There are 6 channels through which the extensor tendons glide as they cross the wrist. A given point on a wrist or finger extensor moves a distance of a few or several centimeters. With the wrist in neutral a given point on such a tendon moves in a straight line and with the wrist in full extension it would do the same (bowstringing), but for the presence of these channels which cause the movement through space of a point on the contracting muscle tendon unit to now be curved the channel roof called the extensor retinaculum acting as a pulley.
Several conditions interfere with this mechanism many resulting in changes within the lining of the tendon ( tenosynovium). When this structure thickens the work required for the tendon to move is increased. Friction is increased. There may be changes in the structural characteristics of the retinaculum which are either reactive changes or aging changes which render the pulley less compliant. There is no compelling evidence to definitively outline the pathophysiologic interaction of these changes in tenosynovium and retinaculum.
The currently extent hypothesis is that current work technologies, specifically manufacturing in an assembly line format which underpins most of our consumer culture presents a potentially deleterious exposure by virtue of the number of cycles the extreme of joint position, the level of force exerted involved in the proscribed work activity. The counter hypothesis has equally ardent subscribers.
The evidence which is presented in favor of this hypothesis falls into several categories one of which employs the statistical
paradigm of relative risk ratios. Populations are compared which are composed either of workers or non-workers. This paradigm of course depends
heavily on the nature of the physical demands of the non worker being distinctly different, generally less physically demanding but also more varied and self paced in distinction to the assembly line worker composing the study group.
When a given condition such as carpal tunnel syndrome, dequervains, or trigger finger is noted to occur in the study group with a greater incidence than in the control group then the implication is embraced which identifies the work as contributing to the de novo development of or exacerbation of the malady. Some extend the same analysis though with less compelling data to osteoarthritis which is highly prevalent in the adult population over 40 years of age.
In the case of osteoarthritis we find an added dimension of evidence from osteology available from deceased populations with a known work history.
In addition we have evidence from preindustrial populations who might be largely agrarian, and from hunter gatherer populations. This evidence generally finds a decreasing incidence of osteoarthitis allowing for the greater longevity of the modern postindustrial cohort. The salient point is then to provide the perspective that the control group which we select in our relative risk studies, if it is composed of executive or privileged home maker with abundant labor saving devices and a lifestyle of leisure accented perhaps with episodic recreational sporting activity, this may understate what might overwise be consequential negative health impacts of lifestyles which without industrial employment would be our necessary means of sustaining ourselves.
Ultimately we find a political cast to our outlook in this regard. On the left is a perspective that somehow affluent society has an obligation to provide the benign healthy qualities of a leisure existence, whereas on the right, we would judge the potential occupational condition against the comparable effects expected as a hunter gather or an agrarian, not to lose sight of the associated potential for violence, accident and uncertainly of diet associate with those lifestyles. So it is that a right leaning point of view would lead to a narrow definition of what constitutes work that is so hard it is damaging.