Prosthetic knee -- MEDICA - World Forum for Medicine


DCA Design International

Prosthetic knee

Electronic monitoring device

An electronic module provides accurate measurement of each step. Analysis of step timing allows the amputee to view the number of steps taken, the activity level attained and the distance travelled. This information also provides accurate assessment of servicing requirements.

- Innovative step measurement system provides reliable detection of different activities

- Ultra low power electronics allow sealed for life construction

- Non-contact step detection for reliable operation

- Fast download to PC to display analysis of activity.

Ortho Europe has many years of experience in prosthetics and the associated hydraulic engineering. A development partnership with DCA has now resulted in an exciting new product, the Sensor Knee. A small electronic device is incorporated into the knee assembly; this monitors and records the movement of the knee.

The Sensor knee is supplied with a simple to use software application, which enables the amputee to view the number of steps taken, the activity level attained, the distance travelled, and an indication of servicing requirements.

The versatile Sensor Knee uses a combination of hydraulic and electronic technology to control and monitor the knee. This provides maximum freedom of movement with minimal energy expenditure whilst recording functions to monitor the rehabilitation progress. Sensor Knee can suit a new amputee right through to the enhanced mobility and control required for activities such as golf, cycling, hiking and gardening. Sensor Knee allows natural gait, walking over uneven ground, negotiating slopes and steps with ease and confidence.

Electronic control was achieved at very low power levels allowing the complete assembly including the battery to be encapsulated in resin.

During development, an extensive testing programme proved the electronic technology used in the Sensor Knee to be 100% accurate in the measurement of activity, which was not the case with the more conventional measuring devices used for comparison.

A 3D CAD model capable of simulating the motion of the knee model was constructed to assist the optimum layout of the on-board sensor PCB. The model was used to determine the ideal positions of the reed switch and magnet, influencing the layout of components on the PCB to best suit the given space envelope.

A test platform was subsequently prototyped from the existing components with adjustable positioning to ‘fine-tune’ the reed switch PCB relative to the knee-magnet arrangement. (A specially constructed pocket within the knee allowed different magnet geometries to be tested).

The prototyping phase meant it was possible to into account tolerances due to reed switch position during PCB assembly, potting (the position of the PCB in the resin housing) and assembly to the shin to ensure a reliable operation of the switch. This enabled the optimum position of the reed switch within the shin to be determined, and a suitable magnet selected.

A mould tool was developed to locate and pot the production PCBs using the prototyping facilities provided by DCA.