According to the statistics from WHO, worldwide obesity has nearly tripled since 1975. In 2016, more than 1.9 billion adults were overweight. Of these over 650 million were obese, indicating a tough challenge to the public health [16]. Many surgeons have found along with the extra pounds, overload on spine especially in lumbar vertebrae increases the risk of the LDH and degenerative lumbar spondylolisthesis through case-control studies and biomechanical analysis in human and animal specimens [17, 18]. Compared with the conventional posterior lumbar surgery, MIS-TLIF has definite effects and fewer complications and has become the routine surgical technique worldwide to treat LDH with severe neurological symptoms [11]. Nevertheless, some studies reported longer surgery time, more blood loss and longer length of hospital stay were observed in obese patients after MIS-TLIF [19]. In addition, the decrease in lumbodorsal muscle strength after MIS-TLIF, especially in overweight patients, may become a latent factor inducing postoperative low back pain.
In 1992, Kambin introduced the innovative method to treat LDH with arthroscopy, taking a significant step to the micro-invasive surgery in the spine field [20]. After subsequent development in the Yeung endoscopic spine system (YESS) by Yeung et al and transforaminal endoscopic spine system (TESS) by Hoogland et al, the modified percutaneous endoscopic lumbar discectomy (PELD) has become one of the most popular surgical methods that is equivalent to open spine surgery in terms of efficacy and entails less trauma and complication [21, 22]. Additionally, PELD reduced the paraspinal muscle trauma significantly compared with the open surgery, even the MIS-TLIF, which alleviated the low back pain in the normal and obese patients. PELD is favourable for obese patients because it minimizes incision length, which decreases the rate of postoperative unhealed wound and infectious complications. Obese patients are easily exposed to postoperative infection due to the poor blood supply in adipose tissue and fat liquefaction caused by the electrotome during surgery [23]. Furthermore, PELD under local anesthesia can also avoid the adverse events associated with general anesthesia, such as respiratory obstruction, hypotension and arrhythmia [24].
However, some researchers also have investigated the difficult and crucial points of PELD when treating obese patients. The finding of meta-analysis by Yin et al reconfirmed that the prevalence of recurrent herniation after PELD was significantly higher in obese (BMI ≥ 25) patients [25]. The conclusion is reasonable given that the excess weight with the cyclical increase of the intradiscal pressure could lead to higher shear strains in the posterolateral part of the annulus fibrosus, which would cause disc herniation. It remains complex in the guiding process and navigating for the optimal trajectory especially in the obese patients, which may constitute a steep learning curve. More difficulties in PELD unfolded while these obese patients catch a calcified LDH or high iliac crest for the L5/S1 level. All the limitations above lead to much exposure of X-ray, long duration of operation, and restrict the application of PELD.
After summarizing the pros and cons of all those previous endoscopic techniques and instruments, we introduced percutaneous transforaminal endoscopic surgery (PTES) in 2017 and confirmed it was an effective and safe method to treat almost all kinds of LDH, including L5/S1 level with high iliac crest, herniation with scoliosis or calcification, recurrent herniation, and adjacent disc herniation after decompression and fusion, with a shallow learning curve [14, 15, 26, 27]. The present study is the first analysis to date exploring the impact of obesity on surgical and functional outcomes following PTES for single-level LDH with or without high iliac crest, scoliosis or calcification. No significant difference was found in operative events and postoperative outcomes between obese and normal groups, which showed a different consequence from the PELD. Herin, we intend to further introduce and discuss the advantages of this effective technique.
First, PTES innovatively introduced modified entrance point, also named as “Gu’s point”, was located at the corner of the flat back turning to the lateral side, which was more medial than other transforaminal endoscopic techniques. The modified “Gu’s point” has four advantages, (1) Avoid interfering with the exiting nerve root which leaves the foramen from superomedial to inferolateral. If the entrance point locates laterally, the foraminotomy may injure the exiting nerve root more possibly and the patient may complain of pain in lower extremities under the local anesthesia surgery. (2) Avoid blockage by the high iliac crest for the L5/S1 level. Peak of the iliac crest locates at the lateral side of the waist and the height lowers down when getting closer to the midline. Height of the iliac crest at “Gu’s Point” is relatively lower, reducing the difficulty of puncture and subsequent operation. (3) Shorten the surgical path. Routine PELD surgery has a more lateral entrance point from the midline, which makes the path for surgical target longer. Especially in obesity patients, more subcutaneous adipose tissue makes the puncture point more distal from surgical target, which needs very long working channel for transforaminal endoscopic surgery, raising the risk of dead space formation and issue necrosis. (4) Avoid injuring abdominal viscera and main blood vessels. Puncture from a lateral entrance point could be dangerous if penetrating into the abdomen. With this simplified entrance point, it was not necessary to take the extra fluoroscopy projection and measuring the distance to the midline for determination. In addition, it is essential to enlarge the foramen through a simple and convenient method, especially in those obese patients who have thicker subcutaneous tissues and more calcified discs. We introduced “press-down enlargement of foramen” technique, which allows the cannula docking at the facet and make the angle of cannula to horizontal plane smaller and a 7.5-mm reamer is performed to remove more ventral bone of articular process for enlarging the intervertebral foramen. For those who had bilateral symptoms, “press-down” technique could decompress not only the ipsilateral nerve root, but also the central dura and the contralateral nerve root. In the present study, we got a satisfactory outcome and low recurrence rate in both obese group and control group. An effective postoperative education also matters in addition to a successful operation. 4 tips were conveyed to patients to prevent recurrence. (1) Avoid bending down. (2) Avoid lifting heavy stuff. (3) Avoid maintaining a posture for a long time. (4) Avoid focusing force on waist while sneezing or coughing. The only one recurrent case in the obese group was found not following these instructions and resumed his work as a porter only one week after surgery.
However, the research has some limitations. First, the sample size of this retrospective cohort study may be slightly small, which could induce bias in the results. Second, the follow-up time is relatively short. The low recurrence rate will be more persuasive to reflect the long-term therapeutic effect of PTES especially on obese patients.