In this study, a CT scan was used to produce digital images, and from the data the morphometry of the lumbar vertebra was calculated. The choice of using CT scan images in this study was because the resulting three-dimensional image can be rotated without changing its shape, and the axis of the resulting digital image can be determined and maintained. Research by Wu et al. in 2015 showed that data obtained by CT scan had the same value compared to the results of direct cadaveric measurements.5
In the practice, during the process of inserting a needle posterior and laterally into the disc, the clinician must determine the appropriate distance from the midline and the right angle for the type of pathology being treated. Needle alignment was easier at all lumbar levels except at the L5-S1 level, which requires special consideration. If the needle was targeted too vertically, it was possible to penetrate the contents of the peritoneum, especially the sigmoid colon on the left side. This risk was of great concern if the same needle that has penetrated the colon was mistakenly used to pierce the disc. This makes a very high chance of contamination from the avascular disk space which eventually leads to postoperative infections. The exiting nerve root is also very close to the instrument pathway. Extreme horizontal passage of the needle can cause dural injury if it tries to penetrate the disc over the midpedicular line.
All of the above-mentioned challenges exist in this procedure. These complications would be the least expected outcomes of this procedure. Starting from the most common complications of PELD, the main risks are transient paresthesia, postoperative hematoma, and dura sac tear. There was 4.06% (406/10,120) estimated incidence rate of transient paresthesia. The compression of the working tools to the exiting nerve root was the most common cause of transient paresthesia. Reduced foramen height, intraforaminal or far lateral disc herniation, and the wrong location of the working tools were all risk factors.3,4 Next, the hemorrhagic complications reported after transforaminal PELD were minor and did not necessitate extensive care. However, the current situation was very frequent and inconvenient. The key cause of bleeding was an injury to the internal vertebral venous plexus and cancellous bone.6 The last common complication is dura sac tear. Instrument or radiofrequency damaging to the dura mater, spinal canal adhesion, giant disc fragments, and a loosened dura are all risk factors for dural sac tear. The majority of dural sac tears occur during disc resection. Some lacerations may be identified and fixed during surgery, while others may be overlooked due to their minor scale.
Another rare complication of PELD should not be neglected. Incidence of intervertebral infection after spine surgery span from 0.1–0.4% with most cases caused by bacterial infection. Recurrence of disc herniation could also be another complication of PELD due to the lack of operator skill and experience or due to patient conditions such as obesity and age.4
Needle insertion angle
From the results of this study, we obtained the angle of insertion of needles in the axial plane of 22–48° and the sagittal plane of 78°. In the Yeung and Tsou PELD techniques, they chose a needle insertion angle of 25–30° in the axial plane. According to Kim et al. in 2018, the angles can range from 38–68° at the T12-L3 level and 40–65° at the L3-S1 level. The inclination angles in the sagittal plane required for needle insertion are very subjective and vary from patient to patient, depending on the location of the pathology. But usually, the needle was directed from the cranial to the caudal, towards the inferior endplate at an angle of 10–15° from the axial plane or 77–80°.7,8
Needle insertion distance
Yeung and Tsou describe a general technique for all types of disc herniation using an endoscope inserted via the transforaminal route. The entry points of the skin are described as being at around 12 ± 2 cm from the midline of the body.7
Lew et al. also reported their experiences in handling far lateral and foraminal herniation using transforaminal endoscopic techniques in 47 patients. Their technique was not much different from the Yeung technique and chose an entry point that was located 8–12 cm from the midline.9
From other studies, the insertion distance of the needle from the midline of the body between ranged between 8–14 cm (Shin et al.), 10–13 cm (Xu et al.), 10–15 cm depending on the patient's body size (Ahn et al.), and 12 cm (Li et al.). According to Kim et al. in 2018, the portal can be made at a distance of 7.5–10 cm from the midline of the body where the discoscopy can be performed safely in the triangular zone.8,10,11
One key to success from endoscopic spinal surgery is proper surgical techniques; a practitioner must be very skilled in performing endoscopic operations. We can find various conditions in actual practice at the L5-S1 or C6-7 levels or other inaccessible levels as herniation of migrated discs, highly compromised spinal canals, stenotic foramen, and advanced spondylosis. For such cases, special techniques may be needed for effective decompression to avoid complications.11,12
Regarding the transforaminal approach, the needle landing point should be as close as possible to the pathological target and as far as possible from the exiting nerve root. The various needle insertion points obtained in this study were around 8–17 cm, while other studies were in the range of 8–15 cm depending on the patient. Accordingly, these results show that there are variations in needle entry but they are still in the close range as in other studies.13