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1. General Principles & Basic Science MCQs

Practice Set 611 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 12201

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMPs) are used to augment spinal fusions. BMPs induce osteogenesis primarily by binding to transmembrane serine/threonine kinase receptors. Which intracellular signaling molecules are subsequently phosphorylated to translocate to the nucleus and initiate transcription?

. JAK-STAT
. cAMP
. Smad proteins
. Beta-catenin
. Inositol triphosphate (IP3)

Correct Answer & Explanation

. JAK-STAT

Explanation

BMPs signal through serine/threonine kinase receptors, leading to the phosphorylation of intracellular Smad proteins (primarily Smad 1, 5, and 8). These phosphorylated Smads then bind to Smad 4, translocate to the nucleus, and regulate the transcription of osteogenic genes.

Question 12202

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently administered during orthopedic procedures to reduce perioperative blood loss. What is the specific mechanism of action of this medication?
. Inhibition of cyclooxygenase-1 (COX-1)
. Activation of antithrombin III
. Direct inhibition of Factor Xa
. Competitive inhibition of plasminogen activation
. Promotion of platelet aggregation via ADP receptors

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively inhibits the activation of plasminogen to plasmin, thereby preventing the degradation of fibrin clots (fibrinolysis).

Question 12203

Topic: 1. General Principles & Basic Science

A 45-year-old female presents with bilateral ulnar deviation of the MCP joints and morning stiffness. Serological testing for Rheumatoid Arthritis is positive. Which autoantibody is considered the most specific for the diagnosis of this condition?

. Antinuclear antibody (ANA)
. Rheumatoid factor (RF)
. Anti-cyclic citrullinated peptide (Anti-CCP)
. Anti-double-stranded DNA (Anti-dsDNA)
. Anti-Smith (Anti-Sm)

Correct Answer & Explanation

. Antinuclear antibody (ANA)

Explanation

Anti-cyclic citrullinated peptide (anti-CCP) antibodies are highly specific (up to 95-98%) for rheumatoid arthritis and can often be detected before clinical symptoms develop. While Rheumatoid Factor (RF) is sensitive, it is found in many other inflammatory conditions.

Question 12204

Topic: Surgical Anatomy & Approaches

A surgeon is performing the Smith-Petersen approach to the hip. To safely access the joint, the surgeon must utilize the internervous plane between which two muscles?

. Sartorius and Tensor fasciae latae
. Tensor fasciae latae and Gluteus medius
. Gluteus maximus and Gluteus medius
. Rectus femoris and Vastus lateralis
. Adductor longus and Pectineus

Correct Answer & Explanation

. Sartorius and Tensor fasciae latae

Explanation

The Smith-Petersen (anterior) approach to the hip utilizes the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). This true internervous plane allows for safe access to the anterior capsule.

Question 12205

Topic: Surgical Anatomy & Approaches

Following a mid-shaft humerus fracture, a patient demonstrates a complete radial nerve palsy. Electromyography (EMG) is ordered to evaluate the extent of the injury. How long after the injury should the EMG be performed to reliably detect fibrillation potentials in the denervated muscles?

. 24 to 48 hours
. 1 week
. 3 to 4 weeks
. 6 to 8 weeks
. 3 months

Correct Answer & Explanation

. 24 to 48 hours

Explanation

Fibrillation potentials and positive sharp waves, which indicate muscle denervation following Wallerian degeneration, typically take 3 to 4 weeks to appear on an EMG. Early EMG (before 3 weeks) may yield false-negative results for denervation.

Question 12206

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with increasing head size, hearing loss, and bowing of his tibiae. Histological examination of his affected bone would most likely reveal which of the following pathognomonic features?

. Abundant osteoid seams with delayed mineralization
. A mosaic pattern of lamellar bone with prominent cement lines
. Sheets of small round blue cells
. Loss of the osteoclast ruffled border
. Extensive replacement of bone marrow by fibrous tissue and cysts

Correct Answer & Explanation

. Abundant osteoid seams with delayed mineralization

Explanation

Paget's disease of bone is characterized by abnormal bone remodeling. The hallmark histological finding is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with prominent cement lines, representing chaotic cycles of rapid bone resorption and disorganized formation.

Question 12207

Topic: 1. General Principles & Basic Science

In the design of orthopedic plates, what is the biomechanical consequence of increasing the thickness of the plate by a factor of two?

. The bending stiffness increases by a factor of 2
. The bending stiffness increases by a factor of 4
. The bending stiffness increases by a factor of 8
. The area moment of inertia decreases
. The tensile strength decreases by half

Correct Answer & Explanation

. The bending stiffness increases by a factor of 2

Explanation

The bending stiffness of a plate is proportional to its area moment of inertia, which is calculated as (base x height^3)/12. Therefore, doubling the thickness (height) of the plate increases its bending stiffness by a factor of 2^3, or 8.

Question 12208

Topic: Infection, Pharmacology & VTE
A patient undergoing total knee arthroplasty is prescribed enoxaparin for deep vein thrombosis prophylaxis. What is the primary molecular target by which enoxaparin exerts its anticoagulant effect?
. Direct inhibition of thrombin (Factor IIa)
. Vitamin K epoxide reductase
. Antithrombin III, leading to preferential inhibition of Factor Xa
. Inhibition of ADP binding to the P2Y12 receptor
. Inactivation of Factor VIIIa and Va via Protein C

Correct Answer & Explanation

. Antithrombin III, leading to preferential inhibition of Factor Xa

Explanation

Enoxaparin, a low-molecular-weight heparin (LMWH), binds to antithrombin III. This complex primarily inhibits Factor Xa (with a much higher ratio of anti-Xa to anti-IIa activity compared to unfractionated heparin), effectively preventing clot formation.

Question 12209

Topic: 1. General Principles & Basic Science

A patient sustains a peripheral nerve injury that exhibits Wallerian degeneration, but the endoneurium, perineurium, and epineurium remain intact. Spontaneous recovery is expected. According to Sunderland's classification, what grade is this injury?

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

Correct Answer & Explanation

. First degree

Explanation

A second-degree injury (axonotmesis in Seddon's classification) involves disruption of the axon with Wallerian degeneration, but the supporting connective tissue remains intact. This allows the regenerating axon to use the intact endoneurial tube, predicting excellent recovery.

Question 12210

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with bowing of the legs, frontal bossing, and widened wrists. Laboratory tests reveal low serum calcium, low phosphorus, and elevated alkaline phosphatase. Which of the following defines the primary histopathologic defect at the growth plate in this patient?

. Defective osteoclast apoptosis
. Failure of mineralization of the osteoid in the zone of provisional calcification
. Premature closure of the reserve zone
. Lack of type II collagen production
. Hyperproliferation of the secondary spongiosa

Correct Answer & Explanation

. Defective osteoclast apoptosis

Explanation

Nutritional rickets is caused by Vitamin D deficiency, leading to impaired mineralization of bone and cartilage. At the growth plate, there is a failure of mineralization of the osteoid in the zone of provisional calcification, resulting in a widened and irregular physis.

Question 12211

Topic: Biology, Genetics & Bone Healing

During fracture healing, Bone Morphogenetic Proteins (BMPs) initiate the osteoinductive cascade. Which of the following intracellular signaling molecules is directly phosphorylated following BMP receptor activation?

. Beta-catenin
. Smad 1/5/8
. NF-kappa B
. JAK-STAT
. c-Fos

Correct Answer & Explanation

. Beta-catenin

Explanation

BMPs bind to serine/threonine kinase receptors, leading to the phosphorylation of Smad 1/5/8. These then form a complex with Smad 4 and translocate to the nucleus to regulate target gene expression for osteoblast differentiation.

Question 12212

Topic: Biomechanics & Biomaterials

A patient undergoes anterior cruciate ligament (ACL) reconstruction with a soft tissue allograft. Tension is applied to the graft prior to fixation. Over time, the tension required to maintain the graft at a constant length decreases. This viscoelastic property is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the decrease in stress (tension) over time when a viscoelastic material is held at a constant length. Creep is the increase in deformation (length) over time under a constant load.

Question 12213

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with severe osteoporosis is started on teriparatide. How does the intermittent administration of this medication promote bone formation?

. Inhibiting the RANK/RANKL interaction
. Decreasing sclerostin production by osteocytes
. Inhibiting osteoclast ruffled border formation
. Promoting osteoblast survival and stimulating Wnt signaling
. Inhibiting farnesyl pyrophosphate synthase

Correct Answer & Explanation

. Inhibiting the RANK/RANKL interaction

Explanation

Teriparatide (recombinant PTH) given intermittently has an anabolic effect by promoting osteoblast differentiation and survival, largely through modulation of the Wnt signaling pathway. Continuous PTH, conversely, promotes bone resorption.

Question 12214

Topic: Biology, Genetics & Bone Healing

Which of the following components of the extracellular matrix is primarily responsible for the compressive stiffness and water-retaining capacity of articular cartilage?

. Type II collagen
. Type I collagen
. Aggrecan
. Fibronectin
. Lubricin

Correct Answer & Explanation

. Type II collagen

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage. Its highly negatively charged glycosaminoglycan chains (chondroitin and keratan sulfate) attract water, creating a swelling pressure that resists compressive loads.

Question 12215

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with bowing of the lower extremities, hypocalcemia, and normal 25-hydroxyvitamin D levels but extremely low 1,25-dihydroxyvitamin D levels. What is the most likely underlying genetic defect?

. Mutation in the vitamin D receptor
. Deficiency of 25-hydroxylase
. Deficiency of 1-alpha-hydroxylase
. Mutation in the PHEX gene
. Mutation in the FGF23 gene

Correct Answer & Explanation

. Mutation in the vitamin D receptor

Explanation

Vitamin D-dependent rickets type I is caused by a deficiency in 1-alpha-hydroxylase, the renal enzyme that converts 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D. Type II is caused by a defect in the vitamin D receptor.

Question 12216

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the precise mechanism of action of this pharmacological agent?
. Directly inhibits thrombin (Factor IIa)
. Enhances antithrombin III activity against Factor Xa
. Competitively inhibits vitamin K epoxide reductase
. Directly inhibits activated Factor X (Factor Xa)
. Inhibits ADP-induced platelet aggregation

Correct Answer & Explanation

. Directly inhibits activated Factor X (Factor Xa)

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by directly inhibiting Factor Xa, interrupting the common pathway of the coagulation cascade. Unlike heparins, they do not require antithrombin III for their activity.

Question 12217

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with breast cancer metastases to the spine is treated with a monoclonal antibody to prevent skeletal-related events. This medication mimics the physiologic action of which of the following endogenous proteins?

. Cathepsin K
. Sclerostin
. Osteoprotegerin (OPG)
. Parathyroid hormone (PTH)
. Matrix metalloproteinase-13 (MMP-13)

Correct Answer & Explanation

. Cathepsin K

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to RANK on osteoclasts. This mimics the action of osteoprotegerin (OPG), a natural decoy receptor produced by osteoblasts to inhibit osteoclastogenesis.

Question 12218

Topic: 1. General Principles & Basic Science
In the pathogenesis of osteoarthritis, degradation of the type II collagen network is a critical and irreversible step. Which enzyme is primarily responsible for the cleavage of type II collagen in osteoarthritic cartilage?
. MMP-1
. MMP-3
. MMP-13
. ADAMTS-4
. ADAMTS-5

Correct Answer & Explanation

. MMP-13

Explanation

Matrix metalloproteinase-13 (MMP-13) is the primary collagenase responsible for the degradation of type II collagen in osteoarthritis. ADAMTS-4 and ADAMTS-5 are aggrecanases that primarily degrade the proteoglycan aggrecan.

Question 12219

Topic: Biology, Genetics & Bone Healing

A researcher is evaluating bone turnover markers in a cohort of patients with Paget's disease. Which of the following serum markers is considered the most specific indicator of bone formation and osteoblast activity?

. Tartrate-resistant acid phosphatase (TRAP)
. N-telopeptide (NTx)
. Bone-specific alkaline phosphatase (BSAP)
. Osteocalcin
. Hydroxyproline

Correct Answer & Explanation

. Tartrate-resistant acid phosphatase (TRAP)

Explanation

Osteocalcin is a non-collagenous protein secreted almost exclusively by osteoblasts, making it a highly specific marker of late osteoblast differentiation and bone formation. TRAP and NTx are markers of bone resorption.

Question 12220

Topic: Biology, Genetics & Bone Healing

Malignant infantile osteopetrosis is a fatal genetic disorder characterized by dense, brittle bones and pancytopenia. The most common genetic defect in this condition impairs which of the following mechanisms?

. Synthesis of type I collagen
. Function of the osteoclast ruffled border via TCIRG1 mutation
. Wnt-beta catenin signaling pathway
. Differentiation of mesenchymal stem cells
. Secretion of osteoprotegerin

Correct Answer & Explanation

. Synthesis of type I collagen

Explanation

Malignant infantile osteopetrosis is most commonly caused by a mutation in the TCIRG1 gene, which encodes a subunit of the vacuolar proton pump (V-ATPase). This prevents osteoclasts from acidifying the resorption pit, leading to defective bone resorption.

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