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1. General Principles & Basic Science MCQs

Practice Set 218 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 4341

Topic: Surgical Anatomy & Approaches

During open reduction and internal fixation of a severe proximal humerus fracture using an extended deltopectoral approach, the surgeon decides to split the deltoid muscle longitudinally to improve distal exposure. Which of the following structures is at greatest risk, and what is its approximate distance from the lateral tip of the acromion?

. Radial nerve; 10 cm
. Axillary nerve; 5 to 7 cm
. Musculocutaneous nerve; 3 to 5 cm
. Axillary nerve; 2 to 3 cm
. Radial nerve; 14 cm

Correct Answer & Explanation

. Axillary nerve; 5 to 7 cm

Explanation

The axillary nerve runs transversely across the deep surface of the deltoid muscle, typically 5 to 7 cm distal to the lateral tip of the acromion. A longitudinal deltoid split should not extend more distal than this threshold to avoid denervating the anterior portion of the deltoid.

Question 4342

Topic: Surgical Anatomy & Approaches

During a modified Stoppa approach for the treatment of an anterior column acetabular fracture, the surgeon must carefully identify and potentially ligate the 'corona mortis' to prevent catastrophic hemorrhage. This structure represents a vascular anastomosis between which two systems?

. Internal pudendal and superior gluteal vessels
. Inferior epigastric (or external iliac) and obturator vessels
. Superior epigastric and internal pudendal vessels
. Deep circumflex iliac and internal pudendal vessels
. Inferior gluteal and obturator vessels

Correct Answer & Explanation

. Inferior epigastric (or external iliac) and obturator vessels

Explanation

The corona mortis ('crown of death') is a critical vascular anastomosis connecting the external iliac or inferior epigastric system to the obturator system. It traverses the superior pubic ramus and is highly vulnerable to iatrogenic injury during the intrapelvic (modified Stoppa or ilioinguinal) approach to the acetabulum.

Question 4343

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly utilized to downstage unresectable or metastatic giant cell tumors of bone (GCT). Which of the following accurately describes the primary cellular mechanism by which Denosumab exerts its therapeutic effect in this specific tumor?

. Inhibition of the RANK ligand (RANKL) expressed by the neoplastic spindle-shaped mononuclear cells
. Binding directly to the RANK receptors on the surface of the reactive multinucleated giant cells
. Direct induction of apoptosis in the multinucleated giant cells via the p53 pathway
. Direct inhibition of vascular endothelial growth factor (VEGF) leading to tumor necrosis
. Stimulation of osteoprotegerin (OPG) production by native osteoblasts

Correct Answer & Explanation

. Inhibition of the RANK ligand (RANKL) expressed by the neoplastic spindle-shaped mononuclear cells

Explanation

In Giant Cell Tumor of bone (GCT), the true neoplastic cells are the spindle-shaped mononuclear cells, which express high levels of RANKL. This RANKL recruits and activates reactive, normal osteoclast-like giant cells that cause bone destruction. Denosumab is a monoclonal antibody that binds to RANKL on the neoplastic mononuclear cells, preventing them from activating the giant cells.

Question 4344

Topic: Biology, Genetics & Bone Healing

A 32-year-old female is diagnosed with a giant cell tumor of the distal femur. The lesion is eccentric, expansile, and lytic. Histology reveals multinucleated giant cells in a background of mononuclear stromal cells. If neoadjuvant targeted pharmacotherapy is utilized, what is its primary mechanism of action?

. Inhibition of VEGF receptors
. Activation of the p53 tumor suppressor gene
. Inhibition of RANKL
. Tyrosine kinase inhibition of c-KIT
. Cross-linking of DNA double strands

Correct Answer & Explanation

. Inhibition of RANKL

Explanation

Giant cell tumor of bone (GCT) consists of neoplastic mononuclear stromal cells that express RANKL. RANKL recruits and activates normal multinucleated osteoclast-like giant cells, causing extensive bone resorption. Denosumab, a monoclonal antibody against RANKL, inhibits this process and is an effective targeted therapy for GCT.

Question 4345

Topic: 1. General Principles & Basic Science

The anterolateral ligament (ALL) of the knee has been increasingly recognized for its role in controlling rotational laxity. During an anatomic reconstruction, what are the precise origins and insertions of the ALL?

. Originates anterior to the FCL on the femur and inserts on the fibular head
. Originates posterior and proximal to the FCL on the femur and inserts on the proximal tibia midway between Gerdy's tubercle and the fibular head
. Originates distal to the FCL and inserts on Gerdy's tubercle
. Originates anterior and distal to the FCL on the femur and inserts on the proximal tibia
. Originates on the lateral epicondyle and inserts on the lateral meniscus

Correct Answer & Explanation

. Originates posterior and proximal to the FCL on the femur and inserts on the proximal tibia midway between Gerdy's tubercle and the fibular head

Explanation

The anterolateral ligament (ALL) originates on the lateral femoral epicondyle, slightly posterior and proximal to the origin of the fibular collateral ligament (FCL). It runs distally and anteriorly to insert on the proximal tibia, midway between Gerdy's tubercle and the fibular head, deep to the iliotibial band.

Question 4346

Topic: Biomechanics & Biomaterials

A 55-year-old female experiences a 'pop' in her posterior knee while squatting. MRI demonstrates a medial meniscus posterior root tear with 4 mm of meniscal extrusion. Which of the following best describes the biomechanical consequence of this injury?

. Decreased peak contact pressures in the medial compartment
. Loss of hoop stresses leading to contact pressures equivalent to a total meniscectomy
. Increased varus alignment of the knee by 5 degrees
. Shift of the mechanical axis laterally
. Hypertrophy of the adjacent medial articular cartilage

Correct Answer & Explanation

. Loss of hoop stresses leading to contact pressures equivalent to a total meniscectomy

Explanation

A complete tear of the medial meniscus posterior root disrupts the circumferential hoop stresses of the meniscus. Biomechanically, this results in altered kinematics and elevated peak contact pressures that are nearly equivalent to those seen following a total meniscectomy.

Question 4347

Topic: Biology, Genetics & Bone Healing

A 32-year-old male presents with a purely lytic, expansile lesion extending into the subchondral bone of the distal femur. Biopsy reveals multinucleated giant cells intermixed with mononuclear stromal cells. Which targeted medical therapy directly inhibits the specific molecular pathway driving this pathology?

. Imatinib
. Denosumab
. Methotrexate
. Zoledronic acid
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Giant Cell Tumor of Bone (GCTB) is driven by neoplastic mononuclear stromal cells that overexpress RANKL, recruiting reactive osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, directly targets this pathway and is highly effective in treating GCTB.

Question 4348

Topic: Biology, Genetics & Bone Healing
During the evaluation of a patient suspected of having a lumbar disk herniation, T1- and T2-weighted MRI scans reveal a hyperintense lobular, well-defined lesion in the L2 vertebral body. What is the most likely diagnosis?
. Metastatic focus
. Bony island
. Intravertebral disk herniation
. Osteoporosis
. Hemangioma

Correct Answer & Explanation

. Hemangioma

Explanation

The findings are characteristic of hemangioma. When the hemangioma is large enough, vertical striations may be visible on plain radiographs. Axial CT scans commonly reveal a speckled appearance. Metastatic lesions are typically hypointense on T1-weighted images because they replace the fatty marrow. Bony islands, like cortical bone, are dark on T1- and T2-weighted images. Intravertebral disk herniation would have characteristics similar to the disk and be in continuity with the disk. Osteoporosis is more diffuse.

Question 4349

Topic: Biomechanics & Biomaterials

The ability of compressed cortical bone to resist greater applied force in the longitudinal plane than in the transverse plane is an illustration of what material property?

. Yield strength
. Elastic modulus
. Viscoelasticity
. Anisotropy

Correct Answer & Explanation

. Elastic modulus

Explanation

Material properties characterize mechanical functional limits of a material independent of the size or shape of that material. Anisotropic materials are those for which properties behave differently dependent on the direction of applied force. Yield strength is the load at which permanent plastic deformation begins to occur. Elastic modulus is the mathematical description of the tendency of a material to be deformed elastically in response to an applied force. The elastic modulus of a material is defined as the slope of its stress-strain curve in the elastic deformation region. Viscoelastic materials such as bone exhibit time-rate-dependent stress-strain behavior as a function of internal friction. The modulus of viscoelastic materials increase as the strain rate increases.

Question 4350

Topic: 1. General Principles & Basic Science

During a lateral closing wedge high tibial osteotomy, a fibular osteotomy is required to allow the tibial osteotomy to close. To minimize the risk of peroneal nerve injury, at what level should the fibular osteotomy ideally be performed?

. At the fibular head
. Through the fibular neck
. At the middle third of the fibular shaft
. At the distal third of the fibular shaft
. Through the lateral malleolus

Correct Answer & Explanation

. At the middle third of the fibular shaft

Explanation

To minimize the risk of iatrogenic injury to the common peroneal nerveโ€”which wraps around the fibular neckโ€”a fibular osteotomy required for a lateral closing wedge HTO is typically performed in the middle third of the fibular shaft.

Question 4351

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in arthroplasty to reduce blood loss. What is the primary mechanism of action of TXA?
. Direct thrombin inhibition
. Vitamin K antagonism
. Competitive inhibition of the activation of plasminogen to plasmin
. Direct inhibition of Factor Xa
. Enhancement of antithrombin III activity

Correct Answer & Explanation

. Competitive inhibition of the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic derivative of the amino acid lysine. It functions as an antifibrinolytic by reversibly and competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from converting into active plasmin, thereby stabilizing fibrin clots and reducing bleeding.

Question 4352

Topic: 1. General Principles & Basic Science

A surgeon is performing an anteriorly based medial opening wedge high tibial osteotomy (HTO). To maintain the patient's native posterior tibial slope, how should the osteotomy gap be managed?

. The gap must be equal anteriorly and posteriorly
. The gap must be larger anteriorly than posteriorly
. The gap must be smaller anteriorly than posteriorly
. A fibular osteotomy must be performed simultaneously
. A laterally based wedge must be utilized instead

Correct Answer & Explanation

. The gap must be smaller anteriorly than posteriorly

Explanation

To maintain the normal posterior tibial slope during an anteriorly based medial opening wedge HTO, the anterior osteotomy gap must be approximately half the size of the posterior gap. An equal gap will inadvertently increase the posterior slope.

Question 4353

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is routinely used in total knee arthroplasty to reduce blood loss. Which of the following best describes its primary mechanism of action?

. Inhibits cyclooxygenase enzymes
. Competitively inhibits plasminogen activation
. Cross-links fibrin threads directly
. Activates thrombin synthesis
. Blocks factor Xa in the coagulation cascade

Correct Answer & Explanation

. Competitively inhibits plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic by competitively inhibiting the activation of plasminogen to plasmin, thereby preventing the degradation of fibrin clots.

Question 4354

Topic: Physiology & Rehabilitation
What type of exercise is used early in the rehabilitation process to safely stimulate co-contraction of the scapular and rotator cuff muscles?
. Resistive active motion
. Facilitated active motion
. Plyometrics
. Open kinetic chain
. Closed kinetic chain

Correct Answer & Explanation

. Closed kinetic chain

Explanation

Closed kinetic chain exercises are used early in the rehabilitation process. The distal segment is fixed, and an axial load is applied which provides glenohumeral compression and reduces the demand on the rotator cuff. These exercises stimulate co-contractions of the scapular and rotator cuff muscles, load scapular stabilizers, and facilitate active motion.

Question 4355

Topic: Surgical Anatomy & Approaches

A 35-year-old female sustains a Bryan-Morrey Type I capitellum fracture. The surgeon elects to perform an open reduction and internal fixation utilizing the Kaplan approach. Which inter-nervous/inter-muscular interval is utilized in this approach, and which nerve is most at risk during distal dissection?

. Interval between ECU and Anconeus; PIN at risk
. Interval between ECRB and EDC; PIN at risk
. Interval between ECRL and ECRB; Radial nerve at risk
. Interval between Brachioradialis and Triceps; Radial nerve at risk
. Interval between FCU and FCR; Ulnar nerve at risk

Correct Answer & Explanation

. Interval between ECRB and EDC; PIN at risk

Explanation

The Kaplan approach to the lateral elbow utilizes the interval between the extensor carpi radialis brevis (ECRB) and the extensor digitorum communis (EDC). During distal dissection, the posterior interosseous nerve (PIN) is at risk as it courses through the supinator muscle. The Kocher approach uses the interval between the anconeus and the extensor carpi ulnaris (ECU).

Question 4356

Topic: Surgical Anatomy & Approaches
A 35-year-old male sustains a posterior hip dislocation following a high-speed motor vehicle collision. CT imaging post-reduction reveals an associated fracture of the femoral head that is located inferior to the fovea capitis. According to the Pipkin classification, what type of fracture is this, and what is the preferred surgical approach if open reduction and internal fixation is indicated?
. Type I; Anterior approach (Smith-Petersen or Hueter)
. Type II; Anterior approach (Smith-Petersen or Hueter)
. Type I; Posterior approach (Kocher-Langenbeck)
. Type III; Posterior approach (Kocher-Langenbeck)
. Type IV; Surgical hip dislocation (Ganz approach)

Correct Answer & Explanation

. Type I; Anterior approach (Smith-Petersen or Hueter)

Explanation

According to the Pipkin classification, a Type I fracture involves the femoral head inferior to the fovea capitis (non-weight-bearing portion). If ORIF is indicated (e.g., irreducible fragment, joint incongruity), an anterior approach (Smith-Petersen or Hueter) is preferred. A posterior approach in the setting of a posterior dislocation further jeopardizes the already tenuous medial femoral circumflex artery (MFCA) blood supply, significantly increasing the risk of avascular necrosis.

Question 4357

Topic: Biology, Genetics & Bone Healing

A 60-year-old Asian male presents with progressive hand clumsiness and gait disturbances. Radiographs and MRI demonstrate a continuous band of ossification along the posterior aspect of the cervical vertebral bodies, causing severe spinal canal stenosis. Which of the following molecular factors is most significantly implicated in the pathogenesis of this condition?

. Fibroblast growth factor receptor 3 (FGFR3) mutation
. Deficiency of tissue-nonspecific alkaline phosphatase (TNAP)
. Overexpression of Bone Morphogenetic Protein (BMP) and Transforming Growth Factor-beta (TGF-beta)
. Mutations in the COL1A1 gene
. Elevated levels of circulating parathyroid hormone (PTH)

Correct Answer & Explanation

. Overexpression of Bone Morphogenetic Protein (BMP) and Transforming Growth Factor-beta (TGF-beta)

Explanation

Ossification of the posterior longitudinal ligament (OPLL) is characterized by ectopic bone formation in the spinal ligaments. Research has shown that overexpression of osteogenic factors, particularly Bone Morphogenetic Proteins (BMP-2) and TGF-beta, plays a crucial role in the hyperostotic process of the posterior longitudinal ligament. It is highly prevalent in East Asian populations, and while genetics (like ENPP1 variants) play a role, BMP/TGF-beta signaling is a central downstream mechanism of the ossification process.

Question 4358

Topic: Surgical Anatomy & Approaches

During a modified Stoppa (anterior intrapelvic) approach for fixation of an anterior column acetabular fracture, significant hemorrhage occurs when dissecting superior to the superior pubic ramus. Which vascular anastomosis was most likely injured?

. External iliac artery to the internal pudendal artery
. Deep circumflex iliac artery to the obturator artery
. Inferior epigastric artery (or external iliac) to the obturator artery
. Superior gluteal artery to the internal pudendal artery
. Internal pudendal artery to the inferior vesicular artery

Correct Answer & Explanation

. Inferior epigastric artery (or external iliac) to the obturator artery

Explanation

The 'corona mortis' (crown of death) is a vascular anastomosis between the obturator system (internal iliac) and the external iliac system (most commonly the inferior epigastric artery or vein). It typically crosses the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis. Dissection in this area during ilioinguinal or modified Stoppa approaches must be done meticulously to identify and ligate these vessels to prevent life-threatening hemorrhage.

Question 4359

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach for acetabular fracture fixation, significant arterial bleeding is encountered near the superior pubic ramus. This bleeding is most likely originating from an anastomosis between which two vessels?

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

Correct Answer & Explanation

. External iliac and obturator arteries

Explanation

The corona mortis is a vascular anastomosis between the external iliac (or inferior epigastric) and the obturator vessels. It is located over the superior pubic ramus and is highly vulnerable during the anterior intrapelvic approach.

Question 4360

Topic: Surgical Anatomy & Approaches
A 30-year-old man presents with a posterior hip dislocation and a femoral head fracture located superior to the fovea capitis. According to the Pipkin classification, what type of fracture is this, and what is the preferred surgical approach for fixation?
. Pipkin I, anterior approach
. Pipkin I, posterior approach
. Pipkin II, anterior approach
. Pipkin II, posterior approach
. Pipkin III, lateral approach

Correct Answer & Explanation

. Pipkin II, anterior approach

Explanation

A femoral head fracture superior to the fovea capitis (involving the primary weight-bearing portion) is a Pipkin Type II fracture. The anterior (Smith-Petersen) approach is generally preferred for optimal visualization and perpendicular screw fixation of anterior/superior femoral head fragments.

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