Importance of Pasterns and Hocks
All dogs have two sets of pasterns that are the shock absorbers - two front pasterns, or "wrists", (metacarpus) and two rear pasterns, (metatarsus) .
The rear pastern is the region between the hock and the rear foot.
Then hock is the joint found above the rear pastern.
The hock angel is the angle formed between the lower thigh and the rear pastern.
The front pastern is the region between the wrist and the foot.
The front pasterns are energy absorbing mechanisms and the rear pasterns, or hocks, are propellers.
Metacarpus (Front Pastern)
An important feature of the dog's stance is the slope of the front pastern. Some slope in the front pastern prevents knuckling, absorbs shock and helps lift a dog's center of gravity (Hollenbeck, p56). You do not want the pastern to be either sunken down or straight upright. The forequarters are responsible for supporting more than half of the dog’s weight.
Metatarsus (Rear Pastern)
In a dog standing four square, the rear pastern lines are vertical to the ground viewed from the side and parallel when viewed from the rear. Look for straight hocks (see photo) and avoid Cow hocks, sickle hocks, over angulated, wide, or narrow (see photos).
No matter the gait, the heel of the dog’s lead foot will hit the ground first. This heel must consume the shock of impact. For these reasons, dogs’ feet have padded heels for softening impacts, these being the communal and digital pads. They also have a series of tendons and leverages in the feet and lower legs for pushing off. "A short hock functions at a better mechanical advantage and imparts better endurance." (Practical Canine Anatomy & Movement)
In order to propel, the muscles of the lower leg (below the stifle) connect to the tendons of the calcaneal process, which in turn, when drawn, snap the rear pastern, foot and digits, mobilizing the hindquarters. This is one aspect of the launching stage of the dog’s trunk and weight in a forward motion. The length of the calcaneal process (length of hock) will directly affect the function of the dog. A shorter hock is typical of staying power for a dog who is not inclined to sprint, but needs has stamina. This is referred to as a ‘well let down in the hock' or 'short in hock'. This means the hock is close to the ground. (Shock Absorbers)
A sickle hock refers to the shape and outline of the hock when viewed from the side. Sickle hocked dogs usually can't straighten the hock joint o the backward reach of the hind leg.
"Practical Canine Anatomy & Movement" by Claudia Waller Orlandi PhD
"Shock Absorbers" by Lisa Dube Forman