With advancements in MI techniques and concepts, OLIF and MI-TLIF have become well-established surgical techniques and are extensively used with satisfactory outcomes.[6–8,24,25] Nevertheless, high quality comparative articles are urgently needed to determine the superiority of OLIF versus MI-TLIF procedures. Hence, we conducted this study and obtained preliminary research results, which were generally in agreement with other studies[7,10–13] (Table 3). To the best of our knowledge, this is the first prospective cohort study to evaluate these procedures' outcomes to date.
Consistent with several previous studies,[7,12,13] OLIF was associated with shorter operation times, less estimated blood loss, and muscle injury (lower serum CK level 1 day postoperatively) compared with MI-TLIF. In MI-TLIF, it is time consuming to establish the trans-multifidus decompression channel and complete laminectomy under magnification, damaging the posterior bony structure and paraspinal muscles to some extent and causing massive bleeding. Conversely, it is convenient and almost noninvasive for experienced operators to take the path of the retroperitoneal anatomic corridor and achieve indirect decompression through the restoration of DH in OLIF; the posterior bony structure and paraspinal muscles were preserved and bleeding rarely occurs. Additionally, we found that hospital stays were shorter in OLIF than in MI-TLIF, which was controversial in previous studies.[7,12] In our experiences, preserving the multifidus and posterior column structures in OLIF contributed to earlier off-bed activity and hospital discharge compared with MI-TLIF.
Nevertheless, operation time, estimated blood loss, and muscle injury in OLIF may vary depending on surgical expertise, especially for beginners. Hence, we have provided two technical improvements previously (Video 1 [Supplemental Digital Content 1, https://links.lww.com/BRS/B841]). First, a minimal skin incision is recommended 2 cm back from the normal OLIF incision, facilitating oblique placement in the working channel and the orthogonal maneuver for the cage placement. Second, two special custom-made retractors are used to pull the psoas muscle to the dorsal side and pull the abdominal organs to the ventral side under direct visualization, allowing the convenient and safe exposure of the working channel without radiation.
Recent studies[7,10–12] have reached a consensus that indirect decompression, performed in OLIF, can yield similar clinical outcomes compared with MI-TLIF, as denoted by the ODI score and VAS score of back or leg postoperatively. However, a matched-pair retrospective study demonstrated that the improvement in the VAS for back pain was significantly greater in OLIF than in MI-TLIF 6 weeks postoperatively, although no differences between the two groups were found at further follow-up, explained by avoidance of iatrogenic violation of posterior lumbar elements in OLIF. We found OLIF demonstrated similar improvement of the ODI score and VAS score of back and leg pain compared with MI-TLIF at 1, 3, and 12 months postoperatively. However, not all patients with leg pain could benefit from OLIF. In our experiences, OLIF was effective for dynamic radicular pain, mostly relieved in resting state, but was poor for static radicular pain, existing persistently in resting state. Given the expansion of spinal canal and nerve root canal from dynamic state to resting state, we suppose the degree of nerve compression of static radicular pain may be more severe than that of dynamic radicular pain, which could not be completely relieved by OLIF. Hence, patients with static radicular pain were excluded in our study. Regarding neurogenic intermittent claudication pain, the present study suggest that variation of dynamic mechanical stress on the lumbar spinal nerve roots may be the major cause, rather than static mechanical stress on the spinal nerve roots with each posture or nerve root ischemia. Therefore, patients with neurogenic intermittent claudication pain could benefit from OLIF due to the restoration of vertebral displacement and intervertebral stability and were included.
It is reasonable to conclude that both OLIF and MI-TLIF are associated with satisfactory complication rates, based on the findings of previous studies.[18,28–31] However, only two comparative studies focus on the complication rates of both surgical approaches and draw different conclusions.[7,13] Li et al found that a lower complication rate in MI-TLIF than in OLIF (12.1% vs.29.5%), while Lin et al reported similar complication rates of the two surgical approaches (32% vs. 36%). In our study, MI-TLIF showed a distinct advantage over OLIF with respect to the complication rates (9.7% vs. 29.4%, P < 0.05). Endplate injury, cage sedimentation, and transient thigh pain/numbness primarily accounted for the difference in the complication rates.
In OLIF, the reason for cage sedimentation is multifactorial and includes endplate injury, over-distraction, osteoporosis, or distraction of a severely narrowed disc, etc. Among these factors, endplate injury occupies an important position, mainly resulting from osteoporosis and improper practice. Despite the high incidence of endplate injury and cage sedimentation, the fusion rate of OLIF was similar to that of MI-TLIF in our study, comparable with Li et al's results. Therefore, some researchers believe that cage sedimentation may provide intervertebral stability with efficient bony fusion, enabling better contact with the bone, and facilitating sound fusion. We found five patients experienced transient thigh pain and/or numbness in OLIF, mainly due to the violation of the psoas major and lumbar plexus. Although the low incidence of lumbar plexus intervention in our patients is in line with reported results,[7,32,34] reasonable precautions should be taken to reduce the incidence. Fortunately, the symptoms were transient and resolved completely with conservative treatment 1 to 2 weeks postoperatively.
Literature revealed that the postoperative restoration of DH, SLA, and LLA between OLIF and MI-TLIF is still debatable.[7,10–13,35] A recent meta-analysis demonstrated very similar restoration of DH, SLA, and LLA between OLIF and MI-TLIF. Conversely, several studies[10–13] concluded that OLIF is superior to MI-TLIF with regard to the restoration of DH, either in the immediate postoperative period or long-term follow-up but not in the restoration of SLA and LLA. We found that OLIF had a distinct advantage over MI-TLIF in terms of the restoration of DH and LLA, both in the immediate postoperative period and long-term follow-up, but not in the case of SLA. This finding may be associated with several reasons. First, the cage of OLIF is much bigger than that of MI-TLIF, which results in bigger restoration of DH directly and can be placed on the rigid epiphysis ring around the vertebral body, in favor of distracting disc space and compressing the posterior column to restore LLA. Second, the cage radian from front to back is 6° or 12° in OLIF, but 0° in MI-TLIF, which is beneficial to the restoration of LLA directly. Third, compared with OLIF, the greater damage of paraspinal muscle and posterior tension band in MI-TLIF may decrease the stability of the spine and break the balance of the posterior column element of the abdominal muscles, leading to a compensatory decrease in LLA,[36,37] which may be the reason for the correction loss of LLA after MI-TLIF at the long-term follow-up.
Direct evidence of the effectiveness of spinal decompression was based exclusively on radiological parameters. From above results, the indirect decompression of OLIF has certain advantages over MI-TLIF, but only if patients meet certain indications of OLIF, listed in the inclusion criteria. Unfortunately, the exact indications for indirect decompression remain inconclusive and contradictory. Specifically, some patients were reported unsuitable for indirect decompression, such as those with calcified discs, severe facet hypertrophy, synovial cysts, severe central canal stenosis, uncontained disc herniations, and osteophytes arising from the posterior endplates.[38–40]
This study has some limitations. First, in our study, patients grouping were not random, resulting in some bias, such as cofounding bias and selection bias, and compromising the outcomes. Second, the statistical results with "P > 0.05" of our study, especially for patient-reported outcomes, have a high possibility of type II error resulting from small population differences (δ), big individual differences (SD) and small sample size. Hence, multicenter, large sample prospective randomized trials with long-term follow-up periods are warranted for a more comprehensive evaluation.
In conclusion, compared with MI-TLIF, OLIF showed similar results in terms of patient-reported outcomes and fusion rate, and superior results with regard to perioperative data and radiographic outcomes. The complication rate of OLIF was higher than that of MI-TLIF, primarily owing to the endplate injury, cage sedimentation, and lumbar plexus intervention, which do not adversely affect the clinical and radiographic outcomes. Hence, with a rich experience in lumbar anterior or lateral surgery, surgeons could give preference to OLIF for the treatment of lumbar degenerative diseases.
This work was sponsored by the National Key R&D Program of China (No. 2020YFC1107100), National Natural Science Fund of China (81472064, 81672150), Zhejiang medical and health science and technology project (2018KY117, 2019ZD041), new talent in medical field of Zhejiang Province, and the fundamental research funds for the central universities (2019QNA7027).
No relevant financial activities outside the submitted work.
Spine. 2022;47(6):E233-E242. © 2022 Lippincott Williams & Wilkins