A New Concept In Swivel Walkers - A Comparison With The Conventional (Canadian) Type
R. M. Barry R. J. Duncan
*Technical Officer and Prosthetist of the Central Development Unit, Central Office, Repatriation Department, Melbourne, Australia, respectively.
The Central Development Unit (C.D.U.) has manufactured and used a number of Canadian-type swivel walkers1. The design features of this unit are shown in Fig. 1 . While satisfactory results were obtained with these walkers, it was considered that some functional improvements might be obtained by altering certain design characteristics. For example, the swivel ankle joint did not give the desired function and the two knife edges of the foot-plates resulted in some lateral instability and also had an abrasive action on the floor surface and the foot-plate rubbers. In addition, during some stages of the walking cycle the knife edges of the foot-plates did not land flat on the floor. This lack of plantigrade contact caused undesirable rotation of the foot-plate and to some degree upset the harmonious relationship between lateral displacement and forward rotation.
It was noticed that the rotation actually commenced before the center of gravity crossed the line of support owing to the lateral thrust of the body in the dynamic condition. This factor seemed to limit forward progression. Moreover, a considerable amount of lateral displacement was apparently necessary in order to maintain a reasonable rate of progression.
The actual tilt of the ankle bearings in the Canadian swivel walker (a maximum of six degrees with the foot flat) depends upon the amount of lateral displacement of the patient's center of gravity and varies continually during walking. It was felt that, if the angle of tilt of the bearings were fixed, a smoother walking pattern would result.
A new design for the functional mechanism was suggested by one of the authors (Duncan) and several prototype models were produced.
The torsion-type ankle joints used on the ambulator2 were included in the new design. These ankle units are manufactured as "neutrals" and can be set for application to either the left or right pylon.
The socket-tilting mechanism which raises the "foot" from the floor features a four-bar linkage (Fig. 2 ) in an attempt to reduce the amount of lateral displacement. The linkage was placed proximally, under the socket-mounting platform. With side tilt of the pelvic socket, vertical lift of the opposite pylon occurs, thus providing floor clearance for each step taken. The stops on the four-bar linkage may be adjusted to vary the amount of lateral tilt and hence the floor clearance. Since the axes of the four-bar linkage are more closely spaced than are the lines of support of the Canadian-type walker, the inclusion of small medial extensions on the footplates was necessary (Fig. 2 ). Experience tends to indicate that the significant increase in patients' stability thus achieved offsets this cosmetically undesirable feature.
The pylons are adducted at an angle of three degrees to the vertical (to accommodate the rubber torsion bars of the ankle mechanism), thus maintaining the ankle rotation bearings at a fixed angle. As a result of the purely vertical lift of the pylons, the footplates always make total contact with the floor. This characteristic offers greater stability both in standing and in walking. The combination of these features (foot flat and a small, fixed degree of socket tilt) contributes to a straighter line of progression than is the case with the Canadian design.
The new design allows the patient to stand on one foot. Since lateral displacement and/or rotation can be adjusted independently, the fine positional maneuvering required for duties such as writing at a desk and similar activities can be more easily achieved.
The pelvic socket is constructed so as to permit self-entry and exit at walker height by patients with some residual upper-extremity function. Flesh-colored cosmetic shank and foot covers are placed over the tubular pylons. It is proposed that in future models the soles of the feet will be manufactured of a transparent material.
Experience with Canadian swivel walkers in Melbourne has indicated that the lateral shift of the body mass was of the order of three and one-quarter inches in each direction to give an average step length of two and one-half inches. The corresponding amount of lateral shift of the body mass on the modified (C.D.U.) walker was two inches. As the time taken for each lateral body sway would, for a given rate of progression, be equal for both designs, the velocity of lateral mass transfer will be proportionally less for the C.D.U. walker. It is suggested therefore that the energy consumption would also be similarly reduced with the use of the new design. Limited trials of the one prototype fitted to date appear to support this hypothesis3
The authors wish to acknowledge the general assistance and guidance of Dr. R. W. Klein, M.B.E., Director, and Mr. R. E. Spielrein, Senior Engineer, of the Central Development Unit. Their thanks are also due to the Chairman of the Repatriation Commission for his permission to publish this material.
1. Motloch, W.M. and Elliott, J.: "Fitting and Training Children With Swivel Walkers," Artificial Limbs, 10:27-38, Autumn 1966.
2. Spielrein, R.E.: "A Simple Walking Aid for Legless People," J. Institution of Engineers, 35:321-326, Dec. 1963.
3. "Current Activities of Central Development Unit," J. Repatriation Artificial Limb and Appliance Service, 10:4-6, Apr. 1968.