PLIF and TLIF are established procedures for lumbar fusion. However, these techniques are associated with complications like paraspinal muscle injury, damage to posterior support structures, prolonged muscle retraction, difficulty in disc space visualisation and preparation, need for revision surgery [1, 10]. These led surgeons towards indirect decompression which relies on restoration of disc height leading to increase in foraminal height, stretching of ligamentum flavum and posterior longitudinal ligament restoring central spinal canal [11]. OLIF and lateral lumbar interbody fusion (LLIF) provide advantages like, indirect neural decompression with solid bone fusion, large cage insertion, low risk of cage subsidence, less incidence of dural tears. Compared to posterior procedures, there is better restoration of coronal and sagittal profile [12, 13]. One of the indirect decompression procedures is LLIF which utilizes trans-psoas route [14]. But LLIF has unique disadvantages like lumbar plexus injury and psoas muscle weakness [15]. With conventional LLIF, C-arm usage is necessary and navigated implants and instruments are difficult to use. For these reasons, OLIF has received considerable attention as it provides enhances the visual operative field, reduces, neurological complications, approach is anterior to psoas and navigated implants are available [1, 13, 16].
Traditionally with OLIF procedure, a cage is inserted in lateral position and PPS is done in prone position. This needs change of position leading to increase surgical time. It has been proved that single position OLIF reduced surgery time by almost 60 minutes [7, 8]. Another comparative study reported that, navigated single position OLIF reduces operative time by 30 minutes compared to repositioning OLIF [17]. With our technique, OLIF can be performed under navigation in lateral position in single sitting with simultaneous interbody fusion and PPS fixation. With our procedure, mean operative time reduces by around 60 minutes compared group P/T. This less operative time reduces medical cost and allows faster turnover of cases. With OLIF there is less tissue trauma and no damage to posterior structure. Due to this reason patients can be mobilized and discharged earlier [16]. The time for ambulation in our study for group SO was 2.7 ± 1.0 days while that in group P/T was 3.9 ± 2.4 days. Clinical results of ODI and VAS were no difference between two groups. This indicates indirect decompression was effective for group SO (OLIF cases). In our patients operated with OLIF, DH increased by 64%, FH by 25% and FA by 30% due to indirect decompression. Lin et al. in their study showed that after OLIF, DH, FH, FA increased by 49%, 19% and 64% respectively [6].
The total complication rate in group SO was 6.3% and that in group P/T was 14.1%. In the study by Lin et al complication rate was 36% in the OLIF group and 32% [16]. A meta-analysis reported that complication rate after OLIF was 26.7% with psoas weakness being most common complication [18]. There are less complications in OLIF our cases compared to literature [19–21]. This can be because of use of neuromonitoring and O-arm navigation. Though not statistically significant group P/T showed better correction of SL compared to group SO in our patients. This can be because of use of lateral position for OLIF which does not allow for greater correction of lordosis.
There is concern about radiation hazard is for MIS surgeons and staff working high volume centres. Our O-arm navigated C-arm free technique is without any radiation exposure to operating staff. There is argument about increased radiation to patients, but it has been observed that it takes around 20 to 24 seconds to get O-arm scan. This is equivalent to 1.5 minutes of fluoroscopy [22]. We further reduce radiation exposure to patient by setting low field of view and low dose mode of O-arm.
Though indirect decompression being an excellent method, it too has some limitations. It has been reported that indirect decompression fails to give good results in severe central canal stenosis, gross motor deficit and cauda equina syndrome [22]. There are limitations of our study. Foremost, sample size in group P/T was relatively smaller than in group SO, with increased sample size required to confirm our findings. The preoperative FH was higher in group SO than group P/T, this can be selection bias of surgeon towards PLIF or TLIF for severely stenotic cases. Further research is warranted to clarify the long-term clinical outcome.