Skeletal Infections — MCQs
A child presents with painful limp and restricted hip rotation. ESR and CRP are elevated. Initial plain radiograph is normal. What is the next best imaging study?
What is the best imaging modality for detecting early osteomyelitis?
All of the following are true regarding ankylosing spondylitis except:
An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9°C, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?
Most common organism in acute osteomyelitis is
Tuberculosis of the spine; what is the most common site affected?
A 23-year-old woman with a history of sickle cell disease presents with fever and severe bone pain localized to her left tibia. X-ray reveals a lytic lesion, and blood cultures reveal infection. A bone culture grows gram-negative rods. Which of the following best describes the infecting organism?
The earliest radiological change to appear in a case of acute osteomyelitis is:
A 10 year old child came to the OPD with pain and mass in right lumbar region with no fever, with right hip flexed. The pain increased on extension and X ray showed spine changes. Most probable diagnosis is:
Earliest investigation for diagnosis of Ankylosing spondylitis:
Skeletal Infections Indian Medical PG Practice Questions and MCQs
Question 1: A child presents with painful limp and restricted hip rotation. ESR and CRP are elevated. Initial plain radiograph is normal. What is the next best imaging study?
- A. CT Scan
- B. MRI with contrast (Correct Answer)
- C. Bone Scan
- D. Plain Radiograph
Explanation: ***MRI with contrast*** - An **MRI with contrast** is the most sensitive and specific imaging modality for detecting early changes in **osteomyelitis** or **septic arthritis**, which are serious conditions given the child's symptoms and elevated inflammatory markers. - It can visualize soft tissue and bone marrow edema, joint effusions, and abscesses, guiding immediate treatment. *CT Scan* - While useful for bony detail, a CT scan is **less sensitive than MRI** for detecting early bone marrow changes or soft tissue inflammation in the hip joint. - It also involves **radiation exposure**, which should be limited in children when other effective modalities are available. *Bone Scan* - A bone scan using **technetium-99m** is sensitive for detecting increased bone turnover, but it is **not specific for infection** and cannot differentiate between inflammatory processes, tumors, or fractures. - It provides less anatomical detail compared to MRI, making precise localization of an infection more challenging. *Plain Radiograph* - Plain radiographs are typically the **initial imaging study** for orthopedic complaints but are often **normal in early stages** of septic arthritis or osteomyelitis. - Significant radiographic changes, such as bone erosion or joint space widening, usually appear much later in the disease process.
Question 2: What is the best imaging modality for detecting early osteomyelitis?
- A. CT scan
- B. X-ray
- C. MRI (Correct Answer)
- D. Bone scintigraphy
Explanation: ***MRI*** - **Magnetic Resonance Imaging (MRI)** is considered the **gold standard** for detecting early osteomyelitis due to its excellent soft tissue contrast and ability to visualize **bone marrow edema**, which is an early sign of infection. - It can identify changes within **3-5 days** of infection onset, much earlier than other modalities. *CT scan* - While useful for showing **bone destruction**, cortical integrity, and sequestra, **CT scans** are less sensitive than MRI for detecting early marrow edema. - Its ability to diagnose osteomyelitis is usually delayed until significant **bony changes** have occurred, typically around 1-2 weeks. *X-ray* - **Plain radiographs** are often the initial imaging study but are **insensitive** for early osteomyelitis, showing changes only after 10-14 days or more. - Early findings on X-rays can be subtle, such as **periosteal elevation** or **soft tissue swelling**, but frank bone destruction is a late finding. *Bone scintigraphy* - **Bone scintigraphy** (e.g., technetium-99m) is sensitive for detecting increased bone turnover associated with infection but lacks **specificity**, as it can be positive in other conditions like trauma or tumors. - While it can detect changes earlier than X-rays, typically within 2-3 days, it cannot clearly differentiate infection from other processes, and its spatial resolution is poor compared to MRI.
Question 3: All of the following are true regarding ankylosing spondylitis except:
- A. 50% of patients may have urinary infection (Correct Answer)
- B. Involvement of sacroiliac joint
- C. Bamboo spine may be a radiological feature
- D. Most of people are HLAB27 positive
Explanation: ***50% of patients may have urinary infection*** - Urinary tract infections are **not a characteristic feature** or a common complication of **ankylosing spondylitis**. - This statement is incorrect as there is no significant epidemiological or pathophysiological link between AS and a high incidence of UTIs. *Involvement of sacroiliac joint* - **Sacroiliitis**, inflammation of the sacroiliac joints, is one of the **hallmark features** and often the earliest sign of ankylosing spondylitis [1]. - It is typically **bilateral and symmetrical**, and its presence is crucial for diagnosis [1]. *Bamboo spine may be a radiological feature* - **Bamboo spine** is a characteristic late radiological finding in ankylosing spondylitis, resulting from **syndesmophyte formation** (ossification of spinal ligaments) and fusion of vertebral bodies [1]. - This appearance signifies severe spinal rigidity and advanced disease. *Most of people are HLAB27 positive* - The **HLA-B27 allele** is strongly associated with ankylosing spondylitis, being present in around **90% of Caucasian patients** [1]. - While not diagnostic on its own, its presence significantly increases susceptibility and supports the diagnosis in the right clinical context.
Question 4: An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9°C, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?
- A. Hemophilus influenzae
- B. Neisseria gonorrhoeae
- C. Salmonella enterica
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common cause of **acute osteomyelitis** in children. - The clinical presentation with a febrile child, localized leg pain, and radiographic changes strongly points to **bacterial osteomyelitis**, with **_S. aureus_** being the predominant pathogen. *Hemophilus influenzae* - **_Hemophilus influenzae_** was once a significant cause of osteomyelitis in children before widespread **HiB vaccination**. - Its incidence has drastically decreased, making it a less likely cause compared to **_S. aureus_** in an 8-year-old. *Neisseria gonorrhoeae* - **_Neisseria gonorrhoeae_** typically causes **septic arthritis** or osteomyelitis in sexually active adolescents and adults, often in disseminated infections. - It is an **uncommon cause** of osteomyelitis in an 8-year-old child and highly unlikely without a history of sexual abuse or neonatal exposure. *Salmonella enterica* - **_Salmonella enterica_** can cause osteomyelitis, particularly in patients with **sickle cell disease** or other **hemoglobinopathies**. - Without any mention of underlying predisposing conditions like sickle cell disease, **_Salmonella_** is a less probable cause than **_S. aureus_**.
Question 5: Most common organism in acute osteomyelitis is
- A. Staphylococcus aureus (Correct Answer)
- B. Salmonella
- C. Pseudomonas aeruginosa
- D. Streptococcus pneumoniae
Explanation: ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common causative organism in cases of **acute osteomyelitis** across all age groups and is the primary pathogen isolated in most osteomyelitis cases. - Its ability to adhere to bone, form **biofilms**, and produce various virulence factors contributes to its dominance in bone infections. *Salmonella* - **_Salmonella_** species are a common cause of osteomyelitis, particularly in patients with **sickle cell disease** due to their impaired splenic function. - While significant in specific populations, it is not the most common cause of osteomyelitis in the general population. *Pseudomonas aeruginosa* - **_Pseudomonas aeruginosa_** is frequently associated with osteomyelitis in patients with a history of **intravenous drug use**, **puncture wounds** (particularly through athletic shoes), healthcare-associated infections, or those with compromised immunity. - It is an important pathogen in these specific contexts but not generally the most common cause. *Streptococcus pneumoniae* - **_Streptococcus pneumoniae_** can cause osteomyelitis, especially in **neonates** and **young children**, and in individuals with **immunosuppression**. - However, it is not as prevalent as **_Staphylococcus aureus_** as the overall leading cause of acute osteomyelitis.
Question 6: Tuberculosis of the spine; what is the most common site affected?
- A. Sacral
- B. Dorsolumbar (Correct Answer)
- C. Lumbosacral
- D. Cervical
Explanation: ***94ed055d-c7da-4d18-a2fd-52720dfe8b6e*** - The **dorsolumbar (thoracolumbar)** region is the most common site of **spinal tuberculosis (Pott's disease)** [1] due to its high vascularity, facilitating hematogenous spread. - **Spinal tuberculosis** typically affects the vertebral bodies, leading to their destruction, kyphosis (angular deformity), and potentially neurological deficits [1]. *aebdfe6c-98dc-4073-892f-bb24d047bab4* - The **sacral** region can be affected by **tuberculosis**, but it is considerably less common than the thoracolumbar region. - Involvement of the sacrum is often associated with **direct extension** from adjacent structures, such as the sacroiliac joint, rather than primary vertebral involvement. *15c1feef-e3ca-496f-a180-127d52b77bfa* - **Cervical spine tuberculosis** is relatively rare, accounting for a small percentage of all spinal tuberculosis cases. - While possible, it presents with specific challenges due to the proximity of vital neurological and vascular structures. *d05d4d13-bb83-4f26-aa2d-c9c0203d299c* - The **lumbosacral region** (L5-S1) can be involved in **tuberculosis**, but it is less frequently affected than the thoracolumbar region. - While the lumbar spine is a common site, the entire lumbosacral region as a single entity is not the most common spot for spinal TB.
Question 7: A 23-year-old woman with a history of sickle cell disease presents with fever and severe bone pain localized to her left tibia. X-ray reveals a lytic lesion, and blood cultures reveal infection. A bone culture grows gram-negative rods. Which of the following best describes the infecting organism?
- A. It is a facultative intracellular parasite, such as Legionella.
- B. It is a non-motile facultative anaerobe, such as Shigella.
- C. It is comma-shaped and sensitive to acidic pH, such as Vibrio cholerae.
- D. It is motile and does not ferment lactose, such as Salmonella. (Correct Answer)
Explanation: ***It is motile and does not ferment lactose, such as Salmonella.*** - Patients with **sickle cell disease** are at high risk for **Salmonella osteomyelitis** due to impaired reticuloendothelial function in the spleen, which normally clears encapsulated bacteria. - **Salmonella** species are gram-negative rods, typically **motile** due to peritrichous flagella, and most clinically relevant species are **non-lactose fermenters**. *It is a facultative intracellular parasite, such as Legionella.* - **Legionella** is a **facultative intracellular parasite** that causes Legionnaires’ disease (atypical pneumonia) and Pontiac fever, primarily affecting the lungs, not causing osteomyelitis, and is usually diagnosed from respiratory specimens. - While it is a gram-negative rod, it is an unlikely cause of osteomyelitis, especially with a history of sickle cell disease which predisposes to **Salmonella**. *It is a non-motile facultative anaerobe, such as Shigella.* - **Shigella** species are indeed **non-motile** and **facultative anaerobes** that are gram-negative rods, but they primarily cause **dysentery** (bloody diarrhea) and are not a common cause of osteomyelitis, even in immunocompromised patients. - The clinical presentation of severe bone pain and lytic lesion in sickle cell disease points away from **Shigella**. *It is comma-shaped and sensitive to acidic pH, such as Vibrio cholerae.* - **Vibrio cholerae** is a **comma-shaped** (curved) gram-negative rod that causes **cholera**, characterized by severe watery diarrhea, and is indeed sensitive to acidic pH. - It is an extremely rare cause of osteomyelitis and does not fit the typical infectious profile associated with sickle cell disease.
Question 8: The earliest radiological change to appear in a case of acute osteomyelitis is:
- A. Periosteal reaction
- B. Sequestrum formation
- C. Bony sclerosis
- D. Loss of plane between soft tissue and muscle (Correct Answer)
Explanation: ***Loss of plane between soft tissue and muscle*** - This finding, often seen as **soft tissue swelling** and effacement of fat planes on radiographs, is the **earliest detectable radiographic sign** in acute osteomyelitis, typically appearing within 24-48 hours. - It reflects the initial inflammatory changes and **edema** in the soft tissues surrounding the infected bone. *Periosteal reaction* - This occurs later than soft tissue changes, usually appearing after **7-10 days** of infection, as the periosteum is lifted and new bone formation begins. - It is a sign of bone irritation and can be seen as linear or lamellated **new bone growth** parallel to the cortex. *Sequestrum formation* - A sequestrum is a piece of **devitalized (necrotic) bone** that separates from the healthy bone, a much later complication of osteomyelitis. - It typically appears several weeks into the disease course, indicating established bone necrosis and usually requiring surgical intervention. *Bony sclerosis* - **Bony sclerosis**, or increased bone density, is a sign of chronic inflammation and new bone formation in response to persistent infection. - This change is usually observed in the **later stages of osteomyelitis** or in chronic forms, not in the acute phase.
Question 9: A 10 year old child came to the OPD with pain and mass in right lumbar region with no fever, with right hip flexed. The pain increased on extension and X ray showed spine changes. Most probable diagnosis is:
- A. Appendicular lump in retrocecal position
- B. Pyonephrosis
- C. Psoas abscess (Correct Answer)
- D. Torsion of Right undescended testis
Explanation: ***Psoas abscess*** - A **psoas abscess** can present as a lumbar mass with pain, and the classic **psoas sign** (pain on hip extension) occurs because the inflamed psoas muscle is stretched. Spine changes on X-ray suggest a potential vertebral source, such as **spinal tuberculosis (Pott's disease)**, which is a common cause of psoas abscess in children. - The absence of fever does not rule out chronic infections like tuberculosis, and the **flexed hip posture** is a common compensatory mechanism to relieve tension on the inflamed psoas muscle. *Appendicular lump in retrocecal position* - While a retrocecal appendicular lump can cause a right lumbar mass, the pain would typically worsen with hip flexion, not extension, and it is less likely to be associated with **spine changes** on X-ray. - Appendicular lumps are usually accompanied by a history of appendicitis with pain that is often more diffuse in the right lower quadrant, and may be associated with **fever and leukocytosis**. *Pyonephrosis* - **Pyonephrosis** (pus in the kidney) would typically present with significant systemic symptoms of infection, such as **fever, chills, and flank pain**. - While it can cause a flank mass, the characteristic **hip flexion and pain on extension (psoas sign)**, along with spine changes, are not typical features. *Torsion of Right undescended testis* - **Testicular torsion** presents with sudden, severe scrotal pain (or inguinal/pelvic pain if undescended) and swelling, not a lumbar mass or psoas signs. - It would also not be associated with **spine changes** on an X-ray.
Question 10: Earliest investigation for diagnosis of Ankylosing spondylitis:
- A. CT scan
- B. Bone scan
- C. X-ray
- D. MRI STIR sequence (Correct Answer)
Explanation: ***MRI STIR sequence*** - An **MRI STIR (Short Tau Inversion Recovery) sequence** is highly sensitive for detecting early inflammatory changes in the **sacroiliac joints** and spine, such as **bone marrow edema**, which is a hallmark of early ankylosing spondylitis. - It can identify disease activity and structural changes *before* they are visible on conventional X-rays, making it the earliest diagnostic tool. *CT scan* - While a **CT scan** provides excellent detailed images of bone, it is not as sensitive as MRI for detecting early inflammatory changes like **bone marrow edema** in the sacroiliac joints. - It involves significant **radiation exposure** and is typically used for more advanced structural assessment rather than early diagnosis. *Bone scan* - A **bone scan** (scintigraphy) shows areas of increased bone turnover but is **not specific** for ankylosing spondylitis and has lower spatial resolution compared to MRI. - It can indicate inflammation or increased metabolic activity but cannot differentiate specific causes or provide detailed anatomical information as effectively as MRI. *X-ray* - **X-rays** are often the initial imaging modality due to their accessibility, but they only show **structural changes** (like erosions, sclerosis, or fusion) in the sacroiliac joints and spine at a later stage of the disease. - Early inflammatory changes, such as **bone marrow edema**, are typically not visible on plain radiographs, leading to a delay in diagnosis compared to MRI.
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