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1. General Principles & Basic Science MCQs

Practice Set 715 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 14281

Topic: Biomechanics & Biomaterials

In biomechanics, which of the following terms describes the phenomenon where a viscoelastic material experiences a decrease in stress over time when held at a constant strain?

. Creep
. Hysteresis
. Fatigue
. Stress relaxation
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress over time when a material is held at a constant strain. Creep is the progressive deformation (strain) over time under a constant load (stress).

Question 14282

Topic: Biomechanics & Biomaterials
Which of the following manufacturing processes most effectively reduces adhesive and abrasive wear in ultra-high-molecular-weight polyethylene (UHMWPE) for total hip arthroplasty?
. Sterilization in air
. Gamma irradiation followed by melting
. Ethylene oxide sterilization
. Decreasing the cross-linking density
. Adding barium sulfate

Correct Answer & Explanation

. Gamma irradiation followed by melting

Explanation

Highly cross-linked polyethylene is created using gamma or electron beam irradiation to create free radicals that form cross-links. Subsequent melting or annealing quenches these free radicals, preventing long-term oxidative degradation.

Question 14283

Topic: 1. General Principles & Basic Science

During the repair of a Zone II flexor digitorum profundus (FDP) laceration, the surgeon decides on a core suture technique. Which of the following factors is most directly proportional to the tensile strength of the repair?

. Number of core suture strands crossing the repair site
. The use of a running epitenon suture
. The thickness of the suture material
. The type of knot used
. The distance of the core suture purchase from the cut edge

Correct Answer & Explanation

. Number of core suture strands crossing the repair site

Explanation

The tensile strength of a flexor tendon repair is directly proportional to the number of core strands crossing the repair site. A 4-strand or 6-strand repair provides significantly more strength than a 2-strand repair, allowing for early active mobilization.

Question 14284

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections caused by Staphylococcus epidermidis, which of the following is primarily responsible for facilitating the initial adherence to the implant and subsequent biofilm formation?

. Protein A
. Alpha toxin
. Polysaccharide intercellular adhesin (PIA)
. Panton-Valentine leukocidin (PVL)
. Coagulase

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Polysaccharide intercellular adhesin (PIA) is crucial for the cell-to-cell adhesion and biofilm formation of Staphylococcus epidermidis on foreign bodies. This biofilm protects the bacteria from host immune responses and antibiotics.

Question 14285

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft materials possesses osteoconductive, osteoinductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous allograft
. Recombinant human bone morphogenetic protein-2 (rhBMP-2)
. Iliac crest autograft
. Calcium phosphate ceramics

Correct Answer & Explanation

. Iliac crest autograft

Explanation

Autograft (like iliac crest) is the only graft material that possesses all three properties: osteoconduction (scaffold), osteoinduction (growth factors like BMPs), and osteogenesis (live osteoblasts and progenitor cells).

Question 14286

Topic: Biomechanics & Biomaterials
To decrease volumetric wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular liners, cross-linking is performed via irradiation. What is the primary mechanical trade-off of utilizing highly cross-linked polyethylene compared to conventional UHMWPE?
. Increased yield strength
. Decreased fatigue and fracture resistance
. Increased oxidation potential if melted post-irradiation
. Increased elastic modulus
. Decreased oxidative stability if remelted

Correct Answer & Explanation

. Decreased fatigue and fracture resistance

Explanation

Highly cross-linking UHMWPE significantly improves its wear resistance by reducing the generation of submicron wear particles. However, the process fundamentally alters the polymer chain network, which compromises its bulk mechanical properties, most notably decreasing its fatigue strength, fracture resistance, and ultimate tensile strength.

Question 14287

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized in the treatment of osteoporosis and giant cell tumor of bone. Which of the following best describes its specific molecular mechanism of action?

. Binds directly to the RANK receptor on osteoclasts
. Acts as a decoy receptor for RANKL, mimicking osteoprotegerin (OPG)
. Binds to RANKL, preventing its interaction with the RANK receptor
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Stimulates the Wnt/beta-catenin signaling pathway to increase osteoblastogenesis

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), neutralizing it and preventing it from binding to the RANK receptor on the surface of osteoclasts and their precursors. This mimics the physiologic action of osteoprotegerin (OPG), thereby powerfully inhibiting osteoclast survival and function.

Question 14288

Topic: Physiology & Rehabilitation

During the normal human gait cycle, at which specific phase is the anterior tibial muscle maximally active?

. Midstance
. Terminal stance
. Heel strike to foot flat
. Midswing
. Toe-off

Correct Answer & Explanation

. Heel strike to foot flat

Explanation

The tibialis anterior acts eccentrically from heel strike (initial contact) to foot flat (loading response) to decelerate plantar flexion and prevent the foot from slapping the ground. This eccentric contraction represents its period of peak electrical activity during the normal gait cycle.

Question 14289

Topic: 1. General Principles & Basic Science

When designing a cortical screw to maximize pullout strength in osteopenic bone, which of the following geometric modifications will be most effective?

. Decreasing the outer diameter
. Increasing the inner (root) diameter
. Decreasing the thread pitch
. Decreasing the thread depth
. Decreasing the screw length

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength of a screw is directly proportional to the outer diameter, thread depth, and length of purchase, and inversely proportional to thread pitch. Decreasing the pitch means there are more threads per unit length engaging the bone, which significantly increases the pullout strength.

Question 14290

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent and tenacious pathogen in prosthetic joint infections, primarily due to its ability to form a robust biofilm. Which phase of biofilm formation critically involves the production of poly-N-acetylglucosamine (PNAG)?

. Planktonic phase
. Reversible attachment
. Irreversible attachment
. Maturation phase
. Dispersion phase

Correct Answer & Explanation

. Maturation phase

Explanation

During the maturation phase (also known as the accumulation phase) of biofilm formation, bacteria produce an extracellular polymeric substance (EPS). In S. epidermidis, a major component of this matrix is polysaccharide intercellular adhesin (PIA), which is primarily composed of poly-N-acetylglucosamine (PNAG). This matrix protects the bacteria from host immunity and antibiotics.

Question 14291

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with deep, aching thigh pain and increasing hat size. Labs show elevated alkaline phosphatase with normal calcium and phosphate levels. A core biopsy of the femur is most likely to reveal which of the following histological patterns?

. Defective mineralization of osteoid with widened osteoid seams
. Prominent, irregular cement lines arranged in a mosaic pattern
. Marked thinning of trabeculae with normal bone mineralization
. Subperiosteal bone resorption with collections of osteoclasts and brown tumors
. Woven bone with a hypercellular stroma lacking osteoblastic rimming

Correct Answer & Explanation

. Prominent, irregular cement lines arranged in a mosaic pattern

Explanation

The clinical presentation (thigh pain, increasing hat size, isolated elevated alk phos) is classic for Paget's disease of bone. Histology in the mixed/sclerotic phase demonstrates chaotic, disorganized bone turnover characterized by prominent, irregular, and intersecting cement lines forming a pathognomonic 'mosaic' or 'jigsaw puzzle' pattern.

Question 14292

Topic: Biology, Genetics & Bone Healing
Following a closed femur fracture treated with a locked intramedullary nail, fracture healing occurs primarily via endochondral ossification. During the hard callus formation phase, which specific collagen type is synthesized predominantly by hypertrophic chondrocytes to facilitate cartilage matrix calcification?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type X

Explanation

Type X collagen is exclusively produced by hypertrophic chondrocytes during the process of endochondral ossification. It plays a critical regulatory role in the calcification of the cartilage matrix, paving the way for vascular invasion and subsequent replacement by woven bone (osteoblasts producing Type I collagen).

Question 14293

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a second-degree injury corresponds to which of the following physiological descriptions?

. Focal demyelination with intact axon and connective tissue
. Axonal disruption with intact endoneurium
. Disruption of the axon and endoneurium with an intact perineurium
. Disruption of the perineurium with an intact epineurium
. Complete functional and anatomical nerve transection

Correct Answer & Explanation

. Axonal disruption with intact endoneurium

Explanation

A Sunderland second-degree injury corresponds to Seddon's 'axonotmesis'. In this injury, the axon is disrupted and undergoes Wallerian degeneration distally, but the basal lamina tube (endoneurium) remains fully intact. This intact endoneurial tube guides regenerating axons, typically leading to excellent recovery.

Question 14294

Topic: 1. General Principles & Basic Science

The primary, vital blood supply to the adult femoral head is derived from branches of which of the following vessels?

. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Artery of the ligamentum teres (foveal artery)
. Inferior gluteal artery
. First perforating artery of the profunda femoris

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The medial femoral circumflex artery (MFCA) provides the predominant blood supply to the adult femoral head. Specifically, the deep branch of the MFCA gives rise to the posterosuperior and posteroinferior retinacular vessels, which are the main sources of perfusion. The lateral circumflex artery and artery of the ligamentum teres contribute minimally in adults.

Question 14295

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for venous thromboembolism (VTE) prophylaxis following major orthopedic adult reconstruction surgery. What is its specific mechanism of action within the coagulation cascade?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via complexing with antithrombin III
. Direct and selective inhibition of Factor Xa
. Inhibition of the vitamin K epoxide reductase enzyme
. Irreversible antagonism of the P2Y12 ADP receptor on platelets

Correct Answer & Explanation

. Direct and selective inhibition of Factor Xa

Explanation

Rivaroxaban is an oral anticoagulant that functions as a direct, highly selective inhibitor of Factor Xa. Unlike low-molecular-weight heparins (LMWH) and fondaparinux, which require antithrombin III to indirectly inhibit factor Xa, rivaroxaban binds directly to the active site of Factor Xa, interrupting the common pathway of the coagulation cascade.

Question 14296

Topic: Biology, Genetics & Bone Healing

In the pathophysiology of Rheumatoid Arthritis, inflammatory cytokines drive joint destruction. Which cytokine is primarily responsible for inducing the robust expression of RANKL on synovial fibroblasts, thereby promoting aggressive osteoclast-mediated marginal bone erosions?

. IL-10
. TGF-beta
. TNF-alpha
. IL-4
. Interferon-gamma

Correct Answer & Explanation

. TNF-alpha

Explanation

TNF-alpha is a master pro-inflammatory cytokine in the pathogenesis of Rheumatoid Arthritis. It powerfully stimulates synovial fibroblasts and macrophages to express RANKL, which is the primary driver of osteoclastogenesis and the subsequent characteristic marginal bone erosions seen in the disease.

Question 14297

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what maximum percentage of interfragmentary strain allows for the direct formation of lamellar bone during fracture healing?

. 1%
. 2%
. 10%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Under Perren's strain theory, lamellar bone can only form when the interfragmentary strain is less than 2%. Cartilage can tolerate up to 10% strain, and granulation tissue can tolerate up to 100% strain before tearing.

Question 14298

Topic: 1. General Principles & Basic Science

Which of the following alterations to a cortical screw design most significantly increases its pullout strength?

. Increasing the inner root diameter
. Decreasing the thread pitch
. Decreasing the outer thread diameter
. Changing the thread profile from a V-shape to a square
. Using a cannulated screw design

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the outer thread diameter and the length of thread engagement, and inversely proportional to thread pitch. Decreasing the thread pitch increases the number of threads engaged in the cortex, thereby increasing pullout strength.

Question 14299

Topic: Biology, Genetics & Bone Healing

A 12-year-old child presents with recurrent fractures and is noted to have a "rugger jersey" spine on radiographs. Genetic testing reveals a mutation in the carbonic anhydrase II gene. What is the primary cellular dysfunction in this disorder?

. Failure of osteoblast differentiation
. Defective osteoclast ruffled border sealing
. Inability of osteoclasts to acidify the resorption pit
. Abnormal collagen cross-linking by lysyl oxidase
. Overactivity of tissue-nonspecific alkaline phosphatase

Correct Answer & Explanation

. Inability of osteoclasts to acidify the resorption pit

Explanation

Osteopetrosis is characterized by non-functioning osteoclasts. The carbonic anhydrase II mutation prevents the generation of hydrogen ions necessary to acidify the Howship lacuna (resorption pit), leading to dense but brittle bones.

Question 14300

Topic: 1. General Principles & Basic Science

During the stance phase of gait, a patient demonstrates a sudden backward thrust of the trunk immediately following heel strike. Which nerve is most likely compromised?

. Superior gluteal nerve
. Inferior gluteal nerve
. Femoral nerve
. Obturator nerve
. Tibial nerve

Correct Answer & Explanation

. Inferior gluteal nerve

Explanation

A backward thrust of the trunk at heel strike describes a gluteus maximus lurch, caused by weakness of the gluteus maximus muscle. This muscle is exclusively innervated by the inferior gluteal nerve.

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