Three-Dimensional Morphological Classification of the Atlas Vertebral Artery Groove Ring: Anatomical Distribution and Health Care-Seeking Behavior — A Retrospective Study of 1192 Cases

Deep within the neck, just below the skull, lies a small but vital bone known as the atlas. It is the first vertebra of the spine, named after the giant who held up the heavens in Greek mythology, because it supports the weight of the head. Running along the top edge of this bone is a natural groove that serves as a highway for the vertebral artery, a major blood vessel that carries oxygen-rich blood to the brain. In most people, this groove remains an open channel, allowing the artery to pass freely. However, in some individuals, a small bridge of bone grows across this groove, partially or completely closing it off. This structure, called the vertebral artery groove ring, turns an open trench into a tunnel. While this might sound like a minor anatomical curiosity, it holds significant importance for doctors. If a surgeon needs to place a screw to stabilize the neck, they must know exactly where this bone bridge is. Mistaking the bridge for the normal bone edge could lead to a dangerous injury to the artery, causing severe complications. Understanding how often these bridges appear, what they look like, and who has them is essential for safe medical care.

A team of researchers at Beijing Shijingshan Hospital set out to map these hidden structures with greater precision than ever before. They looked back at the medical records of 1,192 patients who had undergone detailed three-dimensional CT scans of their necks between 2023 and 2024. The researchers were careful to exclude anyone who had suffered a recent neck injury or had previous neck surgery, ensuring they were studying the natural, unaltered anatomy of the spine. Using high-resolution images, they reconstructed the bones in three dimensions to see the tiny details of the atlas that standard X-rays might miss. Their goal was not just to count how many people had these bone bridges, but to sort them into specific categories based on their shape and location, and to see if these shapes were linked to the patients' age, gender, or how often they visited doctors for symptoms like dizziness or headaches.

The study revealed that these bone bridges are far more common than many people realize. Out of the 1,192 patients scanned, 431, or roughly 36 percent, had some form of vertebral artery groove ring. The researchers divided these findings into three distinct types based on how much the bone closed off the groove. The most common type, found in about 26 percent of the total group, was the "groove process." This is a small bony bump or protrusion that juts out but does not form a complete circle. The second type, the "groove ring," appeared in about 8 percent of patients; this is an incomplete bony circle that partially covers the artery. The rarest form, seen in only about 2 percent of cases, was the "groove canal," where a complete bony tunnel fully encloses the artery. The researchers found that these variations were not tied to a person's age or gender. Men and women were equally likely to have them, and they appeared with similar frequency across all age groups, from young adults to the elderly. This suggests that these bone bridges are likely a congenital trait, something a person is born with, rather than a condition that develops later in life due to wear and tear.

What the researchers found most intriguing was how the shape of the bone bridge related to where it was located and whether it appeared on one side or both. When the bone bridge appeared on both sides of the neck, it was almost always the small "groove process" type, occurring in more than 80 percent of bilateral cases. In contrast, when the bridge appeared on only one side, it was much more likely to be the "groove ring" type. The location also mattered significantly. Bridges found at the back of the atlas were overwhelmingly the small "groove process" type. However, bridges found on the side of the atlas were much more varied and were the only location where the complete "groove canal" type appeared frequently. Perhaps most surprisingly, the study linked the shape of the bone to the patient's experience with the healthcare system. Patients who had the "groove ring" type visited significantly more medical departments and made more doctor visits than those with the small "groove process" type. While the study could not prove that the bone bridge directly caused the symptoms, the data suggests that people with this specific partial ring shape are more likely to seek help for issues like dizziness or headaches.

The implications of these findings extend directly to the operating room. For surgeons planning to fix the neck with screws, knowing the specific type of bone bridge is a matter of safety. A complete bony canal, though rare, poses the highest risk because the artery is completely trapped inside bone; placing a screw in the wrong spot could sever the vessel. The study confirms that a three-dimensional CT scan is the best tool for identifying these structures before surgery begins. By classifying the bone bridges into these clear categories, doctors can better predict where the artery lies and choose a safer path for their instruments. The research also highlights that while these bone bridges are common, they are not a single uniform feature. They vary in shape, location, and frequency, and these variations seem to influence how patients interact with the medical system. Ultimately, this work provides a clearer map of the human neck, turning a complex anatomical puzzle into a practical guide for preventing injury and improving patient care.