@domiha ALIF (anterior lumbar interbody fusion) is the name of the procedure to remove discs and fuse from the frontal approach. The reason for 2 surgeries is that there must be 2 different surgical paths, one from the front (anterior) to access removal of discs and placing spacers or cages. You can't access that from the back of the spine because you cannot severe the spinal cord that is right behind the discs to get to the discs. The rods must be attached on the back of the vertebrae on both sides and you can't do that with a patient on the table laying on their back.

There are other factors like how long does a surgery take with however many levels that are involved?, the anesthesia time, and fatigue of the surgical team. Most surgeons are standing on their feet leaning against and over the table to operate which is tiring, If you compare that to washing dishes leaning over at a sink, you have probably experienced back, neck and shoulder fatigue. Imagine doing that for 4 to 5 hours. I know my single level cervical fusion required about an hour of surgeon time, the rest was the pre-surgery prep and setting up the sterile field and anesthesia and breathing machines. The surgeon needs to know they will do a good job, and doing surgery with excessive fatigue is not a good choice. On long extended surgeries, sometimes there is a 2nd surgical team that comes in to continue the procedure. There are also the schedules of other hospital workers involved with surgeries and they try to keep to an expected schedule to accommodate operating room time schedules among all the patient surgeries being done there with various surgeons. Between every case, the operating room must be cleaned and sterilized and a freshly sterilized set of instruments and supplies is brought in for the the next procedure.

If your surgeon was to add rods at the same time, it would require turning an anesthetized patient over on a narrow table without disturbing any of the work they just completed. Then the sterile fields would need to be set up again. I understand not wanting 2 surgeries, but that is standard practice for how this is done. They have to do what has the least risks to the patient.