Could have been a tie-up? (was dark urine/muscle damage)

["guest@endurance.net" <guest@endurance.net>]

Kristi iluvdez@yahoo.com
Thanks to those who emailed me on my original post re: my loose
horse with the dark red urine. Several of you believe that he 
actually tied up. My vet didn't think he did because there was no
tightness at all in his hindquarters. So, ? for those of you who have
dealt with horses tying up. Can it happen without any sign except
the dark urine? The only other thing I can think of is that when
the horses were caught by a landowner, they stood tied for 1/2 
hour before we found them. So, was it possible he had all his other
tie-up "signs" in that 1/2 hour and we weren't there to see them?
It's been 3 days since it happened, but the vet comes back today 
and I'm going to see if she can draw blood to see if there's any
evidence of tying up (several of you wondered why she didn't draw
blood the day after - now I wish she had!)   Kristi