Operative technique

Each patient in Group A was placed in the prone position under general anaesthesia. A 4–6 cm posterior midline incision was made with the deteriorating segment positioned in the centre. The lumbar fascia was exposed, and the attachment of the spinalis muscle was cut near the spinous process so that the supraspinous and interspinous ligaments were preserved. The soft tissue behind the laminae was stripped to reveal the intervertebral space, upper and lower lamina and small joints. A laminar rongeur was used to remove the ligamentum flavum between the lamina and small portions of the upper and lower lamina adjacent to the deteriorating segment; thus, interlaminar fenestration was performed. A neuroexfoliator was used to separate and gently retract the nerve root, revealing the intervertebral disc. The fibrous ring was cut, and the nucleus pulposus was removed with dedicated forceps. The incision was closed [4, 12].

Each patient in Group B was placed in the lateral recumbent position. C-arm X-ray was used to locate the surface projection of the intervertebral space of interest. An entry point was made 12–14 cm from the posterior midline of the spine at the level of the disc. Local anaesthesia was administered (1% lidocaine). A puncture needle was slowly advanced to the fibrous ring in the intervertebral space and positioned at the outer edge of the superior articular process. It was located lateral to the intervertebral space near the upper edge of the lower vertebra. One millilitre of methylene blue was injected into the intervertebral disc for contrast radiography. A guidewire was inserted, and X-ray was used to confirm that the tip of the guidewire had crossed the articular process and then the puncture needle was withdrawn. An 8 mm incision was made at the entry point. The cannulas were passed from thin to thick along the guidewire, and the superior articular process was partially removed with a ring drill. The working cannula was then inserted into the epidural space. A transforaminal endoscope (TESSYS® [transforaminal endoscopic spine system], joimax® GmBH, Germany) was inserted, and the degenerative, blue-stained intervertebral disc was removed. Part of the nucleus pulposus was ablated by a radiofrequency electrode (Ellman, USA). The spinal canal was assessed carefully, and the nerve root was detached. After the wound was rinsed, the fenestrated fibrous ring was repaired by electrocoagulation. The working cannula was then removed, and the incision was closed [8].