The bio-mechanical factors and their effects that may determine spinal pathology and lead to backache (Low Back Pain. LBP & further pathology) are discussed.

These adverse effects need to be addressed for effective REMEDIATION →

 The final common pathway …

 to IV Disc pathology at the joints of the lumbar-sacral junction (L3/4, L4/5, L5/S1) is reduction of the L/S joint angle resulting in posterior movement of the intervertebral disc (IVD) contents and can be seen, on pMRI scan (Smith F 2006).    This retropulsion of disc contents can progress to protrusion and extrusion (see ☛The intervertebral disc→).   Also CTD→

1. Axial loading.

With  the currently advocated upright sitting posture there is an increase of compression on the L3 disc is x2.5 above that when lying supine (Nachemson).   This has been questioned by later work and determined by  Wilke (Wilke1999) as 0.10 MPa for standing and  sitting  0.55 MPa.  With  the currently advocated upright sitting posture there is an increase of spinal loading 500% above that of lying supine which is relevant to the 2T reclined mode.   For more detail see ☛ Loading→

  The intra-discal pressure is augmented In the flexed position, largely due to tension of the posterior ligaments,  while the anterior portion of the annulus fibrosis (AF) undergoes compression   In full flexion this can be as much as 100%.   The pressure gradient increases anteriorly,   tending to retropulsion of the nucleus pulposus (NP).

2. Axial compression + flexion. 

Disc prolapse  occurred more frequently when the vertebral segments were wedged to simulate extreme forward bending of the spine (Adams and Hutton, 1982). In this position, the anterior portion of the annulus fibrosis undergoes compression while the posterior portion is under tensile stress. Over 40% of the cadaver discs tested by Adams and Hutton (1982) prolapsed when tested in this hyper flexed posture, and with an average of only 5,400 N of compression force applied. This finding shows that the disc is particularly susceptible to bending stresses. In a later study in which Adams and Hutton (1985) simulated repetitive loading of the disc, previously healthy discs failed at 3,800 N, again mostly through trabecular fractures of the vertebral bodies. Taken together, these studies show that the disc, especially the vertebral endplate, is susceptible to damage when loading is repetitive or when exposed to large compressive forces while in a severely flexed posture.

3. Backward pelvic tilt. An effect of upright sitting.

When sitting there is backward tilting (anat; forward rotation) of the pelvis, which reduces or reverses the protective wedge angle of the lower lumbar joints  ☛(See Lumbar & spinal support→).

←Flexion  The axial loading force comes to lie posterior to the pivot point at the Ischial Tuberosities. A backward turning movement results in backward tilt in of the pelvis.

• The  backward pelvic  tilt flattens the lumbar lordosis and reduces the protective wedge angle of the lower intervertebral discs.  Resulting in  Posterior translation of the disc contents (NP),, see below→

• The loss of low lumbar lordosis reduces or even reverses the protective wedge angle of the lower lumbar joints
•  

4. Posterior elements

• Stretching of the posterior elements (including ligaments) which can become permanent and allow instability. (☛Ligaments & CTD→) & (see ☛ ‘Liagament integrity & creep’)→ 
• The likely forces that must be resisted by the ilio-lumbar and the supraspinous ligament (shown in blue) when sitting in the usual lumbar support seat, which allows backward tilting of the pelvis, with a bodyweight 40kg (excluding the legs) can be calculated.  Simple moments about the centre of the L5 disk suggests a ligament tension of about 70 kg (700 Newtons).  This is probably a worst-case estimate.   (JD Gorman)

5. Constrained upright sitting

The adverse effects have been long and variously described     Prolonged constrained static postures are uncomfortable and deleterious for both spinal and general health.   ☛Importance of MOVEMENT→.  Recently there has been interest in continuous small amplitude movement for upright chairs, the chair re-aligning with the users centre of gravity,  and termed  ‘Dynamic Seating’.     Exercise is required to maintain this position. This provides proprioceptive feedback and frequent small amplitude pressure changes which may be comforting for short periods and helps multifidus muscle action. Rani  Lueder  gives a review account (Lueder R 2002) and the referenced evidence→is considerable.

Recapitulation :-

For the scientific research  details, see ☛ bio-mechanics→

    See ☛ Remediation→ 

The mid-upright mode is the worst possible position. How did it happen?   ☛ Why? Mandal explains→

Advocates a Forward Tilted Seat (FTS).   The FORWARD TILTED SEAT (FTS).

The upright seat  is still recommended….Some of these diagrams suggest that iliac back support is incorporated.  This is a partial solution providing it is correctly configured. See ☛ Lumbar support→

The pMRI evidence

An investigation using Whole-body Positional MRI (pMRI), by FW. Smith, Bashir W (2007) who found that the upright position, at 90°, caused disc contents to move the most, while the relaxed position (135°/45° reclined) caused disc contents to move the least. This confirms that the upright position is the worst for the back, while the relaxed position is the best.   See  Positional MRI →

See  ☛  Biomechanics research for safe sitting.→

Bogduk N, Macintosh JE. The applied anatomy of the thoracolumbar fascia. 1984; Spine 9: 164-170.

Bogduk N, Macintosh JE, Pearcy MJ. A universal model of the lumbar back muscles in the standing position. 1992; Spine 17: 897-913

Bogduk N. Clinical anatomy of the lumbar spine. 1997; 3rd Ed. Churchill Livingstone, Edinburgh

Gracevetsky S, Farfan H, Helleur C. The abdominal mechanism. 1985; Spine 10: 317-324.

Granata KP. Marras WS. Cost-benefit of muscle cocontraction against protecting against spinal instability. 2000;

Kamali N. Evaluation of total and semental lumbar lordosis using radiographic interpretation. 2003; Babol Quarterly Journal Volum 5 , Number 3:

Hides JA, Stokes MD, Saide M, Jull GA, Cooper ID. Evidence of lumbar multifidus muscle wasting ipselateral to symptoms in patients with acute/subacute low back pain. 1994; Spine;19.165-

Hides JA, Richardson CA & Jull GA. Multifidus recovery is not automatic following resolution of acute  first episode low back pain. 1996;Spine

Johansson H et al. A sensory role for the cruciate ligaments. 1991;Clinical orthopaedic and related research.268.161-178.

Saal JA & Saal JS.   Nonoperative treatment of herniated lumbar intervertebral discs with radiculopathy. An outcome study. 1989;Spine:14,431-437.

Wilke, H.-J., Wolf, S., Claes, L. E., Arand, M., Wiesend, A. Stability increase of the lumbar spine with different muscle groups.- A biomechanicaJ in vitro study. 1995 Spine 20, 192-198.

NERVES

Cavanaugh, Kallakuri, and Ozaktay. Lumbar facet pain:biomechanics, neuroanatomy and neurophysiology.  1996;J Biomech 29: 1117-1129

Schwarzer AC, Aprill CN, and Bogduk N. The sacroiliac joint in chronic low back pain.1995; Spine 20:31-37.

NUTRITION

Wilke H-J, Neef P,  Caimi M, Hoogland T,  Lutz E.  New In Vivo Measurements of Pressures in the Intervertebral Disc in Daily Life1999; SPINE Volume 24: 755–762

Adams MA, Hutton WC. The effect of posture on the fluid content of lumbar intervertebral discs. 1983;Spine 8:665-671

Aaras, A, Horgen, G., and Ro, O. (2000) Work with Visual Display Unit: Health consequences. International J Human-Computer Interaction. 12(1) 107-134.

Lueder R. Anatomical, physiological and health Considerations relevant to the SwingSeat. 2002; Ergonomics Review.

Gorman JD. The cause of Lumbar Back Pain; Eversley, England, Gorman, 1983. Ibid pp 95-106

AXIAL LOADING

29 Jayson MIV. Herbert CM. Barks JS.Intervertebral disc: Morphology and bursting pressure. 1975: Ann Rheum Dis 32:308-315.

30 Hutton WC, Adams MA. Can the lumbar spine be crushed by heavy lifting?. 1982; 7: 586-90.

31 Nachemson A. Morris JM. In vivo measurements of intradiscal pressure. J Bone Joint Surg (Am) 1964;46:1077.)

33 Nachemson, A. L., Disc pressure measurements. 1981; Spine, 6:93-97

34 Sato, K., Kikuchi, S., and Yonezawa, T. In vivo intradiscal pressure measurement in healthy individuals and in patients with ongoing back problems. 1999; Spine, 24(23):2468- 2474.,

35 Wilke H-J, Neef P,  Caimi M, Hoogland T,  Lutz E.  New In Vivo Measurements of Pressures in the Intervertebral Disc in Daily Life. 1999; SPINE 24, pp 755–762

37 Adams M, McNally D, Chinn H et al. Posture and compressive strength of the lumbar spine. 1994; Clin biomech 9:5-14

38 Wilke, H.-J., Wolf, S., Claes, L. E., Arand, M., Wiesend, A. Stability increase of the lumbar spine with different muscle groups.- A biomechanicaJ in vitro study. 1995 Spine 20, 192-198.

RECLINED MODE

68 Nachemson A. Morris JM. In vivo measurements of intradiscal pressure. 1964; J Bone Joint Surg (Am);46:1077.

74 Sato, K., Kikuchi, S., and Yonezawa, T. In vivo intradiscal pressure measurement in healthy individuals and in patients with ongoing back problems. 1999; Spine, 24(23):2468- 2474.

89 Wilke H.-J,  Neef P, Hinz B, Seidel H, Claes L.  Intradiscal pressure together with anthropometric data ± a data set for the validation of model. 2001 Clinical Biomechanics 16 Suppl; 1: 111-126

EXERCISE

4 Croft PR, Papageorgiou AC, Thomas E et al. Short term physical risk factors  for new episodes of low back pain.  Prospective evidence from the South Manchester Back Pain Study. 1999; Spine 24: 1556-1561.

3 Croft PR et al. Outcome of low back pain in general practice: a prospective study. 1998; BMJ 316: 1356-9.

98 Linton SJ, van Tulder MW.  Preventive interventions for back and neck pain problems: what is the evidence?   2001 Spine  1;26(7):778-87..

151 Patel A.  Am J Epidem;172:419, Quoted in New Scientist 29/6/2013:45

39 Hides JA, Richardson CA & Jull GA. Multifidus recovery is not automatic following resolution of acute  first episode low back pain. 1996;Spine

The general account of remediation of the adverse effects of the Mid-upright seated mode can be seen at   The upright seated posture.→

• IV discs prolapse occurred more frequently when the vertebral segments were wedged to simulate extreme forward bending of the spine (Adams and Hutton, 1982) in addition to when loading is repetitive or when exposed to compressive forces while in a flexed posture.   See ☛ IV Dscs→
• Lordosis occurs at two levels of the human spine, cervical and lumbar.  The spinal joints subject to internal derangement are the 4th, 6th  & 7th cervical and the 4th & 5th lumbar” (Cyriax JH. 1946).
• Both these spinal levels are where mobile segments meet a solid mass, the skull and the pelvis, and where mechanical spinal pathology mostly occurs (Harrison DD 1998)and differences are found when comparing LBP patients with healthy patients (Jackson RP, 1994).
• Approximately two-thirds of total lumbar lordosis occurs at the inferior two segments (L4-L5-S1) (Kamali, 2003).
• This configuration occurred as a result of hominins adopting an upright (orthograde) stance for efficient bipedalism (see pages on  Paleo-anthropology).
• The lordotic configuration involves a large wedge angle (16-24° at L5/S1) at the lower lumbar joints.  The point of the wedge lies posterior. (See ‘Angles & Lordosis)
• The wedge angle reduces any tendency for retropulsion of the disc contents.
• Retropulsion can lead to impingement on pain sensitive structures ( ) and protrusion and extrusion of disc contents.
• Retropulsion occurs on axial loading with joint flexion (See ‘Effects on sitting posture’).
• The wedge angle is reduced when the pelvis is tilted backwards which occurs with upright sitting.
• This adverse effect is augmented by reduction of the hip flexion angle (occurs with a seat parallel to the floor) and pelvic support set too high.
• A large wedge angle is protective and occurs in people with a low incidence of LBP and where there is no tendency for reversal of the angle (ie. to go to 0° or below).
• Retropulsion is corrected (reduced) in a reclined position or with hip extension (Smith 2006).
• Excessive extension (lordosis) transfers pressure to the posterior pain sensitive structures.  In moderation this is not evident clinically in the lumbar joints (but is in the cervical region).
• Movement to ensure intra-discal pressure changes is essential to provide dis nutrition (See ‘Disc nutrition’).

LIGAMENTS

• Ligaments limit joint movement in a specific direction and provide stabilisation (See Anatomy/ligaments ).
• Ligaments are visco-elastic and can be lengthened by excessive, prolonged stretching.
• Excessive joint range and instability can lead to CTD (Solomonow 2003).
• Excessive joint range can disable the normal protective action of muscles (See Anatomy/muscles).
• Adams et al. (1980) showed that the supraspinous-interspinous ligaments segments are the first ligamentous tissues to become stressed with forward bending of the lumbar spine.     Ligaments appear to require long periods of time to regain structural integrity, and compensatory muscle activities are recruited (Solomonow et al., 1998; Stubbs et al., 1998; Gedalia et al., 1999; Solomonow et al., 2000; Wang et al., 2000). The time needed for recovery can easily exceed the typical work-rest cycles observed in industry.   See ☛Ligaments→

MUSCLES & NEUROLOGY

• Muscle cocontraction, can substantially increase the mechanical loads (compression, shear, or torsion) or change the nature of the loads placed on the body’s articulations during an exertion or motion.   See ☛ Muscles→
• Neurological pathways.   Pain pathways have been identified for joint pain, pain of disc origin, longitudinal ligaments, and mechanisms for sciatica.   See ☛ neurology→

Requirements for optimising the bio-mechanics of prolonged sitting.

•Reduction of axial loading→

•Preserve the lumbar lordosis→

•avoid backward tilting of the pelvis→

•Ensure disc nutrition by pressure changes with movement→

Requirements for optimising the bio-mechanics of prolonged sitting.

• Reduction of axial loading→
• Preserve the lumbar lordosis→
• avoid backward tilting of the pelvis→
• Ensure disc nutrition by pressure changes with movement→

Combined these can be difficult to achieve, for office and home, but can be done using the 2 Tilt concept→.

Systems in use at present, partial remediation

• Pelvic support→
• Forward tilted seat (FTS)→
• Reclined work mode (Okamura)→

See Origins of lumbar vulnerability (Paleoanthropology)→

Next ☛ HOW WE SIT NOW →

 People with ‘special needs’ are universal and these needs require to be addressed,  particularly in a reclined mode.

SPECIAL NEEDS

The 2T concept is intended for office use or in the home for those who spend much time working or gaming or just browsing.  The concept also has a number of medical /hospital uses.  I was advised in Cambridge to keep these under wraps as they might subtract from the perception of it’s more general use.   However people with ‘special needs’ are universal and their needs require to be addressed  particularly in a reclined mode.

This occurred to me after talking to an academic ex-orthopaedic surgeon.  I wrote

“Dear Chris

I have been thinking about your comment on patients and realised that it referred to potential surgical cases and those with deformity of whatever cause.  I think this adds a new dimension to the 2T concept under the heading ‘Special Needs’.

I would propose that 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.

The ‘CC Chair’ perhaps?”

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.

In relation to the 2T concept,  see ‘Execise & movement→

A continuation of the comments in the PROLOGUE.

  For a copy of the above, that is easier to read,

To postulate a hypothesis for limiting LBP on prolonged sitting existing background scientific knowledge of spinal pathology and bio-mechanics, in combination with clinical experience, arguing from cause to effect,  was easily achieved and resulted in the 2T concept which is shown above.  Conventionally this would need to be confirmed or falsified by experiment, in this case by field trials.   With no commercial chair models available this was not possible, to date.  Subsequently a different approach has emerged, closer to ‘inverse probability’ of ‘Bayes Theorem’.  The process is reversed, watching the effects to determine the cause.  In this instance later research has confirmed the original assumptions with a complete theoretical confirmation by pMRI sudies.

The original 2T model has remained intact except that the transition from reclined to upright conferring physiological advantages and has becomr recognised as a mode in its own right,    The bi-modal, 2T concept  becoming a tri-modal (3M) concept.    The desk-less workstation version, allowing a ‘standing’ mode became a 4 mode concept (4M).  ☛work station→ .

Interestingly the prototype1 shown was a desk-less version.  In time this has become recognised as a ‘Workstation’, with no help from me.    At that time IT components were clunky.   The advances in IT hardware now make a desklessworkstation an obvious solution and has added advantages.    I am now (2015) returning to this as a Tri-Modal (3M) concept with an additional Sit/Stand mode, transforming the 2T to 4M. →WORKCHAIRS, a new breed with a reclined mode.

An upright chair at a desk may become to look decidedly retro-.   

The concept has not changed since then. Additional evidence has accrued along the way and perceptions have progressed to become more supportive.

Concept Evolution.

Orginally it was met with blank incomprehension!  At first sight, it seemed odd that the office
worker of the near future would be lying in work chairs in a reclined position for some, or most, of the time while using a computer and was regarded as a ‘paradigm shift’.  In the next 17 years I have noticed a softening of this incomprehension and an adoption of at least some new ideas.  Now, in 2015, a chair is proposed, the Altmark,(☛Some chairs→ )that has at least an upright and reclined work position.    This work, I hope, shows the evolution of thinking from early to later work in relation to sitting and chair design, commonly designated ‘ergonomics’. Although intended as a medico-scientific study it started with the experience of patients and I have included their interests.   Patient input and clinical observation is dismissed by scientists as ‘merely’ anecdotal’.   However, with several decades of seeing patients with backache, I make no excuse for including some insights as the start of the scientific process which proceeds to systematic analysis, experimentation and efforts towards falsification.   HAS  

 Examples oh ‘high-end’ office chairs with partial remediation.   For a full remediation see ↓

• The only full solution,  The obvious, and perhaps only, solution was for prolonged work to be performed in a chair that has a stable, correctly supported, supine  Reclined mode→

The criticism

I have heard only three precise criticisms of the 2Tilt chair concept.

• 
  “This is too comfortable. My staff will go to sleep”.  Although on the P1 prototype (above) with no upholstery, just ply-wood. (Sleep & productivity→)
• “Female staff will not like lying in their office with legs in the air”.

These are good examples of ‘familiarity bias’ resulting in denial and prejudice for such an unfamiliar concept.

• “Office managers and CEOs will find the footprint bigger than ordinary office chairs”    The third has substance in that in the reclined mode any reclined chair inevitably has a larger footprint than an upright chair. When not in use the default upright mode of the 2T chair is probably less than most chairs.
• This becomes irrelevant with the 4M chair.  A workstation has a smaller foot print than a desk/chair combination.
• A further difficulty has been suggested, arising from CAD studies, relating to the relationship between a 2T chair and a simple, non height adjustable, desk. This is being addressed.  Ditto the above.
• From leading chair designers  (2015).  “I agree but this concept is ahead of its time.  Familiarity bias will strike in and uptake will be poor.” (see Implications & uptake→ and A new breed of reclined work-chairs→)
• From an Orthopaedic surgeon – “Without clear unarguable scientific evidence that the current models of chair on the market are truly bad and can be proven to produce the backache of which the majority of the population sooner or later develop, current models will continue to be used without supportable criticism of their use. Anecdotes regarding theories of back pain produced by chairs already on the market will not be sufficient to topple the plethora of current chair models recommended for the comfortable ‘ergonomic’ (a term I dislike) seating position.“ . A valid point but ignores the pMRI evidence. This type of global response is often an example of ‘familiarity bias’ (see Implications & uptake)  It may be based on lack of knowledge of recent biomechanical research or occurs in experts who see innovation as a threat and seize on any ambiguities. It is almost impossible to argue effectively with ignorance if it is entrenched with prejudice, as was explained to me in a diplomatic context by an ambassador. However arguments, likely to be put forward by the powerful chair manufacturing lobby, will be cut short if it can be shown by field trials that a 2T work chair fares better in reducing symptoms than any existing chairs.

Footprint

The argument for limiting footprint is that offices are priced by the area of floorspace. The overall cost (2011, rent, tax, maintenance) of a 11sq ft workstation in the London ‘West End’ is £14,1530 pa. It is less in the City ‘Square Mile, £8,720 and less still out of London being £4,250 in Birmingham. Costs in the City have reduced by 7.3% but risen by 12.5% in the West End (Times, London14/2/20). Obviously managements will have to rethink their strategies to reduce these costs. Limiting workstation footprint is a shortsighted option. It is a false economy to cram work stations into a given space, especially as better layouts become usual and when well designed desk/chair workstations become more universal. Jukes showed that productivity is reduced, by as much as 30%, in a stressful working environment. Costs are increased by low level morbidity, absenteeism and staff turnover. The improved ergonomics removes at least one cause of stress in the office environment and this translates into increased individual productivity leading to reduction in staff numbers and with better layout, increase usable office space. The slightly greater cost of the footprint is more than offset by increased productivity and this is what eventually improves the ‘Bottom Line’.  (See ‘2T & office design’).

This consideration becomes largely obsolete as The 4M concept, with a smaller footprint than a desk/chair workstation becomes mainstream.

Sleep.

 I responded that a nap might benefit productivity and it was unreasonable to keep staff awake with uncomfortable chairs.   I was unaware of the later research.    (see ☛ SLEEP→)

Market and uptake

The 2t concept is a ‘paradigm change’ and will create PR with the large insurance & media interest,

2T concept

With this, uptake is likely to be large and quick.   It could be said that a paradigm change could be equivalent to a potential disaster to a firm if there is a failure to recognise it’s implications .  Chair manufacturers which do not have a 2T model in their range   may react with normalcy bias..”(See Uptake?/Implications?).