Menu

1. General Principles & Basic Science MCQs

Practice Set 492 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 9821

Topic: Infection, Pharmacology & VTE

Which of the following radiographic findings is typically the earliest sign of osteomyelitis in a patient being evaluated for a chronic diabetic foot ulcer?

. Complete bone resorption of the metatarsal head
. Focal osteopenia and subtle periosteal reaction
. Gas outlining the fascial planes
. Pathologic fracture with severe displacement
. Sclerosis of the medullary canal

Correct Answer & Explanation

. Focal osteopenia and subtle periosteal reaction

Explanation

The earliest radiographic signs of osteomyelitis include focal osteopenia, cortical erosion, and subtle periosteal reaction. These changes typically require 10-14 days of progressive infection to become visible on plain radiographs.

Question 9822

Topic: Infection, Pharmacology & VTE

Total Contact Casting (TCC) is considered the gold standard for offloading plantar diabetic foot ulcers. Which of the following is an absolute contraindication for applying a TCC?

. Wagner Grade 1 ulcer on the plantar hallux
. Wagner Grade 2 ulcer without clinical signs of infection
. Presence of active deep space infection or osteomyelitis
. Loss of protective sensation in the contralateral foot
. History of previous successful TCC treatment

Correct Answer & Explanation

. Presence of active deep space infection or osteomyelitis

Explanation

Total contact casting relies on enclosing the foot to redistribute pressure. It is absolutely contraindicated in the presence of active deep infection, untreated osteomyelitis, severe ischemia, or highly exuding wounds due to the risk of enclosing an active infection.

Question 9823

Topic: Infection, Pharmacology & VTE

A patient with long-standing diabetes is evaluated for progressive foot deformity. The examiner notes profound sensory loss and a 'rocker-bottom' deformity. Radiographs show tarsometatarsal destruction, fragmentation, and new bone formation. What is the most likely diagnosis?

. Gouty arthropathy
. Rheumatoid arthritis
. Charcot neuroarthropathy (coalescence phase)
. Acute hematogenous osteomyelitis
. Severe osteoarthritis

Correct Answer & Explanation

. Charcot neuroarthropathy (coalescence phase)

Explanation

The combination of profound sensory loss, rocker-bottom deformity, and radiographic findings of destruction, fragmentation, and bony consolidation (new bone formation) is hallmark for the coalescence/remodeling phases of Charcot neuroarthropathy.

Question 9824

Topic: Physiology & Rehabilitation

The Semmes-Weinstein 10g monofilament evaluates sensory pathways carried primarily by which anatomical tract in the spinal cord?

. Lateral spinothalamic tract
. Anterior spinothalamic tract
. Dorsal column-medial lemniscus pathway
. Corticospinal tract
. Spinocerebellar tract

Correct Answer & Explanation

. Dorsal column-medial lemniscus pathway

Explanation

The 10g monofilament tests fine touch and proprioception mediated by large A-beta nerve fibers. These sensory modalities are transmitted centrally via the dorsal column-medial lemniscus pathway.

Question 9825

Topic: Biology, Genetics & Bone Healing

When utilizing the 10-gram (5.07) Semmes-Weinstein monofilament to screen for loss of protective sensation, which of the following describes the correct application technique?

. Apply perpendicular to the skin over a callus until it buckles for 3 seconds
. Apply perpendicular to the skin avoiding calluses until it buckles for 1 to 2 seconds
. Apply at a 45-degree angle avoiding calluses until it buckles for 1 to 2 seconds
. Stroke the monofilament across the skin over the metatarsal heads
. Tap the monofilament rapidly 3 times over the heel

Correct Answer & Explanation

. Apply perpendicular to the skin avoiding calluses until it buckles for 1 to 2 seconds

Explanation

The monofilament should be applied perpendicular to the skin, strictly avoiding calluses, scars, and necrotic tissue. It must be pressed until it bows or buckles and held in place for 1 to 2 seconds to assess sensation accurately.

Question 9826

Topic: Biology, Genetics & Bone Healing

Histological examination of a lesion in a patient with Fibrous Dysplasia typically reveals which of the following features?

. Well-organized lamellar bone with prominent osteoblastic rimming
. Irregular trabeculae of woven bone in a fibrocellular stroma without osteoblastic rimming
. Nests of hyaline cartilage with hyperchromatic nuclei
. Large multinucleated giant cells in a vascular stroma
. Sheets of small round blue cells with Homer-Wright rosettes

Correct Answer & Explanation

. Irregular trabeculae of woven bone in a fibrocellular stroma without osteoblastic rimming

Explanation

Correct Answer: BFibrous dysplasia is characterized histologically by 'Chinese character' or 'alphabet soup' patterns of irregular woven bone trabeculae. A key diagnostic feature is the absence of osteoblastic rimming, which helps differentiate it from other fibro-osseous lesions like ossifying fibroma.

Question 9827

Topic: 1. General Principles & Basic Science

Which of the following statements regarding the inheritance of Enchondromatosis (Ollier disease) is correct?

. It follows an Autosomal Dominant pattern with variable penetrance
. It is an X-linked recessive disorder
. It is a non-hereditary condition caused by somatic mosaicism
. It is caused by a germline mutation in the EXT2 gene
. It is only seen in patients with a family history of Maffucci syndrome

Correct Answer & Explanation

. It is a non-hereditary condition caused by somatic mosaicism

Explanation

Correct Answer: COllier disease and Maffucci syndrome are not inherited. They are sporadic conditions caused by somatic mosaic mutations, most commonly in the IDH1 or IDH2 genes, occurring early in development.

Question 9828

Topic: Biology, Genetics & Bone Healing

A 7-year-old child presents with a waddling gait, bilateral knee pain, and restricted joint mobility. Radiographs demonstrate delayed, irregular ossification of multiple epiphyses and a characteristic "double-layered" patella. A mutation in which gene is most commonly associated with this phenotype?

. COL2A1
. FGFR3
. COMP
. RUNX2
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) is most commonly caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene. A double-layered patella on lateral knee radiographs is highly characteristic of MED.

Question 9829

Topic: Biology, Genetics & Bone Healing

A 14-year-old male presents with delayed eruption of secondary teeth and the ability to easily approximate his shoulders anteriorly. Radiographs show delayed ossification of the cranial sutures and midline structures. Which gene is mutated in this condition?

. SOX9
. RUNX2 (CBFA1)
. Cathepsin K
. COL10A1
. GNAS

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is characterized by hypoplastic or absent clavicles, delayed suture closure, and dental anomalies. It is caused by an autosomal dominant mutation in the RUNX2 (CBFA1) transcription factor gene.

Question 9830

Topic: Biology, Genetics & Bone Healing

An infant with malignant osteopetrosis presents with cranial nerve palsies, hepatosplenomegaly, and recurrent fractures. Radiographs show a "bone-in-bone" appearance. What is the primary cellular defect responsible for this condition?

. Enhanced osteoblast differentiation and hyperactivity
. Defective formation of the ruffled border and failure of hydrogen ion pumping
. Overexpression of RANKL leading to rapid bone turnover
. Absence of circulating osteoclast progenitor cells
. Defective synthesis of type I collagen by osteoblasts

Correct Answer & Explanation

. Defective formation of the ruffled border and failure of hydrogen ion pumping

Explanation

Osteopetrosis is caused by defective osteoclast function, specifically the inability to acidify the resorption pit due to mutations affecting the ruffled border (e.g., Carbonic Anhydrase II or TCIRG1 mutations).

Question 9831

Topic: Biology, Genetics & Bone Healing

A newborn presents with respiratory distress, severe anterolateral bowing of the femora and tibiae, and pretibial skin dimpling. Genetic testing reveals a mutation in SOX9. This condition is most closely associated with which of the following anomalies?

. Precocious puberty
. XY sex reversal (phenotypic females with an XY karyotype)
. Blue sclerae and hearing loss
. Craniosynostosis and syndactyly
. Multiple renal cysts and hepatic fibrosis

Correct Answer & Explanation

. XY sex reversal (phenotypic females with an XY karyotype)

Explanation

Campomelic dysplasia is caused by a SOX9 mutation and is classically associated with severe bowing of the long bones, pretibial dimples, and sex reversal where 75% of XY individuals appear phenotypically female.

Question 9832

Topic: Biology, Genetics & Bone Healing

In a pediatric patient with severe Osteogenesis Imperfecta receiving cyclical intravenous pamidronate therapy, what is the exact cellular mechanism by which this medication improves bone density?

. Direct stimulation of osteoblast proliferation and matrix synthesis
. Blocking the RANK receptor on osteoclast progenitor cells
. Inhibition of farnesyl pyrophosphate synthase leading to osteoclast apoptosis
. Binding directly to and neutralizing cathepsin K in the resorption pit
. Increasing systemic production of osteoprotegerin (OPG)

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase leading to osteoclast apoptosis

Explanation

Nitrogen-containing bisphosphonates (like pamidronate) act by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents prenylation of small GTPases, ultimately causing osteoclast apoptosis.

Question 9833

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy with a history of recurrent fractures, blue sclerae, and dentinogenesis imperfecta is treated with intravenous pamidronate. What is the primary cellular mechanism of action of this medication in this patient?

. Stimulates osteoblast proliferation
. Inhibits osteoclast-mediated bone resorption
. Enhances type I collagen cross-linking
. Promotes calcium absorption in the gut
. Replaces defective fibrillin-1 molecules

Correct Answer & Explanation

. Inhibits osteoclast-mediated bone resorption

Explanation

Bisphosphonates like pamidronate inhibit osteoclast-mediated bone resorption by inducing osteoclast apoptosis. This increases cortical thickness and trabecular bone density, thereby reducing fracture risk in Osteogenesis Imperfecta.

Question 9834

Topic: Biology, Genetics & Bone Healing

A 14-year-old patient presents with a broad skull, delayed tooth eruption, and the ability to appose both shoulders anteriorly across the chest. Which gene mutation is responsible for this condition?

. RUNX2 (CBFA1)
. SOX9
. SHOX
. LRP5
. PTPN11

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by a mutation in the RUNX2 (CBFA1) gene, an essential transcription factor for osteoblast differentiation. It classically leads to absent or hypoplastic clavicles and delayed cranial suture closure.

Question 9835

Topic: Biology, Genetics & Bone Healing

An infant presents with diffuse bone sclerosis on radiographs demonstrating a "bone-within-bone" appearance, hepatosplenomegaly, and cranial nerve palsies. Which of the following is the definitive curative treatment for the malignant infantile form of this disease?

. High-dose intravenous bisphosphonates
. Hematopoietic stem cell transplantation
. Enzyme replacement therapy
. Repeated blood transfusions and splenectomy
. Systemic high-dose corticosteroids

Correct Answer & Explanation

. Hematopoietic stem cell transplantation

Explanation

Malignant infantile osteopetrosis is caused by defective osteoclasts (often a TCIRG1 mutation). Because osteoclasts are derived from the hematopoietic macrophage lineage, hematopoietic stem cell transplantation is the only definitive curative treatment.

Question 9836

Topic: Biology, Genetics & Bone Healing

A neonate presents with severe respiratory distress, anterior bowing of the tibiae, skin dimples over the tibial convexities, and hypoplastic scapulae. Chromosomal analysis reveals a 46,XY karyotype, but the patient has female external genitalia. What is the mutated gene?

. SOX9
. FGFR3
. COL1A1
. CBFA1
. COMP

Correct Answer & Explanation

. SOX9

Explanation

Camptomelic dysplasia is caused by a mutation in the SOX9 gene. This leads to severe skeletal bowing, respiratory distress due to tracheobronchomalacia, and often sex reversal (XY patients with female phenotype) due to SOX9's role in testis determination.

Question 9837

Topic: Biology, Genetics & Bone Healing
An infant presents with severe rickets-like bone deformities, failure to thrive, and paradoxical hypercalcemia. Laboratory testing shows markedly reduced serum alkaline phosphatase and elevated urinary phosphoethanolamine. What is the underlying genetic defect?
. Mutation in the PHEX gene
. Mutation in the FGF23 gene
. Mutation in the ALPL gene (tissue-nonspecific alkaline phosphatase)
. Mutation in the CASR gene (calcium-sensing receptor)
. Mutation in the VDR gene (vitamin D receptor)

Correct Answer & Explanation

. Mutation in the ALPL gene (tissue-nonspecific alkaline phosphatase)

Explanation

Hypophosphatasia is an inherited disorder characterized by defective bone mineralization. It is caused by a mutation in the ALPL gene, resulting in a deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) and accumulation of inorganic pyrophosphate.

Question 9838

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with short stature, waddling gait, and bilateral coxa vara. Radiographs show widened and irregular physes with metaphyseal flaring, predominantly in the lower extremities. Spine radiographs are completely normal. The mutation associated with this condition involves which collagen type?

. Type I collagen
. Type II collagen
. Type IX collagen
. Type X collagen
. Type XI collagen

Correct Answer & Explanation

. Type X collagen

Explanation

Schmid type metaphyseal chondrodysplasia is an autosomal dominant condition caused by a mutation in the COL10A1 gene, leading to defective type X collagen. Type X collagen is localized to the hypertrophic zone of the growth plate, and the disorder typically spares the spine.

Question 9839

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy presents with delayed closure of cranial sutures, an unusually broad forehead, and the ability to appose his shoulders anteriorly to the midline. A defect in the RUNX2 (CBFA1) gene is identified. This mutation primarily disrupts which of the following processes?

. Intramembranous ossification
. Endochondral ossification
. Osteoclast-mediated bone resorption
. Collagen triple-helix cross-linking
. Chondrocyte hypertrophy

Correct Answer & Explanation

. Intramembranous ossification

Explanation

The patient has Cleidocranial Dysplasia, which is caused by mutations in the RUNX2 (CBFA1) transcription factor. This gene is critical for osteoblast differentiation, and its defect predominantly impairs intramembranous ossification, affecting the clavicles and skull.

Question 9840

Topic: Biology, Genetics & Bone Healing

An infant presents with profound anemia, hepatosplenomegaly, and recurrent fractures. Radiographs reveal uniformly dense bones with an absent medullary canal and a 'bone-within-a-bone' appearance. The underlying pathogenesis of this condition most commonly involves a deficiency in which of the following?

. Carbonic anhydrase II
. Cathepsin K
. Tissue-nonspecific alkaline phosphatase
. Fibroblast growth factor receptor 3
. Type 1 collagen

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

The patient has infantile malignant osteopetrosis, characterized by dense but brittle bones due to failed osteoclast resorption. The most common underlying defect impairs the acidification of the osteoclast resorption pit, frequently involving carbonic anhydrase II or the TCIRG1 gene.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page