CNS sensitization in subacromial pain (SAPCNS trial)

Project title: Central nervous system sensitization, muscle function, and pain profiling in patients with subacromial pain (the SAPCNS-1 trial)

Principal investigator: Bjarki Þór Haraldsson

Principal supervisor: Thomas Bandholm

Research initiative: PMR-C and Metropolitan University Collage

Time frame: 2016-18


Deficits associated with subacromial pain (SAP) include: reduced muscle strength, reduced submaximal control of force, reduced proprioception, altered shoulder kinematics, and increased shoulder pain. With respect to shoulder pain, persistent shoulder pain in SAP may sensitize the central nervous system – known as central sensitization – and seems to be present in some patients with SAP, likely related to symptom duration. Central sensitization is defined as an "amplification of neural signaling within the central nervous system that elicits pain hypersensitivity". Central sensitization may help explain why the degree of shoulder pain relates poorly to the degree of subacromial tissue damage in patients with SAP.

Pertaining to that reviewed above, the most recent systematic review on the role of central sensitization in shoulder pain concluded that: "…. our understanding of the role central sensitization plays in the shoulder pain population is still in its infancy. Future studies with high methodical quality are therefore required to investigate this further". Indeed the present study will aim to investigate this further. To accommodate this, deficits in patients with SAP, will be examined using new methods of quantitative sensory testing, pain mapping, and shoulder motor control.


The primary aim of this study is to compare central nervous system sensitization (central sensitization), shoulder muscle function and shoulder pain distribution in patients with subacromial pain to that in healthy matched controls.

The secondary aim of this study is to investigate if (symptom) dose/response relationships exist between shoulder symptom duration and: central sensitization, shoulder muscle function and shoulder pain distribution in patients with subacromial pain.    

Experimental approach

 The study, which is called the Subacromial Shoulder Pain and Central Nervous System Sensitization Metropol 1 (SAPCNS-1) Trial, is a case-control study, in which the methods electromyography [EMG], isometric dynamometry, pressure algometry, and pain area drawing will be applied to patients with shoulder pain and healthy controls to quantify muscle activity, muscle strength, central sensitization, and pain distribution, respectively. Further, data on patient self-reported pain and function, and kinesiophobia will be collected using 'SPADI' and 'Pain Catastrophizing Scale' respectively.

Additional information will be added, once the trial is registered.


Bjarki Þór Haraldsson

Responsible editor