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1. General Principles & Basic Science MCQs

Practice Set 738 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 14741

Topic: Biomechanics & Biomaterials

When preparing an articulating polymethylmethacrylate (PMMA) antibiotic spacer for a two-stage revision of an infected total knee arthroplasty, which specific characteristic of the chosen antibiotic is most crucial to ensure effective local elution and efficacy?

. High thermal lability to dissolve quickly in the joint.
. A strictly bacteriostatic rather than bactericidal mechanism of action.
. Availability in a fine powder form and high thermostability.
. A high systemic toxicity profile to ensure local potency.
. Rapid degradation at body temperature (37°C).

Correct Answer & Explanation

. Availability in a fine powder form and high thermostability.

Explanation

Antibiotics mixed into PMMA bone cement must be thermostable to withstand the high exothermic temperatures of the curing process without losing efficacy. They must also be in a powder form (not liquid) to allow uniform mixing and proper elution from the cement mantle (e.g., vancomycin, tobramycin).

Question 14742

Topic: Biology, Genetics & Bone Healing

A 73-year-old man presents with diffuse back and lower extremity pain. A technetium-99m bone scan demonstrates widespread, discrete osteoblastic lesions throughout the axial and appendicular skeleton. Which of the following medications is most appropriate to decrease pain and reduce the incidence of skeletal-related events in this patient?

. Methotrexate
. Bisphosphonates
. Teriparatide
. Denosumab
. Infliximab

Correct Answer & Explanation

. Bisphosphonates

Explanation

Correct Answer: BThe patient's age, gender, and widespread osteoblastic lesions on bone scan are highly characteristic of metastatic prostate cancer. In patients with widespread bone metastases from prostate cancer, bisphosphonates (such as zoledronic acid) play a critical role in treatment by decreasing bone pain, reducing the number of pathologic fractures, and delaying the onset of skeletal-related events.

Question 14743

Topic: Surgical Anatomy & Approaches

A 6-year-old boy presents with a displaced supracondylar humerus fracture. Examination reveals an inability to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which of the following represents the second most common nerve palsy associated with this specific fracture pattern?

. Ulnar nerve palsy
. Radial nerve palsy
. Posterior interosseous nerve palsy
. Musculocutaneous nerve palsy
. Axillary nerve palsy

Correct Answer & Explanation

. Radial nerve palsy

Explanation

Correct Answer: B. Radial nerve palsyThe patient's clinical presentation (inability to flex the IP joint of the thumb and DIP joint of the index finger) is classic for an anterior interosseous nerve (AIN) palsy. AIN palsy is the most common nerve injury associated with pediatric supracondylar humerus fractures. The second most common nerve injury in this setting is a radial nerve palsy. Most of these nerve injuries are neurapraxias that resolve spontaneously with observation.

Question 14744

Topic: Surgical Anatomy & Approaches

During the anterior (Smith-Petersen) approach to the hip, the internervous plane is developed between the sartorius and the tensor fascia lata. Which of the following vascular structures crosses this interval and must be routinely identified and ligated to prevent significant hemorrhage?

. Medial femoral circumflex artery
. Ascending branch of the lateral femoral circumflex artery
. Descending branch of the lateral femoral circumflex artery
. Superior gluteal artery
. Inferior gluteal artery

Correct Answer & Explanation

. Ascending branch of the lateral femoral circumflex artery

Explanation

Correct Answer: B. Ascending branch of the lateral femoral circumflex arteryThe ascending branch of the lateral femoral circumflex artery crosses the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fascia lata (innervated by the superior gluteal nerve) in the anterior approach to the hip. It must be identified and ligated or coagulated to prevent excessive bleeding.

Question 14745

Topic: 1. General Principles & Basic Science

A 45-year-old man presents with chronic lower back pain. MRI shows degenerative changes in the L4-L5 intervertebral disk. Which of the following biochemical changes is most characteristic of the natural aging and degeneration process of the intervertebral disk?

. Increased water content and increased glycosaminoglycan content
. Reduced water content, reduced glycosaminoglycan content, and increased noncollagen glycoprotein
. Reduced water content, increased glycosaminoglycan content, and reduced noncollagen glycoprotein
. Increased water content, reduced glycosaminoglycan content, and increased collagen content
. Reduced water content, reduced glycosaminoglycan content, and reduced noncollagen glycoprotein

Correct Answer & Explanation

. Reduced water content, reduced glycosaminoglycan content, and increased noncollagen glycoprotein

Explanation

Correct Answer: BGradual desiccation of the disk begins in the third decade as glycosaminoglycan levels within the nucleus begin to decline. The original water content of 88% decreases to 70% in the sixth decade and beyond. As glycosaminoglycan content decreases, there is a corresponding increase in noncollagen glycoprotein.

Question 14746

Topic: Surgical Anatomy & Approaches

During an anterior (Smith-Petersen) approach to the hip, the internervous plane is developed between the sartorius and the tensor fascia lata. Which of the following vascular structures crosses this interval and must be routinely identified and ligated to prevent significant hemorrhage?

. Medial femoral circumflex artery
. Ascending branch of the lateral femoral circumflex artery
. Descending branch of the lateral femoral circumflex artery
. Superficial circumflex iliac artery
. Profunda femoris artery

Correct Answer & Explanation

. Ascending branch of the lateral femoral circumflex artery

Explanation

Correct Answer: BThe ascending branch of the lateral femoral circumflex artery crosses the gap between the tensor fascia lata and the sartorius in the anterior approach to the hip. It must be carefully identified and ligated or coagulated to prevent significant bleeding. The other vessels listed are out of the immediate field of dissection for this specific internervous plane.

Question 14747

Topic: Surgical Anatomy & Approaches

During the anterior (Smith-Petersen) approach to the hip, the internervous plane is developed between the sartorius and the tensor fascia lata. Which of the following vascular structures crosses this interval and must be routinely identified and ligated to prevent significant hemorrhage?

. Medial femoral circumflex artery
. Descending branch of the lateral femoral circumflex artery
. Ascending branch of the lateral femoral circumflex artery
. Superior gluteal artery
. Profunda femoris artery

Correct Answer & Explanation

. Ascending branch of the lateral femoral circumflex artery

Explanation

Correct Answer: CThe anterior approach to the hip utilizes the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fascia lata (innervated by the superior gluteal nerve). Within this interval, the ascending branch of the lateral femoral circumflex artery crosses the surgical field transversely and must be identified and ligated or coagulated to prevent significant bleeding.

Question 14748

Topic: 1. General Principles & Basic Science

A 25-year-old carpenter sustains a laceration to the volar aspect of his index finger, resulting in a Zone II flexor tendon injury. Following primary surgical repair, what rehabilitation protocol is currently considered optimal to minimize adhesion formation while protecting the repair?

. Immediate unresisted active flexion and extension without a splint
. Six weeks of rigid cast immobilization followed by aggressive therapy
. Early active mobilization utilizing a controlled active motion protocol
. Strict passive flexion and active extension only for the first 8 weeks
. Immediate unrestricted weight-bearing and grip strengthening

Correct Answer & Explanation

. Early active mobilization utilizing a controlled active motion protocol

Explanation

Early active mobilization protocols for Zone II flexor tendon repairs have been shown to significantly reduce adhesion formation while maintaining repair integrity. These protocols typically utilize dorsal blocking splints to prevent over-extension while allowing controlled active flexion.

Question 14749

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman is diagnosed with an unresectable giant cell tumor of the sacrum. She is started on denosumab therapy. What is the mechanism of action of this medication?

. Inhibits vascular endothelial growth factor (VEGF)
. Binds to RANK ligand (RANKL), inhibiting osteoclast formation
. Directly induces apoptosis in neoplastic giant cells
. Inhibits matrix metalloproteinases in the bone microenvironment
. Stimulates osteoblast differentiation via the Wnt/beta-catenin pathway

Correct Answer & Explanation

. Binds to RANK ligand (RANKL), inhibiting osteoclast formation

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing its interaction with the RANK receptor on osteoclast precursors. This inhibits osteoclast formation, function, and survival, which is highly effective in treating giant cell tumors of bone.

Question 14750

Topic: Biology, Genetics & Bone Healing
During the process of endochondral ossification at the epiphyseal growth plate, which specific collagen type is primarily synthesized by hypertrophic chondrocytes to prepare the matrix for calcification?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type X collagen

Explanation

Type X collagen is a specific marker for hypertrophic chondrocytes in the growth plate. It plays a critical role in facilitating the calcification of the extracellular matrix during endochondral ossification.

Question 14751

Topic: Biology, Genetics & Bone Healing

A 30-year-old female undergoes a biopsy for an eccentric, lytic epiphyseal lesion in her distal femur. The pathology report confirms a Giant Cell Tumor (GCT) of bone, describing a mix of mononuclear cells and multinucleated giant cells. Which of the following best describes the pathogenesis involving these mononuclear cells?

. They are non-neoplastic reactive cells attempting to clear tumor debris
. They are the true neoplastic cells that secrete RANKL to stimulate osteoclast differentiation
. They are derived strictly from the monocyte-macrophage hematopoietic lineage
. They secrete Denosumab to inhibit excessive local bone resorption
. They display characteristic reciprocal translocations t(11;22)

Correct Answer & Explanation

. They are the true neoplastic cells that secrete RANKL to stimulate osteoclast differentiation

Explanation

In Giant Cell Tumor (GCT) of bone, the spindle-shaped mononuclear cells are the actual neoplastic cells. They strongly express RANK ligand (RANKL), which recruits and activates the non-neoplastic, multinucleated giant cells (osteoclast-like cells) to destroy bone.

Question 14752

Topic: 1. General Principles & Basic Science

During the histologic evaluation of normal articular cartilage, which zone demonstrates the highest concentration of proteoglycans, highest compressive modulus, and contains chondrocytes arranged in vertical columns?

. Superficial tangential 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 highest concentration of proteoglycans, conferring the highest compressive modulus. Its collagen fibers are oriented perpendicular to the joint surface, and chondrocytes are characteristically arranged in vertical columns parallel to the collagen fibers.

Question 14753

Topic: Biology, Genetics & Bone Healing

A 7-year-old boy presents with a waddling gait. His mother has similar features. Physical exam reveals an unusually large head, a delayed closure of the anterior fontanelle, and the ability to bring his shoulders together anteriorly.

Which of the following genes is most likely mutated in this condition?

. FGFR3
. COMP
. RUNX2
. COL1A1
. SLC26A2

Correct Answer & Explanation

. RUNX2

Explanation

The clinical presentation and image demonstrate absent or hypoplastic clavicles typical of cleidocranial dysplasia. This is an autosomal dominant condition caused by a mutation in the RUNX2 (CBFA1) gene, which is essential for osteoblast differentiation.

Question 14754

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with a history of recurrent fractures and newly diagnosed facial nerve palsy. Radiographs reveal generalized, extreme osteosclerosis and a classic "bone-in-bone" appearance of the vertebrae. What is the primary cellular defect responsible for this condition?

. Defective osteoblast differentiation
. Failure of osteoclast ruffled border formation
. Overactivity of osteoclasts
. Defective collagen type I cross-linking
. Impaired mineralization of osteoid

Correct Answer & Explanation

. Failure of osteoclast ruffled border formation

Explanation

Osteopetrosis is caused by defective osteoclast function, frequently due to mutations (e.g., carbonic anhydrase II or TCIRG1) preventing ruffled border formation and acid secretion. This results in incredibly dense, brittle bones and narrowed neural foramina leading to cranial nerve entrapment.

Question 14755

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with severe genu varum and short stature. Laboratory evaluation reveals normal serum calcium, low serum phosphate, normal PTH, normal 25-hydroxyvitamin D levels, and highly elevated FGF-23. What is the most appropriate medical management?

. High-dose Vitamin D supplementation alone
. Calcium and Vitamin D supplementation
. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)
. Intravenous bisphosphonates
. Recombinant growth hormone injections

Correct Answer & Explanation

. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX gene mutation leading to excess FGF-23, which inappropriately wastes phosphate in the kidneys. Standard treatment includes frequent oral phosphate replacement combined with calcitriol to prevent secondary hyperparathyroidism.

Question 14756

Topic: Biology, Genetics & Bone Healing
A 2-year-old presents with bowing of the long bones, premature loss of fully rooted deciduous teeth, and a history of recurrent respiratory infections. Laboratory testing reveals strikingly low serum alkaline phosphatase levels and elevated urinary phosphoethanolamine. What is the primary deficiency in this condition?
. Vitamin D receptor
. Tissue-nonspecific alkaline phosphatase (TNSALP)
. Carbonic anhydrase II
. Fibroblast growth factor 23 (FGF-23)
. Type I collagen

Correct Answer & Explanation

. Tissue-nonspecific alkaline phosphatase (TNSALP)

Explanation

Hypophosphatasia is a rare metabolic bone disease caused by an ALPL gene mutation, leading to tissue-nonspecific alkaline phosphatase (TNSALP) deficiency. This results in defective bone mineralization, classic premature tooth loss, and characteristically low serum alkaline phosphatase.

Question 14757

Topic: Biology, Genetics & Bone Healing

A 10-year-old girl is evaluated for short stature and delayed dental eruption. On physical examination, she is able to bring her shoulders together anteriorly in the midline.

What is the genetic mutation responsible for this condition?

. FGFR3
. COMP
. RUNX2 (CBFA1)
. COL2A1
. SOX9

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by mutations in the RUNX2 (CBFA1) gene. This gene is a critical transcription factor essential for osteoblast differentiation and bone formation.

Question 14758

Topic: Biology, Genetics & Bone Healing

In children with severe osteogenesis imperfecta, cyclical intravenous bisphosphonates are frequently utilized to decrease fracture rates. What is the primary mechanism of action of this medication class at the cellular level?

. Stimulates osteoblast proliferation and differentiation
. Induces osteoclast apoptosis and inhibits bone resorption
. Enhances renal calcium and phosphate reabsorption
. Increases intestinal calcium absorption via vitamin D pathways
. Promotes type 1 collagen cross-linking in the extracellular matrix

Correct Answer & Explanation

. Induces osteoclast apoptosis and inhibits bone resorption

Explanation

Bisphosphonates, such as pamidronate, accumulate in bone and are ingested by osteoclasts during bone resorption. They inhibit the mevalonate pathway, leading to osteoclast apoptosis and a significant reduction in bone resorption.

Question 14759

Topic: Biology, Genetics & Bone Healing

A 6-year-old child presents with progressive genu varum, widening of the wrists, and a rachitic rosary. Laboratory studies reveal a normal serum calcium, low phosphorus, and significantly elevated alkaline phosphatase. Which of the following is the most likely initial step in the pathophysiology of this metabolic bone disease?

. Primary renal tubular defect in phosphorus reabsorption
. Defective intestinal absorption of calcium due to low 1,25-dihydroxyvitamin D
. Autonomous secretion of parathyroid hormone
. Overproduction of Fibroblast Growth Factor 23 (FGF-23)
. Mutation in the PHEX gene leading to phosphate wasting

Correct Answer & Explanation

. Defective intestinal absorption of calcium due to low 1,25-dihydroxyvitamin D

Explanation

Nutritional rickets typically begins with Vitamin D deficiency, leading to decreased intestinal calcium absorption. The resulting secondary hyperparathyroidism normalizes serum calcium at the expense of phosphorus via renal wasting.

Question 14760

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy presents with progressive bowing of the lower extremities. Laboratory tests show normal calcium, extremely low serum phosphorus, and normal PTH levels. He is diagnosed with X-linked hypophosphatemic rickets. What is the primary mediator of renal phosphate wasting in this disease?

. PTH-related peptide (PTHrP)
. Sclerostin
. Fibroblast growth factor 23 (FGF-23)
. Osteocalcin
. Calcitonin

Correct Answer & Explanation

. Fibroblast growth factor 23 (FGF-23)

Explanation

X-linked hypophosphatemic rickets is caused by a mutation in the PHEX gene, which leads to elevated circulating levels of FGF-23. FGF-23 potently decreases renal phosphate reabsorption in the proximal tubule, causing profound hypophosphatemia.

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