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Biology, Genetics & Bone Healing MCQs

Practice Set 9 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 161

Topic: Biology, Genetics & Bone Healing

A 25-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal lesion in the distal femur extending to the subchondral bone. A biopsy confirms Giant Cell Tumor of Bone (GCT). Which medication works by inhibiting RANKL to reduce recurrence in surgically difficult GCTs?

. Zoledronic acid
. Denosumab
. Teriparatide
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab is a monoclonal antibody against RANKL. In Giant Cell Tumors, the neoplastic stromal cells express RANKL, which recruits osteoclast-like giant cells; denosumab breaks this cycle.

Question 162

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman sustains a distal radius fracture. A DEXA scan reveals a T-score of -3.1 in the lumbar spine. She is prescribed teriparatide. What is the mechanism of action of this medication?

. Inhibition of osteoclast proton pumps
. Binding to RANKL to prevent osteoclast activation
. Intermittent administration stimulating osteoblastic bone formation
. Direct incorporation into bone matrix forming degradation-resistant hydroxyapatite
. Selective estrogen receptor modulation

Correct Answer & Explanation

. Intermittent administration stimulating osteoblastic bone formation

Explanation

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

Question 163

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with a history of recurrent fractures, cranial nerve palsies, and diffuse sclerosis of the skeletal system on radiographs, including a "rugger jersey" spine appearance. Which of the following is the primary pathophysiological defect in this condition?

. Defective hydroxylation of collagen
. Carbonic anhydrase II mutation
. Defect in Type I collagen synthesis
. FGFR3 gene mutation
. Vitamin D receptor mutation

Correct Answer & Explanation

. Carbonic anhydrase II mutation

Explanation

This patient has osteopetrosis, a disease characterized by impaired osteoclast function. A common genetic defect is a mutation in carbonic anhydrase II, which prevents osteoclasts from creating the acidic environment necessary for bone resorption.

Question 164

Topic: Biology, Genetics & Bone Healing
A 6-year-old girl is evaluated for recurrent fractures with minimal trauma. Examination reveals a bluish tint to her sclerae and mild hearing loss. This condition is most commonly caused by a mutation affecting which of the following proteins?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type IX collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is most commonly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. This leads to defective synthesis of Type I collagen, the predominant collagen in bone, sclera, and dentin.

Question 165

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive hearing loss, increasing hat size, and deep, aching bone pain in his right thigh. Radiographs show cortical thickening and trabecular coarsening. What is the characteristic histological finding of the bone in the mixed phase of this disease?

. Haphazard arrangement of woven bone
. Mosaic pattern of lamellar bone with prominent cement lines
. Sheets of malignant spindle cells producing osteoid
. Benign cartilage cap overlying medullary bone
. Thickened osteoid seams with unmineralized matrix

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

Paget's disease of bone in its mixed osteoblastic/osteoclastic phase is characterized histologically by a mosaic pattern of lamellar bone with prominent, haphazard cement lines. This results from chaotic and rapid bone turnover.

Question 166

Topic: Biology, Genetics & Bone Healing

A 7-year-old boy with a highly restricted diet presents with bleeding gums, petechiae, and bone pain. Radiographs reveal a periosteal reaction and a dense zone of provisional calcification. The underlying biochemical defect involves the impaired function of which process?

. Hydroxylation of proline and lysine residues
. Defective cross-linking of elastin
. Abnormal cleavage of procollagen
. Inhibition of osteoclast proton pumps
. Impaired primary mineralization of osteoid

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has scurvy due to Vitamin C deficiency. Vitamin C is an essential cofactor for prolyl and lysyl hydroxylases, and its deficiency leads to impaired hydroxylation and subsequent failure of collagen cross-linking.

Question 167

Topic: Biology, Genetics & Bone Healing

A surgeon plans to use demineralized bone matrix (DBM) to augment a posterolateral spinal fusion. Which of the following best describes the biological properties of DBM?

. Osteogenic only
. Osteoconductive only
. Osteoinductive and osteoconductive
. Osteogenic and osteoinductive
. Osteoconductive, osteoinductive, and osteogenic

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) lacks live cells, so it is not osteogenic. It provides a scaffold (osteoconductive) and contains bone morphogenetic proteins (BMPs) that stimulate bone formation (osteoinductive).

Question 168

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing, the transition from a soft cartilaginous callus to a hard bony callus is critically dependent on which of the following microenvironmental changes?

. Increased mechanical instability
. Increasing oxygen tension
. Decreasing oxygen tension
. Highly acidic environment
. Depletion of local vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Increasing oxygen tension

Explanation

Fracture healing transitions from a soft callus (chondrogenesis) to a hard callus (osteogenesis) via endochondral ossification. This process requires neovascularization, which increases local oxygen tension and favors osteoblastic bone formation.

Question 169

Topic: Biology, Genetics & Bone Healing

In the evaluation of bone morphogenetic proteins (BMPs), which BMP has been FDA-approved for use in acute open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-6
. BMP-7

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use as an adjunct in acute, open tibial shaft fractures stabilized with an intramedullary nail. It is also approved for anterior lumbar interbody fusion (ALIF).

Question 170

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with a recent acute osteoporotic vertebral compression fracture is started on Denosumab. What is the specific mechanism of action of this medication?

. Inhibits osteoclast farnesyl pyrophosphate synthase
. Monoclonal antibody against RANKL
. Recombinant parathyroid hormone analog
. Selective estrogen receptor modulator
. Monoclonal antibody against sclerostin

Correct Answer & Explanation

. Monoclonal antibody against RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), preventing it from activating RANK on the surface of osteoclasts, thereby inhibiting osteoclast maturation and survival.

Question 171

Topic: Biology, Genetics & Bone Healing
Articular cartilage relies on a specific extracellular matrix composition for its unique biomechanical properties, including load-bearing and low friction. Which collagen type is the predominant structural protein in the extracellular matrix of normal adult hyaline articular cartilage?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

Type II collagen accounts for 90-95% of the collagen in normal hyaline articular cartilage. It provides the tensile strength and framework that restrains the swelling pressure of the proteoglycans.

Question 172

Topic: Biology, Genetics & Bone Healing

A 35-year-old man undergoes open reduction and internal fixation of a transverse radial shaft fracture using a 3.5mm dynamic compression plate to achieve absolute stability. Which of the following best describes the predominant mechanism of bone healing expected in this scenario?

. Endochondral ossification
. Intramembranous ossification with robust callus
. Primary bone healing via Haversian remodeling
. Chondrocyte hypertrophy followed by calcification
. Fibrous tissue interposition followed by woven bone formation

Correct Answer & Explanation

. Primary bone healing via Haversian remodeling

Explanation

When absolute stability is achieved with compression plating, the fracture heals via primary bone healing (direct contact healing) without the formation of a provisional callus. This process relies entirely on the direct progression of cutting cones and Haversian remodeling across the fracture site.

Question 173

Topic: Biology, Genetics & Bone Healing

Which specific mode of bone healing occurs under conditions of absolute biomechanical stability, such as following anatomic open reduction and internal fixation with a dynamic compression plate?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with callus formation
. Chondrogenesis

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Primary (Haversian) bone healing requires absolute stability. It directly remodels the fracture site via osteoclastic cutting cones and osteoblastic bone formation without an intermediate soft callus.

Question 174

Topic: Biology, Genetics & Bone Healing
During the process of secondary bone healing, a soft callus forms at the fracture site to bridge the gap before endochondral ossification occurs. What type of collagen is most predominant in this soft callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

The soft callus primarily consists of fibrocartilage, making Type II collagen the predominant type during this phase. As endochondral ossification progresses, it is gradually replaced by woven bone, which is predominantly Type I collagen.

Question 175

Topic: Biology, Genetics & Bone Healing

A 55-year-old patient with poorly controlled diabetes mellitus presents with a swollen, erythematous, and warm foot with a new 'rocker-bottom' deformity, but minimal pain. What is the proposed pathophysiology of the bone destruction in the active, acute phase of Charcot neuroarthropathy according to the neurovascular theory?

. Microvascular thrombosis leading to avascular necrosis
. Autonomic neuropathy causing increased perfusion and bone resorption
. Direct bacterial invasion of the bone
. Autoimmune destruction of articular cartilage
. Venous stasis leading to periosteal new bone formation

Correct Answer & Explanation

. Autonomic neuropathy causing increased perfusion and bone resorption

Explanation

The neurovascular theory posits that autonomic neuropathy results in loss of sympathetic tone, causing vasodilation, hyperemia, and increased active bone resorption by osteoclasts, which subsequently leads to mechanical failure and fractures.

Question 176

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with severe osteoporosis is being treated with Denosumab to reduce her risk of pathologic fractures. What is the specific mechanism of action of this medication?

. Binds directly to osteoclast ruffled borders
. Stimulates osteoblast differentiation via Wnt signaling
. Monoclonal antibody targeting RANKL
. Inhibits farnesyl pyrophosphate synthase
. Recombinant parathyroid hormone analog

Correct Answer & Explanation

. Monoclonal antibody targeting RANKL

Explanation

Denosumab is a human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), preventing its interaction with RANK on osteoclasts. This inhibits osteoclast formation, function, and survival.

Question 177

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs show a distinct, eccentrically located lytic epiphyseal lesion in the proximal tibia. Biopsy confirms multinucleated giant cells resembling osteoclasts. Which targeted systemic therapy is most appropriate as an adjuvant?

. Denosumab
. Infliximab
. Rituximab
. Methotrexate
. Teriparatide

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab is a monoclonal antibody against RANKL. It prevents the maturation of osteoclast-like giant cells, making it a highly effective treatment for Giant Cell Tumor of bone.

Question 178

Topic: Biology, Genetics & Bone Healing

A 72-year-old male presents with increasing pain in his right thigh and increasing hat size. Radiographs of the femur show cortical thickening, coarse trabeculation, and a bowing deformity. Laboratory studies show a significantly elevated alkaline phosphatase with normal calcium and phosphorus. Which of the following is the primary cellular defect?

. Decreased osteoblast function
. Increased osteoclast activity followed by chaotic osteoblast activity
. Impaired mineralization of osteoid
. Fibroblast proliferation replacing bone marrow
. Monoclonal plasma cell proliferation

Correct Answer & Explanation

. Increased osteoclast activity followed by chaotic osteoblast activity

Explanation

Paget's disease of bone is characterized by an initial phase of furious osteoclastic bone resorption followed by a disorganized, chaotic phase of osteoblastic bone formation. This results in structurally weak, woven bone.

Question 179

Topic: Biology, Genetics & Bone Healing

A 50-year-old male with end-stage renal disease on hemodialysis presents with diffuse bone pain. Radiographs reveal subperiosteal bone resorption in the phalanges and a "rugger jersey" spine. Which of the following laboratory profiles is expected?

. High calcium, high phosphate, low PTH
. Low calcium, high phosphate, high PTH
. High calcium, low phosphate, high PTH
. Low calcium, low phosphate, low PTH
. Normal calcium, normal phosphate, normal PTH

Correct Answer & Explanation

. Low calcium, high phosphate, high PTH

Explanation

Renal osteodystrophy (secondary hyperparathyroidism) results from phosphate retention and failure of the kidneys to convert Vitamin D to its active form. This leads to hypocalcemia, hyperphosphatemia, and a compensatory significant rise in parathyroid hormone (PTH).

Question 180

Topic: Biology, Genetics & Bone Healing

A 14-year-old girl is evaluated for recurrent fractures following minor trauma. She also has a history of severe anemia and cranial nerve palsies. Radiographs reveal generalized dense, sclerotic bones with absent medullary canals and an "Erlenmeyer flask" deformity of the distal femurs. The pathogenesis involves a defect in which of the following?

. Type I collagen synthesis
. Osteoclast ruffled border function
. Fibroblast growth factor receptor 3 (FGFR3)
. Vitamin D receptor
. Runx2/Cbfa1 transcription factor

Correct Answer & Explanation

. Osteoclast ruffled border function

Explanation

Osteopetrosis (marble bone disease) is caused by defective osteoclastic bone resorption, often due to a failure to form the ruffled border. This results in dense, brittle bones that obliterate the marrow space, leading to cytopenias.

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