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1. General Principles & Basic Science MCQs

Practice Set 757 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 15121

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with severe lower back pain and fatigue. Radiographs demonstrate multiple punched-out lytic lesions in his skull and vertebral bodies. Laboratory testing confirms a monoclonal gammopathy.

Which of the following factors secreted by the neoplastic cells is primarily responsible for the suppression of osteoblastic bone formation in this disease?

. Interleukin-6 (IL-6)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Macrophage inflammatory protein-1 alpha (MIP-1a)
. Dickkopf-1 (DKK-1)
. Transforming growth factor-beta (TGF-beta)

Correct Answer & Explanation

. Dickkopf-1 (DKK-1)

Explanation

Multiple myeloma cells secrete DKK-1, which inhibits the Wnt/beta-catenin signaling pathway, leading to severe suppression of osteoblast differentiation and activity. While MM cells also stimulate osteoclasts via RANKL up-regulation (driven by IL-6 and MIP-1a), DKK-1 is specifically responsible for the characteristic lack of osteoblastic response (uncoupling) seen in these lytic lesions.

Question 15122

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with progressive severe leg pain, easy fatigability, and a waddling gait. Radiographs reveal bilateral symmetrical cortical thickening of the femoral and tibial diaphyses, with sparing of the metaphyses.

What is the most effective medical therapy for achieving symptomatic relief of pain and muscle weakness in this specific condition?

. Systemic corticosteroids
. Intravenous bisphosphonates
. Nonsteroidal anti-inflammatory drugs (NSAIDs)
. High-dose Vitamin D supplementation
. Methotrexate

Correct Answer & Explanation

. Systemic corticosteroids

Explanation

This patient has Camurati-Engelmann disease (progressive diaphyseal dysplasia), caused by a mutation in the TGFB1 gene. Systemic corticosteroids are the mainstay of medical treatment, significantly reducing bone pain, improving muscle weakness, and potentially improving radiographic findings.

Question 15123

Topic: Biology, Genetics & Bone Healing

A 72-year-old man presents with anterior bowing of his tibia and new-onset hearing loss. His serum alkaline phosphatase is markedly elevated, but calcium and phosphorus are normal. What is the primary cellular defect underlying this patient's condition?

. Malignant proliferation of spindle-shaped stromal cells
. Impaired apoptosis of osteocytes leading to dense bone
. Increased numbers of large, hypernucleated, and hyperactive osteoclasts
. Defective osteoclast ruffled border preventing proton secretion
. Decreased expression of RANKL by osteoblasts

Correct Answer & Explanation

. Increased numbers of large, hypernucleated, and hyperactive osteoclasts

Explanation

Paget's disease of bone is characterized by a primary abnormality of the osteoclasts, which are greatly increased in number, abnormally large, and have excessive nuclei (up to 100 per cell). This leads to chaotic and intense osteoclastic bone resorption followed by disorganized osteoblastic bone formation.

Question 15124

Topic: Biology, Genetics & Bone Healing

An infant presents with severe anemia, hepatosplenomegaly, and diffuse sclerosis of all skeletal structures on radiographs, with a lack of medullary canals. Which of the following is the definitive curative treatment for the malignant infantile form of this condition?

. Intravenous bisphosphonates
. Hematopoietic stem cell transplantation
. Parathyroid hormone analogues
. Splenectomy
. High-dose Vitamin C therapy

Correct Answer & Explanation

. Hematopoietic stem cell transplantation

Explanation

Malignant infantile osteopetrosis is caused by defective osteoclast function. Because osteoclasts are derived from the hematopoietic macrophage-monocyte lineage, a hematopoietic stem cell transplant can provide normal osteoclast precursors and is considered the only definitive curative treatment.

Question 15125

Topic: Biology, Genetics & Bone Healing

A 45-year-old recent immigrant presents with diffuse bone pain and proximal muscle weakness. Radiographs reveal bilateral pseudofractures (Looser zones) in the femoral neck. Which of the following laboratory profiles is most consistent with this diagnosis?

. High Calcium, Low Phosphate, High Alkaline Phosphatase, High PTH
. Normal Calcium, Normal Phosphate, Normal Alkaline Phosphatase, Normal PTH
. Low Calcium, Low Phosphate, High Alkaline Phosphatase, High PTH
. Low Calcium, High Phosphate, High Alkaline Phosphatase, High PTH
. High Calcium, Normal Phosphate, Low Alkaline Phosphatase, Low PTH

Correct Answer & Explanation

. Low Calcium, Low Phosphate, High Alkaline Phosphatase, High PTH

Explanation

The clinical picture describes osteomalacia, typically due to severe Vitamin D deficiency. This leads to decreased intestinal calcium and phosphorus absorption, resulting in hypocalcemia, secondary hyperparathyroidism (High PTH), renal phosphate wasting (Low Phosphate), and increased bone turnover (High Alkaline Phosphatase).

Question 15126

Topic: Biology, Genetics & Bone Healing

A 55-year-old man with end-stage renal disease on hemodialysis presents with chronic bone pain. Spine radiographs demonstrate alternating bands of sclerosis and radiolucency parallel to the vertebral endplates (Rugger-Jersey spine). What is the primary driving mechanism of this patient's bone pathology?

. Excessive renal excretion of phosphate leading to hypophosphatemia
. Hyperphosphatemia and decreased 1,25-dihydroxyvitamin D leading to secondary hyperparathyroidism
. Primary overproduction of parathyroid hormone from a parathyroid adenoma
. Accumulation of beta-2 microglobulin amyloid deposits in the bone matrix
. Aluminum toxicity directly inhibiting osteoblast function

Correct Answer & Explanation

. Hyperphosphatemia and decreased 1,25-dihydroxyvitamin D leading to secondary hyperparathyroidism

Explanation

The patient has renal osteodystrophy (osteitis fibrosa cystica). In chronic kidney disease, failing kidneys cannot excrete phosphate or adequately synthesize active Vitamin D (1,25-OH D). This combination causes hypocalcemia, severely driving secondary hyperparathyroidism and resulting in characteristic bone changes like the Rugger-Jersey spine.

Question 15127

Topic: Biology, Genetics & Bone Healing

A 65-year-old man is incidentally found to have an isolated elevation of serum alkaline phosphatase. Radiographs reveal marked cortical thickening and coarsened trabeculae in his right proximal femur, and he is diagnosed with Paget's disease. He is completely asymptomatic. What is the primary indication to initiate bisphosphonate therapy in this patient?

. To prevent secondary malignant transformation to osteosarcoma
. To normalize alkaline phosphatase to prevent cardiovascular events
. To prevent future deformity and secondary osteoarthritis in a weight-bearing bone
. It is contraindicated; asymptomatic patients should never be treated
. To treat concurrent age-related osteoporosis

Correct Answer & Explanation

. To prevent future deformity and secondary osteoarthritis in a weight-bearing bone

Explanation

Treatment of asymptomatic Paget's disease is highly indicated when metabolically active disease involves weight-bearing bones (like the femur or tibia), the spine, or areas near major joints. Medical suppression with bisphosphonates helps prevent disease progression, severe bowing deformities, and secondary osteoarthritis.

Question 15128

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with progressive muscle weakness, a waddling gait, and severe, aching leg pain. Radiographs demonstrate marked, symmetrical bilateral cortical thickening of the femoral and tibial diaphyses, sparing the metaphyses and epiphyses.

Which of the following medical treatments has been shown to provide significant symptomatic relief for this condition?

. Corticosteroids
. Methotrexate
. Etanercept
. Teriparatide
. Denosumab

Correct Answer & Explanation

. Corticosteroids

Explanation

Progressive diaphyseal dysplasia (Camurati-Engelmann disease) is caused by a mutation in the TGFB1 gene. Corticosteroids (and sometimes NSAIDs like indomethacin) are the mainstay of medical treatment, significantly reducing bone pain and improving muscle strength.

Question 15129

Topic: Biology, Genetics & Bone Healing

A 70-year-old man complains of progressive hearing loss and an increasing hat size. Laboratory studies show a markedly elevated serum alkaline phosphatase with normal serum calcium and phosphorus levels. Histologic examination of a bone biopsy reveals a characteristic "mosaic" pattern of lamellar bone. What is the primary cellular defect in this disease?

. Increased osteoblast activity due to abnormal RUNX2 expression
. Abnormal, large, multinucleated osteoclasts containing viral-like inclusion bodies
. Deficient osteoid mineralization secondary to vitamin D deficiency
. Defective type I collagen synthesis
. Abnormal RANKL production by circulating T-cells

Correct Answer & Explanation

. Abnormal, large, multinucleated osteoclasts containing viral-like inclusion bodies

Explanation

Paget's disease of bone is primarily a disorder of osteoclasts, which are unusually large, multinucleated, and hyperactive. They characteristically contain viral-like paramyxovirus inclusion bodies, leading to excessive bone resorption followed by disorganized osteoblastic bone formation (mosaic pattern).

Question 15130

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femoral epiphysis extending to the subchondral bone. Biopsy confirms a giant cell tumor of bone. Denosumab therapy is considered for her locally aggressive disease. What is the mechanism of action of this drug?

. Binds directly to the RANK receptor on osteoclasts
. Binds to RANKL, preventing it from activating the RANK receptor
. Inhibits osteoclast V-ATPase proton pumps
. Induces osteoblast apoptosis
. Incorporates into the bone matrix and poisons osteoclasts upon ingestion

Correct Answer & Explanation

. Binds to RANKL, preventing it from activating the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor on the surface of osteoclasts, thereby inhibiting osteoclast formation, function, and survival.

Question 15131

Topic: Biology, Genetics & Bone Healing

A 60-year-old man presents with a painful, destructive, lytic lesion in his proximal femur. He has a history of a nephrectomy for clear cell renal carcinoma 3 years ago. The lesion is judged to be at high risk for an impending pathologic fracture, and prophylactic intramedullary nailing is planned. What preoperative intervention is highly recommended to minimize surgical morbidity?

. Preoperative external beam radiation therapy
. Neoadjuvant chemotherapy with doxorubicin
. Preoperative transarterial embolization of the lesion
. Intravenous bisphosphonate infusion 24 hours prior to surgery
. Preoperative denosumab injection

Correct Answer & Explanation

. Preoperative transarterial embolization of the lesion

Explanation

Metastatic renal cell carcinoma and thyroid carcinoma lesions are notoriously hypervascular. Preoperative transarterial embolization of the lesion is highly recommended within 24 to 48 hours prior to surgical fixation to minimize massive intraoperative blood loss.

Question 15132

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy with a family history of multiple bony protuberances presents with painless bumps around his knees and shoulders. Radiographs show multiple pedunculated and sessile bone lesions pointing away from the joint lines, with cortex continuous with the host bone. Genetic testing reveals a mutation in the EXT1 gene. What is the normal function of the protein encoded by this gene?

. Receptor tyrosine kinase signaling
. Heparan sulfate biosynthesis
. Transcription factor regulation of osteocalcin
. Osteoclast proton pump functioning
. Calcium-sensing in the parathyroid gland

Correct Answer & Explanation

. Heparan sulfate biosynthesis

Explanation

Multiple Hereditary Exostoses (Osteochondromatosis) is caused by autosomal dominant mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for the biosynthesis of heparan sulfate proteoglycans, which are critical for normal physeal signaling.

Question 15133

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with a pathologic proximal femur fracture. Workup reveals monoclonal gammopathy and Bence-Jones proteinuria. Bone marrow biopsy confirms the diagnosis.

What is the primary cellular mechanism driving the distinct osteolytic lesions seen in this disease process?

. Tumor cell production of parathyroid hormone-related peptide (PTHrP)
. Increased production of RANKL and decreased production of Osteoprotegerin (OPG) by stromal cells
. Direct secretion of matrix metalloproteinases by neoplastic plasma cells
. Disruption of the FGFR3 pathway causing uncoupled bone remodeling
. Overactivation of the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Increased production of RANKL and decreased production of Osteoprotegerin (OPG) by stromal cells

Explanation

Myeloma cells secrete factors like MIP-1 alpha and IL-6 that upregulate RANKL and downregulate OPG. This leads to profound osteoclast activation and the classic punched-out osteolytic lesions.

Question 15134

Topic: 1. General Principles & Basic Science

A 12-year-old girl is evaluated for severe, agonizing pain in both legs and extreme fatigue. Radiographs show pronounced cortical thickening of the bilateral femoral and tibial diaphyses, with sparing of the metaphyses.

Genetic testing confirms a mutation in the TGFB1 gene. Which of the following medical therapies has been shown to be most consistently effective for alleviating her bone pain and muscle weakness?

. Bisphosphonates
. High-dose NSAIDs
. Systemic corticosteroids
. Recombinant human growth hormone
. Intravenous immunoglobulin (IVIG)

Correct Answer & Explanation

. Systemic corticosteroids

Explanation

Systemic corticosteroids are the mainstay of medical treatment for symptomatic Camurati-Engelmann disease. They effectively relieve bone pain, improve muscle strength, and can sometimes reverse radiographic changes.

Question 15135

Topic: 1. General Principles & Basic Science

A 15-year-old female presents with multiple asymmetrical bone deformities and several soft-tissue hemangiomas with phleboliths. Which of the following gene mutations is most strongly associated with this patient's underlying condition?

. EXT1
. GNAS
. IDH1/IDH2
. RB1
. p53

Correct Answer & Explanation

. IDH1/IDH2

Explanation

Maffucci syndrome is characterized by multiple enchondromatosis and soft-tissue hemangiomas. Both Ollier disease and Maffucci syndrome are driven by somatic mosaic mutations in the IDH1 or IDH2 genes.

Question 15136

Topic: 1. General Principles & Basic Science

A 25-year-old female presents with multiple enchondromas and soft-tissue hemangiomas. Which genetic mutation is most strongly associated with her underlying syndrome?

. EXT1
. IDH1
. GNAS
. NF1
. TP53

Correct Answer & Explanation

. IDH1

Explanation

Maffucci syndrome is characterized by multiple enchondromas and soft-tissue hemangiomas. The condition is driven primarily by somatic mosaic mutations in the IDH1 or IDH2 genes.

Question 15137

Topic: Biology, Genetics & Bone Healing

A 70-year-old man with left thigh pain is found to have the lesion shown in the provided imaging. Serum protein electrophoresis confirms a monoclonal gammopathy. Following prophylactic internal fixation with a locked intramedullary rod, which of the following medical therapies is most appropriate to decrease the risk of future pathologic fractures?

. High-dose corticosteroids
. Bisphosphonates
. Teriparatide
. Denosumab
. Methotrexate

Correct Answer & Explanation

. Bisphosphonates

Explanation

Correct Answer: BThe underlying diagnosis is multiple myeloma, presenting with a large lucent lesion in the peritrochanteric region of the proximal femur. After prophylactic internal fixation to address the impending pathologic fracture, postoperative treatment with bisphosphonates and radiation therapy is indicated to decrease the risk of future pathologic fractures. The patient should also be referred to a medical oncologist for comprehensive medical management.

Question 15138

Topic: Biology, Genetics & Bone Healing

A 70-year-old man presents with left thigh pain. Serum protein electrophoresis reveals a monoclonal gammopathy. Radiographs and CT (Figures A and B) show a large lucent lesion in the peritrochanteric region. Which of the following adjuvant medical treatments is most appropriate postoperatively to decrease the risk of future skeletal-related events?

. Denosumab only
. Bisphosphonates and radiation therapy
. High-dose methotrexate
. Teriparatide
. Radioactive iodine

Correct Answer & Explanation

. Bisphosphonates and radiation therapy

Explanation

Correct Answer: BThe patient has multiple myeloma with an impending pathologic fracture of the proximal femur, which requires prophylactic internal fixation with a locked intramedullary nail. Postoperatively, treatment with bisphosphonates and radiation therapy is indicated to decrease the risk of future pathologic fractures and provide local tumor control. Bisphosphonates inhibit osteoclast-mediated bone resorption, which is heavily upregulated in multiple myeloma.

Question 15139

Topic: Biology, Genetics & Bone Healing

A 70-year-old man with multiple myeloma presents with a large lucent lesion in the peritrochanteric region of the left proximal femur, as shown in the imaging studies. He undergoes prophylactic internal fixation with a locked intramedullary rod. Which of the following adjuvant therapies is most appropriate to decrease the risk of future pathologic fractures in this patient?

. Wide resection and endoprosthetic reconstruction.
. Postoperative bisphosphonates and radiation therapy.
. Chemotherapy alone.
. Radiation therapy alone.
. Open curettage and bone grafting.

Correct Answer & Explanation

. Postoperative bisphosphonates and radiation therapy.

Explanation

Correct Answer: BBecause the patient has a large lucent lesion in the peritrochanteric region of the left proximal femur, the risk of pathologic fracture is high, and prophylactic internal fixation with a locked intramedullary rod is indicated. Postoperative treatment with bisphosphonates and radiation therapy is indicated to decrease the risk of future pathologic fractures. Neither chemotherapy nor radiation therapy alone is likely to result in long-term stabilization of the proximal femur.

Question 15140

Topic: Biomechanics & Biomaterials

A stress-strain curve for a typical orthopaedic metallic implant is shown.

What does the area under the curve within the elastic region represent?

. Modulus of resilience
. Toughness
. Ultimate tensile strength
. Fatigue limit
. Plasticity

Correct Answer & Explanation

. Modulus of resilience

Explanation

The area under the stress-strain curve in the elastic region represents the modulus of resilience, which is the energy absorbed by a material before yielding. The total area under the entire curve (elastic and plastic regions) represents the material's toughness.

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