"Aqua-Flex" A Pediatric All-Plastic Prosthetic Knee System


AR children enjoy playing. They are very comfortable in a variety of surroundings that include playing in water, on the beach and at the local playgrounds.

However, prosthetically, this can create anxiety for the prosthetists and parents of children wearing conventional above-knee prostheses, as most conventional pediatric knee joints will not stand up to repeated use in water. Although they are otherwise very durable, due to their metal and wood construction, there has been a need for a knee joint that could be utilized for all recreational activities. This was confirmed after an indepth survey of parents and prosthetic clinics with a large pediatric base. Considering the ultimate use of the knee joint and the rigors it would be subject to, an all-plastic joint was designed (Fig. 1 ).

The joint is made primarily of carbon-reinforced acrylic resins of exoskelletal design, with moveable parts made from polypropylene and nylon bushings and bearings.

The knee joint features an internal extension assist to provide better stability in the stance phase, ensure knee extension at heel strike and better follow through in the swing phase.

The below knee section of the prosthesis is manufactured from an exoskelletal, hollow construction, with several openings to allow water to enter and escape to reduce buoyancy. It has been our experience that a hollow construction for the above knee section is not required.

Our design is currently available in 2 universal sizes, to suit present demand:

Ages 1-5 years 5 cm knee width
Ages 4-7 years 6 cm knee width

After preliminary trials, a third size is currently being designed for the 6-10 year old patient with a knee width of 7.5 cm. "Aqua-Flex" can then be used by children until they are suitable for a commercial product (ie: Otto Bock 3K5), at approximately 10 to 12 years of age (Fig. 2 ).

All fittings and alignments are done in the conventional manner although fabrication is somewhat more complex and requires specific lamination techniques.

The resulting prosthesis has all the features of a conventional child's knee-shin set up, with the following benefits to the wearer and parents:

  • ultra light weight
  • almost silent operation
  • simple cleaning and maintenance
  • excellent cosmesis
  • high patient acceptance
  • reduced wear on clothing

The young amputee can also utilize the "Aqua-Flex" in their daily-wear prosthesis. A locking feature becomes available, with the addition of a simple dacron webbing strap, anterior over the knee.

Little maintenance has been required. The recreational limb can be cleaned easily with a good spray from a garden hose and normal kitchen cleaners can be used for tougher stains. We have not experienced excessive wear to the knee bolt assembly, but this may surface with extended use. No lubrication or patient maintenance is required as the plastic joints are self-lubricating due to the properties of the plastic utilized.


Seven patients have been supplied with this all-plastic knee joint since August 1990. They include: three with PFFD, two with knee disarticulation and two above knee amputees. Ages ranged from three to eight years.

The children were fitted with a surlyn socket and either a Kingsley Dynamic or Seattle child's size foot. The only exception is in the case of the knee disarticulation patients, where surlyn was not utilized.


The "Aqua-Flex" knee joint is extremely suitable for the prosthetic management of young above-knee amputees. To date, no servicing problems have arisen from its use and the children fitted are regularly followed up at our clinic. To date, feedback from patients and parents has been good and the information received will aid us in determining changes to the current design (Fig. 3 ).

Ford Laboratories, Prosthetic/Orthotics, # 106-11400 Bridgeport Road, Richmond, B( V6X 1T2