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1. General Principles & Basic Science MCQs

Practice Set 730 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 14581

Topic: Infection, Pharmacology & VTE

Aspiration of a swollen, erythematous first metatarsophalangeal joint yields cloudy fluid. Microscopy reveals negatively birefringent, needle-shaped crystals, and the WBC count is 65,000 cells/mcL. What is the most appropriate next step regarding the synovial fluid analysis?

. Discard the remaining fluid as the diagnosis of gout is definitively confirmed.
. Ensure the fluid is sent for Gram stain and bacterial culture despite the presence of crystals.
. Send the fluid for specialized fungal cultures only.
. Add uricase to the fluid to dissolve the crystals and repeat the WBC count.
. Perform a rapid point-of-care alpha-defensin test to rule out pseudogout.

Correct Answer & Explanation

. Ensure the fluid is sent for Gram stain and bacterial culture despite the presence of crystals.

Explanation

The identification of monosodium urate crystals establishes a diagnosis of gout, but it does not rule out a concomitant septic arthritis. Because crystal arthropathy and joint infection can coexist, especially with WBC counts exceeding 50,000, Gram stain and culture must always be obtained.

Question 14582

Topic: Infection, Pharmacology & VTE

Which of the following best describes the primary mechanism by which sonication of explanted orthopedic hardware improves the diagnostic yield for periprosthetic joint infection?

. It lyses host immune cells to release intracellular bacteria.
. It physically disrupts the bacterial biofilm to release sessile organisms into the fluid.
. It increases the metabolic rate of dormant persister cells to promote rapid growth.
. It concentrates planktonic bacteria via acoustic cavitation.
. It denatures the bacterial glycocalyx without dislodging the actual organisms.

Correct Answer & Explanation

. It physically disrupts the bacterial biofilm to release sessile organisms into the fluid.

Explanation

Sonication uses low-frequency ultrasound to physically disrupt the extracellular polymeric substance of the biofilm on explanted hardware. This releases the sessile bacteria into the surrounding fluid, significantly improving culture yields.

Question 14583

Topic: 1. General Principles & Basic Science

When performing an anterior ultrasound-guided aspiration of a native hip for suspected septic arthritis, the needle trajectory must carefully avoid which critical structures located medially?

. Femoral nerve and artery
. Lateral femoral cutaneous nerve
. Sciatic nerve
. Superior gluteal artery
. Ascending branch of lateral circumflex femoral artery

Correct Answer & Explanation

. Femoral nerve and artery

Explanation

The femoral neurovascular bundle (femoral vein, artery, and nerve) lies medial to the standard anterior hip aspiration pathway. Ultrasound guidance safely directs the needle lateral to these structures into the anterior joint recess.

Question 14584

Topic: Infection, Pharmacology & VTE

A 55-year-old male presents with an acute, swollen knee. Aspiration yields cloudy fluid with 65,000 WBCs/mcL and intracellular monosodium urate crystals. Gram stain is negative. What is the most appropriate management plan?

. Administer intra-articular corticosteroids and discharge the patient.
. Begin treatment for gout and closely monitor while awaiting final culture results.
. Proceed immediately to surgical arthroscopic irrigation and debridement.
. Prescribe oral allopurinol as monotherapy and discharge.
. Schedule an outpatient MRI to rule out osteomyelitis.

Correct Answer & Explanation

. Begin treatment for gout and closely monitor while awaiting final culture results.

Explanation

The presence of crystals confirms gout but does not definitive rule out concomitant septic arthritis. The safest management is to treat the acute flare while observing the patient and awaiting final synovial fluid culture results.

Question 14585

Topic: Infection, Pharmacology & VTE

The Kocher criteria are utilized to risk-stratify children presenting with an irritable hip. Which of the following is NOT one of the classic four Kocher criteria used to differentiate septic arthritis from transient synovitis?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate > 40 mm/hr
. Serum white blood cell count > 12,000 cells/mm3
. Temperature > 38.5 C (101.3 F)
. C-reactive protein > 2.0 mg/dL

Correct Answer & Explanation

. C-reactive protein > 2.0 mg/dL

Explanation

The classic four Kocher criteria are non-weight-bearing, ESR > 40, WBC > 12,000, and Temp > 38.5 C. Although CRP > 2.0 mg/dL was later identified as a strong independent predictor by Caird et al., it is not one of the original four Kocher criteria.

Question 14586

Topic: 1. General Principles & Basic Science

In the setting of diagnosing periprosthetic joint infection, how does the diagnostic performance of serum procalcitonin generally compare to that of serum C-reactive protein (CRP)?

. Higher sensitivity and higher specificity
. Lower sensitivity but higher specificity
. Higher sensitivity but lower specificity
. Lower sensitivity and lower specificity
. Identical sensitivity and specificity

Correct Answer & Explanation

. Lower sensitivity but higher specificity

Explanation

Serum procalcitonin is highly specific for systemic bacterial infections but demonstrates significantly lower sensitivity than CRP for localized infections like PJI. It is not currently recommended as a first-line screening test for PJI.

Question 14587

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely swollen native knee. Synovial fluid analysis reveals an elevated WBC count. Above what threshold is native joint septic arthritis highly suspected?

. 3,000 cells/uL
. 10,000 cells/uL
. 25,000 cells/uL
. 50,000 cells/uL
. 100,000 cells/uL

Correct Answer & Explanation

. 50,000 cells/uL

Explanation

In native joints, a synovial WBC count greater than 50,000 cells/uL with >90% polymorphonuclear cells is highly suggestive of septic arthritis. Lower thresholds (e.g., 3,000 cells/uL) are typically used for chronic periprosthetic joint infections.

Question 14588

Topic: Biology, Genetics & Bone Healing

A 55-year-old female presents with osteoporosis. Medical therapy targeting osteoclast inhibition is planned. Which of the following best describes the cellular origin and essential signaling molecules required for osteoclast differentiation and activation?

. Mesenchymal stem cell origin; requires BMP-2 and Wnt
. Hematopoietic stem cell origin; requires M-CSF and RANKL
. Hematopoietic stem cell origin; requires OPG and Runx2
. Mesenchymal stem cell origin; requires RANKL and SOX9
. Endothelial progenitor cell origin; requires VEGF and M-CSF

Correct Answer & Explanation

. Hematopoietic stem cell origin; requires M-CSF and RANKL

Explanation

Osteoclasts are derived from the hematopoietic monocyte/macrophage lineage. Their differentiation and activation require Macrophage Colony-Stimulating Factor (M-CSF) and Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). Osteoprotegerin (OPG) acts as a decoy receptor for RANKL, inhibiting osteoclastogenesis. Conversely, osteoblasts are derived from mesenchymal stem cells.

Question 14589

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates compared to conventional polyethylene. What is the primary mechanical trade-off associated with increasing the radiation dose to increase cross-linking?

. Decreased ultimate tensile strength and fatigue crack propagation resistance
. Increased oxidation rate in vivo without remelting
. Decreased volumetric wear
. Increased generation of submicron particles per unit of wear
. Decreased elastic modulus leading to rapid rim failure

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene drastically reduces adhesive and abrasive wear. However, the cross-linking process (via irradiation) compromises the material's mechanical properties, specifically reducing its ultimate tensile strength, elongation to failure, and fatigue crack propagation resistance. This makes it more susceptible to fatigue-related failures such as rim cracking if malaligned.

Question 14590

Topic: Biomechanics & Biomaterials

A new orthopedic implant material is being biomechanically tested. The total area under the stress-strain curve up to the point of fracture represents which of the following material properties?

. Toughness
. Yield strength
. Elastic modulus
. Ductility
. Brittleness

Correct Answer & Explanation

. Toughness

Explanation

The total area under the stress-strain curve from zero strain to the point of failure (fracture) represents the material's toughness, which is the amount of energy absorbed before fracture. Yield strength is the stress at which plastic deformation begins. Elastic modulus is the slope of the linear (elastic) portion. Ductility is the amount of plastic strain before failure.

Question 14591

Topic: 1. General Principles & Basic Science

In normal articular cartilage, what is the primary structural orientation of the collagen fibers in the superficial (tangential) zone?

. Perpendicular to the articular surface
. Randomly oriented
. Parallel to the articular surface
. Oblique to the articular surface
. Arranged in a radial pattern

Correct Answer & Explanation

. Parallel to the articular surface

Explanation

Articular cartilage consists of distinct zones. In the superficial (tangential) zone, collagen fibers are oriented parallel to the articular surface to resist shear stress. In the middle (transitional) zone, they are randomly oriented. In the deep zone, they are oriented perpendicular to the subchondral bone to resist compressive forces.

Question 14592

Topic: Biology, Genetics & Bone Healing

Which of the following describes the primary cellular defect initiating the pathophysiology of Paget's disease of bone (osteitis deformans)?

. Defective mineralization by osteoblasts
. Increased numbers and abnormal activity of osteoclasts
. Hyperactivity of parathyroid hormone receptors
. Accumulation of unmineralized osteoid
. Inhibition of the RANK-RANKL pathway

Correct Answer & Explanation

. Increased numbers and abnormal activity of osteoclasts

Explanation

Paget's disease is initiated by an overactive, abnormal osteoclast phase. The osteoclasts are increased in number, abnormally large, and multinucleated. This initial intensely lytic phase is followed by a mixed phase where osteoblasts rapidly lay down structurally disorganized (woven) bone, resulting in the classic enlarged, weak bones.

Question 14593

Topic: Biology, Genetics & Bone Healing

A 65-year-old male complains of increasing hat size, hearing loss, and deep aching pain in his right thigh. Radiographs demonstrate anterolateral bowing of the femur with cortical thickening. Which of the following is the pathognomonic histologic finding associated with this condition?

. Howship lacunae with multinucleated giant cells
. Mosaic pattern of lamellar bone with prominent cement lines
. Areas of woven bone lacking Haversian systems
. Unmineralized osteoid seams greater than 15 micrometers
. Empty lacunae with pyknotic osteocyte nuclei

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

The patient has Paget's disease of bone (osteitis deformans). The pathognomonic histologic finding in the mixed or osteosclerotic phase is a mosaic pattern of lamellar bone with prominent, haphazard cement lines. This is caused by the erratic and uncoupled activity of osteoclasts and osteoblasts.

Question 14594

Topic: Biomechanics & Biomaterials

During a revision open reduction and internal fixation of a nonunion, a surgeon uses a stainless steel screw through a titanium alloy plate. Several months later, rapid degradation is noted at the screw-plate interface. This is primarily an example of which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in electrical contact within a conductive fluid (such as body fluid). The less noble metal becomes the anode and corrodes at an accelerated rate.

Question 14595

Topic: Infection, Pharmacology & VTE
A 68-year-old female is prescribed fondaparinux for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the mechanism of action of this agent?
. Direct thrombin inhibitor
. Vitamin K epoxide reductase antagonist
. Indirect Factor Xa inhibitor via antithrombin III
. Direct Factor Xa inhibitor
. Irreversible cyclooxygenase inhibitor

Correct Answer & Explanation

. Indirect Factor Xa inhibitor via antithrombin III

Explanation

Fondaparinux is a synthetic pentasaccharide that binds to antithrombin III, accelerating its inhibition of Factor Xa. It is an indirect Factor Xa inhibitor. Rivaroxaban and apixaban are direct Factor Xa inhibitors, while dabigatran is a direct thrombin (Factor IIa) inhibitor.

Question 14596

Topic: Infection, Pharmacology & VTE

A patient develops a surgical site infection after spinal fusion. Cultures grow Methicillin-resistant Staphylococcus aureus (MRSA). The mecA gene is responsible for this resistance by encoding for which of the following?

. A potent beta-lactamase enzyme
. A transmembrane efflux pump
. An altered penicillin-binding protein (PBP2a)
. An aminoglycoside-modifying enzyme
. A dense exopolysaccharide biofilm matrix

Correct Answer & Explanation

. An altered penicillin-binding protein (PBP2a)

Explanation

MRSA resistance is primarily mediated by the mecA gene, which encodes for an altered penicillin-binding protein (PBP2a). PBP2a has a markedly reduced affinity for beta-lactam antibiotics, allowing the bacteria to synthesize cell walls even in the presence of methicillin or other beta-lactams.

Question 14597

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, when a constant load is applied to a viscoelastic tissue such as a ligament or tendon over an extended period, the tissue will slowly continue to elongate. This time-dependent deformation is known as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive time-dependent deformation (strain) of a viscoelastic material when subjected to a constant load (stress). Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant strain/deformation.

Question 14598

Topic: Biology, Genetics & Bone Healing

During a posterolateral lumbar fusion, the surgeon decides to use Demineralized Bone Matrix (DBM) as a bone graft extender. Which of the following accurately describes the biologic properties of DBM?

. It is osteogenic and osteoinductive
. It is osteoconductive and osteoinductive
. It is purely osteogenic
. It relies entirely on surviving donor cells for bone formation
. It provides high structural and mechanical support

Correct Answer & Explanation

. It is osteoconductive and osteoinductive

Explanation

Demineralized Bone Matrix (DBM) contains a collagenous matrix that is osteoconductive (acts as a scaffold) and bone morphogenetic proteins (BMPs) that make it osteoinductive (induces host stem cells to differentiate into osteoblasts). It does not contain live cells, so it is not osteogenic, and it lacks mineral, providing virtually no structural support.

Question 14599

Topic: Biology, Genetics & Bone Healing

Normal bone metabolism depends heavily on Vitamin D. The enzyme 1-alpha-hydroxylase, which converts 25-hydroxyvitamin D to the active form 1,25-dihydroxyvitamin D, is primarily located in which organ and is stimulated by which hormone?

. Liver; stimulated by Parathyroid Hormone (PTH)
. Liver; stimulated by Fibroblast Growth Factor 23 (FGF23)
. Kidney; stimulated by Parathyroid Hormone (PTH)
. Kidney; stimulated by Calcitonin
. Intestine; stimulated by serum Calcium levels

Correct Answer & Explanation

. Kidney; stimulated by Parathyroid Hormone (PTH)

Explanation

1-alpha-hydroxylase is predominantly located in the proximal convoluted tubule of the kidney. Its activity is upregulated by Parathyroid Hormone (PTH) and hypophosphatemia, leading to increased production of the active hormone 1,25-dihydroxyvitamin D (calcitriol).

Question 14600

Topic: Surgical Anatomy & Approaches

Following a closed humerus fracture, a patient exhibits a radial nerve palsy. According to Sunderland's classification, a third-degree nerve injury is characterized by disruption of the axon, myelin, and which of the following connective tissue structures?

. None, the endoneurium remains completely intact
. Epineurium only
. Endoneurium, with an intact perineurium and epineurium
. Endoneurium and perineurium, with an intact epineurium
. Complete transection of the entire nerve trunk

Correct Answer & Explanation

. Endoneurium and perineurium, with an intact epineurium

Explanation

In Sunderland's classification: 1st degree = neuropraxia (local myelin damage); 2nd degree = axonotmesis (axon severed, endoneurium intact); 3rd degree = axon and endoneurium severed, but perineurium intact; 4th degree = axon, endo, and perineurium severed, but epineurium intact; 5th degree = complete nerve transection (neurotmesis).

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