Kissing Spine, medically known as Baastrup’s disease, is a specific cause of low back pain. The condition occurs when the bony projections on the back of the vertebrae, called spinous processes, abnormally approximate, causing them to touch or rub against each other. This contact, or “kissing,” leads to friction, inflammation, and degenerative changes in the surrounding tissue. The underlying causes are related to the cumulative mechanical stresses on the spinal structure.
Understanding the Spinal Structure
The spine is composed of individual bones called vertebrae, each possessing a distinct posterior projection known as the spinous process. These processes extend backward and downward, forming the ridge felt beneath the skin. In a healthy spine, the space between adjacent spinous processes is maintained by the interspinous ligament, which acts as a spacer and limits excessive forward bending.
The lower back, or lumbar spine, is the most common region affected by Kissing Spine, specifically between the fourth and fifth lumbar vertebrae (L4-L5). This area is subjected to high levels of stress and movement, making it susceptible to degenerative changes. The spinous processes are normally separated by a small gap that prevents bony contact during typical movements. When this gap is compromised, the environment for Baastrup’s disease develops.
Immediate Mechanical Causes of Impingement
The direct cause of spinous processes making contact is a reduction in the space separating them, driven by two main biomechanical factors.
Disc Height Loss
The first factor is the progressive loss of height in the intervertebral discs. As these discs degenerate and collapse, the distance between adjacent vertebrae shortens, pulling the spinous processes closer together. This disc height reduction eliminates the normal buffer zone.
Hyperextension
The second factor involves excessive backward bending, or hyperextension. When the spine arches backward, the spinous processes naturally move toward one another. If the spine is held in a position of exaggerated lumbar lordosis (an excessive inward curve), this constantly presses the processes together. This chronic mechanical pressure and repetitive motion initiates tissue breakdown and inflammation in the interspinous ligament.
Chronic friction between the adjacent bones triggers a reactive bone remodeling process. This leads to sclerosis (hardening and thickening of the bone at the points of contact). Over time, the tips of the spinous processes can flatten, enlarge, and even form a new, abnormal joint, termed a neo-articulation or pseudoarthrosis. This dysfunctional joint may also develop an inflamed, fluid-filled sac, known as an interspinous bursa, which directly contributes to the symptoms of Baastrup’s disease.
Factors That Increase Susceptibility
While mechanical collision is the immediate cause, certain conditions and lifestyle elements accelerate the degenerative process that leads to Kissing Spine.
Age is a predominant factor, as the condition is most frequently diagnosed in individuals over 70 years old due to the cumulative effects of decades of spinal wear and tear. The natural decrease in water content and elasticity of the intervertebral discs with age directly results in the height loss that brings the spinous processes closer.
Postural habits and spinal alignments place chronic stress on the posterior spinal structures. An exaggerated inward curve in the lower back, known as hyperlordosis, is frequently associated with the development of the condition.
Lifestyle and physical demands also increase susceptibility. Occupations or sports that require frequent or prolonged hyperextension, such as certain forms of manual labor or gymnastics, can hasten the onset of the disease, even in younger individuals. Furthermore, increased body weight, particularly obesity, places greater compressive loads on the entire spinal column. This heightened pressure accelerates the degenerative changes in the intervertebral discs, contributing to the reduction in disc height.
How the Condition is Diagnosed
The process of confirming a diagnosis of Kissing Spine begins with a detailed clinical examination. A physician looks for localized tenderness and pain directly over the affected spinous processes in the lower back. A highly indicative finding is that the patient’s pain is reliably worsened when the spine is extended (bent backward) and relieved when the spine is flexed (bent forward).
Imaging studies are necessary to confirm the characteristic anatomical changes. Standard lateral view X-rays of the lumbar spine are crucial because they visualize the reduced space and the close approximation of the adjacent spinous processes. These images often show signs of bony remodeling, such as flattening, enlargement, and reactive sclerosis (bone hardening) at the contact points.
While X-rays show the bone structure, Magnetic Resonance Imaging (MRI) is used to evaluate soft tissue components, such as interspinous bursitis and bone marrow edema, which indicate active inflammation. Computed Tomography (CT) scans provide a more detailed cross-sectional view of the bony changes. The most definitive confirmation often involves a targeted diagnostic injection of a local anesthetic into the interspinous space; if the injection temporarily relieves the localized pain, the diagnosis is strongly supported.