Once FLLDH was suspected according to the clinical manifestations, physical and radiological examinations ought to be adopted subsequently. Manual muscle testing, sensory testing, supine straight-leg raising, Lasegue sign, and crossed Lasegue sign were recommended for diagnosis [16]. However, FLLDH was prone to be ignored on conventional sagittal and axial MRI scans because the extrusion was not intracanal. DTI has been proven to be an effective tool to locate injured nerve roots at the very early time [17, 18]. Conservative treatment for FLLDH with only 10% success rate was reported,5 and surgical intervention was necessary.
PELD, with the advantages of minimal injury, postoperative pain relief, short hospital stays, and early return to daily life or work, has been widely used to manage FLLDH. Jang et al. [19] applied PELD to 35 patients with FLLDH. The mean VAS improved from 8.6 before operation to 3.2 after operation, and 30 patients (85.7%) obtained excellent results. Cho et al. [20] utilized PELD in 41 patients with FLLDH, with an average follow-up of 34.1 months, and the excellent and good curative effect rate was 92%. Fifteen patients diagnosed with FLLDH underwent PELD in the study conducted by Liao et al. [10] gained an overall excellent and good rate of 93.3%. Ren et al. [21] concluded that PELD had a shorter operation time and less surgical trauma, being a less invasive and more economical method for middle-aged and elderly FLLDH patients. A research conducted on 22 patients with FLLDH at the L5-S1 level and treated by PELD also revealed that overall excellent or good outcomes were 81.8 % [22].
Nevertheless, when FLLDH was at L5/S1 level, even at L4/5 level in some patients, due to the presence of high iliac crest or/and transverse process hypertrophy, it was difficult to insert the working canula of PELD [23, 24]. Choi et al. [12] retrospectively evaluated 100 consecutive patients underwent PELD via the transforaminal route for L5/S1 disc herniation and concluded that conventional transforaminal access could be utilized with ease in low iliac crest cases where the iliac crest was below the mid-L5 pedicle in lateral radiography. Therefore, some other approaches ought to be considered to be treatment choices for FLLDH patients with high iliac crest. In 2009, Choi et al. [14] first created a transiliac approach to treat a 51-year-old man manifested left gluteal and leg pain due to an up-migrated soft disc herniation at the L4/5 level and achieved complete decompression of the nerve root Bai et al. [11] also employed a transiliac approach in 19 patients and described the safety and clinical efficacy of the technique. They achieved good clinical outcomes. However, no obvious anatomical positioning mark on the ilium surface could be used to locate the vessels superior gluteal artery and other blood vessels accurately, which could lead to severe and uncontrollable bleeding. Besides, the working channel mobility was determined by the diameter of the hole in ilium, while big hole could cause fracture of the ilium.
In 2016, Chun et al. [4] reported a modified PELD technique for one case of FLLDH at L5/S1 level. Based on the preoperative MRI, the skin entry point was closer (9 cm) and the angle of needle insertion was steeper (42°) than those of traditional transforaminal approach (10 − 13 cm, 25 − 30°). The final target point for introducing the spinal needle was the medial pedicular line on the anteroposterior image and the posterior vertebral line on the lateral image. At consecutive follow-ups, the patient continued to report complete pain relief. In 2018, Yang et al. [25] introduced another modified PELD technique to remove extraforaminal disk herniation at the L5/S1 segment. The distance from possible skin entry points to midline varied from 33.28 to 84.18 mm. Clinical symptom relief after surgery was obtained, while no neurologic deficit or surgical site infection occurred.
The modified posterolateral PELD technique in our study was similar to that described by Yang et al. The skin entry point was 6–7 cm lateral to posterior midline in the disc plane and the needle insertion angle was about 20°. The target position was the triangle compassed by sacral ala, L5 transverse process and S1 SAP. The mean incision length was 0.74 cm, operation duration was 55.64 minutes, the blood loss was only about 27.42 ml and hospital stays were less than 4 days. During the follow up, the postoperative VAS and ODI scores dropped while M-JOA scores grew significantly, comparing with those at pre-operation. FA, based on DTI, is a parameter of anisotropic strength. The FA value of the compressed nerve root tended to lower than that of the normal nerve root and could be an indicator for injured nerve root [18, 26, 27]. In our study, the FA value of nerve root at affected side at post-operation was higher than that at pre-operation, which was consistent with the dynamic change of clinical scores, further indicating an effective relief of symptoms. At the final follow-up, the overall excellent and good rate was 94.12%. Above results demonstrated that PELD via a modified posterolateral approach was an effective and minimally invasive choice for FLLDH at L5/S1 with high iliac crest.
In this study, only one patient suffered from recurrent herniation and the overall complication rate was 5.88% (1/17), which was approximately to 3.6%-7% reported by several literatures [28, 29], probably because of the small diameter of the working channel and limited operation window. While the protruded nucleus pulposus was eliminated, the remaining nucleus fragment could herniate through the breach, so it was recommended that the working canula should be appropriately rotated to detect and remove residual nucleus pulposus as fully and widely as possible to reduce the recurrence rate. No other complications, such as neurologic deficit, surgical site infection and cerebrospinal fluid leakage were detected. Above results suggested that PELD via a modified posterolateral approach was safe for FLLDH at L5/S1 with high iliac crest.
PELD could be performed under local anesthesia, and the effective doctor-patient interaction during the operation produced a positive significance for avoiding nerve root damage. Furthermore, the posterior spinal structure was better preserved, which generated little effect on the stability of the spine and permitted early straight exercises. The operation field was clear under constant irrigation with normal saline, which also limited blood loss. Finally, the spinal canal was free to be invaded to avoid interference or accidental injury to the dura sac and nerves.
However, there were some limitations in our study. This was a retrospective study and lack of strict double-blind randomized control. The sample size was relatively small, and the follow-up period was relatively short. The learning curve of PELD remained steep and mass practice was required to avoid iatrogenic injuries.