Freehand System
The Freehand System from Cleveland, OH, USA is an implantable neuroprothesis intended to restore hand function in C5 and C6 level tetraplegics. The Freehand system can stimulate eight different muscles in order to produce a useful grip and key pinch in tetraplegic individuals. The system consists of a surgically implanted receiver/stimulator unit and electrodes with an external controller and power supply/microprocessor. It was first implanted in 1986 (Cornwall & Hausman 2004). The Freehand System has been implanted in more than 250 individuals with C5 and C6 level tetraplegia (Ragnarsson 2008). The NeuroControl Freehand System consists of an active receiver/stimulator that is placed in the chest wall and has eight leads that come from the receiver/stimulator and pass under the skin to a connector site in the upper arm. At this point they are joined to epimyseal electrode leads that are passed under the skin from the forearm and hand. Power and control signals from the unit are passed through the skin to the receiver/stimulator from a skin-mounted coil. The patient controls the device by movement of the opposite shoulder that uses a skin surface mounted position detector. The lateral grasp is generated by first flexing the fingers to provide opposition, which is followed by thumb flexion. Palmar grasp is generated by first forming the opposition between the thumb and palm, followed by simultaneous flexion of both the thumb and fingers. Stimulating the flexor digitorum superficialis and profundus muscles performs finger flexion and finger extension is obtained by stimulating the extensor communis digitorum. Stimulation of the thumb thenar’s muscle or median nerve produces thumb flexion. Hand opening and closure strength are proportional to the distance moved by the shoulder. Both palmar and lateral grasps are possible by pressing a button on the shoulder controller. Taylor et al. (2002) and Keith et al. (1996) reported that most clients will require several surgical procedures are needed for each client for optimal use of the device. The most common surgeries performed are brachioradialis to extensor carpi radialis for voluntary wrist extension and posterior deltoid to triceps for elbow extension (Keith et al. 1996; Taylor et al. 2002). The 1st generation of the Freehand System is no longer available from NeuroControl Corporation. There are devices still available on a selective basis in several centres (Cornwall & Hausman 2004; Ragnarsson 2008).
