Lateral lumbar interbody fusion at the lumbosacral junction

Due to the obstruction of the iliac crest and the retroperitoneal vessels, lateral lumbar interbody fusion (LLIF) is generally considered contraindicated at the lumbosacral junction (LSJ). In particular the 'rise' of the psoas from the vertebral column in the lower lumbar segments has been associated with significant overlap of the lumbar plexus with the vertebral body and exclusion of a safe transpsoas entry. However in selected individuals anatomical variations may help circumvent the difficulties and the anatomical corridor posterior to the lumbar plexus may provide an alternative to the conventional anterior approach. Currently there is a dearth of information in informing the feasibility. We therefore reviewed the records of three patients in whom LLIF was successfully conducted at the LSJ. The patients' spinopelvic parameters and psoas anatomy were analysed by whole spine standing X-rays and MRI respectively. Intraoperative findings and postoperative outcome were examined. We found that in keeping with published morphometric data, low pelvic incidence (40-50°) appeared associated with 'low-lying' iliac crests which had facilitated lateral access to the LSJ in all cases. Patients with scoliosis provided added advantage when the concave side of the curve was utilised for the approach. A very high 'rising' psoas was found conducive to a novel posterior surgical corridor. No significant neurovascular sequelae were noted. In conclusion, LLIF can be safely performed at the LSJ in selected cases. To our knowledge this is the first report to describe the possibility of a safe LLIF working zone posterior to the lumbar plexus.