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1. General Principles & Basic Science MCQs

Practice Set 658 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 13141

Topic: Physiology & Rehabilitation

During a rehabilitation exercise protocol for a patient recovering from a patellar tendon repair, the physical therapist instructs the patient to slowly lower a weight from full knee extension to 90 degrees of flexion. In this phase, the quadriceps muscle is actively generating force while simultaneously lengthening. This type of muscle contraction is defined as:

. Concentric
. Isometric
. Isokinetic
. Isotonic
. Eccentric

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when the muscle lengthens while under tension (generating force). A concentric contraction occurs when the muscle shortens while generating force. An isometric contraction occurs when tension is generated without a change in muscle length. Isokinetic refers to contraction at a constant speed, and isotonic refers to contraction against a constant load.

Question 13142

Topic: 1. General Principles & Basic Science

A surgeon is mixing antibiotic-loaded polymethyl methacrylate (PMMA) cement for a 2-stage revision of an infected total knee arthroplasty. The pathogen is identified as MRSA. To ensure the antibiotic maintains its efficacy despite the highly exothermic polymerization reaction of the cement, which of the following characteristics makes the antibiotic suitable?

. Low powder solubility
. Liquid formulation
. Anaerobic spectrum of activity
. High thermal stability
. Bacteriostatic mechanism of action

Correct Answer & Explanation

. High thermal stability

Explanation

When adding antibiotics to PMMA bone cement, the chosen antibiotic must be available in a powder form (liquid formulations compromise the mechanical properties of the cement) and possess high thermal stability to withstand the exothermic polymerization process, which can reach temperatures up to 80-100°C. Vancomycin and Tobramycin are the most commonly used due to their broad spectrum and heat stability.

Question 13143

Topic: Infection, Pharmacology & VTE

A 45-year-old farmer sustains a severe open tibia fracture after being kicked by a horse inside a dirty barn. According to standard orthopedic guidelines for open fractures with heavy soil or agricultural contamination, what is the most appropriate initial prophylactic antibiotic regimen?

. Cefazolin alone
. Cefazolin and Gentamicin
. Vancomycin and Piperacillin-Tazobactam
. Clindamycin alone
. Cefazolin, Gentamicin, and Penicillin

Correct Answer & Explanation

. Cefazolin, Gentamicin, and Penicillin

Explanation

For open fractures heavily contaminated with soil or occurring in farm environments, there is a high risk of anaerobic infection, specifically Clostridium species. Guidelines recommend a first-generation cephalosporin (Cefazolin) for Gram-positive coverage, an aminoglycoside (Gentamicin) for extended Gram-negative coverage, and high-dose Penicillin (or Metronidazole) specifically for anaerobic/Clostridial coverage.

Question 13144

Topic: Biology, Genetics & Bone Healing

Histologically, the 'cutting cone' is a highly coordinated functional unit composed of an advancing front of osteoclasts followed by a trail of osteoblasts laying down new osteoid. This structure is the primary physiological mechanism for which of the following processes?

. Primary (haversian) bone remodeling
. Endochondral ossification
. Intramembranous ossification
. Secondary callus formation
. Hematoma organization

Correct Answer & Explanation

. Primary (haversian) bone remodeling

Explanation

The cutting cone is the functional unit of primary (haversian) bone remodeling in cortical bone. Osteoclasts at the leading edge resorb a tunnel of old bone, and osteoblasts trail behind to deposit new osteoid concentrically, eventually forming a new osteon (Haversian system). This process is seen in physiologic remodeling and in primary bone healing where rigid internal fixation allows direct bone repair without callus formation.

Question 13145

Topic: Surgical Anatomy & Approaches
A 28-year-old patient sustains a closed midshaft humerus fracture and subsequently develops a complete radial nerve palsy. An EMG at 6 weeks shows fibrillation potentials. If the microscopic architecture reveals disruption of the axons and endoneurial tubes, but the perineurium and epineurium remain intact, how is this injury classified?
. Sunderland Grade I
. Sunderland Grade II
. Sunderland Grade IV
. Sunderland Grade III
. Sunderland Grade V

Correct Answer & Explanation

. Sunderland Grade IV

Explanation

According to the Sunderland classification of nerve injuries: Grade I (Neuropraxia) involves a focal myelin defect with intact axons. Grade II (Axonotmesis) involves axonal disruption but intact endoneurium. Grade III involves disruption of axons and endoneurium, with intact perineurium. Grade IV involves disruption of everything except the epineurium. Grade V (Neurotmesis) is complete nerve transection.

Question 13146

Topic: Biology, Genetics & Bone Healing

During a spinal fusion surgery, the surgeon requires a bone graft. Which of the following graft options uniquely provides osteoconductive, osteoinductive, AND osteogenic properties?

. Iliac crest autograft
. Demineralized bone matrix (DBM)
. Cancellous allograft
. Calcium phosphate cement
. Recombinant BMP-2

Correct Answer & Explanation

. Iliac crest autograft

Explanation

Autogenous bone graft (autograft), typically harvested from the iliac crest, is considered the gold standard because it provides all three properties essential for bone formation: osteoconduction (a scaffold), osteoinduction (growth factors like BMPs to stimulate progenitor cells), and osteogenesis (live osteoblasts and mesenchymal stem cells). Allografts and DBM lack live cells (osteogenesis). Synthetic matrices are typically only osteoconductive.

Question 13147

Topic: Biomechanics & Biomaterials

A 40-year-old male receives a dynamic compression plate for a forearm fracture. Postoperatively, one of the cortical screws is left untightened, allowing microscopic motion between the screw head and the plate during repetitive loading. This condition primarily predisposes the implant to which mechanism of failure?

. Galvanic corrosion
. Creep
. Fatigue failure
. Brittle fracture
. Stress shielding

Correct Answer & Explanation

. Fatigue failure

Explanation

A loose screw in a plate construct will undergo repetitive cyclic loading and micro-motion. This repetitive stress, even below the ultimate tensile strength of the material, leads to crack initiation and propagation, ultimately resulting in fatigue failure. Fretting wear also occurs, but macroscopic fracture of the screw or plate in this scenario is due to fatigue.

Question 13148

Topic: Biology, Genetics & Bone Healing

A 32-year-old female is diagnosed with an expansile, lytic lesion in the distal femur. Biopsy reveals mononuclear cells and multinucleated giant cells. Which of the following best describes the mechanism of action of the targeted medical therapy for this lesion?

. Inhibits RANK ligand (RANKL), preventing osteoclast formation
. Binds directly to RANK on osteoclasts, inducing apoptosis
. Inhibits vascular endothelial growth factor (VEGF), reducing tumor angiogenesis
. Cross-links DNA, preventing tumor cell replication
. Activates the Wnt/beta-catenin pathway, stimulating osteoblastic differentiation

Correct Answer & Explanation

. Inhibits RANK ligand (RANKL), preventing osteoclast formation

Explanation

Denosumab is highly effective for Giant Cell Tumor (GCT) of bone. It is a monoclonal antibody that binds to RANKL (produced by the neoplastic mononuclear stromal cells), preventing it from binding to RANK on the normal osteoclast-like giant cells. This inhibits the maturation and activity of osteoclasts, leading to massive ossification of the tumor.

Question 13149

Topic: 1. General Principles & Basic Science

Articular cartilage relies on its unique extracellular matrix for biomechanical strength. Which zone of articular cartilage has the highest concentration of water and the lowest concentration of proteoglycans?

. 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 comprises 10-20% of the thickness. It contains the highest water content (up to 80%) and the lowest proteoglycan content. The collagen fibers are oriented parallel to the joint surface to resist shear forces. The deep zone has the lowest water content and the highest proteoglycan content.

Question 13150

Topic: Physiology & Rehabilitation

During a rehabilitation protocol following a major orthopedic surgery, a physical therapist emphasizes eccentric muscle contractions. Which of the following statements best describes an eccentric contraction?

. The muscle shortens while generating constant tension
. The muscle lengthens while generating force
. The muscle generates force without changing length
. The muscle shortens at a constant velocity
. The muscle relaxes entirely to allow passive stretch

Correct Answer & Explanation

. The muscle lengthens while generating force

Explanation

An eccentric contraction occurs when a muscle generates force while actively lengthening. This often occurs during deceleration activities (e.g., the quadriceps during the downward phase of a squat). Eccentric contractions can generate the highest forces and are most associated with delayed onset muscle soreness (DOMS).

Question 13151

Topic: 1. General Principles & Basic Science

Compared to cortical bone grafts, cancellous bone grafts incorporate through which of the following histologic sequences?

. Osteoclastic resorption followed by osteoblastic apposition
. Osteoblastic apposition followed by osteoclastic resorption
. Simultaneous endochondral ossification
. Direct membranous ossification without a cartilage model
. Fibrous tissue replacement followed by mineralization

Correct Answer & Explanation

. Osteoblastic apposition followed by osteoclastic resorption

Explanation

Cancellous bone incorporates via creeping substitution where osteoblasts lay down new bone on dead trabeculae first, followed by osteoclastic resorption. Cortical bone, due to its density, requires osteoclastic cutting cones to resorb bone first before osteoblastic apposition.

Question 13152

Topic: 1. General Principles & Basic Science

Which of the following geometric modifications to a standard cortical bone screw will most significantly increase its pullout strength?

. Increasing the core diameter
. Increasing the thread pitch
. Decreasing the thread depth
. Increasing the outer diameter
. Using a non-locking screw design

Correct Answer & Explanation

. Increasing the outer diameter

Explanation

Pullout strength is directly proportional to the outer diameter of the screw. Increasing thread depth (outer minus core diameter) and decreasing thread pitch also enhance the pullout strength of the construct.

Question 13153

Topic: Biomechanics & Biomaterials

A patient with a stainless steel plate undergoes revision fixation where a titanium screw is placed in direct contact with the plate. What type of corrosion is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution, such as the human body. The less noble metal acts as an anode and undergoes accelerated dissolution.

Question 13154

Topic: Biomechanics & Biomaterials
Sterilization of Ultra-High Molecular Weight Polyethylene (UHMWPE) via gamma irradiation in an oxygen-rich environment leads to which of the following material changes?
. Increased cross-linking and improved wear
. Decreased elastic modulus with increased ductility
. Increased crystallinity and enhanced fatigue life
. Resistance to third-body wear
. Chain scission and oxidative degradation

Correct Answer & Explanation

. Chain scission and oxidative degradation

Explanation

Gamma irradiation of UHMWPE in the presence of oxygen causes chain scission and subsurface oxidation, significantly decreasing wear resistance. Modern UHMWPE is sterilized in an inert environment (e.g., vacuum or argon) and highly cross-linked to improve wear.

Question 13155

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is prescribed teriparatide for the treatment of severe osteoporosis. Which of the following best describes its mechanism of action?

. Recombinant PTH analogue that stimulates osteoblast activity
. Inhibits osteoclast ruffled border formation
. Monoclonal antibody against RANKL
. Inhibitor of the Wnt/beta-catenin pathway
. Sclerostin inhibitor

Correct Answer & Explanation

. Recombinant PTH analogue that stimulates osteoblast activity

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently, it acts as an anabolic agent by strongly stimulating osteoblast activity over osteoclast activity.

Question 13156

Topic: 1. General Principles & Basic Science

The compressive stiffness and resilience of articular cartilage are primarily provided by which of the following extracellular matrix components?

. Type II collagen
. Proteoglycans
. Type I collagen
. Elastin
. Lubricin

Correct Answer & Explanation

. Proteoglycans

Explanation

The compressive stiffness of articular cartilage is provided by proteoglycans, particularly aggrecan. Their negatively charged glycosaminoglycan side chains repel each other and draw water into the matrix, resisting compressive forces.

Question 13157

Topic: Biomechanics & Biomaterials

When testing the viscoelastic properties of a tendon construct, a constant submaximal load is applied over time, resulting in progressive deformation. This phenomenon is termed:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation of a viscoelastic material under a constant load. Stress relaxation, in contrast, is the decrease in internal stress over time when a material is held at a constant length or deformation.

Question 13158

Topic: Infection, Pharmacology & VTE

A patient develops a periprosthetic joint infection characterized by bacterial entry into a sessile state and biofilm formation. Which communication mechanism is essential for coordinating this transition based on bacterial population density?

. Chemotaxis
. Quorum sensing
. Opsonization
. Phagocytosis
. Transduction

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is a cell-to-cell communication mechanism used by bacteria to coordinate gene expression based on local population density. It is essential for transitioning from planktonic growth to the organized, protective structure of a biofilm.

Question 13159

Topic: 1. General Principles & Basic Science
In the setting of peripheral nerve injury, a lesion that disrupts the axon and endoneurium but leaves the perineurium and epineurium intact is classified as:
. Sunderland I
. Sunderland II
. Sunderland III
. Sunderland IV
. Sunderland V

Correct Answer & Explanation

. Sunderland III

Explanation

Sunderland III nerve injuries involve disruption of the axon and endoneurium, while the perineurium and epineurium remain intact. Recovery in these injuries is variable and often incomplete due to endoneurial scarring.

Question 13160

Topic: Physiology & Rehabilitation

Delayed onset muscle soreness (DOMS) following intensive physical activity is most strongly associated with which type of muscle contraction?

. Concentric
. Eccentric
. Isometric
. Isokinetic
. Plyometric

Correct Answer & Explanation

. Eccentric

Explanation

Delayed onset muscle soreness (DOMS) is primarily caused by eccentric muscle contractions, where the muscle lengthens while under active tension. This mechanical stress leads to microtrauma of the muscle fibers and a subsequent inflammatory response.

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