Hi, new to the forum wondering if anyone know what a 3mm and 4mm slip means in terms of grading. I have had horrible low back pain for eight years now. I have had two laminectomies, and a decompression and cyst removal. Now my I have slippage at L4-4 and S1 with severe arthritis. I have a lot of injections over the years but get little relief. Nights are so horrible I have so much pain in low back hips and knees. I'm so scared to have a fusion but thinking I may have to.