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1. General Principles & Basic Science MCQs

Practice Set 319 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 6361

Topic: 1. General Principles & Basic Science

A 45-year-old man sustains a tibial shaft fracture. He routinely takes high-dose NSAIDs for ankylosing spondylitis. How do nonsteroidal anti-inflammatory drugs (NSAIDs) negatively impact fracture healing?

. They accelerate osteoclast apoptosis
. They inhibit COX-2 which is required for normal endochondral ossification
. They directly block BMP-2 signaling pathways
. They stimulate excessive callus formation leading to hypertrophic nonunion
. They deplete systemic vitamin D stores

Correct Answer & Explanation

. They accelerate osteoclast apoptosis

Explanation

NSAIDs inhibit cyclooxygenase (COX) enzymes, particularly COX-2, which are essential for mesenchymal stem cell differentiation and robust angiogenesis during early fracture healing. Inhibition of this pathway impairs endochondral ossification and increases the risk of delayed union or nonunion.

Question 6362

Topic: Biology, Genetics & Bone Healing

Intermittent administration of recombinant human parathyroid hormone (PTH 1-34) is utilized in the treatment of osteoporosis. What is the primary mechanism by which intermittent dosing increases bone mass?

. Directly inhibiting osteoclast action
. Upregulating sclerostin production by osteocytes
. Stimulating osteoblastic bone formation more than bone resorption
. Enhancing renal calcium excretion
. Inhibiting the RANKL/RANK interaction

Correct Answer & Explanation

. Directly inhibiting osteoclast action

Explanation

While continuous endogenous PTH exposure leads to net bone resorption, intermittent pharmacological administration (like daily teriparatide injections) preferentially stimulates osteoblast activity over osteoclasts. This creates an anabolic window that leads to increased bone mineral density.

Question 6363

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with bowing of the legs, hypocalcemia, hypophosphatemia, and markedly elevated alkaline phosphatase. A defect in which of the following enzymes is responsible for Vitamin D-dependent rickets type I?

. 25-hydroxylase
. 1-alpha-hydroxylase
. 24-hydroxylase
. Alkaline phosphatase
. PHEX

Correct Answer & Explanation

. 25-hydroxylase

Explanation

Vitamin D-dependent rickets type I is an autosomal recessive disorder caused by a mutation in the 1-alpha-hydroxylase enzyme in the kidney. This prevents the conversion of 25-hydroxyvitamin D into its active form, 1,25-dihydroxyvitamin D, leading to defective bone mineralization.

Question 6364

Topic: 1. General Principles & Basic Science

Osteoclasts create an acidic microenvironment in Howship's lacunae to dissolve bone mineral. Which enzyme is primarily responsible for the generation of protons (H+) necessary to acidify this resorption pit?

. Cathepsin K
. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Matrix metalloproteinase (MMP)
. Alkaline phosphatase

Correct Answer & Explanation

. Cathepsin K

Explanation

Carbonic anhydrase II catalyzes the intracellular formation of carbonic acid from carbon dioxide and water, which subsequently dissociates into bicarbonate and protons. These protons are then actively pumped into the ruffled border to acidify the resorption pit and dissolve hydroxyapatite.

Question 6365

Topic: Biomechanics & Biomaterials

A surgeon encounters a nonunion of a femur fracture previously stabilized with a stainless steel plate. The surgeon plans to augment the construct but only has titanium screws available. Using titanium screws through a stainless steel plate is contraindicated primarily due to the risk of:

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with differing electrochemical potentials are in direct contact within an electrolytic environment, such as bodily fluids. The less noble metal acts as an anode and undergoes accelerated corrosion, compromising implant integrity.

Question 6366

Topic: Surgical Anatomy & Approaches

A 24-year-old overhead athlete presents with posterior shoulder pain and isolated weakness of external rotation, with normal strength in abduction. An MRI reveals an isolated paralabral cyst in the spinoglenoid notch. Which of the following nerves is directly compressed?

. Axillary nerve
. Suprascapular nerve
. Spinal accessory nerve
. Musculocutaneous nerve
. Radial nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

A cyst at the spinoglenoid notch compresses the terminal branch of the suprascapular nerve, causing isolated infraspinatus weakness. The supraspinatus, responsible for initiation of abduction, remains unaffected because its motor branches arise more proximally at the suprascapular notch.

Question 6367

Topic: Surgical Anatomy & Approaches

Which of the following best describes the boundaries of the quadrangular space of the shoulder?

. Teres minor superiorly, teres major inferiorly, long head of triceps medially, surgical neck of humerus laterally
. Teres major superiorly, latissimus dorsi inferiorly, short head of biceps medially, humeral shaft laterally
. Subscapularis superiorly, teres minor inferiorly, long head of triceps laterally, glenoid medially
. Teres minor superiorly, teres major inferiorly, lateral head of triceps medially, surgical neck of humerus laterally
. Infraspinatus superiorly, teres major inferiorly, long head of triceps laterally, surgical neck of humerus medially

Correct Answer & Explanation

. Teres minor superiorly, teres major inferiorly, long head of triceps medially, surgical neck of humerus laterally

Explanation

The quadrangular space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus. It contains the axillary nerve and the posterior circumflex humeral artery.

Question 6368

Topic: Surgical Anatomy & Approaches

During an anterior (Smith-Petersen) approach to the hip, an internervous plane is utilized to expose the joint. This superficial plane lies between muscles supplied by which of the following pairs of nerves?

. Superior gluteal and femoral nerves
. Femoral and obturator nerves
. Superior gluteal and inferior gluteal nerves
. Femoral and sciatic nerves
. Inferior gluteal and obturator nerves

Correct Answer & Explanation

. Superior gluteal and femoral nerves

Explanation

The superficial internervous plane of the Smith-Petersen approach lies between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve). The deep dissection continues between the gluteus medius (superior gluteal nerve) and the rectus femoris (femoral nerve).

Question 6369

Topic: Surgical Anatomy & Approaches

A 35-year-old man sustains a midshaft humerus fracture. During open reduction and internal fixation via a posterior approach, the radial nerve is identified. At what approximate distance from the lateral epicondyle does the radial nerve typically pierce the lateral intermuscular septum to enter the anterior compartment of the arm?

. 5 cm
. 10 cm
. 15 cm
. 20 cm
. 25 cm

Correct Answer & Explanation

. 5 cm

Explanation

The radial nerve passes from the posterior compartment to the anterior compartment by piercing the lateral intermuscular septum approximately 10 cm proximal to the lateral epicondyle. This is a critical anatomical landmark when performing surgical approaches to the humerus.

Question 6370

Topic: Surgical Anatomy & Approaches

During a posterior approach to the shoulder for a glenoid fracture, the surgeon enters the quadrangular space. Which of the following structures form the superior and inferior borders of this space, respectively?

. Teres minor and Teres major
. Teres major and Teres minor
. Infraspinatus and Teres minor
. Teres minor and the long head of the triceps
. Teres major and the long head of the triceps

Correct Answer & Explanation

. Teres minor and Teres major

Explanation

The quadrangular space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus. It contains the axillary nerve and the posterior humeral circumflex artery.

Question 6371

Topic: Surgical Anatomy & Approaches

During a Smith-Petersen (anterior) approach to the hip, there is a risk of injury to the lateral femoral cutaneous nerve (LFCN). To minimize this risk, the surgeon should remember that the LFCN typically enters the thigh by passing beneath the inguinal ligament at what specific location?

. Immediately medial to the anterior superior iliac spine (ASIS)
. Immediately lateral to the ASIS
. Over the anterior inferior iliac spine (AIIS)
. Through the femoral canal medial to the femoral vein
. Lateral to the sartorius muscle belly at the mid-thigh

Correct Answer & Explanation

. Immediately medial to the anterior superior iliac spine (ASIS)

Explanation

The lateral femoral cutaneous nerve typically passes under the inguinal ligament immediately medial (about 1-2 cm) to the anterior superior iliac spine (ASIS). It runs superficial to the sartorius muscle.

Question 6372

Topic: Surgical Anatomy & Approaches

In a patient undergoing a posterior approach to the hip, the sciatic nerve is identified. In approximately what percentage of the population does the common peroneal division of the sciatic nerve pierce directly through the piriformis muscle belly?

. <1%
. 15%
. 30%
. 50%
. 85%

Correct Answer & Explanation

. <1%

Explanation

In roughly 15% of the population, the sciatic nerve bifurcates prematurely, and the common peroneal division exits the pelvis by piercing directly through the piriformis muscle, predisposing the patient to piriformis syndrome.

Question 6373

Topic: Surgical Anatomy & Approaches

During an extended deltopectoral approach to the shoulder, the axillary nerve is at risk as it crosses the deep surface of the deltoid. Approximately how far distal to the lateral edge of the acromion does the axillary nerve typically run?

. 2 cm
. 5-7 cm
. 10-12 cm
. 15 cm
. 20 cm

Correct Answer & Explanation

. 2 cm

Explanation

The axillary nerve runs transversely from posterior to anterior on the deep surface of the deltoid muscle, typically 5 to 7 cm distal to the lateral border of the acromion. Deltoid-splitting incisions must not extend distal to this safe zone.

Question 6374

Topic: Surgical Anatomy & Approaches

A surgeon exploring the posterior humerus identifies a neurovascular bundle passing through the triangular interval. Which structures are found within this anatomical space?

. Axillary nerve and posterior humeral circumflex artery
. Radial nerve and profunda brachii artery
. Ulnar nerve and superior ulnar collateral artery
. Median nerve and brachial artery
. Circumflex scapular artery only

Correct Answer & Explanation

. Axillary nerve and posterior humeral circumflex artery

Explanation

The triangular interval is bounded by the teres major, the long head of the triceps, and the lateral head of the triceps (or humerus). It serves as the passageway for the radial nerve and the profunda brachii artery into the posterior compartment of the arm.

Question 6375

Topic: Surgical Anatomy & Approaches

During a lateral approach to the distal humerus, the radial nerve is identified crossing the lateral intermuscular septum. At what average distance proximal to the lateral epicondyle does the radial nerve pierce the lateral intermuscular septum?

. 5 cm
. 10 cm
. 14 cm
. 18 cm
. 22 cm

Correct Answer & Explanation

. 5 cm

Explanation

The radial nerve pierces the lateral intermuscular septum from the posterior to the anterior compartment approximately 10 cm proximal to the lateral epicondyle.

Question 6376

Topic: Surgical Anatomy & Approaches

A patient develops inability to extend the fingers at the MCP joints following a proximal radius fracture. Wrist extension is maintained but with radial deviation. The injured nerve typically enters the supinator muscle beneath which of the following structures?

. Ligament of Struthers
. Arcade of Frohse
. Lacertus fibrosus
. Osborne's ligament
. Leash of Henry

Correct Answer & Explanation

. Ligament of Struthers

Explanation

The posterior interosseous nerve (PIN) is a branch of the radial nerve that passes beneath the Arcade of Frohse (the proximal aponeurotic edge of the supinator) and provides motor innervation to the extensor compartment.

Question 6377

Topic: Surgical Anatomy & Approaches

During an anterior (Smith-Petersen) approach to the hip, an internervous plane is utilized. The nerve at greatest risk during superficial dissection crosses the sartorius muscle. What is the sensory distribution of this nerve?

. Anterior medial thigh
. Lateral thigh
. Medial leg
. Posterior thigh
. Dorsum of the foot

Correct Answer & Explanation

. Anterior medial thigh

Explanation

The lateral femoral cutaneous nerve (LFCN) is at risk during the Smith-Petersen approach. It provides sensory innervation to the lateral thigh and typically exits the pelvis medial to the anterior superior iliac spine (ASIS).

Question 6378

Topic: Surgical Anatomy & Approaches

A patient sustains an obturator nerve injury during pelvic lymph node dissection. Which of the following muscles will maintain partial function because of its dual innervation?

. Adductor longus
. Gracilis
. Adductor brevis
. Pectineus
. Adductor magnus

Correct Answer & Explanation

. Adductor longus

Explanation

The adductor magnus has dual innervation. The adductor part is innervated by the obturator nerve, while the hamstring (ischial) part is innervated by the tibial division of the sciatic nerve.

Question 6379

Topic: Surgical Anatomy & Approaches

A patient suffers a high-energy motorcycle collision and sustains a traction injury to the brachial plexus affecting the posterior cord. Which of the following movements will be most severely impaired?

. Elbow flexion
. Shoulder abduction
. Finger adduction
. Wrist flexion
. Thumb opposition

Correct Answer & Explanation

. Elbow flexion

Explanation

The posterior cord gives rise to the upper and lower subscapular, thoracodorsal, axillary, and radial nerves. Axillary nerve injury impairs the deltoid, leading to profound weakness in shoulder abduction.

Question 6380

Topic: Surgical Anatomy & Approaches

In anatomical variations of the relationship between the sciatic nerve and the piriformis muscle, the most common variant (Beaton and Anson type B) involves which of the following arrangements?

. The entire nerve passes superior to the piriformis
. The entire nerve pierces the piriformis
. The common peroneal division pierces the piriformis and the tibial division passes inferiorly
. The common peroneal division passes superior to the piriformis and the tibial division passes inferiorly
. The entire nerve passes inferior to the piriformis

Correct Answer & Explanation

. The entire nerve passes superior to the piriformis

Explanation

Type A (normal, 84%) has the entire nerve passing inferior to the piriformis. Type B (about 10%) has the common peroneal nerve piercing the piriformis and the tibial nerve passing inferior to it.

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