Sagittal = the front-to-back direction
Imbalance = lack of harmony or balance
Sagittal imbalance is a front-to-back imbalance in the spine.
Normally, the spine has two gentle front-to-back curves. The lumbar (lower) spine has an inward curve called lordosis. The thoracic (middle) spine has an outward curve called kyphosis. Usually, these curves work in harmony to keep the body’s center of gravity aligned over the hips and pelvis.
However, if one of those curves becomes either too pronounced or too flat, the spine will be out of balance back-to-front. This is sagittal imbalance.
Types of sagittal imbalance include:
- Flatback syndrome: In this condition, the lumbar spine loses its normal lordosis. The outward curve of the thoracic spine is therefore the only curve, and the center of gravity juts too far forward.
- Kyphosis: In this condition (sometimes called hyperkyphosis), the normal kyphosis of the thoracic spine increases to such a degree that the back appears hunched. Chin-on-chest syndrome is one type of severe kyphosis.
Symptoms of sagittal imbalance include low back pain, difficulty walking, and inability to continually look straight ahead when upright. Sagittal imbalance can also cause chronic pain, fatigue, and difficulty with daily tasks. In some cases, sagittal imbalance may be associated with conditions that can put pressure on spinal nerves, leading to weakness, numbness, or pain. Some cases of sagittal imbalance progress, or get worse over time; severe cases can cause difficulty with breathing.
Causes and Risk Factors
Causes of sagittal imbalance include
- Ankylosing spondylitis, a type of arthritis
- Kyphosis, excessive forward curvature in the spine
- Degenerative conditions like degenerative disc disease, wear-nd-tear on the cushiony discs of the spine
- Traumatic injury
- A congenital defect present at birth
- Osteoporosis, a condition of weak and brittle bones
- Neuromuscular conditions such as cerebral palsy, spina bifida, or muscular dystrophy
- Previous spinal fusion that disrupts sagittal balance (For example, sagittal imbalance sometimes develops in patients who receive implanted rods called Harrington rods to correct the side-to-side spinal curvature of scoliosis.)
Tests and Diagnosis
To determine the degree of sagittal imbalance, the doctor may order an X-ray–a test that produces images of the spine and other bones and tissues using invisible electromagnetic rays. The doctor may also order additional diagnostic procedures to obtain a more detailed image of the spine:
- Magnetic resonance (MR) imaging scan – uses a magnet and radio waves to provide detailed images of the spinal cord. This scan can help identify whether the spinal cord has been affected by the spinal curvature.
- Computed tomography (CT) scan – uses X-rays and a computer to produce detailed images of the body. CT scans are more detailed than general X-rays.
Because the causes of sagittal balance vary from patient to patient, no two procedures are identical. The overall goal of these operations, however, is the same: to reestablish overall sagittal spinal balance. As the general problem is that there is either not enough lumbar lordosis or too much thoracic kyphosis, surgery is generally planned to add lordosis or reduce kyphosis, or both.
Most surgeries to correct sagittal imbalance can be explained in three parts.
- Correct the spinal deformity. This is usually accomplished via an osteotomy or osteotomies. During this procedure, the spine is loosened by removing a bone. The extent and location of removal depend on a variety of factors, such as the location and type of spinal deformity.
- Spinal fixation. After the spinal deformity has been corrected, the spine is fixed into its new alignment with metal screws and hooks, which is referred to as fixation. These screws and hooks, each of which attaches to one vertebra (bone in the spine), are then connected with long rods that are shaped to match the new spinal alignment.
- Spinal fusion. The surgeon will implant bone graft material, pieces of bone that bridge gaps. The bones will fuse (grow together), helping to make the spine more stable. The long-term success of sagittal imbalance surgery depends on achieving good bone fusion. Note that certain lifestyle factors, including smoking and obesity, inhibit bone fusion.