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1. General Principles & Basic Science MCQs

Practice Set 207 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 4121

Topic: 1. General Principles & Basic Science

A 28-year-old man falls from a motorcycle, sustaining a traction injury to his right upper extremity. Clinical examination reveals profound weakness of the right upper limb, accompanied by right-sided ptosis, miosis, and anhidrosis. The presence of these specific facial findings most strongly indicates an avulsion injury to which nerve root?

. C5
. C6
. C7
. C8
. T1

Correct Answer & Explanation

. T1

Explanation

Ptosis, miosis, and anhidrosis describe Horner syndrome, which is caused by disruption of the cervical sympathetic chain. In the context of a brachial plexus injury, this reliably indicates an avulsion of the T1 nerve root.

Question 4122

Topic: Surgical Anatomy & Approaches

During an anterior shoulder stabilization procedure, the surgeon is carefully identifying the structures in the axilla to avoid injury to the axillary nerve. The axillary nerve exits the axilla posteriorly through the quadrilateral space. Which vascular structure directly accompanies the nerve through this space?

. Anterior circumflex humeral artery
. Posterior circumflex humeral artery
. Profunda brachii artery
. Circumflex scapular artery
. Thoracoacromial artery

Correct Answer & Explanation

. Posterior circumflex humeral artery

Explanation

The axillary nerve passes through the quadrilateral space accompanied by the posterior circumflex humeral artery. The boundaries of the space are the teres minor (superior), teres major (inferior), long head of triceps (medial), and the surgical neck of the humerus (lateral).

Question 4123

Topic: Surgical Anatomy & Approaches

A 28-year-old man sustains a posterior fracture-dislocation of the hip. Following closed reduction, he is found to have weakness in ankle dorsiflexion and great toe extension, but intact plantar flexion. Sensation is decreased over the dorsum of the foot. Which specific neural structure is most likely injured?

. Femoral nerve
. Tibial division of the sciatic nerve
. Peroneal division of the sciatic nerve
. Superior gluteal nerve
. Obturator nerve

Correct Answer & Explanation

. Peroneal division of the sciatic nerve

Explanation

The peroneal division of the sciatic nerve is most commonly injured in posterior hip dislocations. It is more susceptible to stretch injury than the tibial division because its fascicles are larger, have less protective connective tissue, and are securely tethered at the fibular head.

Question 4124

Topic: 1. General Principles & Basic Science

A 22-year-old motorcyclist sustains a severe traction injury to his right upper extremity, resulting in a flail, insensate arm. He is also noted to have right-sided ptosis, miosis, and anhidrosis. This specific facial presentation indicates an injury at which of the following anatomic levels, and what is its prognostic significance?

. Postganglionic C5-C6; favorable for spontaneous recovery
. Preganglionic T1 root; avulsion injury with poor prognosis for spontaneous recovery
. Postganglionic T1 root; rupture with favorable response to nerve grafting
. Preganglionic C5 root; avulsion injury with poor prognosis
. Trunk level; favorable for spontaneous recovery

Correct Answer & Explanation

. Preganglionic T1 root; avulsion injury with poor prognosis for spontaneous recovery

Explanation

Horner syndrome (ptosis, miosis, anhidrosis) indicates a preganglionic avulsion of the T1 nerve root due to disruption of the proximal sympathetic ganglion. Preganglionic avulsion injuries have an extremely poor prognosis for spontaneous recovery and are not amenable to primary nerve grafting.

Question 4125

Topic: 1. General Principles & Basic Science
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is used to distinguish necrotizing fasciitis from other severe soft tissue infections. Which of the following laboratory parameters awards the highest maximum possible points within the LRINEC scoring system?
. White blood cell count > 25 cells/mm3
. Hemoglobin < 11 g/dL
. Serum sodium < 135 mmol/L
. Serum creatinine > 1.6 mg/dL
. C-reactive protein (CRP) ≥ 150 mg/L

Correct Answer & Explanation

. C-reactive protein (CRP) ≥ 150 mg/L

Explanation

In the LRINEC score, C-reactive protein (CRP) ≥ 150 mg/L awards the most points (4 points). The other variables award a maximum of 2 points each (WBC > 25 = 2 points; Hemoglobin < 11 = 2 points; Sodium < 135 = 2 points; Creatinine > 1.6 = 2 points). A total score ≥ 6 is suspicious for necrotizing fasciitis.

Question 4126

Topic: Infection, Pharmacology & VTE

A 4-year-old boy is evaluated in the emergency department for an acute limp and refusal to bear weight on his right leg. His temperature is 38.6°C (101.5°F). Laboratory studies reveal a WBC count of 10,500/mm3 and an ESR of 45 mm/hr. According to the original Kocher criteria for differentiating pediatric septic arthritis of the hip from transient synovitis, what is the approximate probability that this child has septic arthritis?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The original Kocher criteria consist of four predictors for septic arthritis: 1) Non-weight-bearing, 2) Temperature > 38.5°C, 3) ESR > 40 mm/hr, and 4) WBC > 12,000/mm3. This patient meets exactly three criteria: Non-weight-bearing, Temperature > 38.5°C, and ESR > 40 mm/hr (his WBC is < 12,000). According to the Kocher study, the predicted probability of septic arthritis is 3% for 1 criterion, 40% for 2 criteria, 93% for 3 criteria, and 99% for 4 criteria.

Question 4127

Topic: Biology, Genetics & Bone Healing
A 40-year-old male with a 6-cm infected diaphyseal defect of the tibia is treated with debridement, placement of an antibiotic cement spacer, and external fixation (the first stage of the Masquelet technique). According to histologic studies, at what time point does the induced membrane exhibit the peak expression of osteoinductive factors (such as VEGF, TGF-beta1, and BMP-2), making it the optimal biologic window for the second stage (bone grafting)?
. 2 to 4 weeks
. 1 to 2 weeks
. 6 to 8 weeks
. 10 to 12 weeks
. Greater than 12 weeks

Correct Answer & Explanation

. 1 to 2 weeks

Explanation

Histologic and biological studies of the Masquelet induced membrane technique (e.g., Pelissier et al.) demonstrate that the induced membrane is highly vascular and secretes key osteogenic and angiogenic growth factors (VEGF, TGF-β1, BMP-2). The expression of these factors peaks between 2 and 4 weeks after spacer placement, and steadily declines after 6 weeks. Therefore, the optimal biological window for the second stage (cancellous bone grafting) is typically around 4 weeks.

Question 4128

Topic: 1. General Principles & Basic Science
A 40-year-old male presents with a severe crush injury to the right lower extremity after a high-speed motor vehicle collision. The team calculates a Mangled Extremity Severity Score (MESS) to aid in the decision between limb salvage and primary amputation. Which of the following variables is NOT a component used to calculate the MESS?
. Skeletal/soft-tissue injury extent
. Limb ischemia
. Patient age
. Neurologic deficit (absent plantar sensation)
. Systemic shock

Correct Answer & Explanation

. Neurologic deficit (absent plantar sensation)

Explanation

The Mangled Extremity Severity Score (MESS) is a well-known scoring system designed to help predict the need for amputation. It utilizes four components: 1) Skeletal and soft-tissue injury (1-4 points), 2) Limb ischemia (1-3 points, doubled if >6 hours), 3) Shock (0-2 points), and 4) Patient age (0-2 points). A score ≥ 7 is highly predictive of amputation. Neurologic deficit (e.g., absent plantar sensation) is notably NOT a component of the MESS, though it was controversially used in other older decision-making algorithms.

Question 4129

Topic: Infection, Pharmacology & VTE

A 6-year-old boy with homozygous sickle cell disease develops acute diaphyseal osteomyelitis. While Staphylococcus aureus remains the most common overall cause of osteomyelitis in this patient population, which of the following organisms is uniquely characteristic and disproportionately prevalent due to the underlying pathophysiology of his disease?

. Salmonella typhimurium
. Pseudomonas aeruginosa
. Pasteurella multocida
. Eikenella corrodens
. Brucella melitensis

Correct Answer & Explanation

. Salmonella typhimurium

Explanation

Patients with sickle cell disease are uniquely susceptible to Salmonella osteomyelitis due to intermittent bowel ischemia leading to bacteremia, coupled with autosplenectomy impairing the clearance of encapsulated organisms. Though S. aureus is still extremely common, Salmonella is the classic, uniquely associated pathogen in this population.

Question 4130

Topic: 1. General Principles & Basic Science
A 55-year-old diabetic male presents with an erythematous, exquisitely tender, and swollen right lower extremity. In utilizing the LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score to stratify his risk, which of the following laboratory values contributes to a higher score?
. Serum lactate > 4.0 mmol/L
. Serum sodium < 135 mmol/L
. White blood cell count > 10,000/mm3
. Serum potassium > 5.5 mmol/L
. Elevated serum procalcitonin

Correct Answer & Explanation

. Serum sodium < 135 mmol/L

Explanation

The LRINEC score incorporates six laboratory parameters: C-reactive protein (CRP), total white blood cell count (points given for >15,000), hemoglobin (points for <13.5), serum sodium (2 points for <135 mmol/L), serum creatinine (points for >1.41 mg/dL), and fasting glucose (points for >180 mg/dL). Lactate, potassium, and procalcitonin are not part of the LRINEC score.

Question 4131

Topic: Infection, Pharmacology & VTE

A 3-year-old girl is evaluated in the emergency department for a limp and refusal to bear weight on her right leg. Her temperature is 38.0°C (100.4°F). Laboratory testing reveals an Erythrocyte Sedimentation Rate (ESR) of 50 mm/hr and a White Blood Cell (WBC) count of 13,000/mm3. According to the Kocher criteria, what is her approximate probability of having septic arthritis of the hip?

. < 10%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria for pediatric septic hip are: non-weight-bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm3. This patient meets three criteria (non-weight-bearing, ESR >40, WBC >12,000; she fails the temperature criterion at 38.0°C). The probabilities of septic arthritis are approximately 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.

Question 4132

Topic: Infection, Pharmacology & VTE

A 45-year-old agricultural worker from the San Joaquin Valley develops chronic osteomyelitis of the lumbar spine following a severe respiratory illness. Histopathologic examination of a vertebral biopsy reveals large, thick-walled spherules containing numerous endospores. What is the most appropriate systemic pharmacological therapy for this bone infection?

. Intravenous Penicillin G
. Intravenous Ceftriaxone
. Intravenous Amphotericin B or oral Itraconazole
. Oral Doxycycline
. Oral Rifampin

Correct Answer & Explanation

. Intravenous Amphotericin B or oral Itraconazole

Explanation

The clinical history (San Joaquin Valley) and histology ('spherules containing endospores') are pathognomonic for Coccidioidomycosis. Disseminated extrapulmonary disease, such as Coccidioidal osteomyelitis, is classically treated with prolonged antifungal therapy utilizing azoles (Itraconazole or Fluconazole) or, in severe/refractory cases, intravenous Amphotericin B.

Question 4133

Topic: Infection, Pharmacology & VTE

In the management of a staphylococcal periprosthetic joint infection treated with debridement, antibiotics, and implant retention (DAIR), rifampin is often added to the postoperative antibiotic regimen. What is the primary mechanism of action of rifampin that makes it uniquely effective against biofilm-associated staphylococci?

. Inhibition of cell wall synthesis via penicillin-binding proteins.
. Inhibition of DNA-dependent RNA polymerase.
. Inhibition of protein synthesis via the 30S ribosomal subunit.
. Disruption of the bacterial cell membrane lipid bilayer.
. Competitive inhibition of para-aminobenzoic acid (PABA).

Correct Answer & Explanation

. Inhibition of DNA-dependent RNA polymerase.

Explanation

Rifampin exerts its bactericidal effect by binding to the beta subunit of DNA-dependent RNA polymerase, thereby inhibiting bacterial RNA synthesis. It is highly lipophilic, penetrates biofilms well, and is active against stationary-phase staphylococci, making it a critical adjunct in DAIR procedures for staphylococcal PJIs. To prevent resistance, it must never be used as monotherapy.

Question 4134

Topic: 1. General Principles & Basic Science
An obese 55-year-old male with poorly controlled diabetes presents with extreme leg pain, swelling, and erythema. You calculate a Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score. Which of the following laboratory parameters is NOT a component of the LRINEC score?
. C-reactive protein (CRP)
. White blood cell count (WBC)
. Hemoglobin
. Serum sodium
. Serum potassium

Correct Answer & Explanation

. Serum potassium

Explanation

The LRINEC score helps stratify the risk of necrotizing fasciitis. Its components include CRP (≥150 mg/L), WBC count (>15, >25), Hemoglobin (<13.5, <11), Serum sodium (<135 mmol/L), Serum creatinine (>1.41 mg/dL), and Serum glucose (>180 mg/dL). Serum potassium is not a component of the LRINEC score.

Question 4135

Topic: 1. General Principles & Basic Science

A 45-year-old female presents with a draining sinus tract from her right distal femur, secondary to a fracture treated with ORIF 5 years ago. She has no medical comorbidities but smokes 1 pack of cigarettes a day. According to the Cierny-Mader classification of osteomyelitis, what is her physiological host status?

. A-host
. B-host (local compromise)
. B-host (systemic compromise)
. B-host (local and systemic compromise)
. C-host

Correct Answer & Explanation

. B-host (systemic compromise)

Explanation

The Cierny-Mader classification categorizes the host physiology into A (normal host), B (compromised host), and C (treatment worse than disease). Smoking is strictly considered a systemic compromising factor (Bs). Local factors (Bl) include poor tissue perfusion, venous stasis, major vessel compromise, or radiation. Therefore, a smoker with no other local factors is a Bs-host (B-host, systemic compromise).

Question 4136

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, a limp, and refusal to bear weight. Which inflammatory marker has been shown in subsequent validation studies (e.g., Caird et al.) to be the single best independent predictor of pediatric septic arthritis when combined with the classic Kocher criteria?

. Erythrocyte sedimentation rate (ESR) > 40 mm/hr
. C-reactive protein (CRP) > 2.0 mg/dL
. Procalcitonin > 0.5 ng/mL
. WBC count > 12,000 cells/mm3
. Synovial fluid lactate > 4.0 mmol/L

Correct Answer & Explanation

. C-reactive protein (CRP) > 2.0 mg/dL

Explanation

While the classic Kocher criteria utilized ESR, WBC, inability to bear weight, and fever, subsequent studies (Caird et al.) demonstrated that a CRP > 2.0 mg/dL is an excellent independent predictor. When added as a fifth variable to the original criteria, it significantly increases the diagnostic accuracy for pediatric septic arthritis.

Question 4137

Topic: 1. General Principles & Basic Science

A 19-year-old male is tackled and presents with severe right upper chest pain, stridor, and difficulty swallowing. Imaging confirms a posterior sternoclavicular (SC) joint dislocation. Which of the following structures lies immediately posterior to the medial clavicle and is at greatest risk of direct mechanical injury during this displacement?

. Axillary artery
. Brachiocephalic (innominate) vein
. Superior vena cava
. Thoracic duct
. Recurrent laryngeal nerve

Correct Answer & Explanation

. Brachiocephalic (innominate) vein

Explanation

Posterior SC dislocations are medical emergencies due to the proximity of critical mediastinal structures. The most anterior vascular structure lying directly posterior to the SC joint is the brachiocephalic (innominate) vein. While the trachea, esophagus, and subclavian vessels are also at risk, the innominate vein is geographically the closest major structure at risk of laceration or compression.

Question 4138

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently used to deliver local antibiotics in the treatment of orthopedic infections. Which of the following properties is a critical requirement for an antibiotic to be effectively and safely incorporated into PMMA?

. Thermolability
. High protein binding
. Hydrophobicity
. Bacteriostatic mechanism of action
. Thermal stability and water solubility

Correct Answer & Explanation

. Thermal stability and water solubility

Explanation

To be effectively mixed with PMMA, an antibiotic must possess thermal stability (to withstand the exothermic reaction of cement polymerization which can reach high temperatures) and water solubility (to allow it to elute out of the hydrophobic cement matrix into the surrounding aqueous tissue environment). Aminoglycosides (tobramycin) and glycopeptides (vancomycin) fit these criteria well.

Question 4139

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for the fixation of an anterior column acetabular fracture, a significant bleeding vessel is encountered crossing over the superior pubic ramus at a distance of approximately 5 cm from the pubic symphysis. This vessel, commonly referred to as the corona mortis, represents an anastomosis between which two vascular systems?

. External iliac and obturator
. Internal iliac and pudendal
. Deep circumflex iliac and internal pudendal
. Superior gluteal and obturator
. Inferior gluteal and internal pudendal

Correct Answer & Explanation

. External iliac and obturator

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator vessels (branching from the internal iliac system) and the external iliac or inferior epigastric vessels. It crosses the superior pubic ramus and is highly susceptible to iatrogenic injury during the ilioinguinal approach or the modified Stoppa approach to the acetabulum/pelvis.

Question 4140

Topic: 1. General Principles & Basic Science
According to the Cierny-Mader classification system for osteomyelitis, a 'localized' (Type III) lesion is best defined by which of the following clinical and radiographic characteristics?
. Superficial infection strictly confined to the periosteum
. Medullary infection completely contained within the intramedullary canal without cortical involvement
. A full-thickness cortical sequestration that does not compromise the mechanical stability of the bone prior to debridement
. A diffuse, circumferential infection that requires an intercalary resection for eradication
. Any grade of infection occurring strictly in a systemically compromised host (C-class host)

Correct Answer & Explanation

. A full-thickness cortical sequestration that does not compromise the mechanical stability of the bone prior to debridement

Explanation

The Cierny-Mader classification defines osteomyelitis by anatomy and host status. Type I is medullary, Type II is superficial (periosteal), Type III is localized, and Type IV is diffuse. A Type III (localized) lesion is characterized by a full-thickness cortical sequestration or cavitation that can be surgically excised without compromising the mechanical stability of the bone prior to debridement. Type IV (diffuse) involves circumferential disease that requires segmental resection, leading to mechanical instability.

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