Infection, Pharmacology & VTE MCQs

Staphylococcus aureus is a predominant pathogen in periprosthetic joint infections. Its ability to form a robust biofilm is a key virulence factor. Which of the following molecules mediates the initial phase of biofilm formation, allowing S. aureus to adhere directly to host extracellular matrix proteins on the implant surface?

A 28-year-old farmer sustains a low-velocity gunshot wound to the thigh while hunting. The bullet did not hit the femur, but the entry wound is heavily contaminated with soil. According to orthopaedic principles for gunshot wounds, what is the most appropriate antibiotic prophylaxis?

A 65-year-old patient undergoing total hip arthroplasty is prescribed rivaroxaban for venous thromboembolism prophylaxis. What is the specific mechanism of action of this medication?

During the lifecycle of a bacterial biofilm on an infected orthopedic implant, which phase represents the systemic shedding of bacteria to colonize new sites?

Staphylococcus epidermidis is a frequent cause of prosthetic joint infections. Which of the following molecules primarily mediates the accumulation phase and the structural integrity of its biofilm?

Rivaroxaban is an oral anticoagulant commonly prescribed for deep vein thrombosis prophylaxis following total joint arthroplasty. What is its specific mechanism of action within the coagulation cascade?

A 3-year-old unimmunized child presents with a swollen, erythematous knee and a fever of 39°C. Arthrocentesis yields cloudy fluid with a WBC count of 85,000 cells/µL. Gram stain reveals Gram-negative coccobacilli. Which of the following is the most likely causative organism, and what is the optimal empiric antibiotic therapy?

A 7-year-old boy from an endemic area presents with an acute, massive effusion of his right knee. He is afebrile and tolerating weight-bearing. Joint aspiration yields 45,000 WBCs/mm3 with 80% neutrophils. Serology for Borrelia burgdorferi is positive. What is the most appropriate initial treatment?

Which of the following deep vein thrombosis (DVT) prophylaxis agents functions by directly inhibiting Factor Xa?

A 55-year-old female presents with bilateral knee pain. Joint aspiration yields synovial fluid analyzing for positively birefringent, rhomboid-shaped crystals. Radiographs show linear calcifications within the menisci (chondrocalcinosis). What is the diagnosis?

A 4-year-old girl is brought to the emergency department for refusal to bear weight on her right leg and low-grade fever. To differentiate between transient synovitis and septic arthritis, the Kocher criteria are utilized. Which of the following sets of clinical findings, if all present, provides a 99% predictive probability for a diagnosis of septic arthritis?

A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following total hip arthroplasty. What is the specific mechanism of action of this medication?

In the pathogenesis of orthopedic implant-related infections, which of the following describes the crucial step mediating the irreversible attachment of Staphylococcus aureus to an implant surface?

A 68-year-old woman is prescribed rivaroxaban for postoperative venous thromboembolism prophylaxis following a total hip arthroplasty. Which of the following represents the specific mechanism of action of this medication?

A 55-year-old male presents with a severely painful, swollen first metatarsophalangeal joint. Joint aspiration yields negatively birefringent, needle-shaped crystals under polarized light microscopy. Which of the following medications is most appropriate for the acute management of his symptoms?

During the pathogenesis of a prosthetic joint infection, which phase of biofilm formation is characterized by the down-regulation of bacterial metabolic activity, rendering the organisms highly resistant to systemic antibiotics?

The superficial medial collateral ligament (sMCL) of the knee is the primary restraint to valgus stress. Where is its precise distal anatomic insertion on the tibia?

A 10-year-old boy presents with a pathologic fracture through a central, lytic, expansile lesion in the proximal humerus metaphyseal-diaphyseal junction. A 'fallen leaf' sign is noted on the radiograph. If the lesion had been aspirated prior to fracture, the fluid obtained would typically show high levels of which of the following compared to serum?

What antithrombotic agent is a selective factor Xa inhibitor?

A 72-year-old man with previous total hip arthroplasty developed hip pain of 1 month’s duration. He underwent dental work 6 weeks ago. Aspiration showed a white blood cell count of > 6000 cells/µL (reference range, 4500-11000/µL) and presence of gram-positive cocci in clusters on gram stain. The orthopaedic surgeon recommended urgent debridement and irrigation. The components were judged to be stable with regard to fixation, and the surgeon elected to retain the implants. The patient had a final culture that revealed methicillin-resistant Staphylococcus aureus (MRSA). If the attending physician recommended the 2-stage protocol including the use of an antibiotic-cement spacer, what is the most likely prognosis for this patient?