My 13-year old off-track Standardbred has been weird on her RH recently (last few months) - vet has been out for basic eval but didn’t find anything too concerning. She does have a “dent” in her right semimembrosus muscle under her tail which I assume is from an old injury (was thinking fibrotic myosis but she tracks up fine and doesn’t have the “goose-step” that’s usually characteristic of FM!). She isn’t lame on it, isn’t reactive over any joints or muscles, but when I put my leg on and ask for a trot or canter, she kicks it out (especially at the beginning and when it’s colder outside) and pins her ears and generally seems like a pain response as opposed to a behavioral thing, and it’s ALWAYS the RH. I would put it down to arthritis as she raced and will be 14 in the spring but again she isn’t lame or reactive and has full range of motion in it compared to the LH. I do also think that she has ulcers but not sure if that could possibly affect it (also a work in progress before anyone comes for me!)
Would love to hear thoughts as this has stumped me!
What does she do on a lunge line (tacked and untacked) or free lunging when asked to go forward?
How long have you had her, how long has she been off the track and what’s she done since?
A video of the horse moving and kicking out may help. But instead of us guessing, it may be better to just have the vet out. Could easily be hock or stifle issue.
Check out Becks Nairn on Facebook! She has a lot of dissections about the severe wear and tear on tbs and stbs. Most come with extreme disorders of the musculatal skeletal system that do not get better. Pretty interesting
Could certainly be ulcers
Seconding these questions.
When you had the vet out for a “basic eval”, what did they do? Palpate, flexions, trot off, lunge, etc? Any blocks done? The answer to these questions would help guide the suggestions you get. A video would be fabulous but I totally get it if you don’t have any/are uncomfortable posting one at this time.
Go look at my thread called proximal suspensory desmitis and see if any of that rings a bell 
