 [ Symptoms ] i had a back fusion at l4 s1 now have anterlothesis of l4 on l5 do i need surgery [ Disease ] if your surgery was fusion of l4 l5 andl5 s1 as a whole then it should not be moving anterior slippage of the vertebrae can have complications on your lower limbs and even the spinal cord the degree of slippage differs in treatment if it is 1st degree then physiotherapy is enough with behaviour modification if it is 2nd or 3rd degree then another surgery may be needed