detached muscle?

[Fairynuff]

was just having a womble through Horsedeals and came across this mare. I have no intention of buying but having read her details I have realised that I dont know what they mean by a 'detached muscle'.can someone enlighten me please? There is something about this mare that I like very much although there is something odd about her backend

If I had the dosh and lived near..........fantasy, fantasy

Mairi.
http://www.horsedeals.co.uk/horses/horses_for_sale/Broodmare__10-02-09-58673

 

[spaniel]

erm......well if theres a detatched one I presume she cant move???? Muscles are prety important when it comes to putting one foot in front of the other!