I've watched the replay and can't see any indication that the #1 dog actually connected with the rail. If they are the "dots you are trying to connect" then I think you are barking up the wrong tree.
I thought I'd do some research on gracillis muscle injuries. They are very rarely if ever caused by contact but by the sudden acceleration of a greyhound from a cold start. In this case from my observation it looks clear that the dog pulled the gracillis soon after the start.
Perhaps the issue is inadequate warmups of the dogs prior to racing.
2. Gracilis – We call this ‘the 0-60 mph’ muscle. It’s located on the inside of the thigh at the back. Its closest neighbours are the hamstrings. This muscle attaches from the bottom of the pelvis to the inside of the shin bone, and its job is to provide propulsion and to flex and extend the stifle joint. The gracilis is commonly injured as a result of the dog going from a standing still to accelerating up to 45 mph without a warm up. As the muscle is not prepared for action it commonly strains and the greyhound is left lame or with an irregular gait.