Extension Prostheses For Children With Lower Limb Phocomelia
These reports originally appeared in Progress Report, for April, May and June, 1965, issued by the Ministry of Health, Research Department, Limb Fitting Centre, Roehampton, London, England. They are reprinted with permission.
The standard type of extension prosthesis as used for short lower limbs with normal hip joints has been found to be unsuitable for phocomelia where the hip joint is always absent due either to a deficiency of the proximal end of the femur, or to its complete absence. Since the majority of cases of lower limb phocomelia are bilateral and symmetrical, we have been fitting them at approximately one year of age with simple prostheses.
These consist of blocked leather sockets embracing the buttocks and joined back and front by straps and buckles. Each socket has an aperture for the foot to protrude and hang free. Two lightweight dural struts are attached to each socket and extend to a wooden "rocker" base 8 1/2" long and 2" wide. Sometimes it has been found helpful to have a strap across the dorsum of each foot and secured to the centre of the top of the rocker base to control the limb and prevent 'piston action1 during walking. Once the child has learnt to balance and walk, the height of the prostheses is increased by 2" or 3".
These sockets, which fully embrace the hips, produce a circumducted gait but give maximum stability and are therefore ideal for children who may have associated reduction deformities or complete absence of upper limbs. Those with reasonable length or normal upper limbs can tolerate less stability on the lower limbs, and then the next stage is to make similar extension prostheses but with reduced sockets in a similar fashion to those normally designed for above knee amputees, but reaching as high as possible on the lateral sides. A rigid pelvic band with a single joint allowing flexion and extension at hip level is then incorporated.
As soon as the child has acquired a good sense of balance on these prostheses, the third stage is introduced, this is simply to reduce the back of the "rocker" by 1"-1 1/2" and keeping the base flat posteriorly. The fourth stage is to introduce a shaped wooden foot which is covered with leather in the form of an imitation shoe but without a heel. This has an advantage over a fitted shoe because of the reduced weight and the fact that a child's shoe has a convex curve in the transverse and longitudinal planes, thus causing a degree of instability which is not always well tolerated. As the child grows older, metal prostheses are supplied with more emphasis being given to obtaining a good cosmetic effect.
Proper feet are fitted on which shoes can be worn. Windows are cut in the leather sockets and metal containers through which the phocomelic feet may protrude.
The first production run of a single-acting pneumatic wrist rotator for children under the age of five is now completed. This unit is designed for use in conjunction with the German pneumatic hook. For sensitive control the wrist activator should be operated through a proportional valve system such as the Kiessling type of valve, and a flow rate restrictor is required to bring the speed within manageable limits.
Design criteria have been prepared and a contract placed for the development of a hook and wrist rotation complex suitable for the five-nine-year-old child. Another pneumatic turning unit designed at Oxford is under consideration. This is understood to be a double-acting bellows system using a helix for linear/rotary conversion.
We are now becoming interested in converting the simple pneumatic devices now in clinical use into more sophisticated systems by introducing closed loop systems. Our present feeling is that position servos would be useful for the control of proximal joints, whereas prehension should have a force feedback loop. Work is being done on these concepts at Hendon, at University College, and in Edinburgh.
The miniaturised circuitry for the British myoelectric arm is still awaited. In the meantime a nineteen-year-old girl with a very short (1 1/2") below-elbow hemi-melia has demonstrated two discrete E.M.G. channels in the forearm stump which she was able to isolate after a few minutes' practice and with which she obtained immediate proportional control of the British myoelectric system.
A contract has been placed for the development of an electric runabout for children with quadrimembral reduction deformities. The design of this vehicle is based on the work of Professor Maunder and his team at the University of Newcastle Engineering Department. It is a two-motor system, the driving wheels being powered independently so that steering is achieved by varying the relative speeds of the motors.