The spine, or vertebral column, serves as the central support structure for the body, providing flexibility and protection for the spinal cord. It is composed of individual bones called vertebrae. The main weight-bearing component of each vertebra is the vertebral body, a thick, cylindrical section located at the front. Measuring the height of these vertebral bodies is a routine medical process, as changes in this dimension often signal significant spinal health issues.
Defining the Vertebral Body and Its Height
The vertebral body is the large, anterior portion of the vertebra, shaped like a short cylinder. It is primarily responsible for bearing the mechanical load of the body above it. It consists of a dense outer layer of cortical bone surrounding an inner core of cancellous bone, allowing it to withstand vertical compression forces.
Clinically, the height of a vertebral body is assessed at three specific points: the anterior, middle, and posterior aspects. These three measurements (\(H_a\), \(H_m\), and \(H_p\)) are taken from the superior endplate to the inferior endplate of the bone. Comparing these dimensions reveals the shape of any height loss, which helps determine the type of injury.
The size and height of vertebral bodies vary across the different regions of the spine. Cervical (neck) vertebrae are generally the smallest, while those in the lumbar (lower back) region are the largest to accommodate the increasing load they support. The combined heights of all the vertebral bodies and the intervertebral discs contribute directly to the overall length and natural curvature of the spine.
Primary Causes of Vertebral Height Loss
The most common reason for reduced vertebral body height is a vertebral compression fracture (VCF), which occurs when the bone collapses. Most VCFs occur in people with osteoporosis, a condition characterized by low bone density. Osteoporosis makes the bone brittle, allowing fractures to occur from minor stresses like coughing, sneezing, or bending over, without major trauma.
Vertebral compression fractures are classified by the shape of the collapse. The most common is a wedge fracture, where the front portion of the vertebral body loses height while the back remains intact. A crush fracture involves a uniform loss of height across the entire vertebral body. A burst fracture, often caused by high-energy trauma, involves height loss in both the front and back walls and can be unstable.
While osteoporosis is the main factor, significant trauma from events like a fall or car accident can also cause a VCF in a person with normal bone density. A less common cause is underlying pathology, such as metastatic cancer that has spread to the spine. The tumor weakens the bony structure from within, making it susceptible to collapse under normal stress.
Identifying Height Reduction Through Imaging
Medical professionals use imaging techniques to detect and quantify vertebral height reduction, often starting with a lateral X-ray of the spine. X-rays provide a side view, allowing measurement of the anterior, middle, and posterior heights of each body. More detailed cross-sectional imaging, such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), assesses the extent of the fracture and its effect on surrounding soft tissues.
A vertebral compression fracture is typically diagnosed when a vertebra has lost 15 to 20 percent or more of its original height. To quantify the severity of the height loss, doctors often calculate a vertebral height ratio. This ratio compares the current height of the affected vertebra to the average height of the two adjacent, unfractured vertebrae above and below it.
The Genant semi-quantitative (SQ) method is used for visually grading the severity of a compression fracture on a lateral image. This scale categorizes height loss into three grades: Grade 1 (mild) signifies a 20–25% reduction, Grade 2 (moderate) is a 25–40% reduction, and Grade 3 (severe) indicates a reduction greater than 40%. These measurements and grading systems guide treatment decisions and monitor the progression of bone disease.
Consequences of Reduced Vertebral Height
The most common consequence of vertebral body height loss is acute back pain, which is typically worsened by standing or walking. Over time, multiple compression fractures can lead to chronic pain that persists after the initial fracture has healed. This chronic discomfort is often related to muscle fatigue as the back muscles strain to compensate for altered spinal mechanics.
Mechanically, the collapse of one or more vertebral bodies causes the spine to curve forward, a condition known as kyphosis. This forward curvature is often noticeable as a hunched posture, sometimes called a “dowager’s hump.” The cumulative effect of height loss in several vertebrae also results in a measurable reduction in a person’s overall standing height.
In severe cases, the reduction in spinal length can lead to crowding of the internal organs within the torso. This compression can cause issues like abdominal fullness or affect lung function by restricting expansion space. If fractured bone fragments push backward into the spinal canal, there is a risk of impinging on the nerve roots or spinal cord, resulting in symptoms such as numbness, tingling, or weakness in the limbs.