The wrinkles of Icelandic Horses tell us what is happening with them. They are an indication that the horse is in an unnatural frame. The wrinkles around the throatlatch indicate the head is being crammed into the neck at an odd angle.
The wrinkles around the withers indicate that the horse's neck is being inverted, the base of the neck is being lowered, and the neck is crammed into an unnatural position.
Wrinkles can also be caused by a poorly fitting saddle.