Oyayubi-ippon-ken-tsuki (literally: “thumb-knuckle single-point fist punch”), or the thumbknuckle strike is used like a ridgehand block or inside ridgehand strike to attack soft or easily-breakable body parts. Thumbknuckle strikes use a modified fist, where the thumb presses down on the side of the index finger, as demonstrated in the photo to the right. Thumbknuckle strikes impact with the pointed tip of the thumb’s second knuckle. Thumbknuckle strikes are especially well suited for disabling an attacker’s arm by striking the sensitive nerve cluster on the inside of the upper arm, in the groove between the biceps and triceps.
[photo of a thumb knuckle strike. ] [video of thumbkuckle strike fast and slow, from front as side. ]