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1. General Principles & Basic Science MCQs

Practice Set 32 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 621

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with severe varus bowing of the lower extremities, short stature, and a waddling gait. Laboratory studies reveal normal serum calcium, markedly low serum phosphate, and elevated alkaline phosphatase. Which of the following is the hallmark molecular pathogenesis?

. Vitamin D receptor insensitivity
. Excessive FGF23 production
. Deficiency of 1-alpha-hydroxylase
. Dietary calcium deficiency
. Inactivating mutation of the calcium-sensing receptor

Correct Answer & Explanation

. Excessive FGF23 production

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation leading to elevated FGF23 levels. FGF23 causes profound renal phosphate wasting and inhibits calcitriol synthesis, leading to rickets that does not respond to standard vitamin D supplementation.

Question 622

Topic: Biology, Genetics & Bone Healing

A 9-year-old girl is noted to have excessive mobility of her shoulders, allowing them to touch in the midline. Pelvic radiographs would most likely reveal which of the following abnormalities?

. Severe protrusion acetabuli
. Wide pubic symphysis
. Bilateral hip dislocations
. Slipped capital femoral epiphysis
. Acetabular osteophytes

Correct Answer & Explanation

. Wide pubic symphysis

Explanation

The patient has Cleidocranial Dysplasia, caused by a RUNX2 mutation affecting intramembranous ossification. Key radiographic findings include hypoplastic or absent clavicles, delayed cranial suture closure, and a significantly widened pubic symphysis.

Question 623

Topic: 1. General Principles & Basic Science

A newborn presents with short-limbed dwarfism, "cauliflower" ears, hitchhiker thumbs, and severe rigid clubfeet. This condition is caused by a mutation in a gene responsible for transporting which of the following?

. Calcium
. Phosphate
. Sulfate
. Type I collagen
. Fibroblast growth factor

Correct Answer & Explanation

. Sulfate

Explanation

The patient has diastrophic dysplasia, which is caused by a defect in the SLC26A2 gene. This gene encodes a diastrophic dysplasia sulfate transporter (DTDST), leading to defective sulfation of proteoglycans.

Question 624

Topic: Biology, Genetics & Bone Healing
A patient with severe Osteogenesis Imperfecta (Type III) has been receiving intravenous bisphosphonate therapy. What is the primary cellular mechanism of action for this class of medication?
. Stimulation of osteoblast proliferation and differentiation
. Inhibition of osteoclast apoptosis
. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Upregulation of RANK ligand on osteoblasts
. Inhibition of sclerostin leading to increased bone formation

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts

Explanation

Nitrogen-containing bisphosphonates (like pamidronate) inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents proper protein prenylation in osteoclasts, leading to early apoptosis and reduced bone resorption.

Question 625

Topic: Biology, Genetics & Bone Healing

Which of the following combined clinical features is pathognomonic for Cleidocranial Dysplasia?

. Blue sclerae and brittle bones
. Cafe-au-lait spots and precocious puberty
. Delayed closure of cranial sutures and absent clavicles
. Arachnodactyly and superior lens dislocation
. Stippled epiphyses and flat midface

Correct Answer & Explanation

. Delayed closure of cranial sutures and absent clavicles

Explanation

Cleidocranial dysplasia (RUNX2 gene mutation) is classically characterized by delayed or absent closure of the cranial fontanelles, hypoplastic or absent clavicles, and retained deciduous teeth.

Question 626

Topic: 1. General Principles & Basic Science

A 2-year-old girl is noted to have an abnormal intoeing gait. Examination reveals severe femoral anteversion and internal tibial torsion. What is the typical natural history of this combination of rotational deformities?

. They will progressively worsen requiring early derotational osteotomies
. Femoral anteversion will resolve, but tibial torsion will strictly require bracing
. Spontaneous resolution typically occurs by age 8 to 10 years
. Early onset osteoarthritis of the knee by age 20 is inevitable
. Development of severe genu varum leading to joint degeneration

Correct Answer & Explanation

. Spontaneous resolution typically occurs by age 8 to 10 years

Explanation

Increased femoral anteversion and internal tibial torsion in a toddler generally improve spontaneously with normal skeletal growth. They typically resolve without surgical or orthotic intervention by age 8 to 10 years.

Question 627

Topic: 1. General Principles & Basic Science

A 5-year-old girl is brought to the emergency department because of fever and inability to walk. Her temperature is 100.5° F. She has pain with rotation of the hip. However, if the movement is done slowly, the hip can be rotated internally and externally 45°. Her white blood cell count is 13,000 (upper normal is 12,500 for her age). Her erythrocyte sedimentation rate is 30. Radiographs of the pelvis and hip are normal. You recommend:

. Bed rest with follow-up contact the next day
. Ultrasound of the hip
. Hip aspiration
. Magnetic resonance imaging
. Irrigation and drainage of the hip

Correct Answer & Explanation

. Bed rest with follow-up contact the next day

Explanation

The scenario described above is most consistent with transient synovitis of the hip. Because range of motion is tolerated when performed slowly; it is compatible with a diagnosis of transient synovitis of the hip more than infection. Rest, with or without anti-inflammatory medicine, should produce a dramatic improvement by the next day.

Question 628

Topic: 1. General Principles & Basic Science

Which of the following factors is least likely to predispose a patient to patellar instability:

. Genu varum
. Excessive femoral anteversion
. Patella alta
. External tibial torsion
. Hypoplastic lateral femoral trochlear ridge

Correct Answer & Explanation

. Genu varum

Explanation

Genu varum does not predispose a patient to patellar instability. However, genu valgum, as well as all of the other factors listed above, may predispose a patient to this condition.

Question 629

Topic: 1. General Principles & Basic Science

A 15-year-old girl twists her knee while skiing. She is diagnosed with a patellar dislocation. She has had no prior episodes. Radiographs show the dislocation but no other findings. After reducing the dislocation, you recommend:

. Knee immobilization for 2 to 3 weeks
. Long-leg cast for 6 weeks
. Repair of the medial patellofemoral ligament
. Tibial tubercle transfer
. Proximal realignment

Correct Answer & Explanation

. Knee immobilization for 2 to 3 weeks

Explanation

Acute traumatic patellofemoral dislocations are best treated by brief immobilization followed by early rehabilitation. Surgery is reserved for patients with multiple recurrences that cause significant disability.

Question 630

Topic: Biology, Genetics & Bone Healing

A 20-month-old toddler is brought in because of bowed legs. You note moderate-to-severe genu varum and thigh-foot angles of 35° inward. The child is otherwise healthy, and height and weight are near the 50th percentiles. Radiographs demonstrate tibial metaphyseal-diaphyseal angles of 8° on the right and 9° on the left. Femoral metaphyseal-diaphyseal angles are the same. You recommend:

. Observation, with return only if not improving
. Measurement of electrolytes, alkaline phosphatase, and vitamin D levels
. Serial casting until straight
. Bracing in knee-ankle-foot orthoses
. Osteotomies of the proximal tibias

Correct Answer & Explanation

. Observation, with return only if not improving

Explanation

This child has physiologic genu varum. Only if the metaphyseal-diaphyseal angles were greater than 11° would additional followup be indicated, with possible bracing. Blood tests would be indicated if the bone quality showed evidence of Rickets or if the child was below the 10th percentile in height.

Question 631

Topic: 1. General Principles & Basic Science

Which of the following agents is used to reverse the effects of midazolam:

. Naloxone
. Naltrexone
. Flumazenil
. Fentanyl
. Atropine

Correct Answer & Explanation

. Flumazenil

Explanation

Flumazenil (reversed) is used to reverse the effects of benzodiazepines. Flumazenil has a shorter duration of action than benzodiazepines, so it may need to be readministered. Flumazenil can also precipitate seizures.

Question 632

Topic: 1. General Principles & Basic Science

An adult man with hemophilia A has just announced the birth of his first son. His wife does not have the disease. What is the chance that the newborn has the disorder:

. 100%
. 50%
. 25%
. 10%
. Less than 1%

Correct Answer & Explanation

. Less than 1%

Explanation

Hemophilia A is an X-linked disorder. Therefore, there is no father-son transmission. The chance that the newborn is affected equals that of the general population, which is less than 1%.

Question 633

Topic: Infection, Pharmacology & VTE

In the evaluation of a pediatric patient with an irritable hip, which of the following is NOT one of the original Kocher criteria used to differentiate septic arthritis from transient synovitis?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate (ESR) greater than 40 mm/hr
. Fever greater than 38.5 degrees Celsius
. Serum C-reactive protein (CRP) greater than 20 mg/L
. White blood cell count (WBC) greater than 12,000 cells/mm3

Correct Answer & Explanation

. Serum C-reactive protein (CRP) greater than 20 mg/L

Explanation

The original four Kocher criteria are non-weight-bearing, ESR >40, fever >38.5°C, and WBC >12,000. CRP >20 mg/L was later identified as an excellent independent predictor, but it was not part of the original Kocher criteria.

Question 634

Topic: 1. General Principles & Basic Science

A 9-year-old girl sustains a twisting injury to her knee. She complains of a snapping sensation on the lateral side of the knee. MRI demonstrates a discoid lateral meniscus with normal peripheral attachments. What is the most appropriate treatment if she is symptomatic?

. Observation and physical therapy
. Total meniscectomy
. Saucerization of the meniscus
. Saucerization and peripheral repair
. Anterior horn meniscal repair

Correct Answer & Explanation

. Saucerization of the meniscus

Explanation

Symptomatic incomplete or complete discoid menisci with intact peripheral attachments are treated with arthroscopic saucerization to create a stable, more anatomically shaped meniscus. Peripheral repair is added only if a peripheral tear or instability (like the Wrisberg variant) is present.

Question 635

Topic: Infection, Pharmacology & VTE

A 3-year-old boy refuses to bear weight on his right leg. His temperature is 38.8°C (101.8°F), ESR is 55 mm/hr, WBC is 14,000/mm3, and plain radiographs of the right hip are normal. Joint aspiration yields purulent fluid. What is the most critical immediate intervention?

. Intravenous antibiotics and observation
. Urgent surgical irrigation and debridement of the hip joint
. Serial aspirations of the hip joint
. MRI of the pelvis with contrast
. Application of a spica cast

Correct Answer & Explanation

. Urgent surgical irrigation and debridement of the hip joint

Explanation

Septic arthritis of the hip in a pediatric patient is a surgical emergency. Urgent open or arthroscopic irrigation and debridement is required to decompress the joint, remove purulent material, and prevent avascular necrosis and cartilage destruction.

Question 636

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain and a limp. He is afebrile (37.2 degrees C), WBC is 10,500/mm3, ESR is 15 mm/hr, and he can bear weight with a limp. He refuses internal rotation of the hip. What is the most appropriate next step in management?

. Immediate surgical irrigation and debridement
. Ultrasound-guided hip aspiration
. Observation and administration of NSAIDs
. Intravenous antibiotics
. MRI of the pelvis with contrast

Correct Answer & Explanation

. Observation and administration of NSAIDs

Explanation

The patient has 0 out of 4 Kocher criteria (fever >38.5 C, non-weight bearing, ESR >40, WBC >12,000), making septic arthritis highly unlikely. The most likely diagnosis is transient synovitis, which is treated supportively with NSAIDs and observation.

Question 637

Topic: Infection, Pharmacology & VTE

A 4-year-old boy refuses to bear weight on his right leg. He has a temperature of 38.5 degrees C, ESR of 45 mm/hr, WBC of 13,000/mm3, and refuses to move his hip. According to the Kocher criteria, what is the approximate probability he has septic arthritis rather than transient synovitis?

. 5%
. 40%
. 71%
. 99%
. 100%

Correct Answer & Explanation

. 99%

Explanation

This patient has 4 Kocher criteria: non-weight-bearing, temperature >38.5 C, ESR >40, and WBC >12,000. The presence of 4 criteria predicts a 99% probability of septic arthritis, distinguishing it from transient synovitis.

Question 638

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain, a temperature of 38.8°C (101.8°F), an inability to bear weight, a WBC count of 14,000/mm3, and an ESR of 50 mm/hr. What is the most appropriate next step in management?

. Intravenous antibiotics and observation
. MRI of the right hip
. Ultrasound-guided aspiration of the right hip
. Bone scintigraphy
. Surgical drainage without aspiration

Correct Answer & Explanation

. Ultrasound-guided aspiration of the right hip

Explanation

The patient has 4 out of 4 Kocher criteria, yielding a 99% probability of septic arthritis. Immediate joint aspiration is the gold standard for definitive diagnosis before initiating antibiotic therapy.

Question 639

Topic: 1. General Principles & Basic Science

A 6-year-old girl presents with a painless, snapping sensation in her lateral knee during flexion and extension. MRI confirms an incomplete lateral discoid meniscus without a tear. What is the most appropriate management?

. Total meniscectomy
. Partial meniscectomy (saucerization)
. Observation and reassurance
. Meniscal repair
. Arthroscopic release of the meniscofemoral ligament

Correct Answer & Explanation

. Observation and reassurance

Explanation

Asymptomatic or mildly symptomatic (painless snapping) discoid menisci without tears should be managed non-operatively with observation. Surgical intervention (saucerization) is reserved for torn or persistently painful discoid menisci.

Question 640

Topic: Biology, Genetics & Bone Healing

A 3-year-old girl presents with progressive bilateral bowlegs. Radiographs reveal varus deformity localized to the proximal tibia with a metaphyseal-diaphyseal angle (Drennan's angle) of 18 degrees. What does this finding indicate?

. Physiologic bowing that will spontaneously resolve
. High likelihood of progression to infantile Blount disease
. Vitamin D deficiency rickets
. Achondroplasia
. Normal alignment for her age

Correct Answer & Explanation

. High likelihood of progression to infantile Blount disease

Explanation

A metaphyseal-diaphyseal angle greater than 16 degrees on an AP radiograph strongly indicates a high risk of progression to infantile Blount disease. Angles less than 11 degrees are typically consistent with physiologic bowing.

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