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1. General Principles & Basic Science MCQs

Practice Set 770 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 15381

Topic: 1. General Principles & Basic Science

A 12-year-old boy is evaluated for recent-onset back pain and short stature. Radiographs demonstrate narrowed intervertebral disc spaces and a barrel-shaped chest. Spondyloepiphyseal Dysplasia Tarda (SEDT) is suspected. What is the mode of inheritance for the most common form of this disease?

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

Correct Answer & Explanation

. X-linked recessive

Explanation

The most common form of SEDT is X-linked recessive, primarily affecting males in late childhood. It is caused by mutations in the TRAPPC2 gene.

Question 15382

Topic: Biology, Genetics & Bone Healing

Which of the following describes the primary cellular pathogenesis of the COMP gene mutation responsible for pseudoachondroplasia?

. Overactivation of the fibroblast growth factor receptor 3 pathway
. Accumulation of misfolded protein in the rough endoplasmic reticulum of chondrocytes
. Defective peroxisome biogenesis leading to toxic lipid buildup
. Impaired cross-linking of type I collagen fibers
. Failure of osteoclast-mediated bone resorption

Correct Answer & Explanation

. Accumulation of misfolded protein in the rough endoplasmic reticulum of chondrocytes

Explanation

Mutations in the COMP gene cause misfolded Cartilage Oligomeric Matrix Protein to aggregate in the rough endoplasmic reticulum. This leads to progressive cellular toxicity, premature chondrocyte death, and impaired enchondral ossification.

Question 15383

Topic: 1. General Principles & Basic Science

A 12-year-old boy presents with back pain and decreasing height percentile. Radiographs reveal flattened vertebral bodies with a pathognomonic 'heaped-up' appearance on the posterior portion of the superior endplates. Which of the following is the correct inheritance pattern and mutated gene for this condition?

. Autosomal dominant, COMP
. Autosomal recessive, SLC26A2
. X-linked recessive, TRAPPC2
. Autosomal dominant, COL2A1
. X-linked dominant, EBP

Correct Answer & Explanation

. X-linked recessive, TRAPPC2

Explanation

The patient has Spondyloepiphyseal Dysplasia Tarda, characterized by a hump-shaped mound of bone on the posterior superior vertebral endplates. It is inherited in an X-linked recessive pattern due to mutations in the TRAPPC2 (SEDL) gene.

Question 15384

Topic: 1. General Principles & Basic Science

A 16-year-old girl presents with progressive, bilateral hip and knee pain. She has a history of sensorineural hearing loss, a repaired cleft palate, and a previous retinal detachment. Radiographs show mild epiphyseal flattening and early joint space narrowing in the hips and knees. This patient's syndrome is due to a mutation in which of the following structural proteins?

. Cartilage oligomeric matrix protein
. Type II collagen
. Type X collagen
. Aggrecan
. Fibroblast growth factor receptor 3

Correct Answer & Explanation

. Type II collagen

Explanation

Stickler syndrome is a connective tissue disorder typically caused by mutations in the COL2A1 or COL11A1 genes (Type II and XI collagen). It presents with mild spondyloepiphyseal dysplasia, early-onset osteoarthritis, retinal detachment, hearing loss, and Pierre Robin sequence.

Question 15385

Topic: Biology, Genetics & Bone Healing

A 2-year-old boy undergoes a pelvic radiograph for an unrelated abdominal complaint. The images incidentally reveal bilateral, multi-centric, granular ossification centers of the capital femoral epiphyses. He has a normal height and no pain. What is the most appropriate management?

. Bilateral varus derotational osteotomies
. Application of a hip spica cast
. Observation with reassurance
. Intravenous bisphosphonate therapy
. Core decompression of the femoral heads

Correct Answer & Explanation

. Observation with reassurance

Explanation

This is characteristic of Meyer dysplasia (dysplasia epiphysealis capitis femoris), a benign, self-limiting condition of delayed femoral head ossification. It is often an incidental finding and spontaneously resolves by 5 to 6 years of age without intervention.

Question 15386

Topic: 1. General Principles & Basic Science

A 3-year-old boy is diagnosed with Spondyloepiphyseal Dysplasia Congenita (SEDC). Due to the systemic manifestations of the underlying collagen defect, he is referred for specialized evaluation. Which of the following is the most critical non-orthopedic screening required for this patient?

. Audiology for sensorineural hearing loss
. Ophthalmology for high myopia and retinal detachment
. Cardiology for ascending aortic aneurysm
. Nephrology for focal segmental glomerulosclerosis
. Endocrinology for growth hormone deficiency

Correct Answer & Explanation

. Ophthalmology for high myopia and retinal detachment

Explanation

SEDC is caused by a type II collagen (COL2A1) mutation, which affects both hyaline cartilage and the vitreous humor of the eye. Patients are at exceptionally high risk for severe myopia and retinal detachment, necessitating regular ophthalmologic screening.

Question 15387

Topic: Infection, Pharmacology & VTE

A newborn girl is noted to have stippled epiphyses on radiographs, nasal hypoplasia, and short distal phalanges. Her mother was treated for a chronic medical condition throughout her pregnancy. Maternal use of which of the following medications most likely caused this phenocopy of chondrodysplasia punctata?

. Phenytoin
. Warfarin
. Valproic acid
. Lithium
. Isotretinoin

Correct Answer & Explanation

. Warfarin

Explanation

Warfarin is a known teratogen that inhibits vitamin K-dependent bone proteins like osteocalcin. Fetal warfarin syndrome clinically and radiographically mimics the stippled epiphyses and nasal hypoplasia seen in chondrodysplasia punctata.

Question 15388

Topic: 1. General Principles & Basic Science

A 3-year-old presents with a short trunk, prominent joints, and a flat midface. Radiographs reveal coronal clefts in the vertebral bodies and broad, dumbbell-shaped metaphyses with severely delayed epiphyseal ossification. Which of the following is the most likely diagnosis?

. Metaphyseal chondrodysplasia type Schmid
. Kniest dysplasia
. Chondrodysplasia punctata
. Multiple epiphyseal dysplasia
. Hypochondroplasia

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Kniest dysplasia is a type II collagen disorder characterized by dumbbell-shaped femora, coronal clefts in the vertebrae, severe platyspondyly, and prominent, stiff joints. The presence of coronal clefts is a highly specific radiographic hallmark.

Question 15389

Topic: Infection, Pharmacology & VTE
A 4-year-old boy is brought to the emergency department with a 2-day history of right hip pain, a limp, and refusal to bear weight. He has a temperature of 38.2°C (100.8°F). Laboratory studies reveal a WBC count of 13,500/mm³ and an ESR of 45 mm/hr. According to the Kocher criteria, what is the probability that this child has septic arthritis rather than transient synovitis?
. 3%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis in the pediatric hip include four predictors: non-weight-bearing on the affected side, ESR > 40 mm/hr, fever > 38.5°C (101.3°F), and WBC count > 12,000/mm³. This patient meets 3 criteria (refusal to bear weight, WBC > 12,000, and ESR > 40). His temperature is below the 38.5°C threshold. The probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2 criteria, 93% for 3 criteria, and 99% for 4 criteria.

Question 15390

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the intracellular signaling pathway activated by Bone Morphogenetic Proteins (BMPs) during osteoblast differentiation?

. Wnt/beta-catenin
. JAK/STAT
. Smad 1/5/8
. MAPK/ERK
. Notch/Hes

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to serine/threonine kinase receptors, leading to the phosphorylation of Smad 1, 5, and 8. These form a complex with Smad 4 to enter the nucleus and regulate transcription of osteogenic genes.

Question 15391

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the joint surface?

. Superficial zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicularly to the joint surface, providing resistance to compressive forces. It also has the lowest water content and the highest proteoglycan concentration.

Question 15392

Topic: Surgical Anatomy & Approaches
A 35-year-old male sustains a severely displaced anterior posterior compression (APC III) pelvic ring injury. During surgical exploration via an anterior intrapelvic approach, a significant hemorrhage occurs superior to the superior pubic ramus. Which of the following vascular structures forms the anastomosis most likely injured in this region (corona mortis)?
. External iliac artery and internal pudendal artery
. External iliac vein and pudendal vein
. Deep inferior epigastric vessels and obturator vessels
. Superior gluteal artery and inferior gluteal artery
. Internal iliac artery and femoral artery

Correct Answer & Explanation

. Deep inferior epigastric vessels and obturator vessels

Explanation

The corona mortis is a critical vascular anastomosis connecting the external iliac or deep inferior epigastric system with the obturator system. It is highly susceptible to injury during pelvic trauma or anterior intrapelvic surgical approaches, leading to profuse bleeding.

Question 15393

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, primary (contact) bone healing via osteonal cutting cones requires absolute stability. Which of the following levels of interfragmentary strain is required for primary bone healing to occur?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Greater than 30%
. Strain has no effect on the type of bone healing

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which biomechanically corresponds to an interfragmentary strain of less than 2%. Strains between 2% and 10% favor secondary bone healing with callus formation, while strains above 10% lead to nonunion.

Question 15394

Topic: Infection, Pharmacology & VTE

A periprosthetic joint infection is diagnosed in a patient 3 years after a total knee arthroplasty. Cultures isolate Staphylococcus epidermidis. This pathogen is known to form a resilient biofilm. Which of the following substances is primarily responsible for forming the glycocalyx (slime layer) in this biofilm?

. Hyaluronic acid
. Polysaccharide intercellular adhesin (PIA)
. Fibronectin-binding protein
. Protein A
. Collagenase

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis synthesizes polysaccharide intercellular adhesin (PIA), which is essential for the aggregation of cells and the formation of the biofilm's extracellular polymeric matrix. This glycocalyx heavily shields the bacteria from host immune clearance and systemic antibiotics.

Question 15395

Topic: Biology, Genetics & Bone Healing

A 45-year-old male with an oligotrophic nonunion of a tibial shaft fracture undergoes open debridement and bone grafting. The surgeon decides to augment the site with recombinant bone morphogenetic protein-2 (rhBMP-2) to promote osteoinduction. At the cellular level, which intracellular signaling pathway is directly activated by BMPs to stimulate osteoblastic gene transcription?

. Wnt/beta-catenin pathway
. RANK/RANKL/OPG pathway
. SMAD pathway
. JAK/STAT pathway
. Notch signaling pathway

Correct Answer & Explanation

. SMAD pathway

Explanation

Bone morphogenetic proteins (BMPs) bind to serine/threonine kinase cell surface receptors that directly phosphorylate intracellular SMAD proteins (specifically SMAD 1, 5, and 8). The activated SMAD complex then translocates to the nucleus to upregulate target genes crucial for osteoblastic differentiation.

Question 15396

Topic: Surgical Anatomy & Approaches

During an open posterior approach to the shoulder for a posterior capsulorrhaphy, the surgeon dissects inferior to the teres minor muscle. Which of the following neurovascular structures is at greatest risk of iatrogenic injury in this specific location?

. Suprascapular nerve and vessels
. Axillary nerve and posterior circumflex humeral artery
. Radial nerve and profunda brachii artery
. Musculocutaneous nerve
. Spinal accessory nerve

Correct Answer & Explanation

. Axillary nerve and posterior circumflex humeral artery

Explanation

Correct Answer: BThe axillary nerve and posterior circumflex humeral artery exit the axilla through the quadrangular space, which is bordered superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus. Dissection inferior to the teres minor during a posterior approach places these structures at significant risk of injury.

Question 15397

Topic: Surgical Anatomy & Approaches

A 24-year-old male undergoes an open posterior capsulorrhaphy for recurrent posterior shoulder instability. Postoperatively, he complains of numbness over the lateral aspect of his shoulder and demonstrates weakness in active shoulder abduction beyond 15 degrees. Which of the following nerves was most likely injured during the surgical procedure?

. Suprascapular nerve
. Axillary nerve
. Radial nerve
. Musculocutaneous nerve
. Spinal accessory nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

Correct Answer: Axillary nerveThe axillary nerve is at significant risk during posterior shoulder surgery, particularly when dissecting near the inferior capsule or the inferior border of the teres minor. The axillary nerve exits the axilla through the quadrangular space and courses around the surgical neck of the humerus. Injury to this nerve results in weakness of the deltoid muscle (impairing shoulder abduction) and numbness over the lateral aspect of the shoulder (the "regimental badge" area) supplied by the superior lateral cutaneous nerve of the arm.

Question 15398

Topic: Surgical Anatomy & Approaches

During an open posterior shoulder stabilization, the surgeon dissects inferiorly along the posterior glenoid neck. Which of the following neurovascular structures is at greatest risk of iatrogenic injury in this specific location?

. Suprascapular nerve
. Axillary nerve
. Radial nerve
. Musculocutaneous nerve
. Spinal accessory nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

Correct Answer: B (Axillary nerve)The axillary nerve exits the quadrangular space and courses closely to the inferior capsule and the inferior aspect of the glenoid neck. Dissection inferior to the teres minor or along the inferior glenoid neck places the axillary nerve and the posterior circumflex humeral artery at significant risk of iatrogenic injury during posterior shoulder approaches.

Question 15399

Topic: Surgical Anatomy & Approaches

A 26-year-old male undergoes an open posterior bone block procedure (using an iliac crest autograft) for recurrent posterior shoulder instability with significant posterior glenoid bone loss. Postoperatively, the patient is noted to have weakness in shoulder abduction and decreased sensation over the lateral aspect of the shoulder. Which of the following nerves was most likely injured during the procedure?

. Suprascapular nerve
. Axillary nerve
. Radial nerve
. Musculocutaneous nerve
. Spinal accessory nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

Correct Answer: Axillary nerveThe axillary nerve is at significant risk during the posterior approach to the shoulder, particularly when dissecting inferior to the teres minor or when placing retractors at the inferior aspect of the glenoid neck. The nerve exits the quadrilateral space just inferior to the teres minor and wraps around the surgical neck of the humerus. Injury results in denervation of the deltoid (causing weakness in abduction) and teres minor, as well as numbness over the lateral shoulder (in the distribution of the superior lateral cutaneous nerve of the arm).

Question 15400

Topic: Surgical Anatomy & Approaches

A 28-year-old male is undergoing an open posterior capsular shift for recurrent posterior shoulder instability. During dissection and capsular release at the inferior-most aspect of the glenoid (6 o'clock position), which of the following nerves is at greatest risk of iatrogenic injury?

. Suprascapular nerve
. Musculocutaneous nerve
. Axillary nerve
. Radial nerve
. Median nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

The axillary nerve, specifically its posterior branch, lies in close proximity (often within 10-15 mm) to the inferior and posteroinferior glenoid rim. Care must be taken during capsular dissection and suture passing at the 6 o'clock position to avoid tethering or injuring this nerve.

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