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1. General Principles & Basic Science MCQs

Practice Set 31 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 601

Topic: Surgical Anatomy & Approaches

A 6-year-old girl falls from monkey bars and sustains a widely displaced posterolateral extension-type supracondylar humerus fracture. Which nerve is most at risk in this specific displacement pattern?

. Median nerve (Anterior interosseous branch)
. Radial nerve
. Ulnar nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Median nerve (Anterior interosseous branch)

Explanation

In a posterolateral supracondylar fracture, the proximal fragment is driven anteromedially, putting the median nerve and its anterior interosseous branch (AIN) at highest risk. Posteromedial displacement places the radial nerve at risk.

Question 602

Topic: Biology, Genetics & Bone Healing

A 14-month-old child presents with severe bowing of the legs. Radiographs show widened physes and "cupping and fraying" of the metaphyses. Laboratory evaluation reveals hypophosphatemia, normal serum calcium, and normal parathyroid hormone levels. What is the most likely diagnosis?

. Nutritional rickets
. X-linked hypophosphatemic rickets
. Vitamin D-dependent rickets type 1
. Renal osteodystrophy
. Hypophosphatasia

Correct Answer & Explanation

. X-linked hypophosphatemic rickets

Explanation

X-linked hypophosphatemic rickets is caused by a defect in renal phosphate reabsorption (PHEX gene mutation), leading to isolated hypophosphatemia. Unlike nutritional rickets, calcium and PTH levels typically remain within normal limits.

Question 603

Topic: 1. General Principles & Basic Science

The cause of Ehlers-Danlos syndrome types I (gravis) and II (mitis) is a mutation in which of the following:

. Fibrillin
. Fibroblast growth factor
. C ollagen type I
. C ollagen type II
. C ollagen type V

Correct Answer & Explanation

. C ollagen type V

Explanation

Ehlers-Danlos syndrome is subclassified into at least nine types. Types I and II result from defects in type V collagen.

Question 604

Topic: Surgical Anatomy & Approaches

During a lateral approach to the elbow (Kocher approach), the surgical interval is developed between which two muscles?

. Extensor carpi radialis brevis and extensor digitorum communis
. Anconeus and extensor carpi ulnaris
. Brachioradialis and extensor carpi radialis longus
. Pronator teres and flexor carpi radialis
. Triceps and brachialis

Correct Answer & Explanation

. Anconeus and extensor carpi ulnaris

Explanation

The Kocher approach utilizes the internervous plane between the anconeus (radial nerve) and the extensor carpi ulnaris (posterior interosseous nerve). This provides excellent access to the radial head and capitellum.

Question 605

Topic: Surgical Anatomy & Approaches

In a pediatric patient with an extension-type supracondylar humerus fracture that is displaced posteromedially, which nerve is at the highest risk of injury due to tethering over the proximal fragment?

. Radial nerve
. Median nerve (anterior interosseous branch)
. Ulnar nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Radial nerve

Explanation

In an extension-type supracondylar humerus fracture with posteromedial displacement of the distal fragment, the proximal fragment is directed anterolaterally. This anteriorly displaced bony spike places the radial nerve at the highest risk of injury.

Question 606

Topic: Biology, Genetics & Bone Healing

Following severe elbow trauma or an open surgical contracture release, what is the most effective and widely accepted prophylactic regimen to prevent heterotopic ossification (HO)?

. Indomethacin and/or low-dose single-fraction radiation
. Oral bisphosphonates for 6 weeks
. Intra-articular corticosteroid injections
. Systemic methotrexate
. Prolonged cast immobilization

Correct Answer & Explanation

. Indomethacin and/or low-dose single-fraction radiation

Explanation

Heterotopic ossification is a severe complication following elbow trauma or capsular release. Prophylaxis with oral indomethacin or a single dose of low-dose radiation (typically 700 cGy) is highly effective at preventing ectopic bone formation.

Question 607

Topic: Surgical Anatomy & Approaches

During a single-incision anterior approach for distal biceps tendon repair, excessive radial retraction is applied. Postoperatively, the patient is unable to extend their fingers or thumb at the MCP joints, but wrist extension is preserved with radial deviation. Which nerve was most likely injured?

. Median nerve
. Anterior interosseous nerve
. Posterior interosseous nerve
. Superficial radial nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Posterior interosseous nerve

Explanation

The posterior interosseous nerve (PIN) is highly susceptible to traction injury from radial retractors during the anterior approach to the elbow. PIN palsy presents with loss of digit extension and radial-deviated wrist extension, as ECRL innervation is proximal to the PIN.

Question 608

Topic: Surgical Anatomy & Approaches

Which of the following factors most significantly increases the risk of developing heterotopic ossification (HO) following surgical management of severe traumatic elbow injuries?

. Use of a posterior surgical approach
. Concurrent ipsilateral distal radius fracture
. Use of indomethacin postoperatively
. Early active range of motion
. Concurrent severe traumatic brain injury

Correct Answer & Explanation

. Concurrent severe traumatic brain injury

Explanation

Patients with severe elbow trauma coupled with central nervous system injuries, particularly severe traumatic brain injury, have a markedly increased risk of developing clinically significant heterotopic ossification.

Question 609

Topic: 1. General Principles & Basic Science

Macrodactyly is associated with all of the following syndromes except:

. Neurofibromatosis
. Proteus syndrome
. Klippel-Trenaunay syndrome
. Marfan syndrome
. Multiple enchondromatosis

Correct Answer & Explanation

. Marfan syndrome

Explanation

Macrodactyly is an increase in length and width of a digit or two adjacent digits. It may be associated with all of the above syndromes except for Marfan syndrome. Macrodactyly is also a common isolated condition.

Question 610

Topic: Biology, Genetics & Bone Healing

Which of the following conditions is inherited in an X-linked dominant fashion:

. Hemophilia A
. Familial hypophosphatemic rickets
. Marfan syndrome
. Prader-Willi syndrome
. Sickle cell anemia

Correct Answer & Explanation

. Familial hypophosphatemic rickets

Explanation

Familial hypophosphatemic rickets is inherited in an X-linked dominant fashion, meaning that there is an excess of affected females. Hemophilia A is sex-linked recessive like most X-linked conditions (seen primarily in males). Marfan syndrome is autosomal dominant, sickle cell anemia is autosomal recessive, and Prader-Willi syndrome is a partial deletion of chromosome 15.

Question 611

Topic: 1. General Principles & Basic Science

Which of the following is considered the cutoff for normal loss of C 1-C 2 articular contact in dynamic computed tomography (C T) in normal patients:

. 10%
. 20%
. 40%
. 50%
. 80%

Correct Answer & Explanation

. 80%

Explanation

Up to 80% loss of contact between the C 1 and C 2 facet joints may be seen in normal patients. Therefore, dynamic C T is an oversensitive test and the dynamic feature does not add to C T in diagnosis.

Question 612

Topic: Infection, Pharmacology & VTE

Nonselective nonsteroidal anti-inflammatory drugs (NSAIDs) have the following effect on spinal fusion:

. Increased speed of fusion
. Increased volume of fusion bone
. Decreased bleeding
. Decreased fusion rate
. Unplanned extension of fusion

Correct Answer & Explanation

. Decreased fusion rate

Explanation

Nonselective NSAIDs have been shown to decrease fusion rates in both animal models and in humans. The mechanism is most likely through an inhibition of cyclooxygenase (C OX)-1 because C OX-2 inhibitors do not show this effect.

Question 613

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of intravenous bisphosphonates (e.g., pamidronate) used in treating children with osteogenesis imperfecta?

. Stimulating osteoblast proliferation
. Increasing Type I collagen synthesis
. Inhibiting osteoclast-mediated bone resorption
. Enhancing calcium absorption in the gut
. Promoting cross-linking of collagen fibrils

Correct Answer & Explanation

. Inhibiting osteoclast-mediated bone resorption

Explanation

Bisphosphonates act by disrupting osteoclast function and inducing osteoclast apoptosis. This inhibits bone resorption, increasing overall bone mineral density and reducing fracture rates in osteogenesis imperfecta.

Question 614

Topic: Biology, Genetics & Bone Healing

A patient with delayed closure of the fontanelles, multiple supernumerary teeth, and the ability to appose their shoulders anteriorly in the midline most likely has a mutation affecting which gene?

. FGFR3
. CBFA1 (RUNX2)
. COL1A1
. COMP
. SOX9

Correct Answer & Explanation

. CBFA1 (RUNX2)

Explanation

The clinical picture is diagnostic for cleidocranial dysplasia. It is an autosomal dominant disorder caused by a mutation in the CBFA1 (RUNX2) transcription factor gene, which is essential for osteoblast differentiation.

Question 615

Topic: 1. General Principles & Basic Science

A newborn is diagnosed with diastrophic dysplasia. Which of the following clinical features is classically associated with this condition?

. Blue sclerae and fragile bones
. Hitchhiker thumb and cauliflower ear
. Absent clavicles and delayed cranial suture closure
. Asymmetric limb overgrowth and vascular malformations
. Short stature and frontal bossing

Correct Answer & Explanation

. Hitchhiker thumb and cauliflower ear

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a defect in the SLC26A2 sulfate transporter gene. It is classically associated with short-limbed dwarfism, hitchhiker thumbs, cauliflower ears, and severe clubfeet.

Question 616

Topic: Biology, Genetics & Bone Healing
Spondyloepiphyseal dysplasia (SED) congenita is characterized by a primary defect in which of the following collagen types?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

SED congenita is caused by mutations in the COL2A1 gene, resulting in defective Type II collagen. This affects articular cartilage, the nucleus pulposus, and the vitreous humor of the eye.

Question 617

Topic: Biology, Genetics & Bone Healing

A patient with Cleidocranial Dysplasia is undergoing an orthopedic evaluation. Which of the following is the underlying genetic and pathophysiologic mechanism for this condition?

. Mutation in the RUNX2 (CBFA1) gene affecting membranous bone formation
. Mutation in the COL1A1 gene affecting endochondral ossification
. Defect in the FGFR3 gene causing disordered chondrocyte proliferation
. Mutation in the COMP gene causing abnormal cartilage matrix
. Defect in the fibrillin-1 gene causing connective tissue laxity

Correct Answer & Explanation

. Mutation in the RUNX2 (CBFA1) gene affecting membranous bone formation

Explanation

Cleidocranial dysplasia is an autosomal dominant disorder caused by a mutation in the RUNX2 (CBFA1) gene. It primarily affects bones formed by intramembranous ossification, such as the clavicles and cranial vault.

Question 618

Topic: Biology, Genetics & Bone Healing

Which of the following skeletal dysplasias is inherited in an X-linked dominant fashion and presents with lower extremity bowing, widened physes, and hypophosphatemia that does not respond to standard doses of Vitamin D?

. Hypophosphatasia
. Osteogenesis imperfecta
. Familial hypophosphatemic rickets
. Metaphyseal chondrodysplasia (Schmid type)
. Achondroplasia

Correct Answer & Explanation

. Familial hypophosphatemic rickets

Explanation

Familial hypophosphatemic rickets (Vitamin D-resistant rickets) is typically an X-linked dominant disorder caused by a PHEX mutation. It leads to renal phosphate wasting, presenting with short stature and rickets-like bone changes.

Question 619

Topic: Biology, Genetics & Bone Healing

A 3-year-old with frequent fractures, blue sclerae, and dentinogenesis imperfecta is started on intravenous pamidronate. What is the primary mechanism of action of this medication in treating her condition?

. Stimulates osteoblast differentiation
. Inhibits osteoclast-mediated bone resorption
. Enhances type I collagen cross-linking
. Promotes intestinal calcium absorption
. Stimulates FGF23 production

Correct Answer & Explanation

. Inhibits osteoclast-mediated bone resorption

Explanation

Pamidronate is a bisphosphonate that inhibits osteoclast activity, thereby decreasing bone resorption and increasing overall bone mineral density. This reduces fracture frequency in patients with osteogenesis imperfecta.

Question 620

Topic: Biology, Genetics & Bone Healing

A patient with Spondyloepiphyseal Dysplasia congenita (SEDc) is likely to have a defect involving which of the following molecules?

. Type I collagen
. Type II collagen
. Fibroblast growth factor receptor 3
. Cartilage oligomeric matrix protein
. Heparan sulfate

Correct Answer & Explanation

. Type II collagen

Explanation

SEDc is an autosomal dominant condition caused by mutations in the COL2A1 gene, resulting in defective Type II collagen. This primarily affects hyaline cartilage, leading to a short-trunk dwarfism, coxa vara, and ocular complications.

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