What are the key clinical features to differentiate frozen shoulder from other shoulder pathologies?

The key clinical features used to differentiate frozen shoulder (adhesive capsulitis) from other shoulder pathologies primarily revolve around the characteristic progression of symptoms and specific limitations in joint movement ¹.

• Frozen Shoulder Features: Initially, pain is the main problem, often worsening in bed and disturbing sleep ¹. This pain gradually improves, but stiffness slowly worsens and becomes the primary issue ¹. The stiffness then gradually resolves, with the condition typically being self-limiting, though resolution can take months to years ¹. A crucial diagnostic feature is reduced passive external rotation, which indicates a glenohumeral joint disorder, encompassing both frozen shoulder and arthritis ¹.
• Differentiating from Other Pathologies:
  • Red Flags: Urgent referral to secondary care is necessary if certain red flags are identified, which are not typical of frozen shoulder ¹. These include trauma, pain with weakness, or sudden loss of active arm raising (suggesting an acute rotator cuff tear) ¹. Any shoulder mass or swelling should raise suspicion of malignancy ¹, ((Demazière and Wiley, 1991)). Red skin, a painful joint, fever, or systemic unwellness may indicate septic arthritis ¹. Trauma leading to loss of rotation and an abnormal shape suggests a shoulder dislocation ¹. New symptoms of inflammation in several joints point towards inflammatory arthritis ¹.
  • Rotator Cuff Disorders: These are likely if there is a painful arc of abduction or pain on abduction with the thumb down ¹. An acute rotator cuff tear, especially in a young person with trauma and loss of abduction, requires urgent referral ¹. Unlike frozen shoulder, rotator cuff issues often involve specific active movement limitations rather than global passive stiffness ¹.
  • Shoulder Instability: A diagnosis of instability is likely if there is a history of the shoulder coming out of joint or if the person is concerned about dislocation during certain activities or sports ¹.
  • Acromioclavicular (AC) Joint Disease: This is likely with pain and tenderness over the AC joint, high arc pain, or a positive cross-arm test ¹.
  • Glenohumeral Osteoarthritis: While also presenting with reduced passive external rotation, osteoarthritis is characterized by joint symptoms such as pain, stiffness, reduced function, or progressive joint deformity that significantly impact quality of life ¹,². Atypical features for osteoarthritis, which would differentiate it from typical frozen shoulder, include a history of recent trauma, prolonged morning joint-related stiffness, rapid worsening of symptoms or deformity, the presence of a hot swollen joint, or concerns suggesting infection or malignancy ². Imaging is not routinely used for follow-up or to guide non-surgical management of osteoarthritis ².