Commonest site of bone involvement in hematogenous osteomyelitis:
**Core Concept**
Hematogenous osteomyelitis is a type of bone infection that occurs when bacteria from the bloodstream infect the bone. The site of bone involvement is critical in determining the clinical presentation and treatment outcomes.
**Why the Correct Answer is Right**
The commonest site of bone involvement in hematogenous osteomyelitis is the metaphysis of long bones. This is because the metaphysis has a rich blood supply, which allows bacteria to easily colonize and infect the bone. The metaphysis is also a site of active bone growth, making it more susceptible to infection.
**Why Each Wrong Option is Incorrect**
**Option A:** Diaphysis - The diaphysis is the shaft of the long bone, which has a relatively poor blood supply compared to the metaphysis. It is less likely to be involved in hematogenous osteomyelitis.
**Option B:** Epiphysis - The epiphysis is the end of the long bone, which is separated from the metaphysis by the growth plate. The epiphysis is not typically involved in hematogenous osteomyelitis due to the barrier provided by the growth plate.
**Option C:** Pelvis - While the pelvis can be involved in osteomyelitis, it is not the commonest site of bone involvement in hematogenous osteomyelitis.
**Clinical Pearl / High-Yield Fact**
The metaphysis is the commonest site of bone involvement in hematogenous osteomyelitis due to its rich blood supply and active bone growth. This knowledge is critical for diagnosing and treating osteomyelitis in children.
**Correct Answer: C. Pelvis