How does a frozen shoulder develop?

And what are the processes on a tissue level?

  • Mild but chronic inflammation process is the basis
  • Inflammation is followed by progressive fibrosis
  • Corticosteroid injection only useful in early stages of disorder 

A frozen shoulder is caused by a series of processes which disturb the collagen production around the shoulder joint. Many factors play a role in this process. And even though the trigger that puts everything into motion is still unknown, Dutch scientists could gather enough information from 48 scientific studies to map the cascade of reactions that lead to a frozen shoulder.


Physiotherapy and corticosteroid injections are the most commonly applied treatment options for a frozen shoulder. A corticosteroid injection may reduce the inflammation, but cannot revert the fibrotic changes that occur later. Therefore, such an injection is only effective in the early stages of the disorder. Physiotherapeutic treatment aims more at the mobility of the joint, but the therapist needs to take the loading capacity and irritability of the tissue into account: moderate mechanical stress is needed to remodel the extracellular matrix, but mobilisations are counterproductive if the pain threshold is exceeded. 

Qualitative review

The researchers derive their findings from 48 studies with information about frozen shoulders: thirty studies in which biopsies from the shoulder revealed tissue changes, fifteen studies which indicated an association between the pathological mechanism of other diseases and three studies in rats which described the pathophysiological process into detail. Figure 3 of the – freely accessible – paper schematically shows the successive phases that lead to stiffening of the joint.

> From: Kraal et al., J Exp Orthop 7 (2020) 91 . All rights reserved to The Author(s). Click here for the online summary. Translation by Casper Martens

Link to free full text version

Want to read deeper into this topic? A free version of the full text is available online here!

Expert opinion by Suzanne Wiertsema, PhD

The term Frozen Shoulder (FS) is frequently used in the various consulting rooms of general practitioners, physiotherapists, orthopaedic or trauma surgeons and other healthcare providers. Not in all cases there actually is an FS, but there is confusion with, for example, a postoperative stiff shoulder, osteoarthritis, or an acute bursitis.

It remains difficult to explain to patients (and non-specialised health care providers) the fundamental process that underlie an FS and what the best approach is in each phase. Even more so, because informing, waiting, and giving the natural recovery process time, feels as ‘doing nothing’ for health care providers who are used to ‘doing something’. 

This paper describes very clearly what happens at a tissue level in the shoulder during the three phases and provides insight into when it makes sense to exercise (or apply other interventions) and why. The advice is to not read this article on the most detailed level, but to use the broad outlines and advice to inform patients (and referring physicians) better. For shoulder physiotherapists, however, this is a wonderful paper that really dives deep on the tissue level. 

This paper, in combination with the Dutch practice guideline Frozen Shoulder, provides a very complete image of the background and therapeutic possibilities:

  • The freezing (inflammation) phase takes 4 to 9 months and is characterised by a lot of pain and an increasingly limited range of motion. Therapy is aimed at informing, moving within the pain threshold, relaxation, and maintaining fitness. A corticosteroid injection may be effective in an early stage. 
  • The frozen (stiffness) phase also takes 4 to 9 months. Limitation in range of motion remains stable, and reactivity and pain are slowly reducing. Gradually, more exercises towards the end positions of the joint can be performed.
  • The thawing phase takes 4 to 12 months, depending on therapy compliance. Pain is gone and range of motion slowly comes back. It is allowed to exercise intensively.

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