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Biology, Genetics & Bone Healing MCQs

Practice Set 30 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 581

Topic: Biology, Genetics & Bone Healing

A 28-year-old male develops severe elbow stiffness 3 months following open reduction and internal fixation of a terrible triad injury. Radiographs show mature heterotopic ossification (HO) bridging the radioulnar joint. He is scheduled for excision of the HO and capsular release. What is the optimal postoperative prophylaxis to prevent recurrence of HO in this patient?

. Low-dose aspirin for 6 weeks
. Indomethacin 75 mg SR daily for 3-6 weeks OR single-dose radiation therapy
. Oral bisphosphonates for 3 months
. Colchicine for 2 weeks
. No prophylaxis is needed once the HO is fully mature

Correct Answer & Explanation

. Indomethacin 75 mg SR daily for 3-6 weeks OR single-dose radiation therapy

Explanation

After surgical excision of heterotopic ossification around the elbow, the risk of recurrence is high. Prophylaxis is standard of care. The two most proven and widely used prophylactic regimens are oral NSAIDs (specifically Indomethacin) for 3 to 6 weeks, or a single dose of localized external beam radiation therapy (typically 700 cGy) given within 24-48 hours postoperatively. Bisphosphonates may delay the mineralization of HO but do not prevent the formation of the osteoid matrix, and therefore HO often forms once the drug is stopped.

Question 582

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with a history of osteoporosis on long-term alendronate therapy complains of a 3-month history of prodromal lateral left thigh pain. Radiographs reveal localized lateral cortical thickening of the subtrochanteric femur with a transverse radiolucent line, but no complete fracture. What is the most appropriate management?

. Discontinue alendronate, begin protected weight-bearing, and schedule for prophylactic cephalomedullary nailing.
. Switch alendronate to zoledronic acid and prescribe a cane.
. Observation and repeat radiographs in 6 months.
. Core decompression of the subtrochanteric femur.
. Application of a hinged fracture brace and immediate full weight-bearing.

Correct Answer & Explanation

. Discontinue alendronate, begin protected weight-bearing, and schedule for prophylactic cephalomedullary nailing.

Explanation

This patient has an incomplete atypical femur fracture (AFF) associated with long-term bisphosphonate use, symptomatic with a radiolucent line. Standard of care includes stopping the bisphosphonate and performing prophylactic intramedullary nailing to prevent complete completion.

Question 583

Topic: Biology, Genetics & Bone Healing
In the pathogenesis of aseptic loosening secondary to ultra-high molecular weight polyethylene (UHMWPE) wear debris following a total hip arthroplasty, activated macrophages release inflammatory cytokines. Which specific receptor-ligand interaction is most directly responsible for driving the final common pathway of osteoclastogenesis and subsequent periprosthetic bone resorption?
. CD4 and MHC Class II
. RANK and RANKL
. BMP-2 and BMP Receptor Type IA
. Wnt and Frizzled receptor
. IL-6 and JAK-STAT

Correct Answer & Explanation

. RANK and RANKL

Explanation

Macrophage phagocytosis of UHMWPE wear particles results in the release of TNF-α, IL-1, and IL-6. These cytokines stimulate osteoblasts and fibroblasts to express Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). The binding of RANKL to the RANK receptor on osteoclast precursors drives their differentiation into mature osteoclasts, which resorb periprosthetic bone, leading to osteolysis.

Question 584

Topic: Biology, Genetics & Bone Healing
A 40-year-old male with a 6-cm infected diaphyseal defect of the tibia is treated with debridement, placement of an antibiotic cement spacer, and external fixation (the first stage of the Masquelet technique). According to histologic studies, at what time point does the induced membrane exhibit the peak expression of osteoinductive factors (such as VEGF, TGF-beta1, and BMP-2), making it the optimal biologic window for the second stage (bone grafting)?
. 2 to 4 weeks
. 1 to 2 weeks
. 6 to 8 weeks
. 10 to 12 weeks
. Greater than 12 weeks

Correct Answer & Explanation

. 1 to 2 weeks

Explanation

Histologic and biological studies of the Masquelet induced membrane technique (e.g., Pelissier et al.) demonstrate that the induced membrane is highly vascular and secretes key osteogenic and angiogenic growth factors (VEGF, TGF-β1, BMP-2). The expression of these factors peaks between 2 and 4 weeks after spacer placement, and steadily declines after 6 weeks. Therefore, the optimal biological window for the second stage (cancellous bone grafting) is typically around 4 weeks.

Question 585

Topic: Biology, Genetics & Bone Healing

A 65-year-old female on long-term alendronate therapy presents with progressively worsening prodromal thigh pain. Radiographs demonstrate lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the femur. What is the most appropriate prophylactic management?

. Switching to denosumab and protected weight bearing
. Discontinuation of bisphosphonates and weekly radiographic observation
. Prophylactic cephalomedullary nailing
. Open reduction and dynamic compression plating
. Application of a cortical strut allograft with cerclage wires

Correct Answer & Explanation

. Prophylactic cephalomedullary nailing

Explanation

This patient presents with a symptomatic impending atypical femoral fracture secondary to long-term bisphosphonate use. Prophylactic intramedullary nailing is indicated to relieve pain and prevent completion of the fracture, which is known for a high rate of delayed union or nonunion.

Question 586

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy is undergoing tibial lengthening via distraction osteogenesis. Four weeks into the distraction phase, radiographs show poor regenerate bone formation (the gap is radiolucent, without premature consolidation). Which of the following modifications to the distraction protocol is the most appropriate next step?

. Increase the distraction rate to 1.5 mm/day
. Perform open bone grafting of the distraction gap
. Stop distraction and compress the gap temporarily (accordion technique)
. Switch to acute docking and immediate internal fixation
. Administer bisphosphonates to stimulate bone formation

Correct Answer & Explanation

. Stop distraction and compress the gap temporarily (accordion technique)

Explanation

Poor regenerate bone formation (hypotrophic regenerate) during distraction osteogenesis can be addressed by the 'accordion technique,' which involves temporarily stopping distraction and compressing the site (typically 1 mm/day for several days) followed by resuming distraction. This cyclical compression and distraction mechanically stimulates osteogenesis. Increasing the rate would worsen the gap.

Question 587

Topic: Biology, Genetics & Bone Healing

A 5-year-old child presents with severe bilateral genu varum, short stature, and waddling gait. Laboratory tests reveal low serum phosphate, normal serum calcium, normal parathyroid hormone, and elevated alkaline phosphatase. Genetic testing confirms an X-linked dominant mutation in the PHEX gene. Which of the following medications is currently considered disease-modifying and targets the underlying pathophysiology of this condition?

. High-dose oral Vitamin D3 (Cholecalciferol)
. Burosumab
. Denosumab
. Recombinant human growth hormone
. Pamidronate

Correct Answer & Explanation

. Burosumab

Explanation

The child has X-linked hypophosphatemic rickets (XLH), caused by a PHEX mutation leading to excess FGF23 production. High FGF23 causes renal phosphate wasting and impairs calcitriol synthesis. Burosumab is a monoclonal antibody that binds and inhibits FGF23, directly addressing the pathophysiology of XLH and improving phosphate homeostasis, rickets severity, and lower limb deformity.

Question 588

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy with X-linked hypophosphatemic (XLH) rickets presents with severe genu varum. Prior to surgical deformity correction, medical optimization should ideally include which of the following targeted therapies?

. High-dose oral calcium supplementation
. Intravenous bisphosphonates
. Burosumab
. Teriparatide (recombinant PTH)
. Cinacalcet

Correct Answer & Explanation

. Burosumab

Explanation

XLH is characterized by excess FGF23, which leads to renal phosphate wasting and impaired bone mineralization. Burosumab, an anti-FGF23 monoclonal antibody, normalizes phosphate homeostasis and optimizes bone quality before osteotomy.

Question 589

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis using the Ilizarov method, what is the optimal biological environment for regenerate bone formation?

. Immediate distraction post-osteotomy at 2 mm per day
. A 7-10 day latency period followed by distraction at 1 mm per day in divided doses
. Corticotomy with extensive periosteal stripping followed by distraction at 0.5 mm per day
. Immediate distraction followed by a 14-day latency period
. A 21-day latency period followed by distraction at 1.5 mm per day

Correct Answer & Explanation

. A 7-10 day latency period followed by distraction at 1 mm per day in divided doses

Explanation

Optimal regenerate formation in distraction osteogenesis requires a low-energy corticotomy preserving the periosteum, a 7-10 day latency period to allow soft callus formation, and a distraction rate of roughly 1 mm per day in small, divided increments.

Question 590

Topic: Biology, Genetics & Bone Healing

A 68-year-old female on long-term alendronate for osteoporosis presents with dull aching thigh pain. Radiographs demonstrate lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur. If prophylactic surgical fixation is chosen, which of the following is true regarding her management?

. Bisphosphonates should be continued to augment fracture healing
. Teriparatide is absolutely contraindicated in this scenario
. Cephalomedullary nailing is the preferred construct over plate fixation
. Prophylactic fixation is only indicated if the fracture line crosses the medial cortex
. The contralateral femur rarely requires radiographic evaluation

Correct Answer & Explanation

. Cephalomedullary nailing is the preferred construct over plate fixation

Explanation

Atypical femur fractures are highly associated with prolonged bisphosphonate use. Because the bone biology is altered, plate fixation has a high failure rate. Intramedullary (cephalomedullary) nailing is the preferred construct for prophylactic or definitive fixation. Bisphosphonates must be discontinued, the contralateral femur must be imaged (due to high bilateral incidence), and anabolic agents like teriparatide may actually be considered off-label to aid healing.

Question 591

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman on alendronate for 12 years presents with insidious lateral thigh pain. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric femur. What is the primary cellular mechanism leading to this atypical femur fracture?

. Increased baseline osteoclast activity
. Severe global osteopenia and cortical thinning
. Suppression of targeted bone remodeling leading to microdamage accumulation
. Direct toxic impairment of osteoblast differentiation
. Vitamin D deficiency causing defective mineralization

Correct Answer & Explanation

. Suppression of targeted bone remodeling leading to microdamage accumulation

Explanation

Long-term bisphosphonate use severely suppresses osteoclast-mediated bone remodeling. Physiologic bone remodeling is required to repair everyday microdamage. When suppressed, microcracks accumulate and coalesce, causing the bone to become brittle. This leads to atypical femur fractures, which characteristically begin as a transverse cortical stress reaction on the tension (lateral) side of the subtrochanteric or diaphyseal femur.

Question 592

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis has a T-score of -3.5 and a recent fragility fracture of the lumbar spine. Her endocrinologist recommends romosozumab. What is the primary mechanism of action of this medication?

. Binds and inhibits RANK ligand (RANKL)
. Inhibits osteoclast-mediated cathepsin K
. Acts as a recombinant parathyroid hormone (PTH) analogue
. Monoclonal antibody that binds and inhibits sclerostin
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway

Correct Answer & Explanation

. Monoclonal antibody that binds and inhibits sclerostin

Explanation

Romosozumab is a humanized monoclonal antibody that targets and inhibits sclerostin. By inhibiting sclerostin, it produces a dual effect: it increases osteoblastic bone formation while simultaneously decreasing osteoclastic bone resorption, making it highly effective for severe osteoporosis.

Question 593

Topic: Biology, Genetics & Bone Healing

A 65-year-old female on alendronate for 8 years presents with progressive, activity-related lateral thigh pain. Radiographs of the femur demonstrate lateral cortical thickening and a transverse, incomplete radiolucent line in the subtrochanteric region. What is the most appropriate next step in management?

. Discontinue alendronate, initiate teriparatide, and observe with protected weight-bearing
. Discontinue alendronate and perform prophylactic cephalomedullary nailing
. Switch immediately from alendronate to denosumab
. Perform an ultrasound-guided corticosteroid injection of the trochanteric bursa
. Core decompression of the subtrochanteric lesion

Correct Answer & Explanation

. Discontinue alendronate and perform prophylactic cephalomedullary nailing

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use, characterized by clinical pain and radiographic evidence (lateral cortical beaking and a radiolucent line). Because she has pain and an incomplete fracture line, prophylactic surgical fixation (intramedullary nailing) is the standard of care to prevent a catastrophic complete fracture.

Question 594

Topic: Biology, Genetics & Bone Healing

Which of the following laboratory profiles is most characteristic of severe osteomalacia, helping to differentiate it from primary postmenopausal osteoporosis?

. Normal Calcium, normal Phosphate, normal Alkaline Phosphatase
. Normal Calcium, high Phosphate, normal Alkaline Phosphatase
. Low Calcium, low Phosphate, elevated Alkaline Phosphatase
. High Calcium, low Phosphate, elevated Alkaline Phosphatase
. High Calcium, high Phosphate, low Alkaline Phosphatase

Correct Answer & Explanation

. Low Calcium, low Phosphate, elevated Alkaline Phosphatase

Explanation

Osteomalacia is a defect in bone mineralization commonly caused by severe Vitamin D deficiency. It typically presents with low or low-normal serum calcium and phosphate, accompanied by elevated alkaline phosphatase and secondary hyperparathyroidism (elevated PTH). Primary osteoporosis features normal serum calcium, phosphate, and alkaline phosphatase.

Question 595

Topic: Biology, Genetics & Bone Healing

A 74-year-old female on denosumab therapy for 5 years suddenly discontinues the medication due to a planned dental procedure. Eight months later, she presents with severe back pain, and radiographs reveal three new acute vertebral compression fractures. What is the primary pathophysiological mechanism for this rapid deterioration?

. A sudden sclerostin surge causing rapid but structurally inferior bone formation
. Rapid rebound osteoclastogenesis due to unopposed RANKL activity
. Severe hypocalcemia triggering a massive parathyroid hormone (PTH) surge
. An atypical presentation of medication-related osteonecrosis of the jaw (MRONJ)
. Irreversible depletion of osteoprotegerin (OPG)

Correct Answer & Explanation

. Rapid rebound osteoclastogenesis due to unopposed RANKL activity

Explanation

Discontinuation of denosumab leads to a rapid 'rebound' effect characterized by an immense surge in osteoclastogenesis. The removal of the RANKL inhibitor allows unopposed RANKL to rapidly activate osteoclasts, leading to accelerated bone loss and a significantly increased risk of multiple vertebral compression fractures. A bisphosphonate must be administered when stopping denosumab to prevent this phenomenon.

Question 596

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with severe hip osteoarthritis and severe osteoporosis is scheduled for an elective total hip arthroplasty (THA). She is currently on denosumab therapy, receiving subcutaneous injections every 6 months. Her last injection was 3 months ago. What is the most appropriate recommendation regarding her denosumab therapy and the timing of surgery?

. Delay the surgery until 12 months after her last dose to ensure adequate bone healing.
. Proceed with surgery as scheduled and delay her next denosumab dose until 3 months postoperatively.
. Proceed with surgery as scheduled and ensure her next denosumab dose is administered precisely at the 6-month mark.
. Discontinue denosumab permanently and switch to oral bisphosphonates 4 weeks prior to surgery.
. Hold denosumab and initiate teriparatide immediately after surgery to accelerate implant osseointegration.

Correct Answer & Explanation

. Proceed with surgery as scheduled and delay her next denosumab dose until 3 months postoperatively.

Explanation

Denosumab is a RANKL inhibitor with a rapid offset of action. Delaying a scheduled dose of denosumab by even 1 to 2 months past the 6-month window can lead to a rebound increase in bone turnover, resulting in a significantly elevated risk of multiple spontaneous vertebral fractures. Orthopedic and rheumatologic guidelines strongly recommend that elective surgeries be scheduled mid-cycle (e.g., month 3 or 4) to avoid missing a dose due to perioperative complications, and that the regular 6-month dosing interval be strictly maintained regardless of the surgical date.

Question 597

Topic: Biology, Genetics & Bone Healing

A 74-year-old female with severe postmenopausal osteoporosis is started on romosozumab. What is the specific mechanism of action of this medication?

. Inhibition of the enzyme farnesyl pyrophosphate synthase in the mevalonate pathway
. Binding to and neutralizing receptor activator of nuclear factor kappa-B ligand (RANKL)
. Binding to sclerostin, thereby disinhibiting the Wnt signaling pathway to increase bone formation
. Direct stimulation of the calcium-sensing receptor on parathyroid cells
. Selective estrogen receptor modulation with agonistic effects on bone and antagonistic effects on breast tissue

Correct Answer & Explanation

. Binding to sclerostin, thereby disinhibiting the Wnt signaling pathway to increase bone formation

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin. Sclerostin (produced by osteocytes) normally inhibits the Wnt signaling pathway, decreasing osteoblastogenesis. By inhibiting sclerostin, romosozumab promotes Wnt signaling, resulting in a dual effect: substantially increasing bone formation (anabolic) while simultaneously decreasing bone resorption (antiresorptive). Bisphosphonates inhibit farnesyl pyrophosphate synthase; denosumab targets RANKL; calcimimetics target the calcium-sensing receptor; and raloxifene is a SERM.

Question 598

Topic: Biology, Genetics & Bone Healing

A 75-year-old female presents with an atraumatic dull ache in her left thigh. She has been taking alendronate for 9 years for osteoporosis. Plain radiographs of the left femur reveal localized lateral cortical thickening in the subtrochanteric region with a subtle transverse radiolucent line, consistent with an incomplete atypical femur fracture (AFF). What is the most critical next step in her imaging workup?

. MRI of the left femur to rule out metastatic disease
. CT scan of the left femur to measure cortical thickness precisely
. Full-length orthogonal radiographs of the contralateral right femur
. DEXA scan to reassess current bone mineral density
. Technetium-99m bone scan to detect other sites of impending fracture

Correct Answer & Explanation

. Full-length orthogonal radiographs of the contralateral right femur

Explanation

Atypical femur fractures (AFFs) are strongly associated with prolonged bisphosphonate use (usually >5 years) due to severe suppression of bone turnover. They characteristically present with an insidious onset of thigh pain and characteristic radiographic features (transverse fracture pattern originating at the lateral cortex, focal lateral cortical thickening/beaking, medial spiking). AFFs are frequently bilateral (occurring in up to 28-60% of cases). Therefore, whenever an AFF is identified, it is critical to obtain full-length radiographs of the contralateral femur to evaluate for an asymptomatic or symptomatic contralateral impending fracture.

Question 599

Topic: Biology, Genetics & Bone Healing

Bisphosphonates are the most commonly prescribed first-line therapy for osteoporosis. By which of the following specific cellular mechanisms do nitrogen-containing bisphosphonates (e.g., alendronate) primarily exert their antiresorptive effect?

. Binding to the calcium-sensing receptor on osteoblasts to stimulate proliferation
. Inhibition of the enzyme farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway
. Direct inhibition of cathepsin K within the osteoclast ruffled border
. Downregulation of osteoprotegerin (OPG) secretion by osteocytes
. Neutralization of receptor activator of nuclear factor kappa-B ligand (RANKL)

Correct Answer & Explanation

. Inhibition of the enzyme farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (like alendronate, zoledronic acid, and risedronate) are internalized by osteoclasts and inhibit farnesyl pyrophosphate (FPP) synthase, a key enzyme in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (such as Ras, Rho, and Rab) which are essential for osteoclast function, ruffled border formation, and cell survival, ultimately leading to osteoclast apoptosis.

Question 600

Topic: Biology, Genetics & Bone Healing

A 71-year-old male with a T-score of -3.5 and multiple recent fragility fractures requires aggressive medical management for osteoporosis. You are considering starting teriparatide. Which of the following elements in his past medical history represents an absolute contraindication to teriparatide therapy?

. History of deep vein thrombosis 5 years ago
. End-stage renal disease currently on hemodialysis
. Prior external beam radiation therapy for prostate cancer involving the pelvis
. History of multiple corticosteroid injections for knee osteoarthritis
. Diagnosis of severe gastroesophageal reflux disease (GERD)

Correct Answer & Explanation

. Prior external beam radiation therapy for prostate cancer involving the pelvis

Explanation

Teriparatide is a recombinant parathyroid hormone (PTH) analog that acts as a potent anabolic agent. Historically, it carried a black box warning (which has since been modified but the clinical contraindication remains for high-risk patients) due to an increased incidence of osteosarcoma observed in rat studies. Absolute contraindications include conditions that predispose to osteosarcoma, including prior skeletal radiation therapy, Paget's disease of bone, unexplained elevated alkaline phosphatase, or open epiphyses.

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