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1. General Principles & Basic Science MCQs

Practice Set 736 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 14701

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with severe knee pain. Radiographs reveal an eccentric, lytic epiphyseal-metaphyseal lesion in the proximal tibia.

Biopsy is consistent with a giant cell tumor of bone. Which of the following describes the primary neoplastic cell population in this lesion?

. Multinucleated osteoclast-like giant cells
. Mononuclear spindle cells expressing RANKL
. Mononuclear macrophage-like cells expressing RANK
. Chondroblasts with chicken-wire calcification
. Osteoblasts producing disordered woven bone

Correct Answer & Explanation

. Mononuclear spindle cells expressing RANKL

Explanation

The primary neoplastic cells in a Giant Cell Tumor of bone are the mononuclear spindle cells, which actively secrete RANKL. The multinucleated giant cells are reactive, non-neoplastic osteoclasts recruited by the RANKL expression.

Question 14702

Topic: Biology, Genetics & Bone Healing

A 7-year-old girl is evaluated for delayed eruption of secondary teeth. Examination reveals a persistently open anterior fontanelle, hypermobility of the shoulders allowing them to meet in the midline, and short stature. The gene responsible for this condition is critical for the differentiation of which cell type?

. Osteoclasts
. Chondrocytes
. Osteoblasts
. Fibroblasts
. Schwann cells

Correct Answer & Explanation

. Osteoblasts

Explanation

The patient has cleidocranial dysplasia, caused by an autosomal dominant mutation in the RUNX2 (CBFA1) gene. RUNX2 is a master transcription factor essential for osteoblast differentiation and subsequent intramembranous and endochondral ossification.

Question 14703

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with progressive knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion extending to the subchondral bone in the distal femur.

Biopsy confirms a giant cell tumor. She is treated preoperatively with a monoclonal antibody to facilitate joint salvage. What is the primary mechanism of action of this medication?

. Inhibits vascular endothelial growth factor (VEGF)
. Binds to RANK ligand (RANKL) preventing osteoclast activation
. Inhibits tyrosine kinase receptors on tumor cells
. Cross-links DNA to prevent cellular replication
. Promotes apoptosis by binding CD20

Correct Answer & Explanation

. Binds to RANK ligand (RANKL) preventing osteoclast activation

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK on osteoclast-like giant cells and their precursors. In giant cell tumor of bone, it is used to consolidate the tumor, reducing its vascularity and promoting a neocortical rim to facilitate surgical curettage.

Question 14704

Topic: Biology, Genetics & Bone Healing

A 25-year-old female presents with progressive knee pain. Radiographs reveal an eccentric, expansile, lytic lesion in the distal femoral epiphysis extending to the subchondral bone plate. Biopsy confirms a giant cell tumor of bone.

If pharmacological therapy with denosumab is considered, this drug specifically targets which of the following mechanisms in this pathology?

. Inhibition of RANKL secreted by the neoplastic mononuclear stromal cells
. Inhibition of RANKL secreted by the reactive multinucleated giant cells
. Direct induction of apoptosis in mononuclear stromal cells
. Inhibition of VEGF production to reduce tumor angiogenesis
. Stimulation of osteoprotegerin (OPG) synthesis by osteoblasts

Correct Answer & Explanation

. Inhibition of RANKL secreted by the neoplastic mononuclear stromal cells

Explanation

Denosumab is a monoclonal antibody that binds to RANKL. In giant cell tumor of bone, RANKL is overexpressed and secreted by the neoplastic mononuclear stromal cells, not the giant cells. This drives the recruitment and activation of the reactive osteoclast-like giant cells that cause bone destruction.

Question 14705

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy is referred for delayed eruption of his permanent teeth, prominent frontal bossing, and excessive shoulder mobility. Radiographs demonstrate hypoplastic clavicles and delayed ossification of the pubic symphysis. A mutation in which of the following transcription factors is responsible for this condition?

. COMP
. RUNX2 (CBFA1)
. SOX9
. FGFR3
. COL1A1

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

The patient has cleidocranial dysplasia, an autosomal dominant disorder caused by a mutation in the RUNX2 (CBFA1) gene on chromosome 6. RUNX2 is a master transcription factor essential for osteoblast differentiation and intramembranous ossification.

Question 14706

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with multiple hard, painless masses around his knees and ankles. Radiographs demonstrate multiple bone excrescences pointing away from the joints, with continuity of the medullary cavity into the lesions. What is the underlying pathogenesis of this condition?

. Overactivity of the Wnt/beta-catenin signaling pathway
. Mutation in the EXT1 or EXT2 genes causing defective heparan sulfate synthesis
. Activating mutation of GNAS1 causing abnormal G-protein signaling
. Defect in type I collagen synthesis
. Defect in osteoclast carbonic anhydrase II

Correct Answer & Explanation

. Mutation in the EXT1 or EXT2 genes causing defective heparan sulfate synthesis

Explanation

Multiple hereditary exostoses (MHE) is caused by autosomal dominant mutations in EXT1 or EXT2. These genes encode glycosyltransferases responsible for heparan sulfate synthesis, leading to disorganized Indian hedgehog signaling and abnormal chondrocyte proliferation.

Question 14707

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with severe back pain. Radiographs show multiple dense, osteoblastic lesions throughout the lumbar spine and pelvis. Laboratory evaluation reveals a significantly elevated serum prostate-specific antigen (PSA). The osteoblastic nature of these skeletal metastases is primarily driven by tumor secretion of which factor?

. RANKL
. Parathyroid hormone-related peptide (PTHrP)
. Endothelin-1 (ET-1)
. Interleukin-6 (IL-6)
. Tumor necrosis factor-alpha (TNF-a)

Correct Answer & Explanation

. Endothelin-1 (ET-1)

Explanation

Prostate cancer uniquely produces osteoblastic (bone-forming) metastases. This process is driven by the tumor cells secreting factors that stimulate osteoblasts, most notably Endothelin-1 (ET-1) and bone morphogenetic proteins (BMPs). PTHrP is more commonly associated with osteolytic breast cancer metastases.

Question 14708

Topic: Biology, Genetics & Bone Healing

A newborn is evaluated in the NICU for marked shortening of all limbs, proximally placed "hitchhiker" thumbs, severe clubfeet, and distinct cystic swelling of the pinnae (cauliflower ears). Radiographs show short, thick long bones and a normal skull. The underlying genetic mutation in this condition primarily impairs which cellular process?

. Type II collagen assembly
. Sulfate transport across the cell membrane
. Heparan sulfate polymerization
. Fibroblast growth factor signaling
. Osteoclast attachment to bone matrix

Correct Answer & Explanation

. Sulfate transport across the cell membrane

Explanation

Diastrophic dysplasia is caused by an autosomal recessive mutation in the SLC26A2 (DTDST) gene. This gene encodes a sulfate transporter, leading to intracellular sulfate depletion, undersulfation of proteoglycans in the cartilage matrix, and abnormal chondrocyte function.

Question 14709

Topic: 1. General Principles & Basic Science

In evaluating a patient with persistent low back pain, which finding on physical examination is most indicative of a significant psychological component contributing to their pain experience?

. Localized tenderness over the lumbar paraspinal muscles
. Limited lumbar range of motion in all planes
. Positive straight leg raise test at 30 degrees
. Non-anatomical sensory loss (e.g., stocking-glove distribution or shifting sensory deficits)
. Muscle spasm with active range of motion

Correct Answer & Explanation

. Non-anatomical sensory loss (e.g., stocking-glove distribution or shifting sensory deficits)

Explanation

Non-anatomical sensory loss (e.g., stocking-glove distribution, sensory loss that crosses dermatomal boundaries, or shifting/unreliable sensory deficits) is a 'Waddell's sign' and strongly suggests a non-organic or psychological component to the patient's pain presentation. While not definitive for malingering, it indicates that the subjective experience of pain is not strictly congruent with neuroanatomical pathology. The other options (localized tenderness, limited range of motion, positive straight leg raise, muscle spasm) can all be legitimate signs of organic pathology, although their interpretation requires clinical correlation.

Question 14710

Topic: Surgical Anatomy & Approaches

Which physical examination test is typically used to assess for sacroiliac joint pain?

. Straight Leg Raise (SLR) test
. Femoral Nerve Stretch test
. Hoover test
. FABER (Patrick's) test
. Slump test

Correct Answer & Explanation

. FABER (Patrick's) test

Explanation

The FABER (Flexion, Abduction, External Rotation), or Patrick's test, is a commonly used provocative test for the sacroiliac joint and/or hip pathology. Pain in the posterior buttock/SI region suggests SIJ involvement, while pain in the groin suggests hip pathology. The Straight Leg Raise test and Slump test assess for nerve root irritation/sciatica. The Femoral Nerve Stretch test assesses for upper lumbar nerve root irritation. The Hoover test is used to assess for non-organic weakness.

Question 14711

Topic: Infection, Pharmacology & VTE

A 30-year-old construction worker presents with chronic low back pain and radicular symptoms to his right leg. He has undergone 3 months of physical therapy, NSAIDs, and activity modification without significant relief. MRI shows a contained L4-L5 disc protrusion without significant migration, impinging the L5 nerve root. Neurological exam reveals mild weakness in right great toe extension (4/5) but no bladder/bowel dysfunction. What is the most appropriate next step?

. Continue conservative management for another 3 months
. Urgent microdiscectomy
. Transforaminal epidural steroid injection
. Lumbar fusion surgery
. Psychological counseling

Correct Answer & Explanation

. Transforaminal epidural steroid injection

Explanation

Given the failure of 3 months of conservative management for persistent radicular pain due to a disc protrusion and mild, non-progressive motor weakness, a transforaminal epidural steroid injection is a reasonable next step. It can provide significant pain relief by delivering anti-inflammatory medication directly to the affected nerve root. Surgical intervention (microdiscectomy) is typically considered for intractable pain after a trial of epidural injections, or for progressive neurological deficits. Lumbar fusion is overly aggressive for this presentation. Continuing conservative management foranother3 months without any specific escalation may be prolonged, and psychological counseling is not the primary intervention for this specific clinical picture, although it can be part of a multidisciplinary approach for chronic pain.

Question 14712

Topic: 1. General Principles & Basic Science
Which of the following is most strongly associated with chronic low back pain (>3 months) that is unresponsive to conventional treatments?
. Presence of a single, small disc protrusion on MRI
. Absence of a positive straight leg raise test
. Evidence of severe facet arthropathy on imaging
. High levels of pain catastrophizing and fear-avoidance beliefs
. Mild degenerative changes on plain radiographs

Correct Answer & Explanation

. High levels of pain catastrophizing and fear-avoidance beliefs

Explanation

Psychosocial factors, such as high levels of pain catastrophizing (exaggerating the threat of pain) and fear-avoidance beliefs (avoiding activity due to fear of pain or re-injury), are strong predictors of chronicity and poor outcomes in low back pain, often more so than specific structural findings on imaging. While structural abnormalities can contribute to pain, their correlation with chronic, intractable pain is often weak. The other options describe common imaging findings or clinical signs that, while potentially related to pain, are not as strongly associated with treatment resistance and chronicity as psychosocial factors.

Question 14713

Topic: Biology, Genetics & Bone Healing

A 14-year-old with multiple bony protuberances around his knees and shoulders has a known genetic condition. What is the primary cellular function of the mutated genes responsible for this disorder?

. Synthesis of heparan sulfate
. Regulation of p53 tumor suppression
. Fibroblast growth factor receptor inhibition
. Osteoclast activation via RANKL
. Synthesis of type I collagen

Correct Answer & Explanation

. Synthesis of heparan sulfate

Explanation

Hereditary multiple exostoses (HME) is caused by mutations in the EXT1 and EXT2 genes. These genes act as tumor suppressors that encode glycosyltransferases essential for the synthesis of heparan sulfate proteoglycans.

Question 14714

Topic: Biology, Genetics & Bone Healing

Which of the following genetic abnormalities is most consistently associated with the pathogenesis of Hereditary Multiple Exostoses (HME), and what is the resulting pathophysiologic defect?

. Defective EXT1 or EXT2 genes leading to abnormal heparan sulfate synthesis
. Activating mutation in FGFR3 leading to abnormal chondrocyte proliferation
. Defective COL1A1 gene leading to abnormal type I collagen formation
. Defective RUNX2 gene leading to abnormal osteoblast differentiation
. Activating mutation in GNAS leading to abnormal G-protein signaling

Correct Answer & Explanation

. Defective EXT1 or EXT2 genes leading to abnormal heparan sulfate synthesis

Explanation

HME is an autosomal dominant condition caused by mutations in the EXT1 or EXT2 tumor suppressor genes. This leads to defective synthesis of heparan sulfate, disrupting chondrocyte regulation and causing osteochondroma formation.

Question 14715

Topic: Biology, Genetics & Bone Healing
A 55-year-old male with a history of chronic alcohol abuse presents with palmar nodules and cords causing a flexion contracture of his ring finger. At the cellular level, the pathogenesis of this condition primarily involves the replacement of normal palmar fascia with which of the following?
. Type I collagen replaced by Type III collagen
. Type III collagen replaced by Type I collagen
. Type II collagen replaced by Type I collagen
. Elastin replaced by Type III collagen
. Type I collagen replaced by Type IV collagen

Correct Answer & Explanation

. Type I collagen replaced by Type III collagen

Explanation

Dupuytren's disease, which is highly associated with chronic alcoholism, is characterized by myofibroblast proliferation and the replacement of the normal Type I collagen of the palmar fascia with Type III collagen, leading to nodule and cord formation.

Question 14716

Topic: Biology, Genetics & Bone Healing

A 45-year-old male presents with spontaneous, progressive shoulder weakness and deformity. Radiographs demonstrate complete disappearance of the proximal humerus and clavicle.

Which histological finding is pathognomonic for this disease process?

. Atypical mononuclear cells with scattered osteoclast-like giant cells
. Malignant spindle cells producing osteoid
. Non-neoplastic proliferation of thin-walled vascular and lymphatic channels
. Sheets of small round blue cells with scant cytoplasm
. Lobules of hyaline cartilage with myxoid changes

Correct Answer & Explanation

. Non-neoplastic proliferation of thin-walled vascular and lymphatic channels

Explanation

The images and history describe Gorham-Stout disease (massive osteolysis). Its hallmark is the replacement of normal bone by an aggressive, non-neoplastic proliferation of angiomatous and lymphatic vessels.

Question 14717

Topic: Biology, Genetics & Bone Healing

A 40-year-old male with a history of severe chronic alcohol abuse presents with bilateral groin pain. MRI confirms stage II avascular necrosis (AVN) of both femoral heads. Which of the following best describes the pathophysiology of alcohol-induced AVN?

. Direct toxic effect of ethanol on articular cartilage
. Increased marrow adipogenesis leading to intraosseous hypertension
. Decreased production of intravascular coagulability factors
. Alcohol-induced hypolipidemia causing subchondral ischemia
. Osteoclastic overactivity secondary to parathyroid hormone suppression

Correct Answer & Explanation

. Increased marrow adipogenesis leading to intraosseous hypertension

Explanation

Alcohol abuse induces mesenchymal stem cells to differentiate into adipocytes rather than osteoblasts. This marrow adipogenesis causes cellular hypertrophy, increasing intraosseous pressure and compromising venous outflow, leading to ischemia.

Question 14718

Topic: Infection, Pharmacology & VTE

When treating a staphylococcal periprosthetic joint infection (PJI) with implant retention (DAIR), which of the following antibiotic agents is essential for penetrating the established bacterial biofilm?

. Cefazolin
. Vancomycin
. Rifampin
. Gentamicin
. Linezolid

Correct Answer & Explanation

. Rifampin

Explanation

Rifampin is highly active against stationary-phase staphylococci embedded within biofilms. It is a critical component of combination oral antibiotic therapy following DAIR for staphylococcal PJI.

Question 14719

Topic: Biology, Genetics & Bone Healing

Chronic alcohol abuse significantly increases the risk of fragility fractures. Which of the following is the primary mechanism by which alcohol directly induces osteoporosis?

. Increased intestinal calcium absorption
. Direct inhibition of osteoblast proliferation and function
. Overproduction of active Vitamin D (1,25-dihydroxycholecalciferol)
. Downregulation of osteoclast activity
. Decreased renal excretion of phosphate

Correct Answer & Explanation

. Direct inhibition of osteoblast proliferation and function

Explanation

Chronic alcohol consumption has a direct toxic effect on osteoblasts, inhibiting their proliferation and function, which leads to decreased bone formation. It also indirectly causes bone loss through poor nutrition and altered vitamin D metabolism.

Question 14720

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a destructive, eccentric, lytic lesion in the proximal tibial epiphysis. Biopsy reveals mononuclear cells and numerous multinucleated giant cells. If the patient is treated with denosumab preoperatively, what is its mechanism of action?

. Inhibits osteoblast-mediated bone formation
. Directly induces apoptosis of the multinucleated giant cells
. Binds to RANKL, preventing osteoclast activation and tumor-associated osteolysis
. Inhibits vascular endothelial growth factor (VEGF)
. Cross-links DNA to prevent tumor cell replication

Correct Answer & Explanation

. Binds to RANKL, preventing osteoclast activation and tumor-associated osteolysis

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, which is overexpressed by the neoplastic mononuclear stromal cells in Giant Cell Tumors. This prevents RANK activation on osteoclast precursors, stopping bone resorption.

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