when a patient has an injury that may have involved the flexors of the fingers we need to examine those there are two flexors to each finger one is the FDP the flexor digitorum profundus and the other is the FDS flexor digitorum superficialis so the first thing to look at is whether they have a normal cascade so the normal cascade we can see here when the patient is relaxed the fingers are flexed at different amounts if the patient is for some reason unable to comply with the full examination for instance in a very small child or someone who is unconscious then the thing to do is just squeeze the forearm and you can usually then get gross Composite flexion you move around a little bit you should then get all four fingers in and you can see whether or not there is continuity of the flexor specific examination of them in a patient who is able to comply with you the as I say there are two tendons we want to examine both the FDP and the FDS FDP is a mass action muscle in which one muscle has four tendons and flexes all four fingers so to examine the FDP of the index finger I would stabilize the middle phalanx and ask the patient can you bend down the tip of your finger for me okay and press against me say flexion against resistance off the FDP that one's easier the FDS on the other hand flexes at the proximal interphalangeal joint but so does the FDP so in order to isolate the FDS flexion we have to handicap the FDP and because it's a mass action muscle we can do that by holding all the other fingers straight and asking the patient again to bend that finger down now because the FDP is a mass action muscle we've held it out in full flexion when she bends the proximal interphalangeal joint the only tendon that can be doing that is the FDS if you bend it down and hold it for me I can prove that FDP is not having any action there because it is completely slack at the DI p joint so in summary when I want to examine the FDP I would say to the patient I would immobilize the middle phalanx and arcite's the patient can you bend the tip of the finger down good that's fine and then to examine the FDS i've hold the all the other fingers out straight and say again can you bend that finger down for me there are some exceptions to that the little finger doesn't always have an independent FDS so if I was to hold the FDP for all the other fingers and ask the patient to bend down at the little finger this patient does have an FDS to the little finger however some people myself included if I hold my fingers down I can't bend at the proximal interphalangeal joint of my little finger there are two possible explanations for this one is that I don't have an FDS but the other is that it is tethered to the FDS of my ring finger so then if I tip only if I release the ring finger as well I can flex both the ring and little fingers down