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1. General Principles & Basic Science MCQs

Practice Set 76 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 1501

Topic: Biomechanics & Biomaterials

In locked plate osteosynthesis, preserving periosteal blood supply is achieved by maintaining a stand-off distance between the plate and the bone surface. However, an excessively large stand-off distance critically predisposes the construct to failure by increasing which biomechanical force?

. Axial pull-out force
. Torsional shear force
. Cantilever bending moment
. Compressive preload
. Interfragmentary strain

Correct Answer & Explanation

. Cantilever bending moment

Explanation

Locking plates function as single-beam constructs where screws act as load-bearing cantilevers. Increasing the distance between the plate and the bone directly increases the cantilever bending moment on the screws, elevating the risk of fatigue failure.

Question 1502

Topic: 1. General Principles & Basic Science

Fixed-angle locking plates offer biomechanical superiority in highly osteoporotic bone compared to conventional non-locking plates. Which principle best explains the enhanced resistance to failure under axial loading in locking constructs?

. Locking screws possess a larger core diameter that prevents bending
. Locking plates rely on increased frictional force between the plate and cortex
. Locking screws fail simultaneously, requiring a greater aggregate force for construct pull-out
. Non-locking screws fail simultaneously, whereas locking screws distribute force sequentially
. Locking plates create absolute interfragmentary compression dynamically

Correct Answer & Explanation

. Locking screws fail simultaneously, requiring a greater aggregate force for construct pull-out

Explanation

Because locking screws are rigidly fixed to the plate, the entire construct acts as a single functional unit. Consequently, all screws must fail simultaneously rather than sequentially (toggling), which significantly increases the total force required for construct failure in poor quality bone.

Question 1503

Topic: Biomechanics & Biomaterials

When utilizing a minimally invasive bridge plating technique for a comminuted diaphyseal fracture, what is the generally recommended plate span ratio and screw density to prevent fatigue failure?

. Span ratio < 2, screw density > 0.8
. Span ratio > 3, screw density < 0.5
. Span ratio of 1, screw density 1.0
. Span ratio > 5, screw density > 0.8
. Span ratio < 2, screw density < 0.5

Correct Answer & Explanation

. Span ratio > 3, screw density < 0.5

Explanation

For comminuted fractures, a plate span ratio (plate length divided by fracture length) greater than 3 helps distribute stresses. A screw density (screws inserted divided by total holes) of less than 0.5 ensures a long working length, further lowering the risk of plate fatigue.

Question 1504

Topic: 1. General Principles & Basic Science

Which of the following describes the fundamental biomechanical difference between a conventional non-locking plate construct and a locked plate construct in the diaphysis?

. Locked plates rely entirely on plate-to-bone friction for stability.
. Conventional plates create a fixed-angle construct.
. Locked plate constructs typically fail via sequential individual screw pullout.
. Locked plates do not require direct compression against the bone surface to provide stability.
. Conventional screws possess a larger core diameter to preferentially resist shear forces.

Correct Answer & Explanation

. Locked plates do not require direct compression against the bone surface to provide stability.

Explanation

Locked plates function as fixed-angle devices where stability is derived from the screw-to-plate interface rather than friction between the plate and the bone. This protects the periosteal blood supply, as the plate can sit off the bone surface.

Question 1505

Topic: 1. General Principles & Basic Science

When selecting a screw for fixation in cancellous metaphysis, which combination of thread geometries is ideal for maximizing pullout strength?

. Small outer diameter, large inner diameter, fine pitch.
. Large outer diameter, small inner diameter, fine pitch.
. Large outer diameter, small inner diameter, coarse pitch.
. Small outer diameter, small inner diameter, coarse pitch.
. Large outer diameter, large inner diameter, coarse pitch.

Correct Answer & Explanation

. Large outer diameter, small inner diameter, coarse pitch.

Explanation

Cancellous bone has sparse trabeculae, requiring a larger volume of bone between threads. A large outer diameter and small inner diameter increase thread depth, while a coarse pitch (fewer threads per inch) maximizes the amount of bone trapped between threads, optimizing pullout strength.

Question 1506

Topic: 1. General Principles & Basic Science

A 45-year-old male undergoes bridge plating for a comminuted midshaft femur fracture. The surgeon purposefully leaves three consecutive screw holes empty directly over the fracture site. What is the primary biomechanical effect of this specific technique?

. Decreases working length and increases construct stiffness.
. Increases working length and decreases construct stiffness to promote callus formation.
. Increases the risk of plate fatigue failure by concentrating stress exclusively at the fracture gap.
. Decreases the pull-out strength of the peripheral locking screws.
. Shifts the healing mechanism from secondary to primary bone healing.

Correct Answer & Explanation

. Increases working length and decreases construct stiffness to promote callus formation.

Explanation

Leaving empty holes over a fracture increases the plate's working length, which decreases the overall stiffness of the construct. This permits controlled interfragmentary micro-motion, which is essential for promoting secondary bone healing via callus formation.

Question 1507

Topic: Biomechanics & Biomaterials

A resident is evaluating two hollow intramedullary nails of the identical material and wall thickness. Nail A has an outer diameter of 10 mm, and Nail B has an outer diameter of 12 mm. According to the polar moment of inertia, how does the torsional rigidity of Nail B biomechanically compare to Nail A?

. It is directly proportional to the radius.
. It is proportional to the square of the radius.
. It is proportional to the cube of the radius.
. It is proportional to the fourth power of the radius.
. It is inversely proportional to the radius.

Correct Answer & Explanation

. It is proportional to the fourth power of the radius.

Explanation

The torsional rigidity of an intramedullary nail is defined by its polar moment of inertia. For both solid and hollow cylindrical implants, torsional rigidity is proportional to the radius raised to the fourth power.

Question 1508

Topic: Biology, Genetics & Bone Healing

A rigid construct is applied to a transverse femoral shaft fracture, leaving a 1 mm gap. According to Perren's strain theory, what happens at the fracture site if the interfragmentary strain exceeds 10% but remains below the threshold for catastrophic failure?

. Primary bone healing will occur without callus formation.
. Woven bone will form directly from the fracture hematoma.
. Granulation tissue will transition to fibrous tissue or fibrocartilage, preventing bony union.
. The construct will fail immediately due to acute fatigue fracture of the plate.
. Lamellar bone will bridge the gap through cutting cone formation.

Correct Answer & Explanation

. Granulation tissue will transition to fibrous tissue or fibrocartilage, preventing bony union.

Explanation

Perren's strain theory dictates that primary bone healing requires <2% strain, and secondary bone healing (callus) occurs between 2-10% strain. If strain exceeds 10%, the tissue in the gap can only differentiate into fibrous tissue or fibrocartilage, often leading to nonunion.

Question 1509

Topic: 1. General Principles & Basic Science

An orthopedic engineer is redesigning a dynamic compression plate to make it substantially more resistant to bending forces in the sagittal plane. Based on the area moment of inertia, which geometric modification will most significantly increase the bending stiffness of the plate?

. Increasing the width of the plate by 10%.
. Increasing the thickness of the plate by 10%.
. Increasing the length of the plate by 10%.
. Decreasing the distance between the central screw holes.
. Changing the material from stainless steel to standard titanium.

Correct Answer & Explanation

. Increasing the thickness of the plate by 10%.

Explanation

The bending stiffness of a plate is directly proportional to its area moment of inertia, which is calculated as (width x thickness^3)/12. Because the thickness value is cubed, increasing the plate's thickness has the most profound effect on its resistance to bending.

Question 1510

Topic: Surgical Anatomy & Approaches

When addressing a terrible triad injury surgically, what is the primary advantage of utilizing the Kaplan approach (extensor digitorum communis splitting) over the Kocher approach (ECU and anconeus interval)?

. Improved access to the medial collateral ligament
. Decreased risk to the posterior interosseous nerve
. Better visualization of the anteromedial coronoid facet
. Direct access to the sublime tubercle
. Enhanced exposure of the proximal radioulnar joint avoiding LCL detachment

Correct Answer & Explanation

. Better visualization of the anteromedial coronoid facet

Explanation

The Kaplan approach is located more anteriorly than the Kocher approach, providing better direct visualization of the anteromedial coronoid for fixation. However, it carries a higher theoretical risk to the PIN if dissection is extended too far distally.

Question 1511

Topic: 1. General Principles & Basic Science

When performing a primary repair of a retracted FDP tendon, which of the following is considered the gold standard suture technique for strength and preventing pull-out?

. Epitendinous suture.
. Simple interrupted suture.
. Horizontal mattress suture.
. Modified Kessler or similar core suture (e.g., Lim-Tsai, Modified Becker).
. Running locking suture.

Correct Answer & Explanation

. Modified Kessler or similar core suture (e.g., Lim-Tsai, Modified Becker).

Explanation

Correct Answer: DThe gold standard for flexor tendon repair involves a strong core suture technique that provides robust mechanical strength against gapping and pull-out. The Modified Kessler (or similar variations like Lim-Tsai, Modified Becker, Pennington) is a common and effective core suture. An epitendinous suture is typically used in addition to a core suture to create a smooth gliding surface and add some strength, but it is not sufficient on its own for primary repair strength. Simple interrupted, horizontal mattress, and running locking sutures are not typically used as primary core sutures in flexor tendon repair due to lower strength and potential for gapping or strangulation.

Question 1512

Topic: 1. General Principles & Basic Science

Which of the following statements most accurately describes the 'quadriga effect' as a potential complication following FDP repair, particularly when using advancement techniques?

. Excessive tension on the repaired FDP leading to restricted flexion of adjacent digits.
. Adhesions between the repaired FDP and the flexor retinaculum, limiting full extension.
. Inability to achieve full extension of the repaired digit due to tendon shortening.
. Delayed healing of the FDP tendon due to compromised blood supply.
. Rupture of the FDS tendon secondary to overtensioning during rehabilitation.

Correct Answer & Explanation

. Excessive tension on the repaired FDP leading to restricted flexion of adjacent digits.

Explanation

Correct Answer: AThe quadriga effect is a well-known complication of FDP repair, particularly when the tendon is shortened (e.g., through advancement or overtightening during repair). Because the FDP tendons of the medial four fingers share a common muscle belly (or are closely intertwined proximally), overtensioning of one FDP tendon will restrict full flexion of the adjacent, healthy FDP tendons. This results in the inability of the adjacent digits to fully flex. The other options describe different complications or aspects of tendon repair.

Question 1513

Topic: 1. General Principles & Basic Science

What is the typical presentation of a 'lumbrical plus' phenomenon, which can be a complication of FDP repair or shortening?

. Inability to fully flex the DIP joint due to FDS tethering.
. Paradoxical extension of the DIP joint when attempting to make a full fist.
. Persistent flexion deformity of the PIP joint due to FDP overtensioning.
. Weakness of intrinsic muscle function, leading to clawing.
. Restricted motion of adjacent digits due to a common muscle belly.

Correct Answer & Explanation

. Paradoxical extension of the DIP joint when attempting to make a full fist.

Explanation

Correct Answer: BThe 'lumbrical plus' phenomenon occurs when the FDP tendon is advanced and overtensioned, or the repair site is too stiff, causing the lumbrical muscle to be pulled proximally. When the patient attempts to flex the finger (activating the FDP), the lumbrical is put under tension before the FDP can flex the DIP joint. Since the lumbrical inserts into the extensor mechanism, its contraction paradoxically extends the DIP joint instead of allowing FDP flexion. This results in the DIP joint extending or remaining extended when the patient attempts to make a full fist. Option E describes the quadriga effect.

Question 1514

Topic: Surgical Anatomy & Approaches

When utilizing the standard volar approach (modified Henry) for open reduction and internal fixation of a distal radius fracture, the surgeon initially develops an interval between which two structures to safely access the deeper pronator quadratus?

. Flexor carpi radialis (FCR) tendon and the radial artery
. Flexor carpi radialis (FCR) and palmaris longus (PL) tendons
. Brachioradialis and the radial artery
. Flexor pollicis longus (FPL) and flexor digitorum superficialis (FDS)
. Abductor pollicis longus (APL) and extensor pollicis brevis (EPB)

Correct Answer & Explanation

. Flexor carpi radialis (FCR) tendon and the radial artery

Explanation

The modified Henry approach utilizes the internervous plane between the median nerve (supplying FCR) and the radial nerve (supplying brachioradialis). Superficially, the surgeon develops the interval between the FCR tendon and the radial artery to safely retract the neurovascular structures.

Question 1515

Topic: 1. General Principles & Basic Science

During the repair of a Zone II flexor tendon injury, the surgeon considers the number of core suture strands. Which of the following best describes the biomechanical relationship between the number of core strands and the repair characteristics?

. Increasing strands decreases the risk of gap formation but does not affect ultimate tensile strength
. Increasing strands increases ultimate tensile strength but significantly increases the work of flexion
. A 2-strand repair is sufficient for early active motion protocols
. Increasing strands from 2 to 4 decreases ultimate tensile strength due to tendon ischemia
. Increasing strands has no effect on tendon gliding or work of flexion

Correct Answer & Explanation

. Increasing strands increases ultimate tensile strength but significantly increases the work of flexion

Explanation

Increasing the number of core suture strands increases the ultimate tensile strength of the repair, which is beneficial for early active motion. However, it also increases the bulk of the repair, significantly increasing gliding resistance and the work of flexion.

Question 1516

Topic: Surgical Anatomy & Approaches

During a surgical approach to the proximal ulna for a diaphyseal fracture, a surgeon utilizes the posterior (dorsal) subcutaneous approach. Which of the following structures is the most significant concern for iatrogenic injury with this specific approach?

. Ulnar nerve.
. Posterior interosseous nerve.
. Radial artery.
. Superficial radial nerve.
. No major neurovascular structures are at significant risk with this approach.

Correct Answer & Explanation

. No major neurovascular structures are at significant risk with this approach.

Explanation

Correct Answer: EThe posterior (dorsal) subcutaneous approach to the ulna shaft is generally considered the safest and most direct because the ulna is largely subcutaneous along its posterior border. This approach requires minimal muscle dissection, thereby significantly reducing the risk of injury to major neurovascular structures. The ulnar nerve, radial artery, and radial nerve branches are located more anteriorly or laterally in the forearm, away from the direct path of this approach to the ulna.Incorrect Options:A. Ulnar nerve:The ulnar nerve is located medially and volarly in the forearm, not typically at risk with a direct posterior approach to the ulna shaft.B. Posterior interosseous nerve:The posterior interosseous nerve (PIN) is a branch of the radial nerve and is located in the dorsal compartment of the forearm, but it is typically deep and lateral, not directly in the field of a posterior subcutaneous ulnar approach. It is more at risk with dorsal approaches to the radius.C. Radial artery:The radial artery is located on the volar-radial aspect of the forearm and is at risk with the Henry (anterior) approach to the radius, not the posterior ulna.D. Superficial radial nerve:The superficial radial nerve is also on the radial side of the forearm, deep to the brachioradialis, and is at risk with radial approaches, not the posterior ulna.

Question 1517

Topic: Biology, Genetics & Bone Healing

A 22-year-old active male undergoes hardware removal (plates and screws) 18 months after successful ORIF of a both bones forearm fracture. To minimize the risk of refracture through previous screw holes, what is the most important post-operative instruction?

. Begin immediate, aggressive physiotherapy to restore full range of motion.
. Re-drill and bone graft all previous screw holes.
. Maintain strict immobilization in a long arm cast for 6 weeks.
. Avoid strenuous activity and heavy lifting for 6-12 weeks.
. Prescribe bisphosphonates to improve bone density.

Correct Answer & Explanation

. Avoid strenuous activity and heavy lifting for 6-12 weeks.

Explanation

Correct Answer: DRefracture through previous screw holes after plate removal is a known complication due to the 'stress riser' effect, where the holes create points of stress concentration in the bone. The most important prophylactic measure is to protect the limb from strenuous activity and heavy lifting for an adequate period (typically 6-12 weeks, Option D) post-removal. This allows the screw holes to remodel and regain sufficient strength, reducing the risk of refracture. Gradual return to activity is key.Incorrect Options:A. Begin immediate, aggressive physiotherapy to restore full range of motion:While early motion is generally desirable, immediate aggressive physiotherapy would place excessive stress on the weakened bone, significantly increasing the risk of refracture.B. Re-drill and bone graft all previous screw holes:Re-drilling and bone grafting of screw holes is not a standard or routinely recommended procedure after hardware removal. The bone typically remodels and fills these holes naturally over time.C. Maintain strict immobilization in a long arm cast for 6 weeks:Strict immobilization for 6 weeks would lead to significant stiffness and is generally not necessary after hardware removal for a healed fracture. It would also delay functional recovery.E. Prescribe bisphosphonates to improve bone density:Bisphosphonates are used for osteoporosis and would not acutely strengthen the bone around screw holes to prevent refracture in this timeframe.

Question 1518

Topic: Surgical Anatomy & Approaches

When utilizing the dorsal (Thompson) approach to expose the proximal radius, the surgeon develops the internervous plane between which of the following muscle groups?

. Brachioradialis and Pronator Teres
. Extensor Carpi Radialis Brevis and Extensor Digitorum Communis
. Flexor Carpi Radialis and Palmaris Longus
. Extensor Carpi Ulnaris and Flexor Carpi Ulnaris
. Extensor Carpi Radialis Longus and Extensor Carpi Radialis Brevis

Correct Answer & Explanation

. Extensor Carpi Radialis Brevis and Extensor Digitorum Communis

Explanation

The Thompson approach accesses the radius dorsally through the internervous plane between the extensor carpi radialis brevis (supplied by the radial nerve) and the extensor digitorum communis (supplied by the posterior interosseous nerve).

Question 1519

Topic: Biomechanics & Biomaterials

During rigid plate fixation of a midshaft both-bone forearm fracture in an adult, failure to restore the anatomic radial bow will most likely result in a clinically significant loss of which motion?

. Wrist flexion
. Wrist extension
. Elbow flexion
. Forearm rotation (pronation and supination)
. Digital flexion

Correct Answer & Explanation

. Forearm rotation (pronation and supination)

Explanation

The radial bow is critical for the normal biomechanics of forearm rotation. Failure to accurately restore the magnitude and location of the anatomic radial bow directly restricts pronation and supination.

Question 1520

Topic: Surgical Anatomy & Approaches

When performing a volar (Henry) approach to the mid-shaft radius, the surgeon develops the internervous plane between the brachioradialis and the flexor carpi radialis. Which nerves supply these respective muscles?

. Radial and Ulnar
. Musculocutaneous and Median
. Radial and Median
. Median and Ulnar
. Posterior Interosseous and Anterior Interosseous

Correct Answer & Explanation

. Radial and Median

Explanation

The distal portion of the Henry approach utilizes the internervous plane between the brachioradialis, which is innervated by the radial nerve, and the flexor carpi radialis, which is innervated by the median nerve.

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