Kotehineri begins a new class of techniques in Junana and Nijusan kata - that of wrist manipulations. Previously we were affecting uke's center either directly (atemiwaza) or by controlling the elbow (hijiwaza). Now there is another set of joints (the wrist) involved between uke's and tori's centers. One of the main lessons for tori for this group of techniques as a whole is to control the range of motion of the joints between centers so that tori is able to push on uke's center through the series of joints.
In kotehineri (A.K.A. sankyo) uke's wrist is extended and his forearm is pronated to the end of the range of motion for these joints. The purpose of these wristlocks like hineri is not necessarily to hurt or to injure the wrist, but rather to control the degrees of freedom in the joints between uke's and tori's center. With the wrist controlled in this hineri fashion, the rest of the technique mostly looks like oshitaoshi (ikkyo), but because of the lack of freedom in uke's arm, uke tends to lean forward and turn away to relieve the pressure. Thus tori tends to spiral into the ground above uke, whereas oshitaoshi tends to be a more direct path into the ground.
In aikikai the pin at the end is often done kneeling in seiza and entangling the arm (still in a hineri posture) with one arm then pressing the wrist toward uke's head to force a submission. This is a good basic way to learn the control, and it is a beautiful and effective pin, but we prefer to execute the pin from a standing position. Tori holds uke's palm (still in hineri) on tori's thigh so that he can use his leg and weight to press into the arm while tori's free hand control's uke's elbow. This results in a very effective pin that has the advantage of allowing tori greater opportunity to bail out of the pin and flee if appropriate.