Once you accept a payment in full and final settlement, you have no further comeback. The reason the insurer has made the offer at this stage is because it fears the claim could be larger if your injury is likely to remain troublesome for a time. The knee is a complicated joint and any symptoms can be very disabling. Wait for the results of the x-rays and the doctor’s prognosis; in the meantime speak to the Helpline for information upon the range of damages into which a knee injury may fall. You have nothing to lose by delaying; the insurer has everything to gain by closing the case early.