Spine - anatomy of the spine

Article by Adjunct A/Prof Hee Hwan Tak

Spine - anatomy of the spine

Adjunct A/Prof Hee Hwan Tak

Orthopaedic Surgeon
National University of Singapore(NUS) 1990
Royal College of Surgeons of Glasgow 1995
Royal College of Surgeons of Edinburgh 1995
2000 Clinical Fellowship in Spinal Surgery in USA, training at the Tulane University, New Orleans, Louisiana and the University of Kentucky in Louisville and Lexington 
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Your spine is made up of separate bones called vertebrae. These vertebrae are stacked on top of each other and are connected together. They support your back and let you bend. Various ligaments and muscles connect the vertebrae together and keep them synchronously aligned.

The spinal column provides the main support for your body, allowing you to stand upright, bend, and twist. Protected within the spinal column (which is hollow in the middle to transmit the nervous tissues), the spinal cord connects your body to the brain, allowing movement of your arms and legs.

In a healthy spine, the vertebrae form a straight line when you look at them from the front or the back. When looked from the side, the spine has a natural S shaped curve. The neck (cervical) and low back (lumbar) regions have a slight concave curve, and the thoracic and sacral regions have a gentle convex curve. These curves work like a coiled spring to absorb shock, maintain spinal balance, and allow flexibility throughout the spinal column. Flexibility is most at the neck and the lower back, and significantly less in the middle back (due to the splinting effect of the rib cage).

The two main muscle groups around the spine are the back extensors and flexors. The extensor muscles enable you to stand upright. The extensors are attached to the back of your spine. The flexor muscles are in the front and include the abdominal muscles. These muscles enable you to bend forward, and are important in lifting. The back muscles stabilize your spine. The ligaments are strong fibrous bands that hold your vertebrae together, stabilize your spine, and protect the discs (see next paragraph). The three major ligaments of the spine are the ligamentum flavum (yellow ligament), anterior longitudinal ligament (ALL), and posterior longitudinal ligament (PLL). The ALL and PLL are continuous bands that run from the top to the bottom of the spinal column along the vertebral bodies. They prevent excessive movement of the vertebrae. The ligamentum flavum attaches itself between the lamina of each vertebra. The lamina is located at the back of the spinal column, behind the nervous tissues. In a commonly seen condition in the middle aged and elderly called spinal stenosis, the ligamentum flavum frequently becomes thickened and hard, leading to narrowing of the space for the nerves.

Each vertebra in your spine is separated and cushioned by an intervertebral disc, keeping the bones apart. The function of the discs is to maintain flexibility of your spine, as well as support the weight of your body while you perform your daily tasks. The disc is designed like a car tire. The outer ring, called the annulus fibrosus, has criss-crossing fibrous ands. In the center of the side the disc is the gel-filled nucleus pulposus, which contains water and is responsible for the cushioning effect exerted by your spine. With increasing age, your discs (nucleus pulposus) gradually lose the ability to retain fluid and become dryer and shorter.

Together with your discs, the facet joints of your back allow back motion. Each vertebra has four facet joints, one pair that connects to the vertebra above (superior facets), and another pair that connects to the vertebra below (inferior facets). The facet joints may undergo typical wear and tear changes well documented in other joints e.g knee. Bone spurs may form around the facet joints, and if they form in the vicinity of the nerve(s), then the nerves maybe vulnerable to compression.

The spinal cord is the nervous tissue that runs within the protective spinal canal from the brain to the first lumbar vertebra. After that, the cord separates into the cauda equina. The spinal cord serves to send messages between the brain and the various parts of the body in both directions. Spinal nerves branch off the spinal cord. In the neck or cervical spine, the nerves will reach their eventual destination in the upper extremities. In the lower back, the spinal nerves will reach their final destination in the lower extremities.

In summary, your spine is an extremely important structure of your body. It forms the scaffold where our extremities are attached. It permits mobility and flexibility, either directly via movements of the spinal column, and indirectly via movements of the extremities from relayed messages from the spinal nerves. In order to maintain the long-term health of your spine, you have to start to respect it.

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