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1. General Principles & Basic Science MCQs

Practice Set 577 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 11521

Topic: 1. General Principles & Basic Science

A 28-year-old competitive weightlifter feels a pop in his anterior axillary fold while performing a heavy bench press. Examination reveals loss of the anterior axillary contour and weakness in internal rotation and adduction. MRI shows a rupture of the sternocostal head of the pectoralis major. Where does the sternocostal head normally insert?

. Medial to the clavicular head insertion on the humerus
. Deep and proximal to the clavicular head insertion on the humerus
. Superficial and distal to the clavicular head insertion on the humerus
. Directly onto the coracoid process
. Onto the lesser tuberosity of the humerus

Correct Answer & Explanation

. Medial to the clavicular head insertion on the humerus

Explanation

The sternocostal head of the pectoralis major twists before insertion, attaching deep and proximal to the clavicular head on the lateral lip of the bicipital groove. This anatomy must be accurately restored during surgical repair.

Question 11522

Topic: 1. General Principles & Basic Science

A 19-year-old male is tackled during a football game and sustains a posterior sternoclavicular joint dislocation. He reports mild difficulty swallowing but has normal vital signs. Attempted closed reduction in the operating room under general anesthesia fails. What is the next most appropriate step in management?

. Open reduction and internal fixation with Kirschner wires
. Open reduction and stabilization using figure-of-eight tendon graft with cardiothoracic surgery on standby
. Resection of the medial third of the clavicle
. Observation and conservative management
. Percutaneous pinning of the sternoclavicular joint

Correct Answer & Explanation

. Open reduction and internal fixation with Kirschner wires

Explanation

Irreducible posterior sternoclavicular dislocations require open reduction and graft stabilization. A cardiothoracic surgeon must be available due to the risk of injury to underlying mediastinal vessels. K-wires are contraindicated due to the risk of fatal migration.

Question 11523

Topic: 1. General Principles & Basic Science

A 30-year-old competitive weightlifter feels a sudden "pop" while performing a heavy bench press. Examination reveals loss of the anterior axillary fold and weakness in internal rotation. MRI confirms a rupture of the sternal head of the pectoralis major. Where does the sternal head normally insert relative to the clavicular head on the humerus?

. Proximal and superficial
. Distal and superficial
. Proximal and deep
. Distal and deep
. Directly adjacent and parallel

Correct Answer & Explanation

. Proximal and superficial

Explanation

The pectoralis major tendon undergoes a 180-degree twist before insertion. Consequently, the sternal head fibers pass behind the clavicular fibers to insert proximal and deep on the lateral lip of the bicipital groove.

Question 11524

Topic: 1. General Principles & Basic Science

The superficial zone of articular cartilage is primarily responsible for resisting what type of force, and contains what orientation of collagen fibers?

. Resists compressive forces; collagen fibers are perpendicular to the joint surface
. Resists shear forces; collagen fibers are parallel to the joint surface
. Resists tensile forces; collagen fibers are perpendicular to the joint surface
. Resists shear forces; collagen fibers are arranged randomly
. Resists compressive forces; collagen fibers are parallel to the joint surface

Correct Answer & Explanation

. Resists compressive forces; collagen fibers are perpendicular to the joint surface

Explanation

Articular cartilage is divided into distinct zones. The superficial (tangential) zone makes up 10-20% of the thickness. It contains the highest concentration of water and collagen (Type II), with fibers aligned parallel to the articular surface. This specific orientation allows the superficial zone to primarily resist shear forces. The deep zone, conversely, has collagen fibers arranged perpendicularly to resist compressive forces.

Question 11525

Topic: 1. General Principles & Basic Science

During fracture healing, which of the following scenarios would shift the stress-strain curve of the healing fracture to the left (decreased strain for a given stress)?

. Progression from soft callus to hard callus
. Increased interfragmentary gap size
. Systemic administration of nonsteroidal anti-inflammatory drugs (NSAIDs)
. Increased cyclical motion at the fracture site
. Prolonged exposure to nicotine

Correct Answer & Explanation

. Progression from soft callus to hard callus

Explanation

A shift to the left on a stress-strain curve indicates an increase in the stiffness (Young's modulus) of a material. As a healing fracture progresses from a soft, cartilaginous callus to a hard, bony callus, the tissue becomes significantly stiffer and can tolerate less strain (deformation) for a given amount of stress. NSAIDs and nicotine would delay healing and keep the callus in a less stiff phase.

Question 11526

Topic: Biology, Genetics & Bone Healing

Denosumab is used in the treatment of osteoporosis and giant cell tumor of bone. It inhibits bone resorption through which of the following precise molecular mechanisms?

. Binding directly to the RANK receptor on the surface of mature osteoclasts
. Binding to RANKL, preventing its interaction with RANK
. Mimicking the action of Osteoprotegerin (OPG) by binding to the RANK receptor
. Inhibiting carbonic anhydrase II in the osteoclast ruffled border
. Inducing targeted apoptosis of osteoblasts

Correct Answer & Explanation

. Binding directly to the RANK receptor on the surface of mature osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that acts similarly to the body's natural decoy receptor, Osteoprotegerin (OPG). It binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), thereby preventing RANKL from binding to the RANK receptor on osteoclast precursors. This inhibits osteoclast differentiation, function, and survival.

Question 11527

Topic: Biomechanics & Biomaterials
What is the primary mechanism of degradation of conventional ultra-high molecular weight polyethylene (UHMWPE) components in total joint arthroplasty when they are sterilized via gamma irradiation in an oxygen-rich environment?
. Excessive cross-linking
. Galvanic corrosion
. Chain scission and oxidation
. Creep deformation
. Third-body abrasive wear

Correct Answer & Explanation

. Chain scission and oxidation

Explanation

Historically, gamma irradiation of UHMWPE in air (oxygen) led to the formation of free radicals. These free radicals react with oxygen over time, causing chain scission (breaking of the polymer chains) and oxidation. This chemical degradation drastically reduces the mechanical properties and wear resistance of the polyethylene, leading to premature catastrophic failure. Modern UHMWPE is irradiated in inert environments and subsequently melted or annealed to extinguish free radicals.

Question 11528

Topic: 1. General Principles & Basic Science

Osteoclasts are specialized multinucleated cells responsible for bone resorption. How do they primarily solubilize the inorganic mineral component (hydroxyapatite) of bone?

. Secretion of Cathepsin K
. Secretion of Matrix Metalloproteinases (MMPs)
. Action of tartrate-resistant acid phosphatase (TRAP)
. Pumping of hydrogen ions via a vacuolar-type H+-ATPase
. Release of transforming growth factor-beta (TGF-b)

Correct Answer & Explanation

. Secretion of Cathepsin K

Explanation

Osteoclasts dissolve bone in two stages: solubilization of the mineral phase and degradation of the organic matrix. The mineral component (hydroxyapatite) is dissolved by maintaining an acidic environment in the sealing zone; this is achieved by pumping hydrogen ions (H+) into Howship's lacuna via a vacuolar-type H+-ATPase. The organic matrix (mostly Type I collagen) is subsequently degraded by enzymes such as Cathepsin K.

Question 11529

Topic: 1. General Principles & Basic Science

How do nonsteroidal anti-inflammatory drugs (NSAIDs) negatively affect fracture healing at the cellular and molecular level?

. By inhibiting osteoclast differentiation directly via RANK blockade
. By promoting excessive and disordered endochondral ossification
. By inhibiting cyclooxygenase-2 (COX-2) and subsequent prostaglandin E2 (PGE2) synthesis
. By decreasing the release of bone morphogenetic proteins (BMP-2 and BMP-7)
. By downregulating Wnt/beta-catenin signaling in osteoprogenitor cells

Correct Answer & Explanation

. By inhibiting osteoclast differentiation directly via RANK blockade

Explanation

NSAIDs impair fracture healing by inhibiting the cyclooxygenase (COX) enzymes, particularly COX-2. COX-2 is upregulated during the inflammatory phase of fracture healing and is responsible for synthesizing prostaglandins, notably Prostaglandin E2 (PGE2). PGE2 plays a crucial role in osteoblast differentiation, angiogenesis, and callus formation. Suppressing PGE2 blunts the normal healing cascade.

Question 11530

Topic: 1. General Principles & Basic Science

In skeletal muscle physiology, what is the specific role of calcium ions during excitation-contraction coupling?

. Binds to myosin heads to initiate the ATPase power stroke
. Binds to troponin C, causing a conformational change that moves tropomyosin away from actin
. Binds directly to tropomyosin, exposing the actin-binding site on myosin
. Activates the sodium-potassium pump to restore the resting membrane potential
. Triggers the synthesis of acetylcholine at the neuromuscular junction

Correct Answer & Explanation

. Binds to myosin heads to initiate the ATPase power stroke

Explanation

During excitation-contraction coupling in skeletal muscle, an action potential triggers the release of calcium ions from the sarcoplasmic reticulum. The calcium binds to Troponin C on the thin filaments. This binding induces a conformational change in the troponin-tropomyosin complex, rolling tropomyosin away from the myosin-binding sites on the actin filament, thus allowing cross-bridge cycling to occur.

Question 11531

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopedic biomaterial, the total area under the curve up to the point of material failure represents which of the following properties?

. Toughness
. Resilience
. Yield strength
. Young's modulus
. Ultimate tensile strength

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures, which graphically equates to the total area under the stress-strain curve. Resilience is the area under the elastic portion only (energy absorbed without permanent deformation). Young's modulus is the slope of the elastic region (stiffness), and ultimate tensile strength is the peak stress the material endures.

Question 11532

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 specific structural components?

. Myelin sheath only
. Axon only, with intact supporting connective tissue
. Axon and endoneurium, with intact perineurium
. Axon, endoneurium, and perineurium, with intact epineurium
. Complete transection of the entire nerve trunk including the epineurium

Correct Answer & Explanation

. Myelin sheath only

Explanation

In Sunderland's classification: 1st degree is neuropraxia (demyelination, intact axon). 2nd degree is axonotmesis (disrupted axon, intact endoneurium). 3rd degree involves disruption of the axon and endoneurium, but the perineurium remains intact (scarring can impede regeneration). 4th degree adds perineurial disruption (neuroma-in-continuity). 5th degree is neurotmesis (complete nerve transection).

Question 11533

Topic: 1. General Principles & Basic Science

Which type of joint lubrication is primarily responsible for minimizing wear in articular cartilage during high-load, low-speed conditions, such as transitioning from a seated to a standing position?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Weeping lubrication
. Squeeze-film lubrication

Correct Answer & Explanation

. Hydrodynamic lubrication

Explanation

Boundary lubrication depends on a molecular monolayer (primarily composed of the glycoprotein lubricin) bound to the articular surfaces. It is most effective in preventing surface-to-surface wear during high-load, low-speed, or stationary conditions. Fluid-film lubrication (hydrodynamic or elastohydrodynamic) relies on a wedge of pressurized fluid separating the surfaces, which occurs mostly during high-speed, dynamic motion.

Question 11534

Topic: 1. General Principles & Basic Science

The ability of articular cartilage to resist compressive forces (compressive stiffness) is primarily dependent on the interaction of water with which of the following macromolecular components?

. Type II collagen
. Hyaluronic acid
. Aggrecan
. Fibronectin
. Type IX collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Aggrecan is a large proteoglycan rich in negatively charged chondroitin sulfate and keratan sulfate chains. These negative charges repel each other and highly attract water (Donnan osmotic effect), causing the molecules to swell. This swelling pressure is constrained by the Type II collagen network. The trapped water and swelling pressure provide articular cartilage with its exceptional compressive stiffness.

Question 11535

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, the phenomenon of 'creep' is best defined as:

. Progressive, time-dependent deformation of a material subjected to a constant load
. A time-dependent decrease in stress within a material held at a constant strain
. The exact point at which a material transitions from elastic to plastic deformation
. The loss of energy in the form of heat during cyclical loading and unloading
. The sudden mechanical failure of a material after repeated loading below its ultimate strength

Correct Answer & Explanation

. Progressive, time-dependent deformation of a material subjected to a constant load

Explanation

Creep is the time-dependent, progressive deformation (strain) of a viscoelastic material under a constant applied stress (load). Conversely, stress relaxation is the progressive decrease in stress over time when a material is held at a constant strain (deformation). Both are fundamental properties of viscoelastic biological tissues like tendons, ligaments, and cartilage.

Question 11536

Topic: Biomechanics & Biomaterials

Galvanic corrosion is an electrochemical process that can lead to orthopedic implant failure. Which of the following conditions is necessary for galvanic corrosion to occur?

. Two dissimilar metals must be in physical contact within an electrolytic solution
. Fretting micro-motion must mechanically strip away the titanium passivation layer
. The implant must be exposed to an environment with exceptionally high oxygen tension
. An acidic microenvironment must form in narrow gaps or crevices around screws
. Metal wear debris must aggregate and form immune complexes with local macrophages

Correct Answer & Explanation

. Two dissimilar metals must be in physical contact within an electrolytic solution

Explanation

Galvanic corrosion occurs when two different (dissimilar) metals, which have different electrochemical potentials (anodic/cathodic indices), are placed in direct physical or electrical contact within a conductive fluid (such as human serum or interstitial fluid). The less noble metal acts as an anode and undergoes accelerated corrosion. Using a stainless steel screw with a titanium plate is a classic example.

Question 11537

Topic: 1. General Principles & Basic Science

Proteoglycans are essential components of the extracellular matrix in cartilage. Which of the following glycosaminoglycans (GAGs) is NOT sulfated and forms the central non-covalent backbone of large proteoglycan aggregates?

. Chondroitin sulfate
. Keratan sulfate
. Dermatan sulfate
. Hyaluronic acid
. Heparan sulfate

Correct Answer & Explanation

. Chondroitin sulfate

Explanation

Hyaluronic acid (hyaluronan) is unique among glycosaminoglycans because it is non-sulfated, very large, and is not covalently attached to a protein core. Instead, hundreds of aggrecan monomers non-covalently bind to a single long chain of hyaluronic acid (stabilized by link proteins) to form massive proteoglycan aggregates in the cartilage matrix.

Question 11538

Topic: 1. General Principles & Basic Science
Which of the following statements best describes the structural and biochemical differences between ligaments and tendons?
. Tendons possess a higher concentration of Type III collagen than ligaments
. Ligaments exhibit a strictly parallel arrangement of collagen fibers, while tendons are entirely interwoven
. Ligaments possess a higher elastin content and a slightly less parallel collagen arrangement than tendons
. Tendons rely exclusively on primary bone healing mechanisms at their insertion sites
. Ligaments are avascular, relying entirely on synovial fluid for nutrition, unlike tendons

Correct Answer & Explanation

. Ligaments possess a higher elastin content and a slightly less parallel collagen arrangement than tendons

Explanation

While both tendons and ligaments are composed primarily of Type I collagen, tendons must transmit unidirectional forces from muscle to bone and therefore have a highly parallel alignment of collagen bundles. Ligaments connect bone to bone and experience multidirectional forces; thus, their collagen fibers are slightly more interwoven (less strictly parallel). Additionally, ligaments generally contain a higher proportion of elastin, affording them greater elasticity.

Question 11539

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) plays a critical role in calcium homeostasis by stimulating bone resorption when administered continuously. However, osteoclasts lack receptors for PTH. Which cell serves as the direct target for PTH in bone, subsequently signaling osteoclasts?

. Mature osteoclasts
. Osteoblasts
. Osteocytes
. Chondrocytes
. Bone marrow macrophages

Correct Answer & Explanation

. Mature osteoclasts

Explanation

Parathyroid hormone (PTH) receptors (PTH1R) are located on cells of the osteoblast lineage (osteoblasts and osteocytes). When PTH binds to osteoblasts, it upregulates their expression of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand) and downregulates Osteoprotegerin (OPG). The increased RANKL binds to RANK on osteoclast precursors, stimulating osteoclast differentiation and bone resorption.

Question 11540

Topic: 1. General Principles & Basic Science

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

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone makes up 10-20% of articular cartilage. It contains the highest water content, lowest proteoglycan content, and densely packed type II collagen fibers aligned parallel to the articular surface to resist shear forces.

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