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1. General Principles & Basic Science MCQs

Practice Set 506 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 10101

Topic: Biology, Genetics & Bone Healing

A 9-year-old boy with a history of multiple fractures presents with a painless, limited range of motion in his right forearm. Radiographs reveal calcification of the interosseous membrane and a history of hyperplastic callus formation following previous fractures.

Genetic testing is most likely to show a mutation in which of the following genes?

. COL1A1
. COL1A2
. IFITM5
. SERPINF1
. CRTAP

Correct Answer & Explanation

. IFITM5

Explanation

This presentation is classic for Osteogenesis Imperfecta (OI) Type V, which is characterized by hyperplastic callus formation, radial head dislocation, and calcification of the interosseous membrane. It is caused by an autosomal dominant mutation in the IFITM5 gene.

Question 10102

Topic: Biology, Genetics & Bone Healing

A 5-year-old girl with severe Osteogenesis Imperfecta (OI) is receiving intravenous pamidronate infusions to increase bone mineral density and reduce fracture frequency. Which of the following best describes the molecular mechanism of action of this medication?

. Stimulates osteoblast differentiation via the Wnt/beta-catenin pathway
. Inhibits RANKL to prevent osteoclast activation
. Inhibits farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway
. Directly cross-links collagen fibers in the bone matrix
. Binds to hydroxyapatite and acts as a localized calcium channel blocker

Correct Answer & Explanation

. Inhibits farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway

Explanation

Pamidronate is a nitrogen-containing bisphosphonate. It works by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway, which leads to osteoclast apoptosis and reduced bone resorption.

Question 10103

Topic: Biology, Genetics & Bone Healing

A 12-year-old with multiple fractures has a bone biopsy that demonstrates a distinctive 'fish-scale' lamellation pattern under polarized light microscopy. The patient has shown no clinical improvement with prolonged bisphosphonate therapy. This presentation is most consistent with a mutation in which gene?

. COL1A1
. IFITM5
. SERPINF1
. CRTAP
. LEPRE1

Correct Answer & Explanation

. IFITM5

Explanation

OI Type VI is caused by a mutation in the SERPINF1 gene, which encodes pigment epithelium-derived factor (PEDF). It is characterized histologically by a 'fish-scale' pattern of bone lamellation and typically does not respond to bisphosphonates.

Question 10104

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy with SMA is prescribed Risdiplam. Which of the following accurately describes the administration and mechanism of this medication?

. Intrathecal injection; directly repairs the SMN1 gene
. Intravenous infusion; viral vector delivery of SMN1
. Oral administration; small molecule modifier of SMN2 pre-mRNA splicing
. Intramuscular injection; downregulates myostatin
. Subcutaneous injection; inhibits osteoclast-mediated bone loss

Correct Answer & Explanation

. Oral administration; small molecule modifier of SMN2 pre-mRNA splicing

Explanation

Risdiplam is an orally administered small molecule that modifies the splicing of the SMN2 pre-mRNA, leading to an increased concentration of functional full-length SMN protein.

Question 10105

Topic: Biology, Genetics & Bone Healing
A 2-year-old boy with OI type III receives his first intravenous infusion of pamidronate. Within 24 hours, he develops a fever of 38.5°C, myalgia, and vomiting. What is the most appropriate management of these symptoms?
. Immediate discontinuation of pamidronate permanently due to anaphylaxis
. Administration of broad-spectrum intravenous antibiotics
. Supportive care with antipyretics, as this is a common first-dose acute phase reaction
. Administration of intravenous calcium gluconate for severe hypocalcemia
. Immediate surgical debridement of the infusion site

Correct Answer & Explanation

. Supportive care with antipyretics, as this is a common first-dose acute phase reaction

Explanation

The 'acute phase reaction' is very common (up to 70-80%) after the first infusion of nitrogen-containing bisphosphonates like pamidronate. It consists of fever, myalgias, and flu-like symptoms, which are self-limiting and managed with supportive care.

Question 10106

Topic: Biology, Genetics & Bone Healing
Which of the following cellular processes accurately describes how a fracture heals in a patient with classical Osteogenesis Imperfecta (Type I, III, or IV)?
. Fracture healing is severely delayed with frequent nonunions due to absent osteoblasts.
. Fracture healing occurs at a normal rate with normal callus formation, but the resulting bone is structurally inferior.
. Fracture healing relies exclusively on primary (intramembranous) bone healing, as endochondral ossification is blocked.
. Fractures fail to heal without exogenous bone morphogenetic protein (BMP) administration.
. Fracture healing results in dense, sclerotic bone that is mechanically stronger than the original diaphysis.

Correct Answer & Explanation

. Fracture healing occurs at a normal rate with normal callus formation, but the resulting bone is structurally inferior.

Explanation

In OI, the physiological cascade of fracture healing and callus formation occurs at a normal rate. However, because the collagen matrix is defective (either quantitatively or qualitatively), the newly formed bone remains structurally inferior and prone to re-fracture.

Question 10107

Topic: 1. General Principles & Basic Science

A 6-year-old girl complains of a painful, audible 'popping' sensation in her lateral knee when walking. MRI confirms the presence of a discoid lateral meniscus. Which specific variant of a discoid meniscus lacks normal posterior coronary ligament attachments, directly causing this 'snapping knee' syndrome?

. Incomplete type
. Complete type
. Wrisberg variant
. Ring-shaped variant
. Anterior horn hypermobile variant

Correct Answer & Explanation

. Wrisberg variant

Explanation

The Wrisberg variant of a discoid lateral meniscus lacks normal posterior capsular attachments (the coronary ligaments) and is anchored solely by the meniscofemoral ligament of Wrisberg. This hypermobility allows the meniscus to subluxate into the intercondylar notch during extension, causing a loud and painful 'snap'.

Question 10108

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with a 2-day history of right hip pain and a limp, now refusing to bear weight completely. His temperature is 38.6°C (101.5°F), WBC count is 14,500/mm³, ESR is 45 mm/hr, and CRP is elevated. According to the Kocher criteria, what is the approximate predictive probability of septic arthritis in this patient?
. Less than 5%
. 10%
. 40%
. 93%
. 99%

Correct Answer & Explanation

. 40%

Explanation

The Kocher criteria to differentiate septic arthritis from transient synovitis in children are: 1) Non-weight-bearing, 2) Temperature > 38.5°C, 3) ESR > 40 mm/hr, and 4) WBC > 12,000/mm³. The probability of septic arthritis is approximately 3% for 1 predictor, 40% for 2 predictors, 93% for 3 predictors, and 99% when all 4 predictors are present.

Question 10109

Topic: Biology, Genetics & Bone Healing

A 6-month-old infant presents with multiple fractures of varying ages, blue sclerae, and generalized osteopenia. Genetic testing reveals a mutation in the COL1A1 gene. Which of the following is the primary mechanism of action of the most commonly prescribed class of medications (bisphosphonates) used to treat this condition?

. Inhibition of osteoclast-mediated bone resorption
. Stimulation of osteoblast proliferation and differentiation
. Enhancement of calcium and phosphate absorption in the gut
. Increased synthesis of structurally normal type I collagen
. Direct inhibition of parathyroid hormone secretion

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Osteogenesis Imperfecta (OI) is treated medically with bisphosphonates (e.g., pamidronate or zoledronic acid). Bisphosphonates are analogues of inorganic pyrophosphate that bind to hydroxyapatite and function primarily by inhibiting osteoclast-mediated bone resorption, thereby increasing bone mineral density and decreasing the fracture rate.

Question 10110

Topic: Biology, Genetics & Bone Healing
A 4-year-old child with Osteogenesis Imperfecta (OI) type III is treated with intravenous pamidronate. What is the primary cellular mechanism of action by which this medication improves bone density and reduces fracture burden in this patient population?
. Stimulation of osteoblast-mediated bone formation
. Inhibition of osteoclast-mediated bone resorption
. Enhancement of Type I collagen cross-linking
. Direct mineralization of the osteoid matrix
. Upregulation of the Wnt/beta-catenin pathway

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Bisphosphonates (such as pamidronate) are the medical treatment of choice for moderate to severe Osteogenesis Imperfecta. They function by inhibiting osteoclast activity and inducing osteoclast apoptosis, thereby decreasing bone resorption. This leaves osteoblast activity unopposed, increasing bone volume and density, though it does not correct the underlying genetic defect in Type I collagen synthesis.

Question 10111

Topic: Surgical Anatomy & Approaches

During a Latarjet procedure for recurrent anterior shoulder instability with significant glenoid bone loss, the coracoid process is osteotomized and transferred to the anterior glenoid rim.

Which nerve is most at risk of injury due to overzealous medial retraction of the conjoint tendon?

. Axillary nerve
. Suprascapular nerve
. Musculocutaneous nerve
. Median nerve
. Radial nerve

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The musculocutaneous nerve typically enters the coracobrachialis muscle 3 to 8 cm distal to the tip of the coracoid process. During the Latarjet procedure, aggressive medial retraction of the conjoint tendon can stretch or compress this nerve. The axillary nerve runs inferiorly but is more at risk during capsular release or inferior glenoid preparation.

Question 10112

Topic: 1. General Principles & Basic Science

A 30-year-old powerlifter presents with sudden, severe pain and ecchymosis over the anterior axilla after heavy bench pressing. Examination reveals loss of the anterior axillary fold contour and weakness in internal rotation. MRI confirms a rupture of the pectoralis major.

Which segment of the pectoralis major is usually the first to rupture, and where does it anatomically insert on the humerus relative to the other segment?

. Clavicular head; inserts deep and proximal to the sternal head
. Clavicular head; inserts superficial and distal to the sternal head
. Sternal head; inserts deep and proximal to the clavicular head
. Sternal head; inserts superficial and distal to the clavicular head
. Abdominal head; inserts deep and medial to the coracobrachialis

Correct Answer & Explanation

. Sternal head; inserts superficial and distal to the clavicular head

Explanation

The pectoralis major tendon undergoes a 180-degree twist before inserting onto the lateral lip of the bicipital groove. Because of this twist, the inferior (sternal) head inserts deep and proximal, while the superior (clavicular) head inserts superficial and distal. The sternal head is under maximal tension during eccentric loading with the arm extended and abducted (bench press) and is typically the first segment to tear.

Question 10113

Topic: 1. General Principles & Basic Science

Historically, the arcuate branch of the anterior humeral circumflex artery was considered the primary blood supply to the humeral head. However, modern quantification studies (e.g., Hettrich et al.) have established that the predominant blood supply to the native humeral head is actually provided by which of the following vessels?

. Anterior humeral circumflex artery
. Posterior humeral circumflex artery
. Thoracoacromial artery
. Suprascapular artery
. Subscapular artery

Correct Answer & Explanation

. Posterior humeral circumflex artery

Explanation

Modern anatomical and MRI quantification studies have demonstrated that the posterior humeral circumflex artery provides the majority (approximately 64%) of the blood supply to the humeral head, challenging the classic teaching that the anterior humeral circumflex artery is the primary supplier.

Question 10114

Topic: 1. General Principles & Basic Science

A 28-year-old competitive weightlifter feels a sudden 'pop' and tearing sensation in his anterior chest wall while performing a heavy bench press. Examination reveals loss of the normal anterior axillary fold contour and weakness with internal rotation. In an acute pectoralis major rupture, which head is structurally most vulnerable and typically ruptures first?

. Clavicular head, because it inserts most distally on the humerus
. Clavicular head, because its fibers are under maximum tension in terminal flexion
. Sternal head, because its fibers twist and insert deep and proximal on the humerus
. Sternal head, because it has an inferior blood supply compared to the clavicular head
. Both heads routinely rupture simultaneously due to shared aponeurotic tension

Correct Answer & Explanation

. Sternal head, because its fibers twist and insert deep and proximal on the humerus

Explanation

The sternal head of the pectoralis major undergoes a 180-degree twist before inserting on the humerus, causing its fibers to insert deep and proximal to the clavicular head fibers. During a bench press (arm in extension and abduction), the inferior fibers of the sternal head are under maximal tension and stretch, making them mechanically vulnerable and typically the first to rupture.

Question 10115

Topic: Surgical Anatomy & Approaches

A 35-year-old overhead athlete complains of chronic, vague posterior shoulder pain and numbness over the lateral deltoid. Physical examination demonstrates point tenderness at the posterior aspect of the shoulder, inferior to the teres minor and lateral to the long head of the triceps. Which neurovascular bundle is most likely entrapped in this anatomic space?

. Suprascapular nerve and suprascapular artery
. Axillary nerve and posterior circumflex humeral artery
. Radial nerve and profunda brachii artery
. Musculocutaneous nerve and anterior circumflex humeral artery
. Dorsal scapular nerve and dorsal scapular artery

Correct Answer & Explanation

. Axillary nerve and posterior circumflex humeral artery

Explanation

The patient is describing Quadrilateral Space Syndrome. The quadrilateral space is bordered superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the humeral shaft. Entrapment of the axillary nerve and posterior circumflex humeral artery in this space (often by fibrous bands) leads to posterior shoulder pain and deltoid paresthesias.

Question 10116

Topic: 1. General Principles & Basic Science

A 32-year-old male weightlifter felt a sudden 'pop' and tearing sensation in his anterior axilla while performing a heavy bench press. Examination reveals loss of the anterior axillary fold contour. Operative repair is planned. Which of the following best describes the anatomic insertion of the most commonly ruptured segment of the pectoralis major tendon?

. The sternal head inserts distally and superficial to the clavicular head
. The sternal head inserts proximally and deep to the clavicular head
. The clavicular head inserts proximally and deep to the sternal head
. The abdominal head inserts independently onto the lesser tuberosity
. The two heads blend completely prior to insertion, making them indistinguishable

Correct Answer & Explanation

. The sternal head inserts proximally and deep to the clavicular head

Explanation

Most pectoralis major ruptures occur at or near the humeral insertion and preferentially involve the sternal head. The pectoralis major tendon is bilaminar. As the sternal head courses laterally, it twists 180 degrees so that its fibers insert deep and proximal to the clavicular head. The clavicular head does not twist and inserts distally and superficial.

Question 10117

Topic: Physiology & Rehabilitation

A 30-year-old male presents with severe chest wall bruising, loss of the anterior axillary fold, and weakness in internal rotation and adduction after feeling a "pop" while performing a heavy bench press.

During surgical repair of the ruptured pectoralis major tendon, the surgeon isolates the torn sternocostal head. Relative to the clavicular head footprint on the humerus, where is the anatomic footprint of the sternocostal head located?

. Superficial and distal
. Deep and proximal
. Directly medial on the lesser tuberosity
. Superficial and medial
. Deep and distal

Correct Answer & Explanation

. Deep and proximal

Explanation

The pectoralis major tendon undergoes a 180-degree twist as it inserts onto the lateral lip of the bicipital groove of the humerus. Due to this twist, the sternocostal head (which originates inferiorly on the chest) crosses deep to the clavicular head and inserts deep and proximal (superior) on the humerus. Pectoralis major ruptures most commonly occur at the sternocostal head insertion during maximal eccentric contraction (e.g., bench pressing).

Question 10118

Topic: Surgical Anatomy & Approaches

A 24-year-old rugby player undergoes a Latarjet procedure for recurrent anterior shoulder instability with 25% glenoid bone loss. Postoperatively, he exhibits profound weakness in elbow flexion and decreased sensation over the lateral aspect of his forearm. Which nerve was most likely injured during coracoid retraction?

. Axillary nerve
. Radial nerve
. Musculocutaneous nerve
. Median nerve
. Suprascapular nerve

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The musculocutaneous nerve enters the coracobrachialis muscle 3 to 8 cm distal to the coracoid tip and is at high risk during inferior retraction of the conjoint tendon. Injury causes biceps and brachialis weakness as well as lateral antebrachial cutaneous sensory loss.

Question 10119

Topic: 1. General Principles & Basic Science

A 30-year-old weightlifter feels a pop in his anterior chest while performing a bench press. MRI confirms a complete rupture of the sternal head of the pectoralis major. Compared to the clavicular head, how does the sternal head normally insert onto the humerus?

. Proximal and anterior
. Proximal and posterior
. Distal and anterior
. Distal and posterior
. Conjointly with the latissimus dorsi

Correct Answer & Explanation

. Distal and posterior

Explanation

The pectoralis major tendon undergoes a 180-degree twist before its insertion. As a result, the sternal head inserts deep, distal, and posterior to the clavicular head on the lateral lip of the bicipital groove.

Question 10120

Topic: Surgical Anatomy & Approaches

A 45-year-old male sustains a pelvic ring injury and requires surgical fixation via an anterior intrapelvic (modified Stoppa) approach. During dissection along the superior pubic ramus, brisk arterial bleeding is encountered. This bleeding is most likely originating from the 'corona mortis'. Which of the following describes the most common anatomical configuration of this vascular structure?

. An anastomosis between the internal pudendal artery and the inferior gluteal artery
. An anastomosis between the obturator vessels and the external iliac or inferior epigastric vessels
. An anastomosis between the superior gluteal artery and the iliolumbar artery
. A terminal branch of the internal iliac artery directly supplying the pubic symphysis
. An aberrant branch of the femoral artery traversing the inguinal canal

Correct Answer & Explanation

. An anastomosis between the obturator vessels and the external iliac or inferior epigastric vessels

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator system (internal iliac) and the external iliac or inferior epigastric system. It typically crosses the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis. Injury during ilioinguinal or Stoppa approaches can lead to significant, difficult-to-control hemorrhage.

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