Lateral Spine Fusion Surgery

What is Lateral Spine Fusion Surgery?

Lateral spine surgery — also called lateral interbody fusion (LLIF), extreme lateral interbody fusion (XLIF), direct lateral interbody fusion (DLIF), or prone transpsoas (PTP) fusion — is a minimally invasive technique that accesses the lumbar spine from the side, through the flank, rather than from the back or the abdomen. The approach passes through the psoas muscle under continuous neurophysiological monitoring to reach the intervertebral disc, allowing removal of the disc and insertion of a large interbody cage with bone graft.

This approach offers the advantages of avoiding both the posterior back muscles (as in ALIF) and the anterior abdominal vessels (as in ALIF) — accessing the disc via a lateral corridor between the two. Lateral surgery allows placement of the widest possible interbody cages, achieving excellent disc height restoration and coronal plane deformity correction.

Lateral interbody fusion is typically supplemented with posterior pedicle screw fixation through small back incisions to complete the circumferential stabilisation. At One Brain and Spine, lateral spine surgery is referred to by the anatomical description — lateral interbody fusion — encompassing LLIF and PTP.  

When is Lateral Spine Fusion Surgery Recommended?

Lateral interbody fusion (LIF) may be recommended in situations where a spinal fusion is indicated.  These include:

• Lumbar spondylolisthesis (forward slippage) – the forward slippage often results in nerve compression (clinically sciatica/claudication) due to narrowing of the canal or foramen.  
• Spinal deformity including scoliosis (S-shaped curve) or kyphosis (forward hunch)
• Situations where the degree of nerve compression is so extensive that as part of the decompression to relieve nerve symptoms the joints of the spine will be removed
• Recurrent disc prolapse whereby the disc is deemed incompetent, and a fusion is recommended to minimise further disc prolapse
• Back pain where the radiological findings confirm pain from a disc level 
• Adjacent segment disease after prior lumbar fusion
• Revision lumbar surgery — when posterior anatomy is compromised by prior surgery
• When maximal interbody cage size and disc height restoration is required

Lateral spinal fusion surgery is not available for the L5/S1 spinal level due to the anatomical constraints of the pelvis.

What Happens During Lateral Spine Fusion Surgery?

Lateral spinal fusion surgery can be performed in two ways – one with the patient on their side (lateral decubitus) and one with the patient on their stomach (prone).

Lateral Decubitus Surgery

The patient is positioned on their side (lateral decubitus). A small flank incision is made, and the retroperitoneal space is accessed safely in the corridor posterior to the abdominal contents and anterior to the spinal nerves. The psoas muscle is traversed using sequential tubular dilators under continuous EMG neurophysiological monitoring — real-time nerve monitoring is essential to avoid injury to the lumbar plexus nerves passing through the psoas.

A large working retractor is positioned over the disc space. The disc is thoroughly removed and a wide interbody cage (spanning the full width of the vertebral endplates) is inserted with bone graft. This cage is substantially wider than those used in posterior fusion, providing a large fusion surface and excellent height restoration.  The placement of a large cage also minimises the risk of cage subsidence which is a situation whereby the cage collapses into the surrounding bone.

Posterior pedicle screw fixation is typically added through a separate prone positioning and small posterior incisions on the same day or staged as a second procedure. Intraoperative navigation ensures accurate screw placement. Operative time for a single level is approximately 2-3 hours; multilevel procedures take longer.

Prone Lateral Surgery

The patient is positioned prone (on their stomach).  As per lateral decubitus surgery, a small flank incision is made and the retroperitoneal space accessed safely in the corridor posterior to the abdominal contents and anterior to the spinal nerves. The psoas muscle is traversed using sequential tubular dilators under continuous EMG neurophysiological monitoring — real-time nerve monitoring is essential to avoid injury to the lumbar plexus nerves passing through the psoas.

A large working retractor is positioned over the disc space. The disc is thoroughly removed and a wide interbody cage (spanning the full width of the vertebral endplates) is inserted with bone graft. This cage is substantially wider than those used in posterior fusion, providing a large fusion surface and excellent height restoration.  The placement of a large cage also minimises the risk of cage subsidence which is a situation whereby the cage collapses into the surrounding bone.

The main point of difference of prone lateral surgery compared to lateral decubitus surgery is that the patient is already prone for the posterior pedicle screw fixation.  As such repositioning is not required and there are advantages in terms of operative time with single level prone lateral surgeries being approximate 1-2 hours in duration.

Outcomes of Lateral Spine Fusion Surgery

Lateral interbody fusion achieves excellent fusion rates and is particularly effective for multilevel deformity correction and upper lumbar disc disease. Indirect nerve decompression from disc height restoration and foramen expansion achieves good leg pain relief in most patients. Direct posterior decompression can be added if required.

Risks and Complications

• Lumbar plexus injury (<1%) — the most significant specific risk; manifests as anterior thigh numbness, hip flexor weakness, or rarely more significant neurological deficit; minimised by continuous intraoperative EMG monitoring
• Psoas haematoma (<1%)— bruising within the psoas from approach; usually resolves spontaneously
• Approach-related visceral injury (<0.5%)— bowel, ureter, or vessel injury; rare
• Non-union — similar to other fusion techniques (2-5%)
• Instrumentation failure/malposition requiring reoperation (<1%) – rare in with modern techniques including navigation and spinal robotics.
• CSF leak (2-3%)
• General anaesthetic and medical complications (5-10%) – bleeding, infection, anaesthetic reactions, cardio-respiratory complications, DVT/PE etc.