Baastrup’s Disease, often called “Kissing Spine Syndrome,” is a spinal condition causing significant low back discomfort. This degenerative process occurs in the lumbar spine and is a frequently overlooked cause of positional back pain. While Baastrup’s Disease does not directly affect the hip joint, the resulting pain and biomechanical changes in the lower back often lead to a secondary perception of pain in the hip and buttock area. This connection is rooted in the complex network of nerves and muscles linking the lower spine to the lower limbs, which can make diagnosis challenging.
Understanding Baastrup’s Disease
Baastrup’s Disease is characterized by the close proximity and eventual contact of the spinous processes, the bony projections extending backward from the vertebrae. This “kissing” primarily occurs in the lower lumbar spine, often between the L3 and L5 vertebrae, due to degenerative changes and an exaggerated lower back curvature (hyperlordosis).
The constant friction causes chronic irritation, leading to pathological changes like the development of an adventitious bursa and inflammation (interspinous bursitis). The bony surfaces may also flatten, enlarge, and develop sclerosis. The primary symptom is localized midline low back pain, aggravated by spinal extension (bending backward) or prolonged standing. Patients typically find relief when flexing forward, which separates the bony projections.
The Spinal Mechanism Behind Perceived Hip Pain
The hip pain associated with Baastrup’s Disease is a classic example of referred pain and secondary biomechanical stress. Referred pain occurs because the nerves supplying the lumbar spine share pathways with nerves traveling to the hip, groin, and gluteal areas. Irritation in the lumbar spine, particularly involving lower nerve roots like L4 and L5, sends signals along these shared routes, causing the brain to misinterpret the pain as originating in the hip or buttock.
The chronic back pain also compels the body to adopt an altered posture and gait to avoid painful extension movements. This compensatory mechanism transfers greater stress and mobility demands onto the hip joint and surrounding musculature.
This altered movement pattern frequently results in muscle imbalances and strain on deep hip and buttock muscles, such as the piriformis. The strain can cause muscle tightening or spasms. This tightness may compress the sciatic nerve as it passes through the gluteal region, a condition known as Deep Gluteal Syndrome or Piriformis Syndrome. This condition mimics hip or buttock pain radiating down the leg, demonstrating how the spinal problem indirectly creates a painful hip condition.
Diagnostic Approaches and Differential Diagnosis
Identifying Baastrup’s Disease as the cause of hip pain requires confirming the spinal pathology and ruling out primary hip joint issues. The initial imaging study is typically a lateral view X-ray of the lumbar spine, which shows the close approximation of the spinous processes. Dynamic flexion-extension X-rays are often used to confirm that bony contact occurs or worsens during spinal extension.
Magnetic Resonance Imaging (MRI) is the preferred method for assessing soft tissue involvement, revealing signs of inflammation like interspinous bursitis or fluid accumulation. A Computed Tomography (CT) scan provides superior detail regarding bony changes, including sclerosis and hypertrophy.
A crucial step is the differential diagnosis, actively excluding conditions that mimic spinal-referred pain, such as primary hip osteoarthritis, trochanteric bursitis, or sacroiliac joint dysfunction. The most definitive diagnostic tool is a targeted interspinous injection of a local anesthetic and corticosteroid. Significant relief of both low back and secondary hip pain immediately after the injection provides strong evidence that the Baastrup’s lesion is the source of discomfort.
Treatment Pathways for Relief
Management of Baastrup’s Disease and associated hip discomfort begins with conservative therapies. Nonsteroidal anti-inflammatory drugs (NSAIDs) are used to reduce inflammation and pain. Physical therapy focuses on exercises that promote spinal flexion and strengthen core muscles to minimize bony contact. Patients must also modify activity to avoid movements involving spinal extension.
If conservative management fails, interventional procedures are considered, typically involving fluoroscopically guided corticosteroid injections directly into the painful interspinous space. The injection reduces inflammation and can offer pain relief lasting several months.
In rare cases, surgical intervention may be necessary. Options include partial removal of the affected spinous process to decompress the area, or a minimally invasive procedure known as interspinous plasty, which restores the physiological gap between the vertebrae.