It would mean it's stressed, but not to the point of being a "serious problem." Just baby it, and be very careful so it heals instead of tearing. It could be caused by anything! Moving a "wrong way" in the pasture, or while being ridden, to doing too much in deep footing. Who knows, they're horses. Probably did it in his/her sleep, lol!
(It could also be pointing to a hoof issue, so make sure that isn't the culprit.)
I would relate it to rolling an ankle. You have MANY different levels of severity, from rolling it while walking, to full out rupturing something.
"On the back of a horse I felt whole, complete, connected to that vital place in the center of me...and the chaos within me found balance."
Dealing with this with my mare- she strained her suspensory when she got out of the pasture one night and visited a neighbors' place where she found some barbed wire...that got caught in her blanket and dragged home with her. Let's just say I hope I never see a horse that hot, exhausted, terrified, and stressed again.
You have to watch pretty closely to see the lameness most days. We went through stall rest and rehab only to have her restrain it, so now she's off on a breeding lease- we'll see what she looks like after two years off! The biggest problem is that every time they take a step they essentially restrain that ligament, so getting the inflammation out once it's in there is difficult, even on stall rest. My vet recommended surgery for her since the stall rest didn't do it, but I'm not willing/able to go that route just yet.
Like Laurierace said - inflammation of the suspensory ligament means that the ligament has been strained. The inflammation is the body’s response to that strain. How the inflammation manifests itself depends on whether it was caused by a one-time injury (i.e. landed wrong and strained/pulled the ligament and comes up immediately off or lame) or if it’s a chronic injury that’s taken place over a period of time. With chronic suspensory injuries (like my guy unfortunately has, ergo the first hand experience), the visible lameness is sporadic and when it does show it may only show for a short time. Ultrasound is the diagnostic tool to measure how and where the ligament is inflamed. Stall rest with a limited and controlled amount of exercise - hand walking at first, then short periods of turn out in a very small area, and gradually work your way up from there depending on the healing progress - is the recommended course, and they are more prone to re-injury during the healing process so slow and steady is the key. I’ve had cold laser treatments done and increased the daily amount of MSM my guy is getting and added flaxseed to his diet to increase his Omega-3 intake to help combat the inflamation as well.
The truth will set you free. But first, it will piss you off ~ Gloria Steinem