Baastrup’s disease, commonly referred to as “kissing spine syndrome,” is a spinal condition characterized by the abnormal proximity and contact between the spinous processes of adjacent vertebrae. This contact primarily occurs in the lumbar spine (lower back), causing chronic pain and discomfort. The syndrome results from degenerative changes in the spine that reduce the space between these bony projections, leading to friction and inflammation. It is a recognized cause of low back pain that can significantly impact a person’s mobility and quality of life.
The Anatomy of Baastrup’s Disease
The spinous processes are the thin, bony protrusions extending backward from the center of each vertebra, forming the bumps one can feel along the middle of the back. In a healthy spine, the space between these processes is maintained by soft tissue structures, including the interspinous ligament, which prevents them from touching. This ligament acts as a spacer and stabilizer.
Baastrup’s disease develops when this protective space is lost, often due to degenerative changes like disc height reduction or excessive lumbar lordosis (an exaggerated inward curve of the lower back). This approximation causes the adjacent spinous processes to rub together, leading to chronic mechanical irritation. Repetitive friction triggers the degeneration and collapse of the interspinous ligament.
The continuous rubbing of bone against bone can cause the formation of a false joint, known as pseudosarthrosis. This irritation also stimulates the body to create an adventitious bursa, a fluid-filled sac, in the space, sometimes called interspinous bursitis. Over time, the affected bones show signs of remodeling, including flattening, enlargement, and increased density (sclerosis) at the points of contact. The L4-L5 level is the most frequently affected segment of the spine in this condition.
Recognizing the Symptoms
The hallmark symptom of Baastrup’s disease is localized midline pain in the lower back, directly over the affected spinous processes. This pain is typically exacerbated by movements that increase the spinal curve, such as standing for long periods, arching the back (extension), or walking. Patients often report significant relief when they bend forward (flexion), which opens the space between the kissing spines.
Physical examination often reveals tenderness when the doctor applies pressure directly to the spinous processes at the level of involvement. The pain may sometimes radiate upward or downward along the spine, but it rarely extends laterally into the legs, which helps distinguish it from nerve root compression. In rare instances, when the degenerative process is severe, it can lead to the formation of an epidural cyst that may press on the nerves, causing symptoms like neurogenic claudication.
Diagnostic Procedures
Diagnosing Baastrup’s disease relies on correlating a patient’s specific symptoms with findings from medical imaging. The initial step involves plain X-rays of the lumbar spine, which reveal the close approximation or direct contact of the spinous processes. Dynamic X-rays, taken while the patient is bending forward and backward, can demonstrate how the contact changes with movement.
Computed Tomography (CT) scans offer a more detailed view of the bony anatomy, clearly illustrating degenerative changes like bone enlargement, flattening, and sclerosis at the sites of contact. Magnetic Resonance Imaging (MRI) is utilized as the most sensitive tool for evaluating the associated soft tissue pathology. An MRI can show inflammation, edema, and the presence of an interspinous bursa.
The most definitive diagnostic procedure is a targeted local anesthetic injection into the space between the spinous processes. If the injection of a local anesthetic, sometimes mixed with a corticosteroid, provides immediate and substantial pain relief, it confirms that the pain is originating from the area of the kissing spines. This positive diagnostic block guides subsequent treatment planning.
Management and Treatment Options
Treatment for Baastrup’s disease follows a stepwise approach, generally beginning with conservative methods before progressing to more invasive interventions. First-line management focuses on reducing inflammation and altering mechanics to relieve pressure on the affected area. This includes the use of nonsteroidal anti-inflammatory drugs (NSAIDs) to manage pain and swelling.
Physical therapy plays a significant role, focusing on exercises that strengthen the core and correct posture to reduce excessive lumbar lordosis. The physical therapy regimen specifically emphasizes flexion-based movements, which create space between the spinous processes, while avoiding extension exercises that aggravate the contact. Activity modification is also advised, requiring patients to avoid prolonged postures or activities that force the back into extension.
If conservative strategies fail to provide adequate pain relief, interventional treatments are the next step. A fluoroscopically-guided injection of a corticosteroid and local anesthetic directly into the interspinous space targets the inflamed bursa or pseudoarthrosis. This provides relief that can last for several months, often requiring repeat treatments.
Surgical intervention is considered only when persistent, debilitating pain remains despite exhaustive conservative and interventional management. The goal of surgery is to decompress the area by creating permanent space between the vertebrae. This can be achieved through a partial removal of the enlarged spinous process (osteotomy) or the placement of a spacer device, such as an interspinous process decompression device, to mechanically separate the kissing spines.