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Biology, Genetics & Bone Healing MCQs

Practice Set 99 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 1961

Topic: Biology, Genetics & Bone Healing

A toddler with a known genetic disorder presents for orthopedic evaluation. Radiographs of the lower extremities are shown below. Which of the following best describes the primary underlying pathology affecting these bones?




. Defective intramembranous ossification
. Generalized disorder of the maturation of enchondral ossification
. Overactivity of osteoclasts leading to cortical thinning
. Defective mineralization of osteoid
. Abnormal proliferation of fibrous tissue within the medullary canal

Correct Answer & Explanation

. Generalized disorder of the maturation of enchondral ossification

Explanation

Correct Answer: Generalized disorder of the maturation of enchondral ossificationThe radiographs show short and thick tubular bones characteristic of Ellis-van Creveld syndrome. This syndrome is mainly a generalized disorder of the maturation of enchondral ossification, leading to disproportionate dwarfism and short limbs.

Question 1962

Topic: Biology, Genetics & Bone Healing

Review the radiographs of the lower extremities provided below. In the context of Ellis-van Creveld syndrome, what is the primary underlying pathophysiological defect leading to this appearance?




. Defective intramembranous ossification
. Generalized disorder of the maturation of enchondral ossification
. Osteoclast dysfunction and failure of bone resorption
. Abnormal type I collagen synthesis

Correct Answer & Explanation

. Generalized disorder of the maturation of enchondral ossification

Explanation

Correct Answer: Generalized disorder of the maturation of enchondral ossificationThe radiograph shows short and thick tubular bones. Ellis-van Creveld's syndrome is mainly a generalized disorder of the maturation of enchondral ossification, leading to the characteristic short limbs and disproportionate dwarfism.

Question 1963

Topic: Biology, Genetics & Bone Healing

Ellis-van Creveld syndrome is classified as a ciliopathy. The genetic mutation (EVC1 or EVC2) primarily disrupts which of the following cellular signaling pathways, ultimately leading to defective endochondral ossification?

. Wnt/beta-catenin signaling
. Sonic hedgehog (Shh) signaling
. Fibroblast growth factor (FGF) signaling
. Transforming growth factor-beta (TGF-b) signaling
. Notch signaling pathway

Correct Answer & Explanation

. Sonic hedgehog (Shh) signaling

Explanation

EVC1 and EVC2 proteins localize to the primary cilia of chondrocytes and are essential for normal Sonic hedgehog (Shh) signal transduction. Disruption of this pathway leads to the skeletal dysplasias characteristic of the syndrome.

Question 1964

Topic: Biology, Genetics & Bone Healing

A 68-year-old man with active Paget's disease requires a total hip arthroplasty for severe secondary osteoarthritis. To minimize the significant risk of intraoperative hemorrhage, which of the following should be administered prior to surgery?

. Denosumab
. Teriparatide
. Intravenous bisphosphonates
. Calcitonin
. Methotrexate

Correct Answer & Explanation

. Intravenous bisphosphonates

Explanation

Intravenous bisphosphonates decrease osteoclast activity and subsequently reduce the hypervascularity associated with the active phase of Paget's disease. They should be administered before major orthopedic surgery to minimize intraoperative blood loss.

Question 1965

Topic: Biology, Genetics & Bone Healing

A bone biopsy from a patient with an isolated, markedly elevated serum alkaline phosphatase and an enlarged skull reveals a mosaic pattern of lamellar bone with prominent cement lines. The primary initial pathophysiologic event in this disorder most likely involves which of the following?

. Defective osteoblast mineralization
. Viral infection of osteoclasts
. Monoclonal plasma cell proliferation
. Hypersecretion of parathyroid hormone
. Autoimmune destruction of articular cartilage

Correct Answer & Explanation

. Viral infection of osteoclasts

Explanation

Paget's disease initially features profound osteoclastic overactivity, heavily linked to paramyxovirus (e.g., respiratory syncytial virus or measles) inclusion bodies within the osteoclasts. The hallmark histology is a mosaic pattern with irregular cement lines due to chaotic bone remodeling.

Question 1966

Topic: Biology, Genetics & Bone Healing

A patient presents with diffuse bone pain and the following laboratory profile: markedly elevated Parathyroid Hormone (PTH), low-normal serum calcium, and elevated serum phosphorus. Which of the following is the most likely diagnosis?

. Primary hyperparathyroidism
. Secondary hyperparathyroidism due to renal failure
. Tertiary hyperparathyroidism
. Paget's disease
. Vitamin D toxicity

Correct Answer & Explanation

. Secondary hyperparathyroidism due to renal failure

Explanation

Secondary hyperparathyroidism, usually caused by chronic kidney disease, classically presents with low to normal calcium, high phosphorus, and compensatory high PTH. Primary hyperparathyroidism typically presents with hypercalcemia and hypophosphatemia.

Question 1967

Topic: Biology, Genetics & Bone Healing
Which of the following neurological complications is most frequently associated with the progressive skull changes seen in Paget's disease?
. Trigeminal neuralgia
. Sensorineural hearing loss
. Visual field deficits
. Olfactory dysfunction
. Facial nerve palsy

Correct Answer & Explanation

. Sensorineural hearing loss

Explanation

Sensorineural hearing loss is the most common neurologic complication of Paget's disease of the skull. It occurs due to a combination of compression of the vestibulocochlear nerve (CN VIII) at the neural foramen and cochlear involvement.

Question 1968

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size and bilateral hearing loss. Radiographs show cortical thickening and a 'cotton-wool' appearance of the skull. Which of the following best describes the primary cellular defect in this condition?

. Decreased osteoid mineralization
. Defective osteoclast carbonic anhydrase II
. Excessive proliferation of mononuclear osteoblasts
. Overactivity of giant multinucleated osteoclasts
. Deficiency of tissue nonspecific alkaline phosphatase

Correct Answer & Explanation

. Overactivity of giant multinucleated osteoclasts

Explanation

Paget's disease is primarily a disorder of osteoclast overactivity, characterized by giant, multinucleated osteoclasts. This leads to chaotic bone remodeling and the classic 'cotton-wool' appearance on skull radiographs.

Question 1969

Topic: Biology, Genetics & Bone Healing

A 72-year-old male with known Paget's disease of the femur presents with a severe, sudden increase in thigh pain over the past month. Radiographs show a new destructive, lytic lesion with cortical breakthrough and a soft tissue mass. What is the most significant prognostic factor for this patient's new condition?

. The presence of a paramyxovirus infection
. Development of high-output heart failure
. The histologic grade of the secondary sarcoma
. Serum calcium levels
. Nearly 100% mortality within 5 years despite aggressive treatment

Correct Answer & Explanation

. Nearly 100% mortality within 5 years despite aggressive treatment

Explanation

This patient has developed a secondary osteosarcoma, a rare but lethal complication of Paget's disease (incidence <1%). Pagetic osteosarcoma is highly aggressive, with a 5-year survival rate typically less than 10-20% despite surgery and chemotherapy.

Question 1970

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with severe secondary osteoarthritis of the hip and active Paget's disease is scheduled for a total hip arthroplasty. Her serum alkaline phosphatase is significantly elevated. What is the most appropriate preoperative medical management to optimize her surgical outcome?

. Initiate high-dose corticosteroids 1 week prior to surgery
. Administer a course of bisphosphonates prior to surgery
. Perform preoperative embolization of the internal iliac artery
. Initiate allopurinol therapy to prevent post-operative flare
. No preoperative medical intervention is indicated

Correct Answer & Explanation

. Administer a course of bisphosphonates prior to surgery

Explanation

Preoperative treatment with bisphosphonates or calcitonin is recommended in patients with active Paget's disease before elective bone surgery like THA. This reduces osteoclast activity, thereby significantly decreasing intraoperative blood loss from the highly vascular pagetic bone.

Question 1971

Topic: Biology, Genetics & Bone Healing

Which of the following cellular mechanisms is considered the primary initiating event in the pathophysiology of Paget's disease of bone?

. Osteoblast hypersecretion of osteoid
. Osteoclast overactivity with viral-like inclusion bodies
. Osteocyte apoptosis leading to structural failure
. Chondrocyte hypertrophy in the epiphyseal plate
. Fibroblast proliferation within the bone marrow

Correct Answer & Explanation

. Osteoclast overactivity with viral-like inclusion bodies

Explanation

Paget's disease is primarily initiated by abnormal, hyperactive osteoclasts containing viral-like inclusion bodies, followed by compensatory, disorganized osteoblastic bone formation.

Question 1972

Topic: Biology, Genetics & Bone Healing

A 68-year-old male with Paget's disease of the tibia presents with worsening bone pain and an elevated serum alkaline phosphatase level. What is the first-line pharmacological treatment for this symptomatic patient?

. Calcitonin
. Teriparatide
. Nitrogen-containing bisphosphonates
. Denosumab
. Methotrexate

Correct Answer & Explanation

. Nitrogen-containing bisphosphonates

Explanation

Nitrogen-containing bisphosphonates (such as zoledronic acid or alendronate) are the first-line treatment for symptomatic Paget's disease. They act by deeply inhibiting the overactive osteoclastic bone resorption.

Question 1973

Topic: Biology, Genetics & Bone Healing

A 74-year-old male with Paget's disease involving the skull complains of gradually worsening hearing loss. What is the most common pathophysiologic mechanism for this specific deficit?

. Optic nerve compression
. Conductive hearing loss from ossicular ankylosis
. Sensorineural hearing loss from cochlear nerve compression
. Ototoxicity from bisphosphonate therapy
. Spontaneous vestibular schwannoma

Correct Answer & Explanation

. Sensorineural hearing loss from cochlear nerve compression

Explanation

Hearing loss is a common neurologic complication of Paget's disease involving the skull. It is most often due to sensorineural deficit caused by bony overgrowth compressing the 8th cranial nerve within the temporal bone.

Question 1974

Topic: Biology, Genetics & Bone Healing

Which of the following laboratory profiles is most characteristic of isolated, uncomplicated Paget's disease of bone?

. Elevated serum calcium, elevated alkaline phosphatase
. Normal serum calcium, markedly elevated alkaline phosphatase
. Low serum calcium, normal alkaline phosphatase
. Normal serum calcium, normal alkaline phosphatase
. Elevated serum calcium, normal alkaline phosphatase

Correct Answer & Explanation

. Normal serum calcium, markedly elevated alkaline phosphatase

Explanation

Uncomplicated Paget's disease is characterized by a markedly elevated serum alkaline phosphatase, reflecting immense osteoblastic activity, while serum calcium and phosphorus levels typically remain within normal limits.

Question 1975

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, hearing loss, and anterior bowing of his tibias. What is the primary cellular defect that initiates the pathogenesis of this condition?

. Osteoblast overactivity leading to disorganized lamellar bone
. Defective mineralization of newly formed osteoid
. Osteoclast abnormality with increased cellular number, size, and nucleoli
. T-cell mediated destruction of articular cartilage

Correct Answer & Explanation

. Osteoclast abnormality with increased cellular number, size, and nucleoli

Explanation

Paget's disease initiates with an intense phase of osteoclastic bone resorption followed by chaotic osteoblastic bone formation. The primary defect lies in the osteoclasts, which are abnormal, hypernucleated, and significantly increased in both size and number.

Question 1976

Topic: Biology, Genetics & Bone Healing

An asymptomatic 68-year-old male undergoes a routine pelvic radiograph which demonstrates cortical thickening and sclerosis of the right iliopectineal line (Brim sign).

What is the classic serum laboratory profile associated with this condition?

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

Correct Answer & Explanation

. Normal Calcium, Normal Phosphate, High Alkaline Phosphatase

Explanation

The radiograph demonstrates Paget's disease of the pelvis. Paget's disease is characterized by markedly elevated alkaline phosphatase reflecting high bone turnover, while serum calcium and phosphate levels typically remain within normal limits.

Question 1977

Topic: Biology, Genetics & Bone Healing

A 72-year-old male with symptomatic Paget's disease involving the right hemipelvis and proximal femur is scheduled for a total hip arthroplasty. What perioperative medical management is highly recommended to minimize surgical complications?

. Preoperative administration of bisphosphonates to decrease bone vascularity
. Preoperative administration of teriparatide to stimulate bone formation
. High-dose Vitamin D supplementation to prevent postoperative hypocalcemia
. Prophylactic systemic corticosteroids to prevent acute inflammatory flare

Correct Answer & Explanation

. Preoperative administration of bisphosphonates to decrease bone vascularity

Explanation

Pagetic bone is highly vascular during the active disease phase, which poses a significant risk for massive intraoperative hemorrhage during arthroplasty. Preoperative treatment with bisphosphonates helps decrease bone turnover and vascularity, minimizing intraoperative blood loss.

Question 1978

Topic: Biology, Genetics & Bone Healing
An 80-year-old male complains of progressive bilateral hearing loss. A lateral skull radiograph demonstrates mixed radiolucent and radiopaque areas with marked thickening of the calvarium. What is the classic descriptive term for this radiographic appearance?
. Salt and pepper skull
. Hair-on-end appearance
. Cotton wool appearance
. Punched-out lytic lesions

Correct Answer & Explanation

. Cotton wool appearance

Explanation

The 'cotton wool' skull is the classic radiographic finding in the mixed osteolytic-osteosclerotic phase of Paget's disease. The patient's hearing loss is due to cranial nerve VIII compression from bony overgrowth in the temporal bone.

Question 1979

Topic: Biology, Genetics & Bone Healing

A patient with symptomatic Paget's disease is started on zoledronic acid. What is the specific cellular mechanism of action of this medication?

. It inhibits farnesyl pyrophosphate synthase in the mevalonate pathway of osteoclasts
. It stimulates osteoprotegerin (OPG) production by osteoblasts
. It binds competitively to RANK-ligand, preventing osteoclast activation
. It inhibits osteoblast differentiation and collagen synthesis

Correct Answer & Explanation

. It inhibits farnesyl pyrophosphate synthase in the mevalonate pathway of osteoclasts

Explanation

Nitrogen-containing bisphosphonates, such as zoledronic acid, act by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts essential intracellular signaling in osteoclasts, leading to cytoskeletal dysfunction and apoptosis.

Question 1980

Topic: Biology, Genetics & Bone Healing

A 50-year-old female is incidentally diagnosed with asymptomatic primary hyperparathyroidism during routine labs. Which of the following is considered an accepted criterion for recommending parathyroidectomy in this asymptomatic patient?

. Serum calcium > 0.5 mg/dL above the upper limit of normal
. A dual-energy x-ray absorptiometry (DEXA) T-score < -2.5 at any site
. Age greater than 60 years
. 24-hour urine calcium < 100 mg

Correct Answer & Explanation

. A dual-energy x-ray absorptiometry (DEXA) T-score < -2.5 at any site

Explanation

According to the consensus guidelines, indications for parathyroidectomy in asymptomatic primary hyperparathyroidism include age < 50 years, serum calcium > 1.0 mg/dL above normal, T-score < -2.5 (osteoporosis), and reduced creatinine clearance (< 60 mL/min).

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