Frozen Shoulder vs. Capsulitis: Distinguishing Symptoms, Causes, and Treatments

What is the difference between frozen shoulder and capsulitis?

While often used interchangeably by the public, "frozen shoulder" (medically known as adhesive capsulitis) is a specific, progressive condition affecting the shoulder joint capsule, characterized by distinct stages of pain and severe, global loss of motion. "Capsulitis," on the other hand, is a broader, more general term simply indicating inflammation of any joint capsule.

Understanding the Shoulder Joint

The shoulder joint, or glenohumeral joint, is a ball-and-socket joint known for its extensive range of motion. This mobility is facilitated by a complex arrangement of bones, muscles, ligaments, and a fibrous sac called the joint capsule. The joint capsule encloses the joint, providing stability and containing synovial fluid, which lubricates the joint. Any inflammation of this capsule is termed "capsulitis."

What is Adhesive Capsulitis (Frozen Shoulder)?

Adhesive capsulitis, commonly known as "frozen shoulder," is a chronic and progressive condition characterized by inflammation, thickening, and contraction of the glenohumeral joint capsule. This leads to the formation of adhesions (scar tissue) within the capsule, severely restricting both active and passive range of motion (ROM) in all directions.

Key Characteristics of Adhesive Capsulitis:

• Progressive Loss of Motion: The hallmark of frozen shoulder is a gradual, yet significant, reduction in the ability to move the arm, particularly in external rotation, abduction, and internal rotation.
• Global Restriction: Motion loss is typically observed across all planes of movement, not just in specific directions.
• Distinct Stages: The condition usually progresses through three well-defined phases:
  • Freezing Stage (Painful Stage): Gradual onset of pain, often worsening at night, with a slow loss of shoulder motion. This phase can last from 6 weeks to 9 months.
  • Frozen Stage (Adhesive Stage): Pain may decrease, but stiffness becomes more profound, severely limiting daily activities. This phase can last from 4 to 12 months.
  • Thawing Stage (Recovery Stage): Gradual return of range of motion, which can take anywhere from 5 months to 2 years, or even longer.
• Etiology: While often idiopathic (no clear cause), it is more prevalent in individuals with diabetes, thyroid disorders, Parkinson's disease, or those who have experienced shoulder immobilization (e.g., after surgery or injury).

What is Capsulitis?

Capsulitis is a general medical term used to describe inflammation of a joint capsule. It is a descriptive diagnosis, indicating that the capsule is inflamed, but it does not specify the cause or the extent of the pathology beyond inflammation.

Key Characteristics of Capsulitis (General):

• Localized Pain: Pain is typically felt in the area of the inflamed capsule.
• Tenderness: The joint may be tender to the touch.
• Potential for Restricted ROM: While inflammation can limit movement, the degree and pattern of ROM loss are highly variable and not necessarily global or progressive like in adhesive capsulitis. For example, a capsulitis due to minor trauma might cause pain only with specific movements, rather than a global restriction.
• Diverse Causes: Capsulitis can result from:
  • Trauma: A direct blow or sprain to the joint.
  • Overuse or Repetitive Strain: Microtrauma from repetitive motions.
  • Infection: Septic arthritis, where bacteria infect the joint capsule.
  • Systemic Inflammatory Conditions: Such as rheumatoid arthritis or lupus, which can cause inflammation in various joint capsules throughout the body.

The Critical Distinction: Capsulitis as a Broader Term

The fundamental difference lies in their scope:

• Capsulitis is an umbrella term for any inflammation of a joint capsule.
• Adhesive capsulitis (frozen shoulder) is a specific syndrome that involves not just inflammation but also progressive fibrosis (scarring) and contracture of the capsule, leading to its characteristic global and severe loss of motion.

Think of it this way: All "frozen shoulders" are forms of "capsulitis" because the capsule is inflamed. However, not all instances of "capsulitis" are "frozen shoulder." A person might have capsulitis due to a minor sprain, experiencing temporary pain and mild stiffness, without ever developing the widespread adhesions and progressive, global immobility seen in adhesive capsulitis.

Key Differentiating Factors

Diagnosis and Clinical Presentation

Accurate diagnosis is crucial for effective management. A thorough clinical examination by a healthcare professional is paramount. This includes assessing active and passive range of motion, palpating the joint for tenderness, and evaluating for other potential causes of shoulder pain. Imaging, such as X-rays or MRI, may be used to rule out other conditions (e.g., rotator cuff tears, arthritis) but adhesive capsulitis is often diagnosed clinically based on its characteristic presentation.

Implications for Rehabilitation and Management

The treatment approach for general capsulitis versus adhesive capsulitis differs significantly:

• General Capsulitis: Management typically focuses on reducing inflammation (e.g., NSAIDs, ice), addressing the underlying cause (if identifiable), pain management, and gentle physical therapy to restore specific movements and strength.
• Adhesive Capsulitis: Requires a more specialized and often prolonged rehabilitation program. In the painful "freezing" stage, the focus is on pain control and maintaining motion without aggravating inflammation. In the "frozen" and "thawing" stages, physical therapy emphasizes controlled stretching, mobilization techniques, and strengthening exercises to break down adhesions and gradually restore range of motion and function. Modalities like corticosteroid injections or, in rare severe cases, manipulation under anesthesia or arthroscopic capsular release, may be considered.

Conclusion

While both "frozen shoulder" and "capsulitis" involve inflammation of the shoulder joint capsule, understanding their distinct definitions is critical. "Capsulitis" is a general term for capsular inflammation, whereas "frozen shoulder" (adhesive capsulitis) describes a specific, progressive syndrome characterized by a profound and global loss of shoulder mobility due to capsular fibrosis. Accurate diagnosis ensures that individuals receive the most appropriate and effective treatment plan, optimizing their recovery and return to full function.