The spinous process is a bony projection extending from the back of each vertebra, the individual bones that make up the spinal column. These processes are readily felt as a series of bumps running down the middle of your back. They are an integral part of the vertebral arch, which forms a protective ring around the spinal cord. This feature contributes significantly to spinal mechanics and stability.
Anatomy and Location
Each vertebra in the human spine, except for the first cervical vertebra (C1), possesses a single spinous process. This projection is located centrally on the posterior aspect of the vertebra, extending backward from the point where the two laminae (flat plates of bone) meet. The spinous processes vary in size, shape, and orientation depending on their location within the spinal column.
In the neck region, the spinous processes of vertebrae C2 through C6 are bifid, meaning they split into two parts at their ends. Moving down to the thoracic spine, these processes become longer and are angled obliquely downward and posteriorly. In the lower back, or lumbar spine, the spinous processes are thicker and broader. This regional variation in morphology reflects the different biomechanical demands placed on each section of the spine.
Function and Role
The spinous process primarily serves as an attachment point for various muscles and ligaments that stabilize the spine and facilitate movement. Muscles like the semispinalis cervicis connect to these processes, contributing to spinal extension and rotation. Ligaments, such as the interspinous and supraspinous ligaments, connect adjacent spinous processes, helping to limit excessive flexion and maintain spinal alignment.
Beyond providing attachment sites, the spinous processes act as levers for muscle action, allowing for a range of motions including bending, twisting, and maintaining posture. Their position also contributes to the protection of the delicate spinal cord, which runs through the vertebral canal formed in part by the vertebral arches. The spinous processes, along with other vertebral components, contribute significantly to the overall stability and flexibility of the vertebral column.
Common Issues
Various conditions can affect the spinous process, leading to discomfort or limitations in movement. One common issue is a spinous process fracture, which can result from direct trauma, falls, or sudden, forceful muscle contractions. A specific type, known as a “clay shoveler’s fracture,” is seen in acute traumatic cases or sports. These fractures involve the lower cervical or upper thoracic spinous processes, such as C6, C7, or T1.
Pain upon palpation of the spinous processes can indicate underlying issues such as muscle strain, ligamentous injury, or even a fracture. Degenerative changes like osteoarthritis can also affect the spinous processes, leading to conditions such as Baastrup’s sign, where adjacent spinous processes touch and cause pain, often in the lumbar spine. Additionally, conditions like spinous process apophysitis, an injury to the growth plate where muscles attach, can cause localized pain, particularly in adolescents. While most spinous process issues are managed conservatively with rest and pain relief, severe cases may require further intervention.