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 421
Topic: Infection, Pharmacology & VTE
During an open reduction and internal fixation of a posteromedial tibial plateau fracture, the surgeon utilizes a posteromedial approach. Which structure represents the lateral interval boundary when accessing the posteromedial tibia?
Correct Answer & Explanation
. Medial head of the gastrocnemius
Explanation
The posteromedial approach to the proximal tibia utilizes the interval between the medial head of the gastrocnemius laterally and the pes anserinus medially. Retracting the medial head of the gastrocnemius laterally is critical as it acts as a soft-tissue shield to protect the popliteal neurovascular bundle.
Question 422
Topic: Infection, Pharmacology & VTE
A surgeon is utilizing a posteromedial approach to internally fix a complex shear fracture of the medial tibial plateau. To correctly perform the deep dissection and avoid damaging vital structures, the internervous/intermuscular interval should be developed between which of the following structures?
Correct Answer & Explanation
. Medial head of the gastrocnemius and the pes anserinus
Explanation
The posteromedial approach to the proximal tibia utilizes an intermuscular interval between the medial head of the gastrocnemius (which is retracted laterally/posteriorly to protect the neurovascular bundle) and the pes anserinus tendons (semitendinosus, gracilis, and sartorius, which are retracted medially/anteriorly). The semimembranosus tendon lies deep and must be carefully managed in this plane.
Question 423
Topic: Infection, Pharmacology & VTE
During a revision shoulder arthroplasty for a painful, stiff TSA, intraoperative cultures are obtained. At 10 days, the cultures grow Cutibacterium acnes. Which characteristic of this organism makes it particularly challenging to diagnose and treat in the setting of shoulder arthroplasty?
Correct Answer & Explanation
. It produces a robust biofilm and typically lacks classic systemic inflammatory signs.
Explanation
Cutibacterium acnes (formerly Propionibacterium acnes) is a slow-growing, Gram-positive, anaerobic rod commonly found in the sebaceous glands of the shoulder. It often causes indolent, low-grade periprosthetic joint infections lacking classic clinical signs (e.g., normal CRP/ESR, no fever, no erythema). Its ability to form a protective biofilm on implants makes both diagnosis (requiring extended culture times) and eradication challenging.
Question 424
Topic: Infection, Pharmacology & VTE
A 45-year-old male with a history of intravenous drug use presents with severe back pain. Laboratory tests show elevated ESR and CRP. MRI with contrast reveals signal changes and enhancement of the L3-L4 disc space consistent with discitis/osteomyelitis. Blood cultures are negative. What is the most appropriate next step prior to initiating antibiotic therapy?
Correct Answer & Explanation
. Obtain a CT-guided percutaneous biopsy of the disc space
Explanation
In cases of spontaneous pyogenic discitis/osteomyelitis with negative blood cultures and no neurologic deficit or instability, a CT-guided percutaneous biopsy should be performed to isolate the causative organism before initiating empiric antibiotics.
Question 425
Topic: Infection, Pharmacology & VTE
A 72-year-old female undergoes a debridement, antibiotics, and implant retention (DAIR) procedure for an acute hematogenous periprosthetic joint infection of her total knee arthroplasty. Cultures yield methicillin-susceptible Staphylococcus aureus (MSSA). According to current infectious disease guidelines, what is the optimal timing for the initiation of adjunctive Rifampin therapy?
Correct Answer & Explanation
. Delayed for 3 to 5 days after initiation of appropriate intravenous therapy and surgical debridement
Explanation
Rifampin is highly efficacious against staphylococcal biofilms. However, staphylococci can rapidly develop resistance to Rifampin if it is used as monotherapy or if it is initiated when the bacterial burden is very high (such as during active bacteremia or immediately pre/post-op before source control is achieved). Current guidelines recommend delaying the initiation of Rifampin for 3 to 5 days after the start of active intravenous therapy and surgical debridement. This reduces the bacterial burden and minimizes the risk of rapid resistance development.
Question 426
Topic: Infection, Pharmacology & VTE
Which of the following is considered an absolute contraindication for attempting a debridement, antibiotics, and implant retention (DAIR) procedure in a patient presenting with an acute periprosthetic joint infection?
Correct Answer & Explanation
. Evidence of radiographic loosening of the prosthetic components
Explanation
A loose prosthesis is an absolute contraindication for a DAIR procedure. Successful eradication of infection with implant retention requires components that are stably fixed to the bone. If a component is loose, the interface between the implant and bone is compromised, allowing biofilm and purulence to harbor in areas inaccessible to debridement, necessitating implant removal (1-stage or 2-stage exchange). Symptom duration < 3-4 weeks is an indication for DAIR, not a contraindication.
Question 427
Topic: Infection, Pharmacology & VTE
Staphylococcal species are the most common pathogens in periprosthetic joint infections, largely due to their ability to form resilient biofilms. Which phase of biofilm formation is critically mediated by the synthesis of polysaccharide intercellular adhesin (PIA) via the icaADBC operon?
Correct Answer & Explanation
. Accumulation and maturation phase
Explanation
Biofilm formation occurs in multiple stages: 1) Initial attachment, 2) Irreversible adherence (mediated by MSCRAMMs), 3) Accumulation and maturation, and 4) Detachment. The accumulation and maturation phase is characterized by cellular proliferation and the production of an extracellular polymeric substance (EPS) matrix. In staphylococci, a major component of this matrix is polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC operon.
Question 428
Topic: Infection, Pharmacology & VTE
A patient is identified as a nasal carrier of methicillin-resistant Staphylococcus aureus (MRSA) during routine preoperative screening for a total hip arthroplasty. According to evidence-based protocols, which of the following is the most effective decolonization regimen to reduce the risk of surgical site infection?
Correct Answer & Explanation
. Intranasal mupirocin 2% ointment twice daily and daily chlorhexidine bathing for 5 days pre-operatively
Explanation
The gold standard for MRSA decolonization prior to elective total joint arthroplasty is a 5-day regimen consisting of intranasal 2% mupirocin ointment applied twice daily coupled with daily bathing using chlorhexidine gluconate. This protocol has been shown in numerous studies to significantly decrease the MRSA carrier burden and reduce the incidence of postoperative periprosthetic joint infections.
Question 429
Topic: Infection, Pharmacology & VTE
Based on the results of the Oral Versus Intravenous Antibiotics for Bone and Joint Infection (OVIVA) trial, how does early transition to oral antibiotics compare to standard 6-week intravenous therapy in the management of periprosthetic joint infection?
Correct Answer & Explanation
. Oral therapy is non-inferior to intravenous therapy regarding treatment failure at 1 year
Explanation
The OVIVA trial demonstrated that a highly bioavailable oral antibiotic regimen is non-inferior to intravenous antibiotics for the treatment of bone and joint infections when evaluating treatment failure at 1 year. This paradigm shift supports early transition to oral therapy in appropriately selected patients.
Question 430
Topic: Infection, Pharmacology & VTE
Bacteria residing within a mature biofilm on a prosthetic joint surface exhibit high tolerance to systemic antibiotics. Which of the following mechanisms best explains this phenotypic antibiotic resistance?
Correct Answer & Explanation
. Transition of bacteria into a dormant, metabolically inactive stationary phase
Explanation
Within a mature biofilm, deep-layer bacteria transition into a metabolically dormant, stationary phase. Since many antibiotics (like beta-lactams) rely on active cell wall synthesis and metabolic activity, these dormant 'persister' cells become highly tolerant to antimicrobial therapy.
Question 431
Topic: Infection, Pharmacology & VTE
A 70-year-old female undergoes a 2-stage revision for a Staphylococcus epidermidis periprosthetic joint infection. Her antibiotic regimen includes Rifampin, which is highly effective against biofilm-associated staphylococci. What is the mechanism of action of Rifampin?
Correct Answer & Explanation
. Inhibition of DNA-dependent RNA polymerase
Explanation
Rifampin is a potent bactericidal agent against staphylococci in biofilms because it easily penetrates the biofilm matrix. It exerts its effect by inhibiting bacterial DNA-dependent RNA polymerase, thereby suppressing RNA synthesis.
Question 432
Topic: Infection, Pharmacology & VTE
Figures 32a and 32b show the AP and lateral radiographs of an 11-year-old boy who has a severe limp, a fever, and swelling and tenderness of the thigh. Aspiration of the bone reveals purulent material. The patient has most likely been symptomatic for
Correct Answer & Explanation
. 7 to 14 days.
Explanation
In patients with an osteomyelitic infection, radiographic findings at 1 to 5 days usually show soft-tissue swelling only. Seven to 14 days after symptoms begin, radiographs will most likely show the classic signs of acute osteomyelitis. Reactive bone formation would be expected by 6 months. Kasser JR (ed): Orthopaedic Knowledge Update 5. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1996, pp 149-161.
Question 433
Topic: Infection, Pharmacology & VTE
A 7-year-old boy sustained a 2-cm laceration to the anterior aspect of his left knee after falling on a rock. Examination reveals that the joint surface is not visible through the wound. Radiographs show no evidence of a foreign body or free air in the joint. Management should consist of
Correct Answer & Explanation
. a saline load test.
Explanation
The possibility of an open joint injury should be considered in any patient who has a small periarticular laceration. Failure to promptly diagnose and treat such injuries may lead to septic arthritis. The diagnosis of an open joint is easily made when there is visible communication of the joint through the traumatic wound, or when intra-articular air is present on a radiograph. In the absence of these findings, the diagnosis of an open joint may be established by the saline load test, in which a volume of saline is injected into the joint under sterile conditions. If fluid extravasates through the traumatic wound, the diagnosis of an open joint is established. Voit and associates used a saline load test in 50 patients with periarticular lacerations suggestive of joint penetration. When they compared the clinical prediction of whether or not the laceration had penetrated the joint and the test results, the authors reported a false-positive clinical result in 39% of patients and a false-negative clinical result in 43%. The authors concluded that the saline load test was valuable in evaluating periarticular lacerations. Voit GA, Irvine G, Beals RK: Saline load test for penetration of periarticular lacerations. J Bone Joint Surg Br 1996;78:732-733.
Question 434
Topic: Infection, Pharmacology & VTE
Figure 40 shows the AP radiograph of a 55-year-old man who reports left knee pain. Which of the following conditions is least likely to produce this radiographic presentation?
The radiograph reveals densities within the articular cartilage of the knee commonly referred to as chondrocalcinosis. The term chondrocalcinosis refers to the presence of calcium-containing crystals detected as radiodensities in cartilage. Calcium-containing crystals other than calcium pyrophosphate dihydrate may also deposit in articular cartilage and menisci, producing both radiographically detectable densities in cartilage and joint inflammation or degeneration. Hemochromatosis, alkaptonuria (ochronosis), and Wilson's disease are characterized by cellular deposition of iron, calcium, and copper ions, respectively, into various tissues including articular cartilage and can give this appearance. Septic arthritis does not usually cause chondrocalcinosis. Klippel JH (ed): Primer on the Rheumatic Diseases, ed 11. Atlanta, GA, Arthritis Foundation, 1997, pp 226-229 and 328-331.
Question 435
Topic: Infection, Pharmacology & VTE
A 6-year-old African-American boy with sickle cell disease has had pain and limited use of his right arm for the past 3 days. History reveals that he sustained a humeral fracture approximately 3 years ago. A lateral radiograph is shown in Figure 25. Based on these findings, a presumptive diagnosis of chronic osteomyelitis is made. What are the two most likely organisms?
Correct Answer & Explanation
. Staphylococcus aureus and Salmonella
Explanation
The risk of Salmonella osteomyelitis is much greater in patients with sickle cell disease than the general population. The exact reason for this increased risk is still unclear, but it appears to be associated with an increased incidence of gastrointestinal microinfarcts and abscesses. Both Staphylococcus aureus and Salmonella have been mentioned as the most prevalent causative organisms.
Question 436
Topic: Infection, Pharmacology & VTE
A 42-year-old woman underwent an instrumented posterior spinal fusion at L3-S1 with transforaminal lumbar interbody fusion. She had an excellent clinical result with complete resolution of leg pain. Three months later she now reports increasing back pain and weakness in her legs. Examination reveals weakness in the quadriceps and tibialis anterior. Radiographs show no interval changes in the position of the hardware. MRI scans are shown in Figures 2a through 2c. What is the next most appropriate step in management?
Correct Answer & Explanation
. Irrigation and debridement of the surgical site
Explanation
The MRI scans reveal a postoperative infection. Observation and antibiotics are not appropriate choices. There is a large fluid collection and this requires decompression because the patient has neurologic changes. There is considerable debate regarding the removal of hardware. Many contend that biofilm on the implants can harbor the infection. However, these complications usually can be treated with serial irrigations, debridements, and IV antibiotics. The incidence of infection has been widely studied with varying rates in fusions with instrumentation. Rates appear to be increased with instrumentation, yet these infections usually can be managed without hardware removal. Glassman SD, Dimar JR, Puno RM, et al: Salvage of instrumental lumbar fusions complicated by surgical wound infection. Spine 1996;21:2163-2169.
Question 437
Topic: Infection, Pharmacology & VTE
An 8-year-old boy has had pain and swelling around the right knee for the past 4 weeks. He recalls bumping it about 4 weeks ago. He has no pain in other joints, and denies any fevers, chills, or other symptoms. A radiograph is shown in Figure 13. Laboratory studies show a WBC count of 9,700/mm3, an erythrocyte sedimentation rate of 18 mm/h, and a C-reactive protein level of 3.7 mg/L. What is the next most appropriate step in management?
Correct Answer & Explanation
. Open biopsy and debridement of the site, followed by intravenous antibiotics
Explanation
The history and laboratory findings are consistent with osteomyelitis of the patella. The radiograph reveals bone destruction in the patella; therefore, the next most appropriate step is open biopsy and debridement of the site. Aspiration of the knee joint may be needed to rule out septic arthritis prior to patellar debridement. With this amount of bone destruction, surgical debridement is helpful to obtain cultures and to remove necrotic material. Administering antibiotics without any prior culture increases the risk of negative cultures later and a potentially incorrect choice of antibiotic. A neoplasm should be included in the differential. It would be inappropriate to initiate chemotherapy and radiation therapy without a biopsy-confirmed diagnosis. A bone scan is likely to demonstrate uptake, but radiographs have already localized the abnormality to the patella. Morrisy RT: Bone and joint sepsis, in Morrissy RT, Weinstein SL (eds): Lovell and Winter's Pediatric Orthopaedics, ed 5. Philadelphia, PA, Lippincott Williams & Wilkins, 2001, pp 466-470.
Question 438
Topic: Infection, Pharmacology & VTE
A 7-year-old boy has had low back pain for the past 3 weeks. Radiographs reveal apparent disk space narrowing at L4-5. The patient is afebrile. Laboratory studies show a WBC count of 9,000/mm3 and a C-reactive protein level of 10 mg/L. A lumbar MRI scan confirms the loss of disk height at L4-5 and reveals a small perivertebral abscess at that level. To achieve the most rapid improvement and to lessen the chances of recurrence, management should consist of
Correct Answer & Explanation
. IV antibiotics.
Explanation
The patient has diskitis. Administration of IV antibiotics speeds resolution and minimizes recurrence. Bed rest and cast immobilization have been successfully used to treat this disorder but can be associated with prolonged recovery and frequent recurrence, even when oral antibiotics are administered. A perivertebral abscess seen in association with this condition usually resolves without surgery. Ring D, Johnston CE II, Wenger DR: Pyogenic infectious spondylitis in children: The convergence of discitis and vertebral osteomyelitis. J Pediatr Orthop 1995;15:652-660.
Question 439
Topic: Infection, Pharmacology & VTE
A 3-year-old child has refused to walk for the past 2 days. Examination in the emergency department reveals a temperature of 102.2°F (39°C) and limited range of motion of the left hip. An AP pelvic radiograph is normal. Laboratory studies show a WBC count of 9,000/mm³, an erythrocyte sedimentation rate (ESR) of 65 mm/h, and a C-reactive protein level of 10.5 mg/L (normal < 0.4). What is the next most appropriate step in management?
Correct Answer & Explanation
. Aspiration of the left hip
Explanation
Examination reveals an irritable hip, creating a differential diagnosis of transient synovitis versus pyogenic hip arthritis. Kocher and associates described four criteria to help predict the presence of infection: inability to bear weight, fever, ESR of more than 40 mm/h, and a peripheral WBC count of more than 12,000/mm³. This patient meets three of the four criteria, with a positive predictive value of 73% to 93% for joint infection. Therefore, aspiration of the hip is warranted, with a high likelihood that emergent hip arthrotomy will be indicated. Ideally, intravenous antibiotics should be administered after culture material has been obtained from needle aspiration of the hip. An urgent bone scan is better indicated as a screening test for sacroiliitis or diskitis. If the arthrocentesis proves negative, CT or MRI of the pelvis may be indicated to rule out a pelvic or psoas abscess.
Question 440
Topic: Infection, Pharmacology & VTE
The parents of a previously healthy 3-year-old child report that she refused to walk on awakening. Examination later in the day reveals that the patient can walk but with a noticeable limp. She has a temperature of 99.5 degrees F (37.5 degrees C). Range of motion measurements are shown in Figure 50. An AP pelvis radiograph is normal. Laboratory studies show a WBC count of 9,000/mm3 and an erythrocyte sedimentation rate of 10 mm/h. Management should consist of
Correct Answer & Explanation
. observation.
Explanation
The patient has the typical history and presentation of transient synovitis of the hip, a condition that is more common in children age 2 to 5 years but which may affect children up to 12 years. The discomfort typically is noted on awakening, and the child will refuse to walk. Later in the day, the pain commonly improves and the child can walk but will have a limp. Mild to moderate restriction of hip abduction is the most sensitive range-of-motion restriction. The extent of the evaluation for transient synovitis depends on the intensity and duration of symptoms. Because she has been afebrile for the past 24 hours, observation is the management of choice. In the differential diagnosis of suspected transient synovitis, septic arthritis of the hip is the primary disorder to exclude. Osteomyelitis of the proximal femur also should be considered. In most patients, clinical examination will differentiate of these disorders to a reasonable certainty. Plain radiographs are normal in the early stage of an infectious process. Ultrasonography shows increased fluid in the hip joint in both transient synovitis and septic arthritis. MRI can differentiate the two conditions; however, this test would require general anesthesia and is not required in most patients in this age group. If a child with transient synovitis has a concurrent infectious process such as an upper respiratory tract infection or otitis media, the temperature will most likely be elevated. In this situation, a full evaluation for an infectious process and initiation of IV antibiotics should be considered. This would include radiographs, CBC count, erythrocyte sedimentation rate, blood cultures, aspiration of the hip joint, and IV antibiotics. Del Beccaro MA, Champoux AN, Bockers T, Mendelman PM: Septic arthritis versus transient synovitis of the hip: The value of screening laboratory tests. Annals Emerg Med 1992;21:1418-1422.
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