Ante-Psoas Approach for Lumbar Interbody Fusion

(1)

Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA

(2)

Department of Spine Surgery, New York-Presbyterian/The Allen Hospital, New York, NY, USA

Keywords

Posterior lumbar interbody fusionTransforaminal lumbar interbody fusionAnte-psoas

Background

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.

As interest in interbody fusion has risen, various approaches have been developed to achieve fusion in a minimally invasive fashion (Fig. 21.1). Traditional posterior lumbar interbody fusion (PLIF ) and also transforaminal lumbar interbody fusion (TLIF ) techniques approach the intervertebral space posteriorly by traversing the paraspinal musculature; without wide facetectomies and meticulous disc space preparation, these for most surgeons induce kyphosis with insertion of small interbody cages. Anterior approaches have been popularized to obtain fusion in minimally invasive fashions. These anterior approaches include the anterior lumbar interbody fusion (ALIF ), the lateral lumbar interbody fusion (LLIF) , and the oblique lumbar interbody fusion (OLIF ). The ALIF technique allows surgeons to gain access to the lower spinal levels but is associated with risks such as vascular injury and retrograde ejaculation. LLIF has been developed to approach more proximal lumbar levels but is often unable to reliably access caudal levels; it also involves an approach through the psoas muscle, which puts the lumbosacral plexus at risk.

../images/441526_1_En_21_Chapter/441526_1_En_21_Fig1_HTML.png — Fig. 21.1

Axial image of the L4–5 level in a patient with prior Harrington instrumentation down to L4. Arrows indicate various approaches to the lumbar interbody space including (clockwise): ALIF, OLIF, LLIF, TLIF, and PLIF

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 [1]. In 1997, Mayer first described the ante-psoas approach and then reported on 20 cases with mean 11-month follow-up [2]. 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 [3]. 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 [1]. 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.

Anatomy

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 [2]. 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 [4].

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 [5]. These corridors can be expanded with gentle retraction, although care must be taken to avoid injuring the lumbar plexus [6]. 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 [7]. Since the ante-psoas approach by definition does not traverse the psoas muscle, neuromonitoring is not required.

Surgical Technique

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.

Then, the patient should be positioned in right lateral decubitus position so that the left-sided approach can be utilized (Fig. 21.2). A radiolucent table in slight Trendelenburg should be used for radiographic visualization, and the patient should be placed anteriorly on the table so that the abdominal contents hang ventrally away from the operative field. Bony prominences should be padded, and tape should be used to prevent movement of the patient during the operation. A 270-degree prep and drape should be applied to allow for complete abdominal and posterior access as needed.