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1. General Principles & Basic Science MCQs

Practice Set 230 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 4581

Topic: 1. General Principles & Basic Science

In the biomechanical design of a pedicle screw, which of the following modifications most effectively increases the screw's pullout strength in osteoporotic bone?

. Decreasing the thread density (pitch length)
. Increasing the major (outer) diameter of the screw
. Increasing the minor (inner core) diameter while maintaining the major diameter
. Using a partially threaded rather than fully threaded screw
. Decreasing the length of thread engagement

Correct Answer & Explanation

. Increasing the major (outer) diameter of the screw

Explanation

Pullout strength of a screw is primarily determined by the major (outer) diameter of the screw, the length of thread engagement, thread shape, and bone density. The equation for pullout strength shows it is directly proportional to the major diameter. Increasing the minor (core) diameter without changing the major diameter actually decreases the volume of bone trapped between the threads, thereby decreasing pullout strength. Decreasing the pitch length (which increases the thread density, meaning more threads per inch) also increases pullout strength, but increasing the major diameter is the most powerful design modification to improve pullout strength.

Question 4582

Topic: Infection, Pharmacology & VTE
A 55-year-old male with long-standing, poorly controlled type 2 diabetes presents with a red, hot, swollen right foot. He denies any recent trauma, fevers, or systemic illness. Laboratory studies reveal a normal white blood cell count, ESR of 25 mm/h, and CRP of 1.0 mg/L. Radiographs demonstrate soft tissue swelling, profound joint subluxation at the tarsometatarsal joints, and bony fragmentation without focal osteopenia. What is the most appropriate initial treatment?
. Intravenous antibiotics and surgical debridement
. Oral antibiotics and non-weight bearing
. Immediate open reduction and internal fixation of the midfoot
. Total contact casting and strict non-weight bearing
. Primary below-knee amputation

Correct Answer & Explanation

. Total contact casting and strict non-weight bearing

Explanation

This patient presents with Stage I (Developmental/Fragmentation phase) Charcot arthropathy, characterized by a red, hot, swollen foot, joint laxity, and radiographic fragmentation and debris. Normal inflammatory markers and lack of systemic signs help distinguish this from acute osteomyelitis or septic arthritis. The gold standard initial treatment for an acute Charcot neuroarthropathy is immobilization and offloading, typically achieved via a total contact cast, until the active inflammatory phase subsides and the bones begin to consolidate (Stage II/III).

Question 4583

Topic: Biology, Genetics & Bone Healing

Fracture healing can occur via endochondral or intramembranous ossification. Intramembranous ossification occurs without a cartilaginous intermediate and is primarily seen in flat bones and during rigid plate fixation (primary bone healing). Which of the following transcription factors is the critical master regulator that directs multipotent mesenchymal stem cells down the osteoblastic lineage during intramembranous bone formation?

. SOX9
. MyoD
. RUNX2 (Cbfa1)
. PPAR-gamma
. HIF-1 alpha

Correct Answer & Explanation

. RUNX2 (Cbfa1)

Explanation

RUNX2 (also known as Cbfa1) is the master transcription factor required for osteoblast differentiation and is absolutely essential for both intramembranous and endochondral bone formation. Mice lacking RUNX2 are devoid of osteoblasts and completely lack bone. SOX9 is the master regulator for chondrocyte differentiation. PPAR-gamma regulates adipocyte differentiation. MyoD regulates myoblast differentiation.

Question 4584

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with known multiple myeloma presents with escalating back pain. Radiographs reveal diffuse osteopenia and multiple 'punched-out' lytic lesions in her vertebral bodies. The profound osteolysis seen in multiple myeloma is primarily driven by an imbalance in bone remodeling. Which of the following factors is directly secreted by myeloma cells to upregulate osteoclast activity via the RANK/RANKL pathway?

. Osteoprotegerin (OPG)
. Transforming growth factor-beta (TGF-beta)
. Macrophage inflammatory protein-1 alpha (MIP-1 alpha)
. Bone morphogenetic protein-2 (BMP-2)
. Parathyroid hormone (PTH)

Correct Answer & Explanation

. Macrophage inflammatory protein-1 alpha (MIP-1 alpha)

Explanation

Multiple myeloma bone lesions are characterized by uncoupled bone remodeling: increased osteoclast activity and markedly decreased osteoblast activity. Myeloma cells directly secrete several osteoclast activating factors, prominently Macrophage Inflammatory Protein-1 alpha (MIP-1 alpha) and RANK Ligand (RANKL). They also suppress osteoblastogenesis via Dickkopf-1 (DKK-1) and sclerostin. Osteoprotegerin (OPG) acts as a decoy receptor for RANKL and inhibits osteoclast activity; its levels are typically decreased in myeloma.

Question 4585

Topic: Biology, Genetics & Bone Healing

Wnt/beta-catenin pathway activation in mesenchymal stem cells directly promotes differentiation into which of the following cell lineages?

. Chondrocytes
. Osteoblasts
. Osteoclasts
. Adipocytes
. Fibroblasts

Correct Answer & Explanation

. Osteoblasts

Explanation

Activation of the Wnt/beta-catenin signaling pathway in multipotent mesenchymal stem cells strongly directs them toward the osteoblastic lineage while simultaneously inhibiting chondrogenic and adipogenic differentiation. Beta-catenin translocates to the nucleus and interacts with TCF/LEF transcription factors to upregulate genes such as Runx2.

Question 4586

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE) is associated with which of the following material property changes?
. Increased yield strength
. Decreased wear resistance
. Decreased fatigue crack propagation resistance
. Increased ductility
. Increased ultimate tensile strength

Correct Answer & Explanation

. Decreased fatigue crack propagation resistance

Explanation

Cross-linking of polyethylene significantly improves its wear resistance, which is highly beneficial for the longevity of THA bearings. However, this process alters the mechanical properties of the material, leading to decreased fatigue crack propagation resistance, reduced ductility, decreased ultimate tensile strength, and decreased yield strength.

Question 4587

Topic: 1. General Principles & Basic Science

Biomechanical studies of the flexor tendon pulley system of the fingers indicate that which combination of pulleys is absolutely essential to prevent bowstringing and preserve full digital flexion?

. A1 and A2
. A2 and A3
. A2 and A4
. A3 and A5
. A1 and A5

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the major biomechanical components of the flexor tendon sheath in the digits. They arise from the periosteum of the proximal and middle phalanges, respectively. Loss of both the A2 and A4 pulleys leads to significant bowstringing, reduced excursion efficiency, and loss of full digital flexion.

Question 4588

Topic: 1. General Principles & Basic Science

Which of the following antibiotics is NOT typically mixed with polymethylmethacrylate (PMMA) bone cement due to its thermolability and inability to withstand the exothermic curing process?

. Vancomycin
. Tobramycin
. Gentamicin
. Erythromycin
. Tetracycline

Correct Answer & Explanation

. Vancomycin

Explanation

Antibiotics added to PMMA must be heat-stable because the polymerization of PMMA is highly exothermic (reaching temperatures > 80-100ยฐC). Aminoglycosides (tobramycin, gentamicin), vancomycin, and erythromycin are heat-stable and commonly used. Tetracyclines and most beta-lactams are heat-labile and will be inactivated by the curing process.

Question 4589

Topic: Biomechanics & Biomaterials

In the context of orthopedic biomechanics, which of the following accurately defines the 'Young's modulus' of a material?

. The point at which the material permanently deforms
. The area under the stress-strain curve representing toughness
. The slope of the stress-strain curve in the elastic region
. The maximum stress a material can withstand before failure
. The point of total structural failure

Correct Answer & Explanation

. The slope of the stress-strain curve in the elastic region

Explanation

Young's modulus (or elastic modulus) is a measure of the stiffness of a solid material. It is defined mathematically as the slope of the linear, elastic portion of the stress-strain curve. The higher the Young's modulus, the stiffer the material.

Question 4590

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with pain in her distal radius. Imaging reveals an eccentric, lytic epiphyseal lesion. Biopsy shows characteristic multinucleated giant cells.

Which targeted biologic therapy is FDA-approved for unresectable or recurrent cases of this specific bone tumor?

. Imatinib
. Denosumab
. Rituximab
. Doxorubicin
. Methotrexate

Correct Answer & Explanation

. Denosumab

Explanation

The presentation and histology describe a Giant Cell Tumor (GCT) of bone. The neoplastic stromal cells in GCT express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells). Denosumab is a monoclonal antibody against RANKL and is an effective targeted therapy for locally advanced, unresectable, or recurrent GCTs.

Question 4591

Topic: Biology, Genetics & Bone Healing

A 30-year-old female undergoes biopsy of an eccentric, lytic lesion in the distal femoral epiphysis. Histology reveals numerous multinucleated giant cells in a background of mononuclear stromal cells. She is initiated on denosumab therapy prior to planned surgical intervention. What is the specific mechanism of action of denosumab in treating this lesion?

. It binds to the RANK receptor on osteoclasts, preventing activation.
. It binds directly to RANKL, preventing it from interacting with RANK on osteoclasts.
. It serves as a recombinant analog of osteoprotegerin (OPG), directly destroying neoplastic cells.
. It inhibits Vascular Endothelial Growth Factor (VEGF), leading to tumor necrosis.
. It induces apoptosis primarily in the multinucleated giant cells.

Correct Answer & Explanation

. It binds directly to RANKL, preventing it from interacting with RANK on osteoclasts.

Explanation

Giant cell tumor of bone (GCTB) is characterized by neoplastic mononuclear stromal cells that express high levels of Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL). This RANKL binds to the RANK receptor on osteoclast precursors, leading to the recruitment of the numerous, non-neoplastic multinucleated giant cells that cause massive bone resorption. Denosumab is a humanized monoclonal antibody that binds directly to RANKL (not the RANK receptor), preventing it from binding to RANK, thereby inhibiting osteoclast-mediated bone destruction.

Question 4592

Topic: Biology, Genetics & Bone Healing
A 35-year-old male is recovering from a closed diaphyseal tibial fracture treated with a cast. Secondary bone healing is occurring via endochondral ossification, progressing through the soft callus stage. Which of the following is the predominant collagen type synthesized in the soft callus phase of fracture healing?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Secondary bone healing involves formation of a callus. The soft callus phase is characterized by the formation of cartilaginous tissue bridging the fracture site, which stabilizes the fracture and acts as a scaffold. Because this tissue is essentially fibrocartilage and hyaline cartilage, Type II collagen is the predominant collagen type. Type X collagen is produced later by hypertrophic chondrocytes during endochondral ossification. Type I collagen predominates in mature bone (the hard callus phase).

Question 4593

Topic: Biology, Genetics & Bone Healing

A 68-year-old female presents with atraumatic thigh pain. She has been taking oral alendronate for 8 years. Radiographs reveal cortical thickening of the lateral cortex of the subtrochanteric femur and a transverse fracture.

Which of the following best describes the pathomechanism of this injury?

. Overactivity of osteoblasts
. Accumulation of microdamage due to suppressed targeted remodeling
. Inadequate mineralization of osteoid
. Increased osteoclastic resorption leading to weakened woven bone
. Mutation in COL1A1 gene

Correct Answer & Explanation

. Accumulation of microdamage due to suppressed targeted remodeling

Explanation

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption. Long-term use severely suppresses bone turnover, preventing the targeted remodeling of normal microdamage. This accumulation of microdamage leads to atypical femoral fractures, classically presenting with lateral cortical thickening and a transverse or short oblique fracture pattern.

Question 4594

Topic: Infection, Pharmacology & VTE

A 40-year-old male presents with an acutely swollen and painful knee. Arthrocentesis yields cloudy yellow fluid. Fluid analysis reveals a white blood cell count of 65,000 cells/ยตL with 85% polymorphonuclear leukocytes (PMNs). Gram stain is negative. Which of the following is the most likely diagnosis?

. Osteoarthritis
. Traumatic hemarthrosis
. Septic arthritis
. Lyme arthritis
. Gout

Correct Answer & Explanation

. Septic arthritis

Explanation

Synovial fluid analysis is critical for distinguishing joint pathologies. Fluid with >50,000 WBC/ยตL and >75% PMNs is highly suspicious for septic arthritis. Although crystalline arthropathies (gout, pseudogout) and severe inflammatory arthropathies can occasionally produce counts this high, septic arthritis must be the presumed diagnosis until proven otherwise. Note: Lyme arthritis can also present with very high WBC counts (averaging 60,000 cells/ยตL), but septic arthritis remains the most urgent and likely diagnosis in an acutely swollen, hot joint without a specific tick exposure history.

Question 4595

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is commonly used to reduce wear. Which of the following mechanical properties is significantly decreased as a direct result of the irradiation used to create highly cross-linked polyethylene?
. Abrasive wear resistance
. Oxidation resistance
. Fatigue strength
. Elastic modulus
. Hardness

Correct Answer & Explanation

. Fatigue strength

Explanation

Irradiation is used to cross-link UHMWPE chains, which significantly improves its adhesive and abrasive wear resistance. However, cross-linking decreases certain mechanical properties, particularly fatigue strength, yield strength, ultimate tensile strength, and ductility. To prevent oxidation from free radicals generated during irradiation, the material is typically remelted, annealed, or blended with an antioxidant like vitamin E.

Question 4596

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, which type of tissue is expected to form within a fracture gap if the mechanical strain environment is maintained between 2% and 10%?

. Primary osteonal bone
. Granulation tissue
. Hyaline cartilage
. Lamellar bone
. Woven bone and cartilage (Callus)

Correct Answer & Explanation

. Woven bone and cartilage (Callus)

Explanation

Perren's strain theory dictates the type of tissue that can survive and differentiate in a fracture gap based on deformation (strain).- Strain < 2%: Allows for primary bone healing (lamellar bone formation) without a callus.- Strain between 2% and 10%: Tolerated by cartilage and woven bone, leading to secondary bone healing via endochondral ossification (callus formation).- Strain > 10%: Tissues tear, and only granulation tissue can survive, leading to nonunion if not stabilized.

Question 4597

Topic: Biomechanics & Biomaterials

In the context of modularity in total hip arthroplasty (THA), which of the following is the primary mechanism of failure associated with trunnionosis at the head-neck junction?

. Galvanic corrosion due to dissimilar metals in a static environment
. Mechanically assisted crevice corrosion and fretting
. Pitting corrosion from high chloride physiological fluids
. Intergranular corrosion at grain boundaries
. Stress corrosion cracking from cyclic loading only

Correct Answer & Explanation

. Mechanically assisted crevice corrosion and fretting

Explanation

Trunnionosis refers to wear and corrosion at the modular head-neck junction of a THA. The primary mechanism is mechanically assisted crevice corrosion (MACC), which involves a combination of fretting (micromotion between the surfaces) that disrupts the passive oxide layer, and crevice corrosion (a localized drop in pH and oxygen depletion in the crevice) once the bulk material is exposed. While galvanic corrosion can contribute when mixed metals are used (e.g., CoCr head on Ti stem), fretting and MACC are the predominant driving factors.

Question 4598

Topic: 1. General Principles & Basic Science

Which of the following statements most accurately describes the vascular anatomy and healing potential of the meniscus?

. The inner third is highly vascularized by the middle genicular artery
. The medial meniscus receives a significantly more robust blood supply than the lateral meniscus
. The blood supply penetrates from the peripheral capsule via the medial and lateral inferior genicular arteries
. Vascularity progressively increases with age, improving healing potential in older adults
. The popliteal artery provides direct terminal branches to the anterior horns of both menisci

Correct Answer & Explanation

. The blood supply penetrates from the peripheral capsule via the medial and lateral inferior genicular arteries

Explanation

The blood supply to the menisci originates from the medial, lateral, and middle genicular arteries (predominantly the inferior genicular arteries). The vessels form a perimeniscal capillary plexus within the synovial and capsular tissues. Only the peripheral 10% to 30% of the menisci (the 'red-red' zone) is vascularized in adults, making this zone capable of healing after repair. The inner portions ('white-white' zone) are avascular and rely on diffusion from synovial fluid. Vascularity actually decreases with age.

Question 4599

Topic: 1. General Principles & Basic Science

In healthy hyaline articular cartilage, which of the following macromolecular components is primarily responsible for providing the tissue with its compressive strength and stiffness?

. Type II collagen
. Aggrecan
. Type I collagen
. Fibronectin
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, a large proteoglycan, is the primary source of compressive strength in articular cartilage. It contains numerous negatively charged glycosaminoglycans (GAGs), such as chondroitin sulfate and keratan sulfate, which repel each other and attract water via the Donnan osmotic effect. This creates a swelling pressure that resists compressive loads. In contrast, the Type II collagen network provides the tensile strength and restrains the swelling pressure of the proteoglycans.

Question 4600

Topic: 1. General Principles & Basic Science
Following a primary Zone II flexor tendon repair, which of the following biological processes characterizes the 'proliferation' phase of tendon healing (typically peaking between 1 to 4 weeks post-repair)?
. Inflammatory cell infiltration, hematoma formation, and minimal tensile strength
. Maximum weakness of the repair site due to phagocytosis of necrotic tissue
. Increased collagen synthesis primarily orchestrated by epitenon and endotenon fibroblasts
. Remodeling of disorganized Type III collagen into longitudinally oriented Type I collagen
. Complete resolution of tissue edema with normalization of the extracellular matrix

Correct Answer & Explanation

. Increased collagen synthesis primarily orchestrated by epitenon and endotenon fibroblasts

Explanation

Tendon healing occurs in three phases: inflammatory (days 1-7), proliferative (days 7-21/28), and remodeling (weeks to months). During the proliferative phase, fibroblasts (from the epitenon and endotenon) migrate to the repair site and synthesize abundant Type III collagen, increasing the mass and strength of the repair. The inflammatory phase is characterized by hematoma and macrophage activity (where the tendon is weakest), and the remodeling phase is characterized by the conversion of Type III to Type I collagen and cross-linking.

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