The fourth thoracic vertebra, otherwise known as the T4 vertebra, is located in the upper region of the middle back, and is an important support structure for the rib cage. This vertebra is similar to the other twelve vertebrae in the thoracic spine in that it is designed for strength and support more than for flexibility. This stability means that, not surprisingly, middle back pain is less common than lower back or neck pain because of the limited mobility.
The thoracic spine has one main role: provide support for the rib cage. Where the lumbar and cervical spine segments also support significant weight, they additionally are required to provide a wider range of motion, exponentially increasing the likelihood of wear and tear. Conversely, the thoracic spine needs only to be marginally flexible, so the T4 vertebra and its comrades are instead built to bear the burden of supporting the ribs with a stable foundation. This stability is accomplished two ways:
- First, the T4 vertebra, like most vertebrae, has two sets of matching facet joints. These cartilage-coated facet joints connect to the adjacent vertebrae, in this case T3 and T5, and are encapsulated with a thick lubricating fluid. This allows the joints to articulate –providing limited motion – but also ensure an extremely strong bond by limiting the degree of flexibility.
- Second, the first ten thoracic vertebrae (T1 through T10) also connect to individual ribs, bonding the backbone to the rib cage. This stabilizes the rib cage and protects the vital internal organs in the torso.
Over time, however, the facet joints in the thoracic spine, like all joints in the body, are prone to arthritis and other forms of deterioration, which can lead to painful symptoms.