In medicine , a finger tip unit ( FTU ) is defined as the amount of ointment , cream or other semi-solid dosage form expressed from a tube with a 5mm diameter nozzle, applied from the distal skin-crease to the tip of the index finger of an adult.   The "distal skin-crease" is the skin crease over the joint nearest the end of the finger. One FTU is enough to treat an area of skin twice the size of the flat of an adult's hand with the fingers together, . a “handprint”. Two FTUs are approximately equivalent to 1g of topical steroid .
Authors' Conclusions : The effectiveness of local corticosteroid injections was studied in only two small randomized controlled trials of poor methodologic quality. Both studies showed better short-term effects of corticosteroid injection combined with lidocaine compared with lidocaine alone on the treatment success outcome. In one study, the effects of corticosteroid injections lasted up to four months. No adverse effects were observed. The available evidence for the effectiveness of intratendon sheath corticosteroid injection for trigger finger can be graded as a silver level evidence for superiority of corticosteroid injections combined with lidocaine over injections with lidocaine alone.
The injection site is just above the wrist. In fact, exactly where you put it seems to make no difference to how effective it is as long as you are within a couple of inches of the carpal tunnel so most people now choose an injection site for both comfort and safety - which usually means about 1-2 cm up the arm from the wrist crease. The patient experience following injection is heavily modified by whether a local anaesthetic is included in the injection. If you do inject an anaesthetic as well as a steroid then you get exactly the same effect which is familiar to most people from dental anaesthetics - numbness of the affected area for a few hours afterwards. There has however never been any real logic to adding a local anaesthetic to this injection. It is certainly not there to influence the pain of the injection itself as the procedure is all over before the local anaesthetic has any chance to take effect. I have heard it argued that numbness in the median nerve territory after injection including anaesthetic proves that you got the injection in the 'right' place, but, as pointed out above, it makes no difference to the outcome where you put it so why does anyone care? We do not include a local anaesthetic.