted, eliminating the need for a separate tapping step. This simplifies the surgical procedure. Self-tapping screws don't always require a larger pilot hole (Option A); the pilot hole size is related to the screw's core diameter. Self-tapping screws are used in both cortical and cancellous bone (Option C). Conventional tapping screws generally providemorepull-out strength (Option D) because the threads are pre-cut, leading to better bone-screw interface, though self-tapping screws have improved significantly. Both types of screws have sharp tips (Option E), but self-tapping screws have flutes for cutting.

Question 1802

Topic: Biomechanics & Biomaterials

A surgeon is fixing a pediatric forearm fracture and wants to minimize the need for future hardware removal. Which screw material would be most appropriate, considering biocompatibility and biomechanics?

. 316L Stainless Steel
. Cobalt-Chrome Alloy
. Commercially Pure Titanium
. Bioabsorbable Polymer (e.g., PLLA)
. Nickel-Titanium Alloy (Nitinol)

Correct Answer & Explanation

. Bioabsorbable Polymer (e.g., PLLA)

Explanation

Correct Answer: DBioabsorbable polymers like Poly-L-lactic acid (PLLA) or polylactide-co-glycolide (PLGA) are specifically designed to degrade over time, eliminating the need for a second surgery for hardware removal. This is particularly advantageous in pediatric fractures where bone remodeling is significant and future growth is a concern. While stainless steel (Option A) and titanium (Option C) are highly biocompatible, they are permanent implants requiring removal if they cause symptoms or interfere with growth. Cobalt-chrome (Option B) is strong but generally used for bearing surfaces in joint replacements. Nitinol (Option E) is a shape-memory alloy used in specific applications like staples or small implants, but less commonly for primary fracture fixation screws meant to absorb.

Question 1803

Topic: Biomechanics & Biomaterials

A 42-year-old patient requires internal fixation for a long bone fracture. The surgeon is debating between a 316L stainless steel plate and a Ti-6Al-4V titanium alloy plate. From a long-term biological and biomechanical perspective, what is a distinct advantage of the titanium alloy plate?

. Titanium plates are significantly more radio-opaque, making postoperative imaging easier.
. Titanium plates offer superior fatigue resistance, leading to fewer implant failures.
. Titanium alloys have a lower modulus of elasticity, which can help mitigate stress shielding.
. Stainless steel plates are more prone to corrosion and metal ion release than titanium.
. Titanium plates are generally less expensive and easier to manufacture.

Correct Answer & Explanation

. Titanium alloys have a lower modulus of elasticity, which can help mitigate stress shielding.

Explanation

Correct Answer: CTitanium alloys (e.g., Ti-6Al-4V) have a modulus of elasticity that is closer to that of cortical bone compared to 316L stainless steel. This property makes titanium more 'bone-friendly' as it more closely matches the elastic modulus of bone. This congruence can help reduce the magnitude of stress shielding, a phenomenon where the implant bears too much load, leading to disuse osteopenia in the underlying bone. While both materials are strong, the elastic modulus difference is a key biomechanical advantage for titanium in terms of long-term bone health.Option A is incorrect:Stainless steel is generally more radio-opaque than titanium, making titanium implants sometimes harder to visualize clearly on plain radiographs.Option B is incorrect:While modern titanium alloys have excellent fatigue resistance, 316L stainless steel also has very good fatigue properties. The statement 'superior fatigue resistance' is not a universally distinct advantage of titanium over stainless steel in all forms.Option D is incorrect:This statement is true (stainless steel is more prone to corrosion and ion release), but it describes a disadvantage of stainless steel, not an advantage of titanium. The question asks for a distinct advantage of titanium.Option E is incorrect:Titanium alloys are generally more expensive and more challenging to manufacture than stainless steel, making this statement incorrect.

Question 1804

Topic: 1. General Principles & Basic Science

A 55-year-old male sustains a highly comminuted segmental fracture of the midshaft femur. You opt for open reduction and internal fixation with a bridging locking plate. To optimize secondary bone healing via callus formation, what is the most appropriate strategy regarding the 'working length' of the plate construct?

. Maximize the number of screws in the main fragments to create the shortest possible working length.
. Place screws as close to the fracture site as possible to achieve maximum stiffness.
. Create a long working length by placing fewer screws and spreading them further apart in the main fragments.
. Ensure all screws are bicortical to maximize the rigidity of the construct.
. The working length is irrelevant as long as locking screws are used.

Correct Answer & Explanation

. Create a long working length by placing fewer screws and spreading them further apart in the main fragments.

Explanation

Correct Answer: CFor highly comminuted fractures treated with bridging osteosynthesis (e.g., a bridging locking plate), the goal is relative stability to promote secondary bone healing through callus formation. The 'working length' of the plate construct is the segment of the plate that spans the comminuted zone and is not rigidly fixed to bone. A longer working length (achieved by placing fewer screws and spreading them further apart in the main proximal and distal fragments) reduces the stiffness of the construct. This allows for controlled, limited micromotion at the fracture site, which is a potent stimulus for callus formation and secondary bone healing. Conversely, a short working length creates a very stiff construct, which can inhibit callus formation and potentially lead to stress shielding or fatigue failure of the implant if the bone does not heal quickly.Option A and B are incorrect:Maximizing screws close to the fracture creates a short working length and a very stiff construct, which is detrimental to secondary healing.Option D is incorrect:While bicortical screw purchase is generally desirable for strength, thedistributionof screws to achieve an optimal working length is more critical for promoting secondary healing in this context.Option E is incorrect:Working length is a crucial biomechanical principle for all plate constructs, especially bridging plates, and significantly influences the mode of healing.

Question 1805

Topic: 1. General Principles & Basic Science

What is the consequence of 'overtapping' a screw hole in cortical bone?

. Increased pullout strength due to deeper thread engagement.
. Reduced risk of screw breakage during insertion.
. Diminished screw purchase and potential loosening.
. Enhanced interfragmentary compression capabilities.
. Faster healing time due to improved blood flow.

Correct Answer & Explanation

. Diminished screw purchase and potential loosening.

Explanation

Correct Answer: COvertapping refers to cutting threads that are too deep or too wide for the chosen screw. This effectively reduces the amount of bone in contact with the screw threads, diminishing the screw's purchase in the bone. The result is a weaker screw-bone interface, leading to reduced pullout strength and an increased risk of screw loosening. Proper tapping ensures an optimal fit between the screw threads and the bone, maximizing stability.

Question 1806

Topic: Biomechanics & Biomaterials

A 30-year-old patient with a simple transverse midshaft femoral fracture is treated with a stainless steel plate. If a titanium plate of identical geometry were used instead, what would be the primary biomechanical difference relevant to bone healing?

. The titanium plate would provide greater absolute stiffness, leading to faster healing.
. The titanium plate would have a higher fatigue life, reducing implant failure.
. The titanium plate would cause less stress shielding due to a lower modulus of elasticity.
. The titanium plate would be more resistant to corrosion in the biological environment.
. The titanium plate would allow for greater interfragmentary compression at the fracture site.

Correct Answer & Explanation

. The titanium plate would cause less stress shielding due to a lower modulus of elasticity.

Explanation

Correct Answer: CThe primary biomechanical difference between stainless steel and titanium plates of identical geometry, relevant to bone healing, lies in their modulus of elasticity. Titanium and its alloys have a modulus of elasticity closer to that of cortical bone (approximately 110 GPa for titanium vs. 200 GPa for stainless steel vs. 17-20 GPa for cortical bone). A lower modulus of elasticity means the implant is less stiff. When a less stiff implant is used, it shares more load with the bone, allowing more physiological stress to be transmitted to the healing fracture. This reduces the phenomenon of 'stress shielding,' where a very stiff implant carries too much load, leading to disuse osteoporosis in the adjacent bone and potentially delayed healing. While titanium is indeed more corrosion-resistant (Option D) and has excellent biocompatibility, its lower modulus of elasticity is the key biomechanical advantage in terms of load sharing and stress shielding. Fatigue life (Option B) can be complex and depends on many factors, but titanium generally has good fatigue properties. Neither material inherently provides greater stiffness (Option A) or compression (Option E) for the same geometry; rather, it's the relative stiffness to bone that is critical.

Question 1807

Topic: Biomechanics & Biomaterials

During a femoral nailing, a surgeon elects to use a 12 mm solid intramedullary nail instead of a 10 mm solid nail of the exact same material. The torsional rigidity of the 12 mm nail is increased by approximately what factor compared to the 10 mm nail?

. 1.2
. 1.4
. 2.1
. 2.5
. 4.0

Correct Answer & Explanation

. 2.1

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia, which scales with the radius to the fourth power (r^4). Calculating (6^4 / 5^4) yields 1296 / 625, which is an increase by a factor of approximately 2.07.

Question 1808

Topic: 1. General Principles & Basic Science

A comminuted subtrochanteric femur fracture is treated with a bridging locked plate. Compared to Stainless Steel (316L), Titanium alloy (Ti-6Al-4V) is often preferred for bridge plating to promote callus formation because it possesses which material property?

. Higher yield strength
. Lower modulus of elasticity
. Higher fatigue strength
. Higher ultimate tensile strength
. Lower ductility

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloy has a significantly lower modulus of elasticity (closer to cortical bone) than stainless steel, making it more flexible. This decreased rigidity allows for more interfragmentary motion under load, which promotes secondary bone healing (callus formation).

Question 1809

Topic: Biomechanics & Biomaterials

A 25-year-old male sustains a highly comminuted tibia fracture from a high-speed motorcycle crash. Bone fractures with significantly more comminution at high loading rates compared to low-speed falls due to which biomechanical property of bone?

. Anisotropy
. Viscoelasticity
. Osteoconduction
. Creep
. Stress relaxation

Correct Answer & Explanation

. Viscoelasticity

Explanation

Bone is a viscoelastic material, meaning its mechanical properties change based on the rate of loading. At higher strain rates, bone becomes stiffer, absorbs more energy before failure, and ultimately releases that energy explosively, causing high comminution.

Question 1810

Topic: 1. General Principles & Basic Science

A 3-part proximal humerus fracture is treated with a locking plate. Using 'far cortical locking' (FCL) screws provides what specific biomechanical advantage over standard locking screws in a bridge plating construct?

. Provides absolute rigid stability
. Increases the overall construct stiffness
. Reduces interfragmentary micromotion to zero
. Allows biphasic, parallel interfragmentary motion
. Maximizes frictional forces against the near cortex

Correct Answer & Explanation

. Allows biphasic, parallel interfragmentary motion

Explanation

FCL screws have a reduced-diameter shaft that bypasses the near cortex and locks only into the plate and far cortex. This allows the plate to act as a flexible cantilever, providing parallel, symmetric interfragmentary micromotion to stimulate robust callus formation.

Question 1811

Topic: Biomechanics & Biomaterials

During open reduction of a clavicle fracture, the surgeon extensively bends a reconstruction plate back and forth to match the bone's S-shape. This repetitive plastic deformation increases the risk of implant failure primarily by inducing which material phenomenon?

. Stress shielding
. Creep
. Cold working (strain hardening)
. Galvanic corrosion
. Viscoelastic relaxation

Correct Answer & Explanation

. Cold working (strain hardening)

Explanation

Repeated bending of a metal plate beyond its yield point causes cold working (strain hardening), which increases the metal's brittleness and decreases its fatigue life. This makes the implant highly susceptible to early fatigue failure before the fracture heals.

Question 1812

Topic: Biomechanics & Biomaterials

A patient undergoes ORIF of a bimalleolar ankle fracture. A stainless steel plate is applied to the fibula, but titanium screws are mistakenly used to secure it. This mixing of dissimilar metals places the construct at highest risk for which complication?

. Fretting wear
. Galvanic corrosion
. Stress shielding
. Early fatigue failure
. Decreased screw pullout strength

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in electrical contact within an electrolytic environment (like body fluid). This accelerates corrosion of the less noble metal, potentially leading to implant failure or localized tissue toxicity.

Question 1813

Topic: Biomechanics & Biomaterials

A retrieved broken femoral plate from a nonunion is subjected to mechanical testing. Analysis shows the plate failed due to repetitive sub-maximal loading at stress levels well below its ultimate tensile strength. This failure mode is defined as:

. Yield failure
. Fatigue failure
. Creep
. Brittle failure
. Ductile failure

Correct Answer & Explanation

. Fatigue failure

Explanation

Fatigue failure occurs when a material undergoes repetitive cyclic loading at stress levels below its yield point or ultimate tensile strength, eventually leading to microscopic crack propagation and macroscopic failure. It is a common cause of implant failure in nonunions.

Question 1814

Topic: Biomechanics & Biomaterials

Which of the following modifications to a cortical screw will most significantly increase its resistance to bending forces (bending stiffness)?

. Increasing the outer thread diameter
. Increasing the inner core diameter
. Increasing the thread pitch
. Decreasing the screw length
. Decreasing the inner core diameter

Correct Answer & Explanation

. Increasing the inner core diameter

Explanation

The bending stiffness of a screw is proportional to the radius of its core (inner) diameter to the fourth power. Therefore, increasing the core diameter drastically increases its bending strength and resistance to fatigue failure.

Question 1815

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum allowable interfragmentary tissue strain for primary bone healing to occur via cutting cones?

. < 2%
. 2 - 10%
. 10 - 20%
. 20 - 30%
. > 30%

Correct Answer & Explanation

. < 2%

Explanation

Primary bone healing (osteonal reconstruction via cutting cones) requires absolute stability with an interfragmentary gap strain of less than 2%. Strains between 2% and 10% promote secondary bone healing via callus formation.

Question 1816

Topic: Biomechanics & Biomaterials

Cortical bone is a viscoelastic material. How does its biomechanical behavior change when it is loaded at a very high rate, such as during high-energy trauma?

. It becomes more ductile and yields at lower forces
. It exhibits decreased ultimate tensile strength
. It becomes stiffer and can absorb more energy before failure
. Its modulus of elasticity decreases significantly
. It undergoes plastic deformation earlier

Correct Answer & Explanation

. It becomes stiffer and can absorb more energy before failure

Explanation

As a viscoelastic material, cortical bone becomes stiffer and stronger when loaded rapidly. This allows it to absorb more energy before fracturing during high-velocity impacts, which typically leads to more comminuted fracture patterns upon failure.

Question 1817

Topic: 1. General Principles & Basic Science

A surgeon uses a bridging plate for a highly comminuted diaphyseal fracture. Leaving empty screw holes over the fracture site increases the construct's "working length". What is the primary biomechanical effect of this technique?

. Increases the absolute stability of the construct
. Decreases the interfragmentary strain to less than 2%
. Increases the rigidity and stiffness of the construct
. Decreases construct stiffness, distributing stress and promoting secondary callus formation
. Eliminates the risk of plate fatigue failure

Correct Answer & Explanation

. Decreases construct stiffness, distributing stress and promoting secondary callus formation

Explanation

Increasing the working length of a plate (the distance between the two innermost screws) decreases the bending stiffness of the construct. This relative flexibility lowers stress concentrations at any single point and promotes secondary bone healing via callus formation.

Question 1818

Topic: 1. General Principles & Basic Science
The pullout strength of a bone screw is directly proportional to all of the following EXCEPT:
. Outer thread diameter
. Length of thread engagement
. Shear strength of the surrounding bone
. Inner core diameter
. Thread factor (volume of bone between threads)

Correct Answer & Explanation

. Inner core diameter

Explanation

Pullout strength is determined by the outer thread diameter, length of engagement, thread factor, and bone shear strength. The inner core diameter primarily determines the screw's bending stiffness and fatigue resistance, not its pullout strength.

Question 1819

Topic: Biomechanics & Biomaterials

A 45-year-old patient undergoes ORIF using a stainless steel plate and titanium screws. What specific biomechanical or biomaterial complication is most likely to occur at the screw-plate interface over time?

. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Stress shielding
. Aseptic loosening secondary to high modulus mismatch

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as titanium and stainless steel) are placed in direct physical contact within an electrolytic environment like body fluids. This electrochemical reaction leads to the rapid corrosion of the less noble metal.

Question 1820

Topic: Biomechanics & Biomaterials

A rigid, thick plate is applied to the anterior femur. Years later, dual-energy x-ray absorptiometry reveals severe osteopenia of the underlying anterior femoral cortex. What biomechanical principle explains this phenomenon?

. Wolff's law driven stress shielding
. Galvanic corrosion
. Perren's strain theory
. Viscoelastic creep
. Fatigue failure

Correct Answer & Explanation

. Wolff's law driven stress shielding

Explanation

Stress shielding occurs when a highly rigid implant offloads the normal physiological stresses from the underlying bone. According to Wolff's law, bone remodels in response to mechanical stress; therefore, the lack of stress leads to localized osteopenia.

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