For the treatment of L5 spondylolisthesis, ALIF had some advantages such as hardly any damage of paraspinal muscles and bone structures, less blood loss, faster recovery, bigger cage with possible higher fusion rate because of more touch surface between endplate of vertebra and cage and more graft bone, compared with PLIF or TLIF.[10, 16–18] Many studies have proved that ALIF can achieve similar or better clinical outcomes as that in PLIF or TLIF.[17, 19, 20] ALIF was performed through abdominal paramedian retroperitoneal approach in supine position, which may damage rectus abdominis or its sheath. In this study, we undertook OLIF51 between bilateral iliac vessels through abdominal oblique retroperitoneal approach in a right oblique position, and the mini-incision was located in left lateral abdomen with the external oblique, internal oblique and transverse abdominal muscles bluntly separated in turn for L5/S1. It can protect the rectus abdominis and its sheath, paraspinal muscles, and the right oblique position allowed the abdominal contents to fall away from the operative field and the left iliac vessels and psoas could be exposed clearly, which can give more guarantee to operative safety. The results showed that there was no injury of blood vessels, ureter and abdominal organs. Different from OLIF through the corridor between the psoas and the great vessels in the segments above L5, particular attention should be paid to OLIF51 resulting from that the level of bifurcation of the great vessels also affects access at L5/S1.[8] About 28.3% of the population are not suitable for OLIF through the corridor between bilateral iliac vessels at L5/S1 because the entrance is obstructed by the great vessels. [21] So preoperative CTA is critical to assess the feasibility of operation.
The self-lock cage of ALIF was used in OLIF51 in this study and can provide immediate stability and restoration of lumbar anatomy sequence. AISH, PISH, LL and SLA significantly improved after surgery (p < 0.001). Fusion was achieved in all patients at 2-year follow-up and there was no failure of instruments. No subsidence of cage into vertebral body was found, which was related to protection of cortical endplate during preparation of intervertebral space. The results of study showed that anterior and posterior intervertebral space height significantly increased from 9.7 ± 4.2mm and 2.8 ± 1.4mm, respectively to 16.1 ± 1.0mm (P < 0.001) and 5.5 ± 2.1mm (P < 0.001) after surgery. However, the difference of posterior height of L5/S1 space between preoperatively and postoperatively was much less than that of anterior height, which was related with the cage inserted into L5/S1 from the front to back and the posterior disc space could not be distracted enough. This unbalanced distraction of L5/S1 could not tighten the posterior longitudinal ligament, enlarge the cross-sectional area (CSA) of spinal canal and intervertebral foramen and alleviate the pressure on neurologic elements, which made the efficacy of indirect decompression in OLIF51 unsatisfying. Due to the big cage placed into disc space from lateral side to distract anterior and posterior disc space evenly in OLIF25[22–27], the indirect decompression of OLIF25 is better than that of OLIF51.
If neurologic symptoms were not improved after OLIF51, further posterior surgery was needed for direct decompression, which sharply reduced the advantages of OLIF because of longer operative time under general anesthesia and more damage. We performed PTES[11, 12] under local anesthesia combined with OLIF51 for the treatment of L5 spondylolisthesis. PTES was a transforaminal endoscopic surgical technique with reduced steps, simple orientation and easy puncture, which can significantly decrease the times of fluoroscopy projection and shorten the operation duration[11, 12]. The puncture point of PTES is located at the corner of flat back turning to the lateral side, named “Gu’s Point”[11, 12], which is determined not depending on X-ray fluoroscopy, distance measurement, age, gender and body size. Gu’s point is more medial than other transforaminal endoscopic techniques and has four advantages: (1) avoid injuring the exiting nerve root; (2) avoid blockage by the high iliac crest for the L5/S1 level; (3) shorten the manipulation path especially in obesity patients; (4) avoid injuring abdominal viscera and great vessels. [11, 12] During the procedure of PTES, we performed press-down enlargement of foramen to saw off the ventral bone of the superior articular process so that the working channel can be inserted into the spinal canal even if the puncture angle was 85° to the horizontal plane.[11, 12] In addition, the hypertrophic ligamentum flavum and the protruding nucleus pulposus were removed to expand the lateral recess and reduce the pressure of nerve root. The ipsilateral and contralateral nerve roots can be exposed, and the bilateral nerve roots can be decompressed through unilateral approach in a small incision. PTES before OLIF can achieve direct decompression and avoid another entrance into operation room. The reoperation, even PTES, might put more psychological pressure on the patients and the surgeons especially in China where the doctor-patient relationship is sometimes challenging. The results of this study showed that the VAS of leg pain significantly dropped after surgery and ODI was significantly reduced 2 years after surgery, and there was no reoperation for neurologic decompression.
PTES technique under local anesthesia was used to achieve direct decompression with hardly greater trauma, more blood loss and longer operative time of general anesthesia added to OLIF. This combination of two minimally invasive surgeries protected the paraspinal muscles and bone structures as much as possible, and there was only 25(15–45) ml of blood loss. The frequency of intraoperative fluoroscopy during the operation was limited, and both the patients and surgeons were protected against the radiation exposure. Compared with general anesthesia, local anesthesia had little influence on physical status. Although it took 49.1 ± 5.6 minutes to perform PTES under local anesthesia the duration of OLIF under general anesthesia was only 73.6 ± 8.2 minutes. The length of incision was small, 7.5 ± 1.1 mm for PTES and 46.8 ± 3.8 mm for OLIF (Fig. 4g). The natural corridor for OLIF51 and self-lock cage made postoperative drainage fluid little and when less than 20ml/24h the drain tube was removed usually 1 or 2 days after surgery. Patients could leave hospital as soon as possible and the hospital stay was 4(3–5) days. In this study, no patients had any form of permanent iatrogenic nerve damage and a major complication. All these confirmed the safety of combination of two minimally invasive surgeries.