 Pain after a knee replacement can impair recovery and use of the new knee. Having an injection to numb the femoral nerve is known to give good pain relief after the operation but may lead to slower mobilisation as it also prevents the patient from moving the knee. Recent studies have shown that infiltration of local anaesthetic LIA within the new knee joint may also give good pain relief. The null hypothesis is that there is no difference in primary or secondary outcome measures between femoral nerve block and LIA, as anaesthetic techniques for knee replacement. 