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1. General Principles & Basic Science MCQs

Practice Set 542 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 10821

Topic: Biomechanics & Biomaterials

Trabecular metal (highly porous Tantalum) is frequently used in acetabular revision components. What is its main mechanical advantage over traditional sintered titanium bead porous coatings?

. It has a much higher modulus of elasticity, increasing rigidity
. It features extremely high porosity (up to 80%) and a very high coefficient of friction, providing excellent initial scratch fit
. It stimulates bone growth chemically via osteoinduction
. It dissolves over time, leaving only native bone
. It is completely radiolucent

Correct Answer & Explanation

. It features extremely high porosity (up to 80%) and a very high coefficient of friction, providing excellent initial scratch fit

Explanation

Tantalum trabecular metal mimics cancellous bone with high volumetric porosity (70-80%), allowing deep biologic ingrowth. Its very high coefficient of friction against host bone gives it an incredibly strong initial "scratch fit," which is crucial in revision scenarios with compromised bone stock.

Question 10822

Topic: Infection, Pharmacology & VTE

A 55-year-old female presents with bilateral knee pain. Joint aspiration yields synovial fluid analyzing for positively birefringent, rhomboid-shaped crystals. Radiographs show linear calcifications within the menisci (chondrocalcinosis). What is the diagnosis?

. Gout
. Rheumatoid arthritis
. Septic arthritis
. Pseudogout (Calcium Pyrophosphate Deposition Disease)
. Osteoarthritis

Correct Answer & Explanation

. Gout

Explanation

Pseudogout, or Calcium Pyrophosphate Deposition (CPPD) disease, is characterized by chondrocalcinosis on radiographs and positively birefringent, rhomboid-shaped crystals in the synovial fluid.

Question 10823

Topic: Surgical Anatomy & Approaches

Which of the following approaches to the hip has historically been associated with the highest risk of postoperative dislocation if careful soft-tissue repair is not performed?

. Direct Anterior (Smith-Petersen)
. Posterior (Moore/Southern)
. Anterolateral (Watson-Jones)
. Direct Lateral (Hardinge)
. Transtrochanteric

Correct Answer & Explanation

. Direct Anterior (Smith-Petersen)

Explanation

The posterior approach has historically carried the highest risk of posterior dislocation because it involves taking down the posterior capsule and short external rotators. A rigorous enhanced posterior soft-tissue repair significantly reduces this risk to levels comparable to other approaches.

Question 10824

Topic: Surgical Anatomy & Approaches

A 68-year-old man undergoes primary THA via a direct anterior approach. Postoperatively, he has weakness with active knee extension and diminished sensation over the anterior thigh. Which of the following structures was most likely injured during the surgical approach?

. Lateral femoral cutaneous nerve
. Femoral nerve
. Sciatic nerve
. Superior gluteal nerve
. Obturator nerve

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

Weakness in knee extension and anterior thigh sensory loss indicate a femoral nerve injury. In the direct anterior approach, this can occur from excessive retraction medial to the tensor fasciae latae and sartorius interval.

Question 10825

Topic: Biology, Genetics & Bone Healing

Distraction osteogenesis (Ilizarov technique) is a powerful method utilized in orthopedics for limb lengthening and deformity correction. This process primarily relies on which of the following biological mechanisms of bone formation?

. Enchondral ossification
. Intramembranous ossification
. Appositional bone growth
. Creeping substitution
. Haversian remodeling

Correct Answer & Explanation

. Enchondral ossification

Explanation

Distraction osteogenesis is characterized by direct bone formation without a cartilaginous intermediate, which is the definition of intramembranous ossification. The mechanical tension applied across the osteotomy site directly stimulates osteoblastic activity from the periosteum and endosteum.

Question 10826

Topic: Biomechanics & Biomaterials

In the manufacturing of highly cross-linked polyethylene (HXLPE) for total joint arthroplasty, gamma irradiation is used to induce cross-linking to improve wear resistance. However, this process creates free radicals. Which of the following subsequent steps is utilized to eliminate these free radicals and reduce long-term oxidation, despite causing a slight decrease in the material's fatigue strength?

. Ethylene oxide sterilization
. Cold-drawing the polymer under high tension
. Adding cobalt-chromium nanoparticles to the matrix
. Remelting the polyethylene (annealing above the melting point)
. Irradiation in an oxygen-rich environment

Correct Answer & Explanation

. Ethylene oxide sterilization

Explanation

Remelting the polyethylene above its melting point (typically around 150°C) allows free radicals created during the irradiation process to recombine and be eliminated. This prevents long-term oxidative degradation. However, it alters the crystalline structure, which slightly reduces the material's ultimate tensile strength and fatigue properties.

Question 10827

Topic: 1. General Principles & Basic Science

Normal articular cartilage is a highly specialized connective tissue. Which component of the extracellular matrix is primarily responsible for providing compressive stiffness by drawing water into the tissue via the Donnan osmotic effect?

. Type II collagen
. Type X collagen
. Aggrecan
. Decorin
. Hyaluronic acid

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant large proteoglycan in articular cartilage. Its highly negatively charged glycosaminoglycan (GAG) side chains repel each other and attract cations and water into the matrix, providing the tissue with its characteristic compressive stiffness. Type II collagen network provides the tensile strength to resist this swelling pressure.

Question 10828

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve representing the biomechanical properties of an orthopedic implant material, what specific mechanical behavior does the 'yield point' denote?

. The point at which the material physically fractures or breaks
. The maximum stress the material can withstand before necking occurs
. The total area under the curve representing the material's toughness
. The transition point from elastic deformation to plastic deformation
. The slope of the linear elastic region representing stiffness

Correct Answer & Explanation

. The transition point from elastic deformation to plastic deformation

Explanation

The yield point on a stress-strain curve marks the limit of linear elastic behavior. Beyond this specific stress level, the material begins to undergo plastic (permanent) deformation and will not return to its original shape when the load is removed.

Question 10829

Topic: Biomechanics & Biomaterials

Titanium alloys (e.g., Ti-6Al-4V) are extensively utilized in modern orthopaedic implants due to excellent biocompatibility and osseointegration properties. Compared to Cobalt-Chromium (CoCr) alloys, Titanium alloys possess which of the following distinct biomechanical profiles?

. Higher modulus of elasticity and higher fatigue strength
. Identical modulus of elasticity but higher ultimate tensile strength
. Higher modulus of elasticity and poor notch sensitivity
. Lower modulus of elasticity and excellent wear resistance
. Lower modulus of elasticity and poor wear resistance

Correct Answer & Explanation

. Lower modulus of elasticity and poor wear resistance

Explanation

Titanium alloys have a lower modulus of elasticity (closer to that of cortical bone) compared to CoCr or stainless steel, which beneficially reduces stress shielding. However, titanium is highly notch-sensitive and has notoriously poor wear properties, making it entirely unsuitable for use as an articular bearing surface in joint arthroplasty.

Question 10830

Topic: Infection, Pharmacology & VTE
A 4-year-old girl is brought to the emergency department for refusal to bear weight on her right leg and low-grade fever. To differentiate between transient synovitis and septic arthritis, the Kocher criteria are utilized. Which of the following sets of clinical findings, if all present, provides a 99% predictive probability for a diagnosis of septic arthritis?
. Non-weight-bearing, ESR > 40 mm/hr, Temperature > 38.5°C, WBC count > 12,000/mm³
. History of preceding viral illness, limp, ESR > 20 mm/hr, Temperature > 38.0°C
. Positive blood cultures, joint space widening on radiograph, elevated CRP > 2.0 mg/dL, Non-weight-bearing
. Hip held in flexion/internal rotation, normal WBC, ESR > 40 mm/hr, positive joint aspirate
. Inability to ambulate, normal inflammatory markers, normal radiographs, Temperature > 39.0°C

Correct Answer & Explanation

. Non-weight-bearing, ESR > 40 mm/hr, Temperature > 38.5°C, WBC count > 12,000/mm³

Explanation

The classic Kocher criteria are used to differentiate septic arthritis from transient synovitis in children. The four criteria are: 1) Non-weight-bearing on the affected side, 2) Erythrocyte sedimentation rate (ESR) > 40 mm/hr, 3) Fever > 38.5°C (101.3°F), and 4) Serum white blood cell (WBC) count > 12,000/mm³. The presence of all four criteria yields a 99% predicted probability of septic arthritis.

Question 10831

Topic: Biology, Genetics & Bone Healing

A 48-year-old female with a history of celiac disease presents with generalized, diffuse bone pain and muscle weakness. Radiographs reveal bilateral pseudo-fractures (Looser zones) in the femoral neck. Which of the following serum laboratory profiles is most characteristic of her underlying condition?

. Elevated Calcium, Decreased Phosphorus, Elevated Alkaline Phosphatase
. Decreased Calcium, Decreased Phosphorus, Elevated Alkaline Phosphatase
. Normal Calcium, Normal Phosphorus, Elevated Alkaline Phosphatase
. Elevated Calcium, Elevated Phosphorus, Normal Alkaline Phosphatase
. Decreased Calcium, Elevated Phosphorus, Normal Alkaline Phosphatase

Correct Answer & Explanation

. Elevated Calcium, Decreased Phosphorus, Elevated Alkaline Phosphatase

Explanation

The patient has osteomalacia, likely secondary to malabsorption from celiac disease leading to Vitamin D deficiency. The classic laboratory profile for osteomalacia features low-to-normal serum calcium, low phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (secondary hyperparathyroidism).

Question 10832

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct inhibition of thrombin (Factor IIa)
. Inhibition of Vitamin K epoxide reductase
. Direct inhibition of Factor Xa
. Activation of antithrombin III
. Inhibition of ADP-induced platelet aggregation

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that act by directly inhibiting Factor Xa in the coagulation cascade. Dabigatran is a direct thrombin inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Low-molecular-weight heparin primarily activates antithrombin III to inhibit Factor Xa.

Question 10833

Topic: 1. General Principles & Basic Science
During the reparative phase of tendon healing, fibroblasts synthesize a temporary extracellular matrix. Which type of collagen predominates in this early provisional matrix before being remodeled into the mature tendon structure?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type III

Explanation

In the early proliferative/reparative phase of tendon healing, fibroblasts rapidly synthesize Type III collagen. During the remodeling phase, this weaker, disorganized Type III collagen is gradually replaced by stronger, highly organized Type I collagen, which makes up the bulk of mature healthy tendons.

Question 10834

Topic: Biology, Genetics & Bone Healing

A 45-year-old malnourished male presents with generalized joint aches, perifollicular hemorrhages, and poor wound healing. He is diagnosed with a severe vitamin deficiency. At a cellular level, this deficiency primarily impairs which step of collagen synthesis?

. Cleavage of procollagen C-terminals
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Glycosylation of pro-alpha-chain hydroxylysine residues
. Assembly of the triple helix

Correct Answer & Explanation

. Cleavage of procollagen C-terminals

Explanation

The patient has scurvy (Vitamin C deficiency). Vitamin C is an essential cofactor for prolyl hydroxylase and lysyl hydroxylase. Without it, the hydroxylation of proline and lysine residues in the rough endoplasmic reticulum is impaired, preventing proper hydrogen bonding and stabilization of the collagen triple helix.

Question 10835

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, which of the following tissues is capable of tolerating the highest percentage of interfragmentary strain before rupturing?

. Lamellar bone
. Woven bone
. Fibrocartilage
. Granulation tissue
. Hyaline cartilage

Correct Answer & Explanation

. Lamellar bone

Explanation

Perren's strain theory dictates that tissues will only form in a fracture gap if the interfragmentary strain is lower than the strain tolerance of that specific tissue. Granulation tissue can tolerate up to 100% strain, fibrocartilage tolerates roughly 10-15%, and solid bone (woven/lamellar) tolerates very little strain (<2%).

Question 10836

Topic: Biology, Genetics & Bone Healing

A 32-year-old female with an aggressive giant cell tumor of the distal radius is started on denosumab therapy prior to surgical intervention. This monoclonal antibody exerts its therapeutic effect by directly binding to and inhibiting which of the following?

. RANK
. RANKL
. Osteoprotegerin
. TNF-alpha
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. RANK

Explanation

Denosumab is a monoclonal antibody that mimics the action of osteoprotegerin (OPG) by binding directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor on osteoclast precursors, thereby inhibiting osteoclast formation, function, and survival.

Question 10837

Topic: Biology, Genetics & Bone Healing

During the incorporation of a massive structural cortical allograft, the process by which osteoclasts resorb the dead bone graft while osteoblasts simultaneously lay down new viable host bone is termed:

. Osteoinduction
. Osteogenesis
. Creeping substitution
. Osteoconduction
. Callus distraction

Correct Answer & Explanation

. Osteoinduction

Explanation

Creeping substitution is the histomorphologic process of bone graft incorporation where simultaneous osteoclastic resorption of the graft and osteoblastic deposition of new viable host bone occurs. Cortical grafts undergo this process much slower than cancellous grafts.

Question 10838

Topic: Biology, Genetics & Bone Healing

A 68-year-old male is evaluated for an enlarging hat size and right hip pain. Radiographs reveal cortical thickening and coarse trabeculae in the pelvis. A bone biopsy is obtained. Which of the following histologic findings is the hallmark of the mixed phase of this disease?

. Woven bone with prominent osteoblastic rimming
. Mosaic pattern of lamellar bone with prominent, haphazard cement lines
. Sheets of malignant spindle cells producing osteoid matrix
. Non-mineralized osteoid seams surrounding mineralized trabeculae
. Abundant chondroid matrix with enchondral ossification

Correct Answer & Explanation

. Woven bone with prominent osteoblastic rimming

Explanation

The patient has Paget's disease of bone. The classic histologic hallmark of the mixed (intermediate) phase of Paget's disease is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with prominent, disorganized cement lines, reflecting chaotic and rapid cycles of osteoclastic resorption and osteoblastic bone formation.

Question 10839

Topic: 1. General Principles & Basic Science

A 9-year-old boy living in Connecticut presents with an acute effusion of his right knee. A joint aspiration demonstrates 45,000 WBCs/mm3. Serologic testing is positive for Borrelia burgdorferi. What is the primary vector responsible for transmitting this pathogen?

. Amblyomma americanum
. Ixodes scapularis
. Dermacentor variabilis
. Culex pipiens
. Aedes aegypti

Correct Answer & Explanation

. Amblyomma americanum

Explanation

Lyme disease is caused by the spirochete Borrelia burgdorferi and is transmitted by the bite of the black-legged tick, Ixodes scapularis (in the northeastern and midwestern US) or Ixodes pacificus (on the West Coast).

Question 10840

Topic: Biomechanics & Biomaterials

A 65-year-old patient presents with acute, severe pain and swelling in the right knee. Joint fluid aspiration reveals weakly positively birefringent, rhomboid-shaped crystals under compensated polarized light microscopy. Which of the following is the most likely composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Hydroxyapatite
. Cholesterol

Correct Answer & Explanation

. Monosodium urate

Explanation

Calcium pyrophosphate dihydrate (CPPD) crystals, the causative agent in pseudogout, are classically rhomboid-shaped and exhibit weakly positive birefringence. Monosodium urate crystals (gout) are needle-shaped and negatively birefringent.

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