In the early phase of the rehabilitation process for neurological patients or those enduring long bed rests, it is important to mobilize patients to prevent secondary complications caused by immobility. The Erigo by Hocoma AG, Volketswil, Switzerland, is a motor-driven, computer-controlled tilt table system that expands the functionality of traditional tilt tables by integrating advanced robotic stepping technology.
It provides physicians and therapists in neuro-rehabilitation with the means to start intensive movement therapy and loading of the lower limbs at an early stage. (See Figure 1).
The Erigo is a traditional tilt table combined with an integrated leg drive that allows a passive movement of the lower extremities. The leg drive that is connected to the thigh by a cuff induces a hip flexion or extension movement.
As the feet of the patient are fixed to footplates, the knee is also flexed or extended, respectively. In those phases where the hip and knee joints are extended, the leg pushes down a spring-dampened foot plate, which is then again pushed against a foot spring mounted within these plates. This footplate generates a loading force on the foot sole of the patient during extension. Applying this cycle of flexion and extension in an alternating way leads to physiological kinetics that are close to normal walking. (See Figure 2). A special mechanism is mounted under the hip joint and allows for adjustment of hip extension.
Physiological gait-related loading of the feet is achieved with a special spring-damper integrated into the footplates. Load is applied to the sole of the foot during hip and knee extension, while in the case of flexion the spring is released from the plate and no load is generated.
Depending on the blood circulation condition of the patient, the device can be tilted to different angles up to a vertical position. This makes it possible for the patient to become accustomed, step-by-step, to the upright position in combination with passive leg movements. A control panel can adjust the speed of the alternating stepping movements and the range of motion of hip/knee joints. Microcomputer-controlled drives generate physiological movements in such a way that hip, knee and ankle joint movements are comparable to normal walking.
The basic construction consists of a linear drive, with a precision ball screw driven by a synchronous dc motor (RE40, maxonmotor AG, Switzerland) via toothed belt (maximum speed 450 mm/sec, maximum force 1,400N, maximum torque of 400 Nm at the hip joint). The movement frequencies range from 0.2 to 0.5 Hz (i.e. one cycle of flexion and extension takes between 2 and 5 sec). Motors also control tilt table height, tilt and hip extension.