Why L5-S1 Is So Vulnerable to Injury (2024)

The lumbosacral joint, also called L5-S1, is a term used to describe a part of the spine. L5-S1 is the exact spot where the ​lumbar spine ends and the sacral spine begins. The lumbosacral jointconnects these bones.

L5-S1 is vulnerable to misalignment and injury. It can also be the site of a disc herniation or a spine disorder called spondylolisthesis.

Function and Anatomy

The spinal column is the structure that allows you to stand upright. It also helps you twist, bend, and otherwise alter your trunk and neck position.

There are typically 24 movable bones in the spine that connect to the sacrum (a bony structure located below the lumbar vertebrae) and the coccyx (also called the tailbone). The sacrum and the coccyx each consist of multiple bones that fuse over time.

L5-S1 consists of the last bone in the lumbar spine (low back), called L5, and the triangle-shaped bone under it, known as the sacrum. The sacrum is made of five fused bones—S1 is at the top.

Injury Risk

Each area of the spine has a curve, and these curves go in opposing directions. The areaswhere the spinal curve directions change are called junctional levels. Injury risk may be higher at junctional levels because your body weight shifts direction as the curves shift directions.

The L5-S1 junction is located between the lumbar curve and the sacral curve. The lumbar curve sweeps forward. The sacral curve opposes the direction of the lumbar curve, going backward.

The L5-S1 junction is particularly vulnerable to misalignment, wear and tear, and injury. This is because, in most people, the top of the sacrum is positioned at an angle. Aging and injury may increase the vulnerability of the L5-S1 junction even more.

Pain from L5-S1 is typically treated with heat or ice, over-the-counter anti-inflammatory medications, prescription pain medicine or muscle relaxers, physical therapy, chiropractic adjustments, and epidural steroid injections. If these measures do not help, surgery may be required.

Related Conditions

In the low back, the L5-S1 junction is often the site of a problem known as spondylolisthesis.Disc herniation at L5-S1 is also possible and is a common cause of sciatica—a problem with the sciatic nerve that can cause pain and other issues.

Disc Herniation

Discs separate the vertebrae (spinal bones), cushioning the spinal column and allowing for movement between vertebrae. A disc herniation means the disc slips out of place.

A disc herniation at L5-S1 is a common cause of sciatica. Symptoms of sciatica include:

• Burning
• Numbness
• Pain or tingling that radiates from the buttock down the leg to the knee or foot. The pain is often sharp and may feel like an electric shock.

Disc problems at L5-S1 herniation can also cause lower back pain and stiffness, as well as trigger painful muscle spasms that cause your back to go out.

Bowel problems are also possible with disc problems at L5-S1. Some research links irritable bowel syndrome to herniated discs in the lower back. Additional studies found disc problems at L5-S1 can lead to difficulty controlling your anal sphincter.

Initial treatments for disc herniation include rest and pain relievers—and later physical therapy. Most people recover with these interventions. Those who don't may require a steroid injection or surgery.

Spondylolisthesis

Spondylolisthesis occurs when a vertebra slips forward relative to the bone beneath it.

The most common variety of this condition is called degenerative spondylolisthesis. It generally occurs when the spine starts to wear down with age.

Isthmic spondylolisthesis is another common variant. Isthmic spondylolisthesis starts as a tiny fracture in the pars interarticularis—a bone area in the back that connects the adjoining parts of the facet joint. While thesetypes of fractures tend to occur before the age of 15, symptoms often do not develop until adulthood. Degeneration of the spine in later adulthood can further worsen the condition.

The angle of the sacrummay contribute to spondylolisthesis. This is because the S1 tips down in the front and up in the back rather than being horizontal to the ground. Individuals with a greater tilt will usually have a higher risk of spondylolisthesis.

People with spondylolisthesis may not have any symptoms. Those who do may experience:

• Lower back pain (most common)
• Back stiffness
• Hamstring tightness
• Walking and standing difficulties

Spondylolisthesis is typically treated with non-surgical interventions. These could include:

• Pain medications
• Heat and/or ice application
• Physical therapy
• Epidural steroid injections

Spinal fusion surgery can be effective for treating symptoms related to spondylolisthesis. However, it requires a long recovery time and can have additional risks. Usually, non-surgical care is tried for at least six months. If you haven't gotten relief by then, surgery may be an option.

Summary

The L5-S1 is also called the lumbosacral joint. It is the part of the spine where the lumbar spine ends and the sacral spine begins. It helps you twist, bend, and stand upright.

Because of its location, the L5-S1 is vulnerable to wear and tear and injury. One of the more common problems with the L5-S1 is spondylolisthesis, which occurs when a vertebra slips forward. Disc herniation at L5-S1 is also possible. These conditions are usually treated non-surgically.

By Anne Asher, CPT
Anne Asher, ACE-certified personal trainer, health coach, and orthopedic exercise specialist, is a back and neck pain expert.