Understanding Sacrum X-Ray: Technique and Interpretation
The sacrum, a triangular bone at the base of the spine, plays a crucial role in supporting the entire vertebral column and transmitting forces from the upper body to the lower limbs. Imaging the sacrum, particularly via X-ray, is essential for diagnosing various conditions, from fractures to degenerative changes. This article delves into the technique and interpretation of sacrum X-rays.
Sacrum X-Ray Technique
Mastering the technique of sacrum X-ray imaging is vital for obtaining high-quality, diagnostic images. Here are the key steps:
- Patient Positioning: The patient is positioned supine (lying on their back) with the legs slightly internally rotated and the feet together. A pillow may be placed under the knees for comfort.
- Projection: The X-ray beam is directed caudocranially (from the feet towards the head) at a 10-15 degree cephalad angle to the horizontal table.
- Collimation: The field of view should be collimated to include the entire sacrum and the upper margin of the coccyx.
- Exposure Settings: The exposure settings vary depending on the patient's size and the specific X-ray machine. Typically, a medium setting is used, with a range of 60-80 kVp and 4-8 mAs.
Sacrum X-Ray Anatomy and Landmarks
Familiarity with the sacrum's anatomy is crucial for interpreting X-ray images. Key landmarks include:

| Landmark | Description |
|---|---|
| Sacral Curvature | The normal sacrum has a slight convex curvature, known as the sacral curve. This is often accentuated in the elderly due to degenerative changes. |
| Sacral Apex | The most cephalad (towards the head) point of the sacrum, where it articulates with the fifth lumbar vertebra. |
| Sacral Cornua | Two lateral projections at the inferior aspect of the sacrum, where it articulates with the coccyx. |
Interpreting Sacrum X-Rays
Sacrum X-rays can reveal a wide range of abnormalities. Here are some common findings:
- Fractures: Sacral fractures can occur due to high-impact trauma or pathological processes. They may appear as linear lucencies or discontinuities in the bone.
- Degenerative Changes: Degenerative changes, such as osteophytes (bone spurs) and facet joint arthropathy, can lead to narrowing of the spinal canal or foramina, causing nerve compression.
- Spondylolisthesis: This condition occurs when one vertebra slips forward in relation to the adjacent vertebra. In the sacrum, it can lead to narrowing of the lumbosacral disc space and facet joint arthropathy.
Conclusion and Further Reading
Sacrum X-rays are a valuable tool in diagnosing and managing various conditions affecting the lower spine. Understanding the technique and interpretation of these images is crucial for radiologists, orthopedic surgeons, and other healthcare professionals. For further reading, consider exploring the following resources:
- Radiopaedia: Sacrum - Radiopaedia
- American Journal of Roentgenology: Sacral Fractures: Imaging Features and Classification
























