Radiological sign of spondylolysis is
**Core Concept**
Spondylolysis refers to a defect or fracture in the pars interarticularis, a region of the vertebral arch. This condition often affects the L5 vertebra and can lead to spondylolisthesis. The radiological sign of spondylolysis is crucial for diagnosis.
**Why the Correct Answer is Right**
The radiological sign of spondylolysis is typically visible on a lateral X-ray of the spine. It appears as a bilateral or unilateral defect in the pars interarticularis, often referred to as a "Scotty dog" or "collar sign." This sign is caused by the thinning and eventual fracture of the pars interarticularis, which can be due to repetitive stress and microtrauma. The presence of this sign suggests spondylolysis, particularly in the context of other clinical and radiological findings.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the radiological sign of spondylolysis. However, it's worth noting that other radiological signs, such as the "hourglass sign," can be associated with spondylolisthesis, but not spondylolysis.
* **Option B:** This option is not accurate, as the "ring apophysis" is a distinct radiological sign associated with other conditions, such as Scheuermann's kyphosis.
* **Option C:** This option is incorrect, as the "pedicle erosion" is a sign associated with other conditions, such as metastatic disease or infections.
**Clinical Pearl / High-Yield Fact**
Remember the "Scotty dog" sign, which is a classic radiological sign of spondylolysis. This sign is a crucial diagnostic clue, particularly in the context of low back pain and radiographic findings.
**Correct Answer:** C.