Infected Arthroplasty Management — MCQs
Which organism causes prosthetic valve endocarditis within 60 days of surgery?
A 50-year-old woman with a history of rheumatoid arthritis presents with fever and joint pain. Which laboratory test is most definitive in distinguishing between a rheumatoid flare and an infectious process?
Bacteria most commonly involved in prosthetic valvular heart disease within 2 months of surgery is:
What is the treatment of choice for a gonococcal infection that is resistant to penicillin?
What is the most effective management strategy for hemarthrosis?
Most sensitive imaging modality for detecting early osteomyelitis
In acute septic arthritis of hip in children, which finding indicates poor prognosis?
What is the optimum duration of antibacterial treatment for acute bacterial prostatitis?
Which of the following is considered a fenestrated hip prosthesis?
A patient with an orthopaedic hip implant is to undergo dental extraction. What antibiotic prophylaxis is recommended?
Infected Arthroplasty Management Indian Medical PG Practice Questions and MCQs
Question 1: Which organism causes prosthetic valve endocarditis within 60 days of surgery?
- A. Staphylococcus aureus
- B. Staphylococcus epidermidis (Correct Answer)
- C. Fungus
- D. Streptococcus viridans
Explanation: ***Staphylococcus epidermidis*** - This organism is the **most common cause of early prosthetic valve endocarditis (within 60 days of surgery)**, accounting for 30-40% of cases. - As a coagulase-negative Staphylococcus, *S. epidermidis* commonly colonizes the skin and can be introduced during the surgical procedure. - It produces **biofilms**, which allow it to adhere to prosthetic surfaces and resist antibiotic treatment. *Staphylococcus aureus* - *Staphylococcus aureus* is the **second most common cause of early prosthetic valve endocarditis** (20-25% of cases) and can cause both early and late infections. - It typically presents with a more **fulminant, aggressive course** compared to *S. epidermidis*. - While both staphylococcal species cause early PVE, *S. epidermidis* remains more frequent. *Fungus* - **Fungal endocarditis** on prosthetic valves (typically *Candida* species) accounts for 5-10% of early PVE cases. - More commonly seen in immunocompromised patients, those with prolonged antibiotic use, or after complicated cardiac surgery. - Its incidence is significantly lower than staphylococcal causes in the early post-operative period. *Streptococcus viridans* - *Streptococcus viridans* is the **most common cause of native valve endocarditis**, particularly in patients with pre-existing valvular heart disease. - It typically causes a **subacute presentation** and is more associated with **late prosthetic valve endocarditis** (>60 days post-surgery), not early PVE. - Rarely implicated in early prosthetic valve infections.
Question 2: A 50-year-old woman with a history of rheumatoid arthritis presents with fever and joint pain. Which laboratory test is most definitive in distinguishing between a rheumatoid flare and an infectious process?
- A. Erythrocyte sedimentation rate (ESR)
- B. Joint aspiration and culture (Correct Answer)
- C. C-reactive protein (CRP)
- D. Rheumatoid factor (RF)
Explanation: Detailed joint aspiration and culture is the most definitive step [1]. This procedure directly analyzes synovial fluid for **white blood cells**, **bacteria**, or **crystals**, providing a definitive diagnosis for an infectious process such as **septic arthritis** [1]. *Erythrocyte sedimentation rate (ESR)* - While elevated in both inflammation and infection, the **ESR is a non-specific marker** and cannot differentiate between a rheumatoid flare and an infectious process. - It indicates overall inflammation but does not identify the underlying cause of the inflammation. *C-reactive protein (CRP)* - Similar to ESR, **CRP is an acute-phase reactant** [2]. It increases significantly during both inflammatory conditions and infections [2]. - It is a more sensitive marker for inflammation than ESR but **lacks specificity** to distinguish between inflammatory and infectious etiologies [2]. *Rheumatoid factor (RF)* - **Rheumatoid factor** is an autoantibody primarily associated with **rheumatoid arthritis** and is usually present in patients with the disease. - Its presence or elevated levels would not differentiate between an RA flare and a concurrent infection, as it reflects the underlying autoimmune disease rather than an acute infectious process.
Question 3: Bacteria most commonly involved in prosthetic valvular heart disease within 2 months of surgery is:
- A. Staphylococcus epidermidis (Correct Answer)
- B. Streptococcus viridans
- C. Enterococci
- D. Hemophilus
Explanation: ***Staphylococcus epidermidis*** - This coagulase-negative staphylococcus is a common cause of **early-onset prosthetic valve endocarditis (PVE)**, occurring within 2 months of surgery. - It is a normal skin flora, and infections are often related to **intraoperative contamination** during valve replacement surgery. *Streptococcus viridans* - This group of streptococci is a leading cause of **late-onset PVE** and **native valve endocarditis (NVE)**, often following dental procedures. - Infections typically occur more than 2 months post-surgery, differentiating it from early-onset cases. *Enterococci* - Enterococci can cause both **NVE** and **PVE**, but they are more commonly associated with infections in patients with **nosocomial acquisition** or those undergoing genitourinary or gastrointestinal procedures. - While they can occur post-surgery, they are not the most common causative agent within the first 2 months compared to *Staphylococcus epidermidis*. *Hemophilus* - *Haemophilus species* are considered part of the **HACEK group** (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), which are known for causing **culture-negative endocarditis**. - While they can cause endocarditis, they are rare causes of early-onset PVE and are more associated with subacute or chronic forms of endocarditis.
Question 4: What is the treatment of choice for a gonococcal infection that is resistant to penicillin?
- A. Penicillin
- B. Ceftazidime
- C. Ceftriaxone (Correct Answer)
- D. Spectinomycin
Explanation: ***Ceftriaxone*** - **Ceftriaxone** is the recommended first-line treatment for uncomplicated gonococcal infections, especially given increasing resistance to other antibiotics like penicillin. - It is a **third-generation cephalosporin** that targets the bacterial cell wall synthesis effectively. *Penicillin* - **Penicillin** is no longer the recommended treatment for gonorrhea due to widespread resistance, primarily mediated by **beta-lactamase production** by *Neisseria gonorrhoeae*. - Treating with penicillin when resistance is present would lead to treatment failure and continued transmission. *Ceftazidime* - **Ceftazidime** is a third-generation cephalosporin with activity against gram-negative organisms. - However, its activity against *Neisseria gonorrhoeae* is not considered first-line or superior to ceftriaxone, which has better pharmacokinetic properties for treating gonorrhea. *Spectinomycin* - **Spectinomycin** is an alternative treatment for gonococcal infections, particularly in individuals with severe allergy to cephalosporins or in regions where ceftriaxone resistance is emerging. - However, it is not the treatment of choice in regions where ceftriaxone is effective and available.
Question 5: What is the most effective management strategy for hemarthrosis?
- A. Immobilization with a P.O.P. cast
- B. Application of a compression bandage
- C. Needle aspiration to remove excess blood (Correct Answer)
- D. All of the options
Explanation: ***Needle aspiration to remove excess blood*** - **Aspirating the blood** from the joint effectively reduces intra-articular pressure, pain, and inflammation. - This procedure also helps prevent **synovial hypertrophy** and **cartilage damage** caused by the presence of blood in the joint. *Application of a compression bandage* - While helpful for reducing swelling and providing support, a **compression bandage alone** does not remove the accumulated blood. - It may alleviate some discomfort but does not address the underlying issue of **intra-articular blood accumulation**. *Immobilization with a P.O.P. cast* - **Immobilization** can help rest the joint and reduce pain, but it does not remove the blood from the joint space. - Prolonged immobilization can lead to **joint stiffness** and **muscle atrophy**, which are undesirable outcomes. *All of the options* - While compression and immobilization can be supportive measures, they are not the **most effective primary strategy** for managing hemarthrosis. - The direct removal of blood via **aspiration** is crucial for alleviating pressure and preventing long-term joint damage.
Question 6: Most sensitive imaging modality for detecting early osteomyelitis
- A. Nuclear bone scan
- B. CT scan
- C. MRI (Correct Answer)
- D. Plain radiograph
Explanation: **MRI** - **MRI** is the most sensitive imaging modality for detecting **early osteomyelitis** due to its superior ability to visualize **bone marrow edema** and soft tissue changes, which are the earliest signs of infection. - It can differentiate between **bone infection** and other processes like inflammation or tumor, even before cortical bone changes are evident. *Nuclear bone scan* - **Nuclear bone scans** (e.g., technetium-99m) are highly sensitive for detecting **increased bone turnover** but lack specificity for infection. - They can identify areas of **inflammation** or injury but cannot reliably distinguish between osteomyelitis and other conditions like **fractures** or **tumors**. *CT scan* - **CT scans** are excellent for visualizing **cortical bone destruction**, **sequestra**, and **involucrum** in later stages of osteomyelitis. - However, **CT scans** are not as sensitive as MRI for detecting early bone marrow changes and soft tissue involvement, making them less ideal for **early diagnosis**. *Plain radiograph* - **Plain radiographs** are often the first imaging study for suspected osteomyelitis but have **low sensitivity** in the early stages, with changes typically not visible until 10-14 days after infection onset. - Early findings may include **periosteal elevation** or soft tissue swelling, but **bone destruction** or new bone formation is usually required for a definitive diagnosis.
Question 7: In acute septic arthritis of hip in children, which finding indicates poor prognosis?
- A. Age <2 years
- B. Delay in Treatment >48 hours (Correct Answer)
- C. Elevated CRP
- D. Gram Negative Infection
Explanation: ***Delay in Treatment >48 hours*** - A delay in treatment of **acute septic hip arthritis** beyond 48 hours significantly increases the risk of irreversible cartilage damage and long-term functional impairment due to sustained inflammatory and enzymatic degradation. - This delay can lead to more severe joint destruction, avascular necrosis of the femoral head, and post-infectious osteoarthritis, all contributing to a **poor prognosis**. *Age <2 years* - While younger children can have more subtle symptoms and a higher risk of diagnostic delay, age itself is not the most determinant factor for poor prognosis compared to treatment delay. - Management in this age group focuses on early diagnosis and aggressive treatment to prevent growth plate damage. *Elevated CRP* - **Elevated C-reactive protein (CRP)** is a common finding in acute septic arthritis, indicating systemic inflammation and the severity of infection. - While reflecting disease activity, an elevated CRP alone does not directly indicate poor prognosis as it typically responds well to appropriate antibiotic treatment and surgical drainage. *Gram Negative Infection* - Gram-negative infections can be more challenging to treat and may require specific antibiotic regimens, but the type of organism is generally less critical than the **duration of untreated infection** in determining long-term outcomes. - With prompt and appropriate therapy, many gram-negative infections can be successfully managed without causing poor long-term outcomes.
Question 8: What is the optimum duration of antibacterial treatment for acute bacterial prostatitis?
- A. 3 days
- B. 4-6 weeks (Correct Answer)
- C. 7-14 days
- D. 2-14 days
Explanation: ***4-6 weeks*** - Treatment for **acute bacterial prostatitis** requires a prolonged course of antibiotics to ensure eradication of the infection from the prostate gland, which often has poor antibiotic penetration. - A duration of **4 to 6 weeks** is recommended to prevent recurrence and progression to chronic prostatitis. *3 days* - A 3-day course of antibiotics is **too short** for acute bacterial prostatitis. - Such a short duration would likely lead to incomplete bacterial eradication and a high risk of **relapse or chronic infection**. *7-14 days* - A 7-14 day course of antibiotics is typically sufficient for more superficial or readily accessible infections, but it is **insufficient for acute bacterial prostatitis**. - The prostate's unique anatomy and vascular supply necessitate a **longer treatment period** to achieve therapeutic drug levels and eliminate pathogens. *2-14 days* - While suitable for some acute urinary tract infections, a 2-14 day regimen is **inadequate for acute bacterial prostatitis**. - This duration does not account for the **depth and complexity of prostate infection**, increasing the risk of treatment failure.
Question 9: Which of the following is considered a fenestrated hip prosthesis?
- A. Bipolar prosthesis
- B. Austin Moore prosthesis (Correct Answer)
- C. Thompson prosthesis
- D. All of the above
Explanation: **Explanation:** The correct answer is **Austin Moore prosthesis**. In orthopaedic surgery, a **fenestrated prosthesis** refers to an implant with "windows" or openings in its stem. These holes allow for bone to grow through the prosthesis (biological fixation), providing long-term stability. **1. Why Austin Moore is correct:** The Austin Moore prosthesis is a unipolar hemiarthroplasty implant used for femoral neck fractures. Its defining feature is a **fenestrated stem**. During surgery, bone chips are often packed into these fenestrations; over time, bone grows through these holes (osseointegration), anchoring the prosthesis to the femoral shaft without the need for bone cement. **2. Why the other options are incorrect:** * **Thompson prosthesis:** This is also a unipolar prosthesis, but it has a **solid (non-fenestrated) stem**. It is designed to be used with bone cement (Polymethylmethacrylate - PMMA) for fixation. * **Bipolar prosthesis:** This refers to an implant with two points of articulation (one at the acetabulum and one within the prosthetic head). While the stem design can vary, the term "bipolar" describes the head mechanism, not the presence of fenestrations. **High-Yield Clinical Pearls for NEET-PG:** * **Fixation:** Austin Moore = **Uncemented** (Press-fit/Biological); Thompson = **Cemented**. * **Indications:** Austin Moore is preferred in patients with good bone quality; Thompson is preferred in osteoporotic patients where cement provides immediate stability. * **Calcar:** The Austin Moore prosthesis has a collar that rests on the calcar femorale to prevent subsidence. * **Complication:** A common complication of unipolar prostheses (Moore/Thompson) is **acetabular erosion** (protrusio acetabuli) because the metal head rubs directly against the native cartilage.
Question 10: A patient with an orthopaedic hip implant is to undergo dental extraction. What antibiotic prophylaxis is recommended?
- A. Amoxicillin 3 times a day for 3 days before the procedure
- B. Amoxicillin 3 times a day for 1 day before the procedure
- C. Amoxicillin intravenously 1 hour before the procedure
- D. Antibiotic prophylaxis is not required (Correct Answer)
Explanation: **Explanation:** The correct answer is **D. Antibiotic prophylaxis is not required.** **1. Underlying Medical Concept:** Historically, it was believed that dental procedures could cause transient bacteremia leading to Late Prosthetic Joint Infection (PJI). However, current evidence-based guidelines from the **American Academy of Orthopaedic Surgeons (AAOS)** and the **American Dental Association (ADA)** state that there is no direct link between dental procedures and PJI. Routine antibiotic prophylaxis is **not recommended** for patients with prosthetic joint replacements undergoing dental procedures. The risks of antibiotic use (allergic reactions, *C. difficile* infection, and antimicrobial resistance) outweigh the unproven benefits of preventing joint infection. **2. Why Incorrect Options are Wrong:** * **Options A and B:** Prophylaxis is never administered for multiple days or a full day before a procedure. If prophylaxis were indicated (e.g., for infective endocarditis), it would be a single pre-operative dose. * **Option C:** While IV antibiotics are used for surgical prophylaxis (like during the arthroplasty itself), they are not indicated for dental work in patients with joint implants. **3. Clinical Pearls for NEET-PG:** * **Exception:** Prophylaxis may be considered only in **severely immunocompromised** patients (e.g., stage 3 AIDS, chemotherapy, or recent organ transplant) with poorly controlled oral infections, and even then, only after consultation between the dentist and the orthopedic surgeon. * **Timing:** If prophylaxis is deemed necessary for other reasons (like high-risk cardiac conditions), the standard dose is **2g Amoxicillin orally 30-60 minutes before** the procedure. * **High-Yield Fact:** The most common cause of Late PJI is hematogenous spread, but the source is usually skin or urinary tract infections, not dental flora.
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