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1. General Principles & Basic Science MCQs

Practice Set 519 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 10361

Topic: 1. General Principles & Basic Science

Patients with Ollier disease and Maffucci syndrome frequently possess somatic mosaic mutations in which of the following genes?

. EXT1 or EXT2
. IDH1 or IDH2
. GNAS
. RB1
. TP53

Correct Answer & Explanation

. IDH1 or IDH2

Explanation

Enchondromatosis syndromes (Ollier disease and Maffucci syndrome) are driven by somatic mosaic point mutations in the IDH1 or IDH2 genes. EXT mutations are seen in multiple hereditary exostoses.

Question 10362

Topic: 1. General Principles & Basic Science

A 12-year-old boy with multiple enchondromatosis presents with a rapid increase in the size of a thigh lesion. He is also noted to have multiple soft tissue hemangiomas. Which genetic mutation is most strongly associated with this specific syndrome?

. EXT1
. GNAS
. IDH1 or IDH2
. p53
. RB1

Correct Answer & Explanation

. IDH1 or IDH2

Explanation

The patient has Maffucci syndrome, distinguished from Ollier disease by the presence of soft tissue hemangiomas. Both Ollier disease and Maffucci syndrome are strongly associated with somatic mutations in the IDH1 or IDH2 genes.

Question 10363

Topic: Biology, Genetics & Bone Healing

Which of the following histologic features is the most reliable discriminator for diagnosing a low-grade chondrosarcoma rather than a benign enchondroma?

. Presence of hyaline cartilage matrix
. Binucleated cells
. Myxoid degeneration
. Permeation of Haversian canals and trapping of host lamellar bone
. Lobular growth pattern

Correct Answer & Explanation

. Permeation of Haversian canals and trapping of host lamellar bone

Explanation

Trapping of host lamellar bone and permeation into surrounding marrow spaces or Haversian canals are hallmarks of malignancy (chondrosarcoma). Enchondromas grow in a lobular pattern but respect surrounding host bone without permeative infiltration.

Question 10364

Topic: 1. General Principles & Basic Science

Which of the following is an accurate characteristic regarding the inheritance and genetic profile of Ollier disease?

. It is inherited in an autosomal dominant pattern via EXT1 mutations.
. It is inherited in an autosomal recessive pattern.
. It is caused by a germline mutation in the IDH1 gene.
. It is a sporadic condition resulting from a post-zygotic somatic mutation.
. It results from an unbalanced translocation of t(11;22).

Correct Answer & Explanation

. It is a sporadic condition resulting from a post-zygotic somatic mutation.

Explanation

Ollier disease (multiple enchondromatosis) is a non-hereditary, sporadic disorder. It is caused by post-zygotic somatic mosaic mutations in the IDH1 or IDH2 genes.

Question 10365

Topic: 1. General Principles & Basic Science

A 12-year-old boy presents with multiple cartilaginous lesions predominantly affecting the right side of his body, causing limb-length discrepancy. Genetic testing of the lesional tissue is most likely to reveal a somatic mutation in which of the following genes?

. EXT1
. EXT2
. GNAS1
. IDH1
. RB1

Correct Answer & Explanation

. IDH1

Explanation

The patient has Ollier disease, characterized by multiple enchondromas with a unilateral predominance. Both solitary enchondromas and enchondromatosis syndromes (Ollier and Maffucci) are strongly associated with somatic mutations in the IDH1 or IDH2 genes.

Question 10366

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy presents with progressive knee pain. Radiographs reveal a 2 cm eccentric, purely lytic lesion in the distal femoral epiphysis with a thin sclerotic margin. MRI shows extensive surrounding bone marrow edema. What is the most likely histologic finding upon biopsy of this lesion?

. Sheets of uniform, polyhedral chondroblasts with pericellular "chicken-wire" calcification
. Spindle cells mixed with multinucleated giant cells and hemosiderin deposits
. Bland hyaline cartilage with a lobular architecture and peripheral enchondral ossification
. Malignant cartilage cells permeating host lamellar bone trabeculae
. Stellate cells in a loose myxoid background

Correct Answer & Explanation

. Sheets of uniform, polyhedral chondroblasts with pericellular "chicken-wire" calcification

Explanation

The clinical presentation is classic for a chondroblastoma, an epiphyseal lesion occurring in skeletally immature patients. Histology characteristically shows uniform polyhedral mononuclear cells (chondroblasts) and distinct pericellular "chicken-wire" calcifications.

Question 10367

Topic: 1. General Principles & Basic Science

Which of the following genetic mutations is primarily responsible for the development of multiple enchondromatosis (Ollier disease)?

. EXT1 and EXT2
. GNAS
. IDH1 and IDH2
. RB1
. H3F3A

Correct Answer & Explanation

. IDH1 and IDH2

Explanation

Ollier disease is characterized by multiple enchondromas and is associated with somatic mosaic mutations in the IDH1 and IDH2 genes. EXT1 and EXT2 mutations are associated with multiple hereditary exostoses.

Question 10368

Topic: 1. General Principles & Basic Science

Which of the following inheritance patterns correctly describes the genetic transmission of multiple enchondromatosis (Ollier disease)?

. Autosomal dominant
. Autosomal recessive
. X-linked recessive
. Non-hereditary somatic mosaicism
. Mitochondrial inheritance

Correct Answer & Explanation

. Non-hereditary somatic mosaicism

Explanation

Ollier disease (multiple enchondromatosis) typically occurs sporadically due to post-zygotic somatic mosaic mutations in the IDH1 or IDH2 genes. It is not considered an inherited condition.

Question 10369

Topic: Infection, Pharmacology & VTE

A 28-year-old construction worker presents with pain, swelling, and redness over the olecranon bursa, with no history of trauma. He reports a low-grade fever. Aspiration reveals cloudy fluid with elevated white blood cell count and positive Gram stain for Staphylococcus aureus. What is the most appropriate initial management?

. Oral NSAIDs and rest
. Corticosteroid injection into the bursa
. Surgical excision of the bursa
. Oral antibiotics targeting Staphylococcus aureus
. Repeated aspiration and compression

Correct Answer & Explanation

. Oral antibiotics targeting Staphylococcus aureus

Explanation

The presence of signs of infection (redness, swelling, fever, cloudy fluid with elevated WBCs and positive Gram stain for S. aureus) indicates septic olecranon bursitis. The most appropriate initial management is oral antibiotics targeting S. aureus (e.g., a first-generation cephalosporin or clindamycin if MRSA is suspected locally). NSAIDs, rest, and corticosteroid injections are for aseptic bursitis. Surgical excision is reserved for chronic, recurrent, or refractory septic bursitis. Repeated aspiration alone without antibiotics is insufficient for infection.

Question 10370

Topic: 1. General Principles & Basic Science

A 50-year-old male with a history of long-term corticosteroid use presents with insidious onset of left hip pain, worse with weight-bearing. Radiographs are initially normal, but an MRI reveals diffuse low signal intensity on T1-weighted images and high signal intensity on T2-weighted images with a characteristic 'double-line sign' in the femoral head. What is the most likely diagnosis?

. Femoral head osteomyelitis
. Transient regional osteoporosis
. Avascular necrosis of the femoral head
. Stress fracture of the femoral neck
. Septic arthritis of the hip

Correct Answer & Explanation

. Avascular necrosis of the femoral head

Explanation

The clinical history (corticosteroid use, insidious pain) and characteristic MRI findings ('double-line sign' on T2-weighted images representing the reactive interface between viable and necrotic bone, and T1 hypointensity/T2 hyperintensity indicative of bone marrow edema and necrosis) are diagnostic of avascular necrosis (osteonecrosis) of the femoral head. Femoral head osteomyelitis, transient regional osteoporosis, stress fracture, and septic arthritis have different clinical and imaging presentations.

Question 10371

Topic: Infection, Pharmacology & VTE

In the management of chronic osteomyelitis, what is the most important factor for successful treatment?

. Long-term intravenous antibiotics alone
. Surgical debridement of infected and necrotic bone
. Hyperbaric oxygen therapy
. Bone graft application
. External fixation

Correct Answer & Explanation

. Surgical debridement of infected and necrotic bone

Explanation

Surgical debridement of infected and necrotic (non-viable) bone is the cornerstone of successful treatment for chronic osteomyelitis. Antibiotics alone are often insufficient due to poor penetration into avascular necrotic tissue and biofilm formation. While long-term antibiotics are crucial post-debridement, they are ineffective without source control. Hyperbaric oxygen therapy can be an adjunctive treatment but is not primary. Bone grafting and external fixation are reconstructive or stabilizing procedures performed after successful debridement.

Question 10372

Topic: Infection, Pharmacology & VTE

What is the most common cause of acute hematogenous osteomyelitis in children?

. Pseudomonas aeruginosa
. Escherichia coli
. Staphylococcus aureus
. Group A Streptococcus
. Kingella kingae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus is by far the most common causative organism of acute hematogenous osteomyelitis in children across all age groups. While other organisms can cause osteomyelitis (e.g., Kingella kingae in infants/toddlers, Pseudomonas in puncture wounds through sneakers), S. aureus remains the predominant pathogen.

Question 10373

Topic: Surgical Anatomy & Approaches

A patient presents with a wrist drop following a humeral shaft fracture. Which nerve is most likely to be injured?

. Median nerve
. Ulnar nerve
. Axillary nerve
. Musculocutaneous nerve
. Radial nerve

Correct Answer & Explanation

. Radial nerve

Explanation

A 'wrist drop' is the classic sign of radial nerve palsy, which commonly occurs with humeral shaft fractures due to the proximity of the radial nerve to the humeral shaft in the spiral groove. The radial nerve innervates the extensors of the wrist and fingers. Median nerve injury would affect wrist and finger flexion and thumb opposition. Ulnar nerve injury would affect intrinsic hand muscles and sensation to the small and ulnar half of the ring finger. Axillary nerve injury affects the deltoid, leading to shoulder abduction weakness. Musculocutaneous nerve injury affects biceps and brachialis.

Question 10374

Topic: Infection, Pharmacology & VTE

A patient presents with acute, severe pain, swelling, and exquisite tenderness of the great toe metatarsophalangeal joint. Aspiration reveals negatively birefringent, needle-shaped crystals. What is the most likely diagnosis?

. Pseudogout (Calcium pyrophosphate deposition disease)
. Septic arthritis
. Rheumatoid arthritis
. Gout
. Osteoarthritis

Correct Answer & Explanation

. Gout

Explanation

The classic presentation of acute, severe pain, swelling, and exquisite tenderness of the great toe MTP joint (podagra), combined with the finding of negatively birefringent, needle-shaped crystals on synovial fluid analysis, is pathognomonic for gout. Pseudogout involves positively birefringent, rhomboid-shaped crystals. Septic arthritis would have pus and bacteria. Rheumatoid arthritis typically affects smaller joints symmetrically and has specific serologic markers. Osteoarthritis is a degenerative condition and does not present with acute inflammation or crystal findings like gout.

Question 10375

Topic: Biology, Genetics & Bone Healing

Which metabolic bone disease is characterized by generalized decreased bone mineral density and normal bone mineralization, leading to increased fracture risk?

. Osteomalacia
. Paget's disease
. Rickets
. Osteoporosis
. Hyperparathyroidism

Correct Answer & Explanation

. Osteoporosis

Explanation

Osteoporosis is characterized by a reduction in bone mineral density and microarchitectural deterioration of bone tissue, leading to increased bone fragility and fracture risk, but with normal bone mineralization. Osteomalacia and rickets (in children) are characterized by defective bone mineralization. Paget's disease involves abnormal bone remodeling with localized areas of increased bone turnover. Hyperparathyroidism causes bone resorption due to elevated PTH, leading to osteopenia but is a distinct etiology.

Question 10376

Topic: Infection, Pharmacology & VTE

A 72-year-old female undergoes an elective total hip arthroplasty for severe osteoarthritis. On postoperative day 2, she develops acute shortness of breath, pleuritic chest pain, and hypoxemia. What is the MOST likely diagnosis?

. Pneumonia
. Myocardial infarction
. Atelectasis
. Pulmonary embolism
. Fat embolism syndrome

Correct Answer & Explanation

. Pulmonary embolism

Explanation

Pulmonary embolism (PE) is a serious and well-recognized complication after total hip arthroplasty, especially within the first few weeks post-op. The symptoms of acute shortness of breath and pleuritic chest pain in a postoperative patient are highly suggestive of PE. While pneumonia, MI, and atelectasis are possibilities, PE must be ruled out urgently. Fat embolism syndrome, though possible after orthopedic trauma, is less common after elective arthroplasty and typically presents with a classic triad of respiratory insufficiency, neurological impairment, and petechial rash.

Question 10377

Topic: Biology, Genetics & Bone Healing

Which of the following conditions is MOST likely to impair bone healing (fracture union)?

. Young age
. High calcium intake
. Stable fracture fixation
. Nicotine use
. Adequate Vitamin D levels

Correct Answer & Explanation

. Nicotine use

Explanation

Nicotine use (smoking) is a well-established and significant risk factor for impaired bone healing, delayed union, and non-union. Nicotine causes vasoconstriction, impairs osteoblast function, and reduces blood supply to the fracture site. Young age, high calcium intake, stable fixation, and adequate Vitamin D levels are generally favorable for bone healing.

Question 10378

Topic: Infection, Pharmacology & VTE

A 4-year-old child presents with acute onset severe right hip pain, refusal to bear weight, and fever. On examination, the hip is held in flexion, abduction, and external rotation, and any attempt at passive range of motion elicits significant pain. ESR and CRP are markedly elevated. What is the MOST critical immediate management step?

. Start broad-spectrum oral antibiotics
. Obtain plain radiographs of the hip
. Urgent hip aspiration and initiation of intravenous antibiotics
. Bed rest and anti-inflammatory medications
. MRI of the hip to rule out osteomyelitis

Correct Answer & Explanation

. Urgent hip aspiration and initiation of intravenous antibiotics

Explanation

This clinical scenario is highly concerning for septic arthritis of the hip, which is an orthopedic emergency. The most critical immediate management step is urgent hip aspiration to obtain synovial fluid for cell count, culture, and gram stain. This is essential for definitive diagnosis and guiding antibiotic therapy. Concurrently, broad-spectrum intravenous antibiotics should be initiated immediately after aspiration. Delay in diagnosis and treatment can lead to rapid cartilage destruction and long-term joint damage. Radiographs are often normal early on, and oral antibiotics are insufficient.

Question 10379

Topic: Infection, Pharmacology & VTE

A 10-year-old boy presents with a 2-week history of worsening right tibia pain, fever, and refusal to bear weight. Blood tests show elevated ESR and CRP. Radiographs show subtle periosteal reaction. What is the MOST sensitive imaging modality for early diagnosis of acute osteomyelitis?

. Plain radiographs
. CT scan
. Bone scintigraphy (Technetium-99m)
. Magnetic resonance imaging (MRI)
. Ultrasound

Correct Answer & Explanation

. Magnetic resonance imaging (MRI)

Explanation

Magnetic Resonance Imaging (MRI) is the MOST sensitive imaging modality for early diagnosis of acute osteomyelitis, especially in children. It can detect bone marrow edema and early changes before they are visible on plain radiographs or CT scans. Bone scintigraphy can also detect early changes but is less specific than MRI. Plain radiographs often lag behind clinical symptoms by 10-14 days. CT is good for cortical bone but less for marrow changes.

Question 10380

Topic: 1. General Principles & Basic Science

A 30-year-old active male complains of intermittent catching and locking sensation in his knee, particularly after twisting injuries. He also experiences pain along the medial joint line. What is the MOST likely diagnosis?

. Patellofemoral pain syndrome
. ACL tear
. Medial collateral ligament sprain
. Meniscal tear
. Osteoarthritis

Correct Answer & Explanation

. Meniscal tear

Explanation

Intermittent catching and locking sensations, especially after twisting injuries, combined with pain along the joint line, are classic symptoms of a meniscal tear. Mechanical symptoms like catching and locking are highly indicative of meniscal pathology. ACL tears present with instability. MCL sprains with valgus instability. Patellofemoral pain is typically anterior knee pain, worse with stairs. Osteoarthritis causes diffuse pain and stiffness, usually without acute locking.

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