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Biology, Genetics & Bone Healing MCQs

Practice Set 78 of 212

This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1541

Topic: Biology, Genetics & Bone Healing

What is the primary function of the Volkmann's canals in cortical bone?

. To house osteocytes and their canaliculi
. To connect adjacent Haversian canals and provide vascular and neural communication
. To provide channels for nutrient diffusion to chondrocytes
. To serve as a reservoir for bone marrow
. To facilitate communication between trabeculae in cancellous bone

Correct Answer & Explanation

. To house osteocytes and their canaliculi

Explanation

Volkmann's canals are horizontal channels that connect adjacent Haversian canals (which run longitudinally) and also connect Haversian canals to the periosteal and endosteal surfaces. They contain blood vessels and nerves, facilitating the intricate vascular and neural network within cortical bone. Lacunae house osteocytes, and canaliculi connect lacunae. Cancellous bone structure is different.

Question 1542

Topic: Biology, Genetics & Bone Healing

Which type of collagen is predominantly found in fibrocartilage, such as that of the meniscus or intervertebral disc?

. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type IX collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Fibrocartilage, found in structures like the menisci, intervertebral discs, and labrum, is primarily composed of Type I collagen, providing significant tensile strength. Type II collagen is characteristic of hyaline cartilage. Type III is found in skin and blood vessels. Type IV is found in basement membranes. Type IX is a minor component of hyaline cartilage.

Question 1543

Topic: Biology, Genetics & Bone Healing

A common mechanism for bone loss in metabolic conditions involves an imbalance in the RANKL/OPG ratio. An increase in which of these would lead to increased bone resorption?

. Increased OPG production
. Decreased RANKL production
. Increased RANKL expression by osteoblasts and stromal cells
. Increased binding of OPG to RANK
. Decreased activation of RANK receptors

Correct Answer & Explanation

. Increased OPG production

Explanation

An increase in RANKL expression by osteoblasts and stromal cells leads to more RANKL available to bind to RANK receptors on osteoclast precursors, thereby increasing osteoclast differentiation, activation, and survival, resulting in increased bone resorption. Increased OPG production or increased binding of OPG to RANK would inhibit osteoclast activity. Decreased RANKL production or decreased activation of RANK receptors would also lead to reduced bone resorption.

Question 1544

Topic: Biology, Genetics & Bone Healing

What is the key histological feature distinguishing osteoid from mature bone matrix?

. Presence of collagen fibers
. Presence of osteocytes
. Lack of mineralization
. Higher cellularity
. Presence of Haversian systems

Correct Answer & Explanation

. Presence of collagen fibers

Explanation

Osteoid is the unmineralized organic matrix produced by osteoblasts. Mature bone matrix is osteoid that has subsequently undergone mineralization with hydroxyapatite crystals. Both contain collagen fibers (primarily type I) and osteocytes. Haversian systems are features of cortical bone structure, not a distinction of osteoid itself.

Question 1545

Topic: Biology, Genetics & Bone Healing

A patient with a distal radius fracture is treated with closed reduction and casting. Which of the following cells are the first to arrive and initiate the fracture healing cascade?

. Osteoblasts
. Chondrocytes
. Fibroblasts
. Polymorphonuclear leukocytes (neutrophils)
. Macrophages and lymphocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

In the initial inflammatory phase of fracture healing, the first cells to arrive at the fracture site are polymorphonuclear leukocytes (neutrophils), followed shortly by macrophages and lymphocytes. These cells are crucial for clearing debris and initiating the inflammatory cascade. Osteoblasts and chondrocytes appear later as the repair phase begins.

Question 1546

Topic: Biology, Genetics & Bone Healing

Which major cell type is primarily responsible for the degradation of the cartilaginous callus during endochondral ossification in fracture healing?

. Osteoblasts
. Osteoclasts
. Chondrocytes
. Fibroblasts
. Macrophages

Correct Answer & Explanation

. Osteoblasts

Explanation

During endochondral ossification, osteoclasts are the primary cells responsible for resorbing the calcified cartilage matrix (the cartilaginous callus) to create space for invading blood vessels and subsequent osteoblast-mediated bone formation. Chondrocytes produce the cartilage, and osteoblasts lay down new bone matrix. Macrophages clear debris.

Question 1547

Topic: Biology, Genetics & Bone Healing

What is the primary role of vitamin D in bone metabolism?

. Directly stimulates osteoclast activity.
. Increases intestinal absorption of calcium and phosphate.
. Inhibits parathyroid hormone secretion.
. Promotes collagen synthesis by osteoblasts.
. Enhances renal excretion of calcium.

Correct Answer & Explanation

. Directly stimulates osteoclast activity.

Explanation

The primary role of activated vitamin D (calcitriol) is to increase intestinal absorption of calcium and phosphate, thereby ensuring adequate mineral availability for bone mineralization. It also has direct effects on bone remodeling and kidney function, but intestinal absorption is its most prominent and critical function for bone health. It does not directly stimulate osteoclast activity, but adequate calcium levels are essential for bone turnover.

Question 1548

Topic: Biology, Genetics & Bone Healing

What is the characteristic histological feature seen in Paget's disease of bone?

. Increased number of inactive osteoblasts
. Decreased osteoclast activity leading to dense bone
. A disorganized 'mosaic' pattern of woven and lamellar bone
. Replacement of bone by fibrous tissue and immature cartilage
. Excessive osteoid accumulation without mineralization

Correct Answer & Explanation

. Increased number of inactive osteoblasts

Explanation

Paget's disease (osteitis deformans) is characterized by highly disorganized bone remodeling, leading to a 'mosaic' or 'jigsaw' pattern of woven and lamellar bone. There is increased, chaotic osteoclastic resorption followed by rapid, disorganized osteoblastic bone formation. It does not involve decreased osteoclast activity, fibrous tissue replacement, or unmineralized osteoid accumulation primarily.

Question 1549

Topic: Biology, Genetics & Bone Healing

A 70-year-old female presents with acute onset back pain and a vertebral compression fracture. Which of the following is the most effective pharmacologic agent for preventing future osteoporotic fractures by inhibiting osteoclast function?

. Calcium and Vitamin D supplements
. Teriparatide
. Denosumab
. Strontium ranelate
. Calcitonin

Correct Answer & Explanation

. Calcium and Vitamin D supplements

Explanation

Denosumab is a monoclonal antibody that targets RANKL, preventing osteoclast formation and function, leading to a potent antiresorptive effect and significant reduction in fracture risk. Bisphosphonates also inhibit osteoclast function and are first-line. Teriparatide is an anabolic agent. Calcium/Vitamin D are essential supplements but not direct anti-osteoporosis agents alone. Strontium ranelate has dual action but is less commonly used. Calcitonin has modest efficacy.

Question 1550

Topic: Biology, Genetics & Bone Healing

Which type of fracture healing involves direct apposition of fracture ends with minimal callus formation, typically seen with absolute stability provided by rigid internal fixation?

. Secondary healing
. Endochondral ossification
. Primary healing
. Stress fracture healing
. Nonunion

Correct Answer & Explanation

. Secondary healing

Explanation

Primary (or direct) bone healing occurs when there is absolute stability and direct contact between the fracture ends, typically achieved with rigid internal fixation. This process involves direct remodeling by osteoclasts and osteoblasts, with minimal or no external callus formation. Secondary healing involves a callus, and endochondral ossification is part of secondary healing. Stress fractures heal like secondary fractures. Nonunion is a failure of healing.

Question 1551

Topic: Biology, Genetics & Bone Healing

A surgeon utilizes a structural cortical allograft to manage a massive diaphyseal bone defect during a revision total femur arthroplasty. Which of the following best describes the classical biological sequence of graft incorporation for this specific type of structural graft?

. Osteoblastic apposition occurs on dead trabeculae prior to osteoclastic resorption
. Osteoclastic resorption of Haversian canals precedes osteoblastic new bone formation
. The graft incorporates primarily through direct endochondral ossification mediated by host chondrocytes
. Neovascularization proceeds at a rate of 1 mm per day without any preceding osteoclastic resorption
. Revascularization and cellular penetration are significantly faster and more complete than in cancellous autografts

Correct Answer & Explanation

. Osteoblastic apposition occurs on dead trabeculae prior to osteoclastic resorption

Explanation

Cortical bone grafts incorporate via creeping substitution, but unlike cancellous grafts, the sequence is uniquely osteoclastic first. Osteoclasts must bore out the existing Haversian canals to allow vascular ingrowth before osteoblasts can lay down new bone. This initial resorptive phase leads to a temporary, significant decrease in the mechanical strength of cortical allografts. In contrast, cancellous grafts undergo initial osteoblastic apposition on dead trabeculae, followed by remodeling.

Question 1552

Topic: Biology, Genetics & Bone Healing

A 45-year-old male is treated with a minimally invasive bridge plate for a severely comminuted midshaft tibia fracture. According to Perren's strain theory, direct (primary) bone healing with lamellar bone formation can only occur when the interfragmentary strain is kept below which of the following thresholds?

. 2%
. 10%
. 15%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that a specific tissue type can only form if the local mechanical strain does not exceed the strain tolerance of that tissue. Lamellar bone is highly rigid and can tolerate strains up to only 2%; thus, primary bone healing requires absolute stability (<2% strain). Woven bone tolerates up to 10% strain, cartilage tolerates up to 10%, and granulation tissue can tolerate up to 100% strain.

Question 1553

Topic: Biology, Genetics & Bone Healing

Following a primary flexor tendon repair in Zone II of the hand, a structured early active mobilization protocol is initiated. At the cellular and tissue level, what is the primary biological advantage of this protocol during the early stages of tendon healing?

. It promotes intrinsic over extrinsic healing, leading to improved collagen alignment and a reduction in restrictive adhesion formation
. It drastically increases the formation of disorganized Type III collagen, creating a much stronger initial callus
. It intentionally prolongs the inflammatory phase to heavily recruit extrinsic fibroblasts from the surrounding tendon sheath
. It promotes rigid, immobile adherence of the epitenon to the surrounding sheath to improve early tensile strength
. It stimulates rapid endochondral ossification at the repair site to mechanically bridge the tendon gap

Correct Answer & Explanation

. It promotes intrinsic over extrinsic healing, leading to improved collagen alignment and a reduction in restrictive adhesion formation

Explanation

Flexor tendons heal through both intrinsic (proliferation of epitenon and endotenon cells) and extrinsic (ingrowth of fibroblasts from the surrounding tendon sheath) mechanisms. Extrinsic healing is largely responsible for the formation of motion-limiting peritendinous adhesions. Early controlled mobilization heavily suppresses extrinsic healing and favors intrinsic healing. It also applies mechanical stress that aligns the newly synthesized collagen fibrils longitudinally, greatly improving the tendon's tensile strength and functional gliding capacity.

Question 1554

Topic: Biology, Genetics & Bone Healing

A 72-year-old male presents with deep, aching thigh pain, progressive hearing loss, and noticeable anterior bowing of his femur. Laboratory studies reveal an isolated, significantly elevated serum alkaline phosphatase level with normal calcium and phosphorus. A bone biopsy of the affected femur is most likely to demonstrate which of the following histological hallmarks?

. Extensive unmineralized osteoid seams surrounding normal osteoblast morphology
. A disorganized mosaic pattern of lamellar bone interspersed with prominent, haphazard cement lines
. Extremely dense cortical bone with absent Haversian systems and fibrous replacement of the medullary marrow space
. Collections of malignant, pleomorphic spindle cells producing delicate, lace-like malignant osteoid
. Subperiosteal bone resorption, dissecting osteitis, and numerous multi-nucleated giant cells forming 'brown tumors'

Correct Answer & Explanation

. Extensive unmineralized osteoid seams surrounding normal osteoblast morphology

Explanation

The clinical scenario (bone pain, bowing, hearing loss, isolated elevated alk phos in an elderly male) is classic for Paget's disease of bone (osteitis deformans). The disease involves phases of excessive osteoclastic resorption followed by frantic, disorganized osteoblastic bone formation. The resulting histologic hallmark, particularly during the mixed or sclerotic phase, is a 'mosaic' or 'jigsaw puzzle' pattern of woven and lamellar bone with prominent, haphazard cement lines reflecting the chaotic remodeling process.

Question 1555

Topic: Biology, Genetics & Bone Healing

During the reparative phase of secondary fracture healing, a cartilaginous soft callus forms and is subsequently replaced by bone. Which specific type of collagen is most predominantly synthesized by the cells during the peak of this soft callus formation?

. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Secondary fracture healing involves endochondral ossification. During the soft callus phase, chondrocytes rapidly proliferate and synthesize a cartilage matrix that is predominantly rich in Type II collagen. Later in the process, hypertrophic chondrocytes express Type X collagen to facilitate calcification, before osteoblasts finally lay down Type I collagen to form woven bone.

Question 1556

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of early osteoarthritis, which of the following represents the earliest biochemical change in the articular cartilage matrix?

. Increase in total proteoglycan content
. Decrease in total water content
. Increase in total water content
. Increase in collagen type II synthesis
. Decrease in chondrocyte metabolism

Correct Answer & Explanation

. Increase in total proteoglycan content

Explanation

The earliest recognizable biochemical change in osteoarthritis is an increase in the water content of the articular cartilage. This occurs due to the breakdown of the superficial collagen meshwork, which normally constrains the hydrophilic proteoglycans. Once the collagen network is damaged, the proteoglycans swell and absorb more water. As the disease progresses to later stages, the total proteoglycan content eventually decreases.

Question 1557

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain that allows for the formation of lamellar bone during fracture healing?

. 1 to 2 percent
. 10 percent
. 30 percent
. 50 percent
. 100 percent

Correct Answer & Explanation

. 1 to 2 percent

Explanation

Perren's strain theory dictates that a specific tissue will not form if the interfragmentary strain exceeds the maximum strain that the tissue can tolerate before failure. Lamellar bone is rigid and can only tolerate up to 2% strain. Woven bone can tolerate up to 10% strain, cartilage can tolerate 10-30%, and granulation tissue can tolerate up to 100%. Therefore, absolute stability (strain <2%) is required for primary (lamellar) bone healing.

Question 1558

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis and a recent vertebral compression fracture is started on teriparatide. Which of the following best describes the cellular mechanism of action of this medication?

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Binding to RANKL to prevent interaction with RANK on osteoclasts
. Intermittent activation of osteoblast PTH receptors stimulating bone formation
. Downregulation of sclerostin leading to increased Wnt signaling
. Selective estrogen receptor modulation in bone tissue

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently (e.g., via daily subcutaneous injection), it exerts an anabolic effect by directly stimulating osteoblasts via the PTH/PTHrP receptor, leading to increased bone formation. Continuous exposure to endogenous PTH (as in hyperparathyroidism) leads to net bone resorption. Option A describes bisphosphonates, Option B describes denosumab, and Option D describes romosozumab.

Question 1559

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with hypophosphatemic rickets, diffuse bone pain, and muscle weakness. Laboratory studies demonstrate significantly elevated levels of Fibroblast Growth Factor 23 (FGF23). What is the primary physiologic effect of FGF23 on the kidneys?

. Increased calcium reabsorption
. Decreased phosphate excretion
. Inhibition of 1-alpha-hydroxylase
. Stimulation of 25-hydroxylase
. Increased parathyroid hormone secretion

Correct Answer & Explanation

. Increased calcium reabsorption

Explanation

FGF23 is a hormone secreted primarily by osteocytes that regulates phosphate homeostasis. In the kidney, it decreases phosphate reabsorption (causing phosphaturia) and inhibits the enzyme 1-alpha-hydroxylase, leading to decreased synthesis of active 1,25-dihydroxyvitamin D. This ultimately reduces intestinal absorption of calcium and phosphate.

Question 1560

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing and spine fusion. Which of the following BMPs is most strongly associated with the FDA-approved use for acute, open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for acute, open tibial shaft fractures treated with an intramedullary nail, as well as for single-level anterior lumbar interbody fusions. rhBMP-7 (OP-1) was previously utilized for recalcitrant long bone nonunions under a Humanitarian Device Exemption. BMP-3 actually acts as an antagonist to osteogenesis.

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