AC Joint Sprain: Causes, Symptoms, Diagnosis, and Treatment

What is an AC joint sprain?

An AC joint sprain is an injury to the ligaments surrounding the acromioclavicular (AC) joint, located at the top of the shoulder where the collarbone (clavicle) meets the shoulder blade's highest point (acromion), typically caused by a direct blow or fall onto the shoulder.

Understanding the AC Joint: Anatomy and Function

The acromioclavicular (AC) joint is a small, yet crucial, synovial joint at the top of the shoulder. It's formed by the articulation of two bones:

• Clavicle (Collarbone): The long, slender bone that runs horizontally across the top of your chest.
• Acromion: The bony projection at the end of the spine of the scapula (shoulder blade), forming the highest point of the shoulder.

This joint is stabilized by a complex network of ligaments:

• Acromioclavicular (AC) Ligaments: These ligaments directly connect the acromion to the clavicle, providing horizontal stability to the joint capsule.
• Coracoclavicular (CC) Ligaments: Comprising the conoid and trapezoid ligaments, these are much stronger and connect the clavicle to the coracoid process (a hook-like projection from the scapula). They provide crucial vertical stability, preventing the clavicle from separating upwards from the scapula.

Function: The AC joint allows for subtle movements of the scapula relative to the clavicle, facilitating the full range of motion of the arm, especially during overhead activities. It acts as a pivot point, enabling the scapula to rotate and glide, optimizing the position of the glenohumeral (shoulder) joint.

What is an AC Joint Sprain?

An AC joint sprain, also known as a shoulder separation, occurs when the ligaments stabilizing the AC joint are stretched or torn. Unlike a "dislocation" which typically refers to the glenohumeral joint (ball and socket joint), an AC joint sprain specifically involves the separation of the clavicle from the acromion. The severity of the sprain depends on which ligaments are damaged and to what extent.

The mechanism of injury most commonly involves a direct impact to the top or side of the shoulder while the arm is adducted (close to the body). This force drives the acromion downwards, while the clavicle remains relatively stationary, causing the ligaments to stretch or tear.

Causes and Risk Factors

AC joint sprains are common injuries, particularly in active individuals. The primary causes include:

• Direct Trauma:
  • Falls: Falling directly onto the point of the shoulder is the most frequent cause. This can happen during everyday activities, but is especially common in sports.
  • Direct Blows: A forceful impact to the shoulder, such as during a tackle in football or a collision in hockey.
• Indirect Trauma: Less common, but can occur with a fall onto an outstretched hand, where the force is transmitted up the arm to the shoulder.

Risk Factors:

• Contact Sports: Football, rugby, hockey, wrestling.
• Gravity Sports: Cycling (falling over handlebars), skiing, snowboarding (falling onto the shoulder).
• Martial Arts: Activities involving throws or takedowns.
• Occupational Hazards: Jobs that involve working at heights or in environments prone to falls.

Signs and Symptoms

The symptoms of an AC joint sprain can vary based on the severity of the injury, but commonly include:

• Pain: Localized pain at the top of the shoulder, directly over the AC joint. This pain is often sharp and worsens with arm movement, especially lifting the arm overhead, across the body, or carrying heavy objects.
• Swelling and Bruising: Visible swelling and tenderness around the AC joint. Bruising may develop a few days after the injury.
• Deformity (Step-off): In more severe sprains, a visible bump or "step-off" deformity may be present at the top of the shoulder, indicating that the clavicle has been displaced upwards relative to the acromion.
• Limited Range of Motion: Difficulty and pain when moving the arm, particularly when attempting to raise it above shoulder height or reach across the body.
• Tenderness: The AC joint will be very tender to touch.
• Weakness: Perceived weakness in the shoulder due to pain inhibition.

Grading AC Joint Sprains

AC joint sprains are typically graded on a scale of I to VI, with increasing numbers indicating more severe damage to the ligaments and greater displacement of the clavicle.

• Grade I:
  • Damage: Mild stretch of the AC ligaments; no tearing. Coracoclavicular (CC) ligaments are intact.
  • Appearance: No visible deformity.
  • Symptoms: Mild pain, localized tenderness, minimal swelling. Full range of motion possible with some discomfort.
• Grade II:
  • Damage: Partial tear of the AC ligaments. The CC ligaments are stretched but intact.
  • Appearance: Slight widening of the AC joint, subtle "step-off" deformity may be present.
  • Symptoms: Moderate pain, more pronounced tenderness, swelling. Significant pain with arm movement, especially overhead.
• Grade III:
  • Damage: Complete tear of both the AC and CC ligaments.
  • Appearance: Obvious "step-off" deformity, as the clavicle is significantly displaced upwards.
  • Symptoms: Severe pain, significant swelling, marked tenderness. Very limited and painful range of motion. Shoulder instability is evident.
• Grade IV: Complete tear of AC and CC ligaments with posterior displacement of the clavicle into the trapezius muscle.
• Grade V: Complete tear of AC and CC ligaments with severe superior displacement of the clavicle, tearing through the deltoid and trapezius fascia.
• Grade VI: Complete tear of AC and CC ligaments with inferior displacement of the clavicle, often under the coracoid process.

Grades IV, V, and VI are rare and involve more extensive soft tissue damage and significant displacement, often requiring surgical intervention.

Diagnosis

Accurate diagnosis is crucial for appropriate treatment. It typically involves:

• Physical Examination: The healthcare provider will inspect the shoulder for deformity, swelling, and bruising. They will palpate (feel) the AC joint for tenderness and assess the range of motion of the arm, noting any pain or instability. Specific tests may be performed to stress the AC joint.
• Imaging Studies:
  • X-rays: Standard X-rays are usually the first imaging test. They can reveal the degree of separation between the clavicle and acromion. Stress X-rays (taken while holding a weight in the hand) may be used to better visualize subtle instability.
  • MRI (Magnetic Resonance Imaging): An MRI may be ordered to assess the extent of soft tissue damage, including tears to the AC and CC ligaments, as well as any associated muscle or cartilage injuries.
  • CT Scan (Computed Tomography): Less common, but can provide more detailed bony anatomy, particularly useful for Grades IV-VI or if other bony injuries are suspected.

Treatment and Management

Treatment for an AC joint sprain depends heavily on the grade of the injury, the patient's activity level, and their individual symptoms.

Conservative Management (Typically for Grades I, II, and many Grade III injuries)

The majority of AC joint sprains are managed non-surgically.

• R.I.C.E. Protocol:
  • Rest: Avoid activities that exacerbate pain.
  • Ice: Apply ice packs to the affected area for 15-20 minutes, several times a day, to reduce pain and swelling.
  • Compression: A compression bandage or wrap can help reduce swelling, though often less effective for AC joint.
  • Elevation: Keep the arm elevated to help manage swelling.
• Pain Management: Over-the-counter non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen can help reduce pain and inflammation. In some cases, stronger prescription pain relievers may be used.
• Arm Sling: A sling is often used for the first 1-3 weeks to immobilize the shoulder and provide comfort, allowing the ligaments to heal.
• Physical Therapy (Rehabilitation): Once initial pain and swelling subside, a structured physical therapy program is essential.
  • Phase 1 (Pain and Swelling Reduction): Focus on gentle range-of-motion exercises, passive modalities (ice, heat), and pain control.
  • Phase 2 (Restoration of Range of Motion): Gradual progression to active and assisted range of motion exercises, focusing on regaining full shoulder mobility.
  • Phase 3 (Strengthening): Progressive strengthening exercises for the rotator cuff, scapular stabilizers, and deltoid muscles to restore stability and function.
  • Phase 4 (Return to Activity): Sport-specific drills and functional exercises to prepare for a safe return to pre-injury activities.

Surgical Intervention (Primarily for Grades IV, V, VI, and some symptomatic Grade III injuries)

Surgery may be considered for severe AC joint sprains or when conservative treatment fails to provide adequate stability and function, particularly in high-demand athletes.

• Indications: Significant cosmetic deformity with persistent pain, neurological symptoms, or failure of conservative treatment.
• Types of Surgery: Various surgical techniques aim to reconstruct or repair the torn ligaments and stabilize the clavicle. These may involve:
  • Direct repair: Reattaching torn ligaments.
  • Coracoclavicular (CC) ligament reconstruction: Using grafts (from the patient or a donor) to replace the torn CC ligaments.
  • Internal fixation: Using plates, screws, or wires to temporarily hold the joint in place while healing occurs.

Recovery and Rehabilitation

The recovery timeline for an AC joint sprain varies significantly based on its grade and whether surgery was performed.

• Grade I: Typically 2-4 weeks for return to light activities, with full recovery in 4-6 weeks.
• Grade II: Often requires 6-8 weeks for return to most activities, with full recovery potentially up to 12 weeks.
• Grade III (Conservative): Can take 8-12 weeks for initial return to activity, with full recovery and strength taking 3-6 months.
• Surgical Repair (Grades III-VI): Post-operative rehabilitation is lengthy, often involving 6 weeks of immobilization, followed by 3-6 months of physical therapy. Full return to contact sports may take 6-12 months or longer.

Key aspects of rehabilitation:

• Adherence to Physical Therapy: Crucial for regaining strength, flexibility, and stability.
• Gradual Progression: Exercises are progressively challenging as healing occurs.
• Pain as a Guide: Listen to your body and avoid activities that cause sharp pain.
• Patience: Full recovery takes time and commitment.

Prevention Strategies

While not all AC joint sprains can be prevented, certain strategies can reduce the risk:

• Proper Falling Techniques: Learning how to fall safely (e.g., rolling rather than landing stiffly on the shoulder) can be beneficial for athletes in high-risk sports.
• Protective Gear: Using appropriate padding in contact sports can help absorb impact forces.
• Strengthening Shoulder Girdle: Developing strength in the muscles surrounding the shoulder (rotator cuff, deltoids, scapular stabilizers) can improve joint stability and resilience.
• Awareness and Caution: Being mindful of surroundings and potential hazards, especially in activities with a high risk of falls or collisions.

Understanding the anatomy, causes, and treatment of an AC joint sprain is vital for effective management and a successful return to activity. Always consult with a healthcare professional for an accurate diagnosis and personalized treatment plan.