Prone Transpsoas Lumbar Interbody Fusion for Degenerative Disc Disease.

Abstract

Background: Prone transpsoas lumbar interbody fusion (PTP) is a newer technique to treat various spinal disc pathologies. PTP is a variation of lateral lumbar interbody fusion (LLIF) that is performed with the patient prone rather than in the lateral decubitus position. This approach offers similar benefits of lateral spinal surgery, which include less blood loss, shorter hospital stay, and quicker recovery compared with traditional open spine surgery. PTP offers additional benefits over traditional lateral positioning, with a more familiar patient position for spine surgeons, the ability to perform simultaneous posterior decompression and fusion without repositioning, and improved sagittal alignment.

Description: PTP is performed with the patient under general anesthesia and with use of somatosensory evoked potentials (SSEP) and electromyography (EMG) neuromonitoring. The patient is positioned prone with the aid of specialized patient positioners. Once the patient is positioned and draped, the disc space of interest is marked with use of fluoroscopic guidance. An incision is made, and blunt dissection is performed through the external oblique, internal oblique, and transversalis muscles. The psoas muscle is palpated, and dilators are placed at the target disc level under fluoroscopic guidance, with care taken to protect the peritoneum and lumbar plexus. Specialized retractors are then positioned. Anulotomy and disc removal, disc space preparation, trialing, and final interbody placement are performed. The procedure ends with obtaining hemostasis and closure of the incision.

Alternatives: Before surgery is performed, nonoperative treatment should be attempted, including the use of nonsteroidal anti-inflammatory drugs, physical therapy, and spinal injections. Surgical alternatives include posterior lumbar laminectomy with or without fusion, as well as other procedures in the anterior column, such as LLIF, anterior lumbar interbody fusion, oblique lumbar interbody fusion, transforaminal lumbar interbody fusion, and posterior lumbar interbody fusion. These alternatives must be considered, especially when working at the L4-S1 disc spaces, because of potential limitations to lateral surgery, such as in cases of high-riding iliac crests, a rising psoas, and previous abdominal surgery.

Rationale: Lateral spinal surgery evolved as a means to approach the anterior column of the spine in order to treat various spine disorders, such as degenerative disc disease, tumors, infection, and spinal deformity. With the PTP procedure, the patient is in the prone rather than the lateral decubitus position, which allows the psoas muscle to retract more posteriorly because it is under tension, pulling the lumbar plexus away from the target point of the procedure. In addition, the prone position results in improved sagittal alignment compared with the lateral position. With respect to sagittal alignment, the PTP procedure allows for more appropriate balancing, which improves clinical outcomes. The peritoneum is also farther away from the operative zone during PTP, providing a safer corridor away from the bowel and ureter. For these reasons, PTP can potentially lead to improved outcomes compared with a lateral procedure performed with the patient in the lateral decubitus position, while also minimizing the risk of bowel and bladder injury and neurapraxia. In addition, PTP eliminates the need for repositioning or staged procedures. For instance, posterior laminectomies and fusions can be efficiently performed with the patient in the prone position, possibly simultaneously with the PTP procedure, whereas repositioning and redraping would be required with a lateral approach.

Expected outcomes: PTP has several advantages over traditional posterior spinal surgery. These include a shorter hospital stay, decreased blood loss, and faster return of mobility. Specifically compared with a lateral approach with the patient in the lateral decubitus position, PTP may result in better segmental lordosis and spinopelvic alignment. To date, overall outcomes are otherwise similar between lateral decubitus and prone transpsoas approaches.

Important tips: Make sure to adjust the table to waist height and keep your elbows at 90° of flexion while working on localization of the disc space. When doing disc work through the retractor, either raise the bed or sit in a chair to make sure that the disc space is at eye level, so that you are not straining your neck.During dissection, utilize finger dissection and avoid the use of electrocautery as it can cause neurapraxia and result in flaccid oblique musculature and subsequent pseudohernia.To reduce the risk of peritoneal injury, a 2-incision technique can be performed: Place a finger in an accessory posterior incision (either a midline incision or the percutaneous screw incision) to initially palpate the tip of the transverse process. Next, slide your finger into the retroperitoneal space and feel the psoas medially. Place another finger through the lateral incision, and touch both fingers together to ensure you are in the retroperitoneal space with your dilators.Another trick is to start the incision more posteriorly, as gravity will force you more anteriorly during localization.When placing the cage, the goal is to have it as anterior as possible in order to gain maximal lordosis and to span the apophyseal ring to reduce the risk of subsidence. In addition, placement of the widest possible cage can help reduce subsidence, with 18-mm cages showing greater subsidence than 22-mm cages.

Acronyms and abbreviations: PTP = prone transpsoas lumbar interbody fusionLLIF = lateral lumbar interbody fusionALIF = anterior lumbar interbody fusionOLIF = oblique lumbar interbody fusionTLIF = transforaminal lumbar interbody fusionMRI = magnetic resonance imagingNSAID = nonsteroidal anti-inflammatory drugCT = computed tomographyEMG = electromyographyAP = anteroposteriorK-wire = Kirschner wireIV = intravenousSSEP = somatosensory evoked potentials.