For many years now I have lectured nationally about the harmful effects of non-neutral neck postures. When the head is flexed forward, the weight of the head creates more leverage force at the base of the neck than if the head and neck are held more erect. Holding the head forward of the body activates the neck extensors (erector spinae, semispinalis capitis and cervicis, and splenius capitus) which in turn create a greater force of contraction and increased compression forces on lower cervical discs. Over time this can lead to disc herniations, most commonly in the lower neck, namely at the C5-6 and C6-7 levels.
Even
more stressful than simple neck flexion is the combined forward head and bifocal posture (i.e., the posture that occurs when the head is positioned forward and extended on the neck with the chin titled upward as if looking through the lower lens of bifocals). Sitting at a computer, the “bifocal” posture is made worse by simultaneously sitting slumped with the head thrust forward. To be clear, one does not need to wear bifocals to assume a “bifocal” type posture. All one has to do to experience this stressful posture is to simply sit slumped with the head forward of the body and the chin tilted up as occurs when looking at a computer monitor.
The slumped seated posture will also stress the lower back. However, the danger as it relates to the neck with this posture is that neck extension creates excessive compression on the posterior cervical facet joints, especially in the middle region of the cervical spine. This can lead to degenerative arthritis with associated bone spurs. In addition, this posture increases lower cervical compression forces that can lead to a disc herniation or rupture.
Compression of the vertebral arteries also occurs in the forward head, bifocal posture. With head extension, the pinch point exists in the area where the vertebral arteries pass between the first cervical vertebra (atlas) and the base of the skull (occiput). It is hypothesized that mechanical irritation from the pinch pressure on the vertebral arterial wall causes inflammation that can potentially lead to a stroke. Clinical correlates to the vertebral artery compression stroke hypothesis include case descriptions of “beauty parlor stroke” and “bow hunter stroke”. Both case descriptions can be googled to learn more about how these two types of strokes have been related to the vertebral arteries at the base of the skull.
Although the focus on the potential harmful effects of forward head posture is most frequently directed to office work, the same biomechanical effects of this posture apply in field work. The forward head bifocal posture occurs in the field when reaching and looking straight ahead or upward while leaning the trunk forward. Field workers commonly assume this stressful trunk flexed posture while standing, kneeling, or squatting. In addition to the postural stress on the vertebral arteries, facet joints, and discs, field workers often create excessive compression in their shoulders while reaching with their arms extended in front of their bodies to work on equipment or structures.
Reaching out while the trunk is flexed can cause significant impingement in the shoulder where the upper arm (humerus) moves up against the overlying bony hook of the scapula called the acromion. Shoulder impingement in this posture can lead to damage of the rotator cuff and the subdeltoid bursa located directly beneath the acromion. Thus, field workers who work in this stressful posture have a high risk of experiencing degenerative arthritis of the neck (cervical spondylosis), disc herniations in both the lumbar and cervical regions of the spine, rotator cuff tears, subacromial bursitis, and possible vertebral artery damage.
Therefore, it is critical from an ergonomic perspective to conduct observational postural analyses as described and recommended by NIOSH. Based on postural observations, ergonomic interventions should be directed at proper seating and computer station adjustments that prevent forward head posture and reaching. This can be facilitated by ensuring that the seat pan is of the correct length for the user so as not to force the user to sit on the edge of the seat which facilitates sitting slumped. The computer monitor should be located within the focal range, directly in front of the user, and the position of the keyboard and mouse must be located close enough to the body to avoid reaching. However, it is not sufficient to just set someone up in an ergonomically optimum posture. Employees must be educated about the long term consequences of slumped postures and be consistently corrected if observed to be habitually slumped in their chairs.
In the field, ergonomic interventions should focus on identifying and correcting work designs that force or facilitate trunk flexed postures, particularly when work requires simultaneous reaching. Improve access to work that will eliminate the need to bend the trunk forward (flex the trunk), look up and reach. Remove obstacles that prevent easy access and/or prevents kneeling and forces a person to lean the upper body forward at the waist while reaching. Provide knee pads or cushions when kneeling can offset or prevent the need to work while standing with the back flexed. In addition, have workers perform postural relief exercises for the back, neck and shoulders to help offset poor postures that are not avoidable.
References:
Bunch, R. Bardarson, T., Neck Pain and Strokes Related to Bifocals and Computers – Method of Prevention by the Safety Professional; Proceedings, ASSE 2005 Professional Development Conference
Greene, D. P., & Roberts, S. L. (2005). Kinesiology: Movement in the Context of Activity. 2nd Edition. St. Louis: Elsevier Mosby.
Republished with permission by Dr. Richard Bunch, WorkSaver Systems.
