Understanding the Shoulder: Structure, Function, and Common Injuries

The shoulder is one of the most complex and mobile joints in the human body. It allows for a vast range of motion, making it essential for daily activities and athletic performance. However, this mobility also makes it susceptible to instability, dysfunction, and injury.

This post will cover:

• The anatomy and function of the shoulder

• How muscle imbalances affect shoulder health

• The role of spinal function in shoulder mechanics

• Adhesive capsulitis (frozen shoulder): causes, phases, and treatment

• Rotator cuff tears: causes, symptoms, and treatment options

• Impingement syndrome: causes, symptoms, and treatment options

Anatomy and Function of the Shoulder

The shoulder is a ball-and-socket joint, formed by three primary bones:

• Humerus (upper arm bone)

• Scapula (shoulder blade)

• Clavicle (collarbone)

The glenohumeral joint (between the humerus and scapula) is the main joint responsible for shoulder movement, while the acromioclavicular joint (between the clavicle and scapula) assists in overhead motion.

The Role of the Rotator Cuff

The rotator cuff is a group of four muscles responsible for stabilizing and moving the shoulder:

1. Supraspinatus – Lifts the arm away from the body.

2. Infraspinatus – Assists with external rotation.

3. Teres Minor – Works with infraspinatus for rotation.

4. Subscapularis – Aids in internal rotation.

These muscles work together to maintain shoulder stability and control movement.

How Muscle Imbalances Impact the Shoulder

Muscle imbalances occur when some muscles become tight or overactive while others become weak or underused. This can alter joint mechanics and increase the risk of injury.

Common Causes of Muscle Imbalances

• Poor Posture (e.g., rounded shoulders from prolonged sitting)

• Repetitive Overhead Activities (e.g., swimming, baseball, weightlifting)

• Overuse of Certain Muscles (e.g., dominant chest muscles overpowering weak scapular stabilizers)

• Previous Injuries leading to compensatory movement patterns

Effects of Muscle Imbalances on the Shoulder

• Altered Scapular Positioning: Poor muscle coordination can cause the scapula to rest in a forward-tilted position, increasing stress on the rotator cuff.

• Reduced Shoulder Stability: Weak rotator cuff muscles lead to excessive movement of the humeral head, increasing the risk of impingement.

• Increased Risk of Injury: Imbalances place excessive strain on certain tendons, making them more prone to tears or irritation.

Solution: A well-balanced rehabilitation or strength program should focus on improving scapular stability, rotator cuff endurance, and postural awareness.

The Role of Spinal Function in Shoulder Mechanics

The thoracic spine (mid-back) plays a crucial role in shoulder mobility and function.

How Spinal Dysfunction Affects the Shoulder

• Thoracic Stiffness: Reduced mobility in the upper back forces the shoulder to compensate, leading to overuse injuries.

• Forward Head Posture: Causes rounded shoulders, tightening the pectorals and weakening scapular stabilizers.

• Poor Core Activation: A weak core leads to instability, making it harder for the shoulder to function properly.

Improving Spinal Function for Better Shoulder Health

• Thoracic Extension Exercises (e.g., foam rolling)

• Postural Strengthening (e.g., scapular retraction drills)

• Core Stability Work (e.g., planks, anti-rotation exercises)

A holistic approach addressing both spinal and shoulder mechanics is key to long-term injury prevention.

Adhesive Capsulitis (Frozen Shoulder)

What is Adhesive Capsulitis?

Adhesive capsulitis, or frozen shoulder, is a painful and progressive loss of shoulder motion due to inflammation and tightening of the shoulder capsule.

Causes and Risk Factors

• Idiopathic (unknown cause)

• Secondary to Injury or Surgery (prolonged immobilization)

• Associated Conditions (diabetes, thyroid disorders)

• Autoimmune Responses

Phases of Frozen Shoulder

1. Freezing Stage (6 weeks - 9 months)

   • Gradual onset of severe pain, especially at night

   • Increasing stiffness and limited mobility

2. Frozen Stage (4 - 6 months)

   • Pain may decrease, but stiffness remains severe

   • Significant difficulty with daily tasks

3. Thawing Stage (6 months - 2 years)

   • Gradual improvement in range of motion and function

Treatment Options

• Physical Therapy: Gentle stretching and joint mobilization

• NSAIDs or Corticosteroid Injections: Reduce inflammation

• Manual Therapy & Joint Mobilization

• Hydrodilatation (Fluid Injection Therapy): Expands the joint capsule

• Surgical Intervention (if severe, including capsular release)

Early intervention leads to better long-term outcomes.

Rotator Cuff Tears

What is a Rotator Cuff Tear?

A rotator cuff tear occurs when one or more tendons of the rotator cuff muscles become partially or completely torn.

Causes of Rotator Cuff Tears

• Acute Injury (fall, heavy lifting, sudden jerking motion)

• Chronic Degeneration (age-related wear and tear)

• Repetitive Stress (throwing, swimming, overhead work)

Symptoms

• Pain (especially when lifting or lowering the arm)

• Weakness (difficulty lifting objects)

• Clicking or Popping Sensations

Treatment Options

Conservative (Non-Surgical) Treatment

• Physical Therapy: Strengthening surrounding muscles to compensate

• NSAIDs and Injections: For pain management

• Activity Modification

Success Rate: Many people manage small tears without surgery, especially with structured rehab.

Surgical Treatment

• Indicated for Full-Thickness or Severe Tears

• Common Procedures: Arthroscopic repair, tendon reattachment

• Recovery: Typically 4-6 months, with gradual return to activity

Surgical Outcomes: Success rates are high if post-surgical rehab is followed correctly.

Shoulder Impingement Syndrome

What is Shoulder Impingement?

Shoulder impingement syndrome occurs when the rotator cuff tendons or the subacromial bursa become compressed between the acromion (part of the scapula) and the head of the humerus. This compression leads to inflammation, pain, and restricted movement.

Over time, impingement can progress to rotator cuff tendinitis, bursitis, or even partial or full-thickness rotator cuff tears if left untreated.

Relevant Anatomy

The subacromial space is the small area between the acromion and the humeral head where key soft tissues pass through, including:

• Supraspinatus tendon (one of the rotator cuff muscles)

• Subacromial bursa (fluid-filled sac that reduces friction)

• Long head of the biceps tendon (helps stabilize the shoulder joint)

When this space narrows, it causes increased friction and irritation of these structures, leading to impingement.

Causes of Shoulder Impingement

1. Repetitive Overhead Movements

   • Common in athletes (swimmers, baseball players, weightlifters)

   • Can result from repeated reaching, throwing, or lifting

2. Poor Posture & Scapular Dysfunction

   • Forward head posture & rounded shoulders lead to an altered scapular position, reducing subacromial space

   • Weak scapular stabilizers fail to maintain proper shoulder mechanics

3. Muscle Imbalances

   • Tight pectoral muscles & weak rotator cuff/scapular stabilizers cause improper shoulder alignment

   • Overactive deltoids can overpower the rotator cuff, pushing the humeral head upward

4. Bony Abnormalities

   • Some people have a hooked or curved acromion, which naturally decreases subacromial space

   • Bone spurs from arthritis can further narrow the space

5. Previous Shoulder Injuries

   • Rotator cuff injuries, labral tears, or previous fractures may alter movement patterns, increasing impingement risk

Symptoms of Shoulder Impingement

• Pain when reaching overhead or behind the back

• Painful arc between 60-120 degrees of arm elevation

• Weakness or difficulty lifting objects

• Clicking or popping sensations

• Night pain that disrupts sleep

• Limited internal rotation (e.g., difficulty reaching behind the back)

Treatment Options for Shoulder Impingement

1. Conservative (Non-Surgical) Treatment

Most cases of shoulder impingement can be effectively managed with conservative treatment, including:

• Activity Modification

  • Avoid repetitive overhead motions

  • Modify work or sports activities to reduce stress on the shoulder

• Physical Therapy (Primary Treatment)

  • Postural Correction: Strengthening the scapular stabilizers (lower traps, serratus anterior) and stretching tight pectorals

  • Rotator Cuff Strengthening: External rotation and shoulder stabilization exercises

  • Thoracic Mobility Exercises: Foam rolling and spinal extension work to improve posture

• Anti-Inflammatory Medications (NSAIDs)

  • Reduces pain and swelling

• Corticosteroid Injections

  • Used for severe cases with persistent inflammation

2. Surgical Treatment (For Severe or Chronic Cases)

If conservative treatment fails after 3-6 months, surgical options may be considered:

• Subacromial Decompression (Acromioplasty)

  • Removes bone spurs or reshapes the acromion to increase space

  • Performed arthroscopically (minimally invasive)

• Bursectomy

  • Removal of an inflamed subacromial bursa if it contributes to impingement

• Rotator Cuff Repair (If a tear is present)

Surgical outcomes for impingement are generally positive, with most patients regaining full function after a proper rehabilitation program.

Final Thoughts

Whether dealing with impingement, frozen shoulder, or a rotator cuff tear, early intervention is crucial for successful recovery. A well-structured rehab program focusing on mobility, strength, and proper biomechanics can help restore shoulder function and prevent future injuries.

If you’re experiencing persistent shoulder pain, consider consulting a physical therapist or healthcare provider for a personalized assessment and treatment plan.

References

1. Neviaser, A. S., & Hannafin, J. A. (2010). Adhesive Capsulitis: A Review of Current Treatment. The American Journal of Sports Medicine.

2. Yamamoto, A. et al. (2010). Prevalence and Risk Factors of a Rotator Cuff Tear in the General Population. Journal of Shoulder and Elbow Surgery.

3. Michener, L. A., McClure, P. W., & Karduna, A. R. (2003). Shoulder Impingement Syndrome: Pathoanatomy, Diagnosis, and Treatment. Journal of Orthopaedic & Sports Physical Therapy.

Disclaimer

This article is for informational purposes only and is not a substitute for professional medical advice. Always consult a licensed healthcare provider before starting any treatment or rehabilitation program.