In the 12th Century the Shogunate was formed. The head of this regime was the Shogun, the supreme ruler. Under him where his regional ‘daimyo’ or ‘dukes’. Under each ‘daimyo’ served the Japanese samurai. When a samurai stepped out of line, became too unruly or displeased his ‘daimyo', the samurai would often have to go through a procedure known as yubizume. This procedure is a very barbaric punishment in which the first joint of the little finger on the sword hand would be amputated.
Not only would this be a very painful punishment, but it served a much cleverer purpose. When holding a samurai sword the finger which has the strongest grip is the little finger. Each finger right up to the index has a weaker gripping strength. You can test this yourself. Make a tight fist with what would of been your sword hand, and take a slim object of equal circumference throughout such as a pencil or pen. Now, without causing you harm, take the non-sharp/drawing end and starting with the index finger end of the hand, while retaining a fist, slowly work the pencil/pen into the grip.
You will see the further into the grip the pencil goes, the more resistance there is. You now can see how important the little finger and ring finger would be for gripping samurai swords. To make matters worse, if the samurai further disgraced himself he would be required to take the next joint of his little finger off, and this could even extend onto the other fingers. But what was the use in handicapping the samurai in such a way? Well, not only did it serve as a constant and shameful reminder, but made the samurai more vulnerable than he had been before, therefore more reliant upon his immediate superior, his ‘daimyo’ for protection.
This brutal practice of yubizume is still used today by the Yakuza / Japanese organised crime families as a means of punishing their unruly members.
Article by Nick Johnson of Japanese Samurai Swords Dot Net http://www.japanese-samurai-swords.net