WILMER Appealing Prehensor

The standard split hook prosthesis, despite its functionality, is most often rejected by parents of a child with an upper limb defect because of its deterring outward appearance. The more cosmetically appealing, but less functional, hand prosthesis is usually preferred. A new prosthetic prehensor for children has been developed, with the objective of preserving the functionality of the standard split hook prosthesis, while improving on its outward appearance.

The volume and the outline of the new prehensor are derived from the contour of a hand of a 4- to 6-year-old child. The length of the fingertips and the position of the rotating finger approximate those of a healthy hand. The connection to the forearm is harmonic and smooth. All mechanical parts, including the operating cable, can be placed out of sight in the interior of the prehensor. A four bar linkage mechanism is used to reduce the input forces. A slightly inclining input characteristic ensures controllability for both shoulder harness and elbow-control. The resulting grip force is nearly constant over the full range of opening.

Integrated into the frame of the prehensor is a lightweight friction wrist prosthesis. The frame is enclosed by a cosmetic cover made of flexible polyurethane resin, allowing for several unique features: the outside of the prehensor is rugged and easy to maintain; the cover can be easily removed to access the mechanism; and the cover can be colored. Giving the cover a bright primary color emphasizes the toy-like nature of the prehensor, thus advancing the acceptance and use of the prehensor by the child. It is even possible to supply several covers in different colors, which can be exchanged by the child according to daily moods.

Indications

  • for children with (unilateral) upper limb deficiencies at forearm or upper arm level 

Characteristics

  • appealing appearance
  • covers can be made in almost any color desired
  • smooth connection between terminal device and forearm
  • integrated control cable, therefore less wear of clothing
  • integrated friction wrist
  • insensitive to sand, water, and dirt 

Technical Specifications:

  • available in two sizes: small (4 – 9), and medium (7 – 14])
  • a size large (> 12) is under development.
  • mass, including the friction wrist: 120 g (small), 160 g (medium)
  • opening width: 50 mm (small), 60 mm (medium)
  • length [from front plane of the wrist]: 102 mm (small), 115 mm (medium)
  • wrist diameter: 32 mm (small), 37 mm (medium)
  • prehension force: 6 – 7 N

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