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1. General Principles & Basic Science MCQs

Practice Set 520 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 10381

Topic: Biomechanics & Biomaterials
Which of the following biomaterials is known for its excellent biocompatibility and is commonly used for the acetabular liner in total hip arthroplasty due to its low wear characteristics?
. Cobalt-chromium alloy
. Titanium alloy
. Stainless steel
. Polyethylene (UHMWPE)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Polyethylene (UHMWPE)

Explanation

Ultra-High Molecular Weight Polyethylene (UHMWPE) is the most commonly used material for the acetabular liner in total hip arthroplasty. It is valued for its excellent wear resistance and biocompatibility, minimizing particulate debris which can lead to osteolysis and aseptic loosening. Cobalt-chromium and titanium alloys are used for the femoral head and acetabular shell, respectively. Stainless steel is less common now. PMMA is bone cement.

Question 10382

Topic: Infection, Pharmacology & VTE

A 55-year-old diabetic male with a history of open tibia fracture 10 years ago presents with a chronic draining sinus tract in his lower leg. Radiographs show sclerotic bone and a sequestrum. What is the definitive management for chronic osteomyelitis with a sequestrum?

. Long-term oral antibiotics
. Surgical debridement and sequestrectomy
. Hyperbaric oxygen therapy
. Amputation
. Bone grafting without debridement

Correct Answer & Explanation

. Surgical debridement and sequestrectomy

Explanation

Chronic osteomyelitis with a sequestrum (a piece of dead, infected bone) requires surgical debridement and sequestrectomy (removal of the sequestrum) for definitive treatment. The sequestrum acts as a nidus for infection and cannot be eradicated by antibiotics alone. Antibiotics are adjunctive to surgery. Long-term oral antibiotics alone will not cure it. Amputation is a last resort. Bone grafting should be performed after infection eradication.

Question 10383

Topic: Biology, Genetics & Bone Healing

Which of the following cells is primarily responsible for bone resorption during bone remodeling?

. Osteoblasts
. Osteocytes
. Osteoclasts
. Chondrocytes
. Fibroblasts

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoclasts are specialized multinucleated cells primarily responsible for bone resorption. They secrete acids and enzymes to break down bone matrix. Osteoblasts are responsible for bone formation. Osteocytes are mature bone cells embedded in the matrix. Chondrocytes form cartilage. Fibroblasts form fibrous connective tissue.

Question 10384

Topic: 1. General Principles & Basic Science

A 75-year-old female with severe osteoporosis presents with acute onset severe back pain after a minor fall. Radiographs show a new T12 compression fracture. She has failed conservative management with pain medication and bracing. What is a minimally invasive surgical option to alleviate pain and stabilize the fracture?

. Spinal fusion
. Laminectomy
. Kyphoplasty
. Discectomy
. Vertebroplasty without balloon inflation

Correct Answer & Explanation

. Kyphoplasty

Explanation

For painful osteoporotic vertebral compression fractures that fail conservative management, Kyphoplasty is a minimally invasive surgical option. It involves inflating a balloon within the vertebral body to restore some height, creating a cavity, and then injecting bone cement (PMMA) to stabilize the fracture and relieve pain. Vertebroplasty (without balloon) is similar but just injects cement without height restoration. Spinal fusion, laminectomy, and discectomy are more extensive procedures typically for instability or neurological compression.

Question 10385

Topic: Infection, Pharmacology & VTE

In the management of chronic osteomyelitis, which of the following is considered the MOST crucial aspect of surgical intervention?

. Administration of high-dose intravenous antibiotics
. Stabilization of the affected bone with external fixation
. Thorough debridement of all necrotic and infected bone and soft tissue
. Immediate bone grafting to fill defects
. Application of vacuum-assisted wound therapy (VAC)

Correct Answer & Explanation

. Thorough debridement of all necrotic and infected bone and soft tissue

Explanation

The MOST crucial aspect of surgical intervention for chronic osteomyelitis is thorough debridement of all necrotic and infected bone and soft tissue. Without complete removal of the infected and non-viable tissue, antibiotics alone are unlikely to eradicate the infection. While antibiotics, stabilization, and soft tissue management (like VAC) are important adjunctive therapies, debridement is paramount. Bone grafting is typically performed after infection eradication and soft tissue coverage have been achieved.

Question 10386

Topic: Infection, Pharmacology & VTE

A 65-year-old male with a history of recurrent gout presents with acute onset severe pain, swelling, and redness in his left knee. Arthrocentesis reveals a cloudy synovial fluid with negatively birefringent, needle-shaped crystals. What is the MOST appropriate initial medical treatment?

. Intra-articular corticosteroid injection
. Systemic antibiotics
. Colchicine and NSAIDs
. Allopurinol
. Surgical debridement

Correct Answer & Explanation

. Colchicine and NSAIDs

Explanation

The presence of negatively birefringent, needle-shaped crystals in the synovial fluid is pathognomonic for gout (monosodium urate crystal arthropathy). The MOST appropriate initial medical treatment for an acute gout flare includes colchicine and NSAIDs (such as indomethacin) to reduce inflammation and pain. Intra-articular corticosteroids can be used as an alternative if NSAIDs/colchicine are contraindicated or ineffective. Allopurinol is a long-term urate-lowering therapy and is typically not initiated during an acute attack. Antibiotics are for septic arthritis.

Question 10387

Topic: Biology, Genetics & Bone Healing

Regarding the pathogenesis of osteonecrosis of the femoral head, which of the following is considered the MOST significant initiating factor in non-traumatic cases?

. Mechanical stress
. Genetic predisposition
. Vascular compromise
. Increased intraosseous pressure
. Systemic inflammation

Correct Answer & Explanation

. Vascular compromise

Explanation

Vascular compromise leading to ischemia is the most significant initiating factor in the pathogenesis of osteonecrosis of the femoral head (ONFH), whether traumatic (e.g., femoral neck fracture) or non-traumatic (e.g., steroid use, alcoholism). This compromise can be due to thrombosis, fat emboli, or direct vessel injury, ultimately leading to death of osteocytes and marrow cells. While increased intraosseous pressure can result from the ischemia and contribute to further compromise, it is typically a consequence, not the primary initiator. Mechanical stress can exacerbate the condition but isn't the primary cause. Genetic predisposition and systemic inflammation are associated factors but not the direct initiating mechanism of bone cell death.

Question 10388

Topic: 1. General Principles & Basic Science

What is the primary function of the menisci in the knee joint?

. Provide active stability
. Produce synovial fluid
. Increase articular cartilage thickness
. Distribute compressive loads and absorb shock
. Initiate knee flexion

Correct Answer & Explanation

. Distribute compressive loads and absorb shock

Explanation

The menisci are fibrocartilaginous structures within the knee joint that primarily function to distribute compressive loads evenly across the articular cartilage, thereby increasing the contact area and reducing stress on the joint surfaces. They also contribute to shock absorption, joint stability, and lubrication. They do not produce synovial fluid (that's the synovium), increase articular cartilage thickness (they sit between the cartilage surfaces), or initiate knee flexion (that's muscle action).

Question 10389

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of bisphosphonates in the treatment of osteoporosis?

. Increase osteoblast activity
. Inhibit osteoclast activity
. Promote calcium absorption in the gut
. Stimulate parathyroid hormone release
. Increase bone matrix mineralization

Correct Answer & Explanation

. Inhibit osteoclast activity

Explanation

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption. They bind to hydroxyapatite crystals in the bone and are internalized by osteoclasts, leading to osteoclast apoptosis and reduced bone turnover. This preserves bone mass and increases bone mineral density, thereby reducing fracture risk. They do not primarily increase osteoblast activity (though reduced resorption can indirectly lead to more effective new bone formation), promote calcium absorption, or stimulate PTH release.

Question 10390

Topic: Biology, Genetics & Bone Healing
Which cytokine is primarily responsible for promoting bone resorption by stimulating osteoclast differentiation and activation?
. Bone morphogenetic protein (BMP)
. Transforming growth factor-beta (TGF-β)
. Insulin-like growth factor 1 (IGF-1)
. Receptor activator of nuclear factor kappa-Β ligand (RANKL)
. Osteoprotegerin (OPG)

Correct Answer & Explanation

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

Explanation

RANKL (Receptor Activator of Nuclear factor Kappa-Β Ligand) is a key cytokine produced by osteoblasts and stromal cells that binds to RANK receptors on pre-osteoclasts, promoting their differentiation into mature osteoclasts and activating their bone-resorbing activity. OPG (Osteoprotegerin) acts as a decoy receptor for RANKL, inhibiting its effects and thus preventing bone resorption. BMPs, TGF-β, and IGF-1 are primarily involved in bone formation and remodeling, stimulating osteoblast activity.

Question 10391

Topic: Infection, Pharmacology & VTE

What is the most common organism responsible for acute hematogenous osteomyelitis in otherwise healthy children?

. Escherichia coli
. Pseudomonas aeruginosa
. Staphylococcus aureus
. Streptococcus pyogenes
. Kingella kingae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus is the most common causative organism for acute hematogenous osteomyelitis in all age groups, including otherwise healthy children. While Kingella kingae is an increasingly recognized pathogen in younger children (under 3 years old), S. aureus remains overall the predominant cause. E. coli and Pseudomonas are more common in neonates, immunocompromised individuals, or following puncture wounds (e.g., through a shoe). Streptococcus pyogenes is less common.

Question 10392

Topic: Infection, Pharmacology & VTE

In the context of surgical site infection (SSI) prophylaxis, what is the generally accepted optimal timing for administering intravenous antibiotics prior to incision?

. Within 2 hours before incision
. Immediately at the time of incision
. After the incision but before wound closure
. Within 60 minutes before incision
. Postoperatively, for 24 hours

Correct Answer & Explanation

. Within 60 minutes before incision

Explanation

For most surgical procedures, intravenous prophylactic antibiotics should be administered within 60 minutes prior to the surgical incision to ensure adequate tissue concentration at the time of potential contamination. For certain antibiotics (e.g., vancomycin or fluoroquinolones) with longer infusion times, administration may begin up to 120 minutes prior. Administering too early can reduce efficacy, and too late can miss the critical window of contamination. Postoperative continuation beyond 24 hours is generally not recommended for prophylaxis in clean or clean-contaminated cases.

Question 10393

Topic: 1. General Principles & Basic Science

A 50-year-old overweight male presents with acute onset, excruciating pain, redness, and swelling of the great toe (podagra). He reports similar episodes in the past affecting other joints. Laboratory tests show elevated serum uric acid. What is the most appropriate long-term management to prevent recurrent attacks?

. Colchicine
. Indomethacin
. Prednisone
. Allopurinol
. Aspirin

Correct Answer & Explanation

. Allopurinol

Explanation

This patient presents with classic symptoms of gout. While colchicine, indomethacin, and prednisone are used for acute attack management, allopurinol is the most appropriate long-term therapy to prevent recurrent attacks. Allopurinol is a xanthine oxidase inhibitor that reduces uric acid production, thereby lowering serum uric acid levels and preventing crystal deposition. It should not be started during an acute attack. Aspirin can actually worsen gout by interfering with renal uric acid excretion at low doses.

Question 10394

Topic: Biology, Genetics & Bone Healing

Which metabolic bone disease is characterized by excessive bone resorption followed by disorganized and excessive bone formation, leading to enlarged and weakened bones?

. Osteoporosis
. Osteomalacia
. Paget's disease of bone
. Hyperparathyroidism
. Osteogenesis imperfecta

Correct Answer & Explanation

. Paget's disease of bone

Explanation

Paget's disease of bone (osteitis deformans) is characterized by a focal disorder of bone remodeling, with greatly accelerated, chaotic bone turnover. This involves an initial osteolytic phase, followed by a mixed lytic and blastic phase, and finally a predominant sclerotic phase. The new bone formed is structurally disorganized (woven bone), leading to enlarged, weakened, and deformed bones. Osteoporosis is a decrease in bone mass. Osteomalacia is defective mineralization of new bone. Hyperparathyroidism causes increased bone resorption but not this chaotic pattern. Osteogenesis imperfecta is a genetic collagen disorder.

Question 10395

Topic: Biology, Genetics & Bone Healing
Which type of collagen is primarily found in hyaline cartilage, providing its characteristic strength and resilience?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type V collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Type II collagen is the predominant collagen found in hyaline cartilage (including articular cartilage). Its unique molecular structure and organization contribute to the tensile strength and resilience of cartilage, allowing it to withstand compressive loads. Type I collagen is found in bone, tendons, and ligaments, providing strong tensile strength. Type III collagen is found in extensible connective tissues like skin and blood vessels. Type IV collagen is found in basement membranes. Type V collagen is found in small amounts in various tissues, including cartilage.

Question 10396

Topic: Physiology & Rehabilitation

Which type of gait is characteristic of a patient with weakness of the gluteus medius muscle?

. Foot drop gait (steppage gait)
. Antalgic gait
. Trendelenburg gait
. Cerebellar ataxic gait
. Waddling gait

Correct Answer & Explanation

. Trendelenburg gait

Explanation

A Trendelenburg gait is characterized by the dropping of the contralateral hip during the stance phase of gait. This occurs due to weakness or paralysis of the ipsilateral gluteus medius and minimus muscles, which are crucial hip abductors. When the stance leg's abductors cannot stabilize the pelvis, the opposite side drops. Foot drop gait is due to dorsiflexor weakness. Antalgic gait is pain-avoiding. Cerebellar ataxic gait is uncoordinated. Waddling gait (often bilateral Trendelenburg) can be seen with bilateral abductor weakness or neuromuscular disorders.

Question 10397

Topic: Biology, Genetics & Bone Healing
In the context of bone healing, what is the sequence of events during secondary bone healing (endochondral ossification)?
. Hematoma formation → cartilage callus → bony callus → remodeling
. Hematoma formation → bony callus → cartilage callus → remodeling
. Direct osteoblast activity → woven bone → lamellar bone
. Inflammation → osteoclast activity → osteoblast activity → consolidation
. Fibrous tissue formation → cartilage formation → direct bone formation

Correct Answer & Explanation

. Hematoma formation → cartilage callus → bony callus → remodeling

Explanation

Secondary bone healing, also known as indirect healing or endochondral ossification, involves a cascade of events: 1. Hematoma formation at the fracture site. 2. Inflammation and formation of a soft callus (fibrous tissue and cartilage). 3. Hard callus formation as the cartilage calcifies and is replaced by woven bone. 4. Bone remodeling, where woven bone is gradually replaced by lamellar bone, and the bone reshapes itself. The other options describe direct bone healing or incorrect sequences.

Question 10398

Topic: Surgical Anatomy & Approaches

Which nerve is at highest risk of injury during surgical fixation of a proximal humerus fracture via a deltopectoral approach?

. Axillary nerve
. Radial nerve
. Musculocutaneous nerve
. Median nerve
. Ulnar nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

The axillary nerve (C5-C6) is at highest risk of injury during surgical approaches to the proximal humerus, especially the deltopectoral approach. It courses around the surgical neck of the humerus, approximately 5-7 cm distal to the acromion, making it vulnerable during plate application, screw insertion, or excessive retraction of the deltoid. Injury can lead to deltoid paralysis and sensory loss over the lateral shoulder. The radial nerve is at risk more distally in the humerus (spiral groove). The musculocutaneous, median, and ulnar nerves are generally protected by their more medial and anterior/posterior positions relative to the deltopectoral interval.

Question 10399

Topic: 1. General Principles & Basic Science

Regarding the use of pneumatic tourniquets in orthopedic surgery, what is generally considered the maximum safe duration for a single application on an upper extremity in a normothermic patient without reperfusion?

. 60 minutes
. 90 minutes
. 120 minutes
. 150 minutes
. 180 minutes

Correct Answer & Explanation

. 90 minutes

Explanation

While there is some variability in recommendations, 90-120 minutes is often cited as the typical maximum safe duration for an upper extremity tourniquet application without reperfusion in healthy individuals. For the lower extremity, 120-150 minutes is more common. Prolonged ischemia can lead to muscle and nerve damage. Some guidelines suggest a maximum of 90 minutes for upper extremities to minimize risks, especially nerve injury. Reperfusion intervals typically involve releasing the tourniquet for 10-20 minutes before re-inflation.

Question 10400

Topic: 1. General Principles & Basic Science

A 40-year-old male undergoes arthroscopic knee surgery. The surgeon decides to inflate the tourniquet on the thigh. Which of the following is the most widely accepted physiological basis for determining the appropriate tourniquet inflation pressure, rather than using a fixed absolute pressure?

. Systolic Blood Pressure (SBP) + 50 mmHg
. Mean Arterial Pressure (MAP) + 70 mmHg
. Limb Occlusion Pressure (LOP) + a safety margin
. Diastolic Blood Pressure (DBP) + 60 mmHg
. A fixed pressure of 300 mmHg for lower extremity

Correct Answer & Explanation

. Limb Occlusion Pressure (LOP) + a safety margin

Explanation

The most physiologically sound method for determining tourniquet inflation pressure is to use the Limb Occlusion Pressure (LOP) plus a safety margin. LOP is the minimum pressure required to occlude arterial flow in the limb. Adding a safety margin (e.g., 40-100 mmHg above LOP, depending on the device and patient) ensures complete arterial occlusion while minimizing unnecessary high pressures. Fixed absolute pressures (like 300 mmHg) or pressures based solely on SBP or MAP can be either too low (leading to venous congestion and bleeding) or unnecessarily high (increasing the risk of tissue and nerve damage), especially in patients with varying blood pressures or limb circumferences.

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