Voluntary Opening (VO) Hooks are sadly still #1 seller.
THESE DEVICES ARE ALSO REFERRED TO AS TERMINAL DEVICES.
The VO device (hook) was developed in 1912 by David Dorrance. It has a pivot point, a cable attachment and a rubber band — yes, a rubber band. This is still the number one selling hook according to Hanger prosthetics. Manufacturers generally make them using stainless steel. They are heavy, indestructible and underpowered. However, they are simple, inexpensive and easy to make but rarely meet the needs of the patient/end user. Voluntary opening hooks were a huge improvement in the 1910's but they were engineered with the information available at the time. VO hooks use rubber bands to stay closed. The more rubber bands the more "strength" the hook can exert on an object. However, the user must be able to match the strength to open and keep open the hook. The action of voluntary opening is not intuitive for picking up, grasping or holding. Typically, when a human hand picks up a glass of water the hand closes its grasp around the cup. The hand does not open around the glass. The human hand will use force to stay closed. While using a VO prosthetic hook the user must use force to remain open around the glass.
Voluntary Opening Terminal Device
- Invented in 1912.
- Uses rubber bands.
- Inexpensive.
- Works against normal body functions. (Not intuitive)
- Simple.
- Durable.
Because of simplicity and cost to manufacture, VO devices are the primary terminal devices on the market. Prosthetists steer new prosthetic wearers toward the VO platform. In turn, amputees disproportionally use VO hooks despite their inherit engineering shortfall. Lack of information and the absence of a quality, makes the training process using a VO device all but inevitable. Once an amputee commits to creating muscle memory, for a VO hook, it is difficult to change.
A new amputee quickly learns the truth about prosthetics. Terminal device options, technology and appearance do not match their expectations.