Illustration of spinal sagittal alignment parameters.

Back Pain After Fusion Surgery? Uncover the Link Between Sagittal Alignment and ASD

Rhea Morgan in Health & Wellness December 2025 • 4 min read.

"New research spotlights how your spine's natural curves could predict post-surgery complications. Are you at risk?"

Lower back pain and spinal stenosis can significantly diminish your quality of life, particularly as you age. When conservative treatments fail, spinal fusion surgery becomes a common solution to stabilize the spine and alleviate pain. Posterior lumbar interbody fusion (PLIF) is frequently performed to address degenerative lumbar disorders. It aims to decompress neural foramina and provide solid fixation, but it's not without potential drawbacks.

One notable complication is adjacent segment degeneration (ASD), where the segments above or below the fused area begin to deteriorate. This can lead to new or recurring pain and may necessitate further interventions. Understanding the factors that contribute to early-onset ASD is vital for improving surgical outcomes and patient satisfaction.

Recent research investigates the connection between total spinal sagittal alignment and early ASD after single-level L4-L5 PLIF. The study focuses on patients without severe preoperative sagittal imbalance, aiming to identify specific spinal characteristics that may increase the risk of developing ASD post-surgery. By exploring these factors, medical professionals hope to refine patient selection and surgical planning to minimize the likelihood of this complication.

Decoding Sagittal Alignment: What the Numbers Mean for Your Spine

Illustration of spinal sagittal alignment parameters.

The spine's sagittal alignment refers to its natural curves when viewed from the side. Key parameters include:

Understanding these measurements is crucial because they reflect how your body distributes weight and maintains balance. When these parameters are out of the optimal range, it can lead to increased stress on adjacent spinal segments after a fusion. The featured study meticulously analyzed these parameters to identify potential risk factors for early-onset ASD.

Sagittal Vertebral Axis (SVA): Horizontal distance between a vertical line from the C7 vertebra and the posterior superior corner of the S1 vertebra.
Thoracic Kyphosis (TK): The angle of the thoracic spine's curvature.
Lumbar Lordosis (LL): The angle of the lumbar spine's inward curve.
Pelvic Tilt (PT): The position of the pelvis relative to the sacrum.
Pelvic Incidence (PI): A fixed anatomical parameter representing the relationship between the sacrum and the hip axis.

The study, published in the Asian Spine Journal, retrospectively examined 70 patients who underwent single-level L4-L5 PLIF. These patients were carefully selected to exclude those with pre-existing conditions or severe spinal imbalance. They were then divided into two groups based on whether they developed radiographic progression of L3-L4 degeneration after a 1-year follow-up: the ASD group and the non-ASD (NASD) group. Researchers compared the spinal parameters of both groups to identify any significant differences.

What This Means for You: Taking Control of Your Spinal Health

While this study sheds light on potential risk factors, it’s essential to remember that ASD is a complex issue influenced by numerous factors. Discuss your individual risk profile with your orthopedic surgeon. A comprehensive evaluation of your spinal alignment, along with other considerations, will help determine the most appropriate surgical approach and post-operative care plan.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.31616/asj.2018.12.4.743, Alternate LINK

Title: Postoperative Radiographic Early-Onset Adjacent Segment Degeneration After Single-Level L4–L5 Posterior Lumbar Interbody Fusion In Patients Without Preoperative Severe Sagittal Spinal Imbalance

Subject: Orthopedics and Sports Medicine

Journal: Asian Spine Journal

Publisher: Asian Spine Journal (ASJ)

Authors: Yuji Matsuoka, Kenji Endo, Hidekazu Suzuki, Yasunobu Sawaji, Hirosuke Nishimura, Taichiro Takamatsu, Osamu Kojima, Kazuma Murata, Takeshi Seki, Shinji Horie, Takamitsu Konishi, Kengo Yamamoto

Published: 2018-08-31

Everything You Need To Know

What is Adjacent Segment Degeneration (ASD) and why is it a concern after spinal fusion?

Adjacent Segment Degeneration (ASD) refers to the deterioration of spinal segments located above or below the area that has undergone spinal fusion. This degeneration can lead to new or recurring back pain, nerve compression, and other symptoms, potentially requiring additional medical interventions or surgeries. ASD is a concern because it represents a common long-term complication that can diminish the overall success and longevity of spinal fusion procedures, like Posterior Lumbar Interbody Fusion (PLIF). While the study focused on ASD after PLIF, it's important to note that factors like SVA, TK, PI also influence adjacent segment degeneration in other spinal surgeries. It can significantly impact a patient's quality of life post-surgery.

What spinal alignment parameters are considered important in predicting the risk of ASD after Posterior Lumbar Interbody Fusion (PLIF)?

Several spinal alignment parameters are considered important, including Sagittal Vertebral Axis (SVA), Thoracic Kyphosis (TK), Lumbar Lordosis (LL), Pelvic Tilt (PT), and Pelvic Incidence (PI). Sagittal Vertebral Axis (SVA) measures the horizontal distance from the C7 vertebra to the sacrum, indicating overall sagittal balance. Thoracic Kyphosis (TK) and Lumbar Lordosis (LL) measure the curvature of the thoracic and lumbar spine, respectively. Pelvic Tilt (PT) and Pelvic Incidence (PI) describe the position and angle of the pelvis. These parameters, especially when imbalanced, can increase stress on spinal segments adjacent to a fusion site, increasing the risk of Adjacent Segment Degeneration (ASD). It is worth noting that while this study focused on these parameters, other factors like muscle strength and disc health also contribute to spinal stability.

How does Posterior Lumbar Interbody Fusion (PLIF) address lower back pain and spinal stenosis, and what are its limitations?

Posterior Lumbar Interbody Fusion (PLIF) is a surgical procedure designed to stabilize the spine and alleviate pain associated with lower back pain and spinal stenosis. It involves decompressing neural foramina to relieve nerve compression and using bone grafts and instrumentation to create a solid fusion between vertebrae. While PLIF can effectively reduce pain and improve stability, it has limitations, including the potential for Adjacent Segment Degeneration (ASD). ASD occurs when the spinal segments adjacent to the fused area deteriorate, leading to new pain or other complications. Other limitations can include infection, nerve damage, and failure of the fusion to heal properly. The study underscores the importance of careful patient selection and surgical planning to minimize these risks.

What does the Sagittal Vertebral Axis (SVA) indicate about spinal balance, and why is it important in the context of spinal fusion?

The Sagittal Vertebral Axis (SVA) is a measurement that indicates the degree of sagittal balance in the spine. It represents the horizontal distance between a vertical line drawn from the C7 vertebra and the posterior superior corner of the S1 vertebra. A higher SVA value typically indicates a greater degree of forward imbalance, which can increase stress on the spinal structures. In the context of spinal fusion, an imbalanced SVA can contribute to increased stress on the adjacent segments, potentially leading to Adjacent Segment Degeneration (ASD) after procedures like Posterior Lumbar Interbody Fusion (PLIF). The alignment influences how weight is distributed along the spine. While SVA is important other parameters such as Pelvic Incidence (PI) are important.

Beyond the study's findings, what are some additional factors that patients should consider when evaluating their risk of developing ASD after spinal fusion?

While the study highlights the importance of sagittal alignment parameters such as SVA, TK, LL, PT, and PI, patients should also consider other factors that can influence the risk of Adjacent Segment Degeneration (ASD) after spinal fusion. These factors include age, bone density, pre-existing spinal conditions, smoking status, and activity level. Older patients and those with osteoporosis may be at higher risk. Also, the technique used during the Posterior Lumbar Interbody Fusion (PLIF) procedure, as well as post-operative rehabilitation and adherence to recommended lifestyle modifications, play critical roles. A comprehensive discussion with an orthopedic surgeon is essential to assess individual risk profiles and develop a personalized management plan. The study notes only radiographic progression of L3-L4 degeneration at 1 year was measured. Long term patient satisfaction and return to normal activity levels also needs to be considered.