TLIF stands for Transforaminal lumber interbody fusion. The surgeon goes in from an angle from the back and side. The entire disc can be removed from one side with TLIF. Other methods like the posterior lumbar interbody fusion (PLIF) require two incisions and entry into the disc space from both sides of the midline.
With TLIF there is less blood loss, less chance of nerve injury, and a shorter operative time. Only one side of the spine is weakened using the TLIF to remove the bone that protects the disc. Other methods compromise the stability of both sides of the spine. Likewise the soft tissues (muscles and ligaments) are only disrupted on one side with TLIF compared to PLIF.
The goal is to reduce complications and improve recovery time. The surgeon is able to use a minimally invasive operation and still get a good fusion for the patient.