Adjacent Segment Disease After Spinal Fusion: What the Medical Literature Reports on Incidence and Reported Outcomes

Adjacent segment disease (ASD) refers to degenerative change occurring at a spinal level immediately above or below a fused segment. This article summarizes what the peer-reviewed literature and current clinical practice report about the biomechanics, reported incidence, natural history, and outcomes associated with ASD following cervical and lumbar fusion. It is intended as an educational overview and does not evaluate, address, or offer opinion on any individual patient, provider, or matter.

How the term is defined in the literature

Published series distinguish between radiographic adjacent segment degeneration — imaging findings such as disc-height loss, endplate change, listhesis, or facet arthropathy at a level adjacent to a fusion — and symptomatic adjacent segment disease, in which those radiographic changes are accompanied by new or recurrent clinical symptoms attributable to that level. The literature is consistent that radiographic change is common and symptomatic disease is reported less frequently, and that the two are related but distinct endpoints that should not be conflated when interpreting reported rates.

A further distinction appears in the deformity literature between adjacent segment disease at a mobile lumbar or cervical level and proximal junctional kyphosis or proximal junctional failure, which are discussed as related but mechanistically distinct phenomena occurring at the proximal end of long deformity constructs.

Proposed biomechanical mechanisms

The published biomechanical literature describes fusion as altering the distribution of motion and load along the spinal column. In vitro and computational modeling studies report increased intradiscal pressure, increased range of motion, and increased facet joint loading at levels adjacent to a fused segment compared with the unfused spine. These studies are generally framed in the literature as demonstrating a plausible mechanical pathway rather than as direct proof of a causal relationship to clinical disease in any individual patient.

Reviews of the biomechanical evidence note that the magnitude of altered adjacent-segment loading reported in cadaveric and computational studies varies with construct length, sagittal alignment, and the specific level fused, and that these mechanical findings are one of several proposed contributors to adjacent segment disease alongside the natural history of spinal degeneration that would be expected to occur with or without prior surgery.

Reported incidence in the cervical spine

Long-term follow-up studies of anterior cervical discectomy and fusion (ACDF) are among the most extensively cited natural-history series in the ASD literature. These studies report radiographic adjacent-level degenerative change in a substantial majority of patients over ten or more years of follow-up, while new symptomatic disease at an adjacent level is reported at a considerably lower rate, commonly described in the literature as an approximate annual incidence that compounds with longer observation.

• —Landmark long-term cervical cohorts report cumulative symptomatic adjacent-segment disease continuing to accrue for at least a decade after the index fusion, rather than plateauing shortly after surgery.
• —Systematic reviews comparing ACDF to cervical disc arthroplasty report lower rates of reoperation for adjacent-segment pathology after arthroplasty in several meta-analyses, though heterogeneity in patient selection and follow-up duration is a recognized limitation across this comparative literature.
• —Multilevel cervical fusion is reported in comparative series to carry a higher rate of adjacent-segment findings than single-level fusion, consistent with the biomechanical literature on cumulative altered loading.
• —Pre-existing degenerative change at the adjacent level on preoperative imaging is reported in multiple series as a predictor of subsequent symptomatic disease, independent of the fusion itself.

Reported incidence in the lumbar spine

Lumbar fusion series report a broadly similar pattern: radiographic adjacent-level change is common on long-term imaging, while symptomatic disease requiring treatment is reported in a smaller subset of patients. Reported rates vary substantially across studies depending on the definition of ASD applied, the length of follow-up, and whether the analysis is limited to symptomatic reoperation or includes radiographic findings alone.

Construct length is repeatedly identified in the lumbar literature as associated with reported outcome. Comparative series report higher rates of both radiographic and symptomatic adjacent-segment findings after long-segment or multilevel lumbar fusion than after short-segment fusion, and deformity-specific literature separately discusses proximal junctional pathology as a common indication for revision surgery in long-construct populations.

Across both the cervical and lumbar literature, radiographic adjacent-segment change is reported far more frequently than symptomatic disease, and reported rates of both rise with longer follow-up and longer fusion constructs.

Natural history and the role of pre-existing degeneration

A recurring theme in the ASD literature is the difficulty of separating fusion-accelerated degeneration from the natural history of age-related spinal degeneration that occurs independent of any surgery. Population-based imaging studies of asymptomatic, unoperated adults report a high background prevalence of disc degeneration, facet arthropathy, and disc-height loss that increases with age, which complicates attribution of adjacent-level findings after fusion to the surgery itself versus the expected natural history of the spine.

Some published cohort and case-control studies have attempted to address this by comparing fused patients to nonoperative or motion-preservation control groups over time. These comparative studies report mixed findings regarding the extent to which fusion accelerates adjacent-level degeneration beyond what would be expected from natural history alone, and this remains a described area of ongoing investigation rather than a settled question in the literature.

Reported outcomes of treatment for symptomatic ASD

When adjacent segment disease becomes symptomatic and is treated surgically, published series report outcomes that are generally comparable to, but on average somewhat more variable than, outcomes reported after primary fusion at the same levels. Reoperation for symptomatic ASD is described in the literature as one of the more common indications for revision spine surgery in both the cervical and lumbar literature, and comparative series report that patients undergoing revision surgery for ASD have a measurable but generally lower reported rate of achieving the same magnitude of symptomatic improvement as after an index procedure.

• —Nonoperative management, including physical therapy and injections, is reported as the initial approach in most published treatment algorithms for symptomatic ASD without progressive neurologic deficit.
• —Extension of fusion to the involved adjacent level is the most commonly reported surgical approach in published revision series for symptomatic ASD.
• —Motion-preserving revision options are described in a smaller subset of the published literature and are reported with more limited long-term follow-up than fusion-based revision.
• —Reported reoperation rates after treatment of an initial episode of symptomatic ASD are described in some series as compounding further with additional long-term follow-up, consistent with the broader natural-history literature on progressive multilevel degeneration.

How the literature frames prevention and risk discussion

Published reviews discuss several factors reported to correlate with adjacent-segment findings, including construct length, sagittal alignment, pre-existing adjacent-level degeneration, and patient-level factors such as age and bone quality. Motion-preservation technologies, including cervical disc arthroplasty and, more selectively studied, lumbar approaches, are discussed in the comparative literature as strategies intended to reduce adjacent-segment loading, with systematic reviews reporting lower rates of reoperation for adjacent-segment pathology in some but not all comparative analyses.

Professional-society statements and clinical practice guidelines generally describe adjacent segment disease as an expected long-term consideration to discuss as part of informed decision-making before fusion, rather than as a complication attributable to a specific technical error, and note that the published literature does not support a single universally accepted method of eliminating adjacent-segment risk.

Summary of the published evidence

Across the ASD literature, several points recur. First, radiographic adjacent-segment change is common after both cervical and lumbar fusion and is reported at meaningfully higher rates than symptomatic disease. Second, reported incidence of both radiographic and symptomatic ASD increases with longer follow-up and, in comparative series, with longer fusion constructs. Third, separating fusion-accelerated degeneration from the expected natural history of the aging spine remains a described limitation across the comparative literature. Fourth, when ASD becomes symptomatic, extension of fusion is the most commonly reported surgical treatment, with reoperation for adjacent-segment pathology described as one of the more common indications for revision spine surgery in the published series.

This overview is educational. It is not medical advice, does not evaluate any specific patient or matter, and does not substitute for review of the primary peer-reviewed sources.

Frequently asked

Common questions on this topic