Minimally invasive surgeries including endoscopic surgery and mini-open surgery are current trend of spine surgery, and its main advantages are shorter recovery time and cosmetic benefits, etc. [6
]. However, mini-open surgery is easier and less technique demanding than endoscopic surgery. The advantages of anterior over posterior spinal fusion are numerous, including the physiological loading, ease of dissection, reduced operation time and blood loss, noninterference with the potentially painful posterior elements of the lumbar spine, back muscle function, and avoidance of scarring within the spinal canal [23
Anterior lumbar diseases means the etiologies of the diseases originated from anterior aspect of lumbar spine. That’s why we used the mini-open anterior spine surgery (MOASS) to treat patients with anterior lumbar diseases. MOASS technique can restore disc height at the anterior column and open up the neural canal and foramen, alleviating compression of the dural sac and nerve roots. In this study, the MOASS technique can increase disc height by 10.33 mm, with a further loss of 3.67 mm. Disc height elevation can increase spinal canal volume by 20% and the neural foramen area by 40% [5
]. Lack of paravertebral muscle and facet joint dissection may also reduce the risks of subsequent junctional problems. Therefore, the MOASS technique is justified and an alternative for decompressing neurological compromise, alleviating the instability or mechanical pain of failed-back syndrome.
Since, in 1997, Mayer first reported a new microsurgical technique for minimally invasive anterior lumbar interbody fusion, it has spawned siblings in many fields [9
]. Although endoscopic approach is developing rapidly, mini-open approach is still considered better, especially for the retroperitoneal area [6
]. The endoscopic approach requires a long learning curve, usually by cadaver or animal model. Even an experienced surgeon would need a considerable amount of time. Loss of depth sensation, followed by complications, is not uncommon. This technique can also be quite frustrating [14
]. We prefer the mini-open approach like the MOASS surgical technique for anterior lumbar spinal diseases.
Solid bony fusion was obtained in 82% of patients with posterolateral lumbar fusion; 65% rated themselves significantly improved by the procedure while only 19% achieved a good or excellent Low Back Outcome Score. These results, however, were inferior to a similar series involving anterior lumbar fusion [13
]. Compared to posterior spinal fusion, anterior spinal fusion is much better in terms of physiological loading, back muscle functions, nerve retraction and possible nerve adhesion [14
]. A comparison study proved this point of view [23
]. However, long-term surgical outcomes have been reported only for anterior fusion [22
]. In the surgical technique of MOASS, we avoided ligation of the segmental artery; thus shortened operation time, decreased blood loss, and probably promoted bone fusion. We believe that the bone grafting technique was the key to stability, regardless of the graft used. Filling the decompressed space with strut graft materials was mandatory. Only one rod and screws fixation system was used for holding the grafts, and PMMA cement hybridized with interpore or cement grafts were sometimes used for augmentation of fixation in some osteoporotic patients. Our fusion rate (95%) was better than those reported for combined anterior and posterior fusion [16
], which possibly because of fusion technique and the preservation of segmental vessels. Using the MOASS surgical technique, we can effectively achieve anterior spinal fusion without additional posterior surgery in patients with anterior lumbar diseases.
Although no published studies have proven that this minimally invasive technique is superior to conventional ones, patients benefit from decreased postoperative pain, shorter hospital stays and earlier returns to work, as seen in our patients. In view of our results, the MOASS surgical technique can be applicable to various diagnoses, including vertebral fracture, failed back syndrome for supplemental or remedial fusion, segmental instability or spondylolisthesis, infection, herniated disc, undetermined lesion for biopsy and even resection of hemivertebra.
Posterior lumbar microendoscopic discectomy and percutaneous lumbar discectomy are both feasible and effective treatments for disc herniation [2
]. However, the MOASS technique provides an alternative for disc herniation especially in thoracolumbar junction, and can be considered for lateral artificial disc implantation in the near future.
Complications such as neurovascular injury, pre-sacral plexus injuries, ureter injury, urinary retention and retrograde ejaculation were absent from our series. However, one patient with mycotic aneurysm had maximum blood loss, but was successfully treated by in situ graft replacement. Nine patients had warm legs on the lesion side. The retraction screw and blade decreased the risks of vessel injuries and thrombosis. Normally, vascular injuries occur easily at the L4–L5 levels [1
]. We obliquely inserted polyaxial screws and avoided ligating segmental vessels. None of our cases presented vascular injury, including those with L4–L5 lesions. However, there was still one case of abdominal muscle sagging, which might have been caused by traction neurapraxia of the abdominal nerves.