What is Spine Sagittal Balance?
The body and the spine work together to keep us balanced and upright with the least amount of effort. This balance is achieved through the interaction of different parts of the spine and the pelvis: the neck curved inward (cervical lordosis), the upper back curve outward (thoracic kyphosis), the lower back curve inward (lumbar lordosis), and the shape of the pelvis. The main goal is to maintain balance from the center of the head, hips, and lower body parts, both side-to-side (coronal plane) and front-to-back (sagittal plane).
In the past, scoliosis or spinal deformity surgery was mainly focused on balancing the spine side-to-side. But research has now shown that restoring front-to-back balance is more clinically important since it’s more connected to function and pain relief than just focusing on side-to-side balance during spinal correction surgery.
What Causes Spine Sagittal Balance?
Sagittal imbalance happens when something pushes the body’s balance point too far forward. There are many reasons why this might occur – these reasons might be present from birth, as a result of wear and tear, from physical injury or because of medical procedures.
One example is congenital scoliosis, a condition that people are born with, where the spine has a sideways curve. This condition could involve stiff, hunched areas or underdeveloped vertebrae (bones) which can throw off the balance of the spine.
Injury to the spine, whether treated with or without surgery, can lead to long-lasting changes in the balance of the spine, especially if the injury occurs around the thoracolumbar junction. This is the area where the spine changes from having a forward curve (kyphosis) to a backward curve (lordosis). If a bone in the spine gets squeezed causing it to become squashed or hunched, this is another typical cause of sagittal imbalance.
Age-related or degenerative changes of the spinal disc can lead to motion loss in these affected segments, causing other parts of the spine to become overstressed. This too can cause a chronic loss of sagittal balance. Diseases that cause degenerating changes in the spine, like rheumatoid arthritis or ankylosing spondylitis, can also display this characteristic.
Certain medical procedures that involve fusion of the thoracolumbar junction can cause hyperlordosis (an excessive curve) in the nearby lumbar area. This means the rest of the lumbar spine and the thoracic portions try to compensate by increasing their own curve. Over time, however, this compensation effect is lost leading to a condition called flat back syndrome with too much thoracic curve (hyperkyphosis).
Risk Factors and Frequency for Spine Sagittal Balance
Sagittal imbalance is a complicated condition that can occur due to many different causes of spinal deformity. A large study found that the causes of sagittal imbalance include adolescent idiopathic scoliosis (making up 30.4% of cases), kyphotic deformity (20.7%), a combination of junctional degeneration and imbalance caused by medical treatment (14%), and neuromuscular issues, birth defects, or different types of scoliosis (25.5%).
Signs and Symptoms of Spine Sagittal Balance
A complete medical history is important, especially regarding past issues with the spine or any previous spine surgeries. It is crucial to pin down the exact type of pain, whether it’s stemming from the spinal discs, due to mechanical issues, or connected to nerve damage.
A full examination of the muscles and nerves should be carried out. The doctor needs to examine the patient while they’re lying down and standing up. It’s also important to look at how the patient walks to check for any unusual compensations they might be making due to pain or discomfort.
Beyond the spine, it’s important to check the patient’s hip movement and pain levels in case there are any contracts or malfunctions. Paying close attention to the head is also necessary to check the neck’s range of motion and for any limitations in looking up, which could be a sign of sagittal imbalance, a condition that affects the spine’s alignment.
Testing for Spine Sagittal Balance
When examining spinal alignment, particularly for any abnormalities or issues, full-size standing X-rays are often used. These images help health professionals to look at the positioning and symmetry of your spine, pelvis and the tops of your thighs known as femoral heads – they also show how these areas balance each other out, which is quite important.
A recent development in this area is the EOS X-ray system. This machine is special because it uses award-winning techniques to create 3D images from two flat X-rays. It allows doctors to measure aspects of the spine’s structure from different angles, which is particularly useful when planning surgeries to fix deformities in the spine. One major advantage of this system is that, in comparison to a CT scan, it exposes patients to significantly less radiation while providing similar image detail.
Other imaging techniques like MRI and CT scans are sometimes used when planning for surgery or evaluating a patient’s specific condition. However, these methods are not used when the patient is standing, and so they provide a different type of image. That said, the majority of diagnoses are still based on standard X-rays. It’s essential to understand that CT and MRI provide complementary information but don’t replace the need for standing images.
Treatment Options for Spine Sagittal Balance
The main aim is to position the body so it requires minimum effort to stay balanced. This is what we call maintaining the body’s ‘cone of equilibrium’.
Treatment options can be non-surgical, which includes using braces for added support, or physical therapy to strengthen muscles.
Surgical treatment varies and might involve removing bits of bone to realign the spine. These procedures can differ in severity, from an operation known as pedicle subtraction osteotomy to vertebral column resection, or even further corrections. The specifics of these surgical techniques are explained in a chapter on ‘spinal osteotomy’ on the StatPearls website.
What else can Spine Sagittal Balance be?
The sagittal alignment refers to the balance between the head, spine, and pelvis. Changes in the structure or positioning of the pelvis can significantly impact this sagittal balance.
There are several conditions that may alter this alignment, including:
- Flatback syndrome, characterized by reduced inward curve (hypolordosis) or outward curve (kyphosis) in the lower back (lumbar spine).
- Kyphosis at the point where the middle and lower back meet (thoracolumbar junction).
- Excessive outward curve (hyperkyphosis) in the middle back (thoracic spine), as seen in a condition called Scheuermann’s kyphosis.
