Interesting problem, hands are crap as you can not really rest them or not work them, plus they are just vitally important. You said it was a tendon injury, how is it injured and is it shortened and pulling on the joint wrong and therefore causing the problems?
well i assume it has damaged and shortened the tendon as i jarred the same finger 3 times in one week playing basket ball, then that following weekend the 3rd proximal interphalangeal joint got crushed whilst working on my car..... basically the engine mount was out, and the jack lowered too quickly and jammed my hand between the engine and the chassy rail (crappy hyundai fwd... first car. lol)
Other than that im not quite sure how the tendons may have shortened, i just find it strange the way the tendon clicks over the top of the 2nd metacarpophelangeal joint.... i know its probably pointless looking for a cure... i just try to stretch it out sometimes and keep it warm whenever i can... its kind of hard working as a mechanic in winter time, cant wear gloves coz i cant pick up anything lol... cant wait untill i finish my PT course so i can get out of this godforsaken trade...