There are 12 thoracic vertebrae in the human spine, labeled T1 through T12. They make up the middle section of your back, sitting between the 7 cervical vertebrae in your neck and the 5 lumbar vertebrae in your lower back. What makes them unique is their direct connection to your rib cage, which gives this part of the spine a rigidity you won’t find anywhere else along your backbone.
Where the Thoracic Vertebrae Sit
Your spine contains 24 individual vertebrae stacked on top of each other, and the 12 thoracic vertebrae account for exactly half of them. They form the longest segment of the spine, running from roughly the base of your neck down to the bottom of your rib cage. Together, the thoracic vertebrae produce a gentle outward curve called a kyphotic curve, giving your upper back its subtle rounded shape when viewed from the side.
The spinal canal running through these vertebrae is slightly narrower than in other parts of the spine. At T1, the canal measures about 16 mm across, narrows to roughly 14.6 mm at T8, then widens again to about 16.7 mm at T12. This narrowing in the mid-thoracic region is one reason injuries here, while uncommon, can be serious when they do occur.
How They Connect to Your Ribs
The defining feature of thoracic vertebrae is their attachment to the ribs. Each vertebra has small cartilage-lined depressions called facets on its body and, for most of them, on its side projections as well. These facets create two types of joints: one where the head of a rib meets the vertebral body, and another where the rib’s bump (its tubercle) meets the side projection. Most ribs actually connect to two neighboring vertebrae and the disc between them, which locks the whole structure together like interlocking puzzle pieces.
Not all 12 thoracic vertebrae connect to ribs in the same way. T2 through T9 follow the standard pattern, with partial facets shared between adjacent vertebrae. T1 is different because it’s the only vertebra that connects to the first rib, so it has a full facet on top rather than a shared one. T10, T11, and T12 are also atypical. T11 and T12 are particularly distinct: they each connect to only one rib, and their ribs don’t attach at the side projections at all. These are your “floating ribs,” the two lowest pairs that don’t wrap around to connect to your breastbone.
Range of Motion in the Thoracic Spine
Because the rib cage essentially splints the thoracic spine in place, this region is the most stable and least flexible part of your back. Bending forward (flexion) allows only about 20 to 45 degrees of motion, and bending backward (extension) gives you roughly 25 to 35 degrees. Side bending reaches about 20 to 40 degrees in each direction.
Rotation is the exception. Your thoracic spine actually provides the greatest rotational range of any spinal segment, allowing roughly 35 to 50 degrees of twisting. This is the motion you use when you turn to look behind you while keeping your hips still, or when you wind up for a golf swing. The combination of high rotational freedom with limited forward and backward bending is what makes the thoracic spine biomechanically distinct from both the neck and the lower back.
Not Everyone Has Exactly 12
While 12 is the standard count taught in anatomy classes, natural variation is more common than most people realize. A study published in the American Journal of Neuroradiology found that nearly 24% of asymptomatic young adults had some variation in their spinal segment count or distribution. Some people have 11 thoracic vertebrae with 6 lumbar vertebrae, while others have 13 thoracic vertebrae with only 4 lumbar. These variations are typically harmless and often go unnoticed unless someone gets imaging for an unrelated reason. The total number of presacral vertebrae (everything above the fused sacrum) is usually 24, but some people have 23 or 25.
These differences matter mainly for surgical planning. If a surgeon is targeting a specific vertebral level based on imaging, knowing whether a patient has a standard or variant count prevents operating at the wrong level.
Common Thoracic Spine Problems
The thoracic spine’s rigidity makes it the least commonly injured section of the back, but it’s not immune to problems. Compression fractures are among the most frequent issues, especially in older adults with weakened bones. In these cases, a vertebral body essentially collapses under load. The cause is often surprisingly minor: daily life accidents account for the vast majority of these fractures in people with bone loss, meaning something as simple as a stumble or lifting a heavy bag can be enough.
Poor posture over years can also exaggerate the natural thoracic curve, leading to a more pronounced hunch (hyperkyphosis). This is different from the structural condition some teenagers develop, where the vertebrae themselves grow unevenly during growth spurts. Both conditions can cause stiffness and discomfort in the mid-back, though they differ in cause and management.
Thoracic disc herniations, where the cushion between two vertebrae bulges or ruptures, are far less common here than in the neck or lower back. The rib cage limits the amount of flexion and extension that wears discs down, so the thoracic discs simply experience less mechanical stress over a lifetime.