Baastrup disease is a degenerative condition of the spine and an often-overlooked cause of chronic lower back pain. It is widely known as “Kissing Spines Syndrome,” referring to the abnormal proximity of bony segments in the spine. This condition involves structural changes that develop over time, leading to localized discomfort and restricted movement. Baastrup disease is a relatively common finding, particularly in older populations experiencing persistent back issues.
The Anatomy of “Kissing Spines”
The name “kissing spines” describes the physical contact between the bony projections extending from the back of the vertebrae, known as the spinous processes. Normally, a gap exists between these processes, maintained by interspinous ligaments and soft tissue. In Baastrup disease, this protective space narrows, causing the adjacent processes to abut one another.
This abnormal, sustained contact leads to chronic friction and mechanical stress on the bone surfaces. The body attempts to adapt to this irritation by forming a fluid-filled sac, known as an adventitious bursa, between the processes. Over time, this constant rubbing can cause the bone surfaces to flatten, enlarge, and develop sclerosis, a hardening of the bone tissue. While it can occur at any level, the lower back segments, particularly L4-L5, are most commonly affected due to biomechanical forces.
Etiology and Contributing Risk Factors
The development of Baastrup disease is primarily linked to degenerative changes within the spine that reduce the distance between vertebrae. Age-related wear and tear, such as the loss of intervertebral disc height, is a major factor, causing the spinal column to collapse and push the spinous processes closer together. This process is often accompanied by osteoarthritis in the facet joints, contributing to structural instability.
A significant mechanical factor is hyperlordosis, an excessive inward curvature of the lower back. This exaggerated posture forces the spinous processes to converge, increasing the likelihood of impingement and friction. Repetitive motions involving spinal extension, such as certain athletic activities or chronic poor posture, place recurrent strain on the interspinous ligaments. Obesity also increases mechanical load on the lumbar spine, promoting excessive curvature and subsequent degenerative changes.
Clinical Presentation and Patient Symptoms
The pain associated with Baastrup disease is typically felt as a localized ache in the midline of the lower back. Patients often describe the discomfort as mechanical pain, meaning it is directly related to specific movements and positions. The pain is significantly exacerbated by spinal extension, such as leaning backward or standing upright. Conversely, patients often find relief when they flex the spine, such as when leaning forward or adopting a fetal position.
Direct pressure applied to the affected area, over the spinous processes, can reproduce intense tenderness. This highly localized pain can sometimes radiate slightly upward or downward along the spine, but it rarely extends far laterally. In some cases, chronic irritation can lead to secondary compression, causing symptoms that mimic other lumbar conditions, including pain that travels down the buttocks or thighs.
Diagnostic Confirmation and Management
Confirming a diagnosis of Baastrup disease begins with a targeted physical examination, where a clinician checks for point tenderness directly over the midline of the affected spinous processes. The definitive clinical test involves observing the patient’s reaction to spinal movements, noting increased pain with extension and relief with flexion. Imaging studies are then used to visualize the degree of contact and the degenerative changes present.
Lateral view X-rays are the standard initial imaging modality, clearly showing the close approximation of the spinous processes and any bony changes, such as enlargement or sclerosis. Magnetic Resonance Imaging (MRI) provides a more detailed view, revealing soft tissue involvement, including the presence of an interspinous bursa or associated inflammation (edema). The most specific diagnostic test is a fluoroscopically guided injection of a local anesthetic into the space between the “kissing” processes; immediate, temporary pain relief confirms the diagnosis.
Management typically follows a stepped approach, beginning with conservative measures. Physical therapy is recommended to focus on core strengthening and postural modification to reduce hyperlordosis and mechanical stress on the spine. Non-steroidal anti-inflammatory medications manage pain and local inflammation. Interventional treatments are the next step for persistent symptoms, involving the injection of a corticosteroid and local anesthetic mixture directly into the interspinous bursa or ligament for prolonged pain relief.
If conservative treatments fail to provide lasting relief, surgical options may be considered to create space between the processes. One common procedure is interspinous process decompression, which involves the partial removal of a section of the spinous process (osteotomy) or the excision of the inflamed bursa. Alternatively, some techniques involve placing a spacer device between the processes to maintain adequate separation. These interventions are reserved for cases where chronic pain significantly impacts quality of life and is resistant to less invasive therapies.