Baastrup disease, sometimes called “kissing spines syndrome,” is a spinal condition in which the bony projections on the back of adjacent vertebrae come so close together that they touch or nearly touch, causing localized low back pain. The name comes from the Danish radiologist Christian Ingerslev Baastrup, who described the phenomenon in the 1930s. Despite being well documented in the medical literature for nearly a century, it remains one of the more commonly overlooked causes of back pain, with some studies reporting that the characteristic imaging findings show up in as many as 81% of people over 80, though the true prevalence in the general population is still unknown.1Cureus. Baastrup’s Disease: An Often Missed Etiology for Back Pain The gap between how often it appears on scans and how rarely it gets blamed for symptoms is one of the more frustrating aspects of the condition.
What Actually Happens in the Spine
Your vertebrae have bony bumps that stick out toward the back, called spinous processes. These are the knobs you can feel if you run your fingers down the center of someone’s back. Normally, the spinous processes of neighboring vertebrae have a comfortable gap between them, cushioned by a ligament called the interspinous ligament. In Baastrup disease, those processes drift closer together until they make contact, essentially “kissing.” The formal definition describes it as close approximation of adjacent spinous processes resulting from general degenerative changes in the spine.2Springer. Baastrup’s disease (kissing spines syndrome): a pictorial review
Once the spinous processes start grinding against each other, the body reacts. The bone surfaces where contact occurs become hardened and flattened. The interspinous ligament between them degenerates. In some cases, a fluid-filled sac called a bursa forms between the spinous processes as the body tries to cushion the repeated friction. That bursa can become inflamed, adding another pain generator to an already irritated area. Over time, the contact surfaces may enlarge, and small cysts can develop in the surrounding bone and soft tissue.
How and Why It Develops
The driving force behind Baastrup disease is usually an exaggerated inward curve of the lower back, known as excessive lordosis. When the lumbar spine curves inward more than it should, the spinous processes at the back of the vertebrae get pushed closer together. Repeated extension movements, like arching the back, create mechanical pressure that strains the interspinous ligament over and over. Eventually that ligament weakens, degenerates, and can no longer keep the spinous processes from touching.2Springer. Baastrup’s disease (kissing spines syndrome): a pictorial review
Baastrup disease rarely shows up in isolation. In most cases it develops alongside other degenerative changes that are happening in the same spinal segment. Loss of disc height is a big one: as the rubbery disc between two vertebrae thins out, the vertebrae settle closer together, which naturally brings the spinous processes into contact. Spondylolisthesis, where one vertebra slips slightly forward over the one below it, alters spinal alignment in ways that also narrow the gap. Spondylosis with osteophyte (bone spur) formation contributes as well.2Springer. Baastrup’s disease (kissing spines syndrome): a pictorial review All of these processes tend to accelerate with age, which explains why Baastrup findings become increasingly common in older adults.
Occupation and body mechanics play a role too. Jobs or sports that involve frequent back extension, heavy lifting with poor posture, or prolonged standing with an exaggerated lumbar curve can speed up the degenerative cascade. Obesity increases the load on the lumbar spine and can worsen lordosis, making it another contributing factor. There is no single “Baastrup gene” that has been identified; the condition is overwhelmingly a mechanical and degenerative process rather than an inherited one.
Who Gets Baastrup Disease
Because the condition is primarily degenerative, it skews heavily toward older adults. The finding of kissing spines on imaging becomes dramatically more common with each decade of life. The statistic that up to 81% of people over 80 show the characteristic changes on imaging sounds alarming, but it comes with an important caveat: not everyone with the imaging finding has symptoms.1Cureus. Baastrup’s Disease: An Often Missed Etiology for Back Pain Many people walk around with spinous processes that are touching on their X-rays and feel perfectly fine. The challenge for clinicians is figuring out when the kissing spines are the actual cause of a patient’s pain versus an incidental finding on a scan done for another reason.
Younger patients can develop the condition, particularly if they have other predisposing factors like prior spinal surgery, a structural abnormality that increases lordosis, or a job that puts repetitive extension stress on the lumbar spine. But these cases are the exception. In clinical practice, Baastrup disease is overwhelmingly a condition of the aging spine.
What the Pain Feels Like
The hallmark of Baastrup disease is midline low back pain. It sits right along the center of the lumbar spine, over the spinous processes, rather than off to one side the way muscle strain or sacroiliac joint problems often present. When the pain radiates, it tends to travel up or down along the spine rather than spreading out laterally into the hips or buttocks.3PubMed Central. Baastrup’s Disease: An Often Missed Etiology for Back Pain
One of the most distinctive features is its relationship with posture and movement. Bending forward, which separates the spinous processes, usually provides relief. Leaning back or arching the spine, which pushes them together, tends to make it worse. If you find that your back pain eases when you sit down and hunch forward but flares when you stand up straight or arch backward, that positional pattern is consistent with Baastrup disease. Pressing directly on the interspinous space between the affected vertebrae also reproduces the pain, which is a useful bedside exam finding.3PubMed Central. Baastrup’s Disease: An Often Missed Etiology for Back Pain
The pain is typically chronic and intermittent rather than sudden and severe. It tends to worsen with activities that involve sustained extension of the lumbar spine, like standing for long periods, walking downhill, or sleeping on the stomach. Some patients describe it as a deep, localized ache that they can almost point to with one finger, which distinguishes it from the more diffuse, band-like pain of muscle spasm or the radiating leg pain of a herniated disc pressing on a nerve.
Why It Often Gets Missed
Low back pain is among the most common reasons people visit a doctor, and the list of possible causes is long. Disc herniation, spinal stenosis, facet joint arthritis, muscle strain, and sacroiliac dysfunction all get more attention in standard clinical workups. Baastrup disease tends to fly under the radar for several reasons. First, many clinicians simply do not think of it. It gets relatively little emphasis in medical training compared to more dramatic spinal pathologies. Second, the imaging findings can be subtle on standard X-rays, and when they are noticed, they are sometimes dismissed as incidental age-related changes rather than a source of pain.
The overlap with other degenerative conditions adds confusion. Because Baastrup disease usually develops alongside disc degeneration and facet joint arthritis, the back pain may be attributed entirely to those better-known conditions while the kissing spines contribution is ignored. A patient might receive treatment aimed at a degenerative disc and see only partial improvement because the interspinous component of their pain was never addressed. This is one reason that some researchers have described Baastrup disease as an “often missed” cause of back pain.1Cureus. Baastrup’s Disease: An Often Missed Etiology for Back Pain
How It Is Diagnosed
Diagnosis typically starts with the clinical picture, that characteristic midline lumbar pain that worsens with extension and improves with flexion, combined with tenderness over the interspinous space. But confirming the diagnosis requires imaging.
Standard lateral X-rays are usually the first step. The most common finding is close approximation or direct contact of adjacent spinous processes along with sclerosis (hardening) of the surfaces where they meet. CT scans provide more detail, showing the sclerosis more clearly as well as flattening and enlargement of the spinous processes. MRI is the most informative single test because it can reveal soft-tissue changes that X-rays and CT miss, including interspinous bursitis, bone edema (swelling within the bone), cystic lesions, and degeneration of the interspinous ligament.4Springer Link. Baastrup’s disease (kissing spines syndrome): a pictorial review
The presence of bone edema and bursitis on MRI is particularly useful because these findings suggest active inflammation rather than old, stable changes. A patient whose MRI shows kissing spines with bone edema and a swollen interspinous bursa is more likely to have pain from Baastrup disease than a patient whose spinous processes are touching but show no inflammatory signal. This distinction helps solve the “is this incidental or is this the problem?” question that dogs so much of spinal imaging.
The most common lumbar levels affected are L4-L5 and L3-L4, which makes sense because these segments bear the most load and have the greatest range of motion in extension. However, the condition can occur at any lumbar level and occasionally at multiple levels simultaneously.
Treatment Options
How to treat Baastrup disease remains genuinely unsettled. Both conservative and surgical approaches exist, but the evidence base for any single treatment is thinner than most patients would probably like to hear.5Oxford Academic. The steps until surgery in the management of Baastrup’s Disease (kissing spine syndrome)
Conservative Approaches
Most patients start with non-surgical treatment, and for many, this is enough. Physical therapy focusing on core strengthening, lumbar flexion exercises, and postural correction forms the backbone of conservative management. The logic is straightforward: strengthen the muscles that support the spine, reduce the excessive lordosis that drives the spinous processes together, and teach the patient movement patterns that avoid sustained extension. Anti-inflammatory medications, both oral and topical, can help manage flares. Weight loss, when applicable, reduces the mechanical load on the lumbar spine.
A more targeted conservative option is an interspinous injection. A local anesthetic, sometimes combined with a corticosteroid, is injected directly into the painful interspinous space. This serves a dual purpose. Therapeutically, the steroid reduces local inflammation and the anesthetic provides immediate pain relief. Diagnostically, if the injection relieves the pain, it confirms that the interspinous space is the pain generator. Evidence suggests this approach can provide meaningful improvement, though relief may be temporary and repeat injections are sometimes needed.5Oxford Academic. The steps until surgery in the management of Baastrup’s Disease (kissing spine syndrome)
Surgical Options
Surgery is reserved for patients who have failed conservative treatment and continue to have significant pain. The classic surgical approach involves partial excision of the spinous process, trimming back the bony bumps so they no longer make contact. Some surgeons remove the interspinous bursa at the same time. The concept is simple, but the results have been mixed. Cohort studies examining this procedure have produced conflicting reports about whether patients actually improve afterward.5Oxford Academic. The steps until surgery in the management of Baastrup’s Disease (kissing spine syndrome)
Part of the problem is patient selection. Because Baastrup disease almost always coexists with other degenerative conditions, isolating the kissing spines as the primary pain source is difficult. A patient who undergoes spinous process excision but whose pain was actually driven more by facet arthritis or disc degeneration is not going to improve, and that patient ends up in the “surgery didn’t work” column. Better diagnostic tools, particularly the combination of MRI inflammatory findings and a positive diagnostic injection, are slowly helping clinicians identify the patients most likely to benefit from surgery, but large, high-quality trials are still lacking.
Interspinous spacer devices, which are small implants placed between the spinous processes to keep them separated, represent another surgical avenue. These devices were originally developed for spinal stenosis, but some clinicians have used them for Baastrup disease as well. The evidence for this specific application remains limited.
How Baastrup Disease Relates to Other Spinal Conditions
One of the more practically important things to understand about Baastrup disease is that it rarely exists in a vacuum. It is part of a constellation of degenerative changes that tend to develop together in the aging lumbar spine. Disc degeneration narrows the space between vertebrae. Facet joints at the back of the spine develop arthritis. Ligaments thicken. Bone spurs form. And the spinous processes start kissing. All of these changes can produce pain independently, and in most patients over a certain age, several are happening at once.
This overlap creates a layered pain picture. A patient might have stenosis causing leg symptoms, facet arthritis causing paraspinal aching, and Baastrup disease causing midline lumbar pain, all at the same time. Effective treatment often requires addressing more than one component. A clinician who focuses only on the stenosis or only on the facet joints may leave the Baastrup component untreated, and the patient continues to hurt. The reverse is also true: treating only the kissing spines when a disc herniation is the bigger driver of pain will not produce a satisfying result.
This is one reason that the condition is worth knowing about even if you have already been diagnosed with something else. If your low back pain has a midline component that worsens with standing and arching and does not fully match your existing diagnosis, asking your doctor whether Baastrup disease could be contributing is a reasonable conversation to have. Given how often it is overlooked, raising the possibility yourself is sometimes what it takes to get it evaluated.
Imaging Findings Without Symptoms
A theme running through spine medicine more broadly is the gap between what shows up on imaging and what actually causes pain. Disc bulges, facet arthritis, and mild stenosis are extremely common on MRI in people with no back pain at all. Baastrup disease follows the same pattern. The structural finding of close or touching spinous processes is frequent in older adults, but only a fraction of them have symptoms attributable to it.1Cureus. Baastrup’s Disease: An Often Missed Etiology for Back Pain
This means that if you get an MRI for any reason and the report mentions kissing spines or Baastrup changes, it does not necessarily mean you have a problem that needs treating. The finding becomes clinically significant when the clinical picture matches: midline pain, worse with extension, better with flexion, and tenderness right over the interspinous space. Without that clinical correlation, the imaging finding is probably an incidental observation. This distinction matters because unnecessary treatment of incidental findings is a real issue in spine care, leading to procedures that carry risk but offer no benefit because the “abnormality” being treated was not the source of pain in the first place.
If you have been told you have Baastrup disease on a scan but your pain pattern does not match the expected presentation, it is worth discussing with your doctor whether the kissing spines are truly responsible or whether a different pain generator is the real culprit. The clinical exam, particularly the response to palpation over the interspinous space and the flexion-extension pattern, is what ties the imaging to the symptoms.