Shoulder Pathology and Disorders

Shoulder pathology covers the disorders of the glenohumeral and surrounding joints — most prominently rotator cuff disease, subacromial pain, adhesive capsulitis, instability, and glenohumeral osteoarthritis. The shoulder trades stability for an exceptional range of motion, and many of its conditions reflect the demands placed on the rotator cuff and surrounding soft tissues that stabilise a shallow ball-and-socket joint.

Definition

Shoulder pathology and disorders comprise the degenerative, traumatic, inflammatory, and instability conditions affecting the glenohumeral joint, rotator cuff, subacromial bursa, and adjacent structures.

Scope

This topic surveys the common structural and degenerative conditions of the shoulder, the anatomy of the rotator cuff and subacromial space, and the recurring challenge that imaging abnormalities are frequently present in people without symptoms. It is a reference-educational overview of shoulder disorders, not a treatment protocol.

Core questions

• What are the principal categories of shoulder disorder — cuff disease, instability, stiffness, and arthritis?
• How does the shoulder's mobility-stability trade-off shape its pathology?
• How common are rotator cuff abnormalities in people without symptoms?
• What does trial evidence say about the benefit of subacromial decompression for shoulder pain?

Key concepts

• Rotator cuff
• Subacromial impingement
• Rotator cuff tear
• Adhesive capsulitis (frozen shoulder)
• Glenohumeral instability
• Glenohumeral osteoarthritis
• Asymptomatic imaging findings

Mechanisms

The glenohumeral joint achieves a wide range of motion at the cost of bony stability, relying on the rotator cuff, capsule, and labrum to keep the humeral head centred. Rotator cuff disease is thought to result from a combination of intrinsic tendon degeneration and extrinsic compression in the subacromial space, and cuff tears become more frequent with age. A central observation is that rotator cuff tears and other abnormalities are common on magnetic resonance imaging of shoulders that have no symptoms, increasing with age, which complicates linking a finding to a patient's pain (Sher 1995). The historical model that subacromial impingement drives pain and that surgical decompression relieves it has been challenged by placebo-controlled trial evidence (Beard 2018).

Clinical relevance

Shoulder disorders are a frequent reason for musculoskeletal consultation, and the discordance between imaging findings and symptoms is central to interpreting the evidence on them. The CSAW trial illustrates how placebo-controlled surgical trials reshape understanding of which interventions add benefit. This entry describes how shoulder conditions are categorised and studied and is not a basis for individual treatment decisions.

Epidemiology

Rotator cuff abnormalities rise steeply with age and are frequently present in asymptomatic shoulders, so prevalence estimates depend heavily on whether symptoms or imaging are used to define disease (Sher 1995). Shoulder pain is among the more common regional musculoskeletal complaints across populations.

History

Twentieth-century shoulder surgery was strongly influenced by the impingement model, which framed subacromial mechanical contact as a driver of cuff pain and motivated decompression surgery. Imaging studies of asymptomatic shoulders (Sher 1995) and later placebo-controlled trials (Beard 2018) prompted a re-examination of that model and of the role of surgery in subacromial pain.

Debates

Does arthroscopic subacromial decompression relieve shoulder pain?

The placebo-controlled CSAW trial found no clinically important benefit of arthroscopic subacromial decompression over placebo surgery or no treatment, challenging a long-standing rationale for the procedure.

How should asymptomatic cuff findings be interpreted?

Because rotator cuff abnormalities are common in shoulders without symptoms and increase with age, attributing a patient's pain to an imaging finding requires caution.

Seminal works

• sher-1995
• beard-2018

Frequently asked questions

Are rotator cuff tears always painful?

No. Rotator cuff tears and other abnormalities are commonly found on imaging of shoulders that have no symptoms, and they become more frequent with age, so a tear on imaging is not always the cause of a person's pain.

Does surgery to decompress the subacromial space help shoulder pain?

A placebo-controlled randomised trial (CSAW) found no clinically important benefit of arthroscopic subacromial decompression compared with placebo surgery or no treatment, which has changed how the procedure is viewed.