Triple Control Harness Kit

This Euro harness uses a clear nylon cable routed medially to produce elbow flexion when the patient flexes their humeral remnant forward.
This Euro harness uses a clear nylon cable routed medially to produce elbow flexion when the patient flexes their humeral remnant forward.

Otto Bock showed a clever updated ring harness kit at the 2001 ISPO meeting, as noted in an earlier Corner [www.oandp.com/news/jmcorner/2001-09/2.asp]. The triple control version [21A35=1] is now in stock at Otto Bock US and presumably in other branches too. A CD with a 10-minute MPEG video demonstrating how to fit and adjust the harness is also available from Bock. To see a short excerpt of the video, click here. Some aspects of harnessing are better visualized with video, so congratulations to the Bock folks for producing this educational clip, and hopefully starting a trend in the industry.

Ever since I first saw this Euro triple control harness method a decade ago, I have been trying to disseminate the information across North America. Clearly, no one harness method is suitable for all amputees, but the more alternatives we can offer the greater the chances we will create a control system that is successful for a specific individual. More importantly, it is very straightforward to delete one or more control straps so once you have mastered fitting a triple control harness, it becomes very simple to convert it into a dual control or single control system.

Rounding the shoulders actuates the cable that is routed across the shoulder joint and opens the terminal device, without affected flexion of the prosthetic elbow joint.
Rounding the shoulders actuates the cable that is routed across the shoulder joint and opens the terminal device, without affected flexion of the prosthetic elbow joint.

To me, the use of a separate control strap to actuate elbow flexion is one of the most valuable aspects of this method. Unlike the traditional "fair lead" cables we use in North America, the Euro approach eliminates the need for any housing over the elbow cable. A clear nylon [Perlon] cable is routed through a mini-D-ring on the medial midline of the socket directly into the forearm itself. The result is sleeker, lighter, and much less "robotic" appearance than routing a split fair lead housing around the lateral side of the elbow mechanism.

The second key principle of this triple control harness is routing the terminal device control cable directly across the glenohumeral joint. This means that biscapular abduction opens and closes the TD independently of the elbow position. Independent, simultaneous control of TD and elbow means that the amputee no longer must lock the elbow in order to open the TD, so grasp and release is faster and more natural than with the more traditional fair lead approach.

This is also a good cabling method to control a microswitch for a hybrid prosthesis, since it generates less excursion than the fair lead style. The primary disadvantage of this harness is that it is somewhat harder for the amputee to don and to learn to operate.

For more discussion of this style of harnessing, there is an excellent article at www.healthcare.ottobock.com/info_download/pdf/bertels_bandagen21.pdf. For a concise summary of North American harness variations, Gerry Stark CP has an article at www.oandp.org/educ/pub/jop/1999/stark.htm.



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