What Is Pseudoarticulation of the Spine?

Pseudoarticulation of the spine is a “false joint” that forms where two bony structures come into abnormal contact or near-contact without a true synovial joint ever developing between them. The most widely recognized example occurs at the base of the spine, where an enlarged transverse process of the lowest lumbar vertebra presses against the sacrum or ilium, creating a joint-like interface that was never supposed to exist. Because these false joints lack the smooth cartilage and lubricating fluid of a real joint, they can become a stubborn source of low back pain, nerve irritation, and accelerated wear on neighboring spinal segments.

Where False Joints Appear in the Spine

The term “pseudoarticulation” shows up in a few distinct spinal contexts, and understanding which one a clinician is referring to matters because the causes, symptoms, and treatments differ.

Lumbosacral transitional vertebrae: The lowest lumbar vertebra has an unusually large transverse process that nearly touches or partially fuses with the sacrum. When the gap between these structures is less than about 2 mm but full bony fusion hasn’t occurred, a pseudoarticulation exists at that junction.¹ This is by far the most commonly discussed form.
Kissing spines (Baastrup’s disease): Adjacent spinous processes at the back of the spine degenerate and enlarge until they touch each other, forming a false joint between structures that normally have a comfortable gap.²
Post-traumatic pseudoarticulation: After a fracture or injury, the transverse processes of two adjacent lumbar vertebrae can form a bony bridge with a narrow pseudo-joint space between them. One documented case showed this between the L3 and L4 transverse processes, accompanied by a 15-degree scoliotic curve.³
Post-surgical pseudarthrosis: When a spinal fusion fails to heal into solid bone, the unfused segment develops a fibrous false joint. This is a different clinical entity but shares the “pseudo-joint” concept.

Bertolotti’s Syndrome and the Lumbosacral Pseudoarticulation

The overwhelming majority of spinal pseudoarticulation discussions center on lumbosacral transitional vertebrae, or LSTV. These are congenital variants where the last lumbar vertebra has characteristics of a sacral bone, or the first sacral segment behaves more like a lumbar one. When the enlarged transverse process of that transitional vertebra comes close enough to the sacrum to form a false joint but doesn’t fully fuse, the result is a pseudoarticulation. The condition becomes symptomatic in some people, and when it does, clinicians call it Bertolotti’s syndrome.

LSTV are surprisingly common. One cross-sectional study of patients with chronic low back pain found LSTV in about 38% of that group, compared with roughly 22% of people without chronic back pain.⁴ A separate study looking at healthy volunteers alongside patients with hip problems found that the more significant types of LSTV (those classified as Type II or higher, meaning pseudoarticulations or full fusions rather than just mildly enlarged processes) were present in about 8.5% of the combined group.⁵ So plenty of people walk around with a pseudoarticulation and never know it. The question is why some become painful and others don’t.

Why a False Joint Becomes a Pain Generator

A true joint has cartilage, a capsule, and synovial fluid to absorb shock and allow smooth movement. A pseudoarticulation has none of that infrastructure. The contact zone between the transverse process and the sacrum is essentially raw bone meeting bone (or bone meeting a thin layer of fibrocartilage that wasn’t designed for repeated loading). Over time, this interface develops arthritic changes, including bone spurs that can grow large enough to press on nearby nerve roots.⁶

The biomechanical damage doesn’t stop at the false joint itself. A pseudoarticulation on one side of the spine creates an asymmetric distribution of forces. The facet joints at the transitional level and the segments above it take on loads they weren’t built for. Research indicates that degenerative changes in the segment next to an LSTV are roughly nine times more frequent than in a normal lumbosacral junction.⁷ This cascade of wear and tear on neighboring levels is one reason the condition can be difficult to pin down clinically. The disc above the transitional segment might degenerate early, the facet joints might become arthritic, or the sacroiliac joint might become inflamed, all as downstream consequences of the original pseudoarticulation. A review in The Spine Journal emphasized that this predisposition toward rapid adjacent segment disease is a key concern when planning treatment.⁸

Symptoms and Why the Diagnosis Gets Missed

The textbook presentation is low back pain in a younger person, sometimes with sciatica-like leg pain if a nerve root gets involved. One case report described a 20-year-old woman who had endured low back pain since age 12 before the pseudoarticulation was finally identified as the cause.⁹ That kind of delay is common. Bertolotti’s syndrome patients undergo longer diagnostic workups and more epidural steroid injections than age-matched patients with ordinary lumbar radiculopathy. Despite this longer road, their physical and mental health scores tend to be worse.¹⁰

One reason for the diagnostic delay is that the pain pattern mimics several other conditions. Clinicians may interpret the symptoms as disc pain, facet joint problems, or sacroiliac dysfunction depending on the location and movement patterns. A Korean Journal of Pain study outlined how the same pseudoarticulation can produce midline pain that looks discogenic, lateral pain that resembles facet arthropathy, or buttock and leg pain that suggests sacroiliitis or a herniated disc.¹¹ Many of those structures may actually be contributing to the pain as well, since the biomechanical cascade described above can damage all of them.

How Pseudoarticulations Are Found on Imaging

A standard X-ray of the lumbar spine is often the first clue. An anteroposterior view will show the enlarged transverse process reaching toward the sacrum or ilium, with a narrow gap visible at the false joint. CT scans provide sharper detail, confirming whether the interface has a corticated (smooth-edged) bony surface consistent with a chronic pseudoarticulation, as opposed to a fresh fracture or incomplete fusion.³

The more clinically useful question is whether a pseudoarticulation that shows up on imaging is actually the source of the pain. Specialized MRI sequences can detect bone marrow swelling near the false joint, which suggests active inflammation. Nuclear imaging such as bone scintigraphy or SPECT-CT can highlight metabolically active pseudoarticulations, those that are actively remodeling or inflamed rather than sitting quietly.¹² These advanced imaging tools help distinguish an incidental anatomical finding from a genuine pain generator.

Diagnostic injections play a complementary role. A physician can inject local anesthetic directly into the pseudoarticulation under fluoroscopic guidance. If the patient’s pain disappears temporarily, that confirms the false joint as a source. In one case, a steroid and anesthetic injection into the pseudoarticulation relieved pain for about three weeks before it returned, confirming the diagnosis and guiding the decision toward surgery.⁹

Kissing Spines as a Separate Form of Pseudoarticulation

Baastrup’s disease is a distinct mechanism that produces a false joint in a different location. Instead of an enlarged transverse process meeting the sacrum, the spinous processes at the back of the vertebrae gradually degenerate, flatten, and enlarge until they physically touch each other. This is overwhelmingly a condition of the lumbar spine, with the L4-L5 level most frequently involved. On imaging, the hallmarks include sclerosis (hardening) of the touching surfaces, fluid-filled cysts at the contact point, and sometimes bursae or epidural masses that develop from chronic irritation.²

Unlike the LSTV-type pseudoarticulation, kissing spines are acquired rather than congenital. They result from age-related disc collapse that brings the spinous processes closer together, or from hyperlordosis (excessive inward curvature of the lower back) that slams these bony protrusions into each other during extension. The pain is typically midline and worsens when you lean backward or stand up straight after bending forward. Baastrup’s disease is often overlooked because clinicians focus on the discs and facet joints when reading lumbar MRI scans, and the spinous process contact can be dismissed as an incidental finding.

Post-Surgical Pseudarthrosis

When a spinal fusion surgery fails to produce solid bone bridging between two vertebrae, the result is a pseudarthrosis, literally a false joint at the fusion site. The tissue that fills the gap is elastic and fibrous rather than mineralized bone. Laboratory analysis of human pseudarthrosis tissue has shown it to be dramatically less stiff than actual bone, with a mechanical stiffness of roughly 12 N/mm compared to about 341 N/mm for healthy bone.¹³ That enormous difference explains why a pseudarthrosis permits ongoing abnormal motion and pain at the intended fusion site.

A systematic review and meta-analysis of risk factors for lumbar fusion pseudarthrosis identified age, smoking, and the number of spinal levels being fused as the main culprits. The risk of pseudarthrosis rose with each additional year of age, roughly doubled to five-fold with smoking, and increased by about 35% for each additional level included in the fusion.¹⁴ Anyone considering spinal fusion surgery who smokes should know that quitting meaningfully reduces the chance of ending up with this complication.

Treatment Options for Lumbosacral Pseudoarticulations

Initial management is conservative. Physical therapy, anti-inflammatory medications, and activity modification are the first line of treatment for symptomatic Bertolotti’s syndrome.¹⁵ Core strengthening exercises that stabilize the lumbar spine and reduce abnormal motion at the pseudoarticulation can be enough for milder cases. Steroid injections into the false joint provide temporary relief and serve double duty as both treatment and diagnostic confirmation.

For patients who don’t respond to conservative measures, minimally invasive options exist. Radiofrequency ablation, which uses heat to disable the small nerves around the pseudoarticulation, has shown promise. In one case, bipolar radiofrequency lesions created around the posterior margin of the false joint produced complete pain relief and full restoration of function lasting 16 months.¹⁶ The advantage of this approach is that it avoids open surgery, though the pain may eventually return as the nerves regenerate.

When surgery becomes necessary, the two main options are resecting (cutting away) the pseudoarticulation or fusing the transitional segment. A comparison of these approaches found that short-term pain relief was comparable, with both resection and fusion patients improving in the first six months. But the long-term picture favored fusion: about 78% of fusion patients reported sustained pain improvement beyond 12 months, compared with only 28% of patients who had the pseudoarticulation resected.¹⁷ The thinking is that simply removing the false joint may not address the underlying biomechanical instability, allowing the pain to return as adjacent structures continue to degrade. Fusion, while a bigger operation, stabilizes the segment more definitively. Surgical cases reported in the literature often involve patients classified as Castellvi Type II or III, meaning they have either pseudoarticulations or partial fusions of the transverse process.¹⁸

The Quality-of-Life Burden and Why Early Recognition Matters

Pseudoarticulations of the lumbosacral spine aren’t life-threatening, but research increasingly shows they carry a quality-of-life cost that has been underappreciated. Patients with Bertolotti’s syndrome score worse on both physical and mental health measures than age-matched patients with standard lumbar disc herniations, a condition most physicians take quite seriously.¹⁰ Both groups showed mild depression and meaningful reductions in quality of life, but the Bertolotti’s patients arrived at that point after more procedures and a longer diagnostic odyssey.

On the encouraging side, patients who do eventually receive targeted treatment can see real improvement. After surgical removal of the pseudoarticulation in patients who failed other treatments, physical health scores improved by an average of nearly 9 points and mental health scores by about 6 points on standardized measures. Patients whose expectations were met by the procedure showed even larger gains.¹⁹ The takeaway for anyone stuck in a cycle of unexplained chronic low back pain, especially if it started at an unusually young age, is that asking a clinician to look specifically for a transitional vertebra and pseudoarticulation on imaging is a reasonable and sometimes overlooked step.

Post-Traumatic Pseudoarticulations and Other Uncommon Variants

Most discussion of spinal pseudoarticulations revolves around congenital LSTV or post-surgical nonunion, but false joints can also form after trauma. Fractured transverse processes that heal with excessive callus formation may bridge toward an adjacent vertebra’s process, creating a bony bar with a narrow pseudo-joint space in between. High-resolution CT imaging can distinguish these from congenital variants by looking at the morphology of the bony surfaces. Congenital pseudoarticulations tend to have smooth, well-corticated margins because they’ve been present since skeletal development, while post-traumatic ones may show irregular surfaces and surrounding callus.³ The clinical significance of post-traumatic pseudoarticulations is less well studied than Bertolotti’s syndrome, partly because they’re rarer and partly because each case is unique to the fracture pattern that produced it. In the reported case, the post-traumatic pseudoarticulation was associated with a mild scoliosis, suggesting that these false joints can influence spinal alignment just as congenital ones do.

Pseudoarticulations between structures other than the transverse process and sacrum have also been described in the spine, though they’re uncommon enough that the literature consists mostly of case reports. The underlying principle is the same in every instance: two bony surfaces that normally don’t touch come into chronic contact, develop sclerotic, flattened articulating surfaces, and can become a pain source through mechanical irritation, inflammation, or nerve compression. Whether the culprits are spinous processes, transverse processes, or unfused surgical segments, recognizing that a false joint exists is the first step toward directing treatment at the right structure rather than chasing symptoms through neighboring anatomy.

1
World Neurosurgery. Redefining the Treatment of Lumbosacral Transitional Vertebrae for Bertolotti Syndrome: Long-Term Outcomes Utilizing the Jenkins Classification to Determine Treatment
2
Insights into Imaging. Baastrup’s disease (kissing spines syndrome): a pictorial review
3
Turkish Journal of Osteoporosis. Lumbar Transverse Process Pseudoarticulation: Congenital Versus Post-traumatic – A Case Report
4
PubMed Central. Prevalence of lumbosacral transitional vertebra in patients with chronic low back pain: a descriptive cross-sectional study
5
PubMed Central. Prevalence of Lumbosacral Transitional Vertebral Anomalies Among Healthy Volunteers and Patients with Hip Pathology Association with Spinopelvic Characteristics
6
PubMed Central. A Review of Symptomatic Lumbosacral Transitional Vertebrae: Bertolotti’s Syndrome
7
Interdisciplinary Neurosurgery. Bertolotti Syndrome: Does it really exist? systematic review
8
The Spine Journal. Clinical assessment and management of Bertolotti Syndrome: a review of the literature
9
PubMed Central. Bertolotti’s syndrome: A commonly missed cause of back pain in young patients
10
PubMed. Understanding quality of life and treatment history of patients with Bertolotti syndrome compared with lumbosacral radiculopathy
11
Korean Journal of Pain. Bertolotti Syndrome: A Diagnostic and Management Dilemma for Pain Physicians
12
PubMed Central. Bertolotti Syndrome in the Pediatric Population: A Literature Review and Management Algorithm
13
Neurosurgery. 283 Decoding Mechanotransduction in Spinal Pseudoarthrosis: A Mouse Model of Spinal Fusion for Developing Mechanosensitive Osteobiologics
14
PubMed Central. Pseudarthrosis risk factors in lumbar fusion: a systematic review and meta-analysis
15
PubMed Central. A Comprehensive Update of the Treatment and Management of Bertolotti’s Syndrome: A Best Practices Review
16
PubMed. Radiofrequency sensory ablation as a treatment for symptomatic unilateral lumbosacral junction pseudarticulation (Bertolotti’s syndrome): a case report
17
PubMed. Operative Treatment of Bertolotti Syndrome: Resection Versus Fusion
18
PubMed Central. Surgical Experience in Symptomatic Bertolotti Syndrome: Clinical Follow-up of Three Patients Refractory to Conservative Management
19
PubMed. Quality-of-life and postoperative satisfaction following pseudoarthrectomy in patients with Bertolotti syndrome