Many different structures in the spine can cause back pain, potentially when:

  • The large nerve roots that go to the legs and arms are irritated
  • The smaller nerves that innervate the spine are irritated
  • The large paired back muscles (erector spinae) are strained
  • The bones, ligaments or joints themselves are injured
  • The disc space itself is a source of pain

Therefore, a review of spinal anatomy is important to understand the causes of back pain, neck pain, and sciatica (leg pain), and evaluate treatment options.

The lumbar spine (lower back)

Lumbar Spine Anatomy Video
Video: Lumbar Spine Anatomy

The lower back has a lot more motion than the thoracic spine and also carries all the weight of the torso, making it the most frequently injured area of the spine.

The motion in the lumbar spine is divided between five motion segments, although a disproportionate amount of the motion is in the lower segments (L3-L4 and L4-L5).

Consequently, these two segments are the most likely to breakdown from wear and tear (e.g. osteoarthritis). The two lowest discs (L4-L5 and L5-S1) take the most strain and are the most likely to herniate.

This can cause lower back pain and possibly numbness that radiates through the leg and down to the foot (sciatica).


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Back Strains and Strains Video
Video: Back Strains and Sprains

The vast majority of episodes of lower back pain are caused by muscle strain. Even though a muscle strain doesn’t sound like a serious injury, trauma to the muscles and other soft tissues (ligaments, tendons) in the lower back can cause severe back pain.

The good news is that soft tissues have a good blood supply, which brings nutrients to the injured area, facilitates the healing process and often provides effective relief of the back pain.

The sacral region (bottom of the spine)

Below the lumbar spine is a bone called the sacrum, which makes up the back part of the pelvis. This bone is shaped like a triangle that fits between the two halves of the pelvis, connecting the spine to the lower half of the body.

The sacrum is connected to part of the pelvis (the iliac bones) by the sacroiliac joints. Pain in the sacrum is often called sacroiliac joint dysfunction, and is more common in women than men. The coccyx – or the tailbone – is in the sacral region at the very bottom of the spine.

Tailbone pain is called coccydynia, which is more common in women than men.

Vertebral Components of the Lumbar Spine

The thick oval segment of bone forming the front of the vertebral segment is the vertebral body.

Each segment of the lumbar spine is comprised of the following structures:

  • The vertebral bodies are attached to a bony arch through which all the nerve roots run. The vertebral arch is comprised of two pedicles, the short stout processes that extend from the sides of the vertebral body and two laminae, the broad flat plates that project from the pedicles and join in a triangle to form a hollow archway (the foramen).
  • The vertebral arches are interconnected by paired facet joints, which in combination with the disc, create a three joint complex at each vertebral motion segment. This three-joint complex at each vertebral segment (the facet joint) allows for motion in flexion, extension, rotation, and lateral bending.
  • The facet joints have cartilage on each surface and a capsule around them. The cartilage can degenerate as one ages, and lead to degenerative arthritis.
  • The spinous process protrudes from the junction of the two laminae and these are the ridges that can be felt through the skin along the back of the spine.
  • Transverse processes project from the junction of the pedicles and lamina. The structures of the vertebral arch protect the spinal nerves that run through the spinal canal. A back surgery known as a lumbar laminectomy involves the removal of the laminae to gain access to the vertebral canal.

Lower Back Motion and Back Pain

Fifty percent of flexion (bending forward) occurs at the hips, and fifty percent occurs at the lumbar spine (lower back). The motion is divided between the five motion segments in the lower back, although a disproportionate amount of the motion is at L4-L5 (lumbar segment 4 and 5) and L3-L4 (lumbar segment 3 and 4).

Consequently, these two segments of the lower back are the most likely to break down with degeneration. As these segments break down they can become unstable with an excess of motion creating lower back pain.

There are a number of non-surgical treatments available to help manage the low back pain, and a surgical fusion can help alleviate the back pain by stopping the motion.

Vertebral Compression Fractures and Back Pain

Since they are major load bearing structures, vertebral bodies are also prone to developing compression fractures, particularly in patients with osteoporosis (which weakens the bone). These fractures can lead to chronic back pain and progressive misalignment or deformity of the spine.

Over time, a misalignment or deformity in the spine places stress on muscles, tendons, ligaments, and bones throughout the back and can result in impaired balance or walking ability.

Nerve Irritation from a Herniated Disc

Herniated Disc Videos
Video: Herniated Disc

The nerve passing to the next level runs over a weak spot in the disc space, which is the reason discs tend to herniate (extrude) right under the nerve root and can cause leg pain (lumbar radiculopathy or sciatica).

Sometimes, a herniated disc will cause only leg pain or arm pain and not lower back pain or neck pain, and may initially be thought to be a problem with the patient’s leg or arm.

  • Arm pain from a cervical disc herniation is usually accompanied by numbness/tingling and runs to the fingers.
  • Leg pain from a lumbar disc herniation will usually run below the knee, and possibly to the foot, and may be accompanied by numbness. Learn more about how a herniated disc in the lower back can affect the sciatic nerve and lead to leg pain and even foot pain.

Pinched Nerve Pathology

The two nerves most commonly pinched in the lower back are L5 (lumbar 5) and S1 (sacral 1).

  • Pinched nerve at L5. The L5 nerve supplies the nerves to the muscles that raise the foot and big toe, and consequently, impingement of this nerve may lead to weakness in these muscles. Numbness for L5 runs over the top of the foot.
  • Pinched nerve at S1. Impingement of the S1 nerve can lead to weakness with the large gastronemius muscle in the back of the calf, causing difficulty with foot push off. Numbness for the S1 nerve runs on the outside of the foot. The S1 nerve root also supplies innervation for the ankle jerk (tap on the achilles tendon and the foot goes down), and a loss of this reflex indicates S1 impingement, although it does not create loss of function.

Most cervical pathology will lead to pinching of either C6 or C7 nerve roots in the neck, although sometimes the C5 or C8 nerves may be pinched.
Depending on which nerve root is pinched, the following symptoms are likely:

  • Pinched nerve at C5. This can cause shoulder pain, deltoid weakness, and possibly a small area of numbness in the shoulder. On physical exam, a patient’s biceps reflex may be diminished.
  • Pinched nerve at C6. This can cause weakness in the biceps and wrist extensors, and pain/numbness that runs down the arm to the thumb. On physical exam, the brachioradialis reflex (mid-forearm) may be diminished.
  • Pinched nerve at C7. This can cause pain/numbness that runs down the arm to the middle finger. On physical exam, the triceps reflex may be diminished.
  • Pinched nerve at C8. This can cause hand dysfunction (this nerve supplies innervation to the small muscles of the hand). Pain/numbness can run to the outside of the hand (little finger) and impair its reflex.

Healing from a Pinched Nerve

The nerve consists of one long cell from the low back or neck down to the foot or hand, so the nerves tend to heal slowly. The nerves heal from the top down, and depending on how much damage is done at the time the nerve becomes impinged (pinched), it may take weeks to months for the nerve to fully to heal.

Treatment of neural impingement is directed at relieving the pain and then allowing the nerve to heal on its own. Nerves need both inflammation and pressure to be painful, so either relieving the inflammation or the pressure can relieve the pain.

Sacroiliac Joint Dysfunction

Sacroiliac Joint Dysfunction Video
Video: Sacroiliac Joint Dysfunction

The sacrum is wider and shorter in women than in men. Young and middle age women are more susceptible to developing sacroiliac joint dysfunction, a condition in which pain typically concentrates on one side of the low back and radiates down the leg to the knee or at times, to the ankle or foot.

Read more: Sacroiliac Joint Dysfunction (SI Joint Pain) (SI Joint Pain)

While the exact root of the pain is difficult to pinpoint, disruption of the normal joint motion between the sacrum and ilium is a likely source of pain arising from either:

  • Hypermobility (too much movement in the sacroiliac joint)
  • Hypomobility (too little movement in the sacroiliac joint)

Sacroiliac joint dysfunction is also difficult to accurately diagnose since the pain symptoms resemble those associated with a herniated disc and sciatica.

The Coccyx (Tailbone)

Coccydynia (Tail Bone Pain) Video
Tailbone Pain Video

Unlike the individual vertebrae in other regions of the spine, the vertebrae in the sacral region as well as the coccyx are fused. The coccyx (also called the tailbone) is located at the base of the spine and is composed of four fused vertebrae. Ligaments attach the coccyx to the sacral hiatus at the synovial sacro-coccygeal joint.

See also: Anatomy of the Coccyx (Tailbone)

Coccydynia (Coccyx Pain)

When sitting, the coccyx shifts forward and acts as a shock absorber. However, falling on the tailbone or events such as childbirth can lead to coccygeal pain, known as coccydynia. In most cases, the pain is caused by an unstable coccyx, which results in chronic inflammation of the sacro-coccygeal joint.

See also: Coccydynia (Tailbone Pain)

Coccydynia (tailbone pain) can also be attributed to a malformed or dislocated coccyx and the growth of bony spurs on the coccyx. Women are more likely to experience coccydynia, since the coccyx is rotated and faces backward in women, which makes it more susceptible to trauma.

Lower Back Pain Exercises

Back muscles, like any other muscle in the body, require adequate exercise to maintain strength and tone.

While muscles like the gluteals (in the thighs) are used any time we walk or climb a step, deep back muscles and abdominal muscles are usually left inactive and unconditioned. Unless muscles are specifically exercised, back muscles and abdominal muscles tend to weaken with age.

Read more about Exercise and Back Pain


Source: Adapted from