A Guide to Physical Therapy for AC Joint Injury

The acromioclavicular joint, also known as the AC joint, is located where the clavicle (collarbone) meets the acromion (the highest point of the shoulder blade). The joint is held together by ligaments, which can be injured if the joint is overextended.

AC joint injuries account for approximately 40% of all shoulder injuries.¹ They are most prevalent in sports that pose a risk of falling on the arm, such as hockey, skiing, biking, and football (making it more likely in males). Additionally, the general population is at risk when falling on an outstretched hand or when experiencing an automobile accident.

An AC joint injury can significantly impact shoulder function due to weakness, stiffness, and pain — making it feel impossible to keep up with daily activities like reaching into the kitchen cabinet, turning a steering wheel, or washing your hair.

Working with a CityPT clinician can help you get relief and regain function as soon as possible. Keep reading to learn more.

Table of Contents

• Understanding AC Joint Injuries
• Symptoms of AC Joint Separation or AC Joint Sprain
• What are the Most Common Causes of AC Joint Injury?
• Diagnosing an AC Joint Sprain vs AC Joint Separation
• What to Expect from Physical Therapy for AC Joint Injury
• What If Conservative Treatment Doesn't Work?
• Preventing AC Joint Injury
• Is It Time to Seek Treatment?

Understanding AC Joint Injuries

As explained in the introduction, the AC joint is at the top of your shoulder complex. It is evident as a bump where two bones meet on the top edge of each shoulder — the collarbone and shoulder blade.

The AC joint plays an important role in shoulder stability and mechanics. Like the shoulder joint itself, it contains synovial fluid (for smooth lubricated movement), cartilage, and a fibrous capsule. The joint's stability is derived from two ligaments: the acromioclavicular ligament and the coracoclavicular ligament.

Overall, its primary purpose is to allow optimal gliding of the shoulder blade along the ribcage. This encourages full unrestricted shoulder joint arm range of motion, particularly with overhead movements like overhead reaching.

Types of AC Joint Injuries

An AC joint injury can be classified based on the severity of the tear.² Let's review the basics:

• AC joint sprain: Ligaments have been stretched, but not completely torn. This typically keeps the joint stable but elicits a lot of pain.
• AC joint separation: A separation is referred to as a complete tear of one or both of the supporting ligaments (sometimes called a subluxation when one ligament is still intact). This causes instability of the joint and can cause a visible deformity.
• AC joint displacement: With severe trauma, the AC joint (particularly the clavicle) is displaced in the direction of the force. Depending on the direction, this can be a medical emergency due to compression of local nerves (brachial plexus) and blood vessels in the shoulder girdle. This is different from a true dislocation, that happens at the shoulder joint, also known as the glenohumeral joint.
• AC joint overuse: Repetitive shoulder use, leading to inflammation and the eventual onset of arthritis.

Symptoms of AC Joint Separation or AC Joint Sprain

Let's review the symptoms of an AC joint injury:

• Pain: Depending on the severity, pain can be sharp or dull (sprain) and is typically worse when using the shoulder or when lying on the affected side.
• Swelling: At the AC joint itself, located at the highest point of your shoulder blade. This area may also feel warm and tender to the touch due to inflammation.
• Shoulder girdle weakness: This is due to the compromised stability of the joint and pain inhibition. You'll likely also notice a reduced range of motion in your shoulder compared to the uninjured side.
• Deformity/bump: In moderate to severe cases, a visible lump or bump may be present at the AC joint.
• Difficulty with daily activities: Including lifting, reaching, and bringing the arm across the body.

Warning: If the clavicle (collar bone) is displaced or fractured posteriorly (backward) or inferiorly (downward), it can lead to serious nerve and vascular complications. Seek medical attention immediately if you experience any of the following: numbness, tingling, or loss of sensation in the arm or hand; coldness of your skin in the affected area; discoloration/bruising in the shoulder; or difficulty breathing.

What are the Most Common Causes of AC Joint Injury?

Ultimately, there are two primary causes of AC joint sprain or separation:

• Trauma: Due to direct impacts, such as a sports injury, fall (especially on an outstretched hand), or motor vehicle accident
• Overuse: Secondary to heavy lifting or frequent overhead arm movement (due to job or sports demands)

Diagnosing an AC Joint Sprain vs AC Joint Separation

For milder cases, a physical exam with a CityPT clinician is comprehensive. This will include an assessment of shoulder range of motion, shoulder girdle mobility, strength, and tenderness/swelling at the AC joint. Your physical therapist will likely also perform special tests to rule out other shoulder injuries.

If a complete tear or clavicular fracture is suspected, imaging such as x-ray, CT scan, or MRI can be ordered by a physician.

What to Expect from Physical Therapy for AC Joint Injury

Physical therapy will initially focus on promoting optimal healing and pain management. Then, your therapist will work with you to restore shoulder strength, improve mobility, and normalize movement patterns related to daily activities. Plus, throughout the recovery process, your CityPT clinician will keep you well-informed with education and self-care strategies.

Let's review the focus on three primary recovery phases:³

• Acute phase: Initial treatment focuses on reducing pain and inflammation, improving mobility, and maintaining strength. This may include modalities such as electrical stimulation, ultrasound, ice/heat therapy, manual stretches, and soft tissue mobilization. In this phase, it is most important to allow the shoulder/AC joint to heal in an optimal position — typically requiring the use of an arm sling.
• Subacute phase: Treatment focuses on restoring shoulder strength, stability, and range of motion — followed by a gradual return to normal activities. This phase will involve biomechanical straining, strengthening exercises, and proprioceptive drills to help restore neuromuscular control and coordination.
• Return to sport: Often overlooked, this final stage is focused on very individualized and sport specific exercise. The ultimate goal is to return to sport and other higher level activities with full confidence, optimal mechanics, and a reduce risk of re-injury.

What If Conservative Treatment Doesn't Work?

With severe AC joint sprains, there is a correlation between injury and the onset of shoulder joint arthritis. Thus, it is generally recommended that surgery is utilized — although there is some controversy over appropriate inclusion criteria for surgery.⁴

Plus, any AC joint sprain that does not respond well to conservative care may need additional interventions. Options include injections to address local inflammation and surgery. Talk to an orthopedic doctor for more options.

Preventing AC Joint Injury

Since an AC joint injury is most often caused by trauma, this injury can be hard to prevent. Regardless, there are some ways to promote basic shoulder tissue health to prevent overuse and injury. These include:

• Keep the shoulder moving: Maintain optimal shoulder strength, coordination, and mechanics with daily activities — focus especially on the rotator cuff and shoulder blade muscles.
• Ergonomics and posture: Maintain optimal tissue health with awareness of your posture at work, at home, and during sports activities.
• Take breaks: Appropriate rest and recovery periods throughout the day (and year) for the shoulders to reduce unnecessary strain.
• Make healthy lifestyle choices: To optimize overall tissue health — including adequate sleep, hydration, nutrition, etc.

Is It Time to Seek Treatment?

If you have suffered a shoulder trauma or have persistent shoulder pain and believe an AC joint injury could be the cause, a CityPT clinician can help. They will assess your symptoms, perform special tests to assess your condition, and customize a treatment plan so you can regain full shoulder function for the long term.

Book an appointment with a CityPT shoulder specialist.

This guide is intended for informational purposes only. We are not providing legal or medical advice and this guide does not create a provider-patient relationship. Do not rely upon this guide (or any guide) for medical information. Always seek the help of a qualified medical professional who has assessed you and understands your condition.

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