Prosthetic Knees

Two new variations using contemporary prosthetic knee technology caught my eye. The first is an interesting-looking polycentric knee with pneumatic swing phase control from Otto Bock. Available in both knee disarticulation and familiar pyramid-connection versions, this latest hybrid design is a bit reminiscent of the children's polycentric knee they introduced last year. It is restricted to Red Class loading not to exceed 75 k or 165 pounds so that will limit applicability in the USA.

The second knee of note was the prototype shown at the Biedemann-Motech booth. This is a microprocessor-controlled hydraulic knee offering both stance and swing phase control, using a magneto-rheologic fluid cylinder from the Lord Corporation in place of a conventional hydraulic damper. The patient models walked well, both on level ground as well as down slopes and stairs. In a brief presentation about the knee, Herr Bidermann noted that it has integrated knee angle and forces sensors but said that the resistance pattern differs from that of the C-Leg.

The Bidermann knee seems to be similar to a virtual Total Knee in that it is programmed to lock the knee hydraulically for a few microseconds at Initial Contact, whereas the C-Leg has a fixed yielding rate making it more like a virtual SNS knee. One other distinction is that the Bidermann knee has all the sensors inside the frame so it may be used with any available ankle-foot mechanism while the C-Leg is restricted to four alternatives from Otto Bock.

As the Blatchford distributor in Germany, Bidermann also showed the Endolite Adaptive Knee but this microprocessor-controlled SNS knee still seems to be in the pre-production phase. The external appearance is sleeker than it was at the ISPO meeting in Amsterdam, so hopefully this will become a commercially available alternative one of these days. In any event, it now seems quite clear that the first decade of this millennium will be characterized by the release of a flurry of microprocessor-controlled lower limb and upper limb devices, reminiscent of the explosion of dynamic response feet 15 years ago.

Otto Bock now has the 4R105 & 6 polycentric knee with pneumatic swing control for small adults, available in both KD and pyramid versions.

This microprocessor-controlled knee from Bidermann is slated for release later this year in the German market. It is the first prosthetic application of magneto-rheologic fluid to provide swing and stance phase control.

The Adaptive Knee from Blatchford has a sleeker, more finished appearance but is not yet commercially available. This microprocessor-controlled design uses a pneumatic cylinder for swing control and a hydraulic cylinder for stance stability.

College Park introduced the use of prefab cast-walkers with their foot attached underneath so non-amputees could get a "feel" for how their foot worked by walking on a pair. This has been popular with attendees over the years, so Flex-Foot and others now have similar psuedo-transtibial prostheses available.

At the Bidermann booth, I saw the next logical extension of this trend: a psuedo-knee disarticulation prosthesis to allow trial walking with prosthetic knees too. Actually, it is simply an adaptation of the historic "bent knee" design that has been used for centuries when advanced prosthetic care is unavailable.