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Frozen Shoulder – a form of arthrofibrosis

Shoulder arthrofibrosis is called “frozen shoulder” and “adhesive capsulitis” [1]-[3]. In fact, arthrofibrosis is known by many names [4], an unfortunate situation that allows misunderstandings to persist and making access to treatments more difficult. The main difference between the joint pathologies is that knee arthrofibrosis is usually the result of trauma, while shoulder arthrofibrosis is typically idiopathic (has no obvious cause), but may arise from a series of small insults that are not noticed, or damaged structures that place stress on the joint [4].

Arthrofibrosis is a pathological wound healing response that can occur in any joint and is characterised by joint contractures, adhesions of tissues and pain. In all joints, including shoulders, these processes manifest as chronic pain and debilitating restriction of joint movement [1]. Pain can disturb sleep, and the loss of motion of the shoulder can make daily living activities extremely difficult [5]. Pain diminishes as inflammation resolves, and the condition can become “residual arthrofibrosis” for a time [4], which is sometimes referred to as the “thawing” phase. Diagnosis relies on symptoms and the exclusion of other problems such as dislocation, infection and fractures [3]. MRI and ultrasound imaging can assist the diagnosis.


Shoulder arthrofibrosis is called “frozen shoulder” and “adhesive capsulitis”

Shoulder arthrofibrosis is a common problem worldwide, afflicting around 8 % of men, and 10 % of women of working age [5], which probably makes it the most common form of arthrofibrosis. A study of twins reported a genetic predisposition for shoulder arthrofibrosis in some people [4] and it’s more common when other conditions increase inflammation. For example, shoulder arthrofibrosis can affect up to 38 % of people with thyroid problems and 76 % of people with diabetes over their lifetime [6]. However, other conditions are not always present. Fibrosis commonly affects the rotator cuff interval, which is formed by the major tendons that attach to the joint [6], and the subcoracoid fat pad and pouch [2].


The pathology of shoulder arthrofibrosis is the same as for other joints [4]. Arthrofibrosis occurs after trauma (including surgery), prolonged immobilisation of the joint and infection [1]. An insult begins a cascade of inflammation, proliferation of myofibroblasts (the cells that cause fibrosis), scar tissue production and joint capsule thickening [3]. Myofibroblasts grow large numbers of adhesion molecules on their surface that stick to surrounding tissues and create adhesions and contractions.


Fibrosis commonly affects the rotator cuff interval

It’s a common assumption that shoulder arthrofibrosis completely resolves over time, but recent studies indicate that this is not accurate [6] and around 40 % of people still have symptoms after 4 years [5]. Increased pain in the affected shoulder is associated with an increase in the density of nerves in the joint [2][6], (see Pain blog), and this may explain why resolution can be difficult. It’s therefore important to understand what helps and what may be harmful, and to get early and gentle treatment.


Unfortunately, it’s not yet clear which treatments for shoulder arthrofibrosis are the most effective; however, injections of corticosteroids and physical therapy, including passive stretching in the pain-free zone, are currently the primary treatments. A recent analysis concluded that physiotherapy, surgical release of adhesions in the capsule and manipulation under anaesthesia helped, but the difference in outcomes was unlikely to be clinically important [5]. It is worth noting that manipulation under anaesthesia (that tears adhesions apart) and surgery can potentially have serious side effects [3][5], and may worsen symptoms by re-injuring the tissues [1][6]. Pain management and reducing inflammation can help people recover with fewer associated risks. Corticosteroids are frequently injected into the joint and can greatly reduce inflammation, but can also have toxic effects on cartilage when repeated. Collagenase injections in the shoulder have shown promise and appear to be safe [3][4]. Non-operative, next generation therapies that target inflammation and fibrosis are currently being sought [3].


Although “frozen shoulder” is easy to say, calling it “shoulder arthrofibrosis”, or simply “arthrofibrosis” instead will help the community and clinicians understand and access better care in the future.


References

  1. Blessing, W. A., Williamson, A. K., Kirsch, J. R. & Grinstaff, M. W. The Prognosis of Arthrofibroses: Prevalence, Clinical Shortcomings, and Future Prospects. Trends Pharmacol Sci, doi:10.1016/j.tips.2021.02.007 (2021).

  2. Fields, B. K. K. et al. Adhesive capsulitis: review of imaging findings, pathophysiology, clinical presentation, and treatment options. Skeletal Radiol 48, 1171-1184, doi:10.1007/s00256-018-3139-6 (2019).

  3. Le, H. V., Lee, S. J., Nazarian, A. & Rodriguez, E. K. Adhesive capsulitis of the shoulder: review of pathophysiology and current clinical treatments. Shoulder Elbow 9, 75-84, doi:10.1177/1758573216676786 (2017).

  4. Usher, K. M. et al. Pathological mechanisms and therapeutic outlooks for arthrofibrosis. Bone Research 7, doi:10.1038/s41413-019-0047-x (2019).

  5. Rangan, A. et al. Management of adults with primary frozen shoulder in secondary care (UK FROST): a multicentre, pragmatic, three-arm, superiority randomised clinical trial. The Lancet 396, 977-989, doi:10.1016/s0140-6736(20)31965-6 (2020).

  6. de la Serna, D., Navarro-Ledesma, S., Alayón, F., López, E. & Pruimboom, L. A Comprehensive View of Frozen Shoulder: A Mystery Syndrome. Frontiers in Medicine 8, doi:10.3389/fmed.2021.663703 (2021).



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