This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 1041
Topic: Infection, Pharmacology & VTE
What is the most significant disadvantage of using a hinged external fixator for elbow instability?
Correct Answer & Explanation
. High risk of infection at pin sites
Explanation
While hinged external fixators allow early range of motion, a significant disadvantage is the high risk of pin tract infection, which can lead to osteomyelitis or necessitate early removal. They are often used after closed or open reduction has restored joint congruity. They do not intrinsically prolong immobilization if designed to allow motion.
Question 1042
Topic: Infection, Pharmacology & VTE
How would you radiographically differentiate septic arthritis of the glenohumeral joint from advanced primary glenohumeral osteoarthritis in an 84-year-old lady?
Correct Answer & Explanation
. Septic arthritis presents with rapid, uniform joint space narrowing and early bone destruction
Explanation
Septic arthritis is characterized by rapid, uniform (concentric) joint space narrowing due to cartilage destruction, along with early subchondral bone erosions and overall periarticular osteopenia. While effusion might be present, it's not always definitively visible on plain X-rays. Osteoarthritis, by contrast, has a slower progression, typically asymmetric joint space narrowing (often inferomedial), prominent osteophytes, subchondral sclerosis, and cysts, without the rapid, destructive pattern of infection.
Question 1043
Topic: Infection, Pharmacology & VTE
On an 84-year-old lady's shoulder X-ray, you observe localized areas of increased bone density, particularly beneath the articular cartilage in the glenohumeral joint. What term describes this finding, and what does it typically indicate?
Correct Answer & Explanation
. Sclerosis, indicating degenerative change
Explanation
Sclerosis refers to increased bone density, often seen as 'whiteness' on an X-ray. Subchondral sclerosis is a classic radiographic sign of degenerative joint disease (osteoarthritis), representing a response to increased stress on the underlying bone. Osteopenia is decreased bone density. Lucency is decreased density. Sequestrum is dead bone in osteomyelitis. Erosion is bone loss, often from inflammatory arthritis.
Question 1044
Topic: Infection, Pharmacology & VTE
An X-ray of an elderly shoulder shows a cyst-like lesion in the humeral head subchondral bone, with sclerotic margins, but no communication with the joint. How would you best describe this finding, and what is its typical etiology?
Correct Answer & Explanation
. Geode (subchondral cyst)
Explanation
Geodes, also known as subchondral cysts, are common findings in osteoarthritis. They are fluid-filled cavities that form within the subchondral bone, often with sclerotic margins. While they can be large, they typically do not communicate with the joint space. Avascular necrosis shows collapse and increased density. A simple bone cyst is a different entity. Metastatic lesions would be more irregular. Septic arthritis causes destruction.
Question 1045
Topic: Infection, Pharmacology & VTE
A patient with a chronically infected TKA caused by methicillin-resistant Staphylococcus aureus (MRSA) is undergoing two-stage revision. During the first stage, extensive debridement is performed. What is the most appropriate empirical intravenous antibiotic regimen to initiate while awaiting definitive culture sensitivities?
Correct Answer & Explanation
. Vancomycin and Rifampin.
Explanation
For known or suspected MRSA PJI, vancomycin is the cornerstone of empirical treatment because of its reliable activity against MRSA. Rifampin is a potent anti-biofilm agent and is often added as a synergistic agent, particularly for staphylococcal infections, but it should never be used as monotherapy due to rapid resistance development. Cefazolin is ineffective against MRSA. Ciprofloxacin, clindamycin, ampicillin/sulbactam, and piperacillin/tazobactam are generally not reliably effective against MRSA. The combination of Vancomycin and Rifampin provides excellent coverage for MRSA and biofilm activity while awaiting sensitivities, although rifampin should be used with caution due to drug interactions and resistance potential.
Question 1046
Topic: Infection, Pharmacology & VTE
Which imaging modality is most sensitive for detecting early osteomyelitis or loosening in a periprosthetic infection setting when plain radiographs are inconclusive?
Correct Answer & Explanation
. Technetium-99m bone scan with Gallium-67 scan or Indium-111 labeled leukocyte scan.
Explanation
While MRI offers good soft tissue and bone marrow assessment, it is severely limited by artifact from metal implants. Nuclear medicine scans (Technetium-99m bone scan combined with Gallium-67 scan or Indium-111 labeled leukocyte scan) are generally considered the most sensitive and specific imaging modalities for detecting early osteomyelitis, implant loosening, and differentiating between aseptic loosening and septic loosening in the presence of metallic implants. Plain radiographs are initial, but often inconclusive. CT is good for bone detail but less sensitive for early infection. Ultrasound is useful for fluid collections but not osteomyelitis or loosening.
Question 1047
Topic: Infection, Pharmacology & VTE
What is the primary role of rifampin in the treatment regimen for staphylococcal periprosthetic joint infections?
Correct Answer & Explanation
. To act synergistically with other antibiotics by disrupting bacterial biofilm.
Explanation
Rifampin is highly effective in disrupting bacterial biofilms, particularly those formed by staphylococci. It is used synergistically with other antistaphylococcal agents (e.g., fluoroquinolones, vancomycin, beta-lactams) and should never be used as monotherapy due to the rapid development of resistance. It does not primarily cover Gram-negative organisms, and its main role is not bone penetration (though it has good penetration) but rather biofilm eradication. It does not directly reduce systemic inflammation as its primary action.
Question 1048
Topic: Infection, Pharmacology & VTE
What is the primary goal of extensive debridement during the first stage of a two-stage revision for PJI?
Correct Answer & Explanation
. To remove all infected and necrotic soft tissue and biofilm.
Explanation
The primary goal of extensive debridement during the first stage of a two-stage revision is to remove all infected and necrotic soft tissue, granulation tissue, and bacterial biofilm from the periprosthetic space and bone. This reduction of bacterial load is crucial for successful infection eradication. While preparing the bone for a spacer is a secondary outcome, the main focus is on meticulously cleaning the entire infected bed. Bone resection for lengthening is not a goal, and harvesting tissue is for closure, not debridement itself. Exposing vessels is not the primary goal.
Question 1049
Topic: Infection, Pharmacology & VTE
A 60-year-old male develops a PJI 1 year post-TKA due to coagulase-negative Staphylococcus. He undergoes a DAIR procedure. Which of the following oral antibiotics is most commonly used in combination with rifampin for suppressive or prolonged post-DAIR therapy for Staphylococcal PJI?
Correct Answer & Explanation
. Levofloxacin.
Explanation
For staphylococcal PJI (including coagulase-negative Staphylococci), a fluoroquinolone (like ciprofloxacin or levofloxacin) is often chosen to combine with rifampin for oral suppressive or prolonged post-DAIR therapy, due to its good bone penetration and synergy with rifampin against biofilm. However, given the options, Levofloxacin is the appropriate fluoroquinolone. Doxycycline can also be used but Levofloxacin is a more common and robust choice in this context. Cephalexin and clindamycin are typically less preferred for suppressive therapy with rifampin due to resistance profiles or less optimal synergy. Metronidazole has no activity against staphylococci.
Question 1050
Topic: Infection, Pharmacology & VTE
What is the recommended minimum duration of antibiotic therapy for a low-virulence PJI (e.g., CoNS) treated with DAIR and polyethylene exchange?
Correct Answer & Explanation
. 2-4 weeks IV + 3-6 months oral.
Explanation
For low-virulence organisms treated with DAIR, the typical recommendation is 2-4 weeks of targeted intravenous antibiotics, followed by a prolonged course of oral antibiotics for 3-6 months. This extended duration of oral suppressive therapy is crucial to prevent recurrence given the challenges of eradicating biofilm with implant retention. Shorter durations are associated with higher failure rates.
Question 1051
Topic: Infection, Pharmacology & VTE
What is the primary concern regarding the use of systemic fluoroquinolones (e.g., ciprofloxacin, levofloxacin) in combination with rifampin for Staphylococcal PJI?
Correct Answer & Explanation
. Rapid development of resistance if used as monotherapy and drug interactions with rifampin.
Explanation
While fluoroquinolones are effective against many Staphylococci and have good bone penetration, the primary concern when used in combination with rifampin is the rapid development of resistance if the fluoroquinolone is used as monotherapy, or if rifampin is not introduced simultaneously with a companion drug. Also, rifampin is a potent inducer of cytochrome P450 enzymes, leading to numerous drug-drug interactions that must be carefully managed. Renal toxicity is more associated with aminoglycosides and vancomycin. Anaphylaxis is not a primary concern for fluoroquinolones. Lack of efficacy is incorrect as they are often used in this setting.
Question 1052
Topic: Infection, Pharmacology & VTE
A patient with a severe fixed valgus deformity undergoes TKA. During surgery, significant tightness of the lateral compartment in both flexion and extension is noted. What is the most appropriate initial soft tissue release to address this?
Correct Answer & Explanation
. Lateral collateral ligament (LCL) release and popliteus tenotomy
Explanation
For a severe fixed valgus deformity with tightness of the lateral compartment in both flexion and extension, the primary structures causing this tightness are the lateral collateral ligament (LCL) and the popliteus tendon. Releasing these structures, along with the posterolateral capsule, is typically required to balance the lateral side. MCL and pes anserinus releases are for medial tightness. PCL release is for a tight flexion gap.
Question 1053
Topic: Infection, Pharmacology & VTE
A 40-year-old male with a history of intravenous drug use presents with septic arthritis of the sacroiliac joint. He is febrile and has severe gluteal pain, worsened by hip flexion and abduction. What is the most appropriate initial management?
Correct Answer & Explanation
. CT-guided aspiration for culture and drainage
Explanation
For suspected septic arthritis of the sacroiliac (SI) joint, especially in a high-risk patient like an intravenous drug user, the immediate priority after clinical suspicion is to confirm the diagnosis and identify the causative organism. A CT-guided aspiration allows for accurate fluid sampling for culture and Gram stain, as well as initial drainage of pus. Once the pathogen is identified, targeted intravenous antibiotics can be initiated. Oral antibiotics alone are insufficient for septic arthritis, and open surgical debridement is reserved for cases that fail percutaneous drainage or have extensive abscess formation.
Question 1054
Topic: Infection, Pharmacology & VTE
A 5-year-old child presents with a high fever, refusal to bear weight on his left leg, and exquisite tenderness over the distal metaphysis of the left femur. Laboratory tests show elevated ESR, CRP, and WBC count. Radiographs initially appear normal. What is the most likely diagnosis, and what is the next most appropriate diagnostic step?
Correct Answer & Explanation
. Osteomyelitis; MRI with contrast
Explanation
The constellation of fever, refusal to bear weight, localized bony tenderness, and elevated inflammatory markers in a child is highly suggestive of acute osteomyelitis. While radiographs may initially be normal, MRI with contrast is the most sensitive and specific imaging modality to confirm the diagnosis, localize the infection, and assess for abscess formation. Septic arthritis presents with joint pain and refusal to bear weight but typically involves joint effusions and pain with range of motion. Transient synovitis is a diagnosis of exclusion, usually with lower inflammatory markers and no specific bony tenderness. Juvenile idiopathic arthritis is a chronic condition. A stress fracture would not present with acute fever and high inflammatory markers.
Question 1055
Topic: Infection, Pharmacology & VTE
A 60-year-old male with a history of alcohol abuse presents with acute, severe pain, swelling, and redness in his right first metatarsophalangeal (MTP) joint. Synovial fluid aspiration reveals needle-shaped, negatively birefringent crystals. What is the most appropriate initial pharmacological treatment for the acute attack?
Correct Answer & Explanation
. Colchicine
Explanation
The clinical presentation and presence of needle-shaped, negatively birefringent crystals in the synovial fluid are diagnostic of acute gouty arthritis. For an acute attack, the primary goal is rapid pain and inflammation control. Colchicine, NSAIDs, and corticosteroids (such as oral prednisone or intra-articular injection) are the mainstays of acute treatment. Allopurinol, febuxostat, and probenecid are urate-lowering therapies used for long-term management to prevent recurrent attacks, but they are generally contraindicated during an acute flare as they can paradoxically worsen the attack by mobilizing urate crystals.
Question 1056
Topic: Infection, Pharmacology & VTE
A 60-year-old diabetic male undergoes an open reduction and internal fixation of a distal tibia fracture. Six months post-operatively, he presents with persistent drainage from the surgical site, pain, and erythema. Plain radiographs show sequestrum formation and involucrum. Laboratory markers indicate mildly elevated CRP, but ESR is normal. A deep tissue culture grows Staphylococcus aureus. What is the most appropriate definitive management for this chronic osteomyelitis?
Correct Answer & Explanation
. Surgical debridement, sequestrectomy, bone grafting, and targeted antibiotic therapy
Explanation
The presence of persistent drainage, radiographic evidence of sequestrum and involucrum, and a positive deep tissue culture confirm chronic osteomyelitis. For chronic osteomyelitis, surgical debridement (including sequestrectomy, removal of infected hardware, and debridement of necrotic bone), followed by reconstruction (e.g., bone grafting, muscle flaps if needed) and prolonged targeted antibiotic therapy (intravenous initially, then oral) is the cornerstone of definitive treatment. Long-term oral antibiotics alone are insufficient due to the presence of devitalized bone and biofilm. Amputation is a salvage procedure. Hyperbaric oxygen therapy is an adjunct, not a standalone definitive treatment.
Question 1057
Topic: Infection, Pharmacology & VTE
A 70-year-old female presents with acute, severe pain in her right knee, accompanied by warmth, swelling, and redness. She is afebrile. Synovial fluid aspiration reveals rhomboid-shaped, positively birefringent crystals. What is the most likely diagnosis?
The presence of rhomboid-shaped, positively birefringent crystals in the synovial fluid is diagnostic of calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, commonly known as pseudogout. Gout is characterized by needle-shaped, negatively birefringent crystals. Septic arthritis requires ruling out with cell count and culture, but crystal findings point away from it. Rheumatoid arthritis is a chronic inflammatory polyarthritis, and an acute flare would not typically show these crystals. Osteoarthritis is degenerative and does not typically involve crystal deposition unless it's a co-existing condition.
Question 1058
Topic: Infection, Pharmacology & VTE
When discussing the complications of a musculoskeletal infection (e.g., septic arthritis), what aspect is most indicative of a thorough understanding beyond just listing the sequelae?
Correct Answer & Explanation
. Explaining the pathophysiology of joint destruction, identifying factors influencing prognosis, and detailing long-term consequences and rehabilitation needs.
Explanation
A deep understanding of septic arthritis involves more than just recognizing the infection. It requires explaining the mechanisms of articular cartilage destruction, identifying prognostic factors (e.g., delay to diagnosis, organism virulence), and outlining the potential long-term sequelae such as joint stiffness, degenerative changes, and the need for ongoing rehabilitation or even reconstructive surgery. This shows a comprehensive grasp of the disease process and its implications.
Question 1059
Topic: Infection, Pharmacology & VTE
During a viva, you are asked about complications of anterior cruciate ligament (ACL) reconstruction. Beyond the standard surgical risks, what advanced complication should you proactively mention to demonstrate comprehensive knowledge?
While basic surgical complications (infection, bleeding, DVT) are expected, a high-scoring candidate will delve into ACL-specific complications. These include graft failure (re-rupture), arthrofibrosis (stiffness), persistent instability, specific nerve injuries related to graft harvest (e.g., saphenous nerve with patellar tendon or hamstring), and anterior knee pain. Discussing these specific issues demonstrates an in-depth understanding of the procedure's unique challenges.
Question 1060
Topic: Infection, Pharmacology & VTE
You are discussing the assessment of a child with a limp. What critical 'must-not-miss' diagnosis should you always consider and actively rule out to demonstrate a safe and thorough approach?
Correct Answer & Explanation
. Septic arthritis or osteomyelitis, given their potential for rapid joint destruction or systemic compromise.
Explanation
In a child with a limp, septic arthritis and osteomyelitis are critical 'must-not-miss' diagnoses due to their potential for rapid joint destruction, systemic sepsis, and long-term morbidity if not promptly diagnosed and treated. While other conditions like transient synovitis are more common, demonstrating vigilance for these severe infections showcases a safe and thorough clinical approach, crucial for high exam marks.
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