A New Wedge-Disc Alignment Unit
George Murdoch, M.B., F.R.C.S.Ed. *
This unit, which embodies the now familiar wedge-disc angular displacement principle, incorporates several distinctive features which will prove valuable to the prosthetist.
An external locking ring is used to facilitate adjustment while the prosthesis is being worn.
The locking ring allows simpler attachment to sockets and eliminates the need for a socket container. Furthermore it is readily fitted to any type of foot or ankle mechanism.
There is axial stability of the unit when unlocked as the design includes a ball with a peg located in a slot thus permitting till but no rotation.
Instability, i.e.. "wobble," is avoided when the unit is unlocked. This is achieved by use of a rigid vertical bolt and an arrangement whereby the wedges slide, one on the other, to compensate the variation in geometry due to tilt. This also ensures that there is no tendency to shift from a given angle to a lesser angle.
A later model of the unit described and illustrated here incorporates a tab washer placed between the locking ring and the adjacent wedge-disc. This modification ensures no loss of setting during tightening.
The unit can easily be fitted with a slide to enable antero-posterior or medio-lateral displacement independent of tilt, the whole unit still being locked with a single locking ring.
The actual holt and locking unit. 3/8" diameter B.S.F.. is made of high tensile steel. The remainder of the unit may be fabricated in dura] or even plastic material with suitable mechanical properties.
The unit is capable of incorporation within the definitive prosthesis once the correct alignment is achieved at the completion of rehabilitation. This can best be accomplished by the use of an epoxy resin.
This device was designed and constructed in the Prosthetic Research Department of Robert Kellie & Sons, Artificial Limb Manufacturers, Dundee, who have a patent pending. An evaluation trial of fifty patients is being carried out.
Fig. 1, Fig. 2, Fig. 3