The increasing mobile use of notebooks poses a problematic ergonomic situation. To circumvent some of the negative effects on the musculoskeletal system that occurs with the unfavorable body position a novel screen system was designed. This height adjustable display was evaluated in the current study. The cervical inclination that corresponded to the five position of the computer display differed significant in all subjects resulting in a reduced flexion in the maximum moved out position.
The vertical strain on the spine is reflected by the force that acts on the intravertebral discs that lead to changes in the intradiscal pressure (PID). It has been suggested that an increased PID may worsen the alimentary status of the intravertebral disc that might contribute to a faster advancing of degenerative processes [8
]. Studying the lumbar spinal region Nachemson and coworker demonstrated that different body postures influence the intradiscal pressure [11
]. The results were confirmed by data from discography and chemonucleolysis [10
]. There are important differences between the sections of the spine. In cervical discs, the nucleus is less able to equalize stress over large distances, and the posterior annulus does not sustain high compressive stresses [13
]. Although most research focused on the lumbar spine, recent data has found a postural dependence also for the cervical spine [8
]. PID is lowest in the middle position between flexion and extension [9
]. This relation has found expression in national guidelines where an only marginal flexion of the neck with the least stress is favored for the working environment.
Next we evaluated factors that might influence the extent of inclination. In this context Nightingale and coworker have found gender specific anatomic differences of the cervical spine. The male upper cervical spine is significantly stiffer and stronger [14
]. In our study population there was no difference between the neck inclination of the male and female subjects.
Also for another possible influencing factor - the wearing of correction lenses - no distinction was found, supporting the relevance of the data.
In summary the moved out position of a new height adjustable notebook display reduces significantly the cervical inclination. From data that the vertical strain on the cervical spine depends on the degree of inclination, it may be assumed that in this position the strain is reduced. The novel screen advances the notebook display ergonomically next to desktops. It may be especially beneficial in rehabilitation.
Future studies will evaluate the novel displays' ability to reverse already set in damages of the musculoskeletal system. Furthermore the influence on the upper body and the position of the keyboard will be future research topics.