Interbody fusion

General

They allow placement of significantly larger interbody implants for greater disc space height restoration and indirect decompression, reducing pseudarthrosis risk.

LLIF and OLIF are ideal for levels from thoracic spine down to L4-5, utilising the retroperitoneal space.
OLIF and ALIF avoid lumbar plexus dissection but require manipulation of aorta and iliac vessels.
Real-time and directional stimulation during LLIF helps ensure optimal entry through safe working zones in the psoas muscle, reducing femoral nerve injury risk.
The L5-S1 disc space cannot be accessed by transpsoas LLIF due to iliac crest anatomy; ALIF and OLIF are used here.

Pre-Operative Evaluation is crucial to reduce complications in ALIF, OLIF and ExLIF:

MRI for vessel, psoas muscle, and visceral structure location.
CT scan for osteophytic changes or ankylosed segments.
Standing 36-inch AP and lateral radiographs to identify iliac crest height and coronal Cobb angle for surgical access from the concave side.

Criteria	MIS TLIF	ALIF	OLIF	UBE Fusion
Op time	Fastest	Slow	Fast	Slowest
Difficulty	Easy	Difficult	Easiest	Difficult
Complication	Rare	Rare but serious	Rarest	Uncertain yet
Neural decompression	Direct Sufficient	Indirect	Indirect	Direct
Advantage	Easy Familiar	Biggest lordotic angle correction	Easiest Safest	Fancy Low level infection rate
Disadvantages	Not fancy Not trendy	Needs access surgeon	Position change Psoas and Oblique muscle symptoms	Technically not familiar Time consuming

ㅤ	Procedure Description	Advantages	Disadvantages
PLIF	Posterior midline incision in prone position; requires laminectomy and retraction of thecal sac and nerve roots to reach the intervertebral disc space	• ▪Favors adequate visualization of the thecal sac and nerve roots • ▪Allows direct decompression of the spinal canal and nerve roots	▪Risk of damage to thecal sac and nerve roots during retraction▪Paraspinal scarring▪Limited coronal correction▪Allows insertion of only smaller cages
TLIF	Posterior incision with a more lateral trajectory; requires facetectomy to allow visualization of nerve roots and perform discectomy	• ▪Limited retraction of nerve roots • ▪Preservation of posterior midline structures • ▪Can be performed as a minimally invasive procedure	▪Risk of damage to thecal sac and nerve roots during retraction▪Paraspinal scarring▪Limited coronal correction▪Allows insertion of only smaller cages
ALIF	Longitudinal midline or paramedian incision to access retroperitoneal space in supine position	• ▪Spares paraspinal musculature • ▪Preservation of posterior elements • ▪Allows for direct implantation of a wide-bodied cage • ▪Optimal restoration of lordosis	▪High risk of injury to visceral and vascular structures due to mobilization of great vessels▪Sympathetic hypogastric plexus injury

Grade I: No fusion connection between upper and lower parts with loss of height and bone graft resorption.
Grade II: No connection, but an increase in bone volume compared to immediate postoperative bone graft volume.
Grade III: Partial (about 50%) connection between upper and lower parts but with significant radiolucent lines.
Grade IV: Good fusion with minimal radiolucent lines.
Grade V: Complete fusion with good shaping.

If patient has back pain that is relieved on bending forwards or lying down then it is likely indirect decompression works