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One-Hole Split Endoscopy Versus Open Laminectomy for Single-Level Thoracic Ossification of the Ligamentum Flavum: A Multicenter Propensity Score-Matched Cohort Study

This multicenter propensity score-matched study demonstrates that one-hole split endoscopy (OSE) offers comparable neurological recovery to open laminectomy for single-level thoracic ossification of the ligamentum flavum while significantly reducing surgical trauma, preserving paraspinal muscles, limiting local Cobb angle progression, and lowering overall complication rates.

Original authors: Xianyi Zhang, Mustafa Abbas Farhood Sultani, Jie Shang, Liang Guo, Guizhu Ji, Ziwei Xia, Chao Ma, Meng Han

Published 2026-07-16

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Xianyi Zhang, Mustafa Abbas Farhood Sultani, Jie Shang, Liang Guo, Guizhu Ji, Ziwei Xia, Chao Ma, Meng Han

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Spine's Invisible Shield and the Battle for Space

Imagine your spine as a high-speed data cable running through a narrow, protective tunnel in your back. This tunnel, made of bone, is supposed to keep the cable safe, but sometimes, a soft, rubbery strap inside the tunnel—the ligamentum flavum—decides to turn into hard, rocky bone. This condition is called Thoracic Ossification of the Ligamentum Flavum (TOLF). When this happens, the "rock" grows inward, squeezing the spinal cord like a kinked garden hose. Since the thoracic (mid-back) area is a tight squeeze to begin with, this pressure can cause serious trouble, like trouble walking or feeling your legs.

For decades, the standard way to fix this was a "big open" surgery. Think of it like a demolition crew tearing down a wall to get to the pipe behind it. They cut through the skin, peeled back the muscles on both sides of the spine, and removed a big chunk of the bone roof to free the cord. It works, but it's rough on the muscles, which can get bruised, starved of blood, or even lose their nerve connections, leading to back pain and a crooked spine later on. Recently, doctors have been trying a "micro-surgery" approach using a tiny camera and tools through a single, small hole. This is like sending a tiny robot explorer through a keyhole to chip away the rock without tearing down the whole house. But, is this tiny robot as good at fixing the problem as the big demolition crew, and does it really save the muscles? That's the big question this study set out to answer.

The Keyhole vs. The Bulldozer: A High-Stakes Showdown

In this study, researchers from four different hospitals in China looked back at 216 patients who had this specific type of spinal rock formation at just one level. They wanted to compare the old-school "Open Laminectomy" (the bulldozer) against the new "One-Hole Split Endoscopy" or OSE (the keyhole robot). To make sure the comparison was fair, they used a statistical trick called "propensity score matching." Imagine lining up two teams of players so that for every player on the robot team, there are two players on the bulldozer team who are exactly the same age, have the same severity of the disease, and the same body type. After this careful matching, they ended up comparing 62 robot-surgery patients against 124 bulldozer-surgery patients.

The Race Against Time and Blood
When the surgeries started, the robot team took a bit longer to finish the job. The OSE group needed an average of 128.5 minutes, while the bulldozer group finished in 105.2 minutes. It makes sense; working through a tiny hole with a camera is like trying to untangle a knot with a pair of tweezers instead of your whole hand. However, the trade-off was huge. The robot team lost significantly less blood (85.3 mL vs. 326.7 mL) and had much less fluid draining out of the wound after surgery (42.6 mL vs. 185.4 mL). Because the body wasn't as battered, the robot patients went home much faster, staying in the hospital for only 5.2 days compared to 9.7 days for the bulldozer group.

Did the Robot Fix the Problem?
The most important question was: Did the robot free the spinal cord just as well as the bulldozer? The answer is a confident "yes." One year after surgery, both groups had improved their ability to walk and function. The "recovery rate" for the robot group was 68.7%, while the bulldozer group was 65.3%. Statistically, these numbers are close enough to say the robot is just as effective at fixing the nerve compression as the big open surgery.

Saving the Muscle and the Curve
Here is where the robot really shines. The researchers measured the health of the back muscles (specifically the multifidus and erector spinae) using MRI scans. Three months after surgery, the bulldozer group had lost about 21.1% of their muscle function area, while the robot group only lost 3.4%. It's the difference between a forest being clear-cut and a forest where only a few trees were trimmed.

Because the muscles were saved, the spine stayed straighter. The "local Cobb angle" (a measure of how much the spine curves forward) increased by only 1.2 degrees in the robot group, but it jumped by 4.2 degrees in the bulldozer group. A smaller curve is better for long-term posture. Additionally, the robot group had fewer total complications overall (16.1% vs. 34.7%), including fewer instances of nerve monitoring alarms and fluid leaks, though some specific complications were rare in both groups.

What Actually Determines the Outcome?
The study also looked at what made some patients recover poorly, regardless of which surgery they had. It turned out the type of surgery didn't matter for the final result. Instead, the outcome depended on how bad the damage was before the surgery started. Patients who had a very low score before surgery (less than 7), a specific "bulky" shape of the bone rock (Modified Sato type III), severe nerve damage signs on the MRI (Grade 2 T2 hyperintensity), or very severe symptoms (Epstein grade IV) were more likely to have a slower recovery. The surgery itself was just the tool; the starting condition was the real boss.

The Verdict: A Smarter Tool for the Right Job

This study suggests that for patients with a single-level rock formation in their mid-back who don't have a wobbly spine, the "One-Hole Split Endoscopy" is a fantastic alternative to the traditional open surgery. It takes a little longer to perform, but it saves a massive amount of blood, gets patients home faster, and, most importantly, preserves the back muscles and keeps the spine straighter.

However, the authors are careful to say this isn't a magic wand for everyone. The robot approach works best when the problem is isolated to one spot and the surgeon is an expert with the camera. If the rock is huge, fused to the nerves, or if the spine is unstable, the "bulldozer" (open surgery) might still be the safer choice. But for the right patient, this tiny keyhole approach offers a way to fix the problem with far less trauma to the body, proving that sometimes, less really is more.

Technical Summary: One-Hole Split Endoscopy Versus Open Laminectomy for Single-Level Thoracic Ossification of the Ligamentum Flavum

Problem Statement
Thoracic ossification of the ligamentum flavum (TOLF) is a leading cause of thoracic myelopathy, particularly in East Asian populations. Once symptomatic spinal cord compression occurs, surgical decompression is the primary treatment. While open posterior laminectomy has long been the standard for providing direct visualization and sufficient decompression, it necessitates extensive bilateral paraspinal muscle stripping and resection of posterior osseoligamentous structures. These maneuvers are associated with ischemic and denervation-related muscle injury, postoperative back pain, loss of functional muscle cross-sectional area, and potential local kyphotic progression. Although minimally invasive endoscopic techniques have been proposed to reduce trauma, evidence comparing them to open surgery—specifically regarding quantitative muscle preservation, local sagittal alignment, and complications in multicenter settings—remains limited.

Methodology
This study employed a multicenter, retrospective cohort design involving 216 patients with single-level TOLF treated across four tertiary hospitals between January 2019 and January 2024. Patients were categorized into two groups: those undergoing One-Hole Split Endoscopy (OSE) decompression ( $n=72$ ) and those undergoing open laminectomy alone ( $n=144$ ).

To mitigate selection bias, a 1:2 propensity score matching (PSM) analysis was performed using a nearest-neighbor algorithm with a caliper of 0.05. Matching covariates included age, sex, disease duration, lesion level, modified Sato morphology type, Epstein myelopathy grade, preoperative Japanese Orthopaedic Association (JOA) score, presence of grade 2 intramedullary T2 hyperintensity, and preoperative multifidus relative functional cross-sectional area (rfCSA). This process yielded a matched cohort of 62 OSE patients and 124 open-surgery patients.

Surgical Techniques:

OSE: Performed under general anesthesia with the patient prone. A single 1.5–2.0 cm longitudinal incision was made near the lamina-facet junction. A split working corridor was established allowing the endoscope and instruments to enter through the same incision but remain relatively separated (non-coaxial). Continuous saline irrigation (30–40 mmHg) was used. Decompression involved drilling the lateral laminar margin and medial facet joint to create a portal, followed by piecemeal or en bloc removal of the ossified ligamentum flavum under neurophysiological monitoring.
Open Laminectomy: Performed via a posterior midline incision with bilateral subperiosteal muscle detachment. Total laminectomy was performed to remove the ossified mass. No internal fixation or fusion was performed in either group.

Outcomes Measured:
The primary endpoint was the 1-year JOA recovery rate. Secondary endpoints included perioperative metrics (operative time, blood loss, drainage, hospital stay), radiographic outcomes (local Cobb angle change, intramedullary T2 signal improvement), paraspinal muscle preservation (multifidus and erector spinae rfCSA measured at 3 months post-op), and complication rates.

Key Results
After propensity score matching, baseline characteristics were well-balanced. The study reported the following comparative findings:

Perioperative Outcomes: The OSE group required a significantly longer operative time (128.5 vs. 105.2 min, $P<0.001$ ) but demonstrated superior metrics in blood loss (85.3 vs. 326.7 mL), postoperative drainage (42.6 vs. 185.4 mL), and hospital stay (5.2 vs. 9.7 days) compared to the open group ( $P<0.001$ for all).
Neurological Recovery: The 1-year JOA recovery rate was statistically comparable between groups (OSE: 68.7% ± 12.5% vs. Open: 65.3% ± 13.2%; $P=0.089$ ).
Radiographic and Muscle Preservation:
- Local Alignment: The OSE group exhibited significantly less progression in local Cobb angle at 1 year (change of 1.2° vs. 4.2°, $P<0.001$ ).
- Muscle Preservation: At 3 months post-operation, the OSE group maintained significantly higher rfCSA values for both the multifidus and erector spinae muscles. The relative reduction in multifidus rfCSA was 3.4% in the OSE group versus 21.1% in the open group ( $P<0.001$ ).
Complications: The overall complication rate was significantly lower in the OSE group (16.1% vs. 34.7%, $P=0.010$ ). While individual complications like cerebrospinal fluid leakage and neurological deterioration showed non-significant trends favoring OSE, the aggregate safety profile was superior.
Risk Factors: Multivariable logistic regression identified preoperative JOA score <7, modified Sato type III, Epstein grade IV, and grade 2 intramedullary T2 hyperintensity as independent risk factors for poor neurological recovery. The surgical approach (OSE vs. Open) was not an independent risk factor.

Significance and Claims
The authors conclude that for strictly selected patients with single-level TOLF who do not exhibit obvious segmental instability, OSE achieves neurological recovery and radiographic decompression comparable to open laminectomy. The study claims that OSE offers distinct advantages by reducing surgical trauma, preserving paraspinal muscle morphology (as evidenced by rfCSA), limiting local kyphotic progression, and lowering the overall complication rate.

The paper posits that OSE is a viable minimally invasive alternative when indications are carefully controlled (single-level, posterior compression, no instability) and when performed by surgeons with thoracic endoscopic expertise. The authors emphasize that the technique's safety relies on careful indication selection, familiarity with thoracic endoscopic anatomy, the use of neuromonitoring, and strict control of irrigation pressure. They acknowledge that open laminectomy remains appropriate for multilevel disease, severe deformity, or cases with fused dural ossification.

Limitations Noted
The authors explicitly note limitations including the retrospective nature of the study, the 1-year follow-up duration (insufficient for long-term kyphosis or muscle recovery assessment), and the lack of data on surgeon learning curves, cost, and quality-of-life metrics. They also highlight that the rarity of modified Sato type IV morphology in their cohort prevented a robust independent analysis of its prognostic value.

The Spine's Invisible Shield and the Battle for Space

The Keyhole vs. The Bulldozer: A High-Stakes Showdown

The Verdict: A Smarter Tool for the Right Job

Technical Summary: One-Hole Split Endoscopy Versus Open Laminectomy for Single-Level Thoracic Ossification of the Ligamentum Flavum

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