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1. General Principles & Basic Science MCQs

Practice Set 103 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 2041

Topic: Biology, Genetics & Bone Healing

A 70-year-old patient with Paget's disease undergoes a total hip arthroplasty. Postoperatively, the patient develops significant heterotopic ossification (HO) around the hip joint. Based on the case discussion, what is the MOST accurate statement regarding HO in Paget's disease patients undergoing THA?

. A. There is no reported increased incidence of heterotopic ossification in Paget's disease patients.
. B. HO is a common complication, and some surgeons routinely give prophylaxis to reduce its risk.
. C. HO is exclusively a complication of cemented THA in Paget's patients.
. D. The risk of HO is directly related to the patient's age, with younger patients having a higher risk.
. E. HO in Paget's disease is typically managed with immediate surgical excision.

Correct Answer & Explanation

. B. HO is a common complication, and some surgeons routinely give prophylaxis to reduce its risk.

Explanation

Correct Answer: BThe case explicitly states under 'Technical issues of performing THA in Paget’s disease': 'There is some controversy as to whether there is an increased risk of heterotopic ossification occurring from the abnormalities of osteogenic differentiation in Paget’s disease patients. Some surgeons routinely give prophylaxis to reduce the risk of HO.' Later, under 'Any special complications that can occur postoperatively?', the candidate correctly identifies 'a reported greater incidence of heterotopic ossification.'Option A is incorrect, as the case clearly indicates a reported greater incidence of HO. Option C is incorrect; the case does not link HO exclusively to cemented THA. Option D is incorrect; the case does not mention age as a direct risk factor for HO in Paget's, although age is discussed in the context of cemented vs. uncemented implant choice. Option E is incorrect; while surgical excision might be a treatment for severe HO, the initial management strategy discussed is prophylaxis, and immediate excision is not the primary or sole management.

Question 2042

Topic: Biology, Genetics & Bone Healing

A 58-year-old patient with Paget's disease of the skull presents with progressive hearing loss and facial weakness. Which of the following is the MOST likely underlying mechanism for these symptoms?

. A. High cardiac output leading to cerebral ischemia.
. B. Osteoporosis circumscripta causing diffuse skull weakening.
. C. Narrowing of neural foramina due to enlarged and deformed pagetic bone.
. D. Malignant transformation to chondrosarcoma within the skull.
. E. 'Cotton wool appearance' causing increased intracranial pressure.

Correct Answer & Explanation

. C. Narrowing of neural foramina due to enlarged and deformed pagetic bone.

Explanation

Correct Answer: CThe case lists complications of Paget's disease, specifically mentioning skull involvement: 'An enlarged and deformed skull can lead to increased intracranial pressure, hydrocephalus or cranial nerve deficits such as facial palsy (narrowing of neural foramina), hearing loss or blindness (pressure on optic nerve).' Therefore, narrowing of neural foramina due to the enlarged and deformed pagetic bone is the most direct and likely mechanism for facial palsy and hearing loss.Option A, high cardiac output, is a rare systemic complication and would not directly cause localized cranial nerve deficits. Option B, osteoporosis circumscripta, is a lytic phase radiographic feature of the skull, but it describes bone lysis, not the enlargement and deformation that leads to nerve compression. Option D, malignant transformation, is a possibility but less common than direct nerve compression from bone enlargement, and the symptoms described are classic for nerve impingement. Option E, 'cotton wool appearance' is a radiographic feature of mixed lytic/blastic skull involvement, and while it indicates thickened calvarium, the direct cause of cranial nerve deficits is thepressureornarrowingof foramina, not the appearance itself, and increased intracranial pressure is a separate complication that can also arise from skull enlargement, but the specific symptoms point to nerve compression.

Question 2043

Topic: Biology, Genetics & Bone Healing

In the initial phase of Paget's disease, what is the primary driving cellular mechanism?

. Decreased osteoblastic activity
. Intensely overactive, multinucleated osteoclasts
. Abnormal chondrocyte hypertrophy
. Defective mineralization of osteoid
. Monoclonal plasma cell proliferation

Correct Answer & Explanation

. Intensely overactive, multinucleated osteoclasts

Explanation

The initial lytic phase of Paget's disease is driven by intensely overactive, excessively large, and multinucleated osteoclasts. This leads to aggressive focal bone resorption.

Question 2044

Topic: 1. General Principles & Basic Science

A 65-year-old man with Paget's disease involving the right hip is scheduled for an elective total hip arthroplasty due to severe secondary osteoarthritis. To minimize intraoperative blood loss, which preoperative medical intervention is most appropriate?

. Intravenous tranexamic acid administration 1 week prior
. Subcutaneous low-molecular-weight heparin
. Preoperative treatment with bisphosphonates
. Discontinuation of non-steroidal anti-inflammatory drugs
. Prophylactic radiation to the hip

Correct Answer & Explanation

. Preoperative treatment with bisphosphonates

Explanation

Preoperative administration of bisphosphonates reduces bone turnover and the extreme vascularity associated with Pagetic bone. This significantly decreases the risk of massive intraoperative hemorrhage.

Question 2045

Topic: Biology, Genetics & Bone Healing

In a patient with Paget's disease, evaluation of bone turnover and the efficacy of antiresorptive therapy is best monitored using which of the following laboratory markers?

. Serum calcium
. Serum 25-hydroxyvitamin D
. Serum alkaline phosphatase and urinary N-telopeptide
. Serum parathyroid hormone
. Serum phosphorus

Correct Answer & Explanation

. Serum alkaline phosphatase and urinary N-telopeptide

Explanation

Serum alkaline phosphatase reflects osteoblast activity, while urinary markers like N-telopeptide or hydroxyproline reflect osteoclast activity. Together, they are the standard for monitoring Paget's disease activity and treatment response.

Question 2046

Topic: Biology, Genetics & Bone Healing

A 70-year-old man with extensive polyostotic Paget's disease presents with shortness of breath and bilateral lower extremity edema. Echocardiography is likely to demonstrate which of the following conditions related to his bone disease?

. Restrictive cardiomyopathy
. High-output cardiac failure
. Aortic stenosis
. Pericardial effusion
. Hypertrophic obstructive cardiomyopathy

Correct Answer & Explanation

. High-output cardiac failure

Explanation

Extensive vascular shunting within widespread Pagetic bone increases the cardiovascular workload. This can eventually lead to high-output cardiac failure.

Question 2047

Topic: Biology, Genetics & Bone Healing

Paget's disease frequently affects the skull. Which of the following complications is a direct result of skull involvement and progressive temporal bone enlargement?

. Trigeminal neuralgia
. Conductive and sensorineural hearing loss
. Central retinal artery occlusion
. Spontaneous cerebrospinal fluid leak
. Pituitary apoplexy

Correct Answer & Explanation

. Conductive and sensorineural hearing loss

Explanation

Enlargement of the temporal bone and narrowing of the internal auditory meatus in Paget's disease frequently lead to both conductive and sensorineural hearing loss.

Question 2048

Topic: Biology, Genetics & Bone Healing

Histological analysis of bone in the mixed phase of Paget's disease demonstrates a highly characteristic appearance. What is this classic histological finding?

. Woven bone with hypercellular marrow
. A mosaic or 'jigsaw puzzle' pattern of lamellar bone with prominent cement lines
. Diffuse sheets of multinucleated giant cells in a fibrous stroma
. Non-mineralized osteoid seams
. Replacement of bone marrow with dense connective tissue

Correct Answer & Explanation

. A mosaic or 'jigsaw puzzle' pattern of lamellar bone with prominent cement lines

Explanation

The hallmark histological feature of the mixed phase of Paget's disease is the mosaic or 'jigsaw puzzle' pattern. This is created by haphazardly arranged lamellar bone intersected by prominent, irregular cement lines.

Question 2049

Topic: Biology, Genetics & Bone Healing

A biopsy of a thickened, bowed femur from an 80-year-old man reveals a 'mosaic pattern' of lamellar bone with irregular cement lines. What is the primary cellular abnormality initiating this disease process?

. Decreased activity of osteoblasts
. Increased number and size of multinucleated osteoclasts
. Defective mineralization of osteoid
. Absence of ruffled borders on osteoclasts
. Malignant proliferation of plasma cells

Correct Answer & Explanation

. Increased number and size of multinucleated osteoclasts

Explanation

Paget's disease is initiated by an overactive, destructive phase driven by large, multinucleated osteoclasts. This leads to chaotic, rapid bone remodeling by osteoblasts, resulting in the classic mosaic pattern of woven and lamellar bone.

Question 2050

Topic: Biology, Genetics & Bone Healing

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

. Elevated Calcium, Elevated Phosphate, Normal Alkaline Phosphatase
. Decreased Calcium, Elevated Phosphate, Elevated Alkaline Phosphatase
. Normal Calcium, Normal Phosphate, Elevated Alkaline Phosphatase
. Elevated Calcium, Normal Phosphate, Elevated Alkaline Phosphatase
. Normal Calcium, Decreased Phosphate, Normal Alkaline Phosphatase

Correct Answer & Explanation

. Normal Calcium, Normal Phosphate, Elevated Alkaline Phosphatase

Explanation

In uncomplicated Paget's disease, serum calcium and phosphate levels remain normal. Alkaline phosphatase is characteristically elevated due to the extremely high rate of bone turnover.

Question 2051

Topic: Biology, Genetics & Bone Healing

A 72-year-old man with active Paget's disease requires an elective total hip arthroplasty (THA). What preoperative medical management is most appropriate to minimize his intraoperative surgical complications?

. Oral calcium supplementation starting 1 week prior
. Intravenous bisphosphonate therapy administered 2 months prior to surgery
. Daily subcutaneous teriparatide for 6 weeks prior to surgery
. Preoperative external beam radiation to the hip
. High-dose oral corticosteroids starting 3 days prior

Correct Answer & Explanation

. Intravenous bisphosphonate therapy administered 2 months prior to surgery

Explanation

Preoperative administration of bisphosphonates reduces the intense disease activity and hypervascularity associated with Paget's disease. This significantly decreases intraoperative blood loss during elective orthopedic procedures.

Question 2052

Topic: Biology, Genetics & Bone Healing

Mutations in which of the following genes are most commonly associated with the pathogenesis of familial Paget's disease of bone?

. COL1A1
. FGFR3
. SQSTM1
. RUNX2
. COMP

Correct Answer & Explanation

. SQSTM1

Explanation

Mutations in the SQSTM1 gene, which encodes the p62 protein involved in the NF-kB signaling pathway for osteoclastogenesis, are found in up to 40% of familial Paget's disease cases.

Question 2053

Topic: Biomechanics & Biomaterials

During the initial 'run-in' phase of a metal-on-metal bearing articulation, wear debris is generated at a higher rate. What is the primary mode of wear occurring during this specific phase?

. Third-body wear from acrylic cement
. Boundary lubrication leading to adhesive and abrasive wear
. Galvanic corrosion at the head-neck taper
. Fatigue wear of the subchondral bone
. Fretting wear at the acetabular rim

Correct Answer & Explanation

. Boundary lubrication leading to adhesive and abrasive wear

Explanation

The 'run-in' phase relies on boundary lubrication where asperities on the metal surfaces interact directly. This early adhesive and abrasive wear eventually smooths the surfaces to allow fluid-film lubrication.

Question 2054

Topic: Biology, Genetics & Bone Healing

Electron microscopy of osteoclasts isolated from a patient with Paget's disease classically reveals intranuclear inclusion bodies. These inclusions most closely resemble the nucleocapsids of which type of virus?

. Herpes simplex virus
. Cytomegalovirus
. Paramyxovirus
. Human papillomavirus
. Epstein-Barr virus

Correct Answer & Explanation

. Paramyxovirus

Explanation

Intranuclear inclusion bodies found in pagetic osteoclasts structurally resemble the nucleocapsids of paramyxoviruses, such as the measles virus or respiratory syncytial virus (RSV). This supports a potential viral etiology for the disease.

Question 2055

Topic: 1. General Principles & Basic Science

Acetabular component malpositioning in MOM hip resurfacing drastically increases edge-loading and wear rates. Which specific orientation most increases the risk of this early mechanical failure?

. Decreased inclination and increased retroversion
. Increased inclination (>50 degrees) and excessive anteversion
. Decreased inclination (<30 degrees) and neutral anteversion
. Anatomical inclination (40 degrees) and 15 degrees of anteversion
. Zero degrees of inclination and 20 degrees of retroversion

Correct Answer & Explanation

. Increased inclination (>50 degrees) and excessive anteversion

Explanation

Acetabular cup inclination greater than 50 degrees reduces the contact patch area, leading to edge loading. This severely disrupts the fluid-film lubrication, causing exponentially increased wear debris and early failure.

Question 2056

Topic: Biology, Genetics & Bone Healing

When utilizing plate and screw constructs to stabilize a 'chalk-stick' tibia fracture in a patient with active Paget's disease, what is a primary biomechanical concern during fixation?

. Excessively high pull-out strength leading to screw stripping during insertion
. Immediate robust primary bone healing bypassing callus formation
. Decreased screw pull-out strength and higher risk of delayed union
. The virtual absence of any periosteal reaction or callus formation
. Complete inability to utilize locking screw technology

Correct Answer & Explanation

. Decreased screw pull-out strength and higher risk of delayed union

Explanation

Despite appearing thick and dense on radiographs, pagetic bone is structurally weak, highly disorganized, and brittle. This results in decreased hardware purchase (lower pull-out strength) and a significantly higher risk of delayed union or nonunion.

Question 2057

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with dull aching thigh pain. Radiographs demonstrate cortical thickening and coarse trabeculae. Labs show an isolated severe elevation of alkaline phosphatase. The primary cellular defect in this condition is most closely associated with which of the following?

. Deficient osteoblast activity
. Mutations in the COL1A1 gene
. Abnormal, hyperactive, multinucleated osteoclasts
. Overproduction of fibroblast growth factor 23 (FGF23)
. Deficient mineralization of osteoid

Correct Answer & Explanation

. Abnormal, hyperactive, multinucleated osteoclasts

Explanation

The clinical picture is classic for Paget's disease of bone. The primary pathophysiological defect lies in the osteoclasts, which are abnormally large, multinucleated, and hyperactive, driving excessive bone resorption and subsequent disorganized bone formation.

Question 2058

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman with known Paget's disease of the right femur is scheduled for a right total knee arthroplasty due to severe secondary osteoarthritis. Her serum alkaline phosphatase is currently 5 times the upper limit of normal. Which of the following pre-operative interventions is most appropriate to minimize intraoperative complications?

. Administration of intravenous antibiotics 24 hours prior
. Preoperative administration of systemic bisphosphonates
. Prophylactic embolization of the femoral artery
. Administration of high-dose vitamin D and calcium
. Preoperative radiation therapy to the distal femur

Correct Answer & Explanation

. Preoperative administration of systemic bisphosphonates

Explanation

Pagetic bone is highly vascular and hyperemic, making excessive intraoperative hemorrhage a major risk during arthroplasty. Preoperative administration of bisphosphonates reduces disease activity and bone vascularity, significantly decreasing surgical blood loss.

Question 2059

Topic: Biology, Genetics & Bone Healing

A 60-year-old asymptomatic woman is referred by her primary care physician due to abnormal routine blood work. Laboratory testing shows a significantly elevated alkaline phosphatase level, but normal serum calcium, phosphorus, and parathyroid hormone. Radiographs of her skull demonstrate large, sharply demarcated radiolucent areas. What is this classic radiographic sign called?

. Cotton wool appearance
. Osteoporosis circumscripta
. Picture frame appearance
. Blade of grass sign
. Rugger jersey spine

Correct Answer & Explanation

. Osteoporosis circumscripta

Explanation

The patient's lab profile is classic for Paget's disease. The initial lytic phase of Paget's disease in the skull is known as osteoporosis circumscripta, presenting as large, sharply demarcated osteolytic areas.

Question 2060

Topic: Biology, Genetics & Bone Healing

Research into the etiology of familial Paget's disease has identified several genetic mutations. The most frequent mutation involves a gene that plays a crucial role in regulating osteoclastogenesis via the RANK-NF-kB signaling pathway. Which gene is most commonly implicated?

. RUNX2
. SOX9
. SQSTM1
. FGFR3
. COL2A1

Correct Answer & Explanation

. SQSTM1

Explanation

Mutations in the SQSTM1 (sequestosome 1) gene are the most common genetic cause of familial Paget's disease of bone. This gene encodes the p62 protein, which is a critical regulatory component in osteoclast activation and the RANK signaling pathway.

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