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1. General Principles & Basic Science MCQs

Practice Set 35 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 681

Topic: Biology, Genetics & Bone Healing

Multiple myeloma bone disease is characterized by uncoupled bone remodeling resulting in severe osteolytic lesions. Which of the following best describes the molecular mechanism responsible for osteoblast suppression in this condition?

. Overexpression of RANKL
. Inhibition of OPG
. Secretion of Dickkopf-1 (DKK-1)
. Production of parathyroid hormone-related peptide (PTHrP)
. Upregulation of transforming growth factor-beta (TGF-beta)

Correct Answer & Explanation

. Secretion of Dickkopf-1 (DKK-1)

Explanation

In multiple myeloma, osteoblast activity is severely suppressed primarily through the secretion of Dickkopf-1 (DKK-1) by myeloma cells, which inhibits the Wnt/beta-catenin signaling pathway. While RANKL drives osteoclast overactivity, DKK-1 is the key suppressor of bone formation.

Question 682

Topic: Surgical Anatomy & Approaches

Which adverse outcome is most common in adults undergoing periacetabular osteotomy for hip dysplasia:

. Sciatic nerve palsy
. Femoral nerve palsy
. Nonunion of the osteotomy
. Persistent or worsening joint pain
. Heterotopic ossification

Correct Answer & Explanation

. Persistent or worsening joint pain

Explanation

Heterotopic ossification occurs in fewer than 5% of patients undergoing various types of periacetabular osteotomy. Femoral nerve palsy and sciatic nerve palsy occur in only 1% to 2% of patients. Nonunion is rare in this region because of abundant cancellous bone contact. Persistent or worsening joint pain is the most frequent adverse outcome and is least common in those patients with preoperative degenerative changes.

Question 683

Topic: 1. General Principles & Basic Science

A 15-year-old girl has a snapping psoas tendon. Abducting and adducting her hip reproduces symptoms of anterior hip pain. Her pain has not been relieved by rest and stretching. The next step of treatment is:

. Excising the bursa
. Releasing the hip from the lesser trochanter
. Intramuscular lengthening of the tendon
. Transferring the psoas tendon to the neck of the femur
. Excising the pectineal eminence

Correct Answer & Explanation

. Intramuscular lengthening of the tendon

Explanation

The initial treatment of snapping psoas tendon is rest, antiinflammatory agents, and stretching. If symptoms remain significant, the next measure to offer the patient is intramuscular lengthening of the tendon.

Question 684

Topic: 1. General Principles & Basic Science

A 12-year-old boy presents with a painful, snapping knee. MRI reveals a Wrisberg variant of a discoid lateral meniscus. This specific variant is hypermobile because it lacks which of the following normal anatomical attachments?

. Anterior horn meniscotibial ligament
. Meniscofemoral ligament of Humphrey
. Posterior meniscotibial (coronary) ligament
. Transverse intermeniscal ligament
. Fibular collateral ligament

Correct Answer & Explanation

. Posterior meniscotibial (coronary) ligament

Explanation

The Wrisberg variant of the discoid lateral meniscus lacks the normal posterior meniscotibial (coronary) ligament attachments, making it highly mobile and prone to snapping.

Question 685

Topic: Infection, Pharmacology & VTE

A 4-year-old presents with fever, inability to bear weight on the right leg, a white blood cell count of 14,000/mm3, and an erythrocyte sedimentation rate (ESR) of 50 mm/hr. According to the Kocher criteria, what is the probability of septic arthritis?

. Less than 10%
. Approximately 40%
. Approximately 70%
. Greater than 90%
. 100%

Correct Answer & Explanation

. Greater than 90%

Explanation

The patient meets all 4 Kocher criteria (fever, non-weight-bearing, WBC >12,000, ESR >40). The probability of septic arthritis with 4 positive predictors is 93-99%.

Question 686

Topic: Infection, Pharmacology & VTE

A 2-year-old girl is brought to the emergency department with a limp, refusal to bear weight on the right leg, and a fever of 38.2 C. Aspiration of the hip yields purulent fluid. Given the patient's age and contemporary vaccination protocols, which of the following organisms is increasingly recognized as a leading cause of pediatric septic arthritis?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Neisseria gonorrhoeae
. Kingella kingae
. Haemophilus influenzae type b

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is now considered the most common bacterial cause of septic arthritis in children aged 6 to 36 months in areas with routine Hib and pneumococcal vaccination.

Question 687

Topic: 1. General Principles & Basic Science

An 8-year-old girl complains of a snapping sensation and lateral joint line pain in her right knee. MRI confirms a discoid lateral meniscus. The Wrisberg variant of a discoid meniscus is uniquely characterized by the absence of which of the following structures?

. Anterior horn attachment
. Posterior meniscofemoral ligament
. Posterior meniscotibial (coronary) ligament
. Transverse meniscal ligament
. Popliteomeniscal fascicles

Correct Answer & Explanation

. Posterior meniscotibial (coronary) ligament

Explanation

The Wrisberg variant of the discoid meniscus lacks the normal posterior meniscotibial (coronary) ligament attachments. It is hypermobile and tethered posteriorly only by the meniscofemoral ligament of Wrisberg.

Question 688

Topic: Infection, Pharmacology & VTE

When evaluating a pediatric patient with a painful hip, the classic Kocher criteria are used to differentiate septic arthritis from transient synovitis. Which of the following is NOT one of the original four parameters described by Kocher?

. History of fever greater than 38.5 C
. Inability to bear weight
. Erythrocyte sedimentation rate (ESR) greater than 40 mm/hr
. White blood cell count greater than 12,000 cells/mm3
. Joint space widening greater than 2mm on plain radiograph

Correct Answer & Explanation

. Joint space widening greater than 2mm on plain radiograph

Explanation

The four classic Kocher criteria are fever >38.5 C, non-weight-bearing status, ESR >40 mm/hr, and WBC >12,000 cells/mm3. Joint space widening on plain films is not part of this specific predictive model.

Question 689

Topic: Biology, Genetics & Bone Healing

A 2-year-old child with frequent fractures, blue sclerae, and dentinogenesis imperfecta is started on intravenous pamidronate. What is the primary mechanism of action of this pharmacological treatment?

. Stimulates osteoblast differentiation
. Inhibits osteoclast farnesyl pyrophosphate synthase
. Promotes type I collagen cross-linking
. Antagonizes the RANKL receptor
. Activates Wnt/beta-catenin signaling

Correct Answer & Explanation

. Inhibits osteoclast farnesyl pyrophosphate synthase

Explanation

Pamidronate is a nitrogen-containing bisphosphonate used in Osteogenesis Imperfecta to increase bone density and reduce fractures. It functions by inhibiting farnesyl pyrophosphate synthase in osteoclasts, leading to osteoclast apoptosis.

Question 690

Topic: Biology, Genetics & Bone Healing

Which of the following molecules is defective in osteogenesis imperfecta:

. Type I collagen
. Type II collagen
. C alcium transport channels
. Vitamin D 1,25-dihydroxylase
. Renal tubular reabsorption of phosphate

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta (OI) is a disorder of type I collagen. Numerous different mutations in the genes for this molecule have been described, accounting for the variable clinical phenotypes. Type II collagen is important for articular cartilage, but it is not implicated in the pathogenesis of OI. The other factors are not abnormal in OI.

Question 691

Topic: 1. General Principles & Basic Science

Regulation of proximal-to-distal development of the limbs is determined by which of the following:

. Fibroblast growth factor gene
. Homeobox genes
. Platelet-derived growth factor gene
. Leptin gene
. Sulfate transport gene

Correct Answer & Explanation

. Homeobox genes

Explanation

Proximal-to-distal development of the limbs in utero is determined by the homeobox genes. These genes are located on a number of different chromosomes (2, 7, 12, and 17), and they guide the proximal-to-distal organization of limb and digital development.

Question 692

Topic: Infection, Pharmacology & VTE

C hronic recurrent multifocal osteomyelitis is caused by which of the following:

. Staphylococcus epidermidis
. Corynebacterium
. Spirochetal infection
. Viral infection
. No organism has been isolated

Correct Answer & Explanation

. No organism has been isolated

Explanation

Chronic recurrent multifocal osteomyelitis presents as chronic joint pain at multiple locations and at different times. No organism has been isolated from patients presenting with chronic recurrent multifocal osteomyelitis. There is no role for surgery or antibiotics because symptoms generally resolve over a period of time.

Question 693

Topic: 1. General Principles & Basic Science

A 4-year-old girl with developmental hip dysplasia is advised to have a Salter innominate osteotomy. When the family asks about the long-term survivorship of the reconstruction, the surgeon tells them that good 30-year follow-up results are likely in at least what percentage of patients:

. 30%
. 50%
. 70%
. 85%
. 98%

Correct Answer & Explanation

. 85%

Explanation

Thirty-year survivorship analysis shows good to excellent results in at least 85% of patients.

Question 694

Topic: 1. General Principles & Basic Science

Which of the following statements best describes the effect of leptin on the skeleton:

. Leptin increases bone formation.
. Leptin increases muscle mass.
. Leptin decreases bone formation.
. Leptin decreases muscle mass.
. Leptin increases longitudinal growth.

Correct Answer & Explanation

. Leptin decreases bone formation.

Explanation

Leptin is a polypeptide secreted by adipocytes and acts upon the hypothalamus as a powerful inhibitor of bone mass.

Question 695

Topic: Infection, Pharmacology & VTE

Which of the following organisms is the most common cause of obturator internus muscle abscess in children:

. Streptococcus A
. Staphylococcus aureus
. Salmonella
. Escherichia coli
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Abscess of the obturator internus muscle may mimic septic arthritis. It is best diagnosed by magnetic resonance image. <1>Staphylococcus aureus is the most common causative organism, accounting for 75% of cases of obturator internus muscle abscess. Antibiotic treatment should be tried first and is successful in most cases.

Question 696

Topic: Infection, Pharmacology & VTE

Which of the following studies is likely to help in distinguishing osteomyelitis from infarct in a patient with sickle cell anemia:

. Magnetic resonance imaging
. C omputed tomography
. Bone and bone marrow scans
. Ultrasound
. Plain radiographs

Correct Answer & Explanation

. Bone and bone marrow scans

Explanation

The combination of bone and bone marrow scan is the only imaging method that is useful in distinguishing osteomyelitis from infarct in patients with sickle cell anemia. The bone marrow scan is normal, but the bone scan shows increased uptake in a patient with osteomyelitis.

Question 697

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with acute atraumatic 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 WBC count is 13,500/mm3. According to the Kocher criteria, what is the approximate probability that this patient has septic arthritis rather than transient synovitis?

. 15%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria include non-weight-bearing status, temperature >38.5 C, ESR >40 mm/hr, and WBC >12,000/mm3. The presence of all four criteria indicates an approximate 99% probability of septic arthritis.

Question 698

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with right hip pain and a limp. According to the Kocher criteria, which set of findings yields the highest probability of septic arthritis?

. Non-weight-bearing, ESR > 40 mm/hr, fever > 38.5 C, and WBC > 12,000/mm3
. Weight-bearing with a limp, normal ESR, fever > 39.0 C, normal WBC
. Non-weight-bearing, normal ESR, no fever, WBC > 15,000/mm3
. Knee pain, ESR > 20 mm/hr, fever > 38.0 C, WBC > 10,000/mm3
. Groin pain, ESR > 10 mm/hr, afebrile, CRP > 1.0 mg/dL

Correct Answer & Explanation

. Non-weight-bearing, ESR > 40 mm/hr, fever > 38.5 C, and WBC > 12,000/mm3

Explanation

The Kocher criteria for septic arthritis of the hip include non-weight-bearing, ESR > 40 mm/hr, fever > 38.5 C, and WBC > 12,000/mm3. Having all four criteria gives a 99% probability of septic arthritis.

Question 699

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy with multiple fragility fractures and blue sclerae is diagnosed with osteogenesis imperfecta. Which pharmacological therapy is the current standard of care to decrease fracture frequency and improve bone mineral density?

. Teriparatide
. Denosumab
. Intravenous bisphosphonates (e.g., pamidronate)
. Recombinant human growth hormone
. Calcitonin

Correct Answer & Explanation

. Intravenous bisphosphonates (e.g., pamidronate)

Explanation

Intravenous bisphosphonates, such as pamidronate, inhibit osteoclast activity. They have been shown to significantly reduce fracture rates and increase bone density in children with osteogenesis imperfecta.

Question 700

Topic: 1. General Principles & Basic Science

A newborn presents with short-limbed dwarfism, bilateral "hitchhiker" thumbs, cauliflower ears, and severe rigid clubfeet. What is the mode of inheritance for this condition?

. Autosomal dominant
. Autosomal recessive
. X-linked recessive
. X-linked dominant
. Mitochondrial

Correct Answer & Explanation

. Autosomal recessive

Explanation

The clinical presentation describes diastrophic dysplasia, which is caused by a defect in the SLC26A2 sulfate transporter. It is inherited in an autosomal recessive manner.

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