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1. General Principles & Basic Science MCQs

Practice Set 786 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 15701

Topic: 1. General Principles & Basic Science

A 55-year-old male presents with deep, aching thigh pain. Radiographs show a mottled, permeative lytic lesion in the femoral diaphysis. MRI reveals extensive bone marrow replacement and a large soft tissue mass, but with remarkable preservation of the cortical bone structure.

Which of the following immunohistochemical marker profiles is most characteristic of the suspected diagnosis?

. CD99(+), FLI-1(+), CD20(-)
. CD20(+), CD45(+), CD3(-)
. S-100(+), CD1a(+), CD20(-)
. CD138(+), Kappa/Lambda restricted, CD20(-)
. Cytokeratin(+), EMA(+), CD45(-)

Correct Answer & Explanation

. CD20(+), CD45(+), CD3(-)

Explanation

The clinical and radiographic presentation with a large soft-tissue mass but minimal cortical destruction is classic for Primary Bone Lymphoma (typically Diffuse Large B-Cell Lymphoma). DLBCL is characteristically positive for B-cell markers (CD20) and Leukocyte Common Antigen (CD45), but negative for T-cell markers (CD3).

Question 15702

Topic: Biology, Genetics & Bone Healing

A 10-year-old child presents with a waddling gait, severe leg pain, and generalized muscle weakness. Radiographs demonstrate symmetrical cortical thickening and sclerosis of the diaphyseal regions of the bilateral femurs and tibiae, sparing the epiphyses.

Which of the following medical treatments has been shown to be most effective in alleviating the pain and improving motor function in this condition?

. Intravenous bisphosphonates
. Systemic corticosteroids
. Recombinant human growth hormone
. Nonsteroidal anti-inflammatory drugs (NSAIDs) alone
. Vitamin D and Calcium supplementation

Correct Answer & Explanation

. Systemic corticosteroids

Explanation

The patient has Camurati-Engelmann disease (Progressive Diaphyseal Dysplasia). Systemic corticosteroids are the mainstay of medical treatment, significantly reducing bone pain, improving waddling gait, and sometimes reversing the radiographic abnormalities.

Question 15703

Topic: 1. General Principles & Basic Science

Which specific glycosaminoglycan (GAG) is predominantly accumulated and excreted in the urine of patients with Morquio syndrome (MPS IV)?

. Heparan sulfate
. Dermatan sulfate
. Keratan sulfate
. Chondroitin-4-sulfate
. Hyaluronic acid

Correct Answer & Explanation

. Keratan sulfate

Explanation

Morquio syndrome (MPS IV) is characterized by the inability to degrade keratan sulfate due to deficiency in either N-acetylgalactosamine-6-sulfatase (Type A) or beta-galactosidase (Type B). Hurler and Hunter syndromes typically show elevated heparan and dermatan sulfate.

Question 15704

Topic: Biology, Genetics & Bone Healing

A 12-year-old girl with a history of recurrent ear infections and progressive hearing loss develops a waddling gait and aching pain in her legs. Radiographs demonstrate marked symmetric endosteal and periosteal thickening of the long bone diaphyses.

This condition is most commonly caused by a mutation in which of the following genes?

. SOX9
. CBFA1 (RUNX2)
. COL1A1
. TGFB1
. COMP

Correct Answer & Explanation

. TGFB1

Explanation

The clinical and radiographic picture represents Camurati-Engelmann disease (progressive diaphyseal dysplasia). It is inherited in an autosomal dominant pattern and is caused by mutations in the TGFB1 (Transforming Growth Factor Beta 1) gene, leading to increased bone formation.

Question 15705

Topic: Biology, Genetics & Bone Healing

Which of the following is a key distinguishing histological feature between Chondromyxoid Fibroma (CMF) and Chondroblastoma?

. CMF predominantly features 'chicken-wire' calcifications.
. Chondroblastoma typically lacks osteoclast-like giant cells.
. CMF has a distinctly lobulated architecture with hypocellular centers and hypercellular peripheries.
. Chondroblastoma is composed primarily of spindle cells in a myxoid stroma.
. CMF cells consistently stain positive for S-100, while Chondroblastoma does not.

Correct Answer & Explanation

. CMF has a distinctly lobulated architecture with hypocellular centers and hypercellular peripheries.

Explanation

Histologically, CMF displays a characteristic lobular architecture with hypercellular peripheries containing spindle/stellate cells and osteoclast-like giant cells, and hypocellular myxoid centers. Chondroblastoma features sheet-like arrangements of chondroblasts, 'chicken-wire' calcifications, and lacks this specific lobular architecture.

Question 15706

Topic: Biology, Genetics & Bone Healing

A pediatric patient with suspected Mucopolysaccharidosis undergoes diagnostic testing. Which of the following confirms the definitive diagnosis and specific subtype of the MPS?

. Urinary spot test for glycosaminoglycans (GAGs)
. Measurement of specific enzyme activities in cultured leukocytes or fibroblasts
. Radiographic skeletal survey showing dysostosis multiplex
. Genomic sequencing of the RUNX2 gene
. Bone marrow aspiration and flow cytometry

Correct Answer & Explanation

. Measurement of specific enzyme activities in cultured leukocytes or fibroblasts

Explanation

While urinary GAG levels are an excellent screening test, the definitive diagnosis and subtyping of Mucopolysaccharidoses require the measurement of specific lysosomal enzyme activities in leukocytes, cultured skin fibroblasts, or plasma.

Question 15707

Topic: 1. General Principles & Basic Science

A 3-year-old boy presents with coarse facial features, hepatosplenomegaly, and joint stiffness. His mother reports that her brother died in childhood of a similar condition. The patient has clear corneas. What is the inheritance pattern of this specific mucopolysaccharidosis?

. Autosomal dominant
. Autosomal recessive
. X-linked dominant
. X-linked recessive
. Mitochondrial

Correct Answer & Explanation

. X-linked recessive

Explanation

The clinical picture describes Hunter syndrome (MPS II), which is distinguished from Hurler syndrome by clear corneas and its inheritance pattern. Hunter syndrome is the only mucopolysaccharidosis that is X-linked recessive; all others are autosomal recessive.

Question 15708

Topic: 1. General Principles & Basic Science
In the context of progressive diaphyseal dysplasia (Camurati-Engelmann disease), which of the following regions of the skeleton is characteristically spared from the hyperostotic process?
. Tibial diaphysis
. Femoral diaphysis
. Skull base
. Epiphyses of long bones
. Clavicular diaphysis

Correct Answer & Explanation

. Tibial diaphysis

Explanation

Camurati-Engelmann disease typically features bilateral, symmetrical cortical thickening and sclerosis of the diaphyses of the long bones. The metaphyses may be involved as the disease progresses, but the epiphyses are classically spared.

Question 15709

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with night sweats, fever, and thigh pain. Radiographs show a permeative diaphyseal lesion mimicking osteomyelitis.

Which MRI feature most strongly suggests a diagnosis of primary bone lymphoma over acute osteomyelitis?

. Presence of a cloaca and involucrum
. A sharply defined sclerotic rim surrounding a central necrotic cavity
. A massive extraosseous soft-tissue mass with relatively preserved cortical bone architecture
. Extensive subperiosteal abscess formation lifting the periosteum
. High T2 signal strictly confined to the medullary canal without extraosseous extension

Correct Answer & Explanation

. A massive extraosseous soft-tissue mass with relatively preserved cortical bone architecture

Explanation

A classic imaging hallmark of primary bone lymphoma is the presence of a large soft-tissue mass that extends outward from the bone with surprisingly little cortical destruction. Osteomyelitis typically shows distinct cortical breakdown, abscesses, or cloacae.

Question 15710

Topic: 1. General Principles & Basic Science

A 4-year-old boy presents with joint stiffness, nodular skin lesions over his scapulae, and behavioral issues. Physical exam reveals clear corneas and hepatosplenomegaly. Which inheritance pattern differentiates this specific mucopolysaccharidosis from the others?

. Autosomal dominant
. Autosomal recessive
. X-linked dominant
. X-linked recessive
. Mitochondrial inheritance

Correct Answer & Explanation

. X-linked recessive

Explanation

This clinical picture is typical of Hunter syndrome (MPS II), which is distinguished by clear corneas and unique nodular skin lesions. Unlike all other mucopolysaccharidoses (which are autosomal recessive), Hunter syndrome is X-linked recessive.

Question 15711

Topic: 1. General Principles & Basic Science

A 5-year-old with suspected mucopolysaccharidosis undergoes a skeletal survey. Dysostosis multiplex is confirmed.

Which classic vertebral radiographic finding differentiates Hurler syndrome from Morquio syndrome?

. Anterior-inferior vertebral beaking in Hurler vs. central anterior beaking in Morquio
. Ivory vertebrae in Hurler vs. codfish vertebrae in Morquio
. Posterior vertebral scalloping in Hurler vs. anterior scalloping in Morquio
. Complete absence of the vertebral body in Hurler vs. hemivertebrae in Morquio
. Central anterior beaking in Hurler vs. anterior-inferior beaking in Morquio

Correct Answer & Explanation

. Anterior-inferior vertebral beaking in Hurler vs. central anterior beaking in Morquio

Explanation

In the mucopolysaccharidoses, vertebral body shape helps differentiate syndromes. Hurler syndrome typically features anterior-inferior beaking of the vertebral bodies, whereas Morquio syndrome characteristically demonstrates central anterior beaking.

Question 15712

Topic: Biology, Genetics & Bone Healing

A patient with Progressive Diaphyseal Dysplasia (Camurati-Engelmann disease) presents with severe, debilitating pain in the lower extremities.

Which of the following pharmacological treatments is considered first-line and highly effective for reducing bone pain and improving gait in these patients?

. Intravenous Bisphosphonates
. Non-steroidal anti-inflammatory drugs (NSAIDs)
. Systemic Corticosteroids
. Recombinant human parathyroid hormone (Teriparatide)
. Monoclonal antibodies targeting RANKL (Denosumab)

Correct Answer & Explanation

. Systemic Corticosteroids

Explanation

Systemic corticosteroids (e.g., prednisone) are uniquely effective in Camurati-Engelmann disease. They not only provide dramatic relief of bone pain and muscle weakness but can also partially reverse the radiographic diaphyseal thickening.

Question 15713

Topic: 1. General Principles & Basic Science

A 4-year-old boy presents with coarse facial features, joint contractures, hepatosplenomegaly, and clear corneas. His mother notes that his maternal uncle had similar clinical features and passed away in his teens. Radiographs demonstrate anterior inferior vertebral body beaking. Which of the following is the deficient enzyme in this patient's condition?

. Alpha-L-iduronidase
. Iduronate-2-sulfatase
. N-acetylgalactosamine-6-sulfatase
. Glucocerebrosidase
. Sphingomyelinase

Correct Answer & Explanation

. Iduronate-2-sulfatase

Explanation

The patient has Hunter syndrome (MPS II), distinguished from Hurler syndrome by clear corneas and an X-linked recessive inheritance pattern (maternal uncle affected). It is caused by a deficiency in iduronate-2-sulfatase.

Question 15714

Topic: 1. General Principles & Basic Science

A patient presents with a gait abnormality characterized by a backward lurch of the trunk immediately after heel strike on the right side. Which muscle group is most likely weak?

. Right Hip Abductors
. Right Hip Extensors
. Right Hip Flexors
. Left Hip Extensors
. Right Knee Extensors

Correct Answer & Explanation

. Right Hip Extensors

Explanation

A backward trunk lean during early stance (gluteus maximus lurch) moves the center of mass posterior to the hip joint. This creates an artificial hip extension moment, compensating for weak hip extensors.

Question 15715

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction, if an osteotomy is performed at a level different from the center of rotation of angulation (CORA) and the axis of correction (hinge) is placed at the osteotomy site rather than the CORA, what is the resulting effect?

. Perfect alignment with no translation
. Creation of a secondary translation deformity
. Joint line convergence angle alteration
. Mechanical axis deviation with no anatomical axis translation
. Premature consolidation

Correct Answer & Explanation

. Creation of a secondary translation deformity

Explanation

Paley's Rule 3 states that if the osteotomy and the hinge are both placed off the CORA, correction of angulation will create a secondary translation deformity. This is distinct from Rule 2, where the hinge remains at the CORA resulting in perfect axis alignment but local translation.

Question 15716

Topic: Infection, Pharmacology & VTE

During a primary TKA for a severe varus deformity, the surgeon notes the knee remains tight medially in both flexion and extension. After completely releasing the deep medial collateral ligament (MCL), what is the next most appropriate structure to release?

. Lateral collateral ligament
. Semimembranosus
. Pes anserinus
. Posteromedial capsule
. Popliteus tendon

Correct Answer & Explanation

. Posteromedial capsule

Explanation

For a tight medial gap in both flexion and extension, the sequential release typically begins with osteophytes and the deep MCL. If tightness persists symmetrically, the posteromedial capsule is released next, followed by the semimembranosus and finally the superficial MCL.

Question 15717

Topic: 1. General Principles & Basic Science

During limb lengthening of the tibia with a circular external fixator, radiographic follow-up at 3 weeks reveals premature consolidation of the regenerate bone. Which of the following adjustments to the protocol would have best prevented this complication?

. Decreasing the frequency of distraction
. Decreasing the rate of distraction
. Increasing the rate of distraction
. Increasing the latency period
. Performing a diaphyseal rather than metaphyseal osteotomy

Correct Answer & Explanation

. Increasing the rate of distraction

Explanation

Premature consolidation occurs when the bone healing outpaces the distraction gap. Increasing the rate of distraction (e.g., from 1.0 mm/day to 1.5 mm/day) helps the mechanical distraction outpace the robust osteogenic response to prevent premature union.

Question 15718

Topic: Physiology & Rehabilitation

A patient exhibits a positive Trendelenburg sign on the right side. During the stance phase of gait on the right leg, what compensatory movement is typically observed to maintain stability?

. Trunk lean away from the right side
. Trunk lean towards the right side
. Circumduction of the left leg
. Excessive right knee flexion
. Vaulting on the right foot

Correct Answer & Explanation

. Trunk lean towards the right side

Explanation

In an uncompensated Trendelenburg gait due to weak right hip abductors, the pelvis drops on the contralateral side. To compensate, the patient will lean their trunk toward the affected (right) side, shifting the center of gravity closer to the hip joint center to reduce the required abductor moment.

Question 15719

Topic: 1. General Principles & Basic Science

A patient presents with a severe recurvatum (apex posterior) deformity of the proximal tibia following premature physeal closure. What effect does this specific deformity have on knee biomechanics and clinical presentation?

. Increases the risk of patella alta
. Creates an apparent extensor lag
. Limits knee flexion severely during swing phase
. Shifts the mechanical axis lateral to the joint center
. Causes a fixed flexion contracture

Correct Answer & Explanation

. Creates an apparent extensor lag

Explanation

A proximal tibial recurvatum deformity effectively increases the posterior slope of the tibial plateau. This alters the resting position of the knee, requiring greater quadriceps excursion to achieve full extension, thereby clinically manifesting as an apparent extensor lag.

Question 15720

Topic: Physiology & Rehabilitation

A patient with a dense common peroneal nerve palsy presents with a 'steppage' gait. During which phase of the gait cycle is the primary compensation (excessive hip and knee flexion) observed?

. Initial contact
. Mid-stance
. Terminal stance
. Swing phase
. Loading response

Correct Answer & Explanation

. Swing phase

Explanation

A steppage gait is a compensation for foot drop (loss of ankle dorsiflexion) to prevent the toes from catching on the ground. Excessive hip and knee flexion are utilized for toe clearance predominantly during the swing phase.

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