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Biology, Genetics & Bone Healing MCQs

Practice Set 128 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 2541

Topic: Biology, Genetics & Bone Healing

A 68-year-old male is evaluated for an enlarging hat size and right hip pain. Radiographs reveal cortical thickening and coarse trabeculae in the pelvis. A bone biopsy is obtained. Which of the following histologic findings is the hallmark of the mixed phase of this disease?

. Woven bone with prominent osteoblastic rimming
. Mosaic pattern of lamellar bone with prominent, haphazard cement lines
. Sheets of malignant spindle cells producing osteoid matrix
. Non-mineralized osteoid seams surrounding mineralized trabeculae
. Abundant chondroid matrix with enchondral ossification

Correct Answer & Explanation

. Woven bone with prominent osteoblastic rimming

Explanation

The patient has Paget's disease of bone. The classic histologic hallmark of the mixed (intermediate) phase of Paget's disease is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with prominent, disorganized cement lines, reflecting chaotic and rapid cycles of osteoclastic resorption and osteoblastic bone formation.

Question 2542

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery to augment fracture healing and spinal fusion. DBM relies primarily on which of the following biological properties?

. Osteogenesis and osteoinduction
. Osteoinduction and osteoconduction
. Osteogenesis and osteoconduction
. Purely osteoinduction
. Purely osteoconduction

Correct Answer & Explanation

. Osteogenesis and osteoinduction

Explanation

DBM provides osteoinduction via bone morphogenetic proteins (BMPs) exposed during the demineralization process, and osteoconduction through its collagen matrix. It lacks live cells, so it is not osteogenic.

Question 2543

Topic: Biology, Genetics & Bone Healing
During the process of secondary bone healing, which type of collagen is predominantly synthesized during the soft callus (chondrogenic) phase before being replaced by hard callus?
. 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 is composed primarily of cartilage, which relies on the synthesis of Type II collagen. As endochondral ossification progresses to hard callus, chondrocytes hypertrophy (producing Type X collagen) and are replaced by osteoblasts producing Type I collagen.

Question 2544

Topic: Biology, Genetics & Bone Healing

Absolute stability with interfragmentary compression is achieved in a transverse radial shaft fracture using a dynamic compression plate. Which of the following histological processes is predominantly responsible for the subsequent bone healing?

. Endochondral ossification
. Intramembranous ossification
. Haversian remodeling
. Callus formation
. Chondrocyte hypertrophy

Correct Answer & Explanation

. Endochondral ossification

Explanation

Absolute stability without a fracture gap leads to primary bone healing, which occurs via direct Haversian remodeling. Osteoclasts at the tips of cutting cones cross the fracture site, followed immediately by osteoblasts depositing osteoid.

Question 2545

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing head size and bowing of his tibiae. Radiographs show thickened cortices and a "cotton wool" appearance of the skull. Which of the following describes the primary cellular defect initiating this condition?

. Defective osteoid mineralization
. Increased osteoblastic activity due to PTH stimulation
. Abnormal osteoclast function with increased resorptive activity
. Failure of osteoclast formation
. Mutation in Type I collagen synthesis

Correct Answer & Explanation

. Defective osteoid mineralization

Explanation

Paget's disease of bone is primarily driven by hyperactive, multinucleated osteoclasts leading to chaotic and excessive bone resorption. This initial lytic phase is later followed by a disorganized, excessive osteoblastic response.

Question 2546

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman with untreated celiac disease presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone. Which of the following is the most likely diagnosis?

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

Correct Answer & Explanation

. Osteoporosis

Explanation

Osteomalacia is characterized by a defect in bone mineralization, often due to severe Vitamin D deficiency from malabsorption. Laboratory findings typically demonstrate low calcium and phosphorus, high alkaline phosphatase, and compensatory secondary hyperparathyroidism.

Question 2547

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with progressive knee pain. Radiographs reveal an eccentric, lytic, epiphyseal lesion in the distal femur. Biopsy shows mononuclear cells and numerous multinucleated giant cells. Which targeted medical therapy is most appropriate for an unresectable lesion of this type?

. Imatinib
. Denosumab
. Doxorubicin
. Methotrexate
. Zoledronic acid

Correct Answer & Explanation

. Imatinib

Explanation

The presentation describes a Giant Cell Tumor of bone, where the neoplastic stromal cells express high levels of RANKL. Denosumab, a monoclonal antibody against RANKL, is highly effective in treating unresectable lesions by inhibiting the recruitment and activation of osteoclast-like giant cells.

Question 2548

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia. Biopsy shows multinucleated giant cells in a background of mononuclear stromal cells. Denosumab therapy is considered for this patient. What is the mechanism of action of this drug?

. Binds to RANK receptor on multinucleated giant cells
. Binds to RANKL secreted by the neoplastic mononuclear stromal cells
. Inhibits osteoprotegerin (OPG) produced by osteoblasts
. Directly induces apoptosis of multinucleated giant cells
. Inhibits vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Binds to RANK receptor on multinucleated giant cells

Explanation

Denosumab is a monoclonal antibody that binds to RANKL. In Giant Cell Tumor of bone, the neoplastic cells are the mononuclear stromal cells, which express high levels of RANKL. This RANKL binds to the RANK receptor on the non-neoplastic osteoclast-like giant cells, promoting their differentiation and leading to osteolysis. Denosumab interrupts this pathway by binding to RANKL, preventing osteoclast formation and bone destruction.

Question 2549

Topic: Biology, Genetics & Bone Healing

A 70-year-old man presents with anterior bowing of the tibia and progressive hearing loss. Labs show an elevated alkaline phosphatase with normal calcium and phosphorus. Biopsy of the tibia shows a mosaic pattern of lamellar bone. The primary cellular defect in this disease is located in which cell type?

. Osteoblast
. Osteoclast
. Osteocyte
. Chondrocyte
. Fibroblast

Correct Answer & Explanation

. Osteoclast

Explanation

Paget disease of bone is initiated by hyperactive, highly multinucleated osteoclasts, often linked to SQSTM1 mutations. The abnormal osteoblastic bone formation (mosaic pattern) is a secondary reactive process.

Question 2550

Topic: Biology, Genetics & Bone Healing

A 30-year-old postpartum woman presents with a firm mass in her abdominal wall. Excisional biopsy reveals a poorly circumscribed proliferation of bland spindle cells surrounded by dense collagen, lacking significant pleomorphism or atypical mitoses. Which of the following signaling pathways is characteristically altered in this lesion?

. Wnt/beta-catenin
. Hedgehog
. Notch
. MAPK/ERK
. PI3K/Akt

Correct Answer & Explanation

. Wnt/beta-catenin

Explanation

Desmoid fibromatosis features mutations in either the APC or CTNNB1 genes, leading to dysregulation of the Wnt/beta-catenin signaling pathway. Nuclear beta-catenin staining is a useful diagnostic marker.

Question 2551

Topic: Biology, Genetics & Bone Healing

A 65-year-old female presents with generalized bone pain, fatigue, and weight loss. Radiographs demonstrate multiple "punched-out" lytic skull lesions. Laboratory workup reveals hypercalcemia and an elevated creatinine level. The profound bone destruction in this condition is primarily mediated by which cytokine profile in the bone marrow microenvironment?

. Increased OPG / Decreased RANKL
. Increased RANKL / Decreased OPG
. Increased BMP-2 / Decreased TGF-beta
. Increased IL-10 / Decreased IL-6
. Increased IFN-gamma / Decreased TNF-alpha

Correct Answer & Explanation

. Increased OPG / Decreased RANKL

Explanation

In multiple myeloma, malignant plasma cells upregulate RANKL and downregulate osteoprotegerin (OPG) production by marrow stromal cells. This extreme imbalance leads to unrestrained osteoclast activation and characteristic lytic lesions without reactive bone formation.

Question 2552

Topic: Biology, Genetics & Bone Healing

A 70-year-old male presents with progressive hearing loss, increasing hat size, and anterolateral bowing of his tibiae. Serum alkaline phosphatase is markedly elevated, while calcium and phosphorus are normal. Familial forms of this highly active bone remodeling disorder are most strongly associated with mutations in which of the following genes?

. SQSTM1
. VDR
. COL1A1
. SOX9
. FGFR3

Correct Answer & Explanation

. SQSTM1

Explanation

Paget disease of bone is driven by primary osteoclast overactivity. Mutations in the SQSTM1 gene (encoding the p62 protein) are the most common genetic cause of familial Paget disease, leading to increased osteoclastogenesis via the RANK/NF-kB pathway.

Question 2553

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with multiple painless, bony protuberances around his knees and ankles pointing away from the joint. His father has similar lesions. The genetic mutation responsible for this condition directly causes a defect in which of the following cellular processes?

. Synthesis of heparan sulfate proteoglycans
. cAMP signal transduction
. Wnt/beta-catenin signaling pathway
. p53 tumor suppressor function
. Osteoclast-mediated bone resorption

Correct Answer & Explanation

. Synthesis of heparan sulfate proteoglycans

Explanation

Multiple Hereditary Exostoses (MHE) is caused by autosomal dominant mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for the synthesis of heparan sulfate, which is crucial for normal physeal regulation.

Question 2554

Topic: Biology, Genetics & Bone Healing

An 80-year-old man presents with increasing hat size and dull, aching pain in his right femur. Laboratory studies show markedly elevated serum alkaline phosphatase with normal calcium and phosphorus levels. Which of the following gene mutations is most strongly implicated in the familial form of this disease?

. SQSTM1
. FGFR3
. COL1A1
. COMP
. RUNX2

Correct Answer & Explanation

. SQSTM1

Explanation

Paget disease of bone is characterized by accelerated bone remodeling, resulting in a mosaic pattern of lamellar bone. A significant proportion of familial cases are associated with mutations in the SQSTM1 gene (encoding p62), which hyperactivates osteoclasts.

Question 2555

Topic: Biology, Genetics & Bone Healing

A 68-year-old female who has been taking alendronate for 8 years presents with a 3-month history of insidious onset left thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line extending partially through the lateral cortex of the left subtrochanteric femur. What is the most appropriate management?

. Reassurance and continuation of alendronate
. Discontinuation of alendronate, protected weight-bearing, and administration of Teriparatide for conservative healing
. Discontinuation of alendronate and prophylactic cephalomedullary nailing of the left femur
. Open biopsy to rule out malignancy
. External beam radiation

Correct Answer & Explanation

. Reassurance and continuation of alendronate

Explanation

This patient presents with a symptomatic, incomplete atypical femur fracture (AFF) associated with long-term bisphosphonate use. The classic radiographic signs include lateral cortical thickening ('beaking') and a transverse fracture line. Because she is symptomatic (thigh pain), the risk of progression to a complete fracture is extremely high. The standard of care for a symptomatic incomplete AFF is prophylactic intramedullary nailing, along with discontinuation of the bisphosphonate. Medical management alone is inadequate for a symptomatic lesion.

Question 2556

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman on long-term alendronate therapy presents with a 3-month history of a dull, aching pain in her right thigh. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur.

What is the recommended standard of care for this patient?

. Discontinue alendronate and begin teriparatide exclusively
. Discontinue alendronate, initiate protected weight-bearing, and observe
. Discontinue alendronate and perform prophylactic intramedullary nailing
. Addition of a bisphosphonate with a different mechanism of action
. Open biopsy of the lesion to rule out a primary bone malignancy

Correct Answer & Explanation

. Discontinue alendronate and begin teriparatide exclusively

Explanation

This patient presents with a symptomatic incomplete atypical femur fracture characterized by the "dreaded black line" (transverse radiolucency) on the tension side of the lateral cortex, associated with long-term bisphosphonate use. Because she has prodromal thigh pain and a visible cortical defect, the fracture is at high risk for completion. Prophylactic intramedullary nailing is the surgical treatment of choice. Medical management includes discontinuing the bisphosphonate and considering teriparatide.

Question 2557

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with a 10-year history of alendronate use presents with sudden, atraumatic thigh pain. Radiographs reveal a transverse fracture of the lateral cortex of the subtrochanteric femur with a focal periosteal reaction ('beaking'). What is the pathophysiological mechanism behind this fracture?

. Increased osteoclastic bone resorption
. Severe vitamin D deficiency leading to osteomalacia
. Suppression of bone remodeling leading to microdamage accumulation
. Primary hyperparathyroidism
. Osteogenesis imperfecta type I

Correct Answer & Explanation

. Increased osteoclastic bone resorption

Explanation

Long-term use of bisphosphonates (typically > 5 years) suppresses osteoclast-mediated bone remodeling. This severe suppression prevents the repair of normal physiological microdamage in the bone, leading to accumulation of microcracks and increased brittleness. This mechanism is responsible for bisphosphonate-related atypical femoral fractures, which characteristically present with lateral cortical thickening, 'beaking', and a transverse or short oblique fracture pattern.

Question 2558

Topic: Biology, Genetics & Bone Healing

Osteoclast differentiation and activation are directly stimulated by the binding of RANK ligand (RANKL) to RANK. Which of the following cell types is the primary source of RANKL in the bone microenvironment?

. Osteoclasts
. Osteoblasts
. Chondrocytes
. Macrophages
. Osteocytes

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoblasts and their precursors are the primary source of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand) in the bone microenvironment. RANKL binds to the RANK receptor on the surface of osteoclast precursors, stimulating their differentiation and activation into mature, bone-resorbing osteoclasts. Osteoprotegerin (OPG), also secreted by osteoblasts, acts as a decoy receptor for RANKL, inhibiting this process.

Question 2559

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is NOT osteoinductive in humans and instead acts as an inhibitor of bone formation?

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

Correct Answer & Explanation

. BMP-2

Explanation

BMP-3 (also known as osteogenin) acts as a negative regulator of bone density and opposes the osteogenic effects of other BMPs like BMP-2 and BMP-7 (OP-1). BMP-2 and BMP-7 are well-known osteoinductive agents used clinically.

Question 2560

Topic: Biology, Genetics & Bone Healing

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

. < 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. 100%

Correct Answer & Explanation

. < 2%

Explanation

Perren's strain theory postulates that the type of tissue that forms in a fracture gap depends on the local strain. Lamellar bone can only form under very low strain environments (< 2%). Woven bone can form up to 10% strain, whereas granulation tissue can tolerate up to 100% strain. Absolute stability (strain < 2%) leads to primary bone healing.

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