Baastrup’s disease is a recognized source of chronic low back pain. Often referred to as “kissing spines,” the condition involves a structural change in the back that can generate significant localized symptoms. This pathology arises from the abnormal proximity of bony structures in the spine, which leads to painful mechanical irritation over time. The primary characteristic is the close contact between adjacent vertebral processes, which sets the stage for a cycle of friction and inflammation.
Anatomy and Definition of Baastrup’s Disease
Baastrup’s disease describes a common degenerative condition where the spinous processes of adjacent vertebrae become abnormally close, or “kiss.” These spinous processes are the bony protrusions extending backward from the center of each vertebra. The condition most frequently affects the lumbar spine, particularly at the L4-L5 level.
The underlying cause is often linked to age-related degeneration and a reduction in the height of the intervertebral discs. As the discs lose volume, the vertebrae move closer together, causing the spinous processes to abut. This close approximation and subsequent friction lead to structural changes, including the enlargement and flattening of the bony surfaces involved.
The term “kissing spines” is also sometimes used synonymously with Baastrup’s sign, which is an imaging finding. While the radiological sign of contacting processes can be present without pain, the disease is defined by the structural changes and the resulting discomfort. These structural changes include the development of a neoarthrosis, or false joint, between the spinous processes.
The Mechanism Causing Pain
The pain in Baastrup’s disease stems from the mechanical friction and chronic inflammatory reaction initiated by the abnormal contact between the spinous processes. When the bony surfaces repeatedly rub against each other, the soft tissues between them, primarily the interspinous ligament, become irritated and damaged. This constant mechanical stress triggers a degenerative cascade within the affected spinal segment.
This friction causes a local inflammatory response, leading to bone marrow edema and reactive changes like subcortical sclerosis and cystic lesions in the adjacent bone. The chronic inflammation often results in the formation of an interspinous bursa, a fluid-filled sac that develops between the contacting processes. This condition is sometimes called interspinous bursitis.
The painful mechanism is further compounded by the irritation of surrounding structures, including the supraspinous ligament and local muscle attachments. The development of a bursa or a false joint can itself become a source of pain when compressed or inflamed. In some cases, the degenerative changes can extend to form dorsal epidural cysts, which may cause nerve root irritation and referred pain.
Recognizing the Specific Symptoms
Patients with symptomatic Baastrup’s disease typically experience a specific pattern of low back pain that helps distinguish it from other spinal issues. The pain is primarily localized to the midline of the lower back, directly over the affected spinous processes. This discomfort is often described as a dull ache or tenderness that can sometimes radiate slightly upward or downward along the spine.
A defining characteristic of this pain is its relationship to spinal movement, as symptoms are notably aggravated by extension, or leaning backward. This motion forcibly pushes the spinous processes together, increasing the friction and compression on the inflamed tissues. Conversely, the pain is usually relieved by spinal flexion, such as bending forward, which opens the space between the kissing spines.
The pain may also worsen with prolonged standing or any activity that increases the lumbar lordosis, the natural inward curve of the lower back. Direct pressure or palpation over the involved spinous processes on a physical exam will typically reproduce the localized tenderness and discomfort. Although less common, the presence of associated epidural cysts can sometimes lead to symptoms of neurogenic claudication, causing pain that travels into the legs.
Treatment Options for Pain Relief
Treatment for the pain associated with Baastrup’s disease generally follows a conservative, stepped approach, starting with the least invasive methods. Initial management typically involves non-steroidal anti-inflammatory drugs (NSAIDs) to reduce local inflammation and targeted physical therapy. Physical therapy focuses on strengthening the core muscles and teaching exercises that encourage spinal flexion while avoiding movements that promote extension.
If conservative measures do not provide adequate relief, the next step involves interventional procedures, most commonly fluoroscopically guided injections. These involve injecting a corticosteroid and local anesthetic directly into the inflamed interspinous space or bursa to reduce swelling and interrupt the pain cycle. Such targeted injections can often provide pain relief lasting up to several months.
For patients whose pain is resistant to injections, radiofrequency ablation may be considered, which uses heat to temporarily halt nerve signals responsible for transmitting the pain. When all non-surgical options fail to relieve severe, persistent pain, surgical intervention becomes a last resort. Surgical options include the removal of the inflamed bursa or a partial removal of the enlarged spinous process (osteotomy) to permanently increase the space between the bones and eliminate the mechanical contact.