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Biology, Genetics & Bone Healing MCQs

Practice Set 8 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 141

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman is diagnosed with an unresectable giant cell tumor of the sacrum. Her oncologist prescribes denosumab. What is the mechanism of action of this medication in the treatment of giant cell tumor of bone?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of the multinucleated giant cells
. Monoclonal antibody targeting the RANK ligand
. Inhibition of the mammalian target of rapamycin (mTOR) pathway
. Stimulation of osteoprotegerin (OPG) breakdown

Correct Answer & Explanation

. Monoclonal antibody targeting the RANK ligand

Explanation

Denosumab is a human monoclonal antibody that binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents the activation and maturation of the osteoclast-like giant cells that cause bone destruction.

Question 142

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, which phase is classically characterized by the highest peak of cellular proliferation, angiogenesis, and the formation of a fibrocartilaginous soft callus?

. Inflammatory phase
. Reparative phase
. Remodeling phase
. Hematoma formation phase
. Woven bone transformation phase

Correct Answer & Explanation

. Reparative phase

Explanation

The reparative phase features massive cellular proliferation, ingrowth of capillaries (angiogenesis), and the deposition of a fibrocartilaginous network that forms the soft callus. This soft callus eventually mineralizes into hard woven bone.

Question 143

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with knee pain. Radiographs demonstrate an eccentric, expansile, lytic, epiphyseal lesion in the proximal tibia. Biopsy reveals numerous multinucleated giant cells within a stroma of mononuclear cells. If medical therapy is considered, denosumab would be used to target which of the following?

. Vascular Endothelial Growth Factor (VEGF)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Tumor Necrosis Factor alpha (TNF-alpha)
. Interleukin-6 (IL-6)
. CD20 receptor

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

The diagnosis is a Giant Cell Tumor of bone. Denosumab is a monoclonal antibody that binds and inhibits RANKL, which normally promotes the recruitment and maturation of the osteoclast-like giant cells that drive tumor osteolysis.

Question 144

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman is started on alendronate for osteoporosis after a distal radius fracture. At the cellular level, what is the primary mechanism of action of this medication?

. Stimulation of osteoblast differentiation
. Inhibition of parathyroid hormone secretion
. Direct stimulation of osteoid mineralization
. Inhibition of osteoclast function and induction of apoptosis
. Upregulation of the RANKL pathway

Correct Answer & Explanation

. Inhibition of osteoclast function and induction of apoptosis

Explanation

Bisphosphonates like alendronate concentrate in bone and are ingested by osteoclasts. They primarily function by inhibiting the enzyme farnesyl pyrophosphate synthase, disrupting osteoclast function and inducing osteoclast apoptosis.

Question 145

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion extending to the articular surface of the distal femur. Biopsy confirms mononuclear cells and multinucleated giant cells. Which targeted pharmacological therapy is specifically indicated for unresectable cases?

. Imatinib
. Denosumab
. Zoledronic acid
. Methotrexate
. Rituximab

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumors of bone are driven by an overexpression of RANKL by the neoplastic mononuclear cells, which recruits osteoclast-like giant cells. Denosumab is a monoclonal antibody against RANKL and is highly effective for locally advanced or unresectable giant cell tumors.

Question 146

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with severe knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion extending into the metaphysis of the distal femur with no sclerotic margins. Biopsy confirms a Giant Cell Tumor (GCT) of bone. If medical management with Denosumab is initiated, the drug exerts its primary therapeutic effect by inhibiting which of the following targets?

. The RANK receptor expressed on the surface of mononuclear stromal cells.
. RANKL produced directly by the multinucleated giant cells.
. RANKL produced by the neoplastic mononuclear stromal cells.
. Osteoprotegerin (OPG) secreted by surrounding reactive osteoblasts.
. Macrophage colony-stimulating factor (M-CSF) in the tumor microenvironment.

Correct Answer & Explanation

. RANKL produced by the neoplastic mononuclear stromal cells.

Explanation

In a Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear stromal cells, which express abnormally high levels of RANKL. Denosumab binds directly to this RANKL, preventing it from activating the RANK receptor on the reactive, bone-resorbing multinucleated giant cells.

Question 147

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman with a recent distal radius fracture has a DEXA T-score of -3.1 at the lumbar spine. She is started on teriparatide therapy. What is the primary mechanism of action of this medication?

. Inhibits the osteoclast ruffled border
. Binds RANKL to prevent osteoclast activation
. Stimulates osteoblast activity via intermittent PTH receptor activation
. Cross-links collagen fibers to increase bone matrix density
. Inhibits sclerostin to promote Wnt signaling

Correct Answer & Explanation

. Stimulates osteoblast activity via intermittent PTH receptor activation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently, it acts as an anabolic agent by directly stimulating osteoblast activity and increasing new bone formation.

Question 148

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman presents with diffuse bone pain and proximal muscle weakness. Laboratory studies show low normal serum calcium, low phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone. Radiographs reveal radiolucent bands perpendicular to the bone cortex. What is the most likely diagnosis?

. Osteoporosis
. Paget's disease
. Osteomalacia
. Primary hyperparathyroidism
. Renal osteodystrophy

Correct Answer & Explanation

. Osteomalacia

Explanation

The clinical and laboratory profile (indicating secondary hyperparathyroidism due to Vitamin D deficiency) combined with radiolucent bands (Looser zones or pseudofractures) is classic for osteomalacia. Osteomalacia is characterized by the defective mineralization of newly formed osteoid.

Question 149

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with progressive bowing of his right tibia and an increasing hat size. Radiographs of the skull show "cotton wool" exudates, and the tibia shows pronounced cortical thickening. Which of the following best describes the classic histologic appearance of his bone?

. Prominent cement lines in a mosaic pattern
. Thin trabeculae with normal mineralization
. Abundant unmineralized osteoid seams
. Granulomas with caseating necrosis
. Neoplastic spindle cells producing osteoid

Correct Answer & Explanation

. Prominent cement lines in a mosaic pattern

Explanation

The patient has Paget's disease of bone, which is characterized by chaotic and excessive bone remodeling. Histologically, this is represented by prominent, disorganized cement lines creating a classic "mosaic" or "jigsaw puzzle" pattern of woven and lamellar bone.

Question 150

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy with a history of multiple low-energy fractures presents with a new diaphyseal femur fracture. On examination, he has blue sclerae and mild hearing loss. Radiographs show generalized osteopenia and severe bowing of the long bones. Which class of medication is commonly used to decrease fracture incidence in this condition?

. Selective estrogen receptor modulators
. Bisphosphonates
. Recombinant parathyroid hormone
. Sclerostin inhibitors
. Vitamin D analogues

Correct Answer & Explanation

. Bisphosphonates

Explanation

The patient has Osteogenesis Imperfecta, typically caused by an autosomal dominant defect in Type 1 collagen. Intravenous bisphosphonates (e.g., pamidronate) are the mainstay of medical therapy to increase bone mineral density and reduce the frequency of fractures in these children.

Question 151

Topic: Biology, Genetics & Bone Healing

Which of the following mechanical factors provides the primary stimulus for secondary bone healing characterized by robust callus formation?

. Absolute stability
. High oxygen tension
. Interfragmentary micro-motion
. Compression plating
. Intramembranous ossification

Correct Answer & Explanation

. Interfragmentary micro-motion

Explanation

Secondary bone healing (via callus formation and endochondral ossification) requires relative stability with interfragmentary micro-motion. Absolute stability, such as that provided by compression plating, leads to primary bone healing without callus.

Question 152

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a radiolucent, eccentric, epiphyseal-metaphyseal lesion in her proximal tibia. Biopsy shows multinucleated giant cells admixed with mononuclear stromal cells. If systemic therapy is indicated, which of the following mechanisms best describes the targeted biologic agent commonly used?

. Inhibition of the mTOR pathway
. Binding to RANKL to prevent osteoclast activation
. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of multinucleated giant cells
. Stimulation of osteoprotegerin (OPG) production

Correct Answer & Explanation

. Binding to RANKL to prevent osteoclast activation

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts and their precursors. In giant cell tumors of bone, the neoplastic mononuclear stromal cells express RANKL, which recruits the reactive multinucleated giant cells.

Question 153

Topic: Biology, Genetics & Bone Healing

A neonate is evaluated for multiple fractures and cranial nerve palsies. Radiographs show diffusely dense, 'bone-within-bone' appearance in the vertebrae and long bones. A defect in which of the following enzymes or proteins is most likely responsible for this condition?

. Alkaline phosphatase
. Type I collagen
. Carbonic anhydrase II
. Fibroblast growth factor receptor 3
. Glucocerebrosidase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis results from defective osteoclast resorption, often due to a deficiency in carbonic anhydrase II or TCIRG1 mutations. This leads to an inability to acidify Howship's lacuna, preventing the breakdown of bone matrix and resulting in dense, brittle bones.

Question 154

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive bowing of his right femur and increasing head size. Laboratory studies show markedly elevated alkaline phosphatase with normal calcium and phosphorus. Histological examination of the affected bone is most likely to show which of the following?

. Woven bone with empty lacunae
. Mosaic pattern of lamellar bone with prominent cement lines
. Sheets of plasma cells with amyloid deposition
. Atypical chondrocytes in a hyaline matrix
. Extensive replacement of marrow space by uniform small cells

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

Paget disease of bone is characterized by chaotic bone remodeling. The classic histologic hallmark is a mosaic pattern of lamellar bone with prominent cement lines due to irregular, rapid episodes of bone resorption and formation.

Question 155

Topic: Biology, Genetics & Bone Healing

A newborn is noted to have rhizomelic shortening of the limbs, frontal bossing, and midface hypoplasia. Genetic testing reveals a gain-of-function mutation in the FGFR3 gene. Which of the following best describes the fundamental defect in bone formation in this condition?

. Defective intramembranous ossification
. Impaired proliferation and hypertrophy of chondrocytes in the physis
. Defective production of type I collagen
. Inadequate mineralization of osteoid
. Overactivity of osteoclasts

Correct Answer & Explanation

. Impaired proliferation and hypertrophy of chondrocytes in the physis

Explanation

Achondroplasia is caused by an activating mutation in FGFR3, which paradoxically inhibits chondrocyte proliferation and hypertrophy in the growth plate. This selectively impairs enchondral ossification, leading to short long bones, while intramembranous ossification (cranial vault) remains relatively unaffected.

Question 156

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman has been diagnosed with lung cancer. Which of the following statements is true?

. Hypercalcaemia associated with bone metastases is best treated with intravenous steroids
. Hypercalcaemia can occur without bone metastasis
. Hypertrophic pulmonary osteoarthropathy (HPOA) is commonly seen patients with small-cell carcinoma
. Inappropriate secretion of antidiuretic hormone (SIADH) is commonly seen in patients with squamous- cell carcinoma
. Paraneoplastic syndromes occur more commonly with squamous-cell carcinomas

Correct Answer & Explanation

. Hypercalcaemia can occur without bone metastasis

Explanation

Correct Answer: B- Hypercalcaemia can occur without bone metastasis Explanation Hypercalcaemia can occur without bone metastasis Hypercalcaemia can occur as a paraneoplastic syndrome with squamous-cell carcinoma. This is caused by the production of a parathyroid hormone-related peptide by the tumour, which increases bone resorption, and renal tubular reabsorption of calcium. Hypercalcaemia associated with bone metastases is best treated with intravenous steroids Hypercalcaemia secondary to bone metastases is best treated with intravenous fluids and bisphosphonates. (Steroids are mainly used for treating hypercalcaemia associated with sarcoidosis). Hypertrophic pulmonary osteoarthropathy (HPOA) is commonly seen patients with small-cell carcinoma Hypertrophic pulmonary osteoarthropathy (HPOA) is characterised by a painful symmetrical arthropathy involving the wrist, ankle and knee joints. It is most commonly seen in patients with non- small cell cancer. Inappropriate secretion of antidiuretic hormone (SIADH) is commonly seen in patients with squamous-cell carcinoma SIADH is most common in patients with small-cell carcinoma. Paraneoplastic syndromes occur more commonly with squamous-cell carcinomas Paraneoplastic syndromes comprise a variety of non-metastatic, metabolic or neuromuscular manifestations of lung cancer. They are commonly associated with small-cell carcinoma, apart from hypercalcaemia which is seen in association with squamous cell cancer.

Question 157

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman suffers a distal radius fracture after a fall from a standing height. Dual-energy X-ray absorptiometry (DEXA) reveals a T-score of -2.8 at the femoral neck. According to the World Health Organization (WHO) criteria, what is her diagnosis?

. Normal bone density
. Osteopenia
. Osteoporosis
. Severe (established) osteoporosis
. Osteomalacia

Correct Answer & Explanation

. Severe (established) osteoporosis

Explanation

A T-score of -2.5 or lower defines osteoporosis. Because she also has a fragility fracture (distal radius), her classification upgrades to severe (or established) osteoporosis.

Question 158

Topic: Biology, Genetics & Bone Healing

A 60-year-old man with squamous cell carcinoma of the lung presents with confusion, lethargy, and severe diffuse bone pain. Laboratory results show a corrected serum calcium of 14 mg/dL. What is the initial treatment of choice?

. Intravenous bisphosphonates
. Intravenous normal saline hydration
. Subcutaneous calcitonin
. Urgent hemodialysis
. Intravenous glucocorticoids

Correct Answer & Explanation

. Intravenous normal saline hydration

Explanation

The most critical and rapid initial treatment for severe hypercalcemia of malignancy is aggressive volume expansion with intravenous normal saline. This restores intravascular volume and promotes renal calcium excretion.

Question 159

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive bowing of his right femur and increasing hat size. Laboratory studies show normal calcium and phosphorus, but markedly elevated alkaline phosphatase. Which of the following is the primary cellular defect in this disease?

. Overactive osteoblasts leading to woven bone formation
. Deficient osteoclast apoptosis resulting in increased bone resorption
. Abnormal osteoclasts with an increased number of nuclei
. Decreased osteoprotegerin (OPG) production by marrow stromal cells
. Impaired mineralization of osteoid by osteoblasts

Correct Answer & Explanation

. Abnormal osteoclasts with an increased number of nuclei

Explanation

Paget's disease of bone is primarily an osteoclast disorder characterized by highly active, multinucleated osteoclasts. This leads to a secondary, disorganized increase in osteoblastic activity.

Question 160

Topic: Biology, Genetics & Bone Healing

Articular cartilage is highly specialized to resist compressive forces. Which component of the extracellular matrix is primarily responsible for its compressive stiffness due to its ability to retain water?

. Type I collagen
. Type II collagen
. Aggrecan
. Fibronectin
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is a large proteoglycan containing negatively charged glycosaminoglycans. These negative charges attract water, providing articular cartilage with its ability to resist compressive loads.

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