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1. General Principles & Basic Science MCQs

Practice Set 418 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 8341

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain. His temperature is 38.6 C (101.5 F), WBC count is 14,000/mm3, ESR is 45 mm/hr, and he refuses to bear weight. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?

. 3%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria include history of fever (>38.5 C), non-weight bearing, ESR >40 mm/hr, and WBC >12,000/mm3. Having all four predictors yields a >99% probability of septic arthritis.

Question 8342

Topic: Infection, Pharmacology & VTE

According to the Kocher criteria, which of the following is NOT one of the four classic predictors used to differentiate septic arthritis of the hip from transient synovitis in children?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate > 40 mm/hr
. C-reactive protein > 2.0 mg/dL
. White blood cell count > 12,000 cells/mm3
. Fever > 38.5 degrees C (101.3 degrees F)

Correct Answer & Explanation

. C-reactive protein > 2.0 mg/dL

Explanation

The original Kocher criteria include non-weight-bearing status, ESR > 40, WBC > 12,000, and Temp > 38.5C. CRP > 2.0 was later added by Caird to improve the predictive model but is not one of the original four.

Question 8343

Topic: 1. General Principles & Basic Science

A 7-year-old girl presents with a painless snapping sensation in her lateral knee. MRI reveals a completely discoid lateral meniscus without any tears or instability. What is the most appropriate management?

. Observation
. Partial meniscectomy
. Total meniscectomy
. Meniscal repair
. Saucerization of the meniscus

Correct Answer & Explanation

. Observation

Explanation

An asymptomatic or painlessly snapping discoid meniscus requires observation only. Surgical intervention is reserved for symptomatic tears or painful mechanical symptoms.

Question 8344

Topic: Infection, Pharmacology & VTE

An 8-year-old boy presents with a limp, fever, and refusal to bear weight on his right leg. Blood cultures are drawn and he is taken for aspiration and debridement of suspected acute hematogenous osteomyelitis. Which of the following organisms is the most common cause of this condition?

. Kingella kingae
. Streptococcus pyogenes
. Staphylococcus aureus
. Haemophilus influenzae
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus is the most common causative organism for acute hematogenous osteomyelitis across all pediatric age groups.

Question 8345

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of 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, WBC count is 13,000/mm3, and serum CRP is 2.5 mg/dL. According to the classic Kocher criteria, what is the approximate probability that this child has septic arthritis?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The child meets three of the four classic Kocher criteria (fever > 38.5 C, non-weight-bearing, ESR > 40, WBC > 12,000). The probability of septic arthritis with 3 criteria is approximately 93%.

Question 8346

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy with recurrent fractures, blue sclerae, and dentinogenesis imperfecta is initiated on intravenous pamidronate therapy. Which of the following best describes the primary mechanism of action of this medication in this patient?

. Stimulation of osteoblast differentiation and proliferation
. Inhibition of osteoclast-mediated bone resorption
. Enhancement of Type 1 collagen cross-linking
. Upregulation of runx2 expression in osteoprogenitor cells
. Inhibition of sclerostin leading to increased bone formation

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Bisphosphonates like pamidronate act primarily by inducing apoptosis in osteoclasts, thereby inhibiting osteoclast-mediated bone resorption. This increases overall bone mineral density and decreases fracture burden in patients with osteogenesis imperfecta.

Question 8347

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with profound lower extremity bowing. Laboratory testing reveals hypophosphatemia, elevated alkaline phosphatase, and normal serum calcium. Genetic testing confirms a mutation in the PHEX gene. The pathophysiology of his bone disease is primarily driven by an excess of which of the following?

. Parathyroid hormone (PTH)
. 1,25-dihydroxyvitamin D
. Fibroblast growth factor 23 (FGF23)
. Alkaline phosphatase
. Calcitonin

Correct Answer & Explanation

. Fibroblast growth factor 23 (FGF23)

Explanation

The patient has X-linked hypophosphatemic (XLH) rickets due to a PHEX mutation. This mutation leads to an overproduction of FGF23, which impairs renal phosphate reabsorption, causing hypophosphatemia and rickets.

Question 8348

Topic: Infection, Pharmacology & VTE

A 3-year-old boy presents with an inability to bear weight on his right leg, a temperature of 38.8 C, a WBC count of 14,000/mm3, and an ESR of 55 mm/hr. According to the Kocher criteria, what is the probability that this child has septic arthritis of the hip?

. 40%
. 71%
. 83%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The patient meets all four Kocher criteria: non-weight-bearing, temperature >38.5 C, WBC >12,000, and ESR >40. The presence of all four criteria carries a 99% probability of septic arthritis, necessitating urgent joint aspiration.

Question 8349

Topic: 1. General Principles & Basic Science

A 6-year-old boy presents with a painless "clunking" in his knee that occurs when transitioning from flexion to extension. MRI reveals a discoid meniscus. The Wrisberg variant of a discoid lateral meniscus is uniquely characterized by the absence of which of the following?

. Anterior horn attachment to the tibia
. Posterior meniscotibial capsular attachment
. Attachment to the meniscofemoral ligament
. Blood supply from the middle genicular artery
. Medial collateral ligament attachment

Correct Answer & Explanation

. Posterior meniscotibial capsular attachment

Explanation

The Wrisberg variant of a discoid meniscus lacks the normal posterior meniscotibial (coronary ligament) capsular attachment. This hypermobility causes the meniscus to snap into the intercondylar notch during extension, resulting in the classic 'snapping knee' syndrome.

Question 8350

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy with multiple recurrent fractures, blue sclerae, and dentinogenesis imperfecta is diagnosed with Osteogenesis Imperfecta (OI) type I. He is started on intravenous pamidronate. What is the primary mechanism of action of this medication in the treatment of OI?

. Stimulation of osteoblast proliferation and differentiation
. Enhancement of intestinal calcium absorption
. Promotion of enzymatic cross-linking of type I collagen
. Inhibition of osteoclast-mediated bone resorption
. Promotion of transforming growth factor-beta release

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Bisphosphonates, such as pamidronate, are the mainstay of medical therapy for moderate to severe Osteogenesis Imperfecta. They function by inhibiting osteoclast activity and inducing osteoclast apoptosis, thereby decreasing bone turnover and increasing bone mineral density.

Question 8351

Topic: Biology, Genetics & Bone Healing
A 6-year-old boy with Osteogenesis Imperfecta Type III is undergoing treatment with intravenous pamidronate. By what mechanism does this medication reduce fracture incidence?
. Stimulating osteoblast bone formation
. Inducing apoptosis of osteoclasts
. Increasing collagen type I synthesis
. Enhancing calcium absorption in the gut
. Promoting endochondral ossification

Correct Answer & Explanation

. Inducing apoptosis of osteoclasts

Explanation

Bisphosphonates like pamidronate accumulate in the bone matrix and are ingested by osteoclasts during resorption, inducing osteoclast apoptosis. This reduces bone turnover and increases bone density in patients with Osteogenesis Imperfecta.

Question 8352

Topic: 1. General Principles & Basic Science

An 8-year-old girl presents with a painful "snapping" knee. MRI reveals a completely discoid lateral meniscus with a peripheral tear and an absence of the posterior meniscofemoral ligament attachments. This represents which type of discoid meniscus?

. Incomplete
. Complete
. Wrisberg variant
. Bucket-handle tear
. Meniscal cyst

Correct Answer & Explanation

. Wrisberg variant

Explanation

The Wrisberg variant of a discoid lateral meniscus lacks the normal posterior capsular attachments, relying only on the meniscofemoral ligament of Wrisberg. This instability leads to the classic "snapping" knee presentation in young children.

Question 8353

Topic: 1. General Principles & Basic Science

A 3-year-old girl is brought to the emergency department for a sudden refusal to bear weight on her left leg. Her temperature is 38.8 C (101.8 F), her erythrocyte sedimentation rate (ESR) is 45 mm/hr, and her white blood cell (WBC) count is 14,500/mm3. She holds her hip in flexion, abduction, and external rotation. What is the most appropriate next step in management?

. MRI of the pelvis and left hip
. Intravenous antibiotics and observation
. Ultrasound-guided hip aspiration
. Corticosteroid injection into the hip joint
. Plain radiographs and discharge on oral antibiotics

Correct Answer & Explanation

. Ultrasound-guided hip aspiration

Explanation

This patient meets all four Kocher criteria (non-weight-bearing, fever >38.5 C, ESR >40, WBC >12,000) for a septic hip, giving a >99% probability of the diagnosis. Immediate ultrasound-guided hip aspiration and subsequent surgical drainage are indicated.

Question 8354

Topic: Biology, Genetics & Bone Healing

Intravenous bisphosphonates are a mainstay of medical management for children with moderate to severe Osteogenesis Imperfecta (OI). What is the primary mechanism of action of this medication class in altering the disease course?

. Stimulation of osteoblast proliferation and differentiation
. Inhibition of osteoclast-mediated bone resorption
. Direct augmentation of type I collagen cross-linking
. Prevention of primary osteoid mineralization
. Upregulation of endochondral ossification at the physis

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Bisphosphonates bind firmly to hydroxyapatite crystals in bone and potently inhibit osteoclast-mediated bone resorption. In OI, this allows bone formation to outpace resorption, leading to increased cortical thickness, greater bone mineral density, and decreased fracture rates.

Question 8355

Topic: 1. General Principles & Basic Science

A 6-year-old girl is brought in by her parents for a painless 'snapping' sound in her lateral knee when walking. She denies giving way, locking, or swelling. MRI confirms a completely intact, un-torn complete lateral discoid meniscus. What is the recommended treatment?

. Observation and reassurance
. Arthroscopic partial meniscectomy
. Arthroscopic saucerization without repair
. Arthroscopic saucerization and peripheral repair
. Total open meniscectomy

Correct Answer & Explanation

. Observation and reassurance

Explanation

An asymptomatic or painlessly snapping discoid meniscus is an incidental finding and should be treated with observation. Surgical intervention (saucerization with or without repair) is strictly indicated only when the meniscus is torn or causing painful mechanical symptoms.

Question 8356

Topic: Surgical Anatomy & Approaches

The Smith-Petersen (direct anterior) approach is frequently utilized for THA and pelvic procedures.

Which two muscles define the true superficial internervous plane of this surgical approach?

. Tensor fasciae latae and sartorius
. Gluteus medius and tensor fasciae latae
. Gluteus maximus and gluteus medius
. Sartorius and rectus femoris
. Pectineus and adductor longus

Correct Answer & Explanation

. Tensor fasciae latae and sartorius

Explanation

The superficial interval of the Smith-Petersen approach utilizes the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep interval is between the rectus femoris and gluteus medius.

Question 8357

Topic: 1. General Principles & Basic Science

A 40-year-old man who sustained a severe traumatic brain injury requires a THA for an un-reconstructable acetabular fracture.

Given his extremely high risk for heterotopic ossification (HO), what is the most effective prophylactic measure?

. Low-dose oral aspirin 81 mg daily for 6 weeks
. A single preoperative or early postoperative dose of 700 cGy external beam radiation
. Aggressive continuous passive motion (CPM) immediately post-op
. Therapeutic enoxaparin for 4 weeks
. Oral bisphosphonates for 6 months postoperatively

Correct Answer & Explanation

. A single preoperative or early postoperative dose of 700 cGy external beam radiation

Explanation

Patients with traumatic brain injuries or prior HO are at immense risk for ectopic bone formation. The most effective proven prophylaxis is localized external beam radiation (typically a single 700 cGy fraction given within 24 hours pre- or postoperatively) or a 6-week course of oral indomethacin.

Question 8358

Topic: Biomechanics & Biomaterials

The creation of highly cross-linked polyethylene (HXLPE) for THA involves irradiating the material. What is the primary purpose of post-irradiation thermal treatment (remelting or annealing) in the manufacturing process of HXLPE?

. To increase the ultimate tensile strength
. To reduce the generation of free radicals
. To increase the crystallinity of the polymer
. To increase the degree of cross-linking
. To make the material more hydrophilic

Correct Answer & Explanation

. To reduce the generation of free radicals

Explanation

Irradiation of polyethylene creates beneficial cross-links but also generates free radicals that can lead to in vivo oxidation and degradation. Post-irradiation thermal treatments extinguish these free radicals and improve long-term oxidative stability.

Question 8359

Topic: Biology, Genetics & Bone Healing
A 32-year-old man on chronic systemic corticosteroids presents with right hip pain. MRI reveals a crescent-shaped subchondral fracture in the superior femoral head, but plain radiographs only show patchy sclerosis without gross collapse. According to the modified Ficat classification, what is the stage and most appropriate joint-preserving recommendation?
. Stage I; Core decompression
. Stage II; Free vascularized fibular graft
. Stage III; Bisphosphonate therapy
. Stage III; Core decompression is no longer indicated
. Stage IV; Hip resurfacing

Correct Answer & Explanation

. Stage III; Core decompression is no longer indicated

Explanation

A subchondral fracture (crescent sign) indicates structural failure and defines Ficat Stage III osteonecrosis. Core decompression is typically indicated for pre-collapse (Stage I and II) disease and is generally ineffective once a subchondral fracture has occurred.

Question 8360

Topic: Biomechanics & Biomaterials
To significantly reduce the wear rate in total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is manufactured by subjecting ultra-high molecular weight polyethylene (UHMWPE) to gamma or electron-beam irradiation. What is the primary mechanical trade-off associated with increasing the irradiation dose?
. Increased susceptibility to oxidation over time
. Decreased fatigue resistance and ultimate tensile strength
. Increased elastic modulus leading to component stiffness
. Decreased volumetric wear but increased linear wear
. Increased melting point leading to difficult machining

Correct Answer & Explanation

. Decreased fatigue resistance and ultimate tensile strength

Explanation

While high doses of irradiation increase cross-linking and drastically reduce wear rates, the primary trade-off is a decrease in the material's mechanical properties, including fatigue resistance, ultimate tensile strength, and fracture toughness.

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