We had a set of twins born last year, one was slightly contracted in her tendons but the other was severe. He could not stand at first, but with help could only put weight on the fetlock (the knuckle above the hoof). Took him to the vet, where he got an IV shot of tetracycline. It loosened him up enough to be able to stand on his own, and 24 hours later got another shot. Within a week he was walking normally. There is NO WAY he would have worked out of it on his own, since he could not even unroll his lower front legs. We were told it happened because there was not enough space in the uterus for both calves (went full term, one was 62 pounds and the other 80 pounds).
We have been told it works most of the time, but you have to do it early on. I am just glad we acted quick!