Radiographic and clinical outcomes of huge lumbar disc herniations treated by transforaminal endoscopic discectomy

Objectives: Large Central disc herniations (occupying more than 50% of canal area) are notorious as they are generally associated with worse outcomes and are technically difficult to manage. Transforaminal endoscopy (TELD) has evolved to become an interesting alternative for lumbar disc herniations. The aim of the paper is to review our technique of transforaminal endoscopy in large central disc herniations and describe the clinical and radiographic results. We also describe an innovative technique of intraoperative epidurography to assess the adequacy of decompression in some cases with severe canal compromise. Patients and methods: We performed a retrospective analysis of all the patients undergoing TELD from December 2012 to October 2018 for huge central lumbar disc herniations. The procedure was done under local anaesthesia and required a more horizontal approach angle, undercutting of superior articular process and posterior annular release to reach the herniated fragment in the epidural space. In severe cases, a radiopaque dye was introduced via trans-sacral catheter to check the adequacy of decompression. The disc height, lumbar lordosis, segmental lordotic angle on standing radiographs and Canal cross sectional area(CSA) on MRI were evaluated preoperatively and compared with postoperative images at the end of 1 year/final follow-up. The Visual analogue scale(VAS) for Back and Leg pain and Oswestry disability index (ODI), MacNab criteria, return to daily activities, return to work, patient satisfaction rate and recommendation to others were the clinical outcomes evaluated. The percentage of patients achieving the Minimal clinically important difference (MCID) of 3 points for VAS and 12 points for ODI was calculated. Results: A total of 18 patients, with an average age of 35.1years (range 20-61), were operated. The mean VAS back improved from 5.7( +/- 1.77) to 1( +/- 0.77) and VAS leg improved from 7.3( +/- 1.37) to 1.1( +/- 1.09). The ODI improved from 49.88( +/- 11.42) to 13.88( +/- 7.28) at final follow-up. According to MacNab criteria, 17 patients had excellent and 1 had good outcome at final follow-up. The patient satisfaction rate was 90.5%, with 94% patient recommendation rate. All the patients returned to daily activities and work/modified work within a median of 5 weeks. There was 1 patient who required conversion to open surgery due to incidental dural tear, 1 patient who had a remnant disc required a revision tubular discectomy and 1 patient who had recurrence at 6 weeks and again at 2 years which was treated by repeat TELD. Five patients had impending cauda equina. All the patients achieved the MCID for VAS and ODI within a median period of 6 weeks and 3 months, respectively. The recovery rate was 90.1%. Five patients had grade 4 weakness of great toe/ankle dorsiflexion, one also had ankle Flexion weakness preoperatively which improved after surgery. The CSA improved from a preoperative mean of 62.26( +/- 30.3)mm(2) to 122.16( +/- 56.5)mm(2) postoperatively. The CSA improved to 141.05( +/- 63.86)mm(2) at 1 year followup. The average disc height which was 9.71 mm( +/- 2.4) was maintained at follow-up of one year which was 9.21 mm( +/- 2.4). The lumbar lordosis and segmental lordotic angle changed from 27.08 degrees( +/- 15.9) and 2.82 degrees( +/- 5.7) to 35.8 degrees( +/- 8.56) and 4.85 degrees( +/- 4.39) respectively. Conclusion: TELD may be considered as an alternative to microdiscectomy or fusion procedures for huge central disc herniations with favourable outcomes. However, sufficient expertise with the procedure is necessary. Intraoperative decompression may be confirmed with intraoperative epidurography. The patient acceptability of the procedure is good and causes minimal disruption of the normal anatomy.