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1. General Principles & Basic Science MCQs

Practice Set 671 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 13401

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with back pain, anemia, and hypercalcemia. Radiographs show multiple 'punched-out' lytic lesions in his skull and pelvis. Which of the following is the primary mechanism responsible for the osseous lesions seen in this disease?

. Stimulation of osteoblast activity by myeloma cells
. Inhibition of the RANKL pathway
. Production of Osteoclast Activating Factors such as IL-6
. Direct mechanical bony destruction by expanding plasma cell clones
. Ischemic necrosis of trabecular bone secondary to hyperviscosity

Correct Answer & Explanation

. Production of Osteoclast Activating Factors such as IL-6

Explanation

Multiple myeloma causes lytic bone lesions primarily through the secretion of Osteoclast Activating Factors, particularly IL-6, MIP-1 alpha, and RANKL by myeloma cells. This leads to marked osteoclast stimulation and uncoupled bone remodeling.

Question 13402

Topic: Biology, Genetics & Bone Healing

A 45-year-old female immigrant presents with proximal muscle weakness and diffuse bone pain. Radiographs demonstrate bilateral pseudofractures (Looser zones) in the femoral necks. Laboratory evaluation reveals hypocalcemia and elevated alkaline phosphatase. What is the fundamental histological defect?

. Defect in Type I collagen synthesis
. Excessive osteoclast-mediated bone resorption
. Defective mineralization of newly formed osteoid
. Abnormal osteoblast differentiation
. Excessive disorganized woven bone production

Correct Answer & Explanation

. Defective mineralization of newly formed osteoid

Explanation

The patient has osteomalacia (adult rickets), which is characterized by defective mineralization of the osteoid matrix, leading to an accumulation of unmineralized osteoid. Looser zones represent these radiolucent bands of unmineralized matrix.

Question 13403

Topic: 1. General Principles & Basic Science
During the remodeling phase of tendon healing, the tensile strength of the tissue increases significantly. This is primarily driven by the transition of which types of collagen?
. Type I replacing Type II
. Type II replacing Type I
. Type III being replaced by Type I
. Type I being replaced by Type III
. Type V being replaced by Type I

Correct Answer & Explanation

. Type III being replaced by Type I

Explanation

During early tendon healing, weaker Type III collagen is laid down rapidly. In the remodeling phase, Type III collagen is gradually replaced by Type I collagen, which undergoes cross-linking to significantly increase the ultimate tensile strength of the tendon.

Question 13404

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with a limp. Which of the following is NOT one of the classic four Kocher criteria used to differentiate septic arthritis from transient synovitis of the pediatric hip?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate greater than 40 mm/hr
. Fever greater than 38.5 C
. Presence of a joint effusion on ultrasound
. Serum white blood cell count greater than 12,000/mm3

Correct Answer & Explanation

. Presence of a joint effusion on ultrasound

Explanation

The four classic Kocher criteria are fever > 38.5 C, non-weight-bearing status, ESR > 40 mm/hr, and WBC > 12,000 cells/mm3. While a joint effusion is supportive of hip pathology, it is not one of the specific predictive criteria.

Question 13405

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, ultra-high-molecular-weight polyethylene (UHMWPE) is often highly cross-linked to improve performance. What is the most significant mechanical trade-off associated with high cross-linking?
. Decreased wear resistance
. Increased oxidative degradation
. Decreased fracture toughness and ductility
. Increased risk of third-body wear
. Decreased elastic modulus

Correct Answer & Explanation

. Decreased fracture toughness and ductility

Explanation

Highly cross-linking UHMWPE significantly improves its resistance to adhesive and abrasive wear. However, this process alters the polymer chains, leading to a reduction in mechanical properties such as fracture toughness, ductility, and fatigue strength.

Question 13406

Topic: 1. General Principles & Basic Science

A patient suffers a peripheral nerve injury that results in disruption of axons and the endoneurial tubes, but the perineurium and epineurium remain intact. According to the Sunderland classification, what degree of nerve injury is this?

. First degree
. Second degree
. Third degree
. Fourth degree
. Fifth degree

Correct Answer & Explanation

. Third degree

Explanation

A Sunderland third-degree nerve injury involves complete disruption of the axon and the endoneurium, while the perineurium and epineurium remain intact. Healing is often compromised by intraneural scarring, potentially requiring surgical intervention.

Question 13407

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials has an elastic (Young's) modulus most closely resembling that of human cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has an elastic modulus of roughly 110 GPa, which is closer to human cortical bone (15-20 GPa) than stainless steel (200 GPa) or cobalt-chromium (220 GPa). This closer match reduces stress shielding around the implant.

Question 13408

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. What is the mechanism of action of TXA?
. Directly inhibits factor Xa in the coagulation cascade
. Competitively inhibits plasminogen activation
. Binds to antithrombin III to inhibit thrombin
. Inhibits cyclooxygenase to prevent platelet aggregation
. Acts as a procoagulant by cross-linking fibrinogen

Correct Answer & Explanation

. Competitively inhibits plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine-binding sites on plasminogen, preventing its activation into plasmin and thereby inhibiting fibrinolysis.

Question 13409

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) play a crucial role in osteoinduction. Once a BMP binds to its transmembrane serine/threonine kinase receptor, which intracellular signaling proteins mediate the transcription of osteogenic genes?

. Wnt/beta-catenin proteins
. Smad proteins
. JAK/STAT proteins
. MAP kinase proteins
. cAMP/PKA effectors

Correct Answer & Explanation

. Smad proteins

Explanation

BMPs are members of the TGF-beta superfamily. Their intracellular signaling is primarily mediated by Smad proteins (specifically Smad 1, 5, and 8), which translocate to the nucleus to regulate the transcription of osteogenic target genes.

Question 13410

Topic: Physiology & Rehabilitation

During rehabilitation of a reconstructed anterior cruciate ligament, understanding muscle physiology is critical. Which type of muscle contraction generates the highest maximal force or tension within the muscle-tendon unit?

. Concentric
. Isotonic
. Isokinetic
. Eccentric
. Isometric

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction, where the muscle lengthens while under tension, is capable of generating the highest maximum force. This is why eccentric exercises are associated with the highest risk of muscle strains and tendinopathies.

Question 13411

Topic: Biology, Genetics & Bone Healing

When a large structural cortical bone autograft is used for diaphyseal reconstruction, what is its primary mechanism of incorporation over time?

. Osteoconduction via creeping substitution
. Direct osteogenesis by surviving donor osteocytes
. Potent osteoinduction via massive BMP release
. Endochondral ossification
. Intramembranous ossification

Correct Answer & Explanation

. Osteoconduction via creeping substitution

Explanation

Cortical bone autografts primarily incorporate through osteoconduction via a slow process known as creeping substitution. Osteoclasts bore cutting cones into the dead graft bone, followed by osteoblasts laying down new bone, gradually replacing the graft.

Question 13412

Topic: Biomechanics & Biomaterials

On a stress-strain curve of a metallic orthopedic implant, what point represents the maximum stress a material can withstand before permanent deformation occurs?

. Proportional limit
. Yield point
. Ultimate tensile strength
. Failure point
. Modulus of elasticity

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the end of the elastic region and the beginning of plastic (permanent) deformation. The modulus of elasticity is simply the slope of the elastic region.

Question 13413

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is FDA-approved for use as an adjunct in acute, open tibial shaft fractures?

. 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 acute, open tibial shaft fractures and anterior lumbar interbody fusions. BMP-7 (rhBMP-7 or OP-1) was previously used for recalcitrant tibial nonunions.

Question 13414

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of Rheumatoid Arthritis, which cytokine is the primary target of the biologic medication etanercept?

. IL-1
. IL-6
. TNF-alpha
. RANKL
. CD20

Correct Answer & Explanation

. TNF-alpha

Explanation

Etanercept is a fusion protein that acts as a decoy receptor to bind and inhibit Tumor Necrosis Factor-alpha (TNF-alpha). Inhibiting TNF-alpha reduces the destructive inflammatory cascade characteristic of rheumatoid arthritis.

Question 13415

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with a resultant radial nerve palsy. Which of the following nerve injury types is characterized by intact endoneurium but disrupted axons?

. Neuropraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade 1
. Sunderland Grade 5

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis (Sunderland Grade 2) involves disruption of the axon and myelin sheath, but the connective tissue framework (endoneurium, perineurium) remains intact. Wallerian degeneration occurs distal to the injury.

Question 13416

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for DVT prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct Factor Xa inhibitor
. Antithrombin III activator
. Platelet ADP receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that selectively and directly inhibits Factor Xa. This interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade.

Question 13417

Topic: 1. General Principles & Basic Science

In which zone of articular cartilage are the collagen fibers oriented perpendicular to the joint surface and contain the highest concentration of proteoglycans?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone contains collagen fibers arranged perpendicular to the articular surface. This zone provides the greatest resistance to compressive forces due to its high proteoglycan content.

Question 13418

Topic: Biology, Genetics & Bone Healing

A patient presents with frequent fractures, cranial nerve palsies, and a "rugger jersey" spine on radiographs. The underlying pathophysiology of this disorder is a failure of which of the following cellular mechanisms?

. Osteoblast differentiation
. Osteoclast ruffled border formation
. Collagen cross-linking
. Mineralization of osteoid
. Chondrocyte hypertrophy

Correct Answer & Explanation

. Osteoclast ruffled border formation

Explanation

Osteopetrosis (marble bone disease) results from impaired osteoclast function, often due to a defect in the ruffled border or carbonic anhydrase II. This leads to a failure of normal bone resorption and remodeling.

Question 13419

Topic: Physiology & Rehabilitation

During a marathon, a runner relies primarily on Type I skeletal muscle fibers. Which of the following best describes the metabolic characteristics of Type I fibers?

. Fast twitch, anaerobic, high glycogen
. Slow twitch, aerobic, high mitochondria
. Fast twitch, aerobic, low myoglobin
. Slow twitch, anaerobic, low capillary density
. Fast twitch, mixed metabolism, high fatiguing

Correct Answer & Explanation

. Slow twitch, aerobic, high mitochondria

Explanation

Type I muscle fibers are slow-twitch, highly oxidative (aerobic), and possess abundant mitochondria and myoglobin. They are highly resistant to fatigue, making them ideal for endurance activities.

Question 13420

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis is treated with denosumab. What is the precise mechanism of action of this agent?

. Binds hydroxyapatite and inhibits osteoclasts
. Stimulates osteoblast differentiation via Wnt pathway
. Monoclonal antibody against RANKL
. Selective estrogen receptor modulator
. Recombinant parathyroid hormone analog

Correct Answer & Explanation

. Monoclonal antibody against RANKL

Explanation

Denosumab is a human monoclonal antibody that directly binds to RANKL, preventing it from activating RANK on the surface of osteoclasts. This effectively inhibits osteoclast formation, function, and survival.

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