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1. General Principles & Basic Science MCQs

Practice Set 547 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 10921

Topic: Biology, Genetics & Bone Healing

A 68-year-old female who has been taking alendronate for 8 years presents with a 3-month history of insidious onset left thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line extending partially through the lateral cortex of the left subtrochanteric femur. What is the most appropriate management?

. Reassurance and continuation of alendronate
. Discontinuation of alendronate, protected weight-bearing, and administration of Teriparatide for conservative healing
. Discontinuation of alendronate and prophylactic cephalomedullary nailing of the left femur
. Open biopsy to rule out malignancy
. External beam radiation

Correct Answer & Explanation

. Reassurance and continuation of alendronate

Explanation

This patient presents with a symptomatic, incomplete atypical femur fracture (AFF) associated with long-term bisphosphonate use. The classic radiographic signs include lateral cortical thickening ('beaking') and a transverse fracture line. Because she is symptomatic (thigh pain), the risk of progression to a complete fracture is extremely high. The standard of care for a symptomatic incomplete AFF is prophylactic intramedullary nailing, along with discontinuation of the bisphosphonate. Medical management alone is inadequate for a symptomatic lesion.

Question 10922

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach to the acetabulum, the surgeon must be careful to identify and ligate the 'corona mortis' to prevent life-threatening hemorrhage. This structure typically represents an anastomosis between which two vascular systems?

. External iliac and obturator arteries
. Internal iliac and pudendal arteries
. External iliac and inferior epigastric arteries
. Internal pudendal and inferior gluteal arteries
. Superior gluteal and internal iliac arteries

Correct Answer & Explanation

. External iliac and obturator arteries

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator and external iliac (or deep inferior epigastric) vascular systems. It courses over the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis. If inadvertently torn during dissection or screw placement, it can retract into the pelvis and cause massive, difficult-to-control hemorrhage.

Question 10923

Topic: Surgical Anatomy & Approaches
A 35-year-old male sustains an anterior-posterior compression type III (APC III) pelvic ring injury. During surgical fixation via an anterior ilioinguinal approach, massive hemorrhage occurs near the superior pubic ramus while developing the medial window. Which of the following vascular structures is most likely injured?
. An anastomosis between the internal pudendal and superior gluteal arteries
. An anastomosis between the inferior epigastric and obturator arteries
. The deep circumflex iliac artery
. The main branch of the internal iliac artery
. The superficial epigastric artery

Correct Answer & Explanation

. An anastomosis between the inferior epigastric and obturator arteries

Explanation

The 'corona mortis' is a vascular anastomosis between the external iliac (or inferior epigastric) and obturator vessels. It is located over the superior pubic ramus and is at high risk during the ilioinguinal approach.

Question 10924

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach for an associated both-column acetabular fracture

, the surgeon develops the 'middle window'. Which structures define the borders of this window, and what critical structure lies within it?

. Borders: Iliopsoas and Sartorius; Contains: Femoral nerve
. Borders: Iliopectineal fascia and modified conjoint tendon; Contains: External iliac artery and vein
. Borders: Modified conjoint tendon and symphysis pubis; Contains: Spermatic cord
. Borders: Inguinal ligament and Cooper's ligament; Contains: Obturator nerve
. Borders: Iliopectineal fascia and anterior superior iliac spine; Contains: Lateral femoral cutaneous nerve

Correct Answer & Explanation

. Borders: Iliopsoas and Sartorius; Contains: Femoral nerve

Explanation

The middle window of the ilioinguinal approach is bounded laterally by the iliopectineal fascia and medially by the modified conjoint tendon. It contains the external iliac vessels.

Question 10925

Topic: Surgical Anatomy & Approaches

A 45-year-old male presents with a hemodynamically unstable pelvic crush injury. Angiography shows active extravasation from the 'corona mortis'. Which of the following describes the most common arterial vessels communicating at this anatomic structure?

. External iliac and internal iliac
. Inferior epigastric and obturator
. Deep circumflex iliac and internal pudendal
. Superior gluteal and internal pudendal
. External pudendal and inferior gluteal

Correct Answer & Explanation

. External iliac and internal iliac

Explanation

The corona mortis is a vascular anastomosis between the external iliac system (typically via the inferior epigastric artery) and the internal iliac system (via the obturator artery). It lies over the superior pubic ramus and is highly susceptible to injury in pelvic ring fractures.

Question 10926

Topic: Surgical Anatomy & Approaches

A 35-year-old male undergoes open reduction and internal fixation of a posterior wall acetabular fracture via the Kocher-Langenbeck approach. Postoperatively, he exhibits a foot drop. Which specific neural structure was most likely injured or overly retracted during the procedure?

. Tibial division of the sciatic nerve
. Peroneal division of the sciatic nerve
. Superior gluteal nerve
. Inferior gluteal nerve
. Femoral nerve

Correct Answer & Explanation

. Tibial division of the sciatic nerve

Explanation

The peroneal division of the sciatic nerve is situated laterally within the nerve bundle, making it most vulnerable to stretch or retractor injury during a posterior (Kocher-Langenbeck) approach to the acetabulum. Injury leads to isolated weakness in ankle dorsiflexion (foot drop).

Question 10927

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman on long-term alendronate therapy presents with a 3-month history of a dull, aching pain in her right thigh. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the right femur.

What is the recommended standard of care for this patient?

. Discontinue alendronate and begin teriparatide exclusively
. Discontinue alendronate, initiate protected weight-bearing, and observe
. Discontinue alendronate and perform prophylactic intramedullary nailing
. Addition of a bisphosphonate with a different mechanism of action
. Open biopsy of the lesion to rule out a primary bone malignancy

Correct Answer & Explanation

. Discontinue alendronate and begin teriparatide exclusively

Explanation

This patient presents with a symptomatic incomplete atypical femur fracture characterized by the "dreaded black line" (transverse radiolucency) on the tension side of the lateral cortex, associated with long-term bisphosphonate use. Because she has prodromal thigh pain and a visible cortical defect, the fracture is at high risk for completion. Prophylactic intramedullary nailing is the surgical treatment of choice. Medical management includes discontinuing the bisphosphonate and considering teriparatide.

Question 10928

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with a 10-year history of alendronate use presents with sudden, atraumatic thigh pain. Radiographs reveal a transverse fracture of the lateral cortex of the subtrochanteric femur with a focal periosteal reaction ('beaking'). What is the pathophysiological mechanism behind this fracture?

. Increased osteoclastic bone resorption
. Severe vitamin D deficiency leading to osteomalacia
. Suppression of bone remodeling leading to microdamage accumulation
. Primary hyperparathyroidism
. Osteogenesis imperfecta type I

Correct Answer & Explanation

. Increased osteoclastic bone resorption

Explanation

Long-term use of bisphosphonates (typically > 5 years) suppresses osteoclast-mediated bone remodeling. This severe suppression prevents the repair of normal physiological microdamage in the bone, leading to accumulation of microcracks and increased brittleness. This mechanism is responsible for bisphosphonate-related atypical femoral fractures, which characteristically present with lateral cortical thickening, 'beaking', and a transverse or short oblique fracture pattern.

Question 10929

Topic: Surgical Anatomy & Approaches

A 30-year-old male is undergoing open reduction of a posterior wall acetabular fracture via a Kocher-Langenbeck approach. The surgeon limits splitting of the gluteus maximus and avoids dissecting more than 5 cm proximal to the greater sciatic notch. This maneuver is specifically performed to protect which of the following nerves?

. Sciatic nerve.
. Superior gluteal nerve.
. Inferior gluteal nerve.
. Pudendal nerve.
. Obturator nerve.

Correct Answer & Explanation

. Sciatic nerve.

Explanation

The superior gluteal nerve exits the greater sciatic notch superior to the piriformis and supplies the abductor musculature. Dissection >5 cm above the notch during the Kocher-Langenbeck approach places this nerve at high risk of iatrogenic injury.

Question 10930

Topic: Biomechanics & Biomaterials

During an ulnar collateral ligament (UCL) reconstruction using the docking technique, where is the optimal location for the humeral tunnel to ensure proper isometry of the graft?

. Isometric point on the anterior aspect of the medial epicondyle
. Center of the native footprint on the medial epicondyle
. Just proximal to the sublime tubercle
. Posterior aspect of the lateral epicondyle
. Anterior and distal to the sublime tubercle

Correct Answer & Explanation

. Isometric point on the anterior aspect of the medial epicondyle

Explanation

To reproduce the native biomechanics and achieve graft isometry, the humeral tunnel should be placed precisely at the center of the native UCL footprint on the medial epicondyle.

Question 10931

Topic: 1. General Principles & Basic Science

A 20-year-old basketball player presents with anterior knee pain localized to the inferior pole of the patella. Conservative measures have failed. Ultrasound reveals a hypoechoic region at the proximal patellar tendon. What is the characteristic histopathologic finding of this lesion?

. Dense inflammatory infiltrate with polymorphonuclear leukocytes
. Angiofibroblastic hyperplasia with disorganized collagen
. Granuloma formation with giant cells
. Microcrystal deposition
. Fibrinoid necrosis of blood vessels

Correct Answer & Explanation

. Dense inflammatory infiltrate with polymorphonuclear leukocytes

Explanation

Patellar tendinopathy (Jumper's knee) is primarily a degenerative condition rather than an inflammatory one. The characteristic histopathologic finding is angiofibroblastic hyperplasia (tendinosis), marked by disorganized collagen, hypercellularity, and neovascularization, without a significant presence of acute inflammatory cells.

Question 10932

Topic: 1. General Principles & Basic Science

A 30-year-old weightlifter feels a tearing sensation in his anterior chest wall while bench pressing. MRI confirms a complete pectoralis major rupture. Which segment of the pectoralis major is most commonly ruptured in this mechanism, and what is its normal anatomic insertion?

. Clavicular head; inserts deep and proximal to the sternal head
. Sternal head; inserts deep and proximal to the clavicular head
. Clavicular head; inserts superficial and distal to the sternal head
. Sternal head; inserts superficial and proximal to the clavicular head
. Abdominal head; inserts directly onto the lesser tuberosity

Correct Answer & Explanation

. Clavicular head; inserts deep and proximal to the sternal head

Explanation

During bench pressing, the sternal head of the pectoralis major is stretched maximally and most commonly ruptures. Anatomically, the sternal head twists 180 degrees to insert deep and proximal to the clavicular head on the lateral lip of the bicipital groove.

Question 10933

Topic: Surgical Anatomy & Approaches

A 22-year-old rugby player with recurrent anterior shoulder instability and 25% glenoid bone loss undergoes a Latarjet procedure. During the coracoid osteotomy and transfer, which nerve is at the greatest risk of iatrogenic injury during deep medial retraction?

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

Correct Answer & Explanation

. Axillary nerve

Explanation

The musculocutaneous nerve enters the coracobrachialis approximately 5-8 cm distal to the coracoid tip. It is at significant risk of traction injury during deep medial retraction or if the coracoid osteotomy is taken too distally.

Question 10934

Topic: Biomechanics & Biomaterials

To minimize stress shielding after total hip arthroplasty, a femoral stem material with a Young's modulus closest to that of cortical bone is desired. Which of the following orthopedic materials possesses the lowest Young's modulus?

. Cobalt-chromium-molybdenum
. 316L Stainless steel
. Titanium-6Aluminum-4Vanadium
. Zirconium
. Alumina

Correct Answer & Explanation

. Cobalt-chromium-molybdenum

Explanation

Titanium alloys have a Young's modulus of approximately 110 GPa, which is lower than that of stainless steel (approx. 200 GPa) and cobalt-chromium alloys (approx. 220-240 GPa). Although still higher than cortical bone (15-20 GPa), titanium provides less stress shielding than the other major load-bearing metal alloys used for femoral stems.

Question 10935

Topic: Biology, Genetics & Bone Healing

Osteoclast differentiation and activation are directly stimulated by the binding of RANK ligand (RANKL) to RANK. Which of the following cell types is the primary source of RANKL in the bone microenvironment?

. Osteoclasts
. Osteoblasts
. Chondrocytes
. Macrophages
. Osteocytes

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoblasts and their precursors are the primary source of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand) in the bone microenvironment. RANKL binds to the RANK receptor on the surface of osteoclast precursors, stimulating their differentiation and activation into mature, bone-resorbing osteoclasts. Osteoprotegerin (OPG), also secreted by osteoblasts, acts as a decoy receptor for RANKL, inhibiting this process.

Question 10936

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the highest concentration of proteoglycans and the lowest concentration of water are found in which of the following zones?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. The superficial zone has the highest water content and lowest proteoglycan content. Collagen fibers in the deep zone are oriented perpendicular to the articular surface to resist compressive forces.

Question 10937

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is NOT osteoinductive in humans and instead acts as an inhibitor of bone formation?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

BMP-3 (also known as osteogenin) acts as a negative regulator of bone density and opposes the osteogenic effects of other BMPs like BMP-2 and BMP-7 (OP-1). BMP-2 and BMP-7 are well-known osteoinductive agents used clinically.

Question 10938

Topic: Biomechanics & Biomaterials

A ligament graft is tensioned and secured during an anterior cruciate ligament (ACL) reconstruction. Over time, the tension in the graft decreases despite the graft remaining at a constant length. This biomechanical phenomenon is known as:

. Creep
. Stress relaxation
. Fatigue failure
. Hysteresis
. Plastic deformation

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the decrease in stress (or tension) over time when a viscoelastic material is held at a constant length (strain). Creep is the progressive deformation (increase in length) over time when a material is subjected to a constant load (stress).

Question 10939

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum tissue strain that allows for the formation of lamellar bone during fracture healing?

. < 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. 100%

Correct Answer & Explanation

. < 2%

Explanation

Perren's strain theory postulates that the type of tissue that forms in a fracture gap depends on the local strain. Lamellar bone can only form under very low strain environments (< 2%). Woven bone can form up to 10% strain, whereas granulation tissue can tolerate up to 100% strain. Absolute stability (strain < 2%) leads to primary bone healing.

Question 10940

Topic: Biology, Genetics & Bone Healing

Sclerostin is a key negative regulator of bone formation that is primarily secreted by osteocytes. Which signaling pathway does sclerostin directly inhibit?

. RANK/RANKL pathway
. Wnt/Beta-catenin pathway
. TGF-beta/Smad pathway
. Notch signaling pathway
. Hedgehog signaling pathway

Correct Answer & Explanation

. RANK/RANKL pathway

Explanation

Sclerostin (encoded by the SOST gene) is produced primarily by osteocytes and inhibits bone formation by antagonizing the Wnt/Beta-catenin signaling pathway. It binds to the LRP5/6 coreceptors on osteoblasts, preventing Wnt ligands from binding, which leads to decreased osteoblastogenesis and bone formation. Romosozumab is a monoclonal antibody against sclerostin used in osteoporosis.

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