Which is the least affected joint in Ankylosing spondylitis
**Core Concept**
Ankylosing spondylitis (AS) is a chronic inflammatory disease primarily affecting the axial skeleton, characterized by sacroiliitis, spinal stiffness, and eventual fusion of vertebrae. The disease involves the entire spine and sacroiliac joints, but some joints are less frequently affected.
**Why the Correct Answer is Right**
The cervical spine (neck region) is generally considered the least affected area in ankylosing spondylitis. This is because the disease primarily targets the sacroiliac joints and the lumbar and thoracic spine, whereas the cervical spine is less frequently involved. The cervical spine may show some inflammatory changes, but it rarely leads to the same level of fibrosis and ankylosis seen in the lower spine and sacroiliac joints.
**Why Each Wrong Option is Incorrect**
* **Option A:** The lumbar spine is a common site for ankylosing spondylitis, with frequent involvement of the lower lumbar vertebrae leading to fusion and reduced mobility.
* **Option B:** The thoracic spine is also frequently affected, with inflammation and eventual fusion of the vertebrae.
* **Option D:** The sacroiliac joints are a hallmark of ankylosing spondylitis, with significant inflammation and potential fusion.
**Clinical Pearl / High-Yield Fact**
In ankylosing spondylitis, the disease tends to progress in a "top-down" fashion, with the cervical spine and upper thoracic spine often being spared until later stages. This is an important consideration for clinical management and surgical planning.
**Correct Answer: C. Cervical spine.**