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1. General Principles & Basic Science MCQs

Practice Set 759 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 15161

Topic: 1. General Principles & Basic Science

Which of the following laboratory profiles is most characteristic of an untreated patient with primary hyperparathyroidism?

. High calcium, low phosphorus, high PTH
. Low calcium, high phosphorus, high PTH
. Low calcium, low phosphorus, high PTH
. High calcium, high phosphorus, low PTH
. Normal calcium, normal phosphorus, high alkaline phosphatase

Correct Answer & Explanation

. High calcium, low phosphorus, high PTH

Explanation

Primary hyperparathyroidism is typically caused by a solitary parathyroid adenoma, resulting in autonomously elevated PTH, hypercalcemia, and hypophosphatemia. In contrast, secondary hyperparathyroidism from chronic kidney disease features low or normal calcium and high phosphorus.

Question 15162

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman with active Paget's disease of the right hemipelvis and femur is scheduled for a total hip arthroplasty due to severe secondary osteoarthritis. Which preoperative pharmacological intervention is highly recommended to reduce intraoperative blood loss?

. Denosumab
. Preoperative irradiation
. Intravenous bisphosphonates
. Teriparatide
. Methotrexate

Correct Answer & Explanation

. Intravenous bisphosphonates

Explanation

Pagetic bone is highly vascular during the active mixed phases, which can lead to life-threatening intraoperative hemorrhage during orthopedic procedures. Preoperative administration of bisphosphonates reduces bone turnover and vascularity, thereby significantly decreasing surgical blood loss.

Question 15163

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with right hip pain and a limp. He refuses to bear weight. His temperature is 38.8°C (101.8°F), ESR is 45 mm/hr, and peripheral WBC count is 14,000/mm³. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 10%
. 40%
. 70%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for pediatric septic arthritis of the hip include non-weight-bearing, fever > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm³. The presence of all four predictors indicates an approximate 99% probability of septic arthritis.

Question 15164

Topic: Infection, Pharmacology & VTE

A 68-year-old male presents with a painful, swollen great toe. Radiographs demonstrate punched-out periarticular erosions with overhanging edges.

Synovial fluid analysis of the affected joint is most likely to reveal which of the following?

. Positively birefringent, rhomboid-shaped crystals
. Negatively birefringent, needle-shaped crystals
. Gram-positive cocci in clusters
. Non-birefringent, envelope-shaped crystals
. Positively birefringent, needle-shaped crystals

Correct Answer & Explanation

. Negatively birefringent, needle-shaped crystals

Explanation

The clinical and radiographic presentation is classic for gout. Synovial fluid analysis in gout reveals monosodium urate crystals, which are needle-shaped and strongly negatively birefringent under polarized light.

Question 15165

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with enlarging hat size, hearing loss, and bowing of the tibiae. Laboratory evaluation reveals an isolated, markedly elevated alkaline phosphatase with normal serum calcium and phosphorus. What is the primary cellular abnormality initiating this disease process?

. Defect in SQSTM1/p62 affecting osteoclasts
. Defect in osteoblast mineralization
. Abnormal collagen type I synthesis
. Parathyroid hormone receptor mutation
. Fibroblast growth factor receptor 3 (FGFR3) mutation

Correct Answer & Explanation

. Defect in SQSTM1/p62 affecting osteoclasts

Explanation

Paget's disease is initiated by intense, disorganized osteoclastic bone resorption, often linked to SQSTM1 (p62) mutations. This is followed by a compensatory but chaotic increase in osteoblastic bone formation.

Question 15166

Topic: Biology, Genetics & Bone Healing

A 68-year-old male with symptomatic Paget's disease of the right hip is scheduled for a total hip arthroplasty due to severe secondary osteoarthritis. To minimize severe intraoperative hemorrhage, which medical management is recommended prior to surgery?

. Methotrexate
. Denosumab
. Teriparatide
. Zoledronic acid
. Allopurinol

Correct Answer & Explanation

. Zoledronic acid

Explanation

Preoperative administration of bisphosphonates (like zoledronic acid) is recommended prior to elective surgery in Pagetoid bone. This effectively decreases the intense vascularity of the bone and reduces intraoperative blood loss.

Question 15167

Topic: Biology, Genetics & Bone Healing

In a patient diagnosed with asymptomatic Paget's disease incidentally on radiographs, which of the following represents an absolute indication for initiating bisphosphonate therapy?

. Moderately elevated alkaline phosphatase alone
. Advanced age over 80
. Involvement of a weight-bearing bone prior to scheduled orthopedic surgery
. Presence of cotton-wool exudates on skull x-ray
. Sclerotic phase of the disease on imaging

Correct Answer & Explanation

. Involvement of a weight-bearing bone prior to scheduled orthopedic surgery

Explanation

Treatment for asymptomatic Paget's disease is generally reserved for patients preparing for orthopedic surgery at involved sites to decrease vascularity. It is also indicated if there is involvement of weight-bearing bones at high risk of fracture or skull involvement threatening hearing.

Question 15168

Topic: 1. General Principles & Basic Science

A 55-year-old male presents with acute, severe pain, swelling, and erythema of the first metatarsophalangeal joint. Joint aspiration is performed. What is the expected crystal analysis result under polarized light microscopy?

. Positively birefringent rhomboid crystals
. Negatively birefringent needle-shaped crystals
. Non-birefringent envelope-shaped crystals
. Positively birefringent needle-shaped crystals
. Negatively birefringent rhomboid crystals

Correct Answer & Explanation

. Negatively birefringent needle-shaped crystals

Explanation

Acute gout is characterized by the deposition of monosodium urate crystals in the joint. Under polarized light microscopy, these appear as negatively birefringent, needle-shaped crystals.

Question 15169

Topic: Biology, Genetics & Bone Healing

A 60-year-old male has a history of recurrent joint pain. Radiographs of his hands demonstrate periarticular erosions with overhanging sclerotic margins and preserved joint spaces.

What is the primary etiology of this disease process?

. Autoimmune destruction of articular cartilage
. Calcium pyrophosphate deposition
. Monosodium urate crystal deposition
. Abnormal osteoclast activation
. Parathyroid adenoma

Correct Answer & Explanation

. Monosodium urate crystal deposition

Explanation

The radiographic findings of "rat-bite" erosions with overhanging margins and relatively preserved joint spaces are hallmark signs of chronic tophaceous gout. This is caused by prolonged monosodium urate deposition.

Question 15170

Topic: Infection, Pharmacology & VTE

A patient with an acute gout flare is evaluated in the emergency department. He has a history of severe chronic kidney disease (Stage IV). Which of the following is the most appropriate initial treatment for his acute flare?

. Indomethacin
. Allopurinol
. Intra-articular or systemic corticosteroids
. High-dose colchicine
. Probenecid

Correct Answer & Explanation

. Intra-articular or systemic corticosteroids

Explanation

In patients with severe chronic kidney disease, NSAIDs and colchicine are generally contraindicated due to toxicity risks. Corticosteroids (intra-articular or systemic) are the safest and most effective option for acute flares in this population.

Question 15171

Topic: Biology, Genetics & Bone Healing

A 45-year-old female with chronic renal failure complains of diffuse bone pain. Laboratory evaluation shows elevated parathyroid hormone (PTH), low serum calcium, and high serum phosphate. Radiographs show subperiosteal resorption in the phalanges. What is the most likely diagnosis?

. Primary hyperparathyroidism
. Secondary hyperparathyroidism
. Tertiary hyperparathyroidism
. Paget's disease
. Osteomalacia

Correct Answer & Explanation

. Secondary hyperparathyroidism

Explanation

Secondary hyperparathyroidism is common in chronic kidney disease and is characterized by elevated PTH in response to hypocalcemia and hyperphosphatemia. Subperiosteal resorption on the radial aspect of the middle phalanges is pathognomonic.

Question 15172

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a sudden onset limp and refuses to bear weight on his right leg. He has a temperature of 38.8 C. Labs show an ESR of 45 mm/h and a WBC count of 13,500/mm3. According to the Kocher criteria, what is the probability that he has septic arthritis of the hip?

. 40%
. 71%
. 93%
. 99%
. 100%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for pediatric septic hip include: non-weight-bearing, temperature >38.5 C, ESR >40 mm/h, and WBC >12,000/mm3. The presence of all 4 criteria yields a 99% predicted probability of septic arthritis.

Question 15173

Topic: Infection, Pharmacology & VTE

A 3-week-old neonate in the NICU develops swelling of the left thigh and pseudoparalysis of the left leg. The hip is held in flexion, abduction, and external rotation.

What is the most common causative organism for this condition in this age group?

. Streptococcus pyogenes
. Neisseria gonorrhoeae
. Staphylococcus aureus
. Kingella kingae
. Haemophilus influenzae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus is the most common cause of pediatric septic arthritis across all age groups, including neonates. Group B Streptococcus and Gram-negative bacilli are also important pathogens in the neonatal period.

Question 15174

Topic: Surgical Anatomy & Approaches

A delay in the surgical drainage of septic coxitis in an infant can lead to devastating sequelae due to increased intra-articular pressure and bacterial chondrolysis. Which of the following structures is at highest immediate risk of irreversible ischemic necrosis?

. The acetabular labrum
. The capital femoral epiphysis
. The greater trochanteric apophysis
. The ligamentum teres
. The femoral nerve

Correct Answer & Explanation

. The capital femoral epiphysis

Explanation

The hip joint is entirely intra-articular, and increased purulent effusion raises intra-articular pressure, compromising the delicate retinacular vessels. This leads to avascular necrosis of the capital femoral epiphysis and profound joint destruction.

Question 15175

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with active Paget's disease is treated with zoledronic acid. What is the primary cellular mechanism of action of this medication?

. Stimulation of osteoblast differentiation via Wnt signaling
. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Binding to RANK ligand to prevent osteoclast activation
. Direct inhibition of parathyroid hormone secretion
. Inhibition of cyclooxygenase-2

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts

Explanation

Nitrogen-containing bisphosphonates (like zoledronic acid) act by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts osteoclast function and promotes osteoclast apoptosis.

Question 15176

Topic: Infection, Pharmacology & VTE

A 6-year-old child presents with atraumatic hip pain and fever. An ultrasound is performed, which reveals an asymmetry in the anterior capsular distance of 3 mm compared to the contralateral hip. Which of the following is the most appropriate next step to confirm the diagnosis?

. Immediate empiric intravenous antibiotics
. Ultrasound-guided hip aspiration
. MRI of the pelvis without contrast
. Bone scintigraphy
. Observation and repeat ultrasound in 48 hours

Correct Answer & Explanation

. Ultrasound-guided hip aspiration

Explanation

An anterior capsular distance asymmetry of >2 mm on ultrasound indicates a significant hip effusion. Ultrasound-guided aspiration is the definitive diagnostic step to differentiate septic arthritis from transient synovitis via cell count, Gram stain, and culture.

Question 15177

Topic: 1. General Principles & Basic Science

A patient with refractory secondary hyperparathyroidism due to end-stage renal disease requires medical optimization. Which of the following medications functions as a calcimimetic to directly lower PTH levels?

. Calcitriol
. Sevelamer
. Cinacalcet
. Denosumab
. Teriparatide

Correct Answer & Explanation

. Cinacalcet

Explanation

Cinacalcet is a calcimimetic agent that increases the sensitivity of the calcium-sensing receptors on the parathyroid gland. This tricks the gland into detecting higher serum calcium levels, thereby reducing PTH secretion.

Question 15178

Topic: 1. General Principles & Basic Science

A 55-year-old man presents with an acute, exquisitely tender, swollen first metatarsophalangeal joint. Joint aspiration yields cloudy fluid. Which of the following best describes the microscopic appearance of the crystals pathognomonic for this condition?

. Weakly positively birefringent rhomboid crystals
. Strongly negatively birefringent needle-shaped crystals
. Non-birefringent envelope-shaped crystals
. Positively birefringent bipyramidal crystals
. Negatively birefringent square crystals

Correct Answer & Explanation

. Strongly negatively birefringent needle-shaped crystals

Explanation

Gout is characterized by monosodium urate crystals, which appear as strongly negatively birefringent, needle-shaped crystals under polarized light microscopy. Positively birefringent rhomboid crystals are indicative of pseudogout.

Question 15179

Topic: Biology, Genetics & Bone Healing

A 48-year-old woman with end-stage renal disease presents with diffuse bone pain. Radiographs of her hands reveal pathognomonic subperiosteal bone resorption on the radial aspect of the middle phalanges. What are the expected serum laboratory findings in this patient?

. High calcium, low phosphorus, high PTH
. Normal or low calcium, high phosphorus, high PTH
. Low calcium, low phosphorus, low PTH
. High calcium, high phosphorus, low PTH
. Normal calcium, normal phosphorus, high PTH

Correct Answer & Explanation

. Normal or low calcium, high phosphorus, high PTH

Explanation

This patient has secondary hyperparathyroidism due to renal osteodystrophy. The kidneys fail to excrete phosphorus and activate Vitamin D, leading to hyperphosphatemia, hypocalcemia, and a compensatory hypersecretion of PTH.

Question 15180

Topic: Biology, Genetics & Bone Healing

A 65-year-old man is incidentally diagnosed with a thickened calvarium and bowing of the tibia. His serum alkaline phosphatase is significantly elevated, but calcium and phosphate are normal. If a biopsy of the affected bone were performed, what would be the characteristic histological finding?

. Woven bone lacking osteoblasts
. Mosaic pattern of lamellar bone with prominent cement lines
. Empty lacunae with necrotic marrow
. Sheets of atypical plasma cells
. Benign cartilage with enchondral ossification

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

The hallmark histological feature of the mixed and sclerotic phases of Paget's disease is a "mosaic" or "jigsaw puzzle" pattern of lamellar bone. This is caused by rapid, haphazard bone resorption and formation, leaving prominent cement lines.

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