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1. General Principles & Basic Science MCQs

Practice Set 742 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 14821

Topic: 1. General Principles & Basic Science
A 10-year-old boy presents to a multidisciplinary genetics and orthopedics clinic. He demonstrates profound, progressive intellectual disability, sleep disturbances, and hyperactive behavior. Orthopedic examination reveals only mild joint stiffness and minimal skeletal abnormalities (mild dysostosis multiplex) compared to other children with related metabolic disorders. This phenotype is most characteristic of which type of mucopolysaccharidosis?
. Type I (Hurler)
. Type II (Hunter)
. Type III (Sanfilippo)
. Type IV (Morquio)
. Type VI (Maroteaux-Lamy)

Correct Answer & Explanation

. Type III (Sanfilippo)

Explanation

Sanfilippo syndrome (MPS III) is distinct because it is characterized by severe, progressive central nervous system degeneration and profound intellectual disability. In sharp contrast to other MPS types, the skeletal dysplasias and somatic features are relatively mild.

Question 14822

Topic: Infection, Pharmacology & VTE

A 52-year-old man with poorly controlled type 2 diabetes presents with a 3-week history of purulent drainage from a plantar ulcer under the first metatarsal head. The ulcer measures 2 cm in diameter. A sterile blunt probe is easily advanced through the ulcer until it strikes a hard, gritty surface. Which of the following statements regarding this clinical finding is most accurate?

. It has a high negative predictive value for osteomyelitis.
. It is highly predictive of osteomyelitis, and empiric antibiotics should be started immediately without further imaging.
. It has a high positive predictive value for osteomyelitis in the setting of a clinically infected ulcer.
. It indicates the need for immediate major lower extremity amputation.
. It is only useful if accompanied by systemic signs of infection such as fever and leukocytosis.

Correct Answer & Explanation

. It has a high positive predictive value for osteomyelitis in the setting of a clinically infected ulcer.

Explanation

Correct Answer: It has a high positive predictive value for osteomyelitis in the setting of a clinically infected ulcer.The probe-to-bone (PTB) test is a valuable clinical tool in the evaluation of diabetic foot ulcers. In the setting of a clinically infected ulcer, a positive PTB test (palpating a hard, gritty surface with a sterile blunt probe) has a high positive predictive value (up to 89%) for underlying osteomyelitis. While a negative test does not completely rule out osteomyelitis (it has a lower negative predictive value), a positive test in a high-prevalence population strongly supports the diagnosis and guides further management, including advanced imaging (MRI) and bone biopsy for culture.

Question 14823

Topic: Infection, Pharmacology & VTE

A 55-year-old diabetic patient is admitted with a severe, limb-threatening diabetic foot infection and suspected osteomyelitis of the great toe. He has not received any recent antibiotics. Deep tissue cultures and a bone biopsy are obtained. Which of the following best describes the most likely microbiological profile and appropriate initial empiric antibiotic therapy?

. Monomicrobial Staphylococcus aureus; treat with narrow-spectrum oral cephalosporin.
. Polymicrobial including aerobic Gram-positive cocci, Gram-negative bacilli, and anaerobes; treat with broad-spectrum intravenous antibiotics.
. Monomicrobial Pseudomonas aeruginosa; treat with oral ciprofloxacin.
. Polymicrobial with a predominance of fungal organisms; treat with intravenous fluconazole.
. Monomicrobial Streptococcus pyogenes; treat with intravenous penicillin.

Correct Answer & Explanation

. Polymicrobial including aerobic Gram-positive cocci, Gram-negative bacilli, and anaerobes; treat with broad-spectrum intravenous antibiotics.

Explanation

Correct Answer: Polymicrobial including aerobic Gram-positive cocci, Gram-negative bacilli, and anaerobes; treat with broad-spectrum intravenous antibiotics.Severe, limb-threatening diabetic foot infections, especially those with suspected osteomyelitis or deep tissue involvement, are typically polymicrobial. The microbiological profile often includes aerobic Gram-positive cocci (e.g., Staphylococcus aureus, Streptococcus species), Gram-negative bacilli (e.g., Enterobacteriaceae, and Pseudomonas in chronic/macerated wounds), and obligate anaerobes (e.g., Bacteroides, Peptostreptococcus). Therefore, initial empiric therapy should consist of broad-spectrum intravenous antibiotics covering these organisms until culture results and sensitivities are available to narrow the therapy.

Question 14824

Topic: Infection, Pharmacology & VTE

A 52-year-old man with poorly controlled diabetes presents with a 3-week history of a purulent ulcer on the plantar aspect of his right great toe. The ulcer measures 2 cm in diameter. A sterile metal probe easily reaches the bone at the base of the ulcer. What is the positive predictive value of this "probe-to-bone" test for diagnosing underlying osteomyelitis in this clinical setting?

. Less than 20%
. 30-40%
. 50-60%
. 85-90%
. 100%

Correct Answer & Explanation

. 85-90%

Explanation

Correct Answer: DThe "probe-to-bone" test is a highly useful clinical tool for evaluating diabetic foot ulcers. In a high-prevalence population (such as a patient with a chronic, clinically infected, purulent ulcer), a positive probe-to-bone test has a high positive predictive value (PPV) of approximately 85% to 90% for underlying osteomyelitis. While it does not replace advanced imaging or bone biopsy for definitive diagnosis, it strongly guides initial empiric management and surgical planning.

Question 14825

Topic: Infection, Pharmacology & VTE

A 52-year-old diabetic man requires surgical debridement and partial ray amputation for a chronic, limb-threatening diabetic foot infection with osteomyelitis. He has a history of multiple recent hospitalizations and antibiotic courses. Which of the following best describes the most likely microbiological profile of his deep bone cultures?

. Monomicrobial Staphylococcus aureus
. Monomicrobial Pseudomonas aeruginosa
. Polymicrobial including Gram-positive, Gram-negative, and anaerobic organisms
. Monomicrobial Streptococcus pyogenes
. Fungal infection primarily with Candida species

Correct Answer & Explanation

. Polymicrobial including Gram-positive, Gram-negative, and anaerobic organisms

Explanation

Correct Answer: CWhile acute, mild diabetic foot infections in antibiotic-naive patients are often monomicrobial (typically Staphylococcus aureus or Streptococcus species), chronic, severe, or limb-threatening infections—especially in patients with a history of recent hospitalization or antibiotic use—are overwhelmingly polymicrobial. These infections typically involve a mix of aerobic Gram-positive cocci, Gram-negative bacilli, and obligate anaerobes. Empiric antibiotic therapy for such severe infections must be broad-spectrum until definitive deep tissue or bone cultures guide targeted therapy.

Question 14826

Topic: Infection, Pharmacology & VTE

A 52-year-old man with poorly controlled diabetes mellitus presents with a 3-week history of purulent drainage from a medial right great toe ulcer. Radiographs show soft tissue swelling and periosteal reaction at the proximal phalanx. Which of the following clinical findings is most highly predictive of underlying osteomyelitis in this patient?

. Erythema extending 2 cm beyond the ulcer margin
. A palpable bounding dorsalis pedis pulse
. Ability to palpate hard, gritty bone with a sterile blunt probe
. An elevated erythrocyte sedimentation rate (ESR) greater than 30 mm/hr
. Presence of a foul-smelling polymicrobial discharge

Correct Answer & Explanation

. Ability to palpate hard, gritty bone with a sterile blunt probe

Explanation

Correct Answer: CThe "probe-to-bone" test is a highly specific and predictive clinical examination maneuver for diagnosing underlying osteomyelitis in the setting of a diabetic foot ulcer. If a sterile blunt probe can be advanced through the ulcer to palpate hard, gritty bone, the test is positive. Studies have shown that a positive probe-to-bone test in a high-prevalence population (such as a diabetic patient with a chronic, deep, draining ulcer) has a positive predictive value of nearly 90% for osteomyelitis. While elevated inflammatory markers (ESR, CRP) and radiographic changes can support the diagnosis, the clinical probe-to-bone test is the most direct and reliable bedside indicator.

Question 14827

Topic: 1. General Principles & Basic Science

A 4-year-old boy with spastic diplegia and severe scissoring gait is scheduled for bilateral adductor tenotomies and anterior branch obturator neurectomies to improve perineal hygiene and positioning. During the surgical approach, the anterior branch of the obturator nerve is typically located between which two muscles?

. Adductor longus and adductor brevis
. Adductor brevis and adductor magnus
. Pectineus and adductor longus
. Gracilis and adductor magnus
. Adductor longus and gracilis

Correct Answer & Explanation

. Adductor longus and adductor brevis

Explanation

Correct Answer: AThe obturator nerve exits the pelvis through the obturator foramen and divides into anterior and posterior branches. The anterior branch of the obturator nerve descends in the thigh between the adductor longus (anteriorly) and the adductor brevis (posteriorly). It supplies motor innervation to the adductor longus, adductor brevis, and gracilis. The posterior branch of the obturator nerve descends between the adductor brevis (anteriorly) and the adductor magnus (posteriorly). Knowledge of this anatomy is critical when performing selective obturator neurectomies for spasticity in cerebral palsy.

Question 14828

Topic: Infection, Pharmacology & VTE

A 52-year-old man with poorly controlled type 2 diabetes presents with a 3-week history of purulent drainage from a medial right great toe ulcer. Examination reveals a 2 cm ulcer with visible bone at the base. What is the most appropriate initial diagnostic step to confirm the presence of osteomyelitis?

. Three-phase technetium bone scan
. Probe-to-bone test
. Positron emission tomography (PET) scan
. Superficial wound swab for aerobic and anaerobic cultures
. Serum inflammatory markers (ESR and CRP)

Correct Answer & Explanation

. Probe-to-bone test

Explanation

Correct Answer: BIn a patient with a diabetic foot ulcer, the probe-to-bone test is a highly specific, cost-effective, and reliable initial clinical test for diagnosing underlying osteomyelitis. If a sterile blunt probe can be advanced through the ulcer to touch hard, gritty bone, the test is positive and highly predictive of osteomyelitis. While MRI is the most sensitive and specific advanced imaging modality for osteomyelitis, the probe-to-bone test is the best initial bedside diagnostic step. Superficial wound swabs are not reliable for identifying the causative organism of osteomyelitis; deep tissue or bone biopsy cultures are required. Bone scans lack specificity in the setting of neuropathic arthropathy or active soft tissue infection.

Question 14829

Topic: Infection, Pharmacology & VTE

A 52-year-old man with poorly controlled diabetes mellitus presents with a 3-week history of purulent drainage from a medial ulcer on his right great toe. On examination, a sterile blunt probe is easily advanced through the ulcer to a hard, gritty surface. Which of the following is the most accurate statement regarding this clinical finding?

. It has a high negative predictive value for osteomyelitis
. It has a high positive predictive value for osteomyelitis
. It indicates the need for immediate below-knee amputation
. It confirms the presence of a deep venous thrombosis
. It is pathognomonic for Charcot neuroarthropathy

Correct Answer & Explanation

. It has a high positive predictive value for osteomyelitis

Explanation

Correct Answer: BThe "probe-to-bone" test is a simple, cost-effective clinical examination maneuver used in the evaluation of diabetic foot ulcers. A positive test occurs when a sterile blunt probe can be advanced through the ulcer to palpate a hard, gritty bony surface. In the setting of an infected diabetic foot ulcer, a positive probe-to-bone test has a high positive predictive value (PPV), often cited around 89%, for the presence of underlying osteomyelitis. While it is highly predictive, a negative test does not definitively rule out osteomyelitis (lower negative predictive value), and further imaging, such as MRI, may be warranted if clinical suspicion remains high.

Question 14830

Topic: Infection, Pharmacology & VTE

A 52-year-old diabetic man is admitted with a deep, purulent ulcer on the medial aspect of his right great toe and confirmed osteomyelitis. He has not received any recent antibiotics. A bone biopsy is performed for culture prior to initiating antimicrobial therapy. Which of the following organisms is most commonly isolated in this clinical scenario?

. Pseudomonas aeruginosa
. Staphylococcus aureus
. Streptococcus pyogenes
. Bacteroides fragilis
. Escherichia coli

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Correct Answer: BDiabetic foot infections, including osteomyelitis, can be polymicrobial, especially in chronic, deep, or previously treated ulcers. However, Staphylococcus aureus is the single most common pathogen isolated from bone biopsies in patients with diabetic foot osteomyelitis. While Gram-negative organisms (like Pseudomonas aeruginosa and Escherichia coli) and anaerobes (like Bacteroides fragilis) are frequently found in mixed infections, particularly in ischemic or necrotic wounds, S. aureus remains the predominant organism. Empiric antibiotic therapy for severe diabetic foot infections must always include coverage for S. aureus, including MRSA if risk factors are present, along with broad-spectrum coverage for Gram-negative and anaerobic bacteria until culture results are available.

Question 14831

Topic: 1. General Principles & Basic Science

A 30-year-old carpenter sustains a laceration to the volar aspect of his index finger, resulting in a Zone II flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) rupture. Following primary repair, early active mobilization is initiated. What is the primary biological benefit of this rehabilitation protocol?

. Increases the inflammatory response to speed up healing
. Stimulates intrinsic tendon healing and reduces adhesion formation
. Promotes extrinsic healing via ingrowth from the tendon sheath
. Decreases the tensile strength required for early function
. Prevents joint contracture by stretching the repaired tendon

Correct Answer & Explanation

. Stimulates intrinsic tendon healing and reduces adhesion formation

Explanation

Early active mobilization promotes intrinsic tendon healing (via tenocytes within the tendon) and limits extrinsic healing, thereby minimizing adhesion formation and improving functional tendon excursion.

Question 14832

Topic: Biology, Genetics & Bone Healing

During fracture healing, intramembranous ossification occurs without a cartilage intermediate. Which of the following transcription factors is most essential for the differentiation of mesenchymal stem cells into osteoblasts during this process?

. Sox9
. MyoD
. PPAR-gamma
. Runx2 (Cbfa1)
. HIF-1 alpha

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the master transcription factor for osteoblast differentiation in both intramembranous and endochondral ossification. Sox9 is essential for chondrogenesis.

Question 14833

Topic: Biology, Genetics & Bone Healing

A 70-year-old female who has been taking alendronate for 12 years presents with an atraumatic, dull, aching pain in her right thigh. Radiographs demonstrate lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur. What is the most appropriate management?

. Reassurance and continuation of alendronate
. Discontinuation of alendronate and initiation of teriparatide only
. Discontinuation of alendronate, protected weight-bearing, and prophylactic cephalomedullary nailing
. Open reduction and internal fixation with a dynamic hip screw
. Switching to denosumab and adding calcium/vitamin D supplementation

Correct Answer & Explanation

. Discontinuation of alendronate, protected weight-bearing, and prophylactic cephalomedullary nailing

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use. Discontinuation of the drug and prophylactic cephalomedullary nailing are indicated to prevent completion of the fracture.

Question 14834

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with an expansile, lytic lesion in the distal radius. Biopsy confirms a giant cell tumor of bone. She is treated medically with denosumab prior to surgery. What is the specific target of this medication?

. Vascular endothelial growth factor (VEGF)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoprotegerin (OPG)
. Tumor necrosis factor-alpha (TNF-alpha)
. Interleukin-6 (IL-6)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts and giant cells, thereby inhibiting bone resorption and tumor progression.

Question 14835

Topic: Biology, Genetics & Bone Healing

A diaphyseal tibial shaft fracture is treated with a rigid compression plate, achieving absolute stability and anatomic reduction. Which mechanism of bone healing will predominantly occur in this scenario?

. Endochondral ossification
. Primary (Haversian) bone healing
. Intramembranous ossification
. Secondary bone healing with exuberant callus formation
. Appositional bone growth

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Rigid internal fixation that achieves absolute stability and anatomic reduction eliminates interfragmentary motion, leading to primary (Haversian) bone healing. This process occurs via cutting cones without the formation of a visible fracture callus.

Question 14836

Topic: Biology, Genetics & Bone Healing

Biopsy of a radiolucent, eccentrically located metaphyseal lesion in a 14-year-old female reveals blood-filled spaces lined by mononuclear cells and multinucleated giant cells, lacking true endothelial lining. Cytogenetic analysis is most likely to show an abnormality in which gene?

. USP6
. RUNX2
. SH3BP2
. SOX9
. PTHLH

Correct Answer & Explanation

. USP6

Explanation

Primary aneurysmal bone cysts (ABCs) are characterized by a recurring t(16;17) translocation that causes upregulation of the USP6 gene. The classic histology for an ABC is blood-filled spaces lacking a true endothelial lining.

Question 14837

Topic: Biology, Genetics & Bone Healing
A 4-year-old girl with osteogenesis imperfecta type III has sustained multiple extremity fractures. Medical management to reduce fracture incidence and improve bone mineral density should primarily involve which of the following agents?
. Teriparatide
. Intravenous bisphosphonates
. Denosumab
. Recombinant human growth hormone
. Calcitonin

Correct Answer & Explanation

. Intravenous bisphosphonates

Explanation

Intravenous bisphosphonates (e.g., pamidronate) are the standard medical therapy for moderate to severe osteogenesis imperfecta in children. They inhibit osteoclast activity, increase bone mineral density, and reduce fracture rates.

Question 14838

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy with a history of recurrent fractures, hepatosplenomegaly, and anemia is diagnosed with osteopetrosis. The primary cellular defect in this condition is characterized by:

. Failure of osteoblast differentiation
. Defective osteoclast resorption due to absent ruffled borders
. Overproduction of structurally abnormal type I collagen
. Excessive production of woven bone
. Mutation in the FGFR3 gene inhibiting chondrocyte proliferation

Correct Answer & Explanation

. Defective osteoclast resorption due to absent ruffled borders

Explanation

Osteopetrosis results from impaired osteoclast function, often due to an inability to acidify Howship's lacunae (lack of a ruffled border). This leads to dense, brittle bones and marrow obliteration causing extramedullary hematopoiesis.

Question 14839

Topic: Biology, Genetics & Bone Healing

A newborn infant is noted to have very dense, thick bones on a skeletal survey, with a "bone-in-bone" appearance. The parents are informed the child may require a bone marrow transplant. What is the primary cellular defect in this condition?

. Decreased osteoblast proliferation
. Defective osteoclast ruffled border sealing zone
. Increased osteocyte apoptosis
. Impaired collagen cross-linking
. Hyperactive osteoclasts

Correct Answer & Explanation

. Defective osteoclast ruffled border sealing zone

Explanation

Osteopetrosis is caused by defective osteoclastic bone resorption, frequently due to mutations in carbonic anhydrase II or TCIRG1. This results in failure to form a functional ruffled border and acidify the resorption pit, leading to dense but brittle bones.

Question 14840

Topic: Biology, Genetics & Bone Healing

A 7-year-old girl is evaluated for delayed dental eruption and abnormal shoulder mobility. Physical examination reveals the ability to approximate her shoulders anteriorly in the midline. Radiographs show absent clavicles and delayed closure of cranial sutures. Which transcription factor is primarily defective in this syndrome?

. SOX9
. COMP
. RUNX2 (CBFA1)
. GLI3
. SHH

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant disorder caused by a mutation in the RUNX2 (CBFA1) gene. This gene encodes a master transcription factor essential for osteoblast differentiation and membranous bone formation.

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