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1. General Principles & Basic Science MCQs

Practice Set 721 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 14401

Topic: Biomechanics & Biomaterials

A 45-year-old male undergoes open reduction and internal fixation for a femur fracture. The surgeon inadvertently uses a stainless steel screw with a titanium plate. Which of the following best describes the resulting electrochemical process that leads to early implant failure?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in physical contact within an electrolytic medium (such as body fluid). This creates an electrochemical cell, leading to the accelerated corrosion of the less noble metal (stainless steel in this case). Fretting corrosion is mechanically induced by micromotion, while crevice corrosion happens in restricted spaces with oxygen depletion.

Question 14402

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that can be tolerated for secondary bone healing via callus formation without leading to nonunion?

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

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Perren's strain theory states that primary bone healing (direct Haversian remodeling) requires less than 2% strain. Secondary bone healing, characterized by the formation of a provisional fracture callus (initially cartilaginous), occurs in environments with 2% to 10% strain. If strain exceeds 10%, neither bone nor cartilage can form across the gap, leading to fibrous tissue interposition and potential nonunion.

Question 14403

Topic: Biology, Genetics & Bone Healing

Articular cartilage has a highly specialized extracellular matrix. Which of the following components is primarily responsible for generating the compressive stiffness of articular cartilage?

. Type I collagen
. Type II collagen
. Aggrecan
. Hyaluronic acid
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage. It features heavily concentrated, negatively charged glycosaminoglycan (GAG) side chains. These repel one another and attract water (the Donnan osmotic effect), causing the molecules to swell against the restraining network of Type II collagen. This interaction provides cartilage with its characteristic compressive stiffness and resilience.

Question 14404

Topic: Physiology & Rehabilitation

A marathon runner sustains an overuse injury to the soleus muscle. Compared to the gastrocnemius, the soleus relies predominantly on a specific muscle fiber type. Which of the following describes the physiological characteristics of the predominant muscle fibers in the soleus?

. Fast twitch, high glycogen content, anaerobic metabolism
. Slow twitch, rich in mitochondria, aerobic metabolism
. Fast twitch, high oxidative capacity, aerobic metabolism
. Slow twitch, low myoglobin content, anaerobic metabolism
. Intermediate twitch, high glycolytic capacity, low mitochondria

Correct Answer & Explanation

. Slow twitch, rich in mitochondria, aerobic metabolism

Explanation

The soleus is primarily composed of Type I (slow-twitch) muscle fibers, which are uniquely designed for sustained postural control and endurance. These fibers rely heavily on aerobic metabolism, meaning they are rich in mitochondria, oxidative enzymes, and myoglobin (giving them a red appearance) and possess a high resistance to fatigue.

Question 14405

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is started on denosumab. What is the specific mechanism of action of this medication?

. Inhibits the enzyme farnesyl pyrophosphate synthase
. Binds to and neutralizes RANK ligand (RANKL)
. Acts as a selective estrogen receptor modulator in osteoblasts
. Stimulates osteoblast differentiation via the Wnt signaling pathway
. Directly binds to the calcium-sensing receptor on the parathyroid gland

Correct Answer & Explanation

. Binds to and neutralizes RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents RANKL from binding to the RANK receptor on osteoclast precursors, thereby profoundly inhibiting osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

Question 14406

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is frequently used in total joint arthroplasty to reduce perioperative blood loss. Which of the following best describes its mechanism of action?

. Inhibits the conversion of prothrombin to thrombin
. Irreversibly inhibits cyclooxygenase-1 in platelets
. Competitively inhibits the activation of plasminogen to plasmin
. Promotes the release of von Willebrand factor from endothelial cells
. Binds directly to and inhibits Factor Xa

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine and serves as an antifibrinolytic agent. It works by competitively and reversibly binding to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin, blocking its activation into plasmin, and thereby preventing the premature degradation of fibrin clots.

Question 14407

Topic: Biomechanics & Biomaterials

When a sustained, constant load is applied to a viscoelastic structure such as a ligament over a period of time, the tissue will continue to slowly elongate. This biomechanical phenomenon is known as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent, progressive deformation (elongation) of a viscoelastic material when it is subjected to a constant, continuous load. Stress relaxation is the inverse phenomenon: the decrease in internal stress over time when a material is held at a constant length. Hysteresis represents the energy lost (dissipated as heat) between the loading and unloading curves.

Question 14408

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and is noted to have a complete radial nerve palsy immediately post-injury. If the nerve injury is classified as an axonotmesis (Sunderland second-degree), which of the following structures remains intact, facilitating optimal regeneration?

. Axon
. Myelin sheath
. Endoneurium
. Perineurium only
. Epineurium only

Correct Answer & Explanation

. Endoneurium

Explanation

In Seddon's classification, axonotmesis involves a disruption of the axon and the myelin sheath, leading to Wallerian degeneration distally. However, the supporting connective tissue framework—most importantly the endoneurium (as well as the perineurium and epineurium)—remains intact. These intact endoneurial tubes act as guides for regenerating axons, usually resulting in excellent spontaneous functional recovery.

Question 14409

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily and act as potent osteoinductive signaling molecules. Which specific BMP is FDA-approved for use in acute, open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for the treatment of acute, open tibial shaft fractures stabilized with an intramedullary nail, as well as for single-level anterior lumbar interbody fusion (ALIF). rhBMP-7 (also known as Osteogenic Protein-1) was previously approved under a Humanitarian Device Exemption for recalcitrant long bone nonunions.

Question 14410

Topic: Biology, Genetics & Bone Healing

An 80-year-old male presents with increasing hat size, dull bone pain, and bilateral hearing loss. Laboratory testing reveals an isolated, markedly elevated alkaline phosphatase level with normal calcium and phosphorus. A biopsy of an affected long bone during the mixed phase of this disease would most likely show which of the following histological patterns?

. Empty osteocyte lacunae with surrounding necrotic trabeculae
. Mosaic pattern of lamellar bone with prominent, haphazard cement lines
. Markedly thickened osteoid seams with delayed mineralization
. Nests of atypical plasma cells replacing the normal marrow space
. Spindle cells arranged in a storiform pattern mixed with multinucleated giant cells

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent, haphazard cement lines

Explanation

The clinical picture is diagnostic of Paget's disease of bone (osteitis deformans). The classic histological hallmark of the mixed (osteoblastic/osteoclastic) and sclerotic phases of Paget's disease is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone. This is characterized by disorganized, prominent cement lines resulting from chaotic, accelerated episodes of bone resorption and subsequent rapid, disorganized bone formation.

Question 14411

Topic: Infection, Pharmacology & VTE
A 45-year-old male presents with a swollen, acutely painful knee. A joint aspiration is performed yielding cloudy, yellow fluid. The synovial fluid analysis reveals a white blood cell count of 45,000 cells/mm³ with 80% polymorphonuclear leukocytes. No crystals are visualized under polarized light. What is the most likely diagnostic category?
. Non-inflammatory (e.g., Osteoarthritis)
. Hemorrhagic (e.g., Traumatic hemarthrosis)
. Inflammatory (e.g., Rheumatoid arthritis)
. Septic (e.g., Bacterial arthritis)
. Crystalline (e.g., Gout)

Correct Answer & Explanation

. Inflammatory (e.g., Rheumatoid arthritis)

Explanation

Synovial fluid analysis categorizes joint effusions based on WBC count. Non-inflammatory (OA) fluid has <2,000 WBCs/mm³. Inflammatory fluid (such as in Rheumatoid Arthritis) typically ranges from 2,000 to 50,000 WBCs/mm³ with >50% PMNs. Septic arthritis generally presents with >50,000 WBCs/mm³ (frequently >100,000) and >90% PMNs. The absence of crystals makes gout or pseudogout unlikely.

Question 14412

Topic: Infection, Pharmacology & VTE

In periprosthetic joint infections, Staphylococcus epidermidis frequently evades the immune system and antibiotics by forming a complex biofilm. The crucial initial stage of biofilm formation is the primary, irreversible attachment of the bacteria to the synthetic polymer surface. Which bacterial component predominantly mediates this initial attachment?

. Exopolysaccharide matrix (slime)
. Protein A
. Fibronectin-binding protein
. Autolysin (AtlE)
. Polysaccharide intercellular adhesin (PIA)

Correct Answer & Explanation

. Autolysin (AtlE)

Explanation

The initial, irreversible attachment of S. epidermidis to hydrophobic synthetic polymer surfaces (implant materials) is heavily mediated by surface-associated proteins, particularly Autolysin (AtlE). Polysaccharide intercellular adhesin (PIA) is vital for the subsequent phase of biofilm development: intercellular adhesion, accumulation, and formation of the mature extracellular matrix 'slime'.

Question 14413

Topic: Biology, Genetics & Bone Healing

Nutritional rickets is caused by a severe deficiency of Vitamin D in growing children, leading to defective mineralization of the growth plate. Prior to any treatment, what are the characteristic serum levels of calcium, phosphate, and parathyroid hormone (PTH) in a patient with nutritional rickets?

. Low Calcium, Low Phosphate, High PTH
. Low Calcium, High Phosphate, Low PTH
. Normal Calcium, Low Phosphate, Normal PTH
. High Calcium, Low Phosphate, High PTH
. Normal Calcium, High Phosphate, High PTH

Correct Answer & Explanation

. Low Calcium, Low Phosphate, High PTH

Explanation

In nutritional rickets (Vitamin D deficiency), diminished intestinal absorption leads to hypocalcemia. The hypocalcemia triggers the parathyroid glands to increase PTH secretion (secondary hyperparathyroidism). The elevated PTH attempts to normalize calcium by increasing bone resorption and renal calcium reabsorption, while simultaneously profoundly increasing renal phosphate excretion, resulting in hypophosphatemia.

Question 14414

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following lower extremity total joint arthroplasty. Which of the following describes the precise pharmacologic mechanism of action of this medication?
. Direct, reversible inhibition of thrombin (Factor IIa)
. Inhibition of Vitamin K epoxide reductase
. Direct, highly selective inhibition of Factor Xa
. Indirect inhibition of Factor Xa via activation of antithrombin III
. Irreversible antagonism of the platelet P2Y12 ADP receptor

Correct Answer & Explanation

. Direct, highly selective inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that function as direct, highly selective, and reversible inhibitors of free and clot-bound Factor Xa. They do not require antithrombin III to exert their effect (unlike indirect inhibitors such as fondaparinux or low-molecular-weight heparins). Dabigatran is a direct thrombin inhibitor.

Question 14415

Topic: Biology, Genetics & Bone Healing

Which of the following integrins is primarily responsible for the attachment of the osteoclast ruffled border to the extracellular bone matrix during resorption?

. Alpha-1 Beta-1
. Alpha-5 Beta-1
. Alpha-v Beta-3
. Alpha-2 Beta-1
. Alpha-v Beta-5

Correct Answer & Explanation

. Alpha-v Beta-3

Explanation

Osteoclasts bind to bone matrix proteins, such as osteopontin and bone sialoprotein, via the Alpha-v Beta-3 integrin. This attachment creates a sealed zone necessary for maintaining the localized acidic environment required for bone resorption.

Question 14416

Topic: 1. General Principles & Basic Science

In articular cartilage, the organization of type II collagen fibers varies by zone. Which of the following best describes the orientation of collagen fibers in the deep zone?

. Parallel to the joint surface
. Randomly oriented
. Perpendicular to the joint surface
. Oblique to the joint surface
. Concentric rings around chondrocytes

Correct Answer & Explanation

. Perpendicular to the joint surface

Explanation

In the deep zone of articular cartilage, type II collagen fibers are oriented perpendicularly to the joint surface and anchor into the calcified zone. This precise orientation provides significant resistance to compressive and shear forces.

Question 14417

Topic: Biology, Genetics & Bone Healing

A structural cortical bone graft is used to reconstruct a diaphyseal defect. Which of the following processes characterizes the primary mechanism of graft incorporation?

. Initial osteoblastic woven bone apposition
. Osteoclastic resorption followed by osteoblastic formation
. Direct endochondral ossification
. Primary bone healing via cutting cones without resorption
. Fibrocartilage callus formation

Correct Answer & Explanation

. Osteoclastic resorption followed by osteoblastic formation

Explanation

Cortical bone grafts incorporate primarily via "creeping substitution", which begins with osteoclastic resorption of the graft followed by osteoblastic bone formation. In contrast, cancellous grafts initially incorporate via osteoblastic apposition onto existing trabeculae.

Question 14418

Topic: Biomechanics & Biomaterials

When analyzing the mechanical behavior of ligaments, the phenomenon where the tension within a ligament gradually decreases while it is held at a constant length is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropic strain

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (tension) within a material decreases over time when it is held at a constant strain (length). Conversely, creep refers to continuous deformation over time under a constant load.

Question 14419

Topic: Biomechanics & Biomaterials

A 65-year-old patient receives a cemented total hip arthroplasty. By what primary mechanism does polymethylmethacrylate (PMMA) secure the femoral component to the surrounding bone?

. Covalent chemical bonding
. Osteoconductive integration
. Mechanical interlock
. Piezoelectric stimulation
. Galvanic adhesion

Correct Answer & Explanation

. Mechanical interlock

Explanation

PMMA bone cement acts as a grout rather than a chemical adhesive. It achieves fixation primarily through mechanical interlock by firmly interdigitating with the interstices of the prepared cancellous bone.

Question 14420

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate, inhibit bone resorption primarily by targeting and inhibiting which of the following intracellular enzymes?

. Cathepsin K
. Carbonic anhydrase II
. Farnesyl pyrophosphate synthase
. Tartrate-resistant acid phosphatase
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of essential small GTPases (like Ras and Rho), ultimately inducing osteoclast apoptosis.

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