Considerations in designing acceptable neuromuscular stimulation systems for restoring function in paralyzed limbs.

Recent progress in the field of functional neuromuscular stimulation (FNS), that is, the restoration of purposeful movement to paralyzed limbs via stimulation, has enabled paraplegic individuals to stand up, walk, and even climb stairs (with assistance) and quadriplegics to hold and manipulate utensils and useful objects. A number of experimental and clinical FNS systems are considered, emphasizing the algorithms used to regulate movement under a variety of conditions (isometric, isotonic, dynamic load, reciprocal control) and the physiologic problems encountered. Further development of FNS systems is required to achieve patient acceptability in daily living. Three important factors will be use of implanted intramuscular or nerve stimulating electrodes, quantitative documentation of FNS-produced movements, and incorporation of force, position, and other modes of feedback to both the controller and the patient.