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Biology, Genetics & Bone Healing MCQs

Practice Set 133 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 2641

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with progressively increasing hat size, hearing loss, and bowing of his tibiae. Radiographs show thickened cortices and a coarse trabecular pattern. Bone biopsy reveals a mosaic pattern of lamellar bone with prominent cement lines. Which of the following gene mutations is most strongly associated with the familial form of this condition?

. SQSTM1
. COL1A1
. FGFR3
. RUNX2
. SH3BP2

Correct Answer & Explanation

. SQSTM1

Explanation

The patient has Paget disease of bone (osteitis deformans), characterized by a mosaic pattern of woven and lamellar bone due to dysregulated bone remodeling. Mutations in the SQSTM1 gene (encoding p62) are identified in 40-50% of familial cases, leading to increased NF-kB activation in osteoclasts.

Question 2642

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy is evaluated for multiple painless, bony bumps around his knees and shoulders. Radiographs show multiple pedunculated excrescences pointing away from the joint line. Genetic testing reveals a loss-of-function mutation in EXT1. The normal product of this gene is essential for which of the following cellular processes?

. Collagen cross-linking
. Tyrosine kinase receptor signaling
. Heparan sulfate synthesis
. Wnt signaling inhibition
. DNA mismatch repair

Correct Answer & Explanation

. Collagen cross-linking

Explanation

Multiple Hereditary Exostoses (MHE) is caused by autosomal dominant mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases that are essential for the synthesis of heparan sulfate, which regulates normal chondrocyte proliferation and differentiation.

Question 2643

Topic: Biology, Genetics & Bone Healing

A 68-year-old female on chronic alendronate therapy for osteoporosis complains of 3 months of vague left thigh pain. Radiographs reveal a transverse radiolucent line with focal cortical thickening on the lateral aspect of her left femoral shaft. What is the fundamental biomechanical reason these atypical femur fractures typically initiate at the lateral cortex?

. The lateral cortex has diminished vascularity compared to the medial cortex
. The lateral cortex undergoes repetitive tensile stress during normal weight-bearing
. Bisphosphonates selectively concentrate in the lateral cortex
. The medial cortex is under tensile stress, pushing the fracture laterally
. The iliotibial band creates a continuous shear force across the lateral diaphysis

Correct Answer & Explanation

. The lateral cortex has diminished vascularity compared to the medial cortex

Explanation

Atypical femoral fractures (AFFs) associated with prolonged bisphosphonate use characteristically begin at the lateral cortex. Biomechanically, the normal bow of the femur causes the lateral cortex to be placed under repetitive tensile stress during weight-bearing, while the medial cortex is under compressive stress. Over-suppression of targeted bone remodeling leads to accumulation of microdamage, which eventually manifests as a stress fracture on the tension (lateral) side.

Question 2644

Topic: Biology, Genetics & Bone Healing

A 72-year-old female on prolonged oral bisphosphonates presents with unremitting anterior thigh pain. Radiographs reveal focal lateral cortical thickening (the 'beak' sign) and a transverse radiolucent line in the proximal third of the femur. What is the prophylactic treatment of choice?

. Prophylactic cephalomedullary nailing
. Prophylactic locked plating
. Immediate cessation of medication and restricted weight-bearing
. Administration of teriparatide and observation

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing

Explanation

Atypical femur fractures associated with bisphosphonate use often present as a symptomatic incomplete fracture on the tension (lateral) side. Prophylactic cephalomedullary nailing is the standard of care to prevent a catastrophic complete fracture.

Question 2645

Topic: Biology, Genetics & Bone Healing

A 71-year-old female who has been taking oral alendronate for 9 years presents with atraumatic lateral thigh pain. Radiographs demonstrate focal lateral cortical thickening of the proximal femoral diaphysis with a subtle transverse radiolucent line. What is the mechanism of action of the medication most strongly associated with this fracture pattern?

. Direct inhibition of osteoblast bone matrix synthesis
. Inhibition of farnesyl pyrophosphate synthase, leading to osteoclast apoptosis
. Blockade of RANKL, preventing osteoclast activation and survival
. Competitive inhibition of calcium absorption in the gastrointestinal tract
. Simulation of Wnt/beta-catenin signaling, causing brittle cortical hypertrophy

Correct Answer & Explanation

. Direct inhibition of osteoblast bone matrix synthesis

Explanation

The patient has a classic atypical femur fracture (AFF) associated with long-term bisphosphonate use. Bisphosphonates (like alendronate) are endocytosed by osteoclasts during bone resorption and act by inhibiting farnesyl pyrophosphate synthase (FPPS), an enzyme in the mevalonate pathway. This disrupts small GTPase signaling, ultimately causing osteoclast apoptosis. Denosumab blocks RANKL. Long-term osteoclast inhibition prevents targeted remodeling of microdamage, leading to AFFs.

Question 2646

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in bone repair and osteoinduction. Following the binding of a BMP molecule to its specific cell surface receptor, which of the following intracellular signaling proteins is primarily phosphorylated to translocate to the nucleus and promote osteoblast differentiation?

. Beta-catenin
. STAT3
. Smad 1/5/8
. ERK 1/2
. NF-kappaB

Correct Answer & Explanation

. Beta-catenin

Explanation

BMP signaling is primarily mediated through the canonical Smad pathway. When BMP binds to its heterodimeric serine/threonine kinase receptor, it phosphorylates receptor-regulated Smads (Smad 1, 5, and 8). These then form a complex with the co-Smad (Smad 4), which translocates to the nucleus to regulate the transcription of osteogenic genes, including Runx2.

Question 2647

Topic: Biology, Genetics & Bone Healing

Denosumab has emerged as an effective medical therapy for locally advanced or unresectable giant cell tumors of bone (GCTB). What is the specific cellular target and mechanism of action of this medication?

. It inhibits VEGF, thereby preventing tumor angiogenesis.
. It is a monoclonal antibody that binds to RANKL, preventing osteoclast precursor activation.
. It is a tyrosine kinase inhibitor that blocks the c-KIT receptor.
. It causes direct apoptosis of the neoplastic mononuclear stromal cells.
. It binds competitively to the RANK receptor situated directly on mature osteoclasts.

Correct Answer & Explanation

. It inhibits VEGF, thereby preventing tumor angiogenesis.

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). In GCTB, RANKL is excessively secreted by the neoplastic mononuclear stromal cells. By neutralizing RANKL, denosumab prevents it from binding to the RANK receptor on osteoclast precursors, dramatically inhibiting osteoclast-mediated bone destruction.

Question 2648

Topic: Biology, Genetics & Bone Healing

A 25-year-old female presents with a lytic, eccentrically located, expansile lesion in the distal femur epiphysis extending to the subchondral bone. Core needle biopsy histology shows sheets of multinucleated giant cells in a stroma of plump mononuclear cells. Neoadjuvant therapy with Denosumab is considered. What is the precise mechanism of action of Denosumab?

. Inhibits Vascular Endothelial Growth Factor (VEGF)
. Binds directly to RANK on osteoclasts
. Monoclonal antibody against RANK Ligand (RANKL)
. Inhibits osteoprotegerin (OPG)
. Tyrosine kinase inhibitor

Correct Answer & Explanation

. Inhibits Vascular Endothelial Growth Factor (VEGF)

Explanation

Giant Cell Tumor of Bone (GCTB) stromal cells express RANK Ligand (RANKL), which recruits and activates the reactive multinucleated osteoclast-like giant cells that cause bone destruction. Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclasts, thus halting osteolysis.

Question 2649

Topic: Biology, Genetics & Bone Healing

Which of the following molecules, produced by osteoblasts, acts as a critical decoy receptor for the receptor activator of nuclear factor-kappa B ligand (RANKL), thereby preventing its binding to RANK and inhibiting osteoclast differentiation and bone resorption?

. Macrophage colony-stimulating factor (M-CSF)
. Osteoprotegerin (OPG)
. Osteocalcin
. Sclerostin
. Cathepsin K

Correct Answer & Explanation

. Macrophage colony-stimulating factor (M-CSF)

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from binding to the RANK receptor on osteoclast precursors. This acts as a negative regulator of osteoclastogenesis. The balance between RANKL and OPG is the primary determinant of bone resorption rate.

Question 2650

Topic: Biology, Genetics & Bone Healing

A 35-year-old male receives systemic denosumab therapy prior to surgical resection of a large, recurrent giant cell tumor of the distal femur. By what mechanism does denosumab alter the histological appearance of this tumor?

. It directly induces apoptosis of the neoplastic mononuclear stromal cells.
. It binds specifically to RANK receptors on multinucleated giant cells, inhibiting their function.
. It binds to RANK-Ligand (RANKL), preventing the activation and differentiation of osteoclast-like giant cells.
. It alkylates DNA in the rapidly dividing neoplastic stromal cells.
. It competitively inhibits the Wnt/beta-catenin signaling pathway.

Correct Answer & Explanation

. It directly induces apoptosis of the neoplastic mononuclear stromal cells.

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANK-Ligand (RANKL), not the RANK receptor. In Giant Cell Tumor (GCT) of bone, the neoplastic mononuclear stromal cells secrete high levels of RANKL, which recruits and activates the reactive multinucleated giant cells. By neutralizing RANKL, denosumab halts giant cell formation and activity, leading to a marked histological depletion of giant cells and replacement with dense woven bone and fibrous stroma.

Question 2651

Topic: Biology, Genetics & Bone Healing

A 68-year-old female on alendronate for 12 years presents with a low-energy transverse subtrochanteric fracture of the right femur with lateral cortical "beaking." She complains of 3 months of aching pain in her left thigh as well. Radiographs of the left femur show lateral cortical thickening but no complete fracture. What is the recommended management for the left femur?

. Immediate cessation of bisphosphonates and close observation
. Prophylactic intramedullary nailing of the left femur
. Application of a custom functional hip brace
. Initiation of teriparatide without surgical intervention
. Core decompression of the left proximal femur

Correct Answer & Explanation

. Immediate cessation of bisphosphonates and close observation

Explanation

This patient has an atypical femur fracture associated with long-term bisphosphonate use. The presence of prodromal pain and radiographic lateral cortical thickening on the contralateral side indicates an impending fracture, necessitating prophylactic intramedullary nailing.

Question 2652

Topic: Biology, Genetics & Bone Healing

Secondary bone healing (healing by callus formation) is characterized by a sequential progression of tissue types following a fracture. What is the correct order of the predominant tissue types bridging the fracture gap during this physiological process?

. Hematoma -> Woven bone -> Cartilage -> Lamellar bone
. Hematoma -> Granulation tissue -> Cartilage -> Woven bone -> Lamellar bone
. Granulation tissue -> Hematoma -> Woven bone -> Cartilage -> Lamellar bone
. Hematoma -> Cartilage -> Granulation tissue -> Lamellar bone -> Woven bone
. Woven bone -> Hematoma -> Granulation tissue -> Cartilage -> Lamellar bone

Correct Answer & Explanation

. Hematoma -> Woven bone -> Cartilage -> Lamellar bone

Explanation

Secondary fracture healing progresses sequentially through distinct phases: Inflammation (Hematoma followed by Granulation tissue), Soft Callus formation (predominantly Cartilage), Hard Callus formation (calcification into Woven bone), and finally Remodeling (replacement of woven bone with mature Lamellar bone along lines of stress).

Question 2653

Topic: Biology, Genetics & Bone Healing
A 75-year-old female with severe osteoporosis complains of unremitting back pain 6 months after a minor fall. Her pain worsens significantly when standing and improves when supine. A lateral radiograph demonstrates an intravertebral vacuum cleft sign within a severely compressed T12 vertebral body. What is the eponymous name of this condition?
. Pott's disease
. Kümmell disease
. Baastrup's disease
. Calvé's disease
. Scheuermann's disease

Correct Answer & Explanation

. Kümmell disease

Explanation

Kümmell disease is delayed post-traumatic avascular necrosis of a vertebral body. It presents as a progressive vertebral collapse following a minor injury, often after an asymptomatic period. The hallmark radiographic finding is the intravertebral vacuum cleft sign on extension films, representing nitrogen gas filling the necrotic cavity.

Question 2654

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with progressive thigh pain 15 years after an uncemented THA. Radiographs reveal extensive endosteal scalloping and localized bone loss around the proximal femur. The stem appears to have subsided 4 mm. What is the primary biological mediator responsible for the activation of osteoclasts in this disease process?

. Interleukin-10 (IL-10)
. Transforming growth factor beta (TGF-b)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Bone morphogenetic protein-2 (BMP-2)
. Interferon gamma (IFN-y)

Correct Answer & Explanation

. Interleukin-10 (IL-10)

Explanation

Particle disease (aseptic loosening) is driven by macrophage phagocytosis of wear debris. This triggers the release of pro-inflammatory cytokines, which ultimately stimulate the production of RANKL, the primary mediator of osteoclast activation.

Question 2655

Topic: Biology, Genetics & Bone Healing

What is the primary cellular cascade responsible for aseptic loosening and periprosthetic osteolysis in a total hip arthroplasty?

. Direct toxicity of cobalt and chromium ions leading to osteoblast apoptosis
. Macrophage phagocytosis of particulate wear debris leading to the release of TNF-alpha and IL-1, and subsequent osteoclast activation
. Neutrophil-mediated respiratory burst causing local tissue necrosis around the implant
. T-cell mediated delayed type IV hypersensitivity reaction to nickel
. Osteoclast activation driven exclusively by mechanically induced sheer stress on the bone-cement interface

Correct Answer & Explanation

. Direct toxicity of cobalt and chromium ions leading to osteoblast apoptosis

Explanation

Periprosthetic osteolysis is primarily a macrophage-mediated biologic response to particulate wear debris (most commonly polyethylene). Macrophages phagocytose these particles but cannot digest them, leading to activation and the release of pro-inflammatory cytokines such as TNF-alpha, IL-1, IL-6, and PGE2. These cytokines increase the expression of RANKL, which strongly activates osteoclasts, leading to bone resorption and eventual implant loosening.

Question 2656

Topic: Biology, Genetics & Bone Healing

A patient presents with aseptic loosening and extensive periprosthetic osteolysis 15 years after a cementless total hip arthroplasty. What is the primary biological mediator responsible for osteoclast activation in this process?

. Interleukin-10 (IL-10)
. Transforming growth factor beta (TGF-beta)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoprotegerin (OPG)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Interleukin-10 (IL-10)

Explanation

Particle wear debris is phagocytosed by macrophages, which release pro-inflammatory cytokines. These cytokines stimulate the expression of RANKL by osteoblasts and fibroblasts. RANKL binds to the RANK receptor on osteoclast precursors, leading to osteoclastogenesis and subsequent osteolysis.

Question 2657

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum gap strain tolerated for lamellar bone formation?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Up to 50%
. Up to 100%

Correct Answer & Explanation

. Less than 2%

Explanation

According to Perren's strain theory, lamellar bone can only form when the interfragmentary strain is less than 2%. Woven bone forms at strains between 2% and 10%, while granulation tissue can tolerate up to 100% strain without rupturing.

Question 2658

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft substitutes or biological agents possesses strictly osteoinductive properties without being osteoconductive or osteogenic?

. Demineralized bone matrix (DBM)
. Cancellous allograft
. Bone morphogenetic protein-2 (BMP-2)
. Calcium phosphate cement
. Autologous iliac crest bone graft

Correct Answer & Explanation

. Demineralized bone matrix (DBM)

Explanation

BMP-2 is a purely osteoinductive agent (it induces differentiation of mesenchymal stem cells into osteoblasts). Demineralized bone matrix (DBM) is both osteoinductive and osteoconductive. Cancellous allograft and calcium phosphate are solely osteoconductive. Autograft provides all three: osteoinduction, osteoconduction, and osteogenesis.

Question 2659

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the medical management of unresectable Giant Cell Tumor of Bone (GCTB). Which of the following accurately describes the molecular target of this medication?

. RANK receptor on osteoclast precursors
. RANK ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. RANK receptor on osteoclast precursors

Explanation

Denosumab is a fully human monoclonal antibody that directly targets and binds to RANK Ligand (RANKL). RANKL is produced by the neoplastic stromal cells in Giant Cell Tumor of Bone. By binding RANKL, Denosumab prevents it from interacting with the RANK receptor on osteoclasts and their precursors, thereby inhibiting osteoclast activation, differentiation, and survival.

Question 2660

Topic: Biology, Genetics & Bone Healing

A severely malnourished patient presents with bleeding gums, perifollicular hemorrhages, and impaired wound healing. Radiographs demonstrate osteopenia and an intensely radiodense line at the metaphysis. The underlying metabolic deficiency primarily impairs which of the following steps in collagen synthesis?

. Cross-linking of collagen via lysyl oxidase
. Hydroxylation of proline and lysine residues
. Cleavage of procollagen C- and N-terminals
. Intracellular assembly of the triple helix
. Glycosylation of hydroxylysine residues

Correct Answer & Explanation

. Cross-linking of collagen via lysyl oxidase

Explanation

The patient has Scurvy (Vitamin C deficiency). Ascorbic acid is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Without Vitamin C, the hydroxylation of proline and lysine residues in the rough endoplasmic reticulum cannot occur, preventing stable triple helix formation of procollagen. Lysyl oxidase (Option A) requires copper and is defective in Menkes disease.

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