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1. General Principles & Basic Science MCQs

Practice Set 609 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 12161

Topic: Surgical Anatomy & Approaches

During a total hip arthroplasty utilizing the direct anterior approach (DAA), the surgeon develops an internervous plane to access the hip joint capsule. This true internervous plane exists between muscles innervated by which of the following pairs of nerves?

. Superior gluteal nerve and femoral nerve
. Femoral nerve and obturator nerve
. Superior gluteal nerve and inferior gluteal nerve
. Femoral nerve and sciatic nerve
. Obturator nerve and sciatic nerve

Correct Answer & Explanation

. Superior gluteal nerve and femoral nerve

Explanation

The direct anterior approach (Smith-Petersen) to the hip exploits a true internervous plane between the tensor fasciae latae (TFL), innervated by the superior gluteal nerve, and the sartorius, innervated by the femoral nerve. Distally, the plane continues between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 12162

Topic: Biology, Genetics & Bone Healing

A 45-year-old female undergoes open reduction and internal fixation of a transverse midshaft radius fracture. The surgeon utilizes absolute stability by applying a dynamic compression plate (DCP). Under these highly stable biomechanical conditions, bone healing occurs primarily via which of the following biological processes?

. Endochondral ossification
. Formation of a soft cartilaginous callus
. Intramembranous ossification with cutting cones
. Chondrocyte hypertrophy and apoptosis
. Periosteal bone bridge formation

Correct Answer & Explanation

. Endochondral ossification

Explanation

Absolute stability (rigid fixation with compression) abolishes interfragmentary strain and completely suppresses callus formation. Bone healing under absolute stability occurs via primary bone healing, which relies on intramembranous ossification and direct remodeling by osteoclastic cutting cones followed by osteoblastic bone deposition. Endochondral ossification (callus formation) is seen with relative stability constructs (e.g., IM nails, external fixators, bridge plating).

Question 12163

Topic: Biology, Genetics & Bone Healing

Denosumab is an increasingly utilized pharmacological agent in orthopedics, particularly in the management of osteoporosis and as a neoadjuvant therapy for Giant Cell Tumor of Bone (GCTB). At a molecular level, Denosumab exerts its primary effect by acting as a monoclonal antibody that binds directly to which of the following targets?

. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Sclerostin
. Cathepsin K

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on the surface of osteoclasts and osteoclast precursors. This inhibits osteoclast formation, function, and survival, thereby potently decreasing bone resorption.

Question 12164

Topic: Biology, Genetics & Bone Healing

During secondary bone healing following a closed diaphyseal fracture treated with a cast, a cartilaginous soft callus forms. Which of the following growth factors is most critical in promoting the differentiation of mesenchymal stem cells into chondrocytes during this phase?

. Platelet-derived growth factor (PDGF)
. Fibroblast growth factor (FGF)
. Transforming growth factor-beta (TGF-b)
. Bone morphogenetic protein-2 (BMP-2)
. Insulin-like growth factor (IGF-1)

Correct Answer & Explanation

. Platelet-derived growth factor (PDGF)

Explanation

Bone morphogenetic proteins, particularly BMP-2, are potent osteoinductive growth factors. They play a critical role in inducing mesenchymal stem cells to differentiate into both chondroblasts and osteoblasts during fracture healing.

Question 12165

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion extending into the metaphysis of the distal femur. Biopsy confirms a Giant Cell Tumor of bone. What is the mechanism of action of denosumab, a potential medical treatment?

. Inhibition of matrix metalloproteinases
. Monoclonal antibody against RANK ligand (RANKL)
. Direct inhibition of osteoblast proliferation
. Tyrosine kinase inhibitor targeting c-Kit
. Monoclonal antibody against VEGF

Correct Answer & Explanation

. Inhibition of matrix metalloproteinases

Explanation

Denosumab is a monoclonal antibody that binds to and inhibits RANK Ligand (RANKL). This prevents the activation of the RANK receptor on osteoclasts and giant cells, thereby halting osteoclast-mediated bone destruction.

Question 12166

Topic: 1. General Principles & Basic Science

When evaluating a severely injured limb to guide the decision between amputation and limb salvage, the Mangled Extremity Severity Score (MESS) is often referenced. Which of the following variables is NOT a formal component of the MESS scoring system?

. Patient age
. Limb ischemia time and severity
. Presence of systemic shock
. Mechanism and extent of skeletal/soft tissue injury
. Presence of major nerve injury

Correct Answer & Explanation

. Patient age

Explanation

The Mangled Extremity Severity Score (MESS) calculates a score based on four distinct criteria: skeletal/soft tissue injury (energy/mechanism), limb ischemia, shock, and patient age. While a complete loss of plantar sensation (tibial nerve injury) strongly influences clinical decision-making, nerve injury itself is not explicitly scored in the traditional MESS criteria.

Question 12167

Topic: Surgical Anatomy & Approaches

A 35-year-old male presents with a transverse plus posterior wall acetabular fracture following a high-speed motor vehicle collision. The anterior displacement is minimal. Which surgical approach is most appropriate for definitive fixation?

. Ilioinguinal approach
. Kocher-Langenbeck approach
. Anterior intrapelvic (Stoppa) approach
. Extended iliofemoral approach
. Smith-Petersen approach

Correct Answer & Explanation

. Ilioinguinal approach

Explanation

The Kocher-Langenbeck approach is the workhorse for posterior column and posterior wall injuries. For a transverse plus posterior wall fracture, if the anterior displacement is minimal and can be reduced indirectly, the Kocher-Langenbeck approach allows direct visualization and fixation of the posterior elements.

Question 12168

Topic: Surgical Anatomy & Approaches

During the anterior ilioinguinal approach for an acetabular fracture, severe hemorrhage is suddenly encountered just posterior to the superior pubic ramus. What vascular structure is most likely injured?

. Corona mortis
. Superior gluteal artery
. Inferior epigastric artery
. Internal pudendal artery
. External iliac vein

Correct Answer & Explanation

. Corona mortis

Explanation

The corona mortis is a critical vascular anastomosis between the obturator and external iliac (or inferior epigastric) vessels, located on the posterior aspect of the superior pubic ramus.

Question 12169

Topic: 1. General Principles & Basic Science

When calculating the Mangled Extremity Severity Score (MESS) for a severely injured lower extremity, which variable carries the most significant weight, doubling its assigned points if present for more than 6 hours?

. Patient age
. Presence of profound systemic shock
. Skeletal and soft tissue injury severity
. Limb ischemia
. Venous outflow obstruction

Correct Answer & Explanation

. Patient age

Explanation

In the MESS criteria, limb ischemia points are doubled if the ischemic time exceeds 6 hours. This reflects the severe irreversible tissue damage and poor salvage prognosis associated with prolonged warm ischemia.

Question 12170

Topic: Surgical Anatomy & Approaches

A 42-year-old male presents with a completely displaced, highly comminuted midshaft clavicle fracture with 3 cm of shortening. He undergoes open reduction and internal fixation with a superiorly placed anatomic locking plate. Which nerve is most at risk of iatrogenic injury during the surgical approach?

. Spinal accessory nerve
. Suprascapular nerve
. Axillary nerve
. Supraclavicular nerve
. Phrenic nerve

Correct Answer & Explanation

. Spinal accessory nerve

Explanation

The supraclavicular nerves (branches of the superficial cervical plexus) cross directly over the clavicle. They are at high risk during the superior approach for clavicle plating, often resulting in postoperative numbness over the anterior chest wall.

Question 12171

Topic: Surgical Anatomy & Approaches

A 25-year-old male sustains a closed spiral fracture of the distal third of the humeral shaft. Initial exam in the ED shows completely intact radial nerve function. Following closed reduction and splint application, the patient immediately develops a new-onset complete radial nerve palsy. What is the most appropriate management?

. Observation and functional bracing
. Immediate surgical exploration of the nerve and fracture fixation
. Re-manipulation of the fracture under sedation
. Urgent MRI of the humerus
. EMG and nerve conduction studies at 3 weeks

Correct Answer & Explanation

. Observation and functional bracing

Explanation

A secondary radial nerve palsy that occurs immediately following a closed reduction maneuver of a humeral shaft fracture is an absolute indication for surgical exploration. The nerve has likely become entrapped within the fracture site during the reduction.

Question 12172

Topic: 1. General Principles & Basic Science

The syndesmotic ligamentous complex provides crucial stability to the distal tibiofibular articulation. Biomechanical studies indicate that which of the following ligaments provides the greatest resistance to lateral displacement of the fibula?

. Anterior inferior tibiofibular ligament (AITFL)
. Posterior inferior tibiofibular ligament (PITFL)
. Interosseous ligament
. Transverse tibiofibular ligament
. Deltoid ligament

Correct Answer & Explanation

. Anterior inferior tibiofibular ligament (AITFL)

Explanation

The posterior inferior tibiofibular ligament (PITFL) provides the strongest resistance to lateral displacement of the fibula (approximately 42%), followed by the AITFL (approx. 35%), the interosseous ligament (22%), and the transverse tibiofibular ligament.

Question 12173

Topic: Infection, Pharmacology & VTE

A 14-year-old boy presents with a rigid flatfoot and recurrent ankle sprains. Radiographs show a continuous C-shaped bony outline involving the medial talar dome and the posteroinferior aspect of the sustentaculum tali. Which of the following is true regarding this patient's condition?

. The deformity typically involves a cavovarus posture.
. It is best visualized on a 45-degree internal oblique radiograph.
. The 'C-sign' is a radiographic indicator of a talocalcaneal coalition.
. Excision of the coalition is indicated regardless of the percentage of joint involvement.
. It is significantly more common than a calcaneonavicular coalition.

Correct Answer & Explanation

. The deformity typically involves a cavovarus posture.

Explanation

The 'C-sign' on a lateral radiograph is formed by the continuous outline of the medial talar dome and the posteroinferior aspect of the sustentaculum tali, strongly indicating a talocalcaneal coalition. Calcaneonavicular coalitions are best seen on a 45-degree internal oblique radiograph. Talocalcaneal coalitions typically present with a rigid pes planovalgus deformity. Resection is generally reserved for coalitions involving less than 50% of the posterior facet.

Question 12174

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient is scheduled to undergo a posterolateral spinal fusion using a structural cortical autograft. What is the primary mechanism by which a cortical autograft is initially incorporated into the host bone?

. Osteoclastic resorption followed by osteoblastic formation
. Osteoblastic apposition directly onto the trabecular scaffold
. Endochondral ossification mediated by chondrocytes
. Direct primary bone healing with cutting cones crossing the graft-host interface
. Intramembranous ossification stimulated by BMP-2

Correct Answer & Explanation

. Osteoclastic resorption followed by osteoblastic formation

Explanation

Cortical autografts incorporate via creeping substitution, which begins with osteoclastic resorption of the dense cortical bone, followed later by osteoblastic bone formation. In contrast, cancellous bone incorporates via early osteoblastic apposition on the existing trabecular scaffold before osteoclastic remodeling occurs.

Question 12175

Topic: 1. General Principles & Basic Science

Articular cartilage is a complex tissue with varying properties across its depth. Which of the following accurately describes the composition of the deep (radial) zone of articular cartilage compared to the superficial zone?

. Highest water content and lowest proteoglycan concentration
. Highest collagen content with fibers oriented parallel to the joint surface
. Lowest water content and highest proteoglycan concentration
. Highest concentration of chondrocytes with a flattened morphology
. Lowest proteoglycan concentration with randomly oriented collagen fibers

Correct Answer & Explanation

. Highest water content and lowest proteoglycan concentration

Explanation

The deep (radial) zone of articular cartilage contains the lowest water content, the highest proteoglycan concentration, and the lowest concentration of chondrocytes. The collagen fibers in this zone are thickest and oriented perpendicularly (vertically) to the joint surface to resist compressive loads.

Question 12176

Topic: Biology, Genetics & Bone Healing

A 70-year-old female treated with alendronate for 8 years presents with thigh pain and a transverse subtrochanteric fracture with lateral cortical thickening. What is the molecular mechanism of action of the medication responsible for this atypical fracture?

. Monoclonal antibody inhibition of RANK ligand
. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway
. Direct inhibition of cathepsin K in the ruffled border
. Reversible binding to the parathyroid hormone receptor
. Binding to sclerostin to upregulate the Wnt pathway

Correct Answer & Explanation

. Monoclonal antibody inhibition of RANK ligand

Explanation

Alendronate is a nitrogen-containing bisphosphonate. Its mechanism of action is the inhibition of farnesyl pyrophosphate synthase (FPPS) within the mevalonate pathway. This prevents the prenylation of small GTPases (like Ras, Rho, Rab), leading to osteoclast apoptosis and decreased bone remodeling, which over time can cause brittle bone and atypical femur fractures.

Question 12177

Topic: Biomechanics & Biomaterials

During a cemented total knee arthroplasty, the surgeon mixes polymethylmethacrylate (PMMA) bone cement. What is the primary role of barium sulfate in the PMMA powder mixture?

. Initiator of the polymerization reaction
. Accelerator of the curing process
. Radiopacifier
. Stabilizer to prevent premature polymerization
. Cross-linking agent to increase tensile strength

Correct Answer & Explanation

. Initiator of the polymerization reaction

Explanation

Barium sulfate (or zirconium dioxide) is added to the PMMA powder specifically to act as a radiopacifier, allowing the cement mantle to be visualized on postoperative radiographs. Benzoyl peroxide is the initiator, N,N-dimethyl-p-toluidine is the accelerator, and hydroquinone is the stabilizer.

Question 12178

Topic: Biology, Genetics & Bone Healing

A 6-year-old child presents with progressive bowing of the lower extremities. Laboratory studies reveal normal serum calcium, critically low serum phosphorus, and elevated alkaline phosphatase. Genetic testing confirms a mutation in the PHEX gene. Which of the following substances is excessively produced in this patient's condition?

. 1,25-dihydroxyvitamin D
. Parathyroid hormone
. Fibroblast growth factor-23 (FGF-23)
. Osteoprotegerin (OPG)
. Sclerostin

Correct Answer & Explanation

. 1,25-dihydroxyvitamin D

Explanation

The patient has X-linked hypophosphatemic rickets, the most common heritable form of rickets, caused by a mutation in the PHEX gene. This leads to an overproduction of FGF-23, which promotes renal phosphate wasting and decreases the activity of 1-alpha-hydroxylase, preventing the activation of vitamin D.

Question 12179

Topic: Biomechanics & Biomaterials

During revision of a modular metal-on-polyethylene total hip arthroplasty, the surgeon observes significant black corrosive debris and tissue staining localized specifically at the modular head-neck taper junction. Which type of corrosion is primarily responsible for this localized wear mechanism?

. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion
. Fretting corrosion
. Crevice corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

The localized wear and corrosion at the modular head-neck taper junction is classically referred to as trunnionosis. This is primarily caused by mechanically assisted crevice corrosion, commonly termed fretting corrosion. Micro-motion at the interface (fretting) repeatedly disrupts the passive oxide layer of the metal, accelerating corrosive degradation in the fluid-filled crevice.

Question 12180

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, the type of tissue that forms in a fracture gap is dictated by the amount of mechanical strain the tissue can tolerate without failing. What is the approximate maximum strain tolerance of granulation tissue?

. 2%
. 10%
. 30%
. 60%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory posits that cells can only produce a given extracellular matrix if the strain in the fracture gap does not exceed the strain tolerance of that matrix. Granulation tissue can tolerate up to 100% strain. Fibrocartilage tolerates roughly 10-15% strain, woven bone tolerates about 2% strain, and lamellar bone can tolerate <2% strain.

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