From an article by Anne Eberhart:

"Proper leg conformation for the equine is highly important in all of its endeavors. This is especially true of horses in the wild, where nature is a ruthless culling agent. The wild horse whose legs give out because of poor conformation might wind up being an evening meal for a predator. While wild horses in general might not look like show ring models, it is seldom that one will find wild horses with serious leg conformation problems. Most wild horses with poor leg conformation don't make it to adulthood."

Icelandic Horses haven't had the benefit of natural selection from predators.

From an article by Christina Cable, DVM, Dipl. ACVS:

"To help you evaluate whether the horse's legs are straight, you can imagine a plum line (a piece of string with a weight at the bottom allowed to swing freely and hang straight). If standing in front of the horse, imagine the line from the point of the shoulder (front) straight to the ground. The line should intersect the carpus (knee), fetlock, pastern, and hoof in the middle of each structure."

Anne Eberhart:

"Now let's step in front of the horse. Here, again, we can use the term "straight leg." When looking at the horse from the front, superimpose a mental vertical line. It should travel in a straight path from the point of the shoulder, through the middle of the forearm and down the cannon bone, pastern, and foot. No angles there. Just a straight line. Any deviations are aspects of poor leg conformation."

Some of the conformational defects that you will want to check for in Icelandic Horses are: toe-ing out, knock knees, offset knees, legs too close, standing under.

Anne Eberhart:

"One of the most serious front leg conformational defects is called toeing out. When looking at the horse with our straight vertical line imposed, we will observe that the toes are turned outward and the line, instead of traversing the center of the foot, will be to the inside."

The conformational defects of the front legs of the Icelandic Horse will affect the swing of the leg (and it's function), shown in the following pictures. If the leg is crooked (i.e. toes out, knock-kneed), the leg will wing and it's flight path will not be straight. The horse may have to wear boots to stop from injuring himself.

As you look at the pictures below, notice the airborn front leg. Is it moving in a straight path? When the leg has reached it's furthest back point, is it under the horse or to the outside of the horse? When the leg is mid-flight (reaching forward) is it directly straight under the horse, or close to or crossing past the midline?

Also notice the grounded front leg... is it straight? or does the horse appear to be leaning?

This video shows the conformation fault of toe-ing out, and the resultant deviation of winging in.

Focus on the horse's legs and their flight.