Hemiveebra is a defect of
**Core Concept**
Hemivertebra is a congenital defect of the spine, characterized by a unilateral hemisegmentation of the vertebra, resulting in an abnormal wedge-shaped vertebra. This anomaly can lead to scoliosis, a lateral curvature of the spine, due to an imbalance in the growth and development of the vertebrae.
**Why the Correct Answer is Right**
Hemivertebra occurs due to a failure of the normal segmentation process during embryonic development, leading to an incomplete or abnormal separation of the vertebral bodies. This results in a unilateral hemisegmentation of the vertebra, causing an uneven growth of the spine. The affected vertebra becomes wedge-shaped, which can lead to an abnormal curvature of the spine.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as hemivertebra is not a defect of the intervertebral disc, but rather a congenital anomaly of the vertebral body itself.
**Option B:** This option is incorrect as hemivertebra is not a defect of the facet joints, which are involved in the articulation of adjacent vertebrae.
**Option C:** This option is incorrect as hemivertebra is not a defect of the spinal cord, which is the central nervous tissue that extends from the base of the brain down to the lower back.
**Clinical Pearl / High-Yield Fact**
It's essential to recognize the clinical presentation of hemivertebra, which can include scoliosis, back pain, and respiratory difficulties in severe cases. A thorough radiographic examination, including X-rays and CT scans, is necessary to diagnose hemivertebra.
**Correct Answer: D.**