The role of sensitization in musculoskeletal shoulder pain
Common shoulder pain impairments include pain, difficulty raising the arm overhead, impaired work and leisure participation and disturbed sleep.
Sensitization is a nervous system phenomenon that can occur in conjunction with pain. With sensitization, normally innocuous input is perceived a painful due to increases in nociception. When sensitization is present, the energy level required to activate nociceptors is decreased leading to increased pain perception.
Sensitization has been reported in many musculoskeletal conditions and it appears to be a regularly occurring phenomenon in unilateral shoulder pain. Although the location of threshold changes differ between peripheral and central sensitization, the manifestation of both types of sensitization is a change in pain perception and/or intensity. When sensitization is present, this stimulus threshold is lowered such that a lower intensity stimulus is painful.
The rotator cuff muscles/tendons, particularly supraspinatus are densely populated with nociceptors that likely contribute to central sensitization at the shoulder.
The consistent presence of central sensitization suggests that spinal cord processes and/or descending pain inhibition have been altered such that peripheral input may be perceived as nociceptive. This may influence the ability to successfully apply interventions that impact joint tissues such as stretching or strengthening exercises. Because of the strong relationship between central sensitization and the development of chronic pain, it is imperative that the mechanisms by which peripheral sensitization transitions to central sensitization are discovered.
Exercise and manual techniques, when applied at the appropriate time and with the right intensity, may be able to modify aberrant peripheral input and positively alter central processing.
> From: Borstad & Woeste, Braz J Phys Ther 0 (2015) (Epub ahead of print). All rights reserved to The Author(s). Click here for the Pubmed summary.