Are you talking about fusing from L1-2 through L4-L5 or L3-L4? In any case, that is a big surgery and will leave you with limited movement, particularly if L4-L5 is included. Even if it is not, it will take the brunt of the stress from the fusion and will have a tendency to break down as you age.
I would advise you to educate yourself about the necessity for this surgery and to not enter into it unless there are no other options. I presume you have tried all conservative treatments and they have failed?
It is always a good idea to get several opinions from either an orthopedic spine surgeon or a neurosurgeon whose practice is limited to the neck and back, before reaching a decision. A fusion is in many ways a life-changing procedure. It will not restore your spine to the way it once way, prior to injury or onset of pain. Some people have unrealistic expectations of what fusion will accomplish, and are then very disappointed with the results...so be sure you do your research before agreeing to such a big surgery.
That being said, I am fused from L3 to S1 and it has worked out very well for me.
If you have specific questions, there are several people currently on the board that have had fusions and could try to answer them.
How I wish I could have had the wise words from Teteri66 prior to my fusion surgery! It is a big surgery and will take a bit of time to heal. I would recommend that you educate yourself about preparing your house prior to the surgery. The most difficult thing i experienced was being able to clean or wipe myself after using the bathroom. My daughter stocked the bathroom with wet wipes which helped a little, but it was just difficult and painful, as it is hard to do this and not twist or bend the spine. My husband made me a contraption that i was able to wrap the wet wipes around and use it as an aide. Sorry if this is too much info, but i wish someone had let me know ahead of time.
Stock your fridge and pantry with foods that will help your digestion process as pain medications really slow down your bowels. Listen to your body and try not to push it too hard or fast in the beginning. Your sleep will be very disrupted when you come home and I found taking naps every few hours really helped. Also walking, even short distances helps to keep your strength up and helps reduce some of the pain.
Keep a journal of how you feel, how far you were able to walk, and what you are able to do. Then you can look back and see your progress. Some days you feel like you are not getting better but when you compare how you are from when you came home from the hospital, you will see how far you have come. Patience will be your new best friend. I have also found having massages, when cleared by your surgeon have really made me feel better.
I just had L5/S1 fused 3 weeks ago after a discectomy 9 months prior. My disc reherniated and I was in so much pain I could hardly walk. I feel a lot better now because at least my sciatic nerve is not being compressed. I'm still on narcotics but starting to wean myself down as much as I can tolerate. Because I only had one level fused and it was on the bottom of the spine I don't really have any problems with movement. My surgeon said that disc space was like a rusty hinge so it wasn't moving before the surgery anyways lol. My surgery was done from the anterior approach ALIF which I would highly recommend. The discectomy was done from the back and even though it was a much smaller surgery, I was in a lot more pain afterward. My back muscles are still sore from it and tilting my head down causes a lot of pain down that erector spinae muscle. I would recommend the surgery for a case like mine but try less invasive procedures first and do your research. Don't be afraid to get a second opinion. The first surgeon I talked to only wanted to do a posterior fusion and not try anything less invasive. I talked to several people who had my surgeon and they all had great outcomes. It pays to shop around.