A stretch reflex is more properly termed a strain reflex. Tensioning by reflex response to strain is the only means of providing for an equal and opposite reaction in a normally passive system. The appropriate links are found automatically, by reflex response to strain, since the reaction follows the strain. Each link is precisely tensioned, by reflex response to strain, since each link continues to strain until the appropriate tension has been achieved. Similarly, interactions between reactions arising from simultaneous actions are blended automatically. It will be seen that the system is self-compensating and therefore error free. It will also be seen that the system is inherently stable.

The implications of tensioning by reflex response to strain are profound. It means that evolution has solved this complex problem of inter-muscular coordination by the introduction of a distinct dynamic coordinating mechanism. The mechanism is distinct in that it does not rely on complex nervous inter-connection to achieve its coordinating role. Stress is the messenger which unites the separate reflex arcs into an integrated system.

We can now complete the coordination puzzle. Add this dynamic mechanism and the pieces will only fit together in one way. We have three variables under nervous control and three controlling elements, each element controlling one variable.

The three variables are muscle length, muscle tension and gain. The three controlling elements are a coordination of activity computer (motor cortex), a distinct dynamic mechanism (DDM) and a remote gain control (cerebellum). The motor cortex creates voluntary movement by controlling muscle length. The DDM tensions muscle by reflex response to strain. The cerebellum controls the ratio of stress to strain. The motor cortex can shorten a muscle but it cannot tension a muscle because no muscle can be tensioned in isolation. Only entire chains can be tensioned, a function of the DDM.

Reflex response to strain raises the question of the quality of that response or 'gain'. Gain alters the ratio of stress to strain. At high gain, the system will be stiff and movement sharp and strong. At low gain, the system will be tender and movement progressive and feeble  eg. prepare for an attack (high gain) .... prepare to thread a needle (low gain). Gain control and muscle tone are inextricably linked. Hence the increased muscle tone we experience with high gain.

AUTHOR' S NOTE

Engineers have long dreamed of building a robot which can reproduce the quality of human movement, but how to do it has remained a mystery. The secret is to build a normally passive DDM system. The author has considered a normally passive DDM system built from piston type actuators and electro-pneumatic components common to industry. Analysis indicates that it will reproduce the quality of human movement and that it will respond to gain control just as we do.

If developed, the system would assist the study of many conditions which affect co-ordination and movement. For example, spasticity appears to relate to lack of gain control over the DDM. The development of a relatively simple normally passive DDM robotic limb would enable this relationship to be explored in a way that would otherwise be impossible.

THE SPINE .... COORDINATION AND STABILITY

It is the function of the spine to provide a supple but stable mast. Ask an engineer for a stable mast and he will give you a rod of steel. Ask him for a supple mast and he will give you a rod of rubber. Ask him for a mast which is both supple and stable and he will protest that these are conflicting demands. He may build an articulated spine supported by artificial muscles and control it with a microprocessor for a brain. However, he will only have succeeded in building a normally rigid system. There is no theoretical design which can produce the supple but stable characteristics of our spine except, that is, for a normally passive DDM system. A normally passive DDM automatically creates supple stability.

As stresses are transmitted through the spine, so the segments strain. As the spine continues to strain until the appropriate tensions have been achieved, the system is inherently stable. If the level of stress is reduced, decay automatically reduces the tension in muscles. Thus, strain controls the balance between gain and decay. It is this continuous interaction between strain, gain and decay which is the secret of supple stability.

Co-ordination in a normally passive system means something very different to the coordination of a normally rigid system. To drive a normally rigid spine we would need to monitor the position of each vertebra and give precise and specific instructions such as ...3^rd thoracic rotate 3.75 degrees ...4th thoracic rotate 3.50 degrees ...5th thoracic rotate 3.25 degrees etc. Compare normally passive. As stresses are transmitted through the spine, so the segments strain. Thus, the segments naturally move and operate in concert (coordination).

This kind of coordination is not comparable to the geometric precision of a normally rigid system. In the course of a change of posture, different vertebrae move by different amounts in different people. Neither are these movements necessarily smooth or continuous. Nor do they need to be. Provided that the joints are sufficiently mobile, the spine will perform its proper function.

AUTHOR'S NOTE

Before reading about altered segmental relationships it is worth taking another look at the skateboard axle assembly and noting an important difference between this assembly and a spinal segment. 

Rotate and release the axle and it springs back to a central or neutral position. This is because the rubber disc behaves like a spring. An intervertebral disc is a jelly filled bag and does not have the 'spring' properties of a rubber disc.  Vertebrae do have muscle attachments but muscles do not behave like springs either. On completion of a task, we do not spring back to a fixed state of attention. Muscle length and muscle tension are independent variables under nervous control. We can, for example, relax the biceps with the arm either flexed or extended or anywhere in between.

ALTERED SEGMENTAL RELATIONSHIPS

As the segments move and operate in concert, the DDM naturally acts to maintain inter-segmental relationships. We can confirm this experimentally. Observe a correctly aligned spine... invite the patient to repeatedly flex, extend and rotate the spine... re-examine the spine and note that it has remained correctly aligned. Observe a pattern of pre-rotated vertebrae... invite the             patient to repeatedly flex, extend and rotate the spine then re-examine and note that the pattern of pre-rotation has remained unchanged.

However, inter-segmental relationships can be altered if the system is overcome by force or speed. There is a natural limit to the power and speed of a strain reflex. We may exceed both power and speed during some violent incident or the system may be overcome by force, during normal activity, if stresses concentrate at a particular segment. When the system is overcome by force or speed, disunited movements take place. Disunited movements alter segmental relationships. We observe these altered relationships as pre-rotation and/or abnormal curvatures.

Full unilateral rotations occur when the forces acting at a segment exceed the strain reflex's ability to resist. Unilateral rotations alter inter-segmental relationships because muscle length and muscle tension are independent variables. Muscles do not have a fixed resting length in the way that a spring has. Adopt and relax in any posture and muscle tone will automatically adjust muscle lengths to fit the geometry. Similarly, following a unilateral rotation, muscle tone will automatically adjust muscle lengths to fit the new geometry. This adjustment represents an altered inter-segmental relationship. Thereafter, the spine will continue to function in this way.  Indeed, altered relationships have no significance except that pre-rotation diminishes the mechanical efficiency of the joint.

The ability of the system to take the strain is a function of gain. Gain is necessarily adequate to the task. For example, it is impossible to lift a heavy object at low gain. However, while the overall level of gain must be adequate, it may be inadequate for a segment where stresses concentrate. In which case, the forces acting at this segment will cause a full disunited rotation.

We can now understand how it is that a man may heave his car out of a ditch without injury and yet 'put his back out' while picking up the soap in the shower. The fault is the concentration of stresses at a particular segment. The ability of this segment to take the strain is a function of gain. Prepare to lift (high gain). Relax and take a shower (low gain). In theory, we should be equally vulnerable during both high and low gain activity. However, patient histories indicate that most people 'put their backs out' during some low gain activity. The probable explanation is that we spend more time doing more with less care at low gain.

We can now understand why the avoidance of high gain activity offers no security. The only solution is to improve mechanical efficiency of the spine. We can also understand the process by which the system becomes progressively muddled. The odd incident produces the odd pre-rotation. Pre-rotation makes the system less efficient and more prone to disorder. Thus, we have a vicious circle by which complex patterns of disorder develop. By middle age, complex patterns are common.

The mechanical consequences depend as much on the pattern of pre-rotation as the number of pre-rotations. Pattern also has a bearing on the effectiveness of protective postural response. The analysis of pattern is complex and is not an essential topic since, no matter how complex the pattern, intervention is simple. Irrespective of pattern, the procedure is the same.

STRESS RELIEVING BY SYSTEM LOGIC

The clue to scientific intervention lies in the realisation that the DDM maintains the stability of the spine. From basic physical principles (vector analysis) we know that in all cases it will take less muscular effort to maintain the stability of a correctly aligned spine. It follows that the direction of least effort is the direction of order. In other words, we will correct inter-segmental relationships if we can stress relieve the system.

A sharp tap at or around the lateral end of a transverse process causes a rapid reflex movement of an individual vertebra. The principle is the same as that used to test the patellar reflex. These rapid reflex movements are of very small amplitude and very short duration but the amplitude and duration are of no consequence. The significance lies in that, in the normal course of events, the segments of the spine operate in concert. The artificial stimulation of the reflex produces an individual or disunited response. In effect, the segment is fleetingly de-clutched. It is this de-clutching procedure which allows the system to stress relieve itself.

To resolve a complex pattern of disorder, it is not enough to work along the length of the spine de-clutching the segments which appear pre-rotated. Neither is it enough to work along the length of the spine de-clutching each segment once. To stress relieve a network of interacting strain reflexes, a great number of reflexes must be stimulated in the correct sequence. One cannot predict what that sequence will be. However, the specialised equipment overcomes this problem.

Stress relief is a one way process. While changes of inter-segmental relationship only occur when the appropriate segment is stimulated, every change of inter-segmental relationship is a step towards stress relief. It follows that we can find the correct sequence by the random stimulation of reflexes. The principle is best illustrated by way of an analogy.

Consider a combination lock designed by an inept locksmith. Due to a design fault, the lock ignores all wrong numbers while a tumbler drops every time we pass a correct number ie. the next number in the sequence. Consequently, we only need to spin the dial back and forth a few times and the safe will open.

This is the principle employed in stress relieving by system logic. In reflex mode, the handset is adjusted so that all four pads are operating as rapidly moving patellar hammers. As the handset is moved up and down the length of the spine, the configuration of the pads and the speed of operation ensures that every segment is stimulated in turn. At each pass, the next segment in the sequence is found. Thus, as the handset is continuously moved up and down the length of the spine, the correct sequence is found automatically.

When the system is stress relieved, patterns of pre-rotated vertebrae and abnormal curvatures of the spine are seen to be resolved. Thereafter, the continued stimulation of reflexes effects no further change of geometry.

COMBINED PROCEDURE

In mobilization mode, the pads or bionic fingers deliver alternating pressures over the lateral ends of the transverse processes so as to cause adjacent pairs of vertebrae to be worked back and forth in counter-rotation. It would be like Maitland's mobilization if only the therapist had four tireless thumbs which could work with impossible energy, accuracy and speed.

As the bionic hand is worked up and down the length of the spine every vertebra is exercised, first by counter-rotation with the vertebra below and then by counter-rotation with the vertebra above. The therapist can feel the response of every joint and even subtle changes in the texture of subcutaneous tissue. They also have touch sensitive control over the movement of the hand and the depth or grade. Combine 'feel' with touch sensitive control over all parameters and you have a bionic hand.

The bionic hand is a tool, not a machine. The high technology is there merely to provide the therapist with touch sensitive control. The skill belongs to the therapist.

At its best, the procedure is highly skilled. As they work their way along the spine, experienced therapists are continuously adjusting their touch in response to the feel of each joint. The more experienced the therapist, the more subtle the procedure. However, even in the hands of a novice, the results can be stunning.

As with all mobilization / manipulation techniques, the secret is to work with the back, not against it. The procedure is gentle, passive and progressive. It is the energy and speed of bionic fingers which makes this gentle / passive / progressive procedure highly efficient.

Clearly, one cannot achieve adequate mobility in the presence of functional disorder ie. in the presence of mechanical muddles which we observe as excessive kyphosis, lordosis, scoliosis and patterns of pre-rotated vertebrae. Neither can one complete the stress relieving procedure and resolve these muddles if there is insufficient mobility in the joints. So as to avoid difficult physics, mobility and functional disorder have been discussed as if they were separate issues. In reality, while mobility affects the performance of the mechanism of co-ordination so functional disorder affects mobility. This interaction continues to be significant even at a subtle level. The solution is a combined procedure which involves alternating between reflex mode and mobilisation mode. With a combination of these modes, there is virtually no spine which cannot be restored to the supple elasticity of youth. Without either mode, the task is hopeless.

 THE FUTURE

The short term objective must be the provision of an effective treatment for common back pain. The long term objective must be the elimination of the back problem. If these goals are to be achieved, then our understanding of the mechanics of back pain must be as clear and as sound as a dentist's understanding of the mechanics of toothache. Moreover, intervention must be as purposeful as dentistry. The scientific and technical problems have been solved. The problems that remain are professional.

Many physical therapists protest that the reduction of common back pain to a rudimentary mechanical problem is simplistic. It is not. There is a clear distinction between mechanical and medical. Although comparatively rare, there are a number of organic disorders which can affect the spine. These disorders are the province of the physician. While the physical therapist may assist the physician in the management of symptoms, the underlying disorder is not mechanical and cannot be resolved by physical therapy.

The vast majority of back complaints stem from the same rudimentary mechanical problem. This mechanical / functional disorder may produce organic symptoms such as structural damage and autonomic effects. However, the underlying disorder is mechanical / functional. Mechanical / functional disorder can be and should be resolved promptly and efficiently. This is the role of the physical therapist.

Many physical therapists are truly vocational. They care only for the welfare of their patients. These therapists are delighted to find the mysteries of functional disorder reduced to purposeful intervention. Moreover, they are so committed and so involved that they take in a mass of subliminal information which comes out in the hands as knowledge. These therapists have little to learn. All they need is the tool for the job and a little technical tuition.

However, the greater number see themselves as physicians and practice according to their particular doctrine. If these therapists were to acknowledge this rudimentary mechanical problem, then they would be forced to abandon doctrine. Moreover, they see a medical / mechanical distinction as a threat to their professional standing. This is misguided insofar as respect stems from proficiency not mystique. Nevertheless, where doctrine resides, science is an intrusion. The value of these doctrines is a matter of record.

The authoritative literature makes sorry reading. Consider papers such as Efficacy of physiotherapy for musculoskeletal disorders: what can we learn from the research ?.....In order to summarize the available clinical evidence for the efficacy of physiotherapy, 400 randomised clinical trials were identified from the literature..... conclusion... on the other hand, because of the prevalence of serious methodological flaws, it cannot be concluded that physiotherapy has no effect.

If physiotherapy does not excel in the treatment of musculoskeletal disorders, then where does it excel ? Osteopathy and chiropractic fare little better.

Disciplined investigation and doctrine make uneasy bedfellows. Consequently, rudimentary tests were not conducted and the connection between loss of supple elasticity, the overstressing of joints and intermittent nerve root compression was not made. Moreover, doctrine dulls the mind. It even dulled the realization that there must be a mechanism of co-ordination which had still to be identified. This gap was already filled with beliefs which owed no allegiance to the rigors of science. Prime examples include the chiropractic subluxation, the osteopathic lesion and physiotherapy's muscle balance.

Physiotherapists seeks to explain idiopathic scoliosis in terms of uneven muscle condition and prescribe exercises to strengthen the weak side. Indeed, muscle balancing exercises are a fundamental plank of physiotherapy. However, the balance between opposing muscles is a function of nervous control, not muscle size. If it were not so, we would be incapable of movement. Condition has everything to do with peak performance but nothing whatever to do with the balance between opposing muscles. It does not take much to realize that muscle contraction and therefore 'balance' is a function of nervous control. And yet, this embarrassing nonsense is still being taught.

This would be more understandable if the exercises actually resolved functional disorders such as idiopathic scoliosis, but they do not. To resolve idiopathic scoliosis, one must address the system of nervous control. This is what the reflex mode does.

That is why stress relieving by system logic can resolve idiopathic scoliosis and muscle balancing exercises cannot. Non-existent subluxations and mythical lesions are similarly irrelevant.

Clearly, there is considerable disparity between the presentation of physical therapy and its efficacy. It is worth taking a look at how the circle is squared.

When introduced to power assisted micro-manipulation, a depressingly common reaction is "Do you mean you have to stand and hold it ?" The short answer is no, you do not stand and hold it, you work your socks off. Even with power assistance, the restoration of supple elasticity is hard work. It is upon discovery of what hard work it is that one hears "We're making a good living with things as they are."

Due to the action of protective postural response, patients naturally recover from a back pain episode. The reason for the recovery was not understood but the incidence of recovery was well known. Consequently, therapists have been free to prescribe a banana. When the patient recovers, they claim it as a triumph for the banana. On that basis, banana therapy can claim a success rate of close to 100%.

Any therapy which does not restore supple elasticity and relieve the overstressing of the affected joint is a banana therapy. There are plenty of banana therapies to choose from. Ultrasound and the other magic boxes of flashing lights rank among the most popular. All the authoritative studies demonstrate that the prognosis is the same with or without these treatments but this fact is conveniently ignored.

Banana therapies can exert a powerful placebo effect. These effects tend to be short lived but when timed to coincide with a back pain episode, which is naturally self-limiting, they can appear particularly impressive to the patient. Just how impressive placebo effects can be was well illustrated by a recent study.

The extraction of wisdom teeth causes pain and swelling. Following extraction, ultrasound was used to treat the affected area. A 40% reduction in pain and swelling was observed. This is very impressive. However, the experiment was then repeated with the ultrasound unit modified so that the lights flashed but there was no output. The results were just the same.

In the hands of a good clinician, placebos can be a powerful tool. The 40°!o reduction in pain and swelling was real enough. In the hands of a bad clinician, placebos can be damaging insofar as the patient is persuaded that they have received the appropriate treatment. If supple elasticity is not restored, the overstressing continues. Money for old rope is not an appropriate criteria for connecting patients up to whatever piece of electrotherapy equipment happens to be available.

Frustration was sure to breed some degree of cynicism. It must be difficult to remain motivated when the vast majority of the demand for your services are 'backs' or back related problems and you have no effective treatment. Nor is this problem confined to the orthodox school of physiotherapy. The distinctions between physiotherapists, osteopaths and chiropractors are greatly exaggerated. Many physiotherapists employ manipulation techniques pioneered by osteopaths and chiropractors. Many osteopaths and chiropractors use ultrasound and other adjuncts pioneered by physiotherapists. These days, one may observe greater differences between one physiotherapist and another, one osteopath and another and one chiropractor and another, than between physiotherapist, osteopath and chiropractor. This is hardly surprising given that physiotherapists, osteopaths and chiropractors are faced with the same problems.

Present a therapist with an ex-rugby football forward, built like a brick outhouse, head protrudes from the front of the chest level with the shoulders and dorsal spine set like cement. What is the therapist supposed to do? Without power assistance, the task is hopeless. Slight patients with plank-like backs can be even harder work than the kyphotic giant. Moreover, how was the therapist supposed to resolve conditions like idiopathic scoliosis and excessive kyphosis and lordosis? With muscle balancing exercises? Traditional manipulation can be employed to make adjustments like the reduction of the angulation described in the section on posture tests and this may deliver some temporary benefit but it cannot resolve functional disorder.

Individual therapists are not responsible for the late arrival of an effective treatment. They are not mechanics. Few even understand the distinction between stress and strain. Moreover, this advance would not have been possible without the identification of the mechanism of coordination. It was not for the therapist to solve an intellectual puzzle that had confounded generations of scientists and robotics engineers. Nor was it for the therapist to undertake the hi-tech engineering that was involved in the development of the bionic hand. Nevertheless, the facts remain and they are as follows:

(i)  The back problem is a rudimentary mechanical problem.

(ii) This rudimentary problem has been very costly both in financial and in human terms.

(iii) Ignorance and bad practice are part of the problem, not part of the solution.

The appalling back pain statistics are a legacy of a branch of medicine which, for far too long, has been sheltered from the rigors of science, bolstered by doctrine and excused by low patient expectation.

There are enough vocational physiotherapists, osteopaths and chiropractors to ensure a revolution. As the numbers using power assisted micro-manipulation grow, there is a corresponding growth in public awareness. To date, every effort has been made to avoid publicity. This has been done to prevent all concerned from being swamped by demand. However, as public awareness grows, the avoidance of publicity is becoming increasingly difficult. It is only a matter of time before a documentary is made. The public will then know the truth of it and that will mark the beginning of the end of the back problem.

However, a better way is to conduct an independent investigation which is designed to nail the mechanics of the problem and the mechanics of the solution to the wall. The profession will then be in a position to provide leadership. It will do much to restore and preserve public confidence if the profession present as the architects of progress rather than the butt.

It is for the mechanic to work out the mechanics of the problem and the mechanics of the solution. It is for the mechanic to develop the tool for the job. It is for the clinician to make clinical reports. It is for the profession to put its house in order.

EVALUATION

There are many difficulties associated with a statistical study. For example, due to the action of protective postural response, patients will recover from a back pain episode at much the same rate with or without treatment. On the other hand, the majority of chronic back pain sufferers have long since given up hope of finding an effective treatment and have dropped out of the system. A disproportionate number of those that remain in the system do so to qualify for disability benefit. At their age and with their record, they have little prospect of finding lasting employment. These patients live in fear of being declared fit to work and the consequential loss of benefit. This is not statistically fertile ground.

To be of value, a statistical study would need to be of an extended nature and the participating patients would require a maintenance treatment every six months. The control group would be sure to learn of an effective treatment and would be free to seek the appropriate treatment privately. Many back pain patients are desperate and few would elect to continue their suffering. As a consequence of these and other difficulties, the study would not be truly randomised and would be blind to neither clinician nor patient.

A flawed statistical study is a waste of time and resources. In the final analysis, there can be only one statistically satisfactory trial, one satisfactory criteria and one satisfactory outcome…the elimination of the back problem.

The efficacy of procedures such as hip replacement, dentistry and power assisted micro-manipulation stem from a clear understanding of the mechanics of the problem. Thereafter, it only remains to observe that intervention resolves the problem. There will be placebo effects associated with every procedure. However, these effects only become significant when at the margins of benefit and when the benefits are short lived. In these circumstances, evaluation means:

(i)                  Observe objective tests and other matters which confirm the mechanics of the problem.

     (ii)       Observe that intervention resolves the problem.

     (iii)      Observe that the benefits are substantial and lasting.

The bionic hand is a tool just as a scalpel is a tool.  Conduct a trial on a scalpel and it will tell you a great deal about the knowledge and skill of the surgeon but very little about the quality of the tool. And so it is with power assisted micro-manipulation. The quality of the tool is self-evident. It does precisely what it is supposed to do. The issue is the knowledge and skill of the therapist.

The value of trials lies in the contribution they can make to the dissemination of knowledge and skill. To be of value, trials must be an examination process which nails the mechanics of the problem and the mechanics of the solution to the wall.

Of the resources devoted to back pain research, a wholly disproportionate amount has been consumed by statistical studies of one sort or another. These studies have contributed nothing to the solution. Of the remaining resources, a disproportionate amount has been consumed by studies in the psychosocial aspects of back pain.. Whilst these studies may tell us something about the way people cope with pain and disability, they tell us nothing about cause.

If cars were prone to axle failure, we would be astonished to learn that engineers had spent most of the research budget comparing the incidence of axle failure in red cars and blue cars. Moreover, we would be singularly unimpressed to discover that the rest of the budget had been spent trying to decide whether or not the psychological profile of the driver was a predictive factor. In reality, the engineer would examine the failing component and identify overstressing as the problem. The engineer would then identify the cause of the overstressing and come up with a solution. If the solution involved routine maintenance, owners and mechanics would be advised accordingly.

And so it is with the spine. The problem relates to the overstressing of particular joints. The cause of the overstressing is lack of maintenance. If the spine came with a manufacturer's warranty, then after the age of twentyfive, a short service every six months would be a condition of that warranty. The spine should then give a lifetime's good service. Failing that, the restoration of supple elasticity is the best that biomechanics can offer.

Needless to say, attention needs to concentrated on the problem and its solution. Psychologists and statisticians can then complete their studies, flawed or otherwise, long after biomechanics have brought the problem under control.

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