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1. General Principles & Basic Science MCQs

Practice Set 647 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 12921

Topic: 1. General Principles & Basic Science
The pull-out strength of a cortical orthopedic screw is directly proportional to all of the following parameters EXCEPT:
. Outer (major) diameter of the screw
. Length of thread engagement in the bone
. Shear strength of the bone material
. Inner (minor/core) diameter of the screw
. Volume of bone caught between threads

Correct Answer & Explanation

. Outer (major) diameter of the screw

Explanation

Pull-out strength = S * L * pi * D (where S is the shear strength of bone, L is the length of engagement, and D is the major diameter). The inner (minor/core) diameter dictates the tensile and bending strength of the screw, not its pull-out strength. Increasing the minor diameter without increasing the major diameter actually decreases the thread depth, which would reduce pull-out strength.

Question 12922

Topic: 1. General Principles & Basic Science

The blood supply to the meniscus is derived primarily from the medial and lateral geniculate arteries. In a healthy adult, what percentage of the meniscus is considered vascularized (the 'red-red' zone)?

. Inner 10-25%
. Outer 10-30%
. Outer 50-70%
. Inner 50-70%
. The entire meniscus is avascular

Correct Answer & Explanation

. Outer 10-30%

Explanation

In adults, only the peripheral (outer) 10% to 30% of the meniscus receives blood supply from the perimeniscal capillary plexus (arising from the medial and lateral geniculate arteries). This peripheral third is the 'red-red' zone and has the greatest healing potential for repair.

Question 12923

Topic: 1. General Principles & Basic Science

Articular cartilage is composed of multiple distinct zones with different collagen orientations. Which structure functionally separates the deep, uncalcified cartilage zone from the calcified cartilage zone?

. Lamina splendens
. Tidemark
. Subchondral bone plate
. Superficial tangential zone
. Middle transitional zone

Correct Answer & Explanation

. Tidemark

Explanation

The tidemark is a distinct basophilic line visible on histological staining that separates the deep zone of true uncalcified articular (hyaline) cartilage from the underlying calcified cartilage. It provides structural anchoring and acts as a barrier to nutrient diffusion from the subchondral bone.

Question 12924

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is prescribed denosumab for osteoporosis. What is the precise cellular mechanism of action for this medication?

. Binds directly to RANK on the osteoclast surface
. Binds to RANKL, preventing its interaction with RANK
. Inhibits cathepsin K secretion from osteoclasts
. Mimics osteoprotegerin (OPG) binding directly to osteoblasts
. Inhibits the H+/K+ ATPase pump on the ruffled border

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with RANK

Explanation

Denosumab is a monoclonal antibody that targets and binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor on osteoclasts, thereby inhibiting osteoclast activation, function, and survival.

Question 12925

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. When a tendon is subjected to a constant, sustained strain over time, the measurable stress within the tendon decreases. What is this biomechanical phenomenon called?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Plastic deformation

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in applied stress over time when a viscoelastic material is held at a constant length (strain). Creep, in contrast, is the gradual increase in length (strain) when a constant load (stress) is applied.

Question 12926

Topic: Biology, Genetics & Bone Healing

When a diaphyseal fracture is treated with absolute stability using rigid internal compression plating, how does the fracture primarily heal?

. Secondary healing via endochondral ossification
. Primary healing via Haversian cutting cones
. Primary healing via intramembranous ossification
. Secondary healing via intramembranous ossification
. Callus formation and gap healing

Correct Answer & Explanation

. Primary healing via Haversian cutting cones

Explanation

Rigid internal fixation with absolute stability suppresses callus formation and promotes primary bone healing. This occurs through direct osteonal remodeling via Haversian cutting cones bridging the fracture site.

Question 12927

Topic: Biology, Genetics & Bone Healing

A 60-year-old immigrant presents with diffuse bone pain and proximal muscle weakness. Laboratory evaluation reveals hypocalcemia, hypophosphatemia, and markedly elevated alkaline phosphatase. What is the most likely metabolic bone disorder?

. Osteoporosis
. Osteomalacia
. Paget's disease of bone
. Primary hyperparathyroidism
. Multiple myeloma

Correct Answer & Explanation

. Osteomalacia

Explanation

Osteomalacia (adult rickets) is characterized by a defect in osteoid mineralization, most commonly due to severe Vitamin D deficiency. This leads to low or normal calcium, low phosphate, elevated alkaline phosphatase, and elevated PTH.

Question 12928

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is often sterilized with gamma irradiation, which generates free radicals. To eliminate these free radicals and prevent long-term in vivo oxidation, the material is frequently remelted. What is the primary mechanical trade-off associated with remelting UHMWPE?
. Decreased fatigue strength
. Increased oxidation risk
. Decreased wear resistance
. Increased elastic modulus
. Decreased cross-linking density

Correct Answer & Explanation

. Decreased fatigue strength

Explanation

Remelting UHMWPE above its melting point eliminates free radicals and prevents oxidation but alters its crystalline structure. This thermal treatment reduces mechanical properties, specifically leading to decreased fatigue strength and yield strength.

Question 12929

Topic: 1. General Principles & Basic Science

In the management of flexor tendon lacerations within Zone II (\"no man's land\"), which of the following postoperative strategies is most critical for optimizing tendon excursion and minimizing adhesion formation?

. Strict immobilization for 6 weeks
. Continuous use of a bulky compressive dressing
. Early active mobilization protocols
. Excision of the entire flexor tendon sheath
. Delayed primary repair at 4 weeks

Correct Answer & Explanation

. Early active mobilization protocols

Explanation

Zone II flexor tendon repairs are highly prone to adhesions within the restrictive fibro-osseous canal. Early active mobilization protocols improve tendon excursion, enhance intrinsic healing, and significantly decrease the formation of restrictive adhesions.

Question 12930

Topic: Biology, Genetics & Bone Healing

A 2-year-old female is evaluated for bowing of the legs and delayed walking. Laboratory evaluation is consistent with nutritional rickets. Which of the following serum laboratory profiles characterizes advanced Vitamin D deficiency?

. Low calcium, Low phosphorus, High PTH, High Alkaline Phosphatase
. High calcium, Low phosphorus, Low PTH, Normal Alkaline Phosphatase
. Normal calcium, High phosphorus, High PTH, High Alkaline Phosphatase
. Low calcium, High phosphorus, Low PTH, Normal Alkaline Phosphatase
. Normal calcium, Normal phosphorus, Normal PTH, High Alkaline Phosphatase

Correct Answer & Explanation

. Low calcium, Low phosphorus, High PTH, High Alkaline Phosphatase

Explanation

Vitamin D deficiency impairs intestinal absorption of calcium and phosphorus, leading to hypocalcemia. This triggers secondary hyperparathyroidism (elevated PTH) which attempts to normalize calcium but causes renal phosphate wasting (lowering phosphorus) and increases bone turnover (elevating alkaline phosphatase).

Question 12931

Topic: Biomechanics & Biomaterials

Trunnionosis, or mechanically assisted crevice corrosion at the head-neck junction, has emerged as a significant complication in modern total hip arthroplasty (THA). Which of the following implant combinations represents the highest risk factor for this phenomenon?

. Large-diameter cobalt-chrome head on a titanium alloy stem
. Ceramic head on a titanium alloy stem
. Small-diameter titanium head on a cobalt-chrome stem
. Highly cross-linked polyethylene liner with a ceramic head
. Use of a cemented, highly polished cobalt-chrome femoral stem

Correct Answer & Explanation

. Large-diameter cobalt-chrome head on a titanium alloy stem

Explanation

Trunnionosis is most strongly associated with the use of large-diameter cobalt-chrome heads on titanium alloy stems. The mismatch in metals promotes galvanic corrosion, while the larger head size and increased offset exert greater torque at the head-neck junction, exacerbating fretting wear.

Question 12932

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is an FDA-approved osteoinductive agent specifically indicated for use in the treatment of acute, open tibial shaft fractures?

. Recombinant human BMP-2 (rhBMP-2)
. Recombinant human BMP-3 (rhBMP-3)
. Recombinant human BMP-4 (rhBMP-4)
. Recombinant human BMP-7 (rhBMP-7)
. Recombinant human BMP-9 (rhBMP-9)

Correct Answer & Explanation

. Recombinant human BMP-2 (rhBMP-2)

Explanation

rhBMP-2 is FDA approved for acute, open tibial shaft fractures treated with an intramedullary nail. rhBMP-7 (also known as OP-1) is indicated for recalcitrant long bone nonunions.

Question 12933

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, the use of large-diameter femoral heads with modular titanium necks has been associated with early failure. What is the primary mechanism of wear leading to adverse local tissue reactions at the head-neck junction?

. Abrasive wear
. Adhesive wear
. Fretting corrosion
. Third-body wear
. Fatigue wear

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion (mechanochemical wear) occurs at the modular taper junctions, such as the trunnion. Micro-motion disrupts the passive oxide layer, leading to localized corrosion and the release of metal ions.

Question 12934

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue designed to withstand compressive loads. Which zone of the articular cartilage contains the highest concentration of proteoglycans and the lowest water content?

. Superficial (tangential) zone
. Transitional (middle) zone
. Calcified cartilage zone
. Deep (radial) zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the highest concentration of proteoglycans, providing maximal resistance to compressive forces. It also has the lowest concentration of water compared to the superficial zones.

Question 12935

Topic: Surgical Anatomy & Approaches

During the anterior intrapelvic (modified Stoppa) approach for fixation of an acetabular fracture, the surgeon must identify and ligate the 'corona mortis' to prevent life-threatening hemorrhage. This structure is an anastomosis between which two vascular systems?

. Internal iliac and internal pudendal vessels
. Superior gluteal and internal iliac vessels
. Inferior gluteal and obturator vessels
. Internal pudendal and obturator vessels
. External iliac (or inferior epigastric) and obturator vessels

Correct Answer & Explanation

. External iliac (or inferior epigastric) and obturator vessels

Explanation

The corona mortis is a vascular anastomosis between the external iliac system (specifically the inferior epigastric vessels) and the obturator vessels. It crosses the superior pubic ramus and is highly susceptible to iatrogenic injury during anterior pelvic approaches.

Question 12936

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain that allows for primary (osteonal) bone healing without the formation of a visible callus?

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

Correct Answer & Explanation

. Less than 2%

Explanation

Primary (osteonal) bone healing requires absolute stability, which correlates to an interfragmentary strain of less than 2%. Strains between 2% and 10% result in secondary bone healing via callus formation, while strains above 10% typically lead to nonunion.

Question 12937

Topic: 1. General Principles & Basic Science
Following a peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for clearing myelin and axonal debris during the first few days of this process?
. Astrocytes
. Schwann cells
. Oligodendrocytes
. Macrophages
. Fibroblasts

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages, recruited to the injury site, are primarily responsible for the phagocytosis and clearance of myelin and axonal debris during Wallerian degeneration. Schwann cells assist and later proliferate to form bands of Bรผngner to guide regenerating axons.

Question 12938

Topic: Infection, Pharmacology & VTE

A patient undergoes debridement for an infected total knee arthroplasty. The pathogen is identified as Staphylococcus aureus. Which antibiotic is most effective at penetrating the biofilm and targeting bacteria in the stationary growth phase?

. Cefazolin
. Vancomycin
. Rifampin
. Gentamicin
. Linezolid

Correct Answer & Explanation

. Rifampin

Explanation

Rifampin has a unique ability to penetrate biofilms and act on slow-growing or stationary-phase organisms within the biofilm. It is typically used as an adjunct (never as monotherapy due to rapid resistance) in the treatment of retained orthopedic implants.

Question 12939

Topic: Infection, Pharmacology & VTE
A 65-year-old female is prescribed apixaban for venous thromboembolism prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibition
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Vitamin K antagonism
. Direct Factor Xa inhibition
. Activation of antithrombin III

Correct Answer & Explanation

. Direct Factor Xa inhibition

Explanation

Apixaban and rivaroxaban are direct, reversible inhibitors of Factor Xa. They block the conversion of prothrombin to thrombin in the coagulation cascade and do not require routine laboratory monitoring.

Question 12940

Topic: 1. General Principles & Basic Science

Within articular cartilage, which zone contains the highest concentration of proteoglycans and is primarily responsible for resisting compressive loads?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. Its collagen fibers are oriented perpendicularly to the articular surface, making it highly adapted to resisting compressive forces.

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