OITE & ABOS Orthopedic MCQs: Trauma & Infection Pt 124

Question 1

A 45-year-old male presents with a draining sinus tract over his tibial shaft fracture, which was treated with an intramedullary nail 6 months ago. Cultures grow Staphylococcus epidermidis. During the process of biofilm formation on the hardware, which specific mechanism regulates the transition from initial bacterial attachment to mature biofilm architecture through complex cell-to-cell communication?

Explanation

Quorum sensing is the mechanism of cell-to-cell communication used by bacteria (such as S. aureus and S. epidermidis) to coordinate gene expression in response to population density. Once a critical threshold is reached, quorum sensing triggers the production of the extracellular polymeric substance (EPS) matrix and leads to biofilm maturation.

Question 2

According to the Fracture-Related Infection (FRI) Consensus Group, which of the following clinical or laboratory findings is considered a 'confirmatory' (absolute) criterion for diagnosing a fracture-related infection?

Explanation

The FRI Consensus definition identifies confirmatory criteria as: 1) a fistula/sinus tract communicating with bone/implant, 2) purulent drainage or pus around the bone/implant, 3) phenotypically identical pathogens isolated from 2 or more separate deep tissue/implant cultures, or 4) presence of microorganisms in deep tissue on histopathological examination. Elevated CRP, local clinical signs, and a single positive culture are 'suggestive' but not confirmatory.

Question 3

A 35-year-old farm worker sustains a Gustilo-Anderson Grade IIIA open tibia fracture that is heavily contaminated with soil and manure. In addition to prompt surgical debridement, which of the following antibiotic regimens classically represents the most appropriate initial prophylaxis for this specific injury pattern?

Explanation

For Grade III open fractures, standard historical protocol includes a first-generation cephalosporin (e.g., Cefazolin) and an aminoglycoside (e.g., Gentamicin). In cases of severe soil or farm contamination, there is a high risk of Clostridium perfringens infection (gas gangrene). Therefore, high-dose penicillin is classically added to the regimen to cover these anaerobic organisms.

Question 4

A 55-year-old diabetic patient presents with severe pain out of proportion to physical exam findings in his lower leg, 3 days after sustaining a minor abrasion.

Radiographs demonstrate tracking of subcutaneous gas. Laboratory workup reveals a WBC of 22,000/µL, CRP 250 mg/L, and Sodium 128 mEq/L. What is the most critical next step in management?

Explanation

This clinical picture, including pain out of proportion, subcutaneous gas, and laboratory derangements (e.g., high LRINEC score indicators like hyponatremia and elevated CRP/WBC), is highly indicative of necrotizing fasciitis. This is a surgical emergency. Immediate aggressive surgical debridement is life-saving and takes precedence over imaging or waiting for antibiotic efficacy.

Question 5

A 28-year-old veterinary technician presents with a painful, swollen, and erythematous right index finger 24 hours after sustaining a deep cat bite to the proximal phalanx. Which of the following pairs correctly matches the most likely causative pathogen with the appropriate empiric oral antibiotic of choice?

Explanation

Pasteurella multocida is the most common and rapidly presenting pathogen following a cat bite (often presenting within 24 hours). The prophylactic and empiric treatment of choice is Amoxicillin-clavulanate (Augmentin). Eikenella is associated with human bites, and Capnocytophaga with dog bites.

Question 6

A 4-year-old boy presents to the emergency department with a 2-day history of right hip pain and complete refusal to bear weight. His temperature is 38.6°C (101.5°F), WBC count is 13.5 x 10^9/L, ESR is 45 mm/hr, and CRP is 25 mg/L. According to the classic Kocher criteria, what is the approximate statistical probability that this child has a septic joint?

Explanation

The Kocher criteria for pediatric septic arthritis of the hip include: Non-weight-bearing, Temperature > 38.5°C, ESR > 40 mm/hr, and WBC > 12.0 x 10^9/L. This patient meets all 4 criteria. The probability of septic arthritis is approximately: 1 criterion = 3%, 2 criteria = 40%, 3 criteria = 93%, 4 criteria = 99%.

Question 7

A 40-year-old aquarium enthusiast presents with a chronic, nodular, non-healing ulcer on the dorsum of his hand.

He recalls a minor scrape on coral while cleaning his fish tank several weeks prior. If cultures are to be sent for the suspected organism, what special instruction must be given to the microbiology lab?

Explanation

The patient's history is classic for 'fish tank granuloma' caused by Mycobacterium marinum, an atypical mycobacterium. M. marinum grows optimally at lower temperatures (30°C to 32°C). Standard bacterial or mycobacterial cultures incubated at normal body temperature (37°C) often yield false-negative results.

Question 8

A 30-year-old construction worker sustains a deep, contaminated puncture wound to his boot from a rusty nail. His medical records confirm he received a full 5-dose childhood tetanus vaccination series, and his last Tdap booster was exactly 8 years ago. According to current guidelines, what is the appropriate tetanus prophylaxis for this patient today?

Explanation

For a 'dirty' or severe wound, a tetanus toxoid booster (Td or Tdap) is indicated if the patient has had a complete primary series but the last booster was more than 5 years ago. Tetanus immune globulin (TIG) is only indicated for dirty wounds if the patient has had fewer than 3 previous doses of tetanus toxoid or if the vaccination history is unknown.

Question 9

A 10-year-old African American girl with sickle cell disease develops osteomyelitis of the diaphysis of her right femur. While S. aureus is a common pathogen, she is at uniquely elevated risk for Salmonella osteomyelitis. Which of the following pathophysiological mechanisms most directly explains the source of the Salmonella bacteremia in this patient population?

Explanation

In patients with sickle cell disease, vaso-occlusion within the microvasculature of the gastrointestinal tract leads to localized bowel ischemia and microinfarcts. This compromises the mucosal barrier, allowing for the translocation of Salmonella species (which colonize the gut) into the systemic circulation. Additionally, infarcted bone marrow provides a favorable nidus for these bacteria to settle and proliferate.

Question 10

According to the Study to Prospectively Evaluate Reamed Intramedullary Nails in Patients with Tibial Fractures (SPRINT trial), how does the choice between reamed and unreamed intramedullary nailing affect outcomes in OPEN tibial shaft fractures?

Explanation

The landmark SPRINT trial evaluated reamed versus unreamed intramedullary nailing in tibial shaft fractures. For the subgroup of patients with OPEN fractures, the study found no statistically significant difference in primary outcomes (including deep infection and nonunion) between the two techniques. Reamed nailing did show a benefit in closed fractures.

Question 11

A 22-year-old male sustains a low-velocity civilian handgun injury to the thigh resulting in a nondisplaced midshaft femur fracture. Physical examination reveals no absent pulses, normal ABI, and soft compartments. Which of the following is the most appropriate management regarding the retained bullet lodged in the vastus lateralis?

Explanation

Low-velocity gunshot wounds (typical civilian handguns) that cause fractures are generally treated similarly to closed fractures or Grade I open fractures. Standard of care is local wound care, 24-48 hours of IV antibiotics, and appropriate fracture fixation. The bullet does not require removal unless it is intra-articular, impinging on a nerve/vessel, in the spinal canal causing a deficit, or causing mechanical block.

Question 12

A 35-year-old mechanic presents with an acutely swollen, painful ring finger 2 days after a puncture wound.

You suspect pyogenic flexor tenosynovitis. Which of the following physical examination findings is NOT one of Kanavel's four cardinal signs?

Explanation

Kanavel's four cardinal signs of flexor tenosynovitis are: 1) fusiform swelling of the digit, 2) finger held in resting slight flexion, 3) tenderness along the flexor tendon sheath, and 4) pain on passive extension. Pain with active flexion is not a Kanavel sign; patients generally refuse to actively move the digit.

Question 13

Polymethylmethacrylate (PMMA) impregnated with antibiotics is commonly utilized for local treatment of dead space in chronic osteomyelitis. Which of the following statements accurately describes the release kinetics and properties of antibiotic-loaded PMMA?

Explanation

Antibiotic release from PMMA is a surface phenomenon. It is characterized by an initial 'burst' effect with high local concentrations within the first 24-48 hours, followed by a rapid exponential decline. PMMA polymerization is highly exothermic (which requires heat-stable antibiotics like vancomycin and aminoglycosides). Adding high doses of antibiotics negatively impacts the mechanical properties of the cement.

Question 14

A 65-year-old male develops an acute hematogenous periprosthetic joint infection (PJI) of his total knee arthroplasty, 2 years postoperatively. The pathogen is identified as Staphylococcus aureus. He undergoes an urgent Debridement, Antibiotics, and Implant Retention (DAIR) procedure. Which of the following antimicrobial agents is uniquely effective against the stationary-phase bacteria embedded within the retained biofilm?

Explanation

Rifampin has unique properties allowing it to penetrate biofilms and effectively kill stationary-phase staphylococci. It is a cornerstone of therapy in DAIR procedures for staphylococcal PJI. However, it must always be used in combination with another active antibiotic (often a fluoroquinolone) because monotherapy leads to rapid emergence of rifampin resistance.

Question 15

A 60-year-old patient with chronic osteomyelitis of the tibia is evaluated for surgical management. The infection is classified as Cierny-Mader Type III-B. What does this classification specifically indicate about the disease pattern and the host?

Explanation

The Cierny-Mader classification evaluates both the anatomic extent of the infection and the physiologic status of the host. Anatomic types: I (Medullary), II (Superficial), III (Localized - full-thickness cortical sequestration but mechanically stable), IV (Diffuse - mechanically unstable). Host types: A (Normal), B (Compromised - local or systemic), C (Treatment worse than the disease). Type III-B indicates localized osteomyelitis in a compromised host.

Question 16

In the management of a severely injured polytrauma patient, the concept of 'Damage Control Orthopedics' (DCO) aims to mitigate the risk of Multiple Organ Dysfunction Syndrome (MODS). According to the 'two-hit' hypothesis, which of the following interventions classically constitutes an iatrogenic 'second hit' if performed during the peak inflammatory window (days 2 to 5 post-injury)?

Explanation

The initial trauma serves as the 'first hit', activating the systemic inflammatory response syndrome (SIRS). A major definitive surgery, such as reamed intramedullary nailing of a femur, acts as an iatrogenic 'second hit' that can amplify the inflammatory cascade, leading to ARDS and MODS. DCO (using external fixation) minimizes this second hit.

Question 17

A 6-year-old boy from Connecticut presents with an acute, painless, massive effusion of his right knee.

Aspiration reveals a WBC count of 45,000 cells/µL with a neutrophil predominance. Serology for Borrelia burgdorferi is positive. What is the most appropriate first-line treatment?

Explanation

This patient has Lyme arthritis. The first-line treatment for Lyme arthritis without neurologic involvement is a 28-day course of oral antibiotics. In children under 8 years of age, amoxicillin is the drug of choice because doxycycline can cause permanent tooth discoloration and enamel hypoplasia. Surgery is not the first-line treatment for Lyme arthritis.

Question 18

A 45-year-old agricultural worker who resides in the San Joaquin Valley of California presents with a 6-month history of right knee pain and swelling. Radiographs show a lytic lesion in the distal femur. Biopsy of the lesion reveals thick-walled spherules containing endospores. Which of the following is the most likely causative organism?

Explanation

Coccidioidomycosis ('Valley Fever') is caused by Coccidioides immitis or C. posadasii, which are endemic to the arid regions of the Southwestern US, including the San Joaquin Valley. The classic histological hallmark of Coccidioides is the presence of thick-walled spherules containing endospores.

Question 19

According to the 2018 International Consensus Meeting (ICM) criteria for Periprosthetic Joint Infection, which of the following synovial fluid biomarkers serves as a highly specific indicator of PJI by directly reflecting the presence of neutrophil-derived antimicrobial peptides?

Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils in response to pathogens. The synovial fluid alpha-defensin test has been incorporated into the ICM criteria as a highly sensitive and specific biomarker for diagnosing periprosthetic joint infection, regardless of prior antibiotic use or systemic inflammation.

Question 20

The 'MESS' (Mangled Extremity Severity Score) is a historical clinical tool designed to help predict the necessity of primary amputation versus limb salvage in severe lower extremity trauma. Which of the following variables is NOT formally included in the calculation of the MESS?

Explanation

The MESS evaluates 4 parameters: Skeletal/soft-tissue injury mechanism (1-4 points), Limb ischemia (1-3 points, doubled if ischemia >6 hours), Shock (0-2 points), and Patient Age (0-2 points). While an absent plantar sensation or sciatic nerve deficit is highly clinically relevant in decision-making, neurological deficit is NOT a mathematically scored variable in the MESS.

Question 21

A 55-year-old diabetic male presents with rapidly progressive leg swelling, erythema, and disproportionate pain after a minor abrasion. Lab work shows CRP 200 mg/L, WBC 18x10^9/L, Hemoglobin 11 g/dL, Sodium 130 mmol/L, Creatinine 1.8 mg/dL, and Glucose 200 mg/dL. Based on the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score, what is the most appropriate next step?

Explanation

The LRINEC score stratifies risk for necrotizing fasciitis based on CRP, WBC, Hb, Na, Creatinine, and Glucose. A score >= 6 indicates a high risk, warranting immediate surgical exploration, which is both diagnostic and life-saving.

Question 22

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) cement for the treatment of chronic osteomyelitis, which of the following properties is characteristic of an ideal antibiotic additive?

Explanation

Ideal antibiotics for PMMA inclusion must be heat stable, available in powder form to avoid altering cement mechanical properties, water-soluble for elution, and have a broad spectrum. Liquid antibiotics severely degrade the structural integrity of the cement.

Question 23

A 42-year-old female presents with chronic osteomyelitis of the femur. The infection is characterized as a diffuse osteomyelitis involving the entire circumference of the segment, necessitating an intercalary resection. She has a history of smoking and poorly controlled diabetes. According to the Cierny-Mader classification, what is her clinical stage?

Explanation

The Cierny-Mader system classifies osteomyelitis by anatomy (I: medullary, II: superficial, III: localized, IV: diffuse) and host status (A: normal, B: compromised, C: treatment worse than disease). Diffuse involvement causing instability or requiring segmental resection in a diabetic host is Type IV B.

Question 24

A 28-year-old male presents with a clenched-fist injury after striking another individual in the mouth, resulting in a laceration over the 3rd metacarpophalangeal joint. In addition to Staphylococcus and Streptococcus, which of the following organisms dictates the specific empiric antibiotic choice?

Explanation

Human bite wounds, particularly clenched-fist injuries, carry a high risk of Eikenella corrodens infection. Empiric treatment typically involves amoxicillin-clavulanate to cover this along with common skin and oral flora.

Question 25

A 30-year-old male sustains a Gustilo-Anderson IIIB open tibia fracture. Following initial definitive skeletal stabilization and thorough debridement, what is the optimal timeframe for definitive soft tissue coverage to minimize the risk of deep infection?

Explanation

Extensive literature demonstrates that definitive soft tissue coverage of severe open tibia fractures within 5 to 7 days significantly decreases the rates of deep infection and flap failure. Delaying coverage beyond this window increases complication rates.

Question 26

During the second stage of the Masquelet technique for an infected tibial nonunion, a surgeon plans to remove the antibiotic cement spacer and place bone graft. What is the optimal timing for this second stage to maximize the osteogenic potential of the induced membrane?

Explanation

The second stage of the Masquelet technique is ideally performed 6 to 8 weeks after spacer placement. At this time, the induced membrane has optimal vascularity and peak expression of osteogenic growth factors like VEGF and BMP-2.

Question 27

A 65-year-old male is undergoing treatment for a retained orthopedic implant infection caused by methicillin-susceptible Staphylococcus aureus. Which of the following antibiotics is uniquely effective against the stationary-phase bacteria residing deep within the established biofilm?

Explanation

Rifampin has high penetrability into biofilms and unique bactericidal activity against stationary-phase staphylococci. It should never be used as monotherapy due to rapid resistance, but is a critical adjunct in retained hardware infections.

Question 28

A 40-year-old farmer sustains a severe, contaminated open forearm fracture from a tractor accident. He is unsure of his tetanus immunization history but believes he had some childhood shots. What is the appropriate tetanus prophylaxis strategy in the emergency department?

Explanation

For a tetanus-prone wound in a patient with an unknown or incomplete (<3 doses) immunization history, both the tetanus toxoid-containing vaccine and tetanus immune globulin (TIG) are indicated.

Question 29

A soldier sustains severe bilateral lower extremity blast injuries from an IED. Several days after initial debridement, the wounds develop a progressive, necrotic appearance with a grayish mold. Histology reveals broad, non-septate hyphae branching at right angles. What is the most appropriate systemic pharmacological treatment?

Explanation

The clinical presentation and histology (broad, non-septate hyphae with right-angle branching) are classic for mucormycosis. Treatment requires extensive surgical debridement and systemic liposomal amphotericin B.

Question 30

A 25-year-old male presents with profound toxemia, tachycardia, and a bronze discoloration of the skin over his thigh 48 hours after sustaining a penetrating dirt-contaminated injury. Crepitus is palpable. Gram stain of the wound exudate shows large Gram-positive rods and an absence of polymorphonuclear leukocytes. Which of the following pathogens is the most likely cause?

Explanation

Clostridium perfringens causes gas gangrene (clostridial myonecrosis), characterized by rapid onset, bronze skin discoloration, crepitus, and systemic toxicity. The absence of PMNs on Gram stain is due to the elaboration of alpha and theta toxins that lyse leukocytes.

Question 31

A 55-year-old diabetic male presents with severe lower extremity pain out of proportion to exam and swelling. A necrotizing soft tissue infection is suspected. According to the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score, which of the following laboratory parameters is most heavily weighted, yielding the maximum possible points for a single variable if highly elevated?

Explanation

The LRINEC score utilizes CRP, WBC, hemoglobin, sodium, creatinine, and glucose. A CRP > 150 mg/L yields the highest individual point value (4 points) in this scoring system.

Question 32

A 32-year-old male is treated for an acute periprosthetic infection of a tibia intramedullary nail with debridement, antibiotics, and implant retention (DAIR). Cultures return positive for methicillin-resistant Staphylococcus aureus (MRSA). Which of the following adjunctive oral antibiotics is most critical for penetrating the established bacterial biofilm on the retained hardware?

Explanation

Rifampin has high activity against staphylococcal species residing in the stationary phase within biofilms. It should never be used as monotherapy due to rapid resistance development, but is an essential adjunct in implant-retained staphylococcal infections.

Question 33

A 24-year-old male sustains an open distal tibia fracture after crashing his ATV into a freshwater lake. He is started on broad-spectrum antibiotics and taken for urgent debridement. To adequately cover the most characteristic virulent pathogen associated with freshwater contamination, which of the following antibiotics is typically recommended?

Explanation

Aeromonas hydrophila is the classic pathogen associated with freshwater injuries. It is typically susceptible to fluoroquinolones, third-generation cephalosporins, and aminoglycosides, making them crucial additions to the antibiotic regimen.

Question 34

A 40-year-old fisherman sustains an open radius fracture from a boat propeller in the Gulf of Mexico. Within 24 hours, he develops rapidly progressive hemorrhagic bullae and septic shock. Which of the following is the most likely causative organism?

Explanation

Vibrio vulnificus is a highly virulent, gram-negative, comma-shaped bacterium found in warm, coastal marine environments. It classically causes rapidly progressive necrotizing wound infections and sepsis, particularly in patients with underlying liver disease.

Question 35

A 12-year-old girl is evaluated for a deep cat bite to her index finger over the MCP joint. Which of the following is the most appropriate prophylactic antibiotic regimen to prevent the most likely infectious complication?

Explanation

Pasteurella multocida is the most common and clinically significant pathogen in cat bite wounds. Amoxicillin-clavulanate provides excellent coverage for Pasteurella, as well as other potential oral flora anaerobes and Staphylococcus species.

Question 36

During the first stage of the Masquelet technique for an infected 6 cm tibial diaphyseal defect, a polymethylmethacrylate (PMMA) spacer is inserted. When performing the second stage 6 to 8 weeks later, what is the primary biological function of the induced pseudosynovial membrane?

Explanation

The PMMA spacer induces the formation of a highly vascularized, fibrous "pseudo-membrane" over 6 to 8 weeks. This membrane secretes critical growth factors like VEGF, TGF-beta, and BMP-2, creating a favorable biological environment for the subsequent bone graft.

Question 37

In the Masquelet technique for managing infected bone defects, a PMMA cement spacer is placed to induce a biological membrane. At what time point does this induced membrane typically exhibit its peak concentration of vascular endothelial growth factor (VEGF) and osteoinductive factors (e.g., BMP-2)?

Explanation

The biological activity of the induced membrane, including peak vascularity and concentrations of VEGF and BMP-2, is highest at 2 to 4 weeks post-implantation. While the second stage (bone grafting) is often practically performed at 6 to 8 weeks, the physiological peak occurs earlier.

Question 38

A 55-year-old poorly controlled diabetic male with peripheral neuropathy presents with a chronic draining sinus tract over his anterior tibia. Imaging shows a cortical sequestrum with a distinct reactive involucrum, but the medullary canal is entirely spared and the bone is biomechanically stable. According to the Cierny-Mader classification, what is the correct designation for this patient's osteomyelitis?

Explanation

This is a Type III (Localized) osteomyelitis because it involves full-thickness cortical sequestration that is mechanically stable, without diffuse medullary involvement (Type IV) or mere superficial involvement (Type II). The patient is a Type B host due to systemic compromise (diabetes, neuropathy).

Question 39

A 34-year-old male sustains a severely contaminated open tibia fracture from a farming accident. He states he has never received any childhood vaccines and does not know his tetanus status. What is the most appropriate tetanus prophylaxis strategy in the emergency department?

Explanation

For a patient with an unknown or incomplete primary tetanus immunization history (<3 doses) who presents with a dirty or contaminated wound, BOTH the tetanus toxoid vaccine (Td or Tdap) and Tetanus Immune Globulin (TIG) are strictly indicated.

Question 40

A 60-year-old male presents with severe leg pain, swelling, and tense erythema out of proportion to physical findings. You calculate a Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score. Which of the following laboratory values contributes the highest possible point value (4 points) to this scoring system?

Explanation

In the LRINEC score, a C-reactive protein (CRP) level greater than 150 mg/L contributes the highest single weight of 4 points. The other variables (WBC, Hb, Sodium, Creatinine, Glucose) contribute 1 to 2 points when abnormal.

Question 41

A 28-year-old female presents with acute purulent drainage, erythema, and fever 16 days after undergoing ORIF of a closed tibial shaft fracture. Radiographs show unchanged, stable hardware alignment. According to the principles of Debridement, Antibiotics, and Implant Retention (DAIR), which of the following features makes this patient an appropriate candidate for hardware retention?

Explanation

DAIR is generally indicated for acute fracture-related infections presenting within 3 to 4 weeks of surgery, provided the hardware remains mechanically stable and the soft tissue envelope can be closed. Loose hardware or chronic infections require implant removal.

Question 42

Systemic antibiotic therapy often fails to eradicate fracture-related infections due to biofilm formation on the orthopedic implants. Which of the following accurately describes the relationship between the minimum inhibitory concentration (MIC) for planktonic bacteria and the minimum biofilm eradication concentration (MBEC)?

Explanation

Bacteria within a mature biofilm enter a stationary metabolic phase and are protected by an extracellular polymeric substance. This makes them highly resistant to antimicrobials, resulting in an MBEC that is 100 to 1000 times higher than the MIC of free-floating (planktonic) bacteria.

Question 43

A 45-year-old male sustains a Gustilo-Anderson IIIB open fracture of the distal third of the tibia with extensive soft tissue loss exposing the bone and hardware. Following serial debridements and negative cultures, which of the following is the most appropriate option for soft tissue coverage of this specific defect?

Explanation

Soft tissue defects of the distal third of the tibia lack adequate local muscle bulk for rotational flaps. They typically require free tissue transfer (e.g., ALT, latissimus dorsi) for definitive coverage. Gastrocnemius covers the proximal third, and soleus covers the middle third.

Question 44

A 22-year-old male presents 3 days after striking an opponent in the mouth during a fistfight. He has a 1 cm laceration over the 3rd metacarpophalangeal joint with surrounding erythema and purulence. During formal surgical I&D, which of the following systemic antibiotic regimens is most appropriate to empirically cover the classic pathogen associated with this specific mechanism?

Explanation

This is a 'fight bite' (clenched fist injury against human teeth). The classic associated pathogen is Eikenella corrodens, alongside other mixed flora. Ampicillin-sulbactam (IV) or amoxicillin-clavulanate (PO) are the empiric treatments of choice.

Question 45

A 30-year-old construction worker sustains a deep, heavily contaminated crush injury to his thigh. 48 hours later, he develops severe pain, tachycardia, and palpable crepitus in the thigh. Gram stain of the wound exudate reveals large Gram-positive rods without spores. Which of the following is the primary virulence factor responsible for tissue destruction in this infection?

Explanation

The clinical picture and Gram stain (large Gram-positive, boxcar-shaped rods without spores) are classic for Clostridium perfringens gas gangrene. Its major virulence factor is alpha-toxin, a lecithinase (phospholipase C) that destroys cell membranes.

Question 46

Which of the following interventions has been shown in the orthopedic literature to have the most significant impact on reducing the risk of deep infection in the management of high-energy open tibia fractures?

Explanation

Early administration of systemic intravenous antibiotics (ideally within 1 hour of injury) is the most critical factor in reducing the infection rate in open fractures. Delays in antibiotic administration significantly increase the risk of osteomyelitis.

Question 47

According to the Fracture-Related Infection (FRI) Consensus Group, diagnosing an FRI involves 'confirmatory' and 'suggestive/suspicious' criteria. Which of the following is considered a 'suggestive' criterion rather than a 'confirmatory' absolute criterion?

Explanation

Elevated serum inflammatory markers (CRP, WBC), fever, and erythema are 'suggestive' criteria for FRI. Confirmatory criteria include a sinus tract, gross purulence, identical pathogens in 2+ separate deep cultures, or positive histopathology (>5 PMNs/HPF).

Question 48

When utilizing local antibiotic delivery vehicles for the treatment of chronic osteomyelitis, synthetic calcium sulfate has gained popularity as an alternative to polymethylmethacrylate (PMMA). Which of the following is a recognized disadvantage or complication specifically associated with calcium sulfate beads?

Explanation

Calcium sulfate is fully bioabsorbable and does not require a second surgery for removal (unlike non-absorbable PMMA). However, its rapid degradation often leads to significant sterile serous wound drainage, which can mimic persistent infection.

Question 49

A 25-year-old male sustains a low-velocity handgun gunshot wound to the right knee. Radiographs reveal a retained bullet lodged within the medial femoral condyle, and a CT scan confirms the bullet trajectory crossed the articular cavity. Which of the following is the most appropriate initial orthopedic management?

Explanation

While extra-articular low-velocity gunshot wounds can often be managed with local wound care, an intra-articular bullet or trajectory transversing the joint requires prompt arthroscopic or open joint debridement, irrigation, and removal of the bullet to prevent septic arthritis and lead arthropathy.

Question 50

A 40-year-old male undergoes excision of an infected tibial nonunion, resulting in a 6-cm diaphyseal defect. The defect is managed via distraction osteogenesis (bone transport) using a circular Ilizarov frame. Following the proximal corticotomy, what is the optimal protocol for latency and rate of distraction?

Explanation

The classic Ilizarov protocol for bone transport and distraction osteogenesis involves a latency period of 7 to 10 days to allow early callus formation, followed by a distraction rate of 1.0 mm per day, optimally divided into four 0.25 mm increments.

Question 51

A healthy 30-year-old male sustains a minor laceration to his forearm that rapidly progresses over 24 hours to severe pain, bullae formation, and skin necrosis. Surgical exploration reveals classic Type II (monomicrobial) necrotizing fasciitis. Which of the following is the most common causative organism for this specific classification?

Explanation

Type II necrotizing fasciitis is monomicrobial and classically caused by Group A Streptococcus (Streptococcus pyogenes). Type I is polymicrobial and typically occurs in immunocompromised or diabetic hosts.

Question 52

In the evaluation of a mangled lower extremity, the Mangled Extremity Severity Score (MESS) is historically utilized to assist in the decision between salvage and amputation. Which of the following parameters in the MESS scoring system has its point value doubled if the delay to treatment exceeds 6 hours?

Explanation

In the MESS criteria, the score for Limb Ischemia (which ranges from 1 to 3 points based on pulse and capillary refill) is doubled if the duration of ischemia exceeds 6 hours. A total MESS score of 7 or higher historically predicted amputation.

Question 53

A 62-year-old male with a 30-year history of chronic osteomyelitis of the tibia secondary to an open fracture presents with a newly enlarging, fungating, exophytic mass arising from his chronic draining sinus tract. What is the most likely pathological diagnosis of this mass?

Explanation

A malignant transformation arising within a chronic osteomyelitis sinus tract or chronic burn scar is known as a Marjolin's ulcer. Histologically, the vast majority of these lesions are squamous cell carcinomas (SCC).

Question 54

When formulating antibiotic-loaded polymethylmethacrylate (PMMA) cement for an articulating spacer in a two-stage revision, certain antibiotics are preferred due to their heat stability and elution properties. Which of the following antibiotics is generally CONTRAINDICATED for mixing into PMMA due to significant disruption of the polymerization process?

Explanation

Rifampin is generally contraindicated for mixing into PMMA cement because it acts as a radical scavenger, severely inhibiting the exothermic polymerization reaction and preventing the cement from curing properly.

Question 55

A 2-year-old child presents with a limp, refusal to bear weight, and low-grade fever. Joint aspiration yields purulent fluid. Gram stain is negative, but the physician suspects an increasingly common fastidious Gram-negative organism. Inoculation of the synovial fluid into which specific medium significantly increases the yield for this particular pathogen?

Explanation

Kingella kingae is a fastidious Gram-negative organism that is now recognized as a leading cause of pediatric septic arthritis. Inoculating the synovial fluid directly into aerobic blood culture vials (e.g., BACTEC) significantly increases the isolation yield.

Question 56

During revision surgery for a suspected fracture-related infection (FRI), intraoperative tissue samples are sent for histopathological analysis. According to the international consensus definition, which of the following findings is an absolute (confirmatory) criterion for FRI?

Explanation

The consensus criteria for FRI define >5 polymorphonuclear neutrophils (PMNs) per high-power field in at least five separate fields as a confirmatory (absolute) sign of infection. A single positive culture or elevated inflammatory markers are considered suggestive, not confirmatory.

Question 57

A 40-year-old male is undergoing the induced membrane (Masquelet) technique for an infected 8 cm tibial bone defect. Following placement of the PMMA spacer, what is the peak timeframe for maximal vascularity and expression of osteoinductive factors (e.g., VEGF) within the newly formed pseudomembrane?

Explanation

Studies demonstrate that the induced membrane in the Masquelet technique reaches its peak vascularity and maximal expression of growth factors (such as VEGF and BMP-2) at approximately 4 weeks post-implantation. Waiting excessively long (e.g., >8 weeks) results in a thicker, less vascular, and fibrotic membrane.

Question 58

A 28-year-old surfer sustains an open tibia fracture after striking a coral reef. The wound is heavily contaminated with saltwater and marine debris. Which of the following organisms should be specifically covered in the initial empiric antibiotic regimen?

Explanation

Saltwater and marine injuries carry a high risk for infection with Vibrio vulnificus. Empiric antibiotic coverage should include a third-generation cephalosporin or a fluoroquinolone to adequately cover this organism, alongside standard open fracture prophylaxis.

Question 59

A 55-year-old farmer sustains a severely crushed, contaminated open femur fracture. He has not received a tetanus booster in 15 years, and his childhood immunization status is unknown. What is the most appropriate tetanus prophylaxis regimen?

Explanation

For a patient with unknown or incomplete initial tetanus immunization (<3 doses) who sustains a tetanus-prone (dirty/contaminated) wound, both the tetanus toxoid-containing vaccine and tetanus immune globulin (TIG) are indicated. Clean wounds in such patients require only the toxoid.

Question 60

A 72-year-old female presents with an acute hematogenous periprosthetic joint infection of her total hip arthroplasty caused by a susceptible strain of Staphylococcus aureus. She undergoes debridement, antibiotics, and implant retention (DAIR). Following initial IV therapy, which oral antibiotic is highly recommended as part of a combination regimen due to its potent anti-biofilm properties?

Explanation

Rifampin has unique efficacy against staphylococcal species residing within biofilms on orthopedic hardware. It should never be used as monotherapy due to rapid resistance emergence, but it is standardly combined with agents like fluoroquinolones for suppressive or step-down therapy following DAIR.

Question 61

According to the Cierny-Mader classification of osteomyelitis, how is a Type III (localized) osteomyelitis best described anatomically?

Explanation

In the Cierny-Mader system, Type III (localized) osteomyelitis involves a full-thickness cortical sequestration. Excision of the lesion does not typically compromise the mechanical stability of the bone, unlike Type IV (diffuse) osteomyelitis, which requires segmental resection.

Question 62

A 24-year-old male sustains a clenched-fist bite wound over the third metacarpophalangeal joint. Cultures subsequently grow Eikenella corrodens. Which of the following antibiotics is this organism characteristically resistant to?

Explanation

Eikenella corrodens is a Gram-negative bacillus frequently found in human bite wounds. It is characteristically resistant to clindamycin, first-generation cephalosporins, and macrolides, making amoxicillin-clavulanate the first-line treatment of choice.

Question 63

A patient with an open tibial fracture develops a methicillin-resistant Staphylococcus aureus (MRSA) infection. Intravenous vancomycin is initiated. What is the precise mechanism of action of this antibiotic?

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis by binding tightly to the D-alanyl-D-alanine portion of cell wall precursors. This prevents the cross-linking of peptidoglycan matrices.

Question 64

When formulating antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for the treatment of an infected tibial nonunion, which of the following physical properties is absolutely essential for the admixed antibiotic?

Explanation

The curing of PMMA is an exothermic reaction that can generate temperatures high enough to denature many drugs. Therefore, any antibiotic mixed into bone cement must be highly thermostable (e.g., vancomycin, tobramycin, gentamicin).

Question 65

The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score utilizes routine laboratory tests to stratify the risk of necrotizing fasciitis. Which of the following parameters carries the highest potential point value in this scoring system?

Explanation

In the LRINEC score, a C-reactive protein (CRP) level > 150 mg/L contributes 4 points, which is the highest single block of points for any individual parameter in the scoring system.

Question 66

A 32-year-old male sustains a Gustilo-Anderson Grade IIIB open tibia fracture. According to Godina’s classic study on early microsurgical reconstruction, free tissue transfer performed within what timeframe is associated with the lowest rates of flap failure and deep infection?

Explanation

Marko Godina's landmark 1986 study demonstrated that early free flap coverage of complex extremity trauma within 72 hours of injury significantly minimized infection rates, flap failure, and time to bone union.

Question 67

A 25-year-old male sustains a low-velocity gunshot wound to the knee. Radiographs reveal a retained bullet fragment entirely within the joint space. Which of the following is the most appropriate management?

Explanation

Intra-articular retained bullets must be surgically removed. If left inside a synovial joint, synovial fluid dissolves the lead, risking systemic lead toxicity (plumbism) and mechanical destruction of the articular cartilage.

Question 68

In the pathogenesis of fracture-related infections, Staphylococcus aureus utilizes a mechanism to regulate virulence factors and biofilm dispersion based on population density. Which specific system is the primary regulator of this quorum sensing?

Explanation

The accessory gene regulator (agr) system in S. aureus is a quorum-sensing system that controls the expression of numerous virulence factors and is critical for biofilm maturation and dispersion.

Question 69

When evaluating a severely traumatized lower extremity to determine the viability of limb salvage, the Mangled Extremity Severity Score (MESS) is often calculated. Which of the following variables is NOT a component of the MESS?

Explanation

The MESS scoring system includes Skeletal/Soft-tissue injury, Limb ischemia, Age, and Shock. Distal neurological status, such as an insensate foot, is an independent factor often debated but is formally excluded from the MESS calculation.

Question 70

A 50-year-old diabetic patient with advanced Charcot neuroarthropathy of the midfoot presents with a new chronic overlying ulcer. MRI is equivocal due to profound architectural distortion. Which advanced imaging modality provides the highest specificity for diagnosing underlying osteomyelitis in this setting?

Explanation

The combined leukocyte/bone marrow scan is highly specific for differentiating osteomyelitis from the sterile inflammation of Charcot arthropathy. Osteomyelitis shows uptake of white blood cells without corresponding marrow uptake, whereas a Charcot flare shows concordant uptake.

Question 71

Which of the following statements most accurately describes the elution profile of antibiotics from polymethylmethacrylate (PMMA) bone cement beads placed in a fracture-related infection?

Explanation

Antibiotic elution from PMMA follows a biphasic pattern characterized by a rapid 'burst' release of the drug in the first 24-72 hours, followed by a precipitous decline to sub-therapeutic levels, often acting as a substrate for biofilm if left in place long-term.

Question 72

A 35-year-old aquarium worker sustains a puncture wound to the hand. Six weeks later, he presents with a chronic, granulomatous nodule and flexor tenosynovitis. Cultures are sent. What is the most likely causative organism and its optimal laboratory growth temperature?

Explanation

Mycobacterium marinum is an atypical mycobacterium associated with aquatic environments (fish tanks, non-chlorinated pools). It requires a cooler incubation temperature of roughly 28-32°C (optimally 30°C) for successful culture growth.

Orthopedic Surgery Board Review MCQs: Arthroplasty, Ligament & Spine | Part 149

OITE & ABOS Orthopedic Board Prep MCQs: Trauma & Infection Part 124

Key Takeaway

OITE & ABOS Orthopedic Board Prep MCQs: Trauma & Infection Part 124

Chapter Index