A Nerve Root-Centered Classification System for Lumbar Disc Herniation: Development and Reliability Assessment

The lower back is a complex machine of bone, muscle, and nerve, and one of its most common failures involves the soft cushions between the vertebrae. These cushions, called intervertebral discs, can sometimes bulge or rupture, pushing material out of place. When this happens, the displaced material often presses against the delicate nerve roots that branch off the spinal cord and travel down the legs. This pressure causes pain, numbness, or weakness, a condition known as a lumbar disc herniation. For decades, surgeons have relied on standard maps to describe these injuries, focusing mostly on the shape of the broken disc or how far it has migrated. However, in the modern era of minimally invasive surgery, where a surgeon operates through a tiny tube with a camera, knowing the exact shape of the disc is not enough. The critical challenge is understanding the precise three-dimensional relationship between the displaced disc and the specific nerve it is crushing. Without a clear mental map of this relationship, a surgeon operating in such a narrow, dark tunnel risks missing the target or accidentally harming the nerve.

To address this gap, a team of spine surgeons from several hospitals in China developed a new way to categorize these injuries, one that places the nerve root at the center of the map rather than the disc itself. They created a system called the Peking University Third Hospital, or PUTH, classification. Instead of just describing the disc, this system asks two specific questions: where does the affected nerve root begin in relation to the disc, and where is the herniated disc sitting relative to that nerve? The researchers tested this new system on 516 patients who underwent a specific type of minimally invasive surgery called percutaneous endoscopic lumbar discectomy. In this procedure, surgeons use a small camera and specialized tools inserted through a tiny incision to remove the offending disc material and relieve pressure on the nerve. The team wanted to see if their new classification could be reliably used by different surgeons to interpret preoperative magnetic resonance imaging scans and if it matched what they actually saw once they were inside the patient's body during surgery.

The study began by reviewing the medical records and preoperative scans of 516 patients who had undergone this surgery between January and December 2022. The researchers first used the new PUTH system to classify each case based on the MRI images. Then, they compared these initial classifications against a "gold standard" reference created by senior surgeons who carefully reviewed the actual video recordings of the operations. This step was crucial because it allowed the team to see if the preoperative images accurately predicted the reality of the surgery. The results showed a high level of agreement: in 486 out of the 516 cases, the classification derived from the MRI matched the classification confirmed by the surgical video. This represents an agreement rate of 94.2 percent. The few cases where the MRI and the surgery did not match were usually due to severe compression that obscured the nerve's origin on the scan, or rare anatomical variations where the nerve started in an unexpected place.

To ensure the system was robust and not just a method that worked for the original team, the researchers tested its reliability with other doctors. Three surgeons from the same hospital and five experienced surgeons from outside institutions were asked to classify the cases using only the preoperative images, without knowing the final surgical outcome. They repeated this process twice, with a two-week break in between, to check for consistency. The internal team showed excellent agreement with themselves and with each other, while the external team also showed strong consistency, though slightly lower than the internal group. This suggests that the system is clear enough to be learned and used by surgeons who did not invent it. The researchers found that the system successfully categorized the nerve root origins into three types based on whether the nerve started above, at, or below the level of the disc. They also categorized the disc location into four zones relative to the nerve, such as the "shoulder" (the side of the nerve) or the "axilla" (the space underneath the nerve). By combining these two pieces of information, a surgeon can create a precise mental map of the surgical field before making the first cut.

The clinical outcomes for the patients in this study were also encouraging. After a minimum follow-up of two years, the patients reported significantly less pain in their backs and legs, and their ability to perform daily activities improved markedly. Only a small number of patients, 13 in total, experienced a return of their symptoms, and complications were rare, occurring in fewer than two percent of cases. These results indicate that using this classification system to guide surgery is safe and feasible. However, the authors are careful to note that this study was a retrospective review, meaning they looked back at data that had already been collected. While the results are positive, they do not prove that the classification system itself caused the good outcomes, nor does it prove that it is superior to other methods. The study demonstrates that the system works well for describing the anatomy and that surgeons can agree on its use, but it does not yet prove that using this specific map leads to better results than other approaches.

The value of this work lies in its potential to help surgeons navigate the difficult terrain of endoscopic spine surgery. Because the view through the endoscope is limited, surgeons must rely heavily on their preoperative understanding of the anatomy to avoid disorientation. The PUTH classification offers a structured way to translate a static MRI image into a dynamic surgical plan. By focusing on the nerve root as the primary landmark, it helps surgeons anticipate where they will find the nerve and where the disc fragment is likely hiding. The study concludes that this nerve-centered framework is a reproducible tool that can assist in preoperative planning and intraoperative orientation. While further large-scale studies involving many different hospitals are needed to confirm its broader impact on surgical decision-making, the system provides a clear, practical language for describing the complex relationship between a herniated disc and the nerve it affects. For the patients, this means a potential for safer, more precise surgeries where the surgeon knows exactly what to look for before entering the body.