KeywordsPosterior lumbar interbody fusionTransforaminal lumbar interbody fusionAnte-psoas
Several different techniques have evolved to manage degenerative conditions in the lumbar spine. In situations where lumbar arthrodesis is indicated, interbody fusion can be implemented to indirectly decompress the neural elements, restore alignment, and improve fusion rates as well.
The OLIF utilizes an ante-psoas approach to combine the benefits of the other techniques while minimizing risks to the neurologic structures as well. This retroperitoneal approach minimizes muscular dissection and avoids the lumbosacral plexus by going anterior to the psoas. By coming at an oblique angle, the OLIF is able to obtain reliable access to L4–5 and L5–S1 regardless of the iliac crest levels, which the LLIF is unable to do. Additionally, by not requiring the table to be broken (or “jackknifed”), there is no additional risk for neuropraxia. Overall, this allows for a minimally invasive approach to interbody fusion from L2–S1 with such low risk to the lumbosacral plexus that neuromonitoring is not even required.
The advent of robotic surgery has made simultaneous anterior and posterior surgery possible as well. The OLIF can be performed in the lateral position; meanwhile, pedicle screws can be placed posteriorly through a minimally invasive percutaneous approach as well. This can help minimize time required in the OR.
Most studies in the literature on OLIF are small series with short-term follow-up . In 1997, Mayer first described the ante-psoas approach and then reported on 20 cases with mean 11-month follow-up . Mean OR time was 111 minutes, mean blood loss of 67.8 mL, there were no complications, and all patients fused.
In 2012, Silvestre et al. reported on the largest to date series of 179 OLIF cases, with mean 11-month follow-up . Mean OR time was 54 minutes. They reported several complications, including sympathetic chain injury (1.7%) and vascular injury (1.7%). Fusion rates were not reported. A recent systematic review included 16 articles with no randomized clinical trials or direct comparative studies with TLIF and PLIF . Despite the promising early results and theoretical benefits, future larger prospective studies are necessary to truly clarify the risks and benefits of the ante-psoas approach.
When compared to the posterior approach to the lumbar spine, there are unique anatomic structures at risk when performing an ante-psoas approach to the lumbar spine. Superficially, the initial muscular layers encountered are the external oblique, internal oblique, and transversus abdominus muscles. These muscles are thin and can be traversed with blunt dissection or electrocautery to reach the retroperitoneal space. Care should be taken to avoid damaging the ilioinguinal and iliohypogastric nerves, both branches of the L1 nerve root, as they may occasionally cross the surgical field deep to the internal oblique at the L4–5 level . The lateral position of the OLIF approach is a distinct advantage at this point, because it allows the peritoneal contents to move away with gravity, thereby expanding the surgical corridor .
The surgical corridor is framed by the psoas major posteriorly and the great vessels anteriorly. Imaging studies have shown that the corridor is 16 mm at L2–3, 14 mm at L3–4, and 10 mm at L4–5 and 10 mm at L5–S1 . These corridors can be expanded with gentle retraction, although care must be taken to avoid injuring the lumbar plexus . The lumbosacral plexus lies within the substance of the psoas major, and is positioned more dorsally in the proximal levels, and more ventrally in the distal levels . Since the ante-psoas approach by definition does not traverse the psoas muscle, neuromonitoring is not required.
An important step of the OLIF is preoperative planning . The common iliac vessels must be studied to determine the corridor of approach. A left-sided approach is conventionally used, but analysis of the MRI will help determine, especially at L4–L5, whether the approach will be lateral to the vessels or in between them as would be the case at L5–S1.