Author Archives: Dr. Henry Sanford

About Dr. Henry Sanford

As a retired consultant in Orthopaedic (Musculo-skeletal) medicine, I was first trained in Orthopaedic Surgery and changed when working with JH Cyriax at St Thomas' Hospital, London, my old teaching hospital. He is regarded as the 'Father' of the subject. I worked as an Associate Consultant in the Rheumatology department, STH, in private practice in Harley St. and the Cromwell Hospital. I have run courses and lectured in in the UK, USA, Belgium, Germany, Scandinavia.

The 2t BASE.

 

 

Some options for the 2T base

Screenshot 2019-09-17 at 18.10.52

 

This basic prototype at Cambridge shows the carcass/shell mounted on the base with a tilt hinge at the level of the fulcrum.   The base is a standard 5 star.   Greater stability when reclined would be improved if the back 2 legs were extended.   This suggests that the rotation of 360° would need to be reduced to about 60° in the anterior direction.

The post Hospital beds shows a number of beds each with a base of great complexity.

Screenshot 2019-09-26 at 15.16.44  Screenshot 2019-09-26 at 17.42.17  AnkitAnkit

Screenshot 2019-09-27 at 17.16.22The Ankit model has a simpler base.  It is possible to incorporate a hinge mechanism onto this sort of 4 wheel base to support the functional carcass.    Screenshot 2019-09-29 at 17.04.48

  • For this
  • The hinge would be at the apex of the base.
  • The hinge could be mounted at the fulcrum
  • or at the front edge of the seat-pan.
  • Damping is required to avoid a jolt at the end of range.
  • The base can be narrower or wider than the carcass.
  • The latter is more stable.
  • Consider :-
    • The mounting of the arm-rests, if any.
    • A shelf, shelves.
    • side restraints for a hospital bed.

 

 

 

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SOME HOSPITAL BEDS

To design a hospital bed to a new concept a knowledge of existing thinking is helpful, with a quick Google search.

Return to ← Hospital Applications

Screenshot 2019-09-25 at 12.07.26A simple hospital bed.   

Retails at £340.

 

  • A home bed with a backrest and some contouring. Screenshot 2019-09-25 at 11.57.09

 

 

 

  • ‘Xb Hospital Bed Profiling Nursing Bed Patient Bed Care Bed Multi Function Electric Smart Home Care Bed Manual Adjustable ‘    from £2,616.97.    The hype states :-
  • Backrest and Leg Lifting: Adjust bed to a comfortable position to meet amusement, dining, Screenshot 2019-09-25 at 12.01.17reading and cleaning.
  • Leg up & Leg Down: Relax patients legs, promote legs blood circulation, preventing varicose veins and easily for legs’ daily care.
  • Backrest Lifting: Patients can sit up and do some daily life activities easily, lessening nursing burden for both patients and nurses.
  • Easy full body lift for nursing and working.

 

  • Looking at these beds, a few ideas emerge to comply with a 2T version.
  • The bed-end would become a variable foot-rest enabling exercise of Screenshot 2019-09-25 at 12.06.04the calf,
  • The side restraints could be added at will.
  • The short base wheels would be back at the level of the end of the seat-pan.  (Tipping might occur if someone should sit distal to this point).
  • This allows the bed to be transformed into a wheel-chair.
  • Screenshot 2019-09-25 at 12.00.23Adjustable head-rest, foot-rest and leg-raise would be integral.
  • The Trendelenberg position available for emergency use.

 

 

Screenshot 2019-09-25 at 12.31.01At Last!   A brave effort going some way towards the 2T concept.  It looks awkward, over-engineered  and is anything but simple.

 

 

 

Ankit

Ankit

Ankit Polyweave Industry provide vast range of best quality hospital bed and other hospital equipment in India.

Expensive, complicated compared to a 2T model.


Screenshot 2019-09-26 at 15.16.44Another example.   The ICU Electric economy model GM7002.   Instead of a simple 2T tilt the carcass is moved forward to achieve a wheelchair mode.

Screenshot 2019-09-26 at 17.42.17HILL-ROM TotalCare Sport 2 P1900M

Electric Hospital bed.  Asking Price :$5,995.00 USD.   At least it has an upright mode.

 

Screenshot 2019-09-27 at 14.46.18The carcass/shell of this model is near correct, except for poor contouring.   A 2T version would be simpler.   Note that the front wheels of the support are below the front edge of the seat-pan which allows a wheel-chair mode.  This has been made awkward by the undue depth of the seat.   Check with the advised dimensions of the 2T version to see how this could be improved.  Could a visitor sitting on the leg-rest tip the whole bed?   Unlikely, I think.

Screenshot 2019-09-25 at 11.59.49It can be seen that a 2T version has the potential to be a major advance on most of these in cost, versatility and comfort. 

Improving an upright chair.

 

OK.  So you use a chair and are liable to backache.  All this is very confusing and so what do you do?   I am no longer in the business of giving advice to patients and organisations.  However my interest in optimising chair design might allow me to offer some tips.

If you have an expensive, top range chair, examine the section on how some of these relate to the 2T concept and could be upgraded (so far, largely ignored) by manufacturers.  This may help you modify your own chair.

Chair remediation.

Only a forward tilted seat (FTS) or the incorporation of ‘Iliac’ support allows a chair of this type to be considered as a semi-partial solution to the adverse effects of mid-upright sitting. It is therefore essential that the support should be of the right type and directed to the right place.   Check with the relevant posts. See ⟵The 2 modes 

Chair remediation. Pelvic (Iliac) support.

Chair remediation

See Pelvic support

Chair remediation. Forward Tilted Seat.

Screen Shot 2013-10-17 at 14.25.36This is an alternative and the preferred option for the 2Tilt concept.

See Forward Tilted Seat

 

A variation of these designs is to have an antero-posterior convex seat surface, the Ischial ‘Off Load’ system.     ⟵Off-load system 

Chair remediation. Possible adjustment.

A good chair can be modified to approach the advantages of the 2T CONCEPT (see ‘A complete solution’).

  • Disable the adjustment that allows the pelvic support to be above 20 cm above the seat (?Chewing gum)    (see ‘Lumbar, pelvic/iliac support’)
  • Arrange for the adjustment control to allow easy back & forward reclination movement.  Make the chair a 2T system – either reclined or forward but not intermediate.
  • Intermediate ranges should be unstable.   They can be used as a rocking chair or as  therapeutic exercise following an acute episode of backache/lumbago.
  • In the upright mode the seat can be either tilted forward (see ‘The forward tilted seat) or arranged to take advantage of the pelvic support providing this is correctly modelled.
  • Apart from chair height and head/foot-rest, adjustments should be set accordingly and then ignored or fixed.
  • And let me know how well it works!

If your chair is more ordinary you may be lucky and have one that has reasonable iliac support or a forward tilted seat.  If you are buying, a back shop can show a number of models and advise but be aware that they are trying to sell you something and tend to feed you the manufacturers hype.

Chair remediation.  If all fails.

If your chair is really basic you may need some widgets. Possibilities are

  • A wedged cushion on the seat which helps approximate to a FTS.
  • A backrest cushion that gives iliac support.  Have a good look at the section here on iliac support that must not be higher than 20 cm above the seat and approximates as near as possible to the original Gorman model.
    • My patients loved the ‘PostureRight’ cushion which was designed by my old St Thomas’ colleague, Dr Bernard Watkins.
    • Various lumbar ‘Rolls’ are OK if correctly placed.
    • I have a cheap (£1) and cheerful wire & net model which works moderately well.

Good Luck!

There is plenty of well intentioned advice to be found on the web.  But please read this first (Sorry, hard work, I know) so that you can distinguish the  rarely well informed from misinformation  and some that is frankly laughable.

The best that I have seen is from Posturite in 4 easy diagrams.   http://www.posturite.co.uk/art-of-sitting     Obviously written by someone who is well informed.

The Hermann Miller account from being almost laughable is now good, probably as a result of being advised by Andersson, the Swedish scientist.

 

Next see  ☛ →

EASY CHAIRS

For HOME & CLUBS

Hitherto  the concern of this work has been only for ‘ergonomic’ work-chairs.   Chairs for Screen Shot 2018-11-24 at 10.29.33the home have been rather ignored as their ergonomics are unimportant compared to chairs required for prolonged work.    Since looking at chairs from a  bio-mechanics viewpoint,  almost all show a total disregard, or oblivion, to even basic concerns for spinal well being.   Designers are obviously ignorant of these factors although comfort also depends on them.   However there should be no excuse for designing a chair that is liable to give spinal dysfunction, or can be categorised as ‘A machine for making Backache’.    The boundaries between contract and home furniture  are decreasing and the division may be disappearing entirely. 

Christopher Bellew wrote in his daily blog “I was a guest at luncheon in a London club and fell into conversation with an affable member in the bar after lunch. His name is Dr Henry Sanford.   After some general chit-chat we digressed to his working life.   After a life time in Orthopaedics, he told me that his patients with backache would ask him to recommend a chair that would not make their problem worse.   I have a suspicion that his invention owes much to his observation of recumbent members of his club after lunch. The Savile would be an admirable name for a chair …”

Screen Shot 2018-11-07 at 18.49.09 It can be seen that the typical club chair makes no pretension to ergonomic concerns.   They are irrelevant as the chairs are not intended for prolonged use and only have  to look comfortable.

Screen Shot 2018-11-16 at 16.10.31The aged Intervertebral Disc. (IVD→)  and the lengthened seat-pan allows a slouched posture which is not seriously adverse.

Easy chairs in the home

Much the same applies to chairs in the home which are not intended to be work-chairs.   Recliners are for home use and probably used by those who sit, or even sleep, for long periods.  As they have features similar to the 2T (3M) concept they have been considered separately.   Will people buy recliners when a cheaper and better designed dual purpose chair comes on the market?  This may also be particularly relevant to the growing ‘gamer’ market. (Recliners→).

Screen Shot 2018-11-07 at 21.35.38The ‘Saddle Chair’ by Timothy  Oulton, at his fantastic new premises in the old Bluebird workshop in the Kings Road, caught my eye.   It is almost reclined Screen Shot 2018-09-22 at 15.05.21with no other concern for ergonomics.  Still on an equestrian theme, Mandal advocated a Forward Tilted Seat.   With a FTS and the back rest with pelvic support this would become an interesting ergonomic chair and the improved ergonomics would also add to the comfort.   The other chairs on show look comfortable and are mostly heavily upholstered.   I am told that this is a good selling point – “After all, they can always Screen Shot 2018-11-24 at 10.29.33use a strategically placed cushion” but would probably be avoided by anyone liable to backache, who would know better.   If the upholstery was of denser foam at the level of the iliac (Pelvic) crest the appearance would be the same but pelvic support would result. ( BACKRESTS. Pelvic support v. Lumbar.→).


The Eames Chair.
  Yes.  This seems to be the best easy home chair.   I have ignored it, not being a work-chair, but it does have some 2T features, a reclined mode and leg support, which accounts for it’s comfort.   For me, It is not an ‘Object of Desire‘.   I do not like it being in two bits Screen Shot 2018-11-27 at 13.07.03when there is a one- piece solution which could be more elegant, simpler and to the contemporary taste using the 2T (3M) concept.   Being more ergonomically compliant it would also be even more comfortable.

Roorkee chairs

For the ‘cool’ uncluttered look a simpler chair is possible.   The old Roorkhee campaign chair which had some ergonomic advantages has many modern derivatives. Roorkee chairsSome of these advantages having been lost in translation.   It is chairs of this sort that are popular with Interior designers although the ergonomic advantages vary. Roorkee chairs have spawned a number of modern designs including Klint’s Safari Chair and also by Marcel Breuer (the Wassily chair), Le Corbusier (the Basculant Chair), Wilhelm Bofinger (the Farmer’s Chair) and Vico Magistretti (the Armchair 905).
Roorkee derivatives

Roorkee chairs are campaign chairs with marvelous design  used in the Army from 1898 to WW2, ‘officers , for the use of’.     Screen Shot 2018-11-20 at 09.35.06The pair from my Uncle Jack (Berrington) during the South African Boer War (c. 1902) was lost in transit so he indented for two more.  The original pair reappeared and now I have all four.  Here is his Brother in Law, my Uncle Gilbert and his sister (Aunt Alice Berrington) sitting in Roorkee chairs in about 1950.   He is in a reclined position and the bottom edge of the tilted back rest gives some pelvic support, and this unexpected ergonomic efficiency is why officers may have found it so comfortable.   Hers has an additional headrest which would allow a sleep mode.
Developed by the Indian Army Corps of Engineers in Roorkee, India, the Roorkee chair is lightweight at about 10 lbs., and breaks down quickly to be stored in a 9″ x 36″ canvas bag.   The ingenuity of the design lies not only in its ease-of-assembly and dis-assembly, but the very act of sitting in the chair reinforces its structure.  The seat canvas is slung between front and rear crossbars and pulls them towards each other, tightening the side rails in their mortises with the legs.

Screen Shot 2018-11-10 at 14.05.18

My Roorkee chair, disassembled.  Shows the backrest.  The original canvas was lighter in colour, replaced here with army tent canvas.   The front strap may have been added later, and broke when being assembled today (17/Nov/2018, not bad after over 100 years).    Assembling needs some expertise which batmen (soldier servants) must have learned quickly.  How it can be done is shown, using a modern version at https://www.youtube.com/watch?v=nwPqQSYUCvM .   Also it requires expertise to get the parts into such a small canvas IMG_20181117_144333731bag.  The original bag 90 x 23 cm.

The ergonomics, I discovered, are good.   Leaning backward results in rotation of the backrest with a slight extension force on the thoracic spine and  extension of the lumbar spine.   This comes close to the 2T CONCEPT  and accounts for it’s recognised comfort.

Screen Shot 2018-11-18 at 11.12.44

 

p5 in reclined modeCompare the position of the user when sitting in a 2T prototype showing an optimal work position.

Core 77 has an account and show a number of archive photographs of the chair being used including one  of Gen. Earl Alexander, sitting in a Roorkee chair beside Churchill,  in a less comfortable upholstered (no correct back support) arm chair, who would have known Roorkee chairs well from his time serving in the 4th Hussars.   Screen Shot 2018-11-20 at 09.23.19

(See https://www.core77.com/posts/65226/MCM-Furniture-Design-History-The-Safari-Chairs-Military-Roots).

The FUTURE is going the 4M way

From a wierd concept in 1998 to become disruptive in 2017?

The ‘Deskless Chair’ derived from the ergonomic importance of a reclined work position, is morphing into the ‘Workstation’. This should reduce the incidence of LBP and other health issues.

In 1903 Ford’s ‘Horseless Carriage’ had morphed into the Model T, capable of 20 horsepower In 1908.  This, at least, solved the “great horse manure crisis of 1894” when it was suggested that London’s streets would be clogged in 9 feet of horse manure in 50 years. It’s descendants are, in turn, being disrupted by ‘the driverless car’.

Screen Shot 2018-11-24 at 17.43.29Disruptive technologies have to prove themselves first. They do so by working on the same infrastructure as the incumbent leaders. Cars had to run on the same streets as horses. Dial-up internet connections in the late 1990s used the copper in the phone networks.  (Dan Denning Publisher, Southbank Investment Research ).   So, work-stations have to use existing office spaces before becoming universal.

We are seeing a number of ‘OFFICE WORK-STATIONS→’ type models which include a reclined work mode and so are superior to the present (2016) upright conventional  models.  The models shown here are a step in the right direction but are not 2T compliant and appear to ignore the science and are based on engineering.    They do not invite a great uptake, in spite of extensive PR.  WORK-CHAIRS, a new breed with a reclined mode →

For further reading, see ☛

←Return to  ☛ 2T CONCEPT a full solution

The CHOTTO

Screen Shot 2017-05-20 at 11.14.27

This highly innovative chair was introduced to me by it’s designer,Thomas Stroman, the Founder of Stroman Design.   He wrote to me “I am an architect by training, but having experienced back surgery, my focus has been on ergonomic seating design for human-computer interaction.  Over the past three years I have designed, prototyped and patented the Chotto® ( chair + ottoman ) .  It is a uniquely human-centric and recumbent seating / task-seating / standup desk that positions the body
into close proximity to the neutral body posture that is produced in microgravity.”  “I believe  this field of study is increasingly important and needs to be pursued given the scope of benefits it can provide those who must sit by choice or physical condition. I would also like extend an open invitation to you to evaluate my prototypes if you are ever in NYC.    Regards,  “

An excellent objective and a very interesting product.  At first glance I might be excused for thinking that it looked as if it were self mobile with caterpillar tracks.  Perhaps an exciting concept for the future.    I wrote back (May 19, 2017)

Dear Tom    I have had another look at your web page  www.stromandesign.com​  At first sight, I admit, I thought the Chatto to be OTT.  But on second thoughts, some might find it attractive, including me, to charge around an open plan office floor in a mini-tank.  But I can see it excites ‘familiarity bias’.  I can see no reason why it cannot be modified to take advantage of the 2T ergonomic optimisation.   This would be a huge selling point.  Even the Chinese put ‘health’ as their top design requirement  Unlike our chair manufacturers who put ‘comfort’.  (See http://sittingsafely.com/comfort/ ).Screen Shot 2017-05-20 at 11.11.16
In the early model, above, I was worried about the apparent calf compression that has the potential for DVT.  “An optional footrest elevates the legs and feet while an immediately mobile, nested and freely rotating task tray provides a universal surface for eating, reading, writing, or digital interaction. This same tray can be repositioned within the optional rear support brackets for use with the pivoting display interface / standup desk ( PDI ).  The PDI is based on design research that favors a human-centered interface that literally revolves around the seated, tension-free and fully supported Screen Shot 2017-05-20 at 11.07.26user.  If paired with a laptop, the PDI can also be used as a dual-screen interface in both the seated or standing position.  With the PDI in the default standup desk position, the Chotto simultaneously accommodates both a standing and seated user – all within a small 15 s.f. footprint.”

Also the user is very happy but looks trapped.   How does she get out?   Leg support is unecessary as it is provided by the long bones of the leg but a foot rest is essential, padded support for the heels, for prolonged work but not for the upright mode.

Screen Shot 2017-05-20 at 11.08.23Dear Tom.     Looking at your diagrams, I would make the following points from the bio-medical viewpoint :-
  • You have a good reclined work position.  But the Chair /body shape interface requires  iliac support at 20 cms above the seat pan. This is important for spinal wellbeing.   (See http://sittingsafely.com/2t-reclined-mode/  bottom half).
  • You have correctly spotted that good design encompasses most body shapes and sizes.  Adjustment is only needed at the extremities, neck and legs.   (See http://sittingsafely.com/adjustment/ ).
  • I like the way your computer screen adjusts to whichever mode.
  • For full 2T compliance I make a point for the intermediate ranges to be unstable for additional health benefits.  Of course, this is not basic (See http://sittingsafely.com/exercise/ & http://sittingsafely.com/the-unstable-intermediate-mode/ ).
  • On further thought, I do not think that a lordotic concave support for the kyphotic/convex thoracic spine, as described in the 2T is strictly required.  The thoracic joints are stable being splinted by the ribs.  Only rotation movement occurs at this spinal level.
    Your configuration depends on the convex shape of the wheel circumference and this can support the fairly solid thorax, providing that it is accompanied by neck/head support in the reclined mode.  You will be glad to hear that I have tested this while having my bath.  In the UK we have prolonged baths and so can think great thoughts.  The iliac support, lower down at the lumbar-sacral junction is very important but can be effected by padding as you have suggested,
     
    Best
    Henry

Another architects chair

Screen Shot 2017-05-20 at 13.48.22Architects have a tradition for designing good furniture. Aaron Chetwynd did this 2T sketch for me. It is deliberately ‘office chair’ looking to reduce ‘familiarity bias’.   It is not intended to be a work-station.

Screen Shot 2017-05-20 at 13.37.15

 Tom
The leg/foot-rest design is important and is wrong in the Aaron view above. There is no need for a leg rest as this is effected by the strong long bones of the leg (Lower end of the femur & lower leg tib/fib).  However this brings point pressure onto the heels which I found to be painful over time and needs to be well padded.  I think your design shows this except the pressure seems to be at the ankles.  This may need further consideration. Also it needs adjustment for leg length.  Pressure on the calf muscles should be avoided as it may limit venous return and cause Deep Vein Thrombosis.
New point
Screen Shot 2017-05-22 at 17.22.25

 

 

About the Chotto:

Design details

‘Two Tilt, (2T),  ‘BiModal’ or (3M) chair   


INTRODUCTION

First see   Office Chair DESIGN, Ergonomics & Low Lumbar Backache→ Screen Shot 2018-12-03 at 17.20.27

2T so called as there are only 2 stable positions, each at either end of range.

  1. Reclined mode. A fully supported reclined work position for prolonged work.   .
  • Screenshot 2019-09-18 at 14.57.1140° from horizontal is assumed to be the most supine reclination as a work mode.  Less becomes impractical, (except for the 4M workstation) and more loses some of the axial compression advantage.
  • For more details, see  ☛The 2Tilt RECLINED MODE for fully safe sitting.
  1. Upright mode for certain short activities and quitting the chair and is the default mode when the chair is unoccupied.   ☛2T Upright modes
  2. An unstable mid range for quick & easy transition between modes.

Screenshot 2019-09-16 at 01.14.06DETAILS & OPTIONS

The 2T chair consists of (essentially) 2 parts :-

  1. Carcass shell
  2. A base, on which the shell is mounted.
  3. A tilt hinge mechanism.

THE CARCASS/SHELL 

  •  Of fundamental importance to achieve  ergonomic optimisation with resulting comfort.
  • Reclined mode configuration the’shell’ components are intended to describe a seat’s supporting interface with the human body.
  • When completed the Shell Chair forms could be employed to assist in creating an actual shell-based seat in various possible ways:
  • Shell1Shows that a slightly flexed thoracic spine + the upper lumbar joints is not adverse.
  • An office version would be narrow with a small telescopic headrest to address height variation and to reduce footprint.
  •  Iliac (Pelvic) support at correct level and shape to prevent a lumbar ‘sag’.
  • Incorrect configuration can engender discomfort (as can be experienced in certain dentists chairs) and more important is potentially dangerous.
  • Head support that ensures a forward vision field.
  • Variability at head and feet only.
  • Leg/foot support.
  • a foot rest of some sort is required in the reclined mode  .
  • Ability to change rapidly to the upright mode.

Screenshot 2019-09-26 at 15.07.48

Screenshot 2019-09-14 at 11.35.50

Screenshot 2019-09-14 at 11.36.41

Screenshot 2019-09-17 at 18.31.05

 

The alternative upright mode

  • Screenshot 2019-09-16 at 12.49.39This alternative upright mode is for certain short tasks only.  Relatively unimportant if the user can be relied on to avoid using this mode for prolonged use.   
  • Better use iliac support or a Forward Tilted Seat .
  • With the 2T chair the upright mode is not maintained for long periods and so the feet can be easily tucked under the seat, making height irrelevant…as in the Balans chairs.
  • Iliac support is included to prevent lumbar spine sagging in the relaxed mode or if used in the upright mode.

Materials

  • Moulded alone in a thin rigid material (as with Aaro Aalto’s ply furniture or the Knoll Saarinen).  Graphene is obviously relevant.
  • Moulded to form a base shell carrying relatively thin textile/foam skin padding (Eero Saarinen Knoll and Eames Vitra collection).
  • As a final form around which a tensile mesh or textile ‘hammock’ design could be generated (Herman Miller Aeron and Knoll Generation chair).
  • As a final form around which various upholstered designs could be generated (Knoll Eames or Herman Miller ranges)
  • As a final form around which other associated furniture or workstation accessories can be generated (modular office systems)
  • Consider Gordon Murray’s system consisting of tubes + composite giving extra strength

http://www.bbc.co.uk/iplayer/episode/b01f11hp/How_to_Go_Faster_and_Influence_People_The_Gordon_Murray_F1_Story/  (Note by Peter Bessey )

CHAIR SIZE

Largely determined  by the the head-rest and foot-rest.

Pelvic (Iliac) support 

Pelvic support was developed for upright by John Gorman an engineer and chiropractor was in contradistinction to the prevailing ‘lumbar support’.  Precise support, shaped to the curve of the iliac crest is  applied to the posterior iliac spine and iliac crest of the pelvis.   A slight forward
nudge at this point is mechanically efficient in extending the two lowest joints and prevents the pelvis rotating backwards.  Pelvic support was designed for upright chairs.   As a component of the cacass ‘shell’ it need only be minimal and not adjustable. Intended to Screen Shot 2017-05-09 at 17.12.05prevent backward pelvic tilting when supine lying.  It cease to be ‘pelvic’ and becomes the adverse ‘lumbar’ support above 20 cm from the seat -pan. 
Do not allow adjustment!   See http://sittingsafely.com/pelvic-support/ →Screenshot 2019-09-19 at 16.29.43

The Forward tilted seat might be preferable.
See  ☛ The FORWARD TILTED SEAT (FTS).→

ANGLES & Backrest variability

CAD drawings suggest that the backrest should be hinged to the seat pan to obtain optimal configuration in the 2 modes.    Adds to manufacturing cost.   These were explored by Peter Bessey as a theoretical exercise in 3D CAD, based on anthropometric (US) data from the well known Henry Dreyfuss book. It commenced around a simple 50percentile male mannequin which was readily available.  The information from this investigation, should first be used to generate a totally adjustable Rig device, that should be used for trialling and true research purposes, before any final design concepts are prepared.

Angles

With the adoption of the 4M deskless, work-station model the constraints imposed by these angles become largely irrelevant   See  ☛ OFFICE WORK-STATIONS→

 

THE SEAT-PAN   

2T reclndTorso/seat interface pressure studies show that most of the body weight is concentrated at and around the ischial tuberosities. Very little at the thighs, except in the Forward TS mode.   Only a ⅓  the thighs require support.

Screenshot 2019-09-19 at 16.29.01

  • “stool height.” The term “sitting height” is reserved for the height to the top of the head when seated.
  • For men, the median popliteal height is 16.3 inches and for American women it is 15.0 inches.
  • The popliteal height, after adjusting for heels, clothing and other issues is used to determine the height of the chair seat. Mass produced chairs are typically 17 inches high.   
  • For someone seated, the buttock popliteal length is the horizontal distance from the back most part of the buttocks to the back of the lower leg. This anthropometric measurement is used to determine the seat depth.
  • Mass produced chairs are typically 15-17 inches deep.

Mandal seaDiagram annotated from Mandal.   The Seat height based on Mandal’s ‘Forward tilted seat’ (FTS),by 15-20°.

Screenshot 2019-09-17 at 18.23.592 holes should be cut near in the  wood base to limit slippage with a FTS seat.  Position of ‘Butt-pockets’ showed by Okamura research (above).

Peripheral details

HEAD-REST Screenshot 2019-09-17 at 18.27.35

  • Essential for full torso support
  • Variability is required.
  • The headrest needs to be minimalised fo reduce the overall footprint.
  • onl.y the base of the skull requires support and the upper neck.
  • This only requires a height of 3-4” and a breadth of 9”
  •   Measurements are shown below.

Head-restThe head-rest should be adjustable in both

  • Longitudinal
  • A-P directions

Hd support2

Head suprt

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Arm-rests

  • Screenshot 2019-09-16 at 14.32.16Are helpful for typing. They might limit some movement.
    • How should they be mounted?
    • On the carcass.   This moves with the user and may be an advantage when modes are changed.
        • On the base.   This has the advantage of a fixed point for  changing mode.  Admittedly this should be unnecessary if the carcass is properly balanced.

Arm-rest

FOOT-REST

Optional only if the heels do not rest on the floor or desk bar. This can be arranged if the chair is lowered when in the reclined mode (as in the Okamura chair).  I regard this as only acceptable if performed easily without complicated manual adjustments.  ( Is it possible to have a mechanism that does this when the user leans backward into the reclined mode?) Screenshot 2019-09-16 at 12.08.56  A SPRUNG SOLE MUST BE OPAQUE FOR ISLAMIC SUSCEPTIBILITIES.

Screen Shot 2013-09-19 at 17.01.57A monococque design is probably unsuitable for an office work chair, but may be possible in a deskless design.  Ideally the leg/foot-rest should retract or fold back when in the upright mode. A simple system is shown in the garden chair. A similar model can be bought cheaply at B&Q.

Screenshot 2019-09-18 at 18.30.28There is no need for the calf support.  This could result in DVT. The lower leg bones (tibia& fibula) give the only support required between  the thigh at the seat pan and the heel at the foot- rest,   However variability of the leg-support is  essential.

 

 

 

TILT-HINGE

  •  To enable the transition between the stable end-ranges.
  • To allow range from 7-135º,
  • and that can be used for short periods as a form of comforting exercise, particularly for rehabilitation for an internal derangement at the low lumbar levels. (See  ☛ http://sittingsafely.com/exercise/ ).  
  • The intermediates are unstable.
  • Controls are avoided because fixed Mid ranges reproduce the conventional adverse sitting posture.
  • Movement is activated by user’s change of posture.
  • Screenshot 2019-09-16 at 12.23.29CONCEPTS
      • Concept1. Fulcrum at point of balance under seat, with damping to avoid jolt at extreme of range.   Simplest,
      • Concept2. Hinge at the anterior border of the seat-pan, using a constant force spring.
      • This makes the fwd tilt the default mode.  The damped spring allows the chair to fall back and to be lowered to the reclined position.
      • Spring tension would have to be adjusted so that user movements would activate the alternative range,
      • Also to allow for an user of unusual weight.

 

Thoughts on MONOCOCQUE solutions for home use
Screenshot 2019-09-18 at 15.10.52

    • 1/ A cushion for headrest. Fixed variably,
    • 2/ Needs to be 2 holes (butt pockets) about 3″ from front edge.
    • 3/ See detail notes for foot-rest
    • 4/  5Star base looks wrong for an iconic chair.
    • 5/  The drinks flap could rotate to become a computer table.

Screenshot 2019-09-18 at 16.19.47Details of the p3 prototype.

Screenshot 2019-09-16 at 12.07.58

 

 

To incorporate a heel-rest to the Aaron monocoque design

The tilt-in-space feature allows the whole chair to tilt up to 30 or 60 degrees,  while maintaining  hip and knee angles.   Applies mainly to wheelchairs but note that also pertains in the 2T monocoque concept.

THE 2t BASE

All the 2T prototypes used a standard 5 star base as shown above.      A 4 wheel base is easily designed and inexpensively manufactured to various standards.    The subject is considered further in the post on the Base→

Screenshot 2019-09-29 at 17.04.48

 

For user ‘special needs’.   A patient would have a shell moulded for the torso that would then be mounted on a suitable version of a 2T chair instead of the standard shell.  This addresses the axial compression and pelvic tilt in the reclined mode.  In the upright mode the backrest stand away from the torso with a Forward Tilted seat and so becomes irrelevant.  But support might be needed and then we would have to think about Gorman’s Iliac version.  This is already built into the standard backrest shell, in a reduced form.  Plaster-of-Paris’ (POP) casts are commonly made in orthopaedic and physio departments and can be used to form a shell for the individual from fibreglass or other material at no great expense.   3D printing could be relevant.     ☛ ‘Special needs’→

Screen Shot 2018-10-23 at 13.59.07

 

HOSPITAL VERSIONS

Hospital applications

I was warned in Cambridge to avoid discussion of medical applications of the 2T concept as this might detract from it’s major office use.    However it could change the hospital experience for the better.   It might also improve the NHS finances!

There seem to be 5 areas with overlapping needs for which a 2T Concept has a perfect application :-

  1. Mass emergency.  With the distressingly increasing frquency of international outrages which involve high volume of casualties which are tended while lying on the floor, a light emergency bed is required.
  2. Hospital resuscitation unit.
  3. Hospital A&E trolley
  4. Hospital bed
  5. For specific hospital requirments such as neck traction.

OPTIONS & DETAIL NOTES

  1. A lightweight bed for emergency use.

Screen Shot 2017-04-12 at 17.15.19A design similar to the p/1 prototype monocoque version or the A&E trolley (gurney)  is suggested.

 

Screen Shot 2017-04-12 at 17.21.51

See Hospital beds→ for a plethora of models.   A 2T version would be a major advance on most of them in cost, versatility and comfort.

  • A 2T version of a trolley for A&E patients (gurney) has advantages
    • Simple and inexpensive
    • For storage and logistics it can be easily disassembled and stacked.
    • Allows an upright (wheel chair) mode,
    • Reclined mode.  As for the 2T version, for comfort.
    • The patient can lie comfortably supported when lying  supine and can be in a sitting position..
      • Strait, full, supine mode modification without semi-reclination is also needed.
      • Lying on side, fully prone or in the recovery position  would then be possible.
      • The slight ‘iliac’ support would be lying above the pelvic brim and limit slippage if the head end is lowered.
      • The slightly elevated legs aids venous return.    It can be addressed by increasing the seat/back-rest
        Screen Shot 2017-04-12 at 17.26.57angle or having these components hinged (an added expense).
    • The patient can be effortlessly put in the Trendelenburg position.   ( the head is lower than the feet).
    • The 2T  principle 8 has to be modified to allow stable positions in the transitional mode.
    • Screenshot 2019-09-18 at 16.59.59Manufacture can be inexpensive.   But see an American example 
      .
  • A 2T version of a bed
    • Simple and inexpensive
    • Allows user movement
    • Incorporates the emergency Trendelenberg position.
    • Allows a more user friendly position for cervical traction.
    • Allows the patient to lie fully flat horizontal.
    • Lying on side, prone or in the recovery position is possible.  The slight ‘iliac’ support would be lying above the pelvic brim and limit slippage if the head end is lowered.  The slightly elevated legs aids venous return.    It can be addressed by increasing the seat/back-rest angle or having these components hinged (an added expense).

Screenshot 2019-09-25 at 11.59.49

  • Looking at this bed, a few ideas emerge for a 2T version
  • The bed-end would become a variable foot-rest enabling exercise of the calf,
  • The side restraints could be added at will.
  • The short base wheels would be back at the level of the end of the seat-pan.  (Tipping might occur if someone should sit distal to this point).
  • This allows the bed to be transformed into a wheel-chair.
  • Adjustable head-rest, foot-rest and leg-raise would be integral.
  • The Trendelenberg position available for emergency use.

Consider a model with greater sophistication and approaches the 2T CONCEPT,      Check with the advised dimensions of the 2T version to see how this could be improved. Screenshot 2019-09-27 at 15.58.04

 

 

 

Hospital beds→

  • Hospital resus

A similar model to the above but of more robust design.  The ability to attend to the patient at a desired height and tilt is an advantage.  Rapid position change, particularly the Trendelenberg position, needed quickly in acute episodes, is a major advantage.

  • Hospital special needs

Cervical traction.  At present the patient lies supine and flat with traction from the skull to a weight attached over the end of the bed.  This is  prolonged and the position becomes uncomfortable, the constraint is a disadvantage and reading is difficult.   With a 2T design the patient can be tilted to a more comfortable, less constrained, semi-reclined position without altering the traction.

c tr2

  • Patient fitting.  A version of the shell for specific needs for individual patients has already been described.      A patient would have a shell moulded for the torso that would then be mounted on a suitable version of a 2T chair instead of the standard shell.  This addresses the axial compression and pelvic tilt in the reclined mode.  In the upright mode the backrest stand away from the torso with a Forward Tilted seat and so becomes irrelevant.  But support might be needed and then we would have to think about Gorman’s Iliac version.  This is already built into the standard backrest shell, in a reduced form.  Plaster-of-Paris’ (POP) casts are commonly made in orthopaedic and physio departments and can be used to form a shell for the individual from fibreglass or other material at no great expense.   3D printing could be relevant.       ☛ ‘Special needs’→

Mass emergency needs

Screenshot 2019-09-26 at 15.54.24BLU-MED’s Portable Ward Beds for Mobile Hospitals has 1-inch aluminium tubing, Weighs only 17-pounds, including IV pole, mattress and decking and Folds to 32-inches x 42.5-inches x 4-inches.   This is impressive but, in addition, a 2T version would be more versatile with a wheelchair mode giving easy mobility.   The 2T prototypes also used 1″ tubing, slightly heavier, using steel, but probably stronger and more stable.

The BASE mounting

  • The 2T prototypes all used a standard 5 star base.
  • This is not essential but if used needs modification.
    • Rotation should be limited, for stability, to 35º in the forward direction.
    • The 2 back legs should be extended for stability when reclined.
    • They can be used to support a shelf.
    • the-2t-base/

 

Aetiology of LBP.

LBP. Cause (Aetiology).

The causes of LBP are multifactorial  and ill understood.    It is suggested (Adam et al.2002)  that  there is a need to integrate the evidence from genetics, biomechanics, biochemistry, cell biology and psychology to construct a comprehensive model.

Twin studies suggest that only 70% of the UK population is liable to LBP (Spector 1999). Other twin studies strongly emphasise the genetic factor in the aetiology of LBP  (Battie et al., 2002).   Genetics are not a cause of LBP but a risk factor acting through, possibly, spinal configuration or components of the disc composition.

Psycho-social factors, regarded as an important in the large increase in the last 20 years (Waddell 1996), is  more a response rather than a cause, resulting increases reporting.     Anecdotal evidence from patients with chronic LBP should not be ignored.  Although usually unaware of any causative incident, they are fully aware of what makes their symptoms better or worse.

The prevalence and incidence of LBP in populations that do not use Western style upright chairs but other ‘natural’ styles of sitting. which are culturally determined, is very low or nil, suggesting an adverse effect of the use of Western style upright chairs.    In Japan, this increases as elements of the population adopt Western chairs (Schlemper 1987).

Nutrition, environment and lifestyle may all play a part in the aetiology of LBP, but the only new factors that might account for the present epidemic is lack of exercise and a sedentary Western lifestyle.    Driving, office work, computers and TV,  the modern worker spends an increasing amount of time in a chair.

Epidemiological studies of  backache prevalence.

The literature on epidemiological evidence is extensive but, in relation to aetiology, confusing due to uncertainties and imprecision in describing reliably the condition that is under review.  Low back ‘trouble’ extends from LBP of psycho-genic origin to a midline IVD protrusion causing a corda equina syndrome, which is a surgical emergency.  Meta-analysis of systematic reviews, useful for evidence based therapeutics, have to be viewed with caution in extrapolating to clinical conditions. (Furfan et al 2001).  I have often seen wrong conclusions in my own field.

A study by the US Department of Health and Human Resources (NIOSH 1997) reviewed a number of factors and the general conclusions seem to suggest that the evidence was contradictory and confusing. There was an emphasis on non-physical psycho-social factors and heavy load handling.   Much of the research into the causation of spinal breakdown has concentrated on violent or inappropriate spinal usage afflicting manual workers today and hominins in prehistory (See Origins of lumbar vulnerability→).

In a Swedish review (Linton, van Tulder.2001) of controlled trials of preventive interventions for back pain problems only exercise gave evidence of relatively moderate significance perhaps suggesting that sitting has no influence on LBP.   The divergence of the  clinical and other evidence from that of some epidemiological studies suggests that the methodology of the latter should be reassessed rather than an immediate conclusion that seating plays no part in the symptomatology of LBP.

Invisibility is possibly due to  the universality of the upright sitting posture on chairs becoming  a part of the human condition in Western orientated populations, so that it fails to become apparent to recognition in systematic reviews.  This impacts on research, where musculo-skeletal funding is minuscule, in spite of the economic, which is about £13billion annually in the UK, and personal cost .

Familiarity bias

Familiarity bias is a factor in holding back the development of ergonomic seating.  Efforts at remediation of upright seating seem to have come to the end of the road. To address the epidemic of LBP a paradigm change is required.

‘Familiarity’, ‘Confirmatory’ and ‘Normalcy’ bias is recognised by Behavioural Psychologists as Cognitive dissonance, first described by Leon Festinger in 1957.   It  is the condition described  as the unease felt by people whose experience or information is inconsistent to other, usually already held, beliefs.  Information and situations are avoided  In an effort to reduce this discomfort and regain psychological consistency.   It can be a factor leading to serious, even catastrophic, situations.

The general familiarity bias ….

We are hardwired to believe the world we live in today and to which we are acclimatised so that we bSed lifestyleecome incapable of comprehending and believing that change is coming.  In general most users have been commanded, since nursery days, to ’Sit up straight’ or worse ’Stop tilting your chair forward’, a normal response of a child to adopt an actual correct position.   Later  ‘expert’ advice on ‘correct’ sitting upright is given with authority.  This is inspite of having been demolished by AC Mandal back in 1985 (See→Why? Mandal’s Homo sedens. ).   This mistaken view of correct seating is still accepted and widely promulgated by authorities who advise on such matters.   'Correct sit

The bias holdup

Failure to understand familiarity bias I have found  pervasive among chair designers.  Peter Bessey comments in this work (→COMFORT)  “Introducing medical-based information to designers and their education, at an early stage in their careers, would be a good way to change the status quo. The question is: how do you get that over to them in a lucid and easily digested manner? It needs to be described and presented in an easily accessible manner and not necessarily couched purely in medico-scientific terminology.”  In other words, they are really not up to speed on the scientific evidence.

Normalcy biasNormalcy bias is slightly different and can lead to serious problems for firms, however big.    It is a dangerous trap for manufacturers of ergonomic office chairs, who may be perfectly happy with the status quo, to fall into and it can blind recognition to a very real and credible threat.

People normally think that the experts are correct.  They have the top jobs and the top positions in the professions and universities, and so generally that’s true.  Until the next scientific advance arrives.  A scientist  at CERN explained “you know, so far my theory is safe, but it might – you know, ask me next week, they might have found out that I’ve been wrong my entire career”.   Good scientists are prepared to admit this but most people are overwhelmed by familiarity bias.

The Ptolemaic system of astronomy seemed to make sense of what was observed in the sky above, that the earth is the centre of the universe.  It worked for 1,500 years even becoming a tenet of Christianity, until Galileo made the mistake of inventing a telescope and Copernicus showed, scientifically, that it was wrong.  The Christian was an example of familiarity bias.  There’s now new research coming out on what’s called the double split experiment, which is a major contributor to the understanding we have of quantum mechanics, which is now maybe violating the popular interpretation of that, 70 or 80 years after it was made.  Change can be slow.  That misplaced advice on ‘correct’ sitting posture is an example.

It is not surprising that most people have difficulty in over-coming the ‘familiarity bias’ engendered.  The exception are many backache sufferers and the younger, millennial, generation who are capable of thinking ‘sideways’.

My own initial training in Biology has made me mistrust sudden jumps (large mutations) in ‘natural selection’ as these are usually deleterious. It is small incremental advances over time that result in progress.  The same can be applied to political ideology which has made me a conservative.  However when real scientific evidence advances it may be time to change.   The 2T or 4M concept, in terms of chair design is only an incremental change.  Most office chairs need only modifications.  But as a concept it seems to excite cognitive dissonance and be regarded as a ‘paradigm’ shift.

 Comment

Screen Shot 2017-03-07 at 17.59.30

From Prof. MC Boulter
The comments in your  interesting blog remind me of the theme that d’Arcy Thompson used to preach a century ago. He must have influenced you also.
Best wishes
– Michael

Screen Shot 2017-03-07 at 17.59.30     Reply from Dr HA Sanford 

d’Arcy Thompson, I think, had a mathematical approach to development and did not understand evolution by natural selection, which is my approach.  I see the 2T concept as an incremental change, along the lines of development by natural selection.   In the world of chair design the 2T concept is perceived as a ‘paradigm change’, a reclined instead of an upright posture, and I have to accept that as being so and say so.   These alternate viewpoints may make my explanation sound contradictory and excite cognitive dissonance.

Many thanks
Henry