Arthrology and Infections Practice Questions

Q: What is the most common osteomyelitis-causing organism in intravenous drug abusers?

Pseudomonas. **Explanation:** The correct answer is **Pseudomonas (Option B)**. While *Staphylococcus aureus* remains the most common cause of osteomyelitis in the general population, **Intravenous Drug Abusers (IVDAs)** represent a specific high-risk group with a unique microbiological profile. In these individuals, there is a significantly increased incidence of infections caused by Gram-negative organisms, specifically **Pseudomonas aeruginosa**. This is often attributed to the use of contaminated water or paraphernalia during drug preparation. A classic clinical presentation in IVDAs is "S-syndrome" involvement—infections affecting the **S**ternoclavicular, **S**acroiliac, and **S**ymphysis pubis joints. **Analysis of Incorrect Options:** * **A. Staphylococcus aureus:** Although it is the overall #1 cause of osteomyelitis across all age groups and categories, the question specifically asks for the organism characteristic of the IVDA population, where *Pseudomonas* is the high-yield differentiator. * **C. Salmonella:** This is the most common cause of osteomyelitis specifically in patients with **Sickle Cell Anemia** (due to functional asplenia and intestinal infarctions). * **D. Pasteurella multocida:** This organism is classically associated with osteomyelitis or septic arthritis following **animal bites** (cats and dogs). **High-Yield Clinical Pearls for NEET-PG:** * **Overall most common:** *Staphylococcus aureus*. * **Sickle Cell Disease:** *Salmonella* (followed by *S. aureus*). * **IV Drug Abusers:** *Pseudomonas aeruginosa*. * **Neonates:** Group B Streptococcus (*S. agalactiae*) and *E. coli*. * **Prosthetic Joints:** *Staphylococcus epidermidis*. * **Puncture wound through footwear:** *Pseudomonas*.

Q: Which of the following statements is NOT true about acute osteomyelitis?

Bone scan can detect changes after 2 weeks. ### Explanation **1. Why Option D is the Correct (False) Statement:** In acute osteomyelitis, a **Technetium-99m (Tc-99m) bone scan** is highly sensitive and can detect increased osteoblastic activity within **24 to 48 hours** of the onset of symptoms. The statement claiming it takes 2 weeks is incorrect; it is the **plain X-ray** that typically requires 10–14 days (or 30–50% bone mineral loss) to show visible changes like periosteal reaction or rarefaction. **2. Analysis of Other Options:** * **A. Metaphysis is involved:** This is true. The metaphysis is the most common site because it has **hairpin-shaped capillary loops** where blood flow slows down, allowing bacteria to settle. It also has a relatively deficient phagocytic system. * **B. Commonly caused by Staphylococcus aureus:** This is true. *S. aureus* is the most common causative organism across almost all age groups. (Note: *Salmonella* is a specific high-yield association for Sickle Cell patients). * **C. May present with pseudoparalysis:** This is true. In infants and young children, the intense pain caused by the infection leads the patient to refuse to move the affected limb, mimicking paralysis (pseudoparalysis). **Clinical Pearls for NEET-PG:** * **Gold Standard Investigation:** MRI is the most sensitive and specific imaging modality for early diagnosis (detects marrow edema within hours). * **Definitive Diagnosis:** Aspiration of pus or bone biopsy for culture. * **Sequestrum:** Dead bone (radiodense); **Involucrum:** New bone formation around the sequestrum (characteristic of chronic osteomyelitis). * **Cloaca:** An opening in the involucrum for the exit of pus/sequestrum. * **Brodie’s Abscess:** A form of subacute osteomyelitis characterized by a circumscribed radiolucent lesion with a sclerotic rim.

Q: What is the most common cause of neuropathic joint?

Diabetes mellitus. **Explanation:** A **Neuropathic Joint (Charcot Joint)** is a progressive, degenerative arthropathy caused by a loss of pain and proprioceptive sensation. Without these protective mechanisms, repetitive microtrauma leads to joint destruction, instability, and deformity. **1. Why Diabetes Mellitus is correct:** Currently, **Diabetes Mellitus** is the most common cause of neuropathic joints worldwide. It primarily affects the **foot and ankle** (tarsal and metatarsal joints) due to peripheral neuropathy. As the prevalence of diabetes has risen, it has surpassed historical causes like syphilis. **2. Analysis of Incorrect Options:** * **Hypertension:** This is a vascular condition and does not cause sensory neuropathy or joint destruction. * **Leprosy:** While a common cause of neuropathy in specific endemic regions (leading to Charcot joints in the hands and feet), it is not the most common cause globally or statistically compared to Diabetes. * **Tabes Dorsalis (Neurosyphilis):** Historically, this was the most common cause, typically affecting the **knee joint**. However, with the advent of antibiotics, it is now rare. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common site (Overall):** Foot and Ankle (due to Diabetes). * **Most common site in Tabes Dorsalis:** Knee. * **Most common site in Syringomyelia:** Shoulder/Upper limb (due to "dissociated sensory loss"). * **Radiological Hallmark:** The **"6 Ds"** (Distension, Density increase/Sclerosis, Debris, Disorganization, Dislocation, and Destruction). * **Clinical Paradox:** The joint often looks "horrible" on X-ray (severe destruction) but is relatively **painless** for the patient.

Q: In osteomyelitis, what is the typical timeframe for observing a solid periosteal reaction on X-ray?

1st week. In acute osteomyelitis, the timing of radiological findings is a high-yield topic for NEET-PG. **Explanation of the Correct Answer:** The correct answer is **1st week (Option A)** because the earliest radiological sign of osteomyelitis is **soft tissue swelling**, which typically appears within **3 to 5 days** of infection. This is followed closely by the elevation of the periosteum. While a mature, "solid" periosteal reaction (new bone formation) becomes clearly visible on X-ray toward the end of the first week or early in the second week, the physiological process and the initial subtle periosteal changes are categorized under the "1st week" timeframe in standard orthopedic textbooks (like Maheshwari) for examination purposes. **Explanation of Incorrect Options:** * **Option B (Less than 2 weeks):** While technically true, it is less specific than "1st week." In competitive exams, the earliest possible timeframe is preferred. * **Option C & D (2nd and 3rd week):** These options are incorrect because **bony changes** (like rarefaction, osteolysis, or the formation of a sequestrum) typically take 10–14 days to appear on a plain X-ray. By the 2nd or 3rd week, the infection is well-established, and the window for "early" detection via periosteal reaction has passed. **Clinical Pearls for NEET-PG:** * **Earliest Sign on X-ray:** Soft tissue swelling (3–5 days). * **Earliest Bony Change on X-ray:** Periosteal reaction (approx. 7 days). * **Bone Destruction:** Requires 30–50% bone mineral loss to be visible on X-ray (usually takes 10–14 days). * **Gold Standard for Early Diagnosis:** **MRI** is the most sensitive imaging modality (detects changes within 24–48 hours). * **Nuclear Medicine:** Technetium-99m bone scan shows increased uptake ("hot spot") within 24–48 hours.

Q: Brodie abscess is most commonly seen in which part of the long bone?

Metaphysis. **Explanation:** **Brodie’s abscess** is a localized form of **chronic osteomyelitis** characterized by a circumscribed collection of pus surrounded by a wall of reactive bone (sclerosis). **Why Metaphysis is the Correct Answer:** The metaphysis is the most common site for Brodie’s abscess because it is the most vascularized part of a growing bone. In children, the **hairpin arrangement of end-arteries** in the metaphysis leads to sluggish blood flow. This creates an ideal environment for circulating bacteria (most commonly *Staphylococcus aureus*) to settle, proliferate, and form a localized infection. Because the host's immunity is relatively high or the organism's virulence is low, the body walls off the infection rather than allowing it to spread. **Analysis of Incorrect Options:** * **Epiphysis:** Rarely the primary site. Infection usually only involves the epiphysis if it crosses the growth plate (more common in infants) or occurs after the growth plate has fused. * **Diaphysis:** While osteomyelitis can involve the shaft, it is less common for a localized Brodie’s abscess to originate here due to the lack of the specific capillary loops found in the metaphysis. * **Epiphyseal cartilage:** This acts as a mechanical barrier to the spread of infection in children; it is not a site for abscess formation. **Clinical Pearls for NEET-PG:** * **Most Common Organism:** *Staphylococcus aureus*. * **Most Common Site:** Proximal tibia (followed by distal femur). * **Classic X-ray Finding:** A well-defined radiolucent (lytic) lesion surrounded by a rim of **sclerotic bone**. * **Clinical Presentation:** Chronic limb pain, often worse at night, relieved by aspirin (mimicking Osteoid Osteoma). * **Treatment:** Surgical curettage and evacuation under antibiotic cover.

Q: What is the most common cause of bony ankylosis?

Septic arthritis. ### Explanation **Correct Option: C. Septic Arthritis** The hallmark of **Septic Arthritis** (pyogenic arthritis) is the rapid destruction of articular cartilage. Pyogenic organisms (like *Staphylococcus aureus*) produce proteolytic enzymes and trigger a massive release of lysosomal enzymes from polymorphonuclear leukocytes. This leads to the complete loss of the joint space and the exposure of subchondral bone. When the two denuded bony surfaces heal together, they form a solid bridge of bone, resulting in **Bony Ankylosis**. **Analysis of Incorrect Options:** * **A & B. Tuberculosis (Hip/Knee):** In skeletal tuberculosis, the infection is chronic and characterized by the formation of "pannus" (granulation tissue). This tissue typically destroys the periphery of the joint first, often sparing the central cartilage for a long time. Healing in TB usually occurs via fibrosis, leading to **Fibrous Ankylosis**, not bony. * **D. Pott’s Spine:** While spinal TB can lead to bony fusion of the vertebral bodies (syndesmophytes or block vertebrae) during the healing phase, it is not the "most common" cause of bony ankylosis when compared to the systemic incidence and rapid destructive nature of pyogenic septic arthritis in peripheral joints. **High-Yield Clinical Pearls for NEET-PG:** * **Bony Ankylosis:** Most common in **Septic Arthritis** and **Ankylosing Spondylitis**. * **Fibrous Ankylosis:** Most common in **Tuberculosis** and **Rheumatoid Arthritis**. * **Exception to the Rule:** Tuberculosis of the **spine (Pott's spine)** is a notable exception where bony ankylosis is more common than in peripheral TB joints. * **Radiology Tip:** On X-ray, bony ankylosis is identified by the presence of trabecular bone crossing the joint space, whereas fibrous ankylosis shows a blurred joint space without bony bridges.

Q: A young child is diagnosed with chronic osteomyelitis of the tibia and has started on sensitive antibiotics. Which of the following parameters is best to monitor the response to antibiotic therapy after 6 days?

C-reactive protein (CRP). **Explanation:** In the management of musculoskeletal infections like osteomyelitis, monitoring the response to therapy is crucial. **C-reactive protein (CRP)** is the most sensitive and reliable marker for this purpose. **1. Why CRP is the Correct Answer:** CRP is an acute-phase reactant with a very short half-life (approximately 19 hours). Its levels rise rapidly (within 6 hours) in response to inflammation and, more importantly, **fall rapidly** once the infection is controlled by effective antibiotics. By day 6 of treatment, a declining CRP level is the most accurate biochemical indicator that the chosen antibiotic is effective. **2. Why Other Options are Incorrect:** * **Erythrocyte Sedimentation Rate (ESR):** While ESR is a good screening tool, it has a slow response time. It takes days to peak and weeks to return to normal (slow lag phase). Therefore, at 6 days, it may still be elevated despite clinical improvement, making it a poor tool for acute monitoring. * **Total and Differential WBC Count:** These are often the first to normalize, sometimes even before the infection is fully under control. They lack the specificity and sensitivity of CRP for monitoring the ongoing inflammatory process in bone. **Clinical Pearls for NEET-PG:** * **CRP vs. ESR:** CRP is the first to rise and the first to fall. ESR is the last to fall. * **Diagnosis vs. Monitoring:** While both ESR and CRP are used for diagnosis, **CRP is the "Gold Standard" for monitoring** treatment response in pediatric osteomyelitis and septic arthritis. * **Prognostic Value:** If CRP does not begin to drop within 48–72 hours of starting antibiotics, it suggests treatment failure, a resistant organism, or the need for surgical drainage.

Q: Which of the following is a differential diagnosis for tuberculous arthritis of the hip joint?

All of the above. **Explanation:** Tuberculous (TB) arthritis of the hip is a chronic, granulomatous infection characterized by an insidious onset, pain, limp, and a gradual reduction in the range of motion. Because its presentation can mimic various inflammatory, degenerative, and infectious conditions, a broad differential diagnosis is essential. **Why "All of the Above" is Correct:** * **Rheumatoid Arthritis (RA):** Like TB, RA causes chronic synovial hypertrophy and joint space narrowing. While RA is typically polyarticular and symmetrical, monoarticular RA of the hip can closely resemble the "Pannus" formation and marginal erosions seen in TB. * **Perthes Disease:** In the early stages (Stage 1: Synovitis), Perthes disease presents with a limp and hip pain in children. TB hip in children often presents similarly with "night cries" and muscle spasms, making it a crucial differential in the pediatric age group. * **Septic Arthritis:** Although septic arthritis is usually acute and pyogenic, subacute or partially treated septic arthritis can present with a more indolent course, overlapping with the clinical picture of TB hip. **High-Yield Clinical Pearls for NEET-PG:** * **Phemister’s Triad:** Characteristic of TB arthritis—1. Juxta-articular osteopenia, 2. Peripherally located osseous erosions, and 3. Gradual narrowing of the joint space. * **Stages of TB Hip:** 1. *Stage of Synovitis:* Apparent lengthening (Abduction, External Rotation). 2. *Stage of Arthritis:* Apparent shortening (Adduction, Internal Rotation). 3. *Stage of Erosion:* True shortening (Wandering Acetabulum). * **Cold Abscess:** Unlike pyogenic infections, TB abscesses lack classical signs of inflammation (heat, redness). * **Gold Standard Diagnosis:** Synovial biopsy and culture (Lowenstein-Jensen medium) or GeneXpert.

Q: A female on steroids developed hip pain. Investigations show evidence of avascular necrosis of the head of the femur. What is the most common fracture site in this patient?

Subchondral region. **Explanation:** The correct answer is **C. Subchondral region.** **Pathophysiology & Mechanism:** The patient presents with **Avascular Necrosis (AVN)** of the femoral head, likely secondary to long-term steroid use. In AVN, the underlying pathology is the death of osteocytes due to compromised blood supply. As the necrotic bone fails to repair itself, it loses its structural integrity. The mechanical stress of weight-bearing leads to **microfractures** specifically in the **subchondral region** (the layer of bone just beneath the articular cartilage). Radiologically, this manifests as the **"Crescent Sign,"** which represents a subchondral fracture or separation of the cartilage from the necrotic bone. This is a hallmark of Ficat and Arlet Stage II/III AVN and precedes the eventual collapse of the femoral head. **Analysis of Incorrect Options:** * **A & B (Subcapital and Transcervical):** These are types of intracapsular femoral neck fractures. While they can *cause* AVN by disrupting the medial circumflex femoral artery, they are not the *result* of steroid-induced AVN. * **D (Trochanteric region):** This is an extracapsular site. Fractures here are typically related to osteoporosis in the elderly or high-energy trauma, not the localized ischemic necrosis seen in AVN. **Clinical Pearls for NEET-PG:** * **Most common cause of AVN:** Trauma (Fracture neck of femur). * **Most common non-traumatic cause:** Alcoholism and Steroid use. * **Earliest Investigation:** MRI (shows marrow edema; T1-weighted images show low signal intensity). * **Crescent Sign:** Pathognomonic for subchondral collapse in AVN (best seen on X-ray/CT). * **Treatment:** Core decompression is preferred in early stages (Ficat I & II) to reduce intraosseous pressure.

Question 1

What is the most common osteomyelitis-causing organism in intravenous drug abusers?

Accepted Answer

Pseudomonas

Answer

Staphylococcus aureus

Answer

Salmonella

Answer

Pasteurella

Question 2

Which of the following statements is NOT true about acute osteomyelitis?

Accepted Answer

Bone scan can detect changes after 2 weeks

Answer

Metaphysis is involved

Answer

Commonly caused by Staphylococcus aureus

Answer

May present with pseudoparalysis

Question 3

What is the most common cause of neuropathic joint?

Accepted Answer

Diabetes mellitus

Answer

Hypertension

Answer

Leprosy

Answer

Tabes dorsalis

Question 4

What is the treatment of triple deformity?

Accepted Answer

Anti-tetanus therapy (ATT), immobilization, and debridement

Answer

Anti-tetanus therapy (ATT)

Answer

Anti-tetanus therapy (ATT) plus immobilization

Answer

None of the above

Question 5

In osteomyelitis, what is the typical timeframe for observing a solid periosteal reaction on X-ray?

Accepted Answer

1st week

Answer

Less than 2 weeks

Answer

2nd week

Answer

3rd week

Question 6

Brodie abscess is most commonly seen in which part of the long bone?

Accepted Answer

Metaphysis

Answer

Epiphysis

Answer

Diaphysis

Answer

Epiphyseal cartilage

Question 7

What is the most common cause of bony ankylosis?

Accepted Answer

Septic arthritis

Answer

Tuberculosis of the hip

Answer

Tuberculosis of the knee

Answer

Pott's spine

Question 8

A young child is diagnosed with chronic osteomyelitis of the tibia and has started on sensitive antibiotics. Which of the following parameters is best to monitor the response to antibiotic therapy after 6 days?

Accepted Answer

C-reactive protein (CRP)

Answer

Erythrocyte Sedimentation Rate (ESR)

Answer

Differential White Blood Cell (WBC) count

Answer

Total White Blood Cell (WBC) count

Question 9

Which of the following is a differential diagnosis for tuberculous arthritis of the hip joint?

Accepted Answer

All of the above

Answer

Rheumatoid arthritis

Answer

Perthes disease

Answer

Septic arthritis

Question 10

A female on steroids developed hip pain. Investigations show evidence of avascular necrosis of the head of the femur. What is the most common fracture site in this patient?

Accepted Answer

Subchondral region

Answer

Subcapital region

Answer

Transcervical region

Answer

Trochanteric region

Arthrology and Infections — MCQs

Arthrology and Infections — MCQs

On this page

Practice by Chapter

Want unlimited practice?