Shoulder Impingement: Causes, Symptoms, Diagnosis, and Treatment

What is a Shoulder Impingement?

Shoulder impingement, also known as subacromial impingement syndrome, occurs when the tendons of the rotator cuff and/or the subacromial bursa become compressed and irritated as they pass through a narrow space in the shoulder joint, leading to pain, weakness, and restricted movement.

Understanding the Shoulder Joint

To grasp shoulder impingement, it's essential to understand the intricate anatomy of the shoulder. The shoulder is a ball-and-socket joint, formed by the head of the humerus (upper arm bone) fitting into the glenoid cavity of the scapula (shoulder blade). Overlying this joint is a bony arch formed by the acromion (a projection of the scapula) and the coracoacromial ligament.

Beneath this arch, in what's known as the subacromial space, lie several crucial structures:

• Rotator Cuff Tendons: Four muscles (supraspinatus, infraspinatus, teres minor, subscapularis) whose tendons merge to form a "cuff" around the head of the humerus, providing stability and enabling a wide range of motion. The supraspinatus tendon is most commonly affected in impingement.
• Subacromial Bursa: A fluid-filled sac that acts as a cushion, reducing friction between the rotator cuff tendons and the overlying acromion during shoulder movement.

What is Shoulder Impingement Syndrome?

Shoulder impingement syndrome is a condition where the structures within the subacromial space, particularly the rotator cuff tendons (most notably the supraspinatus) and the subacromial bursa, are repeatedly compressed or "pinched" against the overlying acromion during arm elevation or rotation. This repetitive compression leads to inflammation, irritation, and potential degeneration of these tissues.

Initially, this may manifest as tendinitis (inflammation of the tendons) or bursitis (inflammation of the bursa). If left unaddressed, chronic impingement can lead to more severe issues, including partial or full-thickness rotator cuff tears.

Causes of Shoulder Impingement

Shoulder impingement typically arises from a combination of factors, rather than a single cause:

• Anatomical Factors:

  • Acromion Shape: The shape of the acromion can vary. Some individuals have a flat (Type I) acromion, while others have a curved (Type II) or hooked (Type III) acromion. A curved or hooked acromion can naturally narrow the subacromial space, predisposing individuals to impingement.
  • Osteophytes (Bone Spurs): Bone spurs can develop on the underside of the acromion due to wear and tear or degenerative changes, further reducing the space.
  • Acromioclavicular (AC) Joint Arthritis: Degeneration of the AC joint can lead to bone spurs that protrude into the subacromial space.

• Biomechanical Factors:

  • Repetitive Overhead Activities: Sports like swimming, baseball, tennis, volleyball, or occupations requiring frequent overhead work (e.g., painters, construction workers) can lead to overuse and inflammation.
  • Poor Posture: Rounded shoulders and a forward head posture can alter the scapular position, reducing the subacromial space and increasing the likelihood of impingement.
  • Muscle Imbalances:
    • Weak Rotator Cuff Muscles: If the rotator cuff muscles are weak, they may not effectively depress and center the humeral head within the glenoid, allowing it to migrate upwards and impinge.
    • Weak Scapular Stabilizers: Muscles that control the movement and position of the scapula (e.g., serratus anterior, rhomboids, trapezius) are crucial for optimal shoulder mechanics. Weakness in these muscles can lead to scapular dyskinesis (abnormal movement), narrowing the subacromial space during arm elevation.
    • Overactive Deltoid/Pectoralis Muscles: An imbalance where the larger, stronger deltoid or pectoralis muscles overpower the rotator cuff can also contribute to superior migration of the humeral head.
  • Improper Movement Patterns: Incorrect technique during exercises or daily activities can place excessive stress on shoulder structures.

• Inflammation and Degeneration:

  • Tendinitis/Bursitis: Acute inflammation of the rotator cuff tendons or bursa can swell the tissues, making them more susceptible to impingement.
  • Age-Related Changes: As we age, tendons can become less elastic and more prone to degeneration, increasing the risk of impingement and tears.

• Trauma: An acute injury, such as a fall onto the shoulder, can also initiate an impingement syndrome.

Common Symptoms

The symptoms of shoulder impingement typically develop gradually and worsen over time. They often include:

• Pain:
  • Usually localized to the front or side of the shoulder, often radiating down the upper arm.
  • Worsens with overhead activities, reaching behind the back, or lifting the arm.
  • Can be sharp or aching.
  • Often causes pain at night, especially when lying on the affected side.
• Weakness: Difficulty lifting or rotating the arm, especially against resistance.
• Stiffness and Reduced Range of Motion: A feeling of tightness or restricted movement, particularly when reaching overhead or behind the back.
• Clicking or Popping Sensation: May be heard or felt during certain shoulder movements.
• Loss of Function: Difficulty performing daily activities like dressing, combing hair, or reaching into cabinets.

Diagnosis

Diagnosing shoulder impingement involves a thorough assessment by a healthcare professional, typically an orthopedic surgeon, sports medicine physician, or physical therapist. The diagnostic process includes:

• Patient History: Gathering information about symptoms, their onset, aggravating and alleviating factors, and activity levels.
• Physical Examination:
  • Observation: Assessing posture, shoulder symmetry, and muscle atrophy.
  • Palpation: Checking for tenderness over specific shoulder structures.
  • Range of Motion Assessment: Measuring active and passive range of motion.
  • Strength Testing: Evaluating the strength of the rotator cuff and other shoulder muscles.
  • Special Impingement Tests: Specific maneuvers (e.g., Neer's test, Hawkins-Kennedy test) are performed to reproduce pain and indicate impingement.
• Imaging Studies:
  • X-rays: Can show the shape of the acromion, bone spurs, and signs of arthritis in the AC joint. They do not show soft tissues.
  • MRI (Magnetic Resonance Imaging): Provides detailed images of soft tissues, revealing inflammation of the bursa (bursitis), tendinitis, and partial or full-thickness rotator cuff tears.
  • Ultrasound: Can also visualize soft tissues and is often used to assess rotator cuff tendons and the bursa in real-time during movement.

Management and Treatment Principles

The primary goal of treating shoulder impingement is to reduce pain and inflammation, restore normal shoulder mechanics, and prevent recurrence. Treatment typically begins with conservative (non-surgical) approaches.

• Conservative Management (First-Line Treatment):

  • Rest and Activity Modification: Avoiding activities that aggravate the shoulder, especially overhead movements, is crucial in the initial stages.
  • Pain and Inflammation Control:
    • NSAIDs (Non-Steroidal Anti-Inflammatory Drugs): Over-the-counter or prescription medications like ibuprofen or naproxen can help reduce pain and inflammation.
    • Ice/Heat Application: Ice packs can reduce acute inflammation, while heat can relax muscles and improve blood flow.
  • Physical Therapy: This is the cornerstone of conservative treatment and is vital for long-term recovery. A physical therapist will design a personalized program that may include:
    • Pain Management Techniques: Modalities such as ultrasound, electrical stimulation, or manual therapy.
    • Restoring Range of Motion: Gentle stretching and mobilization exercises to improve flexibility.
    • Strengthening Exercises: Focusing on the rotator cuff muscles, scapular stabilizers (e.g., serratus anterior, lower trapezius), and postural muscles to improve shoulder stability and mechanics.
    • Posture Correction: Education and exercises to improve overall posture and scapular positioning.
    • Movement Pattern Retraining: Teaching proper technique for daily activities and exercises to avoid re-impingement.
    • Patient Education: Understanding the condition, self-management strategies, and prevention.
  • Corticosteroid Injections: An injection of corticosteroid medication into the subacromial bursa can provide significant, but often temporary, pain relief by reducing inflammation. These are typically used as an adjunct to physical therapy.

• Surgical Intervention:

  • Surgery is typically considered only after a prolonged period (usually 3-6 months) of comprehensive conservative treatment has failed to provide adequate relief, or if there is a significant rotator cuff tear.
  • The most common surgical procedure is arthroscopic subacromial decompression (acromioplasty). This minimally invasive procedure involves removing a small portion of the acromion and/or any bone spurs to increase the subacromial space and relieve pressure on the tendons and bursa. If a rotator cuff tear is present, it may be repaired concurrently.
  • Post-surgery, a structured rehabilitation program with a physical therapist is essential for regaining strength, range of motion, and function.

Prevention Strategies

While not all cases of shoulder impingement are preventable, adopting certain strategies can significantly reduce the risk, especially for those involved in overhead activities or with predisposing factors:

• Proper Warm-up and Cool-down: Always prepare the shoulder muscles for activity and aid recovery afterward.
• Correct Lifting and Movement Mechanics: Learn and apply proper form for exercises, especially overhead movements. Avoid compensating with the shoulder when other muscles (e.g., core, legs) should be doing the work.
• Strengthening Rotator Cuff and Scapular Muscles: Incorporate exercises that specifically target these muscles (e.g., external rotations, internal rotations, Y-T-W-L exercises, push-ups plus).
• Maintain Good Posture: Be mindful of posture throughout the day, especially when sitting or working at a computer. Avoid prolonged rounded shoulder or forward head positions.
• Gradual Progression: Increase intensity, duration, or resistance of activities gradually to allow tissues to adapt.
• Listen to Your Body: Do not push through pain. If an activity causes shoulder pain, modify it or take a break. Early intervention can prevent minor issues from becoming chronic.
• Cross-Training: Varying your activities can reduce repetitive stress on the shoulder joint.

Prognosis

The prognosis for shoulder impingement is generally good with appropriate conservative treatment, especially when addressed early. Most individuals experience significant improvement in pain and function with consistent physical therapy and adherence to activity modifications. For those who require surgery, outcomes are also generally positive, provided they commit to the post-operative rehabilitation program. However, complete recovery can take several months, emphasizing the importance of patience and adherence to the prescribed treatment plan.