Wedge vertebrae, also known as hemivertebrae, are a specific type of congenital vertebral anomaly where a spinal bone is malformed. Unlike the typical rectangular shape of a healthy vertebra, this bone develops a distinct wedge or triangular shape. This incomplete formation of a single vertebral body creates an inherent structural imbalance within the spinal column from birth.
Understanding the Congenital Anomaly
This structural irregularity originates from a failure in the normal process of vertebral formation during the first trimester of pregnancy. The defect occurs when the vertebral body fails to properly form or segment during the fifth to eighth week of gestation. This critical period involves the development of skeletal building blocks, and a disruption prevents one side of the bone from fully growing.
The severity of the anomaly is determined by its segmentation, which classifies the two main types of hemivertebrae. A fully segmented hemivertebra is separated from the adjacent vertebrae by normal disc spaces. This type is often the most severe because it has independent growth potential, acting as an enlarging wedge that aggressively drives spinal curvature as the child grows.
In contrast, a non-segmented hemivertebra is fused to one or both neighboring vertebrae, limiting its ability to grow independently. Because this type is structurally tethered, it has less potential to cause aggressive, progressive spinal deformity over time. Another type, the incarcerated hemivertebra, is small and accommodated by the surrounding vertebrae, often resulting in minimal clinical impact.
How Wedge Vertebrae Affect Spinal Alignment
The physical effect of a wedge vertebra is the creation of an uneven, asymmetrical column that forces the spine into a progressive curvature. Since the malformed bone is shorter on one side, it acts as a permanent, rigid fulcrum that tilts the entire stack of vertebrae. The resulting deformities are a direct consequence of the physical location of the wedge within the spinal axis.
A laterally positioned wedge vertebra, where the bone is shorter on one side, primarily causes scoliosis, an abnormal sideways curvature of the spine. If the wedge is positioned dorsally, meaning the front of the bone is shorter than the back, it causes kyphosis, an excessive forward hunching of the upper back. The location of the hemivertebra, such as in the highly mobile thoracolumbar region, often dictates a higher rate of curve progression.
The overall severity of the resulting spinal deformity depends heavily on the type and growth potential of the hemivertebra. Fully segmented hemivertebrae continue to grow on the normal side while the defective side remains short. This continuous, uneven growth necessitates close monitoring and often requires intervention to prevent severe trunk imbalance.
Identifying and Tracking the Condition
The diagnostic process begins with imaging studies to confirm the presence of the congenital anomaly and evaluate the resulting spinal curve. Plain X-rays are the initial tool, providing a clear visual representation of the bone structure and the characteristic wedge shape. X-rays are also used to measure the curve’s angle, typically using the Cobb method, which quantifies the magnitude of the deformity.
Computed Tomography (CT) scans offer more detailed, cross-sectional visualization of the bony architecture. A CT scan precisely defines the complex morphology of the hemivertebra, including its degree of segmentation and fusion with neighboring segments. Magnetic Resonance Imaging (MRI) is then used to assess the surrounding soft tissues, the spinal cord, and the nerves, especially before surgical planning.
Tracking the condition is a continuous process, particularly in young patients who have significant growth remaining. Regular follow-up imaging monitors the progression of the spinal curve, as progression is often rapid during adolescent growth spurts. This tracking is crucial for determining the optimal timing for intervention, since the progression rate of these congenital curves is variable.
Management and Treatment Options
The management of wedge vertebrae ranges from observation to complex surgical correction, depending on the severity and progression of the spinal curvature. Observation is recommended for patients with mild, non-progressive curves or those with non-segmented hemivertebrae that are less likely to cause significant deformity. These patients are monitored with regular clinical exams and X-rays to ensure the curve remains stable over time.
Non-surgical treatment, primarily involving bracing, has a limited role in managing congenital spine curves. Bracing is ineffective at correcting the rigid curve caused directly by the structural defect of the hemivertebra. However, a brace may be used to manage or slow the progression of compensatory curves that develop above and below the main structural curve.
Surgical intervention is the primary treatment for severe or rapidly progressing curves, especially those that pose a risk of permanent trunk imbalance or neurological compromise. The most definitive surgical procedure is hemivertebra resection and spinal fusion, which involves completely removing the malformed wedge-shaped bone. This removal eliminates the deforming growth center and allows the spine to be straightened.
Following the removal, a spinal fusion stabilizes the remaining vertebrae with instrumentation, such as screws and rods, across a limited segment of the spine. This procedure is often performed at a young age to prevent severe deformity and limit the number of spinal segments that need to be fused. The goal of this complex surgery is to achieve a balanced, stable spine while preserving as much growth and flexibility as possible.