Frozen Shoulder: Understanding Pain Location, Stages, and Differentiation

What part of the shoulder hurts with frozen shoulder?

With frozen shoulder, medically known as adhesive capsulitis, the primary source of pain originates from the glenohumeral joint capsule, the fibrous tissue sac that encloses the shoulder joint. This pain is typically diffuse, deep, and often felt throughout the entire shoulder region, sometimes radiating into the upper arm.

Understanding Frozen Shoulder (Adhesive Capsulitis)

Frozen shoulder is a condition characterized by stiffness and pain in the shoulder joint. It occurs when the strong connective tissue surrounding the glenohumeral joint, called the shoulder capsule, becomes inflamed, thickens, and tightens, restricting movement. While the exact cause is often unknown (idiopathic), it can develop after an injury, surgery, or in individuals with certain systemic conditions like diabetes or thyroid disorders.

The Primary Site of Pain: The Shoulder Capsule

The most significant pain in frozen shoulder emanates directly from the inflamed and thickened joint capsule.

• Anatomy of the Capsule: The glenohumeral joint capsule is a crucial structure that stabilizes the shoulder joint while allowing for extensive range of motion. It's a thin, flexible sac that encloses the humeral head and the glenoid fossa, containing synovial fluid that lubricates the joint.
• Pathology and Pain: In frozen shoulder, this capsule undergoes a process of inflammation, fibrosis (scar tissue formation), and contracture. The normally pliable tissue becomes stiff, rigid, and adheres to itself and the humeral head. This inflammatory process within the capsule, coupled with the stretching of the contracted tissues during movement, is the direct cause of the characteristic deep, aching pain.
• Location of Sensation: Patients typically report pain deep within the shoulder, often difficult to pinpoint to a single spot. It's described as a dull ache that can become sharp with movement, especially at the end-ranges of motion. The pain is often worse at night or when lying on the affected side.

Referral Pain and Surrounding Structures

While the capsule is the primary pain generator, the diffuse nature of frozen shoulder pain means it can often be felt in surrounding areas due to referral patterns and compensatory muscle activity.

• Deltoid Muscle: Pain frequently radiates down the outer aspect of the upper arm, over the deltoid muscle. This is common due to the deltoid's proximity to the joint and its role in shoulder movement, which can be strained by the limited range of motion.
• Rotator Cuff Muscles: The four rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) are intimately associated with the shoulder capsule. While not the primary source of frozen shoulder pain, their tendons can become irritated or strained as they attempt to move a stiff joint, contributing to discomfort.
• Biceps Tendon: The long head of the biceps tendon runs through the shoulder joint and can also be affected by the inflammatory process or compensatory movements, leading to pain in the front of the shoulder and upper arm.
• Neck and Upper Back: Chronic shoulder pain and altered posture due to limited mobility can lead to secondary pain in the neck (cervical spine) and upper back (thoracic spine) muscles as they try to compensate for the shoulder's restricted movement.

The Stages of Frozen Shoulder and Pain Progression

The experience of pain with frozen shoulder typically evolves through distinct stages:

• 1. Freezing (Painful) Stage: This initial stage is characterized by gradual onset of pain, which can be severe and diffuse across the entire shoulder. As the pain worsens, the shoulder's range of motion slowly begins to decrease. This stage can last from 6 weeks to 9 months. During this phase, the inflammation within the capsule is most active, leading to significant discomfort.
• 2. Frozen (Stiffening) Stage: In this stage, the pain may actually start to diminish, but the stiffness becomes much more pronounced. The shoulder's range of motion is severely limited, making everyday activities challenging. This stage can last 4 to 12 months. While the acute inflammatory pain may lessen, the mechanical pain from stretching the contracted capsule remains.
• 3. Thawing (Resolution) Stage: During the thawing stage, the shoulder's range of motion gradually begins to improve. Pain continues to decrease, and mobility slowly returns to normal or near-normal levels. This stage can last from 5 months to 2 years.

Differentiating Frozen Shoulder Pain

A key characteristic that helps differentiate frozen shoulder pain from other conditions like rotator cuff tears or impingement is the global loss of both active and passive range of motion.

• Active Range of Motion: What you can move on your own.
• Passive Range of Motion: What someone else (or you with assistance) can move your arm through. With frozen shoulder, both are severely restricted across all planes of movement (e.g., elevation, external rotation, internal rotation), indicating a capsular issue rather than solely a muscular or tendinous one.

Why Understanding the Pain Location Matters

Understanding that the pain primarily stems from the joint capsule is crucial for:

• Accurate Diagnosis: Helps clinicians distinguish frozen shoulder from other shoulder pathologies.
• Targeted Treatment: Guides interventions such as intra-articular corticosteroid injections, which are delivered directly into the joint capsule to reduce inflammation and pain.
• Patient Education: Allows individuals to better understand their condition and manage expectations regarding recovery.

Seeking Professional Diagnosis and Management

If you experience persistent shoulder pain and stiffness, it is essential to consult a healthcare professional, such as an orthopedic surgeon, sports medicine physician, or physical therapist. Early diagnosis and appropriate management, which often includes physical therapy, pain relief strategies, and sometimes injections, can significantly impact the long-term outcome and help restore shoulder function.