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Biology, Genetics & Bone Healing MCQs

Practice Set 122 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 2421

Topic: Biology, Genetics & Bone Healing

Which of the following conditions is MOST likely to impair bone healing (fracture union)?

. Young age
. High calcium intake
. Stable fracture fixation
. Nicotine use
. Adequate Vitamin D levels

Correct Answer & Explanation

. Nicotine use

Explanation

Nicotine use (smoking) is a well-established and significant risk factor for impaired bone healing, delayed union, and non-union. Nicotine causes vasoconstriction, impairs osteoblast function, and reduces blood supply to the fracture site. Young age, high calcium intake, stable fixation, and adequate Vitamin D levels are generally favorable for bone healing.

Question 2422

Topic: Biology, Genetics & Bone Healing

Which of the following cells is primarily responsible for bone resorption during bone remodeling?

. Osteoblasts
. Osteocytes
. Osteoclasts
. Chondrocytes
. Fibroblasts

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoclasts are specialized multinucleated cells primarily responsible for bone resorption. They secrete acids and enzymes to break down bone matrix. Osteoblasts are responsible for bone formation. Osteocytes are mature bone cells embedded in the matrix. Chondrocytes form cartilage. Fibroblasts form fibrous connective tissue.

Question 2423

Topic: Biology, Genetics & Bone Healing

Regarding the pathogenesis of osteonecrosis of the femoral head, which of the following is considered the MOST significant initiating factor in non-traumatic cases?

. Mechanical stress
. Genetic predisposition
. Vascular compromise
. Increased intraosseous pressure
. Systemic inflammation

Correct Answer & Explanation

. Vascular compromise

Explanation

Vascular compromise leading to ischemia is the most significant initiating factor in the pathogenesis of osteonecrosis of the femoral head (ONFH), whether traumatic (e.g., femoral neck fracture) or non-traumatic (e.g., steroid use, alcoholism). This compromise can be due to thrombosis, fat emboli, or direct vessel injury, ultimately leading to death of osteocytes and marrow cells. While increased intraosseous pressure can result from the ischemia and contribute to further compromise, it is typically a consequence, not the primary initiator. Mechanical stress can exacerbate the condition but isn't the primary cause. Genetic predisposition and systemic inflammation are associated factors but not the direct initiating mechanism of bone cell death.

Question 2424

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of bisphosphonates in the treatment of osteoporosis?

. Increase osteoblast activity
. Inhibit osteoclast activity
. Promote calcium absorption in the gut
. Stimulate parathyroid hormone release
. Increase bone matrix mineralization

Correct Answer & Explanation

. Inhibit osteoclast activity

Explanation

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption. They bind to hydroxyapatite crystals in the bone and are internalized by osteoclasts, leading to osteoclast apoptosis and reduced bone turnover. This preserves bone mass and increases bone mineral density, thereby reducing fracture risk. They do not primarily increase osteoblast activity (though reduced resorption can indirectly lead to more effective new bone formation), promote calcium absorption, or stimulate PTH release.

Question 2425

Topic: Biology, Genetics & Bone Healing
Which cytokine is primarily responsible for promoting bone resorption by stimulating osteoclast differentiation and activation?
. Bone morphogenetic protein (BMP)
. Transforming growth factor-beta (TGF-Ξ²)
. Insulin-like growth factor 1 (IGF-1)
. Receptor activator of nuclear factor kappa-Ξ’ ligand (RANKL)
. Osteoprotegerin (OPG)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-Ξ’ ligand (RANKL)

Explanation

RANKL (Receptor Activator of Nuclear factor Kappa-Ξ’ Ligand) is a key cytokine produced by osteoblasts and stromal cells that binds to RANK receptors on pre-osteoclasts, promoting their differentiation into mature osteoclasts and activating their bone-resorbing activity. OPG (Osteoprotegerin) acts as a decoy receptor for RANKL, inhibiting its effects and thus preventing bone resorption. BMPs, TGF-Ξ², and IGF-1 are primarily involved in bone formation and remodeling, stimulating osteoblast activity.

Question 2426

Topic: Biology, Genetics & Bone Healing

Which metabolic bone disease is characterized by excessive bone resorption followed by disorganized and excessive bone formation, leading to enlarged and weakened bones?

. Osteoporosis
. Osteomalacia
. Paget's disease of bone
. Hyperparathyroidism
. Osteogenesis imperfecta

Correct Answer & Explanation

. Paget's disease of bone

Explanation

Paget's disease of bone (osteitis deformans) is characterized by a focal disorder of bone remodeling, with greatly accelerated, chaotic bone turnover. This involves an initial osteolytic phase, followed by a mixed lytic and blastic phase, and finally a predominant sclerotic phase. The new bone formed is structurally disorganized (woven bone), leading to enlarged, weakened, and deformed bones. Osteoporosis is a decrease in bone mass. Osteomalacia is defective mineralization of new bone. Hyperparathyroidism causes increased bone resorption but not this chaotic pattern. Osteogenesis imperfecta is a genetic collagen disorder.

Question 2427

Topic: Biology, Genetics & Bone Healing
Which type of collagen is primarily found in hyaline cartilage, providing its characteristic strength and resilience?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type V collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Type II collagen is the predominant collagen found in hyaline cartilage (including articular cartilage). Its unique molecular structure and organization contribute to the tensile strength and resilience of cartilage, allowing it to withstand compressive loads. Type I collagen is found in bone, tendons, and ligaments, providing strong tensile strength. Type III collagen is found in extensible connective tissues like skin and blood vessels. Type IV collagen is found in basement membranes. Type V collagen is found in small amounts in various tissues, including cartilage.

Question 2428

Topic: Biology, Genetics & Bone Healing
In the context of bone healing, what is the sequence of events during secondary bone healing (endochondral ossification)?
. Hematoma formation β†’ cartilage callus β†’ bony callus β†’ remodeling
. Hematoma formation β†’ bony callus β†’ cartilage callus β†’ remodeling
. Direct osteoblast activity β†’ woven bone β†’ lamellar bone
. Inflammation β†’ osteoclast activity β†’ osteoblast activity β†’ consolidation
. Fibrous tissue formation β†’ cartilage formation β†’ direct bone formation

Correct Answer & Explanation

. Hematoma formation β†’ cartilage callus β†’ bony callus β†’ remodeling

Explanation

Secondary bone healing, also known as indirect healing or endochondral ossification, involves a cascade of events: 1. Hematoma formation at the fracture site. 2. Inflammation and formation of a soft callus (fibrous tissue and cartilage). 3. Hard callus formation as the cartilage calcifies and is replaced by woven bone. 4. Bone remodeling, where woven bone is gradually replaced by lamellar bone, and the bone reshapes itself. The other options describe direct bone healing or incorrect sequences.

Question 2429

Topic: Biology, Genetics & Bone Healing

A 50-year-old female with a history of hypertension and obesity is scheduled for a prolonged posterior spinal fusion. Her pre-operative labs are unremarkable. During surgery, she loses 1500 mL of blood and receives 4 units of packed red blood cells and 3 liters of crystalloid. Her post-operative sodium is 135 mEq/L, potassium 4.5 mEq/L, and ionized calcium is 0.8 mmol/L (normal 1.1-1.3 mmol/L). What is the most likely cause of her hypocalcemia?

. Hypoparathyroidism
. Acute pancreatitis
. Citrate toxicity from massive transfusion
. Vitamin D deficiency
. Tumor lysis syndrome

Correct Answer & Explanation

. Citrate toxicity from massive transfusion

Explanation

Massive blood transfusions, particularly with packed red blood cells, can lead to hypocalcemia due to citrate toxicity. Citrate is an anticoagulant added to blood products; it chelates calcium, and if infused rapidly or in large volumes, the liver's ability to metabolize citrate can be overwhelmed, leading to a decrease in ionized calcium. This is a common and important complication in major orthopedic surgeries with significant blood loss. Hypoparathyroidism, acute pancreatitis, vitamin D deficiency, and tumor lysis syndrome are less likely acute causes in this context, though some may contribute to baseline risks.

Question 2430

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a recent history of a pathological femur fracture due to metastatic breast cancer undergoes intramedullary nailing. She is receiving zoledronic acid infusions. On post-operative day 2, she complains of paresthesias and muscle cramps. Her serum calcium is 7.2 mg/dL (corrected), phosphate 4.0 mg/dL. What is the most likely cause of her hypocalcemia?

. Hypoparathyroidism
. Vitamin D deficiency
. Acute pancreatitis
. Zoledronic acid-induced hypocalcemia
. Renal failure

Correct Answer & Explanation

. Zoledronic acid-induced hypocalcemia

Explanation

Zoledronic acid (a potent bisphosphonate) is used to treat hypercalcemia of malignancy and reduce skeletal-related events in metastatic bone disease. A known side effect is hypocalcemia, particularly in patients with pre-existing vitamin D deficiency or renal impairment. The symptoms of paresthesias and muscle cramps are classic for hypocalcemia. Hypoparathyroidism would also cause hypocalcemia but is less likely in this context without parathyroid surgery. Vitamin D deficiency often contributes but zoledronic acid is the direct trigger. Acute pancreatitis would have other symptoms. Renal failure could contribute but is not the primary cause of acute symptomatic hypocalcemia here.

Question 2431

Topic: Biology, Genetics & Bone Healing

A 60-year-old female with a history of osteoporosis and multiple fragility fractures is admitted for a hip fracture. She has a serum calcium of 8.0 mg/dL (normal 8.5-10.2 mg/dL) and elevated PTH. What is the most likely cause of her hypocalcemia?

. Hypoparathyroidism
. Vitamin D deficiency
. Pseudohypoparathyroidism
. Primary hyperparathyroidism with 'hungry bone syndrome'
. Chronic kidney disease

Correct Answer & Explanation

. Primary hyperparathyroidism with 'hungry bone syndrome'

Explanation

This patient's presentation of osteoporosis, multiple fractures, hypocalcemia (8.0 mg/dL), and elevated PTH is classic for 'hungry bone syndrome' occurring after the surgical removal of a parathyroid adenoma (for primary hyperparathyroidism) or, in this context, possibly a rebound effect. While the question doesn't explicitly state parathyroidectomy, 'primary hyperparathyroidism with 'hungry bone syndrome' can occur in states of high bone turnover. Given the elevated PTH, it's not hypoparathyroidism. Vitamin D deficiency often causes hypocalcemia and elevated PTH but less commonly with such profound bone disease. Pseudohypoparathyroidism would have elevated PTH but end-organ resistance. Chronic kidney disease can cause secondary hyperparathyroidism and hypocalcemia but with a different clinical picture of kidney failure.

Question 2432

Topic: Biology, Genetics & Bone Healing

Regarding the management of non-unions, which of the following statements is TRUE?

. Hypertrophic non-unions typically require bone grafting.
. Atrophic non-unions usually heal with rigid fixation alone.
. Infection is a contraindication to surgical intervention for non-union.
. The diamond concept for non-union treatment includes stability, biology, growth factors, and mechanical environment.
. Electrical stimulation is the first-line treatment for all types of non-unions.

Correct Answer & Explanation

. The diamond concept for non-union treatment includes stability, biology, growth factors, and mechanical environment.

Explanation

The 'diamond concept' for non-union treatment emphasizes four key factors: adequate stability (mechanical environment), healthy biology (vascularity, tissue viability), growth factors (e.g., bone morphogenetic proteins), and local bone graft. This holistic approach is crucial for successful healing. Hypertrophic non-unions demonstrate sufficient biology but lack stability; therefore, they primarily require stable fixation without the need for additional bone graft. Atrophic non-unions lack both stability and biology, thus requiring rigid fixation AND bone grafting. Infection is a common cause and significant complication of non-unions, and it must be addressed (debridement, antibiotics) before or concurrently with definitive non-union surgery, not a contraindication to intervention. Electrical stimulation is an adjunctive treatment, usually considered after surgical attempts, not a first-line for all non-unions, especially atrophic types.

Question 2433

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of bone morphogenetic proteins (BMPs) in promoting fracture healing?

. Inhibition of osteoclast activity.
. Stimulation of osteoblast apoptosis.
. Induction of mesenchymal stem cell differentiation into osteoblasts and chondroblasts.
. Enhancement of vascular permeability at the fracture site.
. Direct structural bridging of fracture gaps.

Correct Answer & Explanation

. Induction of mesenchymal stem cell differentiation into osteoblasts and chondroblasts.

Explanation

Bone morphogenetic proteins (BMPs) are powerful osteoinductive proteins. Their primary mechanism of action in promoting fracture healing is the induction of mesenchymal stem cells (MSCs) to differentiate into osteoblasts (bone-forming cells) and chondroblasts (cartilage-forming cells), thereby initiating and accelerating the bone repair process. They also recruit undifferentiated mesenchymal cells to the site. BMPs do not primarily inhibit osteoclast activity, stimulate osteoblast apoptosis, enhance vascular permeability, or directly structurally bridge fracture gaps; rather, they stimulate the biological cascade that leads to new bone formation.

Question 2434

Topic: Biology, Genetics & Bone Healing
Which of the following growth factors is most commonly used in clinical practice to enhance bone healing, particularly in non-union scenarios?
. Fibroblast Growth Factor (FGF).
. Vascular Endothelial Growth Factor (VEGF).
. Transforming Growth Factor-beta (TGF-Ξ²).
. Bone Morphogenetic Protein-2 (BMP-2).
. Insulin-like Growth Factor-1 (IGF-1).

Correct Answer & Explanation

. Bone Morphogenetic Protein-2 (BMP-2).

Explanation

Bone Morphogenetic Protein-2 (BMP-2), often delivered in a collagen sponge (e.g., Infuse Bone Graft), is currently the most commonly used growth factor in clinical orthopedic practice to enhance bone healing, particularly in treating recalcitrant non-unions, open tibial fractures, and lumbar spinal fusions. BMPs are potent osteoinductive agents. While other growth factors like FGF, VEGF, TGF-Ξ², and IGF-1 play roles in bone healing, they are not as widely used or approved for direct clinical application as an osteoinductive agent for fracture healing/fusion augmentation as BMP-2 (and BMP-7).

Question 2435

Topic: Biology, Genetics & Bone Healing

What is the primary orthopedic complication associated with an untreated symptomatic pectus excavatum?

. Scoliosis.
. Increased risk of rib fractures.
. Compromised cardiopulmonary function.
. Osteoporosis.
. Patellar instability.

Correct Answer & Explanation

. Compromised cardiopulmonary function.

Explanation

Severe pectus excavatum, a congenital deformity of the sternum and costal cartilages leading to a sunken chest, can cause compression of the heart and lungs. This compression can lead to compromised cardiopulmonary function, including reduced exercise tolerance, shortness of breath, and in severe cases, mitral valve prolapse or arrhythmias due to cardiac displacement. While scoliosis can coexist or be exacerbated by pectus excavatum, the primary concern directly attributable to the pectus deformity itself, particularly if symptomatic, is the impact on the heart and lungs. Rib fractures, osteoporosis, and patellar instability are not direct complications of pectus excavatum.

Question 2436

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with osteoporosis and chronic steroid use for rheumatoid arthritis presents with sudden severe back pain after a minor fall. X-rays show a new compression fracture at T12. Which of the following is an important associated risk to consider, particularly given her steroid use?

. Increased risk of deep vein thrombosis.
. Compromised bone healing.
. Increased susceptibility to gastrointestinal bleeding.
. Worsening of pre-existing diabetes.
. All of the above.

Correct Answer & Explanation

. All of the above.

Explanation

Chronic steroid use (common in rheumatoid arthritis patients) for prolonged periods leads to severe osteoporosis, increasing fracture risk. Steroids also impair bone healing, increase the risk of gastrointestinal bleeding (especially if NSAIDs are also used), and can worsen glucose control in diabetic patients or induce steroid-induced diabetes. Therefore, all these risks are important associated considerations when managing an elderly patient with osteoporosis and chronic steroid use who sustains a compression fracture. The question asks for an associated risk, not just the primary risk, making 'All of the above' the most comprehensive answer.

Question 2437

Topic: Biology, Genetics & Bone Healing

Which of the following metabolic bone disorders, often seen in patients with end-stage renal disease, is characterized by brown tumors and subperiosteal bone resorption, especially in the phalanges?

. Osteomalacia.
. Renal osteodystrophy (specifically secondary hyperparathyroidism).
. Adynamic bone disease.
. Osteoporosis.
. Paget's disease of bone.

Correct Answer & Explanation

. Renal osteodystrophy (specifically secondary hyperparathyroidism).

Explanation

Renal osteodystrophy encompasses several bone abnormalities in chronic kidney disease. Specifically, secondary hyperparathyroidism is characterized by excessive parathyroid hormone secretion in response to hypocalcemia and hyperphosphatemia. This leads to high bone turnover, osteoclastic resorption, subperiosteal bone resorption (classic in phalanges, distal clavicle), and the formation of brown tumors (osteitis fibrosa cystica). Osteomalacia involves impaired mineralization. Adynamic bone disease is low bone turnover. Osteoporosis is generalized bone loss, and Paget's is a localized disorder of bone remodeling.

Question 2438

Topic: Biology, Genetics & Bone Healing

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

. Decreased osteoclast activity
. Increased mineralization of osteoid
. Mosaic pattern of lamellar bone
. Numerous osteophytes at joint margins
. Presence of 'brown tumors'

Correct Answer & Explanation

. Mosaic pattern of lamellar bone

Explanation

Paget's disease of bone is characterized by a disorganized and accelerated remodeling process. Histologically, this leads to a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone due to haphazard deposition of new bone. It involves increased osteoclast activity followed by increased and disorganized osteoblast activity. Brown tumors are seen in hyperparathyroidism. Osteophytes are seen in osteoarthritis.

Question 2439

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis sustains a fragility fracture of the distal radius. Which of the following is the most appropriate long-term pharmacological agent to reduce future fracture risk?

. Calcium and Vitamin D supplementation alone
. Bisphosphonates (e.g., Alendronate)
. NSAIDs
. Oral corticosteroids
. Estrogen replacement therapy (ERT) alone

Correct Answer & Explanation

. Bisphosphonates (e.g., Alendronate)

Explanation

For a patient with a fragility fracture and severe osteoporosis, bisphosphonates (e.g., Alendronate, Risedronate, Zoledronic acid) are the first-line pharmacological agents to significantly reduce the risk of future fractures by inhibiting osteoclast activity. Calcium and Vitamin D supplementation are essential adjuncts but often insufficient alone for severe osteoporosis. NSAIDs are for pain relief, not fracture prevention. Oral corticosteroids can worsen osteoporosis. ERT can be used, but bisphosphonates are generally preferred as first-line for primary osteoporosis treatment due to their efficacy and broader applicability, especially given the age and fracture history.

Question 2440

Topic: Biology, Genetics & Bone Healing

What is the primary role of Vitamin D in bone health?

. Directly stimulates osteoblast activity
. Increases calcium excretion by the kidneys
. Promotes intestinal absorption of calcium and phosphate
. Inhibits parathyroid hormone secretion
. Acts as a cofactor for collagen synthesis

Correct Answer & Explanation

. Promotes intestinal absorption of calcium and phosphate

Explanation

The primary role of Vitamin D (specifically its active form, calcitriol) in bone health is to promote the intestinal absorption of calcium and phosphate. This ensures adequate mineral availability for bone mineralization. It also has effects on osteoblasts and osteoclasts, and PTH regulation, but its main direct action is on gut absorption.

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