What is Lumbar Spine/Back?

WHAT IS LUMBAR SPINE/BACK (ANATOMY)

The lumbar spine is the lower back that begins below the last thoracic vertebra (T12) and ends at the top of the sacral spine, or sacrum (S1). Most people have five lumbar levels (L1-L5), although it is not unusual to have six. Each lumbar spinal level is numbered from top to bottom.

The low back vertebral bodies are larger, thicker block-like structures of dense bone. From the front (or anterior), the vertebral body appears rounded. However, the posterior bony structure is different—lamina, pedicles, and bony processes project off the back of the vertebral body. These processes and vertebral arches create the hollow spinal canal for lumbar nerve structures and the cauda equina.

Lumbar Structures Create Strong Joint Complex

A single intervertebral disc separates two vertebral bodies, and together with the facet joints forms a strong joint complex that enables the spine to bend and twist.

One pair of facet joints from the top (or superior) vertebral body connects to the lower (or inferior) pair of facet joints. The facet joints are true synovial joints, meaning they are lined with cartilage, and the joint’s capsule encases synovial fluid that enables joints to glide during movement.

Facet joint syndrome may develop as a consequence of aging and degenerative spinal changes and cause lower back pain.

Lumbar intervertebral discs are secured in place by the fibrous endplates of the superior and inferior (top and bottom) vertebral bodies. The gel-like center of each disc, called the nucleus pulposus, is encased or surrounded by the annulus fibrosus—a tough layer of fibrocartilage that could be likened to a radial tire.

Discs are integral to the joint complex and function to (1) hold the superior and inferior vertebrae together, (2) bear weight, (3) absorb and distribute shock and forces during movement, and (4) create open nerve passageways called foramen or neuroforamen. The neuroforaminal spaces at either side of the disc level allow nerve rootlets to exit the spinal canal and leave the vertebral column.

Lumbar disc herniation is a common cause of lower back pain that can radiate into one or both legs, called lumbar radiculopathy. This condition can develop when lumbar nerves are compressed.

Low Back Supported by Lumbar Ligaments, Tendons, and Muscles

Systems of strong fibrous bands of ligaments hold the vertebrae and discs together and stabilize the spine by helping to prevent excessive movements. The three major spinal ligaments are the (1) anterior longitudinal ligament, (2) posterior longitudinal ligament, and (3) ligamentum flavum. Spinal tendons attach muscles to the vertebrae and together work to limit excessive movement.

4 Ways to Protect Your Low Back

Considering upwards of 80% of adults will visit a doctor for lower back pain at some point in their life, it pays to take care of your lumbar spine to help avoid painful, unnecessary wear-and-tear to this vulnerable segment of your spinal column. You can minimize your risk of a lower back problem by:

Losing weight – Even a 10-pound loss can help reduce lower back pain.
Strengthening and maintaining core (abdominal) muscles – The abdominal and lower back muscles work together to form a supportive “girdle” around your waist and lower back. Stronger muscles can help stabilize the lower back and can help reduce injury risk.
Stopping smoking – Nicotine reduces blood flow to the spinal structures, including the lumbar discs, and can accelerate age-related degenerative changes.
Using proper posture and body mechanics – Keep your spine erect and lift objects with your legs. Always ask for help to carry heavy objects. Although your lumbar spine is capable of bending and twisting simultaneously, you should avoid doing so.

All About the Sacrum and Coccyx

The sacrum and coccyx are unlike other bones in your spinal column. The sacrum, sometimes called the sacral vertebra or sacral spine (S1), is a large, flat, triangular-shaped bone nested between the hip bones and positioned below the last lumbar vertebra (L5). The coccyx, commonly known as the tailbone, is below the sacrum.

Individually, the sacrum and coccyx are composed of smaller bones that fuse (grow into a solid bone mass) by age 30. The sacrum is made up of five fused vertebrae (S1-S5), and three to five small bones fuse to create the coccyx. Both structures are weight-bearing and integral to functions such as walking, standing, and sitting

Where S1 joins L5 helps form the lumbosacral curves: lumbar lordosis and lumbar kyphosis. Lordotic and kyphotic curvature works together to support the upper body, bear and distribute weight/forces, and helps maintain spinal balance and functional flexibility.

Lordosis is the inward curve. Too much lordosis can cause swayback that is sometimes associated with spondylolisthesis.
Loss of lordosis can cause spinal imbalance and may lead to flatback syndrome.
The term kyphosis refers to a normal outward curve.

Lumbosacral Joint

This joint occurs at L5 and S1—it essentially connects the lumbar spine to the sacrum.

There is a great amount of pressure at this meeting point, as the curve of your spine shifts at L5-S1 from lordotic (lumbar lordosis, forward curve) to kyphotic (sacral kyphosis, backward curve). The L5-S1 level is weight-bearing and absorbs and distributes the upper body’s weight at rest and movement. This is one reason why disc herniation and spondylolisthesis are more common at L5-S1.

Sacroiliac (SI) Joints

The SI joints connect the sacrum to the left and right sides of the pelvis. Unlike other joints in the body (eg, knees), the span of movement of either SI joint is minimal. These joints are essential to walking, standing, and hip stability. Sacroiliitis and SI joint dysfunction are two spinal disorders related to the sacroiliac joints.

Other spinal disorders related to the sacral spine include sciatica, Tarlov cysts, and spinal chordoma, a common type of spinal bone cancer.

Coccyx’s Role and Function

The coccyx, or tailbone, is located just below the sacrum. Though it’s much smaller than the sacrum, it too has an important weight-bearing role. The coccyx helps support your weight while you sit. If you lean back while sitting, such as reclining in a chair, the pressure on your coccyx increases.

An injury in this coccygeal region can cause tailbone pain, which is known as coccydynia. It is often characterized by inflammation of the coccyx’s connective tissue, resulting in tailbone pain that worsens when sitting. Tailbone fracture that may occur from a traumatic event, such as a fall, can also cause this pain.

Sacral and Coccygeal Nerves

The spinal cord ends at L1-L2 creating the cauda equina, a bundle of spinal nerves resembling the tail of a horse. In the sacrum are the sacral nerves, called the sacral plexus—the term “plexus” simply means a network of nerve structures. The sacral plexus with the lumbar plexus create the lumbosacral plexus.

The sciatic nerve is the largest nerve in the sacral plexus. Compression of the sciatic nerve causes a group of symptoms called sciatica that are known for lower back and leg pain. The coccygeal nerve is the one serving the tailbone (ie, coccyx).

There are five sacral nerves (part of the spinal cord) numbered S1 through S5. The first sacral spinal nerve serves your groin area and hips, S2 the back of your thighs, S3 the middle of the buttock area, and S4 and S5 the anus and vagina.

Sacrum and Tailbone Injury Prevention Tips

Your doctor or health care practitioner is an excellent source for information to help you prevent a sacrum-related problem or coccyx pain. These professionals have your medical history and are best equipped to recommend lifestyle changes and preventive measures.

Start the conversation today and consider these sacral spine care tips:

Are you at risk of or do you have osteoporosis? A bone mineral density test may be recommended.
Avoid sports activities that stress the lower spine. In some people, gymnastics requiring extreme lumbosacral flexibility may cause or contribute to lower back and leg pain, numbness, and weakness.
Exercise regularly. Moderate exercises like walking, jogging, yoga, and strength training all help keep your entire spine strong, flexible, and healthy.
Build core (abdominal) muscle strength. Good core muscle strength can help stabilize the sacrum.
Maintain good posture. Avoid slouching when seated, as this puts undue pressure on the lumbosacral spine and the SI joints.
Think good body mechanics before lifting. Always keep your spine straight and use the strength of your legs to lift objects. Avoid twisting your body while lifting and/or holding something heavy, as this can injure (eg, sprain, strain) your lower spine.
Wear your seatbelt. Car accidents represent a major cause of lower spine trauma. Always use a restraint when driving or riding in any vehicle (even a golf cart).

The section of the spinal column called the thoracic spine begins below the cervical spine (C7, neck), roughly at shoulder level and continues downward until it reaches the first level of the low back (L1, lumbar spine). Twelve vertebrae, numbered T1 through T12 from top to bottom, make up the thoracic spine. When viewed from the side, a normal forward curvature called kyphosis (or kyphotic curve) is seen.

Because the ribs attach to the thoracic spine’s vertebrae, this section of the spine is strong and stabilizing, with less range-of-motion than the cervical (neck) levels. While the thoracic spine is less prone to injury than other sections of the vertebral column, it is the most common location for vertebral fracture due to osteoporosis. Scoliosis and abnormal kyphosis are other thoracic spinal disorders.

Thoracic Spine Bone Basics

The thoracic spine helps support the body’s torso and chest areas and provides an attachment point for each of the rib bones, except the two at the bottom of the ribcage.

Like most other spinal vertebrae, the thoracic vertebral bodies are rounded. Bony arches project from the back of each vertebral body, forming a hollow protective space containing the spinal cord. Thoracic facet joints are paired at the back of each vertebrae and allow limited spinal movement.

Multipurpose Thoracic Spinal Discs

A fibrous pad of tissue called an intervertebral disc is held in place by a strong endplate attachment between each level’s upper (superior) and lower (inferior) vertebral body. Each disc acts as an interbody spacer, creating disc height or space between its upper and lower vertebrae. This space creates open nerve passageways called foramen or neuroforamen at both sides. Nerve roots (or rootlets) branch off the spinal cord and exit the spinal canal through neuroforamen.

Soft Thoracic Supporting Structures Allow Movement Within Limits

Common to the entire spinal column are ligaments, tendons, and muscles. These soft tissues attach to the bones and discs and work together to help stabilize the midback at rest and during movement.

Ligaments are strong bands of fibrous tissue that connect and protect vertebrae and discs, provide spinal stability and help prevent excessive movement.
Muscles help hold the body upright and allow spinal flexion (bend forward), extension (bend backward), and rotation (twist from side to side).
Tendons are strong fibrous tissue that attaches muscle to bone.

Role of Thoracic Nerves

Twelve pairs of thoracic nerve rootlets branch off the spinal cord and through the foramen to innervate, or supply sensation (feeling) and function (movement), to specific areas of the body. These nerves feed the midback and chest regions, and transmit signals between the brain and major organs, including the lungs, heart, liver, and the small intestine.

Types of Thoracic Spinal Disorders

Osteoporosis increases the risk for thoracic spinal fracture. A common type is a vertebral compression fracture (VCF) that can cause one or more bony bodies to flatten or become wedge shaped resulting in spinal cord and/or nerve compression. Sudden and acute back pain is associated with a VCF.
Different types of scoliosis—an abnormal side-to-side curvature of the spine—is well known to develop in the thoracic spine and may cause spinal deformity.
Abnormal kyphosis is an exaggerated amount of forward thoracic spinal curvature. While humpback is not a kind expression, it aptly describes the appearance of a kyphotic deformity. Types of kyphosis include congenital (appearing at birth), posture related, or Scheuermann’s disease.
Metastatic cancer (eg, traveling from a breast or lung) is a foremost cause of spinal tumors that can develop in the thoracic spine potentially leading to structural deterioration.

While cervical or lumbar disc herniations are common, thoracic disc herniation is not. This is because of the thoracic spine’s strength and stability created by its attachments to the ribcage.

Maintain Your Thoracic Spine

Ask your doctor for stretches and exercises appropriate for you to keep your core and midback musculature strong to help prevent injury during flexion, extension, and rotation movements.
Be aware of your posture; use good body mechanics.
If you smoke or vape, consider quitting.
Learn your personal risks for osteoporosis and put a preventive bone density maintenance plan in place with your health care providers’ help.