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1. General Principles & Basic Science MCQs

Practice Set 680 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 13581

Topic: Biology, Genetics & Bone Healing

Which of the following scenarios best describes the mechanism of primary bone healing (direct bone healing)?

. Healing via endochondral ossification
. Formation of a robust soft callus followed by a hard callus
. Healing achieved with functional cast bracing
. Intramembranous ossification with cutting cones crossing the fracture site without callus formation
. Healing stimulated by controlled micromotion at the fracture site

Correct Answer & Explanation

. Intramembranous ossification with cutting cones crossing the fracture site without callus formation

Explanation

Primary (direct) bone healing occurs with absolute stability (e.g., rigid compression plating) and anatomic reduction. It bypasses soft callus formation entirely. Osteoclasts create cutting cones that cross the fracture line, followed by osteoblasts laying down lamellar bone directly via intramembranous ossification.

Question 13582

Topic: Biomechanics & Biomaterials

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment. Which of the following combinations of orthopedic implants is most likely to undergo severe galvanic corrosion and is strictly contraindicated?

. Cobalt-chromium alloy and Titanium alloy
. Titanium alloy and Tantalum
. Zirconium and Titanium alloy
. 316L Stainless steel and Titanium alloy
. Cobalt-chromium alloy and Tantalum

Correct Answer & Explanation

. 316L Stainless steel and Titanium alloy

Explanation

Mixing 316L stainless steel and titanium alloy creates a strong galvanic cell due to their disparate positions on the anodic/cathodic index. Titanium is highly noble (cathodic) and stainless steel is relatively anodic, leading to rapid, severe corrosion of the stainless steel.

Question 13583

Topic: Surgical Anatomy & Approaches

A 70-year-old woman undergoes a primary total hip arthroplasty via a posterior approach. Postoperatively, she has a profound foot drop and absent sensation over the anterolateral leg and dorsum of the foot. Plantar flexion and foot inversion are completely intact. Which specific nerve branch was most likely injured?

. Common peroneal division of the sciatic nerve
. Tibial division of the sciatic nerve
. Femoral nerve
. Superior gluteal nerve
. Obturator nerve

Correct Answer & Explanation

. Common peroneal division of the sciatic nerve

Explanation

The sciatic nerve has two distinct divisions. The common peroneal (fibular) division is lateral and more firmly tethered, making it significantly more susceptible to stretch or retractor injury during hip surgery. Injury results in foot drop (weak dorsiflexion/eversion) and sensory loss on the foot dorsum. Intact plantar flexion and inversion indicate the tibial division is spared.

Question 13584

Topic: 1. General Principles & Basic Science

The pullout strength of a pedicle screw is most significantly increased by increasing which of the following screw parameters?

. Inner (root) diameter
. Outer (thread) diameter
. Pitch
. Thread length
. Lead

Correct Answer & Explanation

. Outer (thread) diameter

Explanation

Pullout strength is determined by the formula: F = S * L * pi * D, where S is the shear strength of the bone, L is the length of thread engagement, and D is the outer (thread) diameter. Thus, increasing the outer diameter has the most profound effect on increasing pullout strength.

Question 13585

Topic: Biology, Genetics & Bone Healing

A 65-year-old man with Paget's disease of bone is started on alendronate. Which of the following describes the primary cellular mechanism of action of this medication?

. Inhibition of RANKL
. Binding to sclerostin
. Inhibition of farnesyl pyrophosphate synthase
. Stimulation of osteoblast apoptosis
. Activation of the calcium-sensing receptor

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This disrupts osteoclast intracellular signaling, impairs their ruffled border formation, and induces osteoclast apoptosis.

Question 13586

Topic: Infection, Pharmacology & VTE
A 2-year-old boy presents with a 2-day history of refusal to bear weight on his right leg, a fever of 38.5°C, and an ESR of 55 mm/hr. Joint aspiration yields purulent fluid. Culturing the fluid on traditional solid agar fails to grow organisms, but growth is observed in liquid BACTEC blood culture bottles. What is the most likely pathogen?
. Staphylococcus aureus
. Streptococcus pyogenes
. Kingella kingae
. Haemophilus influenzae type B
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is increasingly recognized as a leading cause of septic arthritis in children aged 6 months to 4 years. It is difficult to grow on standard solid media and requires inoculation into liquid blood culture vials (e.g., BACTEC) for optimal detection.

Question 13587

Topic: 1. General Principles & Basic Science

Which of the following structural zones of articular cartilage contains the highest concentration of water and predominantly parallel-aligned collagen fibers?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains the highest water content (approx. 80%), the lowest proteoglycan content, and densely packed collagen fibers aligned parallel to the joint surface to resist shear forces.

Question 13588

Topic: Biology, Genetics & Bone Healing

During the proliferative phase of secondary fracture healing, the differentiation of mesenchymal stem cells into chondrocytes to form a soft callus is primarily driven by which environmental factor?

. Hyperoxia
. Low pH (acidosis)
. High tissue strain and hypoxia
. Mechanical absolute stability
. High levels of sclerostin

Correct Answer & Explanation

. High tissue strain and hypoxia

Explanation

Secondary fracture healing occurs via endochondral ossification, which is driven by an environment of relative hypoxia and higher mechanical strain. Hypoxia induces Hypoxia-Inducible Factor 1-alpha (HIF-1a), which promotes chondrogenesis and angiogenesis.

Question 13589

Topic: Biology, Genetics & Bone Healing

In the use of bone graft materials, demineralized bone matrix (DBM) possesses which of the following biological properties?

. Osteoconductive only
. Osteoinductive only
. Osteogenic only
. Osteoconductive and osteoinductive
. Osteoinductive and osteogenic

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

Demineralized bone matrix (DBM) provides a collagenous scaffold for new bone growth (osteoconductive) and contains bone morphogenetic proteins (BMPs) that stimulate the differentiation of osteoprogenitor cells (osteoinductive). It lacks live viable cells, so it is not osteogenic.

Question 13590

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is commonly used in total joint arthroplasty. The addition of barium sulfate to PMMA serves what specific purpose?

. Increases compressive strength
. Increases porosity for bone ingrowth
. Acts as a radiopacifier
. Delays the setting time
. Acts as an antibiotic eluter

Correct Answer & Explanation

. Acts as a radiopacifier

Explanation

Barium sulfate (or zirconium dioxide) is added to PMMA to act as a radiopacifier, allowing the cement mantle to be visualized on postoperative radiographs. Its addition actually slightly decreases the mechanical strength of the cement.

Question 13591

Topic: Surgical Anatomy & Approaches

During an arthroscopic Bankart repair, the surgeon places a suture anchor at the 5 o'clock position on the anterior glenoid rim. Which nerve is most at risk of injury if the drill penetrates too deeply at this location?

. Suprascapular nerve
. Axillary nerve
. Musculocutaneous nerve
. Radial nerve
. Long thoracic nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

The axillary nerve courses directly inferior and anterior to the shoulder joint capsule. It is located closest to the inferior glenoid rim (near the 6 o'clock position), making it highly vulnerable during anteroinferior anchor placement (e.g., 5 o'clock position) for a Bankart repair.

Question 13592

Topic: Biomechanics & Biomaterials

A major advantage of using titanium alloy (Ti-6Al-4V) over cobalt-chromium (Co-Cr) for the femoral stem in cementless total hip arthroplasty is related to its mechanical properties. Which of the following best describes this advantage?

. Higher modulus of elasticity reducing stress shielding
. Lower modulus of elasticity reducing stress shielding
. Greater wear resistance at the bearing surface
. Higher yield strength preventing stem fracture
. Increased resistance to galvanic corrosion

Correct Answer & Explanation

. Lower modulus of elasticity reducing stress shielding

Explanation

Titanium alloy has a lower modulus of elasticity (closer to that of cortical bone) compared to cobalt-chromium. This decreases the stiffness mismatch between the implant and bone, significantly minimizing stress shielding.

Question 13593

Topic: Biology, Genetics & Bone Healing

A 40-year-old male undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate (DCP) with absolute stability. Which type of bone healing will predominantly occur?

. Endochondral ossification
. Primary (Haversian) bone healing
. Secondary bone healing with callus formation
. Intramembranous ossification alone
. Fibrous union

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Absolute stability achieved through rigid internal fixation prevents interfragmentary motion, suppressing callus formation. This leads to primary (Haversian) bone healing, where osteoclasts form cutting cones directly across the fracture, followed by osteoblast deposition.

Question 13594

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft options possesses purely osteoconductive properties without any osteoinductive or osteogenic capabilities?

. Autologous iliac crest bone graft
. Demineralized bone matrix (DBM)
. Calcium phosphate ceramics
. Bone morphogenetic protein-2 (BMP-2)
. Reamer-irrigator-aspirator (RIA) graft

Correct Answer & Explanation

. Calcium phosphate ceramics

Explanation

Calcium phosphate ceramics act merely as a scaffold for new bone growth, meaning they are strictly osteoconductive. Autograft is osteogenic, osteoinductive, and osteoconductive, while DBM and BMP-2 are primarily osteoinductive.

Question 13595

Topic: Biology, Genetics & Bone Healing

In a patient presenting with aseptic loosening 10 years after an uncemented total hip arthroplasty, the primary driver of periprosthetic osteolysis is the activation of macrophages. Which signaling molecule is ultimately overexpressed by these cells to induce bone resorption?

. Osteoprotegerin (OPG)
. Bone morphogenetic protein-7 (BMP-7)
. Transforming growth factor-beta (TGF-b)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Interleukin-10 (IL-10)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Phagocytosis of polyethylene wear debris by macrophages stimulates the release of pro-inflammatory cytokines like TNF-alpha and IL-1. This leads to the overexpression of RANKL, which drives osteoclast differentiation and subsequent periprosthetic osteolysis.

Question 13596

Topic: 1. General Principles & Basic Science
A 22-year-old rugby player presents with an inability to actively flex the distal interphalangeal (DIP) joint of his ring finger after grabbing an opponent's jersey. Radiographs reveal a bony avulsion retracted into the palm. According to the Leddy and Packer classification, what type of injury is this?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type I

Explanation

This is a Type I Leddy-Packer flexor digitorum profundus (FDP) avulsion, where the tendon retracts into the palm (Zone II), compromising the vincula and blood supply. It requires urgent surgical repair (within 7-10 days) to prevent tendon necrosis.

Question 13597

Topic: 1. General Principles & Basic Science

Regarding the ultrastructural composition of normal articular cartilage, how does the organization of Type II collagen fibers and chondrocyte morphology change in the deep (radial) zone compared to the superficial (tangential) zone?

. Fibers are parallel to the joint surface; chondrocytes are flattened
. Fibers are parallel to the joint surface; chondrocytes are spherical
. Fibers are perpendicular to the joint surface; chondrocytes are arranged in columns
. Fibers are randomly oriented; chondrocytes are absent
. Fibers are perpendicular to the joint surface; chondrocytes are flattened

Correct Answer & Explanation

. Fibers are perpendicular to the joint surface; chondrocytes are arranged in columns

Explanation

In the deep (radial) zone of articular cartilage, Type II collagen fibers are oriented perpendicularly to the joint surface to resist compressive loads. The chondrocytes in this zone are typically arranged in vertical columns.

Question 13598

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a destructive, eccentrically located lytic lesion in the distal femur epimetaphysis. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered, denosumab may be used. What is its specific mechanism of action?

. Inhibits the formation of the RANK/RANKL complex
. Directly induces apoptosis of the neoplastic mononuclear cells
. Inhibits vascular endothelial growth factor (VEGF)
. Binds directly to osteoclasts to inhibit their ruffled border formation
. Promotes osteoblast differentiation via Wnt signaling

Correct Answer & Explanation

. Inhibits the formation of the RANK/RANKL complex

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on the surface of osteoclast precursors. This inhibits the recruitment and activation of the reactive multinucleated giant cells responsible for the aggressive osteolysis in Giant Cell Tumors.

Question 13599

Topic: Infection, Pharmacology & VTE

During a primary total knee arthroplasty for severe varus osteoarthritis, the knee remains tight medially in both flexion and extension after initial bony cuts. Which sequence of soft tissue release is most appropriate to balance the knee?

. Deep MCL, then posteromedial corner, then superficial MCL
. Superficial MCL, then pes anserinus, then PCL
. Posteromedial corner, then semimembranosus, then deep MCL
. Popliteus, then lateral collateral ligament, then iliotibial band
. PCL, then medial head of gastrocnemius, then superficial MCL

Correct Answer & Explanation

. Deep MCL, then posteromedial corner, then superficial MCL

Explanation

To correct a fixed varus deformity, step-wise medial release is performed starting with osteophytes, followed by the deep medial collateral ligament (MCL). If it remains tight, the release progresses to the posteromedial corner/capsule, and finally the superficial MCL and pes anserinus if necessary.

Question 13600

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the intracellular signaling pathway utilized by Bone Morphogenetic Protein-2 (BMP-2) after it binds to its cell surface receptor?

. Activation of JAK/STAT signaling pathway
. Activation of the SMAD 1, 5, 8 complex
. Inhibition of the Wnt/beta-catenin pathway
. Activation of the SMAD 2, 3 complex
. Direct phosphorylation of RUNX2 by a tyrosine kinase

Correct Answer & Explanation

. Activation of the SMAD 1, 5, 8 complex

Explanation

BMPs (such as BMP-2 and BMP-7) bind to serine/threonine kinase receptors on the cell surface. This binding leads to the intracellular phosphorylation and activation of receptor-regulated SMADs, specifically SMADs 1, 5, and 8. These then form a complex with the co-SMAD (SMAD 4) to translocate into the nucleus and upregulate osteogenic genes like RUNX2. SMADs 2 and 3 are typically activated by TGF-beta, not BMPs.

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