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1. General Principles & Basic Science MCQs

Practice Set 511 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 10201

Topic: Biomechanics & Biomaterials

In orthopedic implants, placing a stainless steel plate in contact with a titanium screw in the presence of body fluids primarily leads to which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are placed in contact within a conductive medium (such as body fluids). The less noble metal becomes the anode and corrodes, while the more noble metal acts as the cathode. While fretting and crevice corrosion are common in modular components of the same material (e.g., head-neck tapers), mixing stainless steel and titanium specifically drives galvanic corrosion.

Question 10202

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) such as BMP-2 and BMP-7 induce osteoblastic differentiation and bone formation primarily through activation of which of the following intracellular signaling pathways?

. Wnt/beta-catenin
. JAK/STAT
. Smad 1/5/8
. Notch/Hes
. MAPK/ERK

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which then phosphorylate intracellular Smad proteins, specifically Smad 1, 5, and 8. These complex with Smad 4, translocate to the nucleus, and upregulate the transcription of osteogenic genes like Runx2. The Wnt pathway uses beta-catenin, which is also osteoinductive but distinct from the direct BMP pathway.

Question 10203

Topic: Physiology & Rehabilitation

During the normal gait cycle, which muscle group undergoes a critical eccentric contraction immediately following initial contact (heel strike) to prevent a 'foot slap'?

. Triceps surae
. Quadriceps femoris
. Tibialis anterior
. Hamstrings
. Gluteus maximus

Correct Answer & Explanation

. Tibialis anterior

Explanation

From initial contact (heel strike) to the loading response (foot flat), the ankle goes from a neutral position into plantarflexion. The tibialis anterior and other ankle dorsiflexors must contract eccentrically to control this descent and absorb shock. Weakness of the tibialis anterior results in a rapid uncontrolled drop of the forefoot known as 'foot slap'.

Question 10204

Topic: 1. General Principles & Basic Science
According to the Sunderland classification of peripheral nerve injuries, a third-degree nerve injury is characterized by the disruption of which of the following histological structures, while preserving the remaining outer layers?
. Myelin sheath only
. Axon only
. Endoneurium
. Perineurium
. Epineurium

Correct Answer & Explanation

. Axon only

Explanation

The Sunderland classification describes 5 degrees of nerve injury. Type I is a local conduction block (myelin disruption). Type II disrupts the axon but leaves all connective tissues intact (axonotmesis). Type III disrupts the axon and the endoneurium, but the perineurium and epineurium remain intact. Type IV disrupts up to the perineurium. Type V is complete transection including the epineurium.

Question 10205

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy is evaluated for recurrent fractures and vision loss. Radiographs reveal generalized dense, 'marble-like' bones with loss of the medullary canal. A mutation affecting which of the following enzymes is most likely responsible for this condition?

. Alkaline phosphatase
. Carbonic anhydrase II
. Type I collagen
. Fibroblast growth factor receptor 3
. Cathepsin K

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

This presentation is typical of osteopetrosis, characterized by defective osteoclast function leading to dense but brittle bones and cranial nerve entrapment (vision loss). A classic mutation responsible for an autosomal recessive form of osteopetrosis affects the carbonic anhydrase II enzyme, which is required by the osteoclast to generate protons for acidifying the resorption pit at the ruffled border. Cathepsin K mutation causes pycnodysostosis.

Question 10206

Topic: Physiology & Rehabilitation

When prescribing a prosthesis for a patient with a transtibial amputation, a Solid Ankle Cushion Heel (SACH) foot is often selected. What is the primary function of the compressible heel wedge in this prosthetic foot during the gait cycle?

. Simulate active plantarflexion during push-off
. Provide medial-lateral stability during swing phase
. Simulate eccentric tibialis anterior contraction at heel strike
. Prevent knee buckling during mid-stance
. Provide energy return during terminal stance

Correct Answer & Explanation

. Simulate eccentric tibialis anterior contraction at heel strike

Explanation

In a SACH foot, the compressible heel wedge absorbs the impact of heel strike and compresses, allowing the foot to transition smoothly into foot flat. This mechanism effectively simulates the eccentric contraction of the tibialis anterior muscle during the loading response of a normal gait cycle.

Question 10207

Topic: Infection, Pharmacology & VTE
Which of the following prophylactic medications for deep vein thrombosis (DVT) functions by directly inhibiting Factor Xa without requiring antithrombin III as a cofactor?
. Enoxaparin
. Fondaparinux
. Warfarin
. Rivaroxaban
. Dabigatran

Correct Answer & Explanation

. Rivaroxaban

Explanation

Rivaroxaban is an oral direct Factor Xa inhibitor that binds directly to the active site of Factor Xa, independent of antithrombin III. Fondaparinux is an indirect Factor Xa inhibitor that binds to and enhances antithrombin III. Enoxaparin (a LMWH) also acts via antithrombin III. Dabigatran is a direct thrombin (Factor IIa) inhibitor.

Question 10208

Topic: Biomechanics & Biomaterials

A pediatric orthopedic surgeon applies a Ponseti cast to an infant with a clubfoot. Over the next week, the constant deformation of the contracted medial soft tissues leads to a gradual decrease in the applied tension within those tissues. This biomechanical phenomenon is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropic behavior

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (internal tension) within a material decreases over time when it is held at a constant strain (deformation). In serial casting, holding the soft tissues in a stretched position leads to stress relaxation. Creep, conversely, is the progressive deformation of a material when subjected to a constant load (stress).

Question 10209

Topic: 1. General Principles & Basic Science

Which of the following systemic physiological changes is most likely to occur immediately following the deflation of a pneumatic tourniquet that has been inflated for 90 minutes on a lower extremity?

. Increased core body temperature
. Decreased end-tidal carbon dioxide
. Decreased central venous pressure
. Increased systemic vascular resistance
. Metabolic alkalosis

Correct Answer & Explanation

. Decreased central venous pressure

Explanation

Upon deflation of a tourniquet, reperfusion of the ischemic limb occurs. This leads to a sudden shift of blood volume back into the limb, resulting in a transient decrease in central venous pressure (CVP) and systemic blood pressure. Systemically, end-tidal CO2 increases (due to washout of accumulated CO2), core temperature decreases (due to mixing with cooler blood from the ischemic limb), and a transient metabolic acidosis occurs.

Question 10210

Topic: Biology, Genetics & Bone Healing
Aseptic loosening and osteolysis following total joint arthroplasty are primarily mediated by the biological response to ultra-high molecular weight polyethylene (UHMWPE) wear debris. Which cell type is the primary initiator of this cascade by phagocytosing particles sized 0.1 to 1.0 micrometers?
. Osteoblast
. Osteoclast
. Macrophage
. T-lymphocyte
. Polymorphonuclear leukocyte

Correct Answer & Explanation

. Macrophage

Explanation

The biological response to particulate wear debris is macrophage-mediated. Macrophages phagocytose the small submicron polyethylene particles and subsequently release pro-inflammatory cytokines such as IL-1, IL-6, and TNF-alpha. These cytokines then stimulate osteoclasts via the RANKL pathway, culminating in periprosthetic osteolysis.

Question 10211

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into distinct zones to resist mechanical forces. Which of the following zones contains the highest concentration of water and features collagen fibers oriented parallel to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Subchondral bone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content, the lowest proteoglycan concentration, and collagen fibers that are oriented parallel to the articular surface to resist shear forces. The deep zone features collagen fibers oriented perpendicular to the surface to resist compressive loads.

Question 10212

Topic: 1. General Principles & Basic Science

A patient develops perioral numbness, tinnitus, and subsequent ventricular arrhythmias 5 minutes after receiving a regional nerve block with bupivacaine. After securing the airway and beginning CPR, what is the most appropriate specific pharmacological intervention?

. Administration of intravenous flumazenil
. Administration of 20% lipid emulsion
. Administration of intravenous calcium gluconate
. Administration of intravenous dantrolene
. Administration of intravenous sodium bicarbonate

Correct Answer & Explanation

. Administration of 20% lipid emulsion

Explanation

This presentation describes Local Anesthetic Systemic Toxicity (LAST), a life-threatening complication, particularly with highly lipid-soluble and potent agents like bupivacaine. The standard, definitive therapy for LAST alongside supportive measures is the intravenous administration of a 20% lipid emulsion, which creates a 'lipid sink' to draw the anesthetic out of myocardial tissues.

Question 10213

Topic: Biomechanics & Biomaterials

When comparing the biomechanics of a locking compression plate (LCP) construct to a conventional non-locking plate construct, which of the following best describes the fundamental mechanism by which a locking plate provides stability?

. Locking plates rely on high friction between the plate and the underlying bone surface.
. Locking plates require perfect anatomical contouring to maintain fracture reduction.
. Locking plates function as a single-beam construct dependent on the secure screw-plate interface.
. Conventional plates provide greater preservation of the periosteal blood supply.
. Conventional plates inherently provide relative stability rather than absolute stability.

Correct Answer & Explanation

. Locking plates function as a single-beam construct dependent on the secure screw-plate interface.

Explanation

Locking plates achieve stability by threading the screw head directly into the plate, creating a fixed-angle, single-beam construct. This does not rely on compressing the plate against the bone, thus it preserves periosteal blood supply and does not require perfect contouring. Conventional plates rely on friction generated by compressing the plate against the bone.

Question 10214

Topic: Biomechanics & Biomaterials

Among the commonly used synthetic bone graft substitutes, which material possesses the highest compressive strength but exhibits the slowest rate of in vivo resorption?

. Calcium sulfate
. Tricalcium phosphate
. Hydroxyapatite
. Demineralized bone matrix
. Cancellous allograft

Correct Answer & Explanation

. Hydroxyapatite

Explanation

Hydroxyapatite is a crystalline calcium phosphate ceramic that has excellent compressive strength but is resorbed extremely slowly in vivo, often taking years or persisting indefinitely. In contrast, calcium sulfate resorbs very rapidly (weeks to months), and tricalcium phosphate has an intermediate resorption rate.

Question 10215

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy suffers a transverse fracture of the femoral shaft after a minor fall. Radiographs demonstrate diffusely dense, 'chalk-like' bones with loss of the medullary canal, and a 'rugger-jersey' appearance of the vertebral bodies. A genetic mutation affecting which of the following proteins is most commonly implicated in the subset of this disease associated with renal tubular acidosis?

. Type I collagen
. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II
. Cartilage oligomeric matrix protein (COMP)
. Core-binding factor alpha-1 (CBFA1)

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

The patient has osteopetrosis, characterized by defective osteoclast function. Mutations in carbonic anhydrase II (CAII) cause the form associated with renal tubular acidosis and cerebral calcifications. The lack of CAII prevents osteoclasts from generating the protons needed to acidify the resorption pit.

Question 10216

Topic: Biology, Genetics & Bone Healing

A 7-year-old girl is evaluated for short stature and delayed tooth eruption. On physical exam, she has a prominent forehead, wide-set eyes, and is able to approximate her shoulders anteriorly to the midline. A mutation in which of the following genes is responsible for her condition?

. RUNX2 (CBFA1)
. COL1A1
. FGFR3
. SHOX
. FBN1

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

The clinical presentation is classic for cleidocranial dysplasia (absent or hypoplastic clavicles, delayed fontanelle closure, dental anomalies). It is caused by an autosomal dominant mutation in the RUNX2 (CBFA1) gene, an essential transcription factor for osteoblast differentiation and membranous ossification.

Question 10217

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest water content, lowest proteoglycan concentration, and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone has the highest water content (approx 80%), lowest proteoglycan content, and collagen fibers oriented parallel to the joint surface to resist shear forces. The deep zone has the lowest water content, highest proteoglycan content, and vertically oriented collagen fibers to resist compressive forces.

Question 10218

Topic: Biomechanics & Biomaterials

When cortical bone is subjected to mechanical loading at higher strain rates (e.g., a high-speed motor vehicle collision compared to a low-speed fall), which of the following describes its biomechanical response?

. It becomes less stiff and fails at a lower load
. It becomes more stiff and fails at a higher load
. Its stiffness remains constant but it undergoes greater plastic deformation
. It becomes more brittle and fails at a lower load
. Its energy-absorbing capacity decreases significantly

Correct Answer & Explanation

. It becomes more stiff and fails at a higher load

Explanation

Bone is a viscoelastic material, meaning its biomechanical properties depend on the rate of loading (strain rate). At higher strain rates, bone becomes stiffer, absorbs more energy before failure, and sustains higher loads before fracturing. The increased stored energy at failure is what leads to highly comminuted fractures in high-energy trauma.

Question 10219

Topic: Biology, Genetics & Bone Healing

A surgeon utilizes demineralized bone matrix (DBM) to augment a posterolateral lumbar spine fusion. Which of the following biological properties does DBM possess that distinguishes it from a processed structural cortical bone allograft?

. Osteogenesis
. Osteoconduction only
. Osteoinduction
. Both osteogenesis and osteoinduction
. Superior mechanical stability

Correct Answer & Explanation

. Osteoinduction

Explanation

Demineralized bone matrix (DBM) is created by acid-extracting the mineral component of bone, which exposes bone morphogenetic proteins (BMPs) and other growth factors. Thus, DBM is both osteoconductive and osteoinductive, whereas a standard processed structural cortical allograft is primarily osteoconductive. Neither possesses osteogenic properties (living osteoblasts/mesenchymal stem cells), which are unique to autograft or bone marrow aspirate.

Question 10220

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the process of 'creeping substitution' during the incorporation of a cortical bone graft?

. Simultaneous osteoclastic resorption and osteoblastic deposition along existing haversian canals
. Rapid revascularization followed by enchondral ossification
. Initial formation of a cartilage model that is subsequently mineralized
. Direct differentiation of mesenchymal stem cells into osteocytes within the graft
. Encapsulation of the graft by fibrous tissue without remodeling

Correct Answer & Explanation

. Simultaneous osteoclastic resorption and osteoblastic deposition along existing haversian canals

Explanation

Creeping substitution is the process by which cortical bone grafts are incorporated. It involves osteoclasts cutting cones through the dense cortical allograft/autograft, closely followed by osteoblasts laying down new bone. This coordinated replacement of dead bone with new host bone occurs along existing haversian systems.

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