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Biology, Genetics & Bone Healing MCQs

Practice Set 31 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 601

Topic: Biology, Genetics & Bone Healing

An 80-year-old female with severe osteoporosis and a recent femoral neck fracture is placed on romosozumab. What is the precise mechanism of action of this medication?

. Monoclonal antibody that binds to and inhibits RANK ligand, preventing osteoclast activation
. Recombinant human parathyroid hormone analog that intermittently stimulates osteoblast activity
. Monoclonal antibody that binds and inhibits sclerostin, increasing bone formation and decreasing bone resorption
. Selective estrogen receptor modulator that exerts estrogenic effects on bone
. Cathepsin K inhibitor that prevents osteoclast-mediated degradation of bone matrix

Correct Answer & Explanation

. Monoclonal antibody that binds and inhibits sclerostin, increasing bone formation and decreasing bone resorption

Explanation

Romosozumab is a humanized monoclonal antibody that targets and binds to sclerostin. Sclerostin is a glycoprotein secreted by osteocytes that naturally inhibits the Wnt signaling pathway, thereby inhibiting bone formation. By blocking sclerostin, romosozumab provides a dual effect: it significantly stimulates bone formation (anabolic) while concurrently decreasing bone resorption (antiresorptive).

Question 602

Topic: Biology, Genetics & Bone Healing

A 72-year-old female on alendronate for 10 years presents with 3 months of progressive anterior thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line involving 30% of the lateral cortex of the subtrochanteric femur. There is moderate varus bowing of the femur. What is the most appropriate next step in management?

. Discontinue alendronate, start teriparatide, and observe with protected weight-bearing
. Discontinue alendronate and switch to denosumab therapy
. Prophylactic cephalomedullary nailing of the affected femur
. Core decompression of the subtrochanteric lesion
. Open reduction and internal fixation with a laterally applied dynamic hip screw

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing of the affected femur

Explanation

This clinical picture represents an impending atypical femur fracture (AFF) associated with prolonged bisphosphonate use, characterized by a transverse radiolucent line (incomplete fracture) in the lateral cortex, cortical thickening, and a prodrome of thigh pain. Given the presence of the radiolucent line and symptomatic pain in a biologically altered bone with mechanical disadvantage (varus bowing), prophylactic intramedullary nailing is highly recommended to prevent completion of the fracture. Nonsurgical management has a high failure rate in the presence of a visible fracture line and pain.

Question 603

Topic: Biology, Genetics & Bone Healing

A 68-year-old female sustains a fragility fracture of the pelvis. A DXA scan reveals a T-score of -3.2 at the femoral neck. An incidental finding on the pelvic radiograph is an asymptomatic area characteristic of Paget's disease involving her right hemipelvis. Which of the following medical treatments for her osteoporosis is strictly contraindicated?

. Alendronate
. Zoledronic acid
. Teriparatide
. Denosumab
. Raloxifene

Correct Answer & Explanation

. Teriparatide

Explanation

Teriparatide (a recombinant human PTH analog) is contraindicated in patients with Paget's disease of bone, prior skeletal radiation therapy, unexplained elevations in alkaline phosphatase, or open epiphyses. This contraindication is due to a theoretical increased risk of osteosarcoma, which was observed in long-term, high-dose rat studies.

Question 604

Topic: Biology, Genetics & Bone Healing

A 74-year-old woman with severe osteoporosis has been receiving denosumab injections every 6 months for the past 4 years. She missed her last two appointments and is now 12 months since her last dose. She presents to the emergency department with acute back pain, and radiographs reveal three new acute vertebral compression fractures. What underlying physiological mechanism best explains this clinical presentation?

. Paradoxical atypical fracture phenomenon from over-suppression of remodeling
. Rapid upregulation of sclerostin production leading to sudden osteoblast apoptosis
. Massive rebound increase in osteoclast number and activity due to uninhibited RANK ligand
. Accumulation of advanced glycation end-products in the collagen matrix weakening the bone
. Secondary hyperparathyroidism due to sudden profound hypocalcemia

Correct Answer & Explanation

. Massive rebound increase in osteoclast number and activity due to uninhibited RANK ligand

Explanation

Denosumab is a potent monoclonal antibody against RANK ligand (RANKL). When denosumab is discontinued, there is a well-documented 'rebound phenomenon.' As the drug clears, the uninhibited RANKL leads to a massive and rapid increase in the formation, function, and survival of osteoclasts. This results in a period of profoundly accelerated bone resorption, severe bone density loss, and a high risk of multiple spontaneous vertebral compression fractures. Patients stopping denosumab must be immediately transitioned to a bisphosphonate to prevent this rebound.

Question 605

Topic: Biology, Genetics & Bone Healing
A 45-year-old premenopausal woman with a history of celiac disease undergoes a dual-energy x-ray absorptiometry (DXA) scan. The report indicates a lumbar spine T-score of -2.6 and a Z-score of -2.8. How should her bone density status be formally classified according to the International Society for Clinical Densitometry (ISCD) guidelines?
. Osteoporosis
. Osteopenia
. Below the expected range for age
. Within the expected range for age
. Severe osteoporosis

Correct Answer & Explanation

. Below the expected range for age

Explanation

According to the ISCD guidelines, in premenopausal women, men under the age of 50, and children, the Z-score should be used rather than the T-score. A Z-score of -2.0 or lower is defined strictly as 'below the expected range for age.' The diagnostic terminology of 'osteoporosis' based on T-score criteria (≤ -2.5) is reserved for postmenopausal women and men aged 50 and older.

Question 606

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis has been treated with denosumab for 4 years but discontinued it 8 months ago due to a dental procedure. What is the most significant skeletal risk she currently faces due to this cessation?

. Atypical subtrochanteric femur fracture
. Osteonecrosis of the jaw
. Rebound multiple vertebral fractures
. Delayed osseointegration of future implants
. Severe hypocalcemia

Correct Answer & Explanation

. Rebound multiple vertebral fractures

Explanation

Discontinuation of denosumab leads to a rapid rebound in bone turnover to above-baseline levels. This rebound phenomenon is strongly associated with a high risk of sustaining multiple rapid vertebral compression fractures.

Question 607

Topic: Biology, Genetics & Bone Healing

A 75-year-old female with osteoporosis sustains a distal femur periprosthetic fracture. Anabolic bone therapy is considered to aid healing and improve overall bone density. Which of the following represents an absolute contraindication to the use of teriparatide?

. History of deep vein thrombosis
. Prior skeletal radiation therapy
. Renal failure (GFR < 30)
. Concurrent use of denosumab
. Peptic ulcer disease

Correct Answer & Explanation

. Prior skeletal radiation therapy

Explanation

Teriparatide (recombinant PTH) has a black box warning and is contraindicated in patients with a history of external beam or implant radiation therapy to the skeleton due to a theoretical increased risk of osteosarcoma.

Question 608

Topic: Biology, Genetics & Bone Healing

A 68-year-old male is initiated on alendronate following a fragility fracture of the femoral neck. What is the primary intracellular molecular mechanism of action of this medication?

. Inhibition of RANKL binding to the RANK receptor
. Inhibition of farnesyl pyrophosphate (FPP) synthase
. Stimulation of osteoblast differentiation via Wnt signaling
. Binding to sclerostin to enhance bone formation
. Direct activation of the calcium-sensing receptor

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis and decreased bone resorption.

Question 609

Topic: Biology, Genetics & Bone Healing

A 70-year-old female on oral alendronate for 8 years presents with a 3-month history of vague, non-traumatic anterior thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric femur. What is the most appropriate change in her medical management?

. Discontinue alendronate and begin teriparatide
. Switch from alendronate to intravenous zoledronic acid
. Switch from alendronate to denosumab
. Continue alendronate and initiate protected weight bearing
. Discontinue alendronate and begin raloxifene

Correct Answer & Explanation

. Discontinue alendronate and begin teriparatide

Explanation

Long-term bisphosphonate use increases the risk of atypical femur fractures. Management involves immediately discontinuing the bisphosphonate and starting an anabolic agent like teriparatide to stimulate bone formation and fracture healing.

Question 610

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with severe osteoporosis is initiated on denosumab therapy by her endocrinologist. What is the precise mechanism of action of this pharmacological agent?

. Binds to RANK ligand to prevent its interaction with RANK receptors
. Directly induces apoptosis of active osteoclasts
. Inhibits sclerostin to promote osteoblast-mediated bone formation
. Acts as a recombinant parathyroid hormone analog
. Selectively modulates estrogen receptors on osteoblasts

Correct Answer & Explanation

. Binds to RANK ligand to prevent its interaction with RANK receptors

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL. This prevents RANKL from binding to the RANK receptor on osteoclast precursors, fundamentally inhibiting osteoclast maturation, function, and survival.

Question 611

Topic: Biology, Genetics & Bone Healing

A 60-year-old female is evaluated for recurrent fragility fractures. Her DEXA T-score is -3.2. Her physician is considering starting teriparatide. Which of the following in her medical history is an absolute contraindication to this therapy?

. Prior history of unprovoked deep vein thrombosis
. History of external beam radiation therapy to the pelvis for cervical cancer
. Chronic kidney disease stage 2
. Documented allergy to sulfonamide antibiotics
. History of bleeding peptic ulcer disease

Correct Answer & Explanation

. History of external beam radiation therapy to the pelvis for cervical cancer

Explanation

Teriparatide carries a warning for the potential risk of osteosarcoma. It is strictly contraindicated in patients with a history of skeletal radiation therapy, Paget's disease, or unexplained elevations in alkaline phosphatase.

Question 612

Topic: Biology, Genetics & Bone Healing

A 55-year-old postmenopausal female has a DEXA T-score of -1.8 at the femoral neck. Her FRAX tool assessment reveals a 10-year probability of a major osteoporotic fracture of 22% and a hip fracture probability of 4%. What is the most appropriate management according to current guidelines?

. Recommend lifestyle modifications, calcium, and Vitamin D only
. Initiate pharmacological treatment with an oral bisphosphonate
. Initiate high-dose teriparatide immediately
. Repeat DEXA scan in 3 years before making a decision
. Start systemic estrogen replacement therapy

Correct Answer & Explanation

. Initiate pharmacological treatment with an oral bisphosphonate

Explanation

Pharmacological intervention is recommended for osteopenic patients (T-score -1.0 to -2.5) if the FRAX 10-year risk for a major osteoporotic fracture is >=20% or the risk for a hip fracture is >=3%.

Question 613

Topic: Biology, Genetics & Bone Healing

A 72-year-old female abruptly stops her osteoporosis medication prior to extensive dental surgery. Six months later, she sustains multiple spontaneous vertebral compression fractures. The abrupt cessation of which of the following medications is most notorious for causing this rapid 'rebound' fracture phenomenon?

. Alendronate
. Zoledronic acid
. Denosumab
. Raloxifene
. Calcitonin

Correct Answer & Explanation

. Zoledronic acid

Explanation

Discontinuation of denosumab leads to a rapid, profound loss of bone mineral density and a well-documented rebound increase in the risk of multiple vertebral fractures. Patients stopping denosumab must be transitioned to a bisphosphonate.

Question 614

Topic: Biology, Genetics & Bone Healing

A 65-year-old female on long-term alendronate therapy for osteoporosis presents with atraumatic thigh pain. Radiographs reveal lateral cortical thickening and a transverse incomplete radiolucent line in the subtrochanteric region. Which of the following is considered an indication for prophylactic intramedullary nailing?

. Medial cortical flaring
. Pain with weight-bearing
. Intramedullary canal diameter < 10 mm
. Bilateral asymptomatic presentation
. Complete relief of pain with NSAIDs

Correct Answer & Explanation

. Pain with weight-bearing

Explanation

In the setting of an incomplete atypical femoral fracture (AFF) associated with bisphosphonate use, prophylactic intramedullary nailing is indicated if the patient experiences prodromal thigh pain with weight-bearing, or if the radiolucent line traverses > 50% of the cortex, as these strongly predict impending complete fracture.

Question 615

Topic: Biology, Genetics & Bone Healing

A 65-year-old female who has been taking alendronate for 10 years presents with 3 months of progressive lateral thigh pain. Radiographs reveal a transverse radiolucent line in the lateral cortex of the subtrochanteric femur with associated focal cortical thickening ('beaking'). There is no history of trauma. What is the most appropriate management?

. Discontinue the bisphosphonate, prescribe teriparatide, and allow protected weight-bearing.
. Discontinue the bisphosphonate and perform prophylactic intramedullary nailing.
. Discontinue the bisphosphonate and perform open reduction with a lateral locking plate.
. Continue the bisphosphonate, add Vitamin D supplementation, and perform core decompression.
. Perform prophylactic cerclage wiring around the focal beaking.

Correct Answer & Explanation

. Discontinue the bisphosphonate and perform prophylactic intramedullary nailing.

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use. Hallmarks include lateral cortical beaking and a transverse radiolucent line. Because she has progressive pain (suggesting mechanical instability/microfracture propagation), prophylactic intramedullary nailing is the gold standard to prevent a complete, displaced fracture, which carries a high risk of nonunion and complication. Discontinuing the bisphosphonate is essential, but medical management alone is insufficient for a symptomatic impending AFF.

Question 616

Topic: Biology, Genetics & Bone Healing

A 68-year-old female who has been taking alendronate for 12 years presents with an atraumatic subtrochanteric fracture characterized by lateral cortical thickening and a transverse fracture pattern. Which of the following best describes the pathophysiology underlying this atypical femoral fracture?

. Increased osteoblastic activity creating brittle woven bone
. Suppressed osteoclast activity leading to the accumulation of targeted microcracks
. Severe vitamin D deficiency causing inadequate mineralization of osteoid
. Hyperparathyroidism inducing rapid cortical tunneling
. Malignant infiltration of the endosteal cavity disrupting normal bone architecture

Correct Answer & Explanation

. Suppressed osteoclast activity leading to the accumulation of targeted microcracks

Explanation

Prolonged bisphosphonate use heavily suppresses osteoclast-mediated bone remodeling. This prevents the normal repair of daily microdamage, leading to the accumulation of microcracks and eventually culminating in a tension-sided stress fracture on the lateral cortex.

Question 617

Topic: Biology, Genetics & Bone Healing

A 65-year-old female presents with a low-energy subtrochanteric femur fracture with a transverse configuration, lateral cortical thickening, and a medial spike. She has been on alendronate for 8 years. What is the most appropriate management regarding her bone health medications?

. Discontinue alendronate and start high-dose calcium/vitamin D only
. Discontinue alendronate and start teriparatide
. Continue alendronate and add denosumab
. Discontinue alendronate and start zoledronic acid
. Switch alendronate to risedronate

Correct Answer & Explanation

. Discontinue alendronate and start teriparatide

Explanation

This presentation is pathognomonic for an atypical femur fracture (AFF) associated with long-term bisphosphonate use, which suppresses normal osteoclastic bone remodeling. Standard medical management includes discontinuing the bisphosphonate and initiating teriparatide, a recombinant parathyroid hormone that acts as an anabolic agent to stimulate bone formation and improve healing rates in AFFs.

Question 618

Topic: Biology, Genetics & Bone Healing

When harvesting an autologous corticocancellous bone graft from the anterior iliac crest for the treatment of a structural atrophic nonunion, what is the primary biological property provided by the cancellous portion of the graft?

. Osteoconduction only
. Rigid mechanical stabilization
. Osteogenesis and osteoinduction
. Prevention of local infection
. Inhibition of osteoclast activity

Correct Answer & Explanation

. Osteogenesis and osteoinduction

Explanation

A corticocancellous bone graft provides multiple properties. The cortical portion primarily provides structural mechanical support and acts as an osteoconductive scaffold. The cancellous portion is rich in mesenchymal stem cells, osteoprogenitor cells, and osteoinductive proteins (like BMPs). Therefore, the cancellous bone primarily provides osteogenesis (living cells that form bone) and osteoinduction (factors that induce host cells to form bone).

Question 619

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMPs) are utilized in orthopedics to promote bone healing. At the cellular level, through which type of cell surface receptor do BMPs primarily initiate their intracellular signaling cascade?

. G-protein coupled receptor
. Tyrosine kinase receptor
. Serine/threonine kinase receptor
. Ligand-gated ion channel
. Intracellular nuclear receptor

Correct Answer & Explanation

. Serine/threonine kinase receptor

Explanation

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-beta (TGF-beta) superfamily. They bind to specific type I and type II transmembrane receptors on the surface of mesenchymal stem cells. These receptors possess intrinsic serine/threonine kinase activity. Upon BMP binding, the type II receptor phosphorylates the type I receptor, which subsequently phosphorylates intracellular Smad proteins (Smad 1, 5, and 8), ultimately translocating to the nucleus to regulate transcription of osteogenic genes.

Question 620

Topic: Biology, Genetics & Bone Healing

When evaluating the regenerative properties of various bone grafting materials, the term 'osteoinduction' refers specifically to which of the following processes?

. The provision of a physical three-dimensional scaffold for new bone growth
. The stimulation of undifferentiated mesenchymal stem cells to differentiate into osteoblasts
. The direct supply of living osteoprogenitor cells and osteoblasts to the graft site
. The promotion of neovascularization through the release of vascular endothelial growth factor (VEGF)
. The mechanical stabilization of a fracture site via osteoclastic cutting cones

Correct Answer & Explanation

. The stimulation of undifferentiated mesenchymal stem cells to differentiate into osteoblasts

Explanation

Bone grafting relies on three primary mechanisms. Osteoconduction provides a passive structural scaffold for cell migration and new bone formation. Osteoinduction is the active chemical process by which growth factors (such as Bone Morphogenetic Proteins - BMPs) stimulate host primitive mesenchymal stem cells to recruit, proliferate, and differentiate into mature bone-forming osteoblasts. Osteogenesis refers to the direct provision of live, viable osteoblasts and osteoprogenitor cells transferred within the graft material itself (e.g., fresh autograft).

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