The healthy cervical spine possesses a gentle, inward, C-shaped curve known as cervical lordosis. This natural curvature helps balance the weight of the head over the body’s center of gravity and allows for flexible movement. Cervical kyphosis occurs when this normal inward curve is lost, becoming straight or reversed into an outward curve. This abnormal forward curvature results from various underlying factors that compromise the integrity of the vertebral column.
Congenital and Developmental Origins
Cervical kyphosis can arise from structural abnormalities that occur during fetal development, meaning the condition is present at birth. These congenital forms stem from errors in the formation or segmentation of the cervical vertebrae. In cases of formation failure, a vertebra may develop only partially, resulting in a wedge-shaped bone called a hemivertebra.
The stacking of these misshapen, wedge-like bones causes an angular deformity that forces the spine into a kyphotic position. A failure of segmentation occurs when two or more adjacent vertebrae fail to separate properly and remain fused together. This lack of proper separation restricts normal spinal growth in that region, which can lead to a progressive kyphotic curve as the child grows.
Trauma and Acute Injury
Kyphosis can result from a sudden, external physical force that causes a mechanical failure in the cervical spine. Acute fractures are a common mechanism, particularly compression or burst fractures of the vertebral bodies. When a vertebral body is crushed, it often heals in a wedge shape, which immediately forces the spine into a forward-flexed, kyphotic alignment.
Traumatic events, such as high-velocity accidents, can also cause severe ligamentous instability without a complete fracture. Disruption of the posterior ligamentous complex—often referred to as the posterior tension band—destabilizes the spine, allowing the vertebrae to slip or collapse into a kyphotic posture. The loss of this posterior support shifts the weight-bearing axis forward, increasing mechanical stress on the spinal elements and promoting progressive deformity.
Iatrogenic Factors (Post-Surgical Development)
Iatrogenic causes refer to conditions resulting from medical intervention; posterior cervical spine surgery is a recognized factor in acquired kyphosis. Post-laminectomy kyphosis is the most frequent surgical complication, developing after the removal of the vertebral lamina and other posterior supporting structures. Removing the lamina and associated ligaments disrupts the posterior tension band, which bears a significant portion of the cervical load.
Without this support, the axial load shifts anteriorly, causing the spine to buckle into a kyphotic alignment. The incidence of this post-operative kyphosis is notably higher in children because their less ossified vertebral bodies are more susceptible to wedging under cumulative stress.
Another mechanism is fusion failure, or pseudoarthrosis, where the bones fail to heal together after a fusion procedure. This lack of solid fixation can allow the segments to collapse or shift, leading to a late-developing kyphotic deformity. Radiation therapy administered for cancer in the neck region is also a risk factor, particularly in pediatric patients, as it can inhibit normal bone growth and development.
Degenerative and Systemic Diseases
Chronic, progressive conditions represent the broadest category of causes for acquired cervical kyphosis in adults. Degenerative Disc Disease (DDD) is a primary driver, where the intervertebral discs lose water content and height over time. This loss of disc height causes the vertebrae to tip forward, gradually reducing the natural lordosis and eventually causing a kyphotic curve.
Inflammatory conditions, specifically seronegative spondyloarthropathies like Ankylosing Spondylitis, lead to the fusion of vertebrae, resulting in a fixed sagittal imbalance. The spine becomes a rigid, unyielding structure, making it highly susceptible to fracture and kyphotic collapse even from minor trauma. Rheumatoid Arthritis can also cause instability in the upper cervical spine, contributing to deformity.
Infectious processes in the spine, such as vertebral osteomyelitis or discitis, destroy the bone and disc material, which compromises the structural integrity of the spinal column. The resulting collapse of the infected vertebral body can rapidly lead to an acute, angular kyphotic deformity.
Osteoporosis, characterized by weakened bones, significantly increases the risk of compression fractures in the vertebral bodies. These small fractures accumulate over time, causing the vertebrae to gradually assume a wedge shape and leading to the progressive development of kyphosis.