The biomechanical design of a walking appliance for a paraplegic adult J. T. Henshaw OBE, MSc, PhD, FRAES, CEng Yaalford Orthopaedic Appliance Unit, University of Salford. Sayord M5 4 W T , Lancashire, UK
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
3ne of the major requirements of the medical consultant treating paraplegic patients is to hare them upright f o r at leas, I few hours a day associated, fi possible with some physical exercise. This paper deals with the construction and operatior ,fan appliance which makes this possible.
3ur environment is designed for an upright population and he person who finds himself confined to a wheelchair is at a ,erious disadvantage. It is impossible for him to enter many )uildings, use telephone kiosks, toilets or urinals, etc., untided. It is inconvenient for such a person to work inside or )utside the house or carry out a multitude of jobs which a
‘ig. I . Adult walking appliance. ( I ) Chest strap, ( 2 ) Axillary band, posterior to chest strap), (3) Sacral pad, ( 4 ) Hip hinge, (5) Glass ‘bre bands, (6) Knee straps, ( 7 ) Knee hinge, (8) Foot straps, ?)Telescopic bar, (10) Shoe plate, (11) Footplate, (12) Bearing.
May, 1977
1
person of normal physique may do. A wheelchair-bound person must look up when speaking to others and, mosf regrettably, is frequently regarded by the general public as an inferior being. Furthermore, a person confined to a wheelchaii may be subject to a variety of secondary afflictions, of circulation, of respiration, muscular atrophy and skeletal deformity, together with impairment of bowel and kidnej function, with the further possibility of pressure sores being created by continually sitting. There are, therefore, considerable physical and psycho. logical disadvantages to bzing confined to a wheelchair and it is understandable that one of the major requirements of the medical consultant is to have his patient upright for at least a few hours a day. This may be achieved by the patient being strapped into a standing frame, tilting table or support box where he must stand immobile for various lengths of time, One or two of these are available at the present time but in general are clumsy and offer little or n o opportunity of ambulation.1v4 Whilst, therefore, such an appliance will assist the biological functions by keeping the patient in an upright position it fails to provide the necessary exercise to keep the patient fit. It is also useless as a means of moving about the house to carry out light household duties or for other purposes and is, therefore, not in the same category as the walking appliance described in this paper. Since the 1950s various universities and research institutions throughout the world have been trying to create an appliance which would enable such people (mainly children) to walk. e-ll Many patients are able to walk very slowly, and often with considerable expenditure of energy, with the aid of calipers and crutches. This, of course, means that their hands are not free and they make progress by what is often called “quadrupedal” gait. At the same time this arrangement helps to meet the medical Consultant’s requirements that the paraplegic patient should spend at least a part of his day with his body in an upright or near upright position and should obtain exercise.l* Others, of course, are even less fortunate and cannot tolerate, or are too weak to use calipers and crutches, in which case they are inevitably confined to a wheelchair and unable to obtain exercise. For the reasons given above this is a very undesirable situation and it is therefore primarily to help such people that research into the design of a suitable walking machine has been carried out. At the University of Salford a range of walking machines has been designed and developed to suit different sizes of patient from small children to adults and this paper deals in some detail with the adult size of appliance which is, of course, the most difficult and sophisticated from the engineering design point of view. It should also be noted that in all cases these appliances have been designed for paraplegic patients, i.e., those whose lower limbs are paralysed usually due to a 141
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
1 fracture of the spinal cord due to accident or to other disease or malformation of the spinal cord.
The appliance The appliance itself, which is shown in Figure 1, consists basically of a stiff lightweight frame mounted on swivelling feet supported on double row turntable bearings. Parallel motion of the feet is achieved during straight walking and a controlled swivelling action of the feet (to facilitate turning) is provided by the spring loaded telescopic bar connecting the two footplates. The footplates themselves, which are of
must be handled either by the paralysed patient himself or by a physiotherapist or attendant. This latter consideration is frequently overlooked in the construction of orthopaedic appliances and, in a large appliance such as the adult walking machine described in this paper, weight can become critical. The weight of this adult appliance is found to be quite handleable. The basic structure, therefore, consists of side struts each with two articulations and two or more posterior stiffening bands to provide lateral rigidity. A high-tensile steel tubular “A” frame up to knee level provides further lateral bracing
Fis. 3. Supporting forces.
142
Journal of Medical Engineering and Technolol
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
Fig. 4. Pafieiif in fraiiie.
Fig. 5. Hinged fiaiiie. Fig. 6. Foot asseiiibly. ~~~
ind helps to give additional rigidity to the foot assembly nounting. To resist lateral loading, therefore, the structure :onsists of several portal frames with additional bracing and has proved to be adequately stiff and strong for the loads ivhich are imposed upon it during ambulation. At the foot platform sturdy gusset plates in high tensile jteel channel and shoe plates to which the light alloy bearings ire bolted directly, as seen in Figure 6. The light alloy honey:omb feet are then secured to the bearings by means of high tensile steel screws reacting through flanged inserts bonded into the honeycomb material. The telescopic bar which links the two feet is spring loaded to control the action of the feet on turning, and stops are provided to prevent excessive strides which might make the appliance unstable.
The mechanics of ambulation The forces acting on a correctly designed swivel walker during normal walking will be as follows : (1) A side thrust F (see Figure 2) to roll the appliance through the dihedral angle of 4" (or partly so) thereby lifting one foot and making the unit free to pivot about the other foot bearing axis. Whilst this angle is not critical, we have found that in all cases walking proficiency is greatly influenced by the sensation transmitted to the wearer by his appliance and in the author's opinion the main component of this is the feeling of safety. In no case have we found an angle of roll greater than 4" acceptable and May, 1971
most patients use very much less. This force F has to be provided by the patient by displacement of the centre of gravity (by moving head, arms and trunk) together with muscle spasm or jerk. The rolling moment required is relatively high and, concentrated at the centre of gravity the force F, is of the ordex of 114 to 116 of the body weight, depending upon the height and weight of the patient and appliance. This force can be created only in small part by the displacemenf of the centre of gravity mentioned above and it is by nc means clear where the remainder comes from : medical colleagues have suggested that activation of the large trapezius muscles in the back may contribute substantiall] to this force and there is, of course, a couple at the fool platform. Some assistance is also given by an inertia force through the centre of gravity as the body accelerates in the roll. This latter force, however, is usually of verq small magnitude as most patients tend to balance on the rocking edge of the foot once the rising foot is clear of the ground thereby minimising this inertial effect. (2) An unbalanced force S (a component of the weight-see Figures 2b and c) acting normal to the inclined axis of the bearing and causing the raised foot to swivel or rotate about the axis of the stationary foot bearing. This force will create rotation only if the centre of gravity of the patient and appliance is forward of the bearing axis. In the Salford designs this feature is built into the fool 143
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
assembly. :3) A twist or rotation of the body about the vertical axis produced by the muscles of the patient’s trunk. The magnitude of this will, of course, depend upon the degree of paralysis and deformity of the patient varying from almost nil for patients with high lesions or serious deformity to a considerable torque produced by patients with low lesions and powerful trunk musculature. This force is, of course, incalculable, but it should be noted that a considerable motivating torque can be exerted by some paraplegics by using their trunk and arms, and it is possible that with some of the more robust patients the contribution of (3) greatly exceeds that of (2). In this research, however, as we are dealing with paraplegics of minimal strength, it has been assumed that force (3) is entirely absent and the optimum design must, therefore, be based on the forces produced by (1) and (2) with any torque from (3) being regarded as a bonus. Theoretically, therefore, a correctly designed swivel walker must start to walk as soon as the force F described in (1) reaches a magnitude sufficiently high to raise one foot Rom the ground. The system of forces is then unbalanced because of the forward position of the centre of gravity described in (2), and both appliance and patient will swivel round the inclined axis of the bearing on the standing foot until the raised foot either strikes the ground or is “grounded” by contra-rocking action of the patient as he returns to the vertical. Whatever the reason for the moving foot returning to the ground its position at that time will determine the length of “stride” which the patient makes. The length of stride and with it the speed of ambulation will, therefore, depend upon: [a) the distance between the centres of the foot bearings [b) the periodic time of the sideways roll, and [c) the angular velocity of the foot assembly. From the above it will be seen that the ambulation of a swivel walker must inevitably be dependent on the following Features : :a) the mechanical readiness of the appliance to roll laterally as indicated in Figure 2. [b) the physical ability of the patient to roll the appliance :c) the physical ability of the patient to rotate the appliance about the vertical axis to help forward progress :d) the positioning of the feet and foot bearings and their geometrical action [e) the contour of the under surface of the footplate.
Design analysis The design cases for an appliance of this kind are, of course, bound to be somewhat arbitrary. Firstly, there are no technical data from previous work to give a reliable lead to the xitical cases for design. Secondly, patients vary greatly in physique, deformity and degree of paralysis. Thirdly, the :onditions under which the appliance will be used vary widely, the surface on which the appliance will be required to walk, the assistance available for putting on the appliance, etc., m d lastly, but by no means least, what the patient will do with the appliance in his efforts and contortions to make it provide him with the mobility for which he yearns. In any study of orthopaedic engineering this latter is profoundly important. If any such basic design is to be sound, however, calculations must be made to assess the order of magnitude of the :xpected loading and so indicate the direction in which design jhould proceed together, of course, with the assessment of strength and stability, the ensuring that weight is not excessive md. of course, that the appliance is safe and reliable. With these points in mind the design cases listed below were proJuced after considerable study of prototype appliances in use under clinical and domestic conditions together with :onsideration of the possibilities of future development of this appliance. Using these cases the relevant analyses were
produced and used in the basic design of the structure and its details. The principal factor in the design is, of course, the estimated bending moment on the frame in the fore and aft plane. Case I After careful study it was decided that the most critical case in design would be that created by a patient being suddenly stopped when moving at a reasonable forward speed of 12 m/min. It is assumed from observation that this speed is uniform. If at this speed the patient’s feet struck an obstruction, for example the edge of a carpet and stopped, say, within 1.5 cm, a deceleration would occur. This in turn would create a considerable overturning moment which would impose bending moments on the frame in the fore and aft plane. Case 2 That of the patient being carried horizontally in the appliance (as on a stretcher) whilst the appliance is supported at the upper (axillary) band and foot. This will cover the case of the patient lying in the appliance when this rests on the feet and the auxiliary band with the intermediate stabilising bands, sacral bands, etc., clear of the ground, for example, after the patient has donned the appliance while lying on the ground. It will also cover the case of the patient being lifted on to his feet by the axillary band. Case 3 Patient putting on appliance whilst on bed or floor and then lifting himself up by a n overhead grab handle or other means and standing upright, with heels in contact with floor. In this case a considerable proportion of the load will be taken by the patient’s arms and transferred to the handle. There will, therefore, be a substantial reduction in the load on the frame and from observation of this case in operation there would seem to be no doubt that it will be well covered by cases 1 and 2 above. Case 4 Patient putting on appliance while on floor and then turning face downwards and lifting himself either on wall bars or other device into an upright position. Again a considerable proportion of load would be taken on the patients’ arms, thereby reducing the magnitude of the load on the frame. There would, however, due to the load on the toes of the appliance and possible reaction between the hands of the appliance and the patient’s body, be reverse loads on the structure and locks at knees and hips. These are, however, not found to be critical.
Patient trials First used by adults in 1971 there are now nine adult size appliances in use in our research. Four of these are in use
Short Communications in the Journal of Medical Engineering and Technology The Editor is always glad to receive articles for publication in this journal, particularly those suitable for publication as Short Communications. Ideally, these should be about 1 ,oo(l words long and should include n o more than two illustrations or tables. They may take the form of instrument or applications notes, may describe modifications of existing procedures or techniques, or may be short, preliminary reports of work in progress. The publication of such a preliminary report as a Short Communication does not necessarily preclude the subsequent publication of a full length article when work has progressed to a stage to justify this. Intending authors should note that Short Communications are subjected to the same scrutiny as are full length articles before being accepted for publication.
Journal of Medical Engineering and Technolog:
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
in the patients’ homes and the rest in hospitals and special schools. Five of the patients are female and it should be noted that all of the patients were previously confined to wheelchairs. The patients vary considerably in stature and the degree and cause of their handicap. Of the female patients, three are approximately forty years of age, one is twenty and the last, a well-built sixteen-year-old. Two are paralysed by poliomyelitis, one by spina bifida and the remaining two are traumatic paraplegics. The weights of these patients varies between 50 and 57 kg. In the cases of the male patients these again vary considerably in stature, but are all traumatic paraplegics weighing between 50 and 80 kg. Two of the patients are adolescents of adult stature, one with a C5/6 lesion and the other with a lesion at T8 level. Another patient with a lesion at T8 is in his thirties and the fourth is aged 50 years. The latter patient has a T12 lesion and can put on the appliance himself and stand up with the aid of a tilting bed. In all cases paralysis is complete from the waist down or higher, but all are able to operate the appliance. The worst traumatic paraplegic has a T4 lesion. In operation the appliances are proving remarkably :ffective giving an ambulatory ability to the patient which they have not had before and enabling them to do household jobs which were previously impossible. Most can walk backwards and forwards and it is interesting to note that m e of the most seriously handicapped (from poliomyelitis) nas a steady walking speed of nearly twelve metres per minute, Nithout any cardiac or respiratory difficulty. This same 3atient can get into the appliance from her wheelchair, maided, but is then unable to stand without assistance. Additional to the above we have had three other adult >atients, all male, none of whom were successful. One, a nan of 64 kg, in his late twenties, with a C5/6 lesion, could :limb into his car and manage to drive, but could not operate .he appliance, partly because of respiration difficulties but nainly, we believe, through lack of the will to d o so. The iecond patient of similar weight, was thirty years old and had t lesion at T3 level but was unable to operate the appliance :ffectively, complaining of back pains when he tried. The hird unsuccessful patient was a multiple sclerosis victim who appeared to be unable to produce the motive power. 4gain, there was doubt about his strength of will to do so. These failures and similar experiences with younger people lave emphasised that not only must the patient have the ,hysical ability to operate the appliance but he must also have he determination to stand again and to ambulate. Without his latter it would seem that little progress will be made.
Discussion The work at the University of Salford has, therefore, shown :onclusively that a safe and effective walking appliance for tdult paraplegics is a practical proposition. The design has roved sound and reliable and the modular construction used :nsures that the appliance can be made at reasonable cost. Whilst, however, the appliance described above has roved to be effective for patients who are able and willing to o-operate, much further development is necessary if it is o give the patient the independence which is the aim of this esearch. Basically the disadvantages are as follows : 1) Ambulation is slow. 2) Adult patients cannot sit down and stand up unaided whilst wearing the appliance. 3) Adult patients cannot put on and take off the appliance unaided. 4) Entering and leaving a car whilst wearing the appliance is not yet possible. 5 ) The appliance can be an encumbrance in toileting and may have to be removed. May, 1974
Research work on all the above is proceeding at presen although it should be stated that the speed of 12m/min which is the maximum that adults have attained may well b considered high enough for safety. There is much experienci to support this view and it would seem likely that if the foo mechanism is further improved the average adult patient wil not wish to move faster than this. If he can make this speec with very little use of energy over uncovered floors an( carpets there is evidence to suggest that this will be enough. The other items listed are more involved but are yieldinl to intensive research. After careful training several childrei can put on the appliance themselves and stand up using wal bars. They can also get in and out of a wheelchair unaided The ability of these children to carry out such difficul manoeuvres satisfactorily gives us hope that with training anc some (perhaps major) modifications to design it will bc possible for adults to do so. Similarly we hope that ca: entry and toileting will yield to further research and traininl thus giving a degree of independence to the paraplegic patien which a few years ago would have seemed impossible.
ACKNOWLEDGEMENTS
The author would like to thank the various patients, physio, therapists and doctors who have helped in this research and alsc Mr. J. C. Griffiths, ChM, FRCS, Consultant Orthopaedic Surgeon Medical Director of the Salford Orthopaedic Appliance Unit Mr. V. H. Wheble FRCS, Mr. A. G. Taylor, Scientific Officer or the project at the University of Salford together with the Depari ment of Health and Social Security who helped to finance the research.
REFERENCES I . Rusk, H. A. Rehabilitation of patient with paraplegia 01 quadriplegia. Chapter 19 in : Rehabilitation Medicine. Edited by H. A. Rusk (C. V. Mosby, S t . Louis, 1971). 2. Rose, G. K. and Henshaw, J. T. (1972) A swivel walker for paraplegics : medical and technical considerations. Biomedical Engineering, 7, 9, 420-425. 3. Rose, G. K. and Henshaw, J. T. (1973) Swivel walkers for paraplegics-considerations and problems in their design and application. Bulletin of Prosthetic Research BPR 10-20,62-74. 4. Prast, M. T. (1974) Parapodium for adult paraplegics. Bulletin of Prosthetics Research, BPR 10-22, 391-403. 5. University of California, School of Medicine. Child Amputee Prosthetics Project. Report, 1960. 6. Hall, C . B. (1962) Ambulation of congenital bileteral lower extremity amelias and/or phocomelias. Inter-Clinic Information Bulletin, College of Engineering, New York University, I , 4, 1-8. 7. Spielrein, R. E. (1963) An engineering approach to ambulation
without the use of external power sources, of severely handicapped individuals. Journal of the Institution of Engineers, Australia, 321-322. 8. Klein, R. W. (1964) An experiment prosthesis for lower extremity amelia. Medical Journal of Australia, I , 13, 476-8. 9. Motlock, W. M. and Elliott, J. (1966) Fitting and training children with swivel walkers. Artificial Limbs, 10, 21-38. 10. Barry, R. M. and Duncan, R. J. (1969) A new concept in
swivel walkers-a comparison with the conventional (Canadian type). Artificial Limbs, 13, 66-8. 11. Nichols, P. J. T., Clarke, M. S . , McCay, G . and Molden, F. R. (1969) Swivel walkers. Annnlsof Physical.Medicine,lO, 3, 106-1 11. 12, Abramson, S. A. (1948) Bone disturbances in injuries to spinal cord and cauda equina (paraplegia). Journal of Bone and Joint SurRery, 30A, 982. 145
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
3ne of the major requirements of the medical consultant treating paraplegic patients is to hare them upright f o r at leas, I few hours a day associated, fi possible with some physical exercise. This paper deals with the construction and operatior ,fan appliance which makes this possible.
3ur environment is designed for an upright population and he person who finds himself confined to a wheelchair is at a ,erious disadvantage. It is impossible for him to enter many )uildings, use telephone kiosks, toilets or urinals, etc., untided. It is inconvenient for such a person to work inside or )utside the house or carry out a multitude of jobs which a
‘ig. I . Adult walking appliance. ( I ) Chest strap, ( 2 ) Axillary band, posterior to chest strap), (3) Sacral pad, ( 4 ) Hip hinge, (5) Glass ‘bre bands, (6) Knee straps, ( 7 ) Knee hinge, (8) Foot straps, ?)Telescopic bar, (10) Shoe plate, (11) Footplate, (12) Bearing.
May, 1977
1
person of normal physique may do. A wheelchair-bound person must look up when speaking to others and, mosf regrettably, is frequently regarded by the general public as an inferior being. Furthermore, a person confined to a wheelchaii may be subject to a variety of secondary afflictions, of circulation, of respiration, muscular atrophy and skeletal deformity, together with impairment of bowel and kidnej function, with the further possibility of pressure sores being created by continually sitting. There are, therefore, considerable physical and psycho. logical disadvantages to bzing confined to a wheelchair and it is understandable that one of the major requirements of the medical consultant is to have his patient upright for at least a few hours a day. This may be achieved by the patient being strapped into a standing frame, tilting table or support box where he must stand immobile for various lengths of time, One or two of these are available at the present time but in general are clumsy and offer little or n o opportunity of ambulation.1v4 Whilst, therefore, such an appliance will assist the biological functions by keeping the patient in an upright position it fails to provide the necessary exercise to keep the patient fit. It is also useless as a means of moving about the house to carry out light household duties or for other purposes and is, therefore, not in the same category as the walking appliance described in this paper. Since the 1950s various universities and research institutions throughout the world have been trying to create an appliance which would enable such people (mainly children) to walk. e-ll Many patients are able to walk very slowly, and often with considerable expenditure of energy, with the aid of calipers and crutches. This, of course, means that their hands are not free and they make progress by what is often called “quadrupedal” gait. At the same time this arrangement helps to meet the medical Consultant’s requirements that the paraplegic patient should spend at least a part of his day with his body in an upright or near upright position and should obtain exercise.l* Others, of course, are even less fortunate and cannot tolerate, or are too weak to use calipers and crutches, in which case they are inevitably confined to a wheelchair and unable to obtain exercise. For the reasons given above this is a very undesirable situation and it is therefore primarily to help such people that research into the design of a suitable walking machine has been carried out. At the University of Salford a range of walking machines has been designed and developed to suit different sizes of patient from small children to adults and this paper deals in some detail with the adult size of appliance which is, of course, the most difficult and sophisticated from the engineering design point of view. It should also be noted that in all cases these appliances have been designed for paraplegic patients, i.e., those whose lower limbs are paralysed usually due to a 141
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
1 fracture of the spinal cord due to accident or to other disease or malformation of the spinal cord.
The appliance The appliance itself, which is shown in Figure 1, consists basically of a stiff lightweight frame mounted on swivelling feet supported on double row turntable bearings. Parallel motion of the feet is achieved during straight walking and a controlled swivelling action of the feet (to facilitate turning) is provided by the spring loaded telescopic bar connecting the two footplates. The footplates themselves, which are of
must be handled either by the paralysed patient himself or by a physiotherapist or attendant. This latter consideration is frequently overlooked in the construction of orthopaedic appliances and, in a large appliance such as the adult walking machine described in this paper, weight can become critical. The weight of this adult appliance is found to be quite handleable. The basic structure, therefore, consists of side struts each with two articulations and two or more posterior stiffening bands to provide lateral rigidity. A high-tensile steel tubular “A” frame up to knee level provides further lateral bracing
Fis. 3. Supporting forces.
142
Journal of Medical Engineering and Technolol
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
Fig. 4. Pafieiif in fraiiie.
Fig. 5. Hinged fiaiiie. Fig. 6. Foot asseiiibly. ~~~
ind helps to give additional rigidity to the foot assembly nounting. To resist lateral loading, therefore, the structure :onsists of several portal frames with additional bracing and has proved to be adequately stiff and strong for the loads ivhich are imposed upon it during ambulation. At the foot platform sturdy gusset plates in high tensile jteel channel and shoe plates to which the light alloy bearings ire bolted directly, as seen in Figure 6. The light alloy honey:omb feet are then secured to the bearings by means of high tensile steel screws reacting through flanged inserts bonded into the honeycomb material. The telescopic bar which links the two feet is spring loaded to control the action of the feet on turning, and stops are provided to prevent excessive strides which might make the appliance unstable.
The mechanics of ambulation The forces acting on a correctly designed swivel walker during normal walking will be as follows : (1) A side thrust F (see Figure 2) to roll the appliance through the dihedral angle of 4" (or partly so) thereby lifting one foot and making the unit free to pivot about the other foot bearing axis. Whilst this angle is not critical, we have found that in all cases walking proficiency is greatly influenced by the sensation transmitted to the wearer by his appliance and in the author's opinion the main component of this is the feeling of safety. In no case have we found an angle of roll greater than 4" acceptable and May, 1971
most patients use very much less. This force F has to be provided by the patient by displacement of the centre of gravity (by moving head, arms and trunk) together with muscle spasm or jerk. The rolling moment required is relatively high and, concentrated at the centre of gravity the force F, is of the ordex of 114 to 116 of the body weight, depending upon the height and weight of the patient and appliance. This force can be created only in small part by the displacemenf of the centre of gravity mentioned above and it is by nc means clear where the remainder comes from : medical colleagues have suggested that activation of the large trapezius muscles in the back may contribute substantiall] to this force and there is, of course, a couple at the fool platform. Some assistance is also given by an inertia force through the centre of gravity as the body accelerates in the roll. This latter force, however, is usually of verq small magnitude as most patients tend to balance on the rocking edge of the foot once the rising foot is clear of the ground thereby minimising this inertial effect. (2) An unbalanced force S (a component of the weight-see Figures 2b and c) acting normal to the inclined axis of the bearing and causing the raised foot to swivel or rotate about the axis of the stationary foot bearing. This force will create rotation only if the centre of gravity of the patient and appliance is forward of the bearing axis. In the Salford designs this feature is built into the fool 143
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
assembly. :3) A twist or rotation of the body about the vertical axis produced by the muscles of the patient’s trunk. The magnitude of this will, of course, depend upon the degree of paralysis and deformity of the patient varying from almost nil for patients with high lesions or serious deformity to a considerable torque produced by patients with low lesions and powerful trunk musculature. This force is, of course, incalculable, but it should be noted that a considerable motivating torque can be exerted by some paraplegics by using their trunk and arms, and it is possible that with some of the more robust patients the contribution of (3) greatly exceeds that of (2). In this research, however, as we are dealing with paraplegics of minimal strength, it has been assumed that force (3) is entirely absent and the optimum design must, therefore, be based on the forces produced by (1) and (2) with any torque from (3) being regarded as a bonus. Theoretically, therefore, a correctly designed swivel walker must start to walk as soon as the force F described in (1) reaches a magnitude sufficiently high to raise one foot Rom the ground. The system of forces is then unbalanced because of the forward position of the centre of gravity described in (2), and both appliance and patient will swivel round the inclined axis of the bearing on the standing foot until the raised foot either strikes the ground or is “grounded” by contra-rocking action of the patient as he returns to the vertical. Whatever the reason for the moving foot returning to the ground its position at that time will determine the length of “stride” which the patient makes. The length of stride and with it the speed of ambulation will, therefore, depend upon: [a) the distance between the centres of the foot bearings [b) the periodic time of the sideways roll, and [c) the angular velocity of the foot assembly. From the above it will be seen that the ambulation of a swivel walker must inevitably be dependent on the following Features : :a) the mechanical readiness of the appliance to roll laterally as indicated in Figure 2. [b) the physical ability of the patient to roll the appliance :c) the physical ability of the patient to rotate the appliance about the vertical axis to help forward progress :d) the positioning of the feet and foot bearings and their geometrical action [e) the contour of the under surface of the footplate.
Design analysis The design cases for an appliance of this kind are, of course, bound to be somewhat arbitrary. Firstly, there are no technical data from previous work to give a reliable lead to the xitical cases for design. Secondly, patients vary greatly in physique, deformity and degree of paralysis. Thirdly, the :onditions under which the appliance will be used vary widely, the surface on which the appliance will be required to walk, the assistance available for putting on the appliance, etc., m d lastly, but by no means least, what the patient will do with the appliance in his efforts and contortions to make it provide him with the mobility for which he yearns. In any study of orthopaedic engineering this latter is profoundly important. If any such basic design is to be sound, however, calculations must be made to assess the order of magnitude of the :xpected loading and so indicate the direction in which design jhould proceed together, of course, with the assessment of strength and stability, the ensuring that weight is not excessive md. of course, that the appliance is safe and reliable. With these points in mind the design cases listed below were proJuced after considerable study of prototype appliances in use under clinical and domestic conditions together with :onsideration of the possibilities of future development of this appliance. Using these cases the relevant analyses were
produced and used in the basic design of the structure and its details. The principal factor in the design is, of course, the estimated bending moment on the frame in the fore and aft plane. Case I After careful study it was decided that the most critical case in design would be that created by a patient being suddenly stopped when moving at a reasonable forward speed of 12 m/min. It is assumed from observation that this speed is uniform. If at this speed the patient’s feet struck an obstruction, for example the edge of a carpet and stopped, say, within 1.5 cm, a deceleration would occur. This in turn would create a considerable overturning moment which would impose bending moments on the frame in the fore and aft plane. Case 2 That of the patient being carried horizontally in the appliance (as on a stretcher) whilst the appliance is supported at the upper (axillary) band and foot. This will cover the case of the patient lying in the appliance when this rests on the feet and the auxiliary band with the intermediate stabilising bands, sacral bands, etc., clear of the ground, for example, after the patient has donned the appliance while lying on the ground. It will also cover the case of the patient being lifted on to his feet by the axillary band. Case 3 Patient putting on appliance whilst on bed or floor and then lifting himself up by a n overhead grab handle or other means and standing upright, with heels in contact with floor. In this case a considerable proportion of the load will be taken by the patient’s arms and transferred to the handle. There will, therefore, be a substantial reduction in the load on the frame and from observation of this case in operation there would seem to be no doubt that it will be well covered by cases 1 and 2 above. Case 4 Patient putting on appliance while on floor and then turning face downwards and lifting himself either on wall bars or other device into an upright position. Again a considerable proportion of load would be taken on the patients’ arms, thereby reducing the magnitude of the load on the frame. There would, however, due to the load on the toes of the appliance and possible reaction between the hands of the appliance and the patient’s body, be reverse loads on the structure and locks at knees and hips. These are, however, not found to be critical.
Patient trials First used by adults in 1971 there are now nine adult size appliances in use in our research. Four of these are in use
Short Communications in the Journal of Medical Engineering and Technology The Editor is always glad to receive articles for publication in this journal, particularly those suitable for publication as Short Communications. Ideally, these should be about 1 ,oo(l words long and should include n o more than two illustrations or tables. They may take the form of instrument or applications notes, may describe modifications of existing procedures or techniques, or may be short, preliminary reports of work in progress. The publication of such a preliminary report as a Short Communication does not necessarily preclude the subsequent publication of a full length article when work has progressed to a stage to justify this. Intending authors should note that Short Communications are subjected to the same scrutiny as are full length articles before being accepted for publication.
Journal of Medical Engineering and Technolog:
J Med Eng Technol Downloaded from informahealthcare.com by Nyu Medical Center on 05/25/15 For personal use only.
in the patients’ homes and the rest in hospitals and special schools. Five of the patients are female and it should be noted that all of the patients were previously confined to wheelchairs. The patients vary considerably in stature and the degree and cause of their handicap. Of the female patients, three are approximately forty years of age, one is twenty and the last, a well-built sixteen-year-old. Two are paralysed by poliomyelitis, one by spina bifida and the remaining two are traumatic paraplegics. The weights of these patients varies between 50 and 57 kg. In the cases of the male patients these again vary considerably in stature, but are all traumatic paraplegics weighing between 50 and 80 kg. Two of the patients are adolescents of adult stature, one with a C5/6 lesion and the other with a lesion at T8 level. Another patient with a lesion at T8 is in his thirties and the fourth is aged 50 years. The latter patient has a T12 lesion and can put on the appliance himself and stand up with the aid of a tilting bed. In all cases paralysis is complete from the waist down or higher, but all are able to operate the appliance. The worst traumatic paraplegic has a T4 lesion. In operation the appliances are proving remarkably :ffective giving an ambulatory ability to the patient which they have not had before and enabling them to do household jobs which were previously impossible. Most can walk backwards and forwards and it is interesting to note that m e of the most seriously handicapped (from poliomyelitis) nas a steady walking speed of nearly twelve metres per minute, Nithout any cardiac or respiratory difficulty. This same 3atient can get into the appliance from her wheelchair, maided, but is then unable to stand without assistance. Additional to the above we have had three other adult >atients, all male, none of whom were successful. One, a nan of 64 kg, in his late twenties, with a C5/6 lesion, could :limb into his car and manage to drive, but could not operate .he appliance, partly because of respiration difficulties but nainly, we believe, through lack of the will to d o so. The iecond patient of similar weight, was thirty years old and had t lesion at T3 level but was unable to operate the appliance :ffectively, complaining of back pains when he tried. The hird unsuccessful patient was a multiple sclerosis victim who appeared to be unable to produce the motive power. 4gain, there was doubt about his strength of will to do so. These failures and similar experiences with younger people lave emphasised that not only must the patient have the ,hysical ability to operate the appliance but he must also have he determination to stand again and to ambulate. Without his latter it would seem that little progress will be made.
Discussion The work at the University of Salford has, therefore, shown :onclusively that a safe and effective walking appliance for tdult paraplegics is a practical proposition. The design has roved sound and reliable and the modular construction used :nsures that the appliance can be made at reasonable cost. Whilst, however, the appliance described above has roved to be effective for patients who are able and willing to o-operate, much further development is necessary if it is o give the patient the independence which is the aim of this esearch. Basically the disadvantages are as follows : 1) Ambulation is slow. 2) Adult patients cannot sit down and stand up unaided whilst wearing the appliance. 3) Adult patients cannot put on and take off the appliance unaided. 4) Entering and leaving a car whilst wearing the appliance is not yet possible. 5 ) The appliance can be an encumbrance in toileting and may have to be removed. May, 1974
Research work on all the above is proceeding at presen although it should be stated that the speed of 12m/min which is the maximum that adults have attained may well b considered high enough for safety. There is much experienci to support this view and it would seem likely that if the foo mechanism is further improved the average adult patient wil not wish to move faster than this. If he can make this speec with very little use of energy over uncovered floors an( carpets there is evidence to suggest that this will be enough. The other items listed are more involved but are yieldinl to intensive research. After careful training several childrei can put on the appliance themselves and stand up using wal bars. They can also get in and out of a wheelchair unaided The ability of these children to carry out such difficul manoeuvres satisfactorily gives us hope that with training anc some (perhaps major) modifications to design it will bc possible for adults to do so. Similarly we hope that ca: entry and toileting will yield to further research and traininl thus giving a degree of independence to the paraplegic patien which a few years ago would have seemed impossible.
ACKNOWLEDGEMENTS
The author would like to thank the various patients, physio, therapists and doctors who have helped in this research and alsc Mr. J. C. Griffiths, ChM, FRCS, Consultant Orthopaedic Surgeon Medical Director of the Salford Orthopaedic Appliance Unit Mr. V. H. Wheble FRCS, Mr. A. G. Taylor, Scientific Officer or the project at the University of Salford together with the Depari ment of Health and Social Security who helped to finance the research.
REFERENCES I . Rusk, H. A. Rehabilitation of patient with paraplegia 01 quadriplegia. Chapter 19 in : Rehabilitation Medicine. Edited by H. A. Rusk (C. V. Mosby, S t . Louis, 1971). 2. Rose, G. K. and Henshaw, J. T. (1972) A swivel walker for paraplegics : medical and technical considerations. Biomedical Engineering, 7, 9, 420-425. 3. Rose, G. K. and Henshaw, J. T. (1973) Swivel walkers for paraplegics-considerations and problems in their design and application. Bulletin of Prosthetic Research BPR 10-20,62-74. 4. Prast, M. T. (1974) Parapodium for adult paraplegics. Bulletin of Prosthetics Research, BPR 10-22, 391-403. 5. University of California, School of Medicine. Child Amputee Prosthetics Project. Report, 1960. 6. Hall, C . B. (1962) Ambulation of congenital bileteral lower extremity amelias and/or phocomelias. Inter-Clinic Information Bulletin, College of Engineering, New York University, I , 4, 1-8. 7. Spielrein, R. E. (1963) An engineering approach to ambulation
without the use of external power sources, of severely handicapped individuals. Journal of the Institution of Engineers, Australia, 321-322. 8. Klein, R. W. (1964) An experiment prosthesis for lower extremity amelia. Medical Journal of Australia, I , 13, 476-8. 9. Motlock, W. M. and Elliott, J. (1966) Fitting and training children with swivel walkers. Artificial Limbs, 10, 21-38. 10. Barry, R. M. and Duncan, R. J. (1969) A new concept in
swivel walkers-a comparison with the conventional (Canadian type). Artificial Limbs, 13, 66-8. 11. Nichols, P. J. T., Clarke, M. S . , McCay, G . and Molden, F. R. (1969) Swivel walkers. Annnlsof Physical.Medicine,lO, 3, 106-1 11. 12, Abramson, S. A. (1948) Bone disturbances in injuries to spinal cord and cauda equina (paraplegia). Journal of Bone and Joint SurRery, 30A, 982. 145
