Article by John Miller
What is an AC Joint Injury?
(also known as Acromioclavicular Joint Injury)
An acromioclavicular (AC) joint injury is commonly referred to as "shoulder separation" and should not be confused
with a shoulder dislocation.
Your acromioclavicular joint (or AC Joint) is the joint at the top of your shoulder between your clavicle (collarbone) and your scapula (shoulder blade).
The AC joint is important in allowing overhead and across the body movements of your arm, as well as transmitting forces from the arm to the rest of
the body during activities such as pushing, pulling and lifting. There are a number of ligaments which help to stabilise this joint.
An acromioclavicular joint sprain refers to an injury where the ligaments supporting the acromioclavicular joint are overstretched. The degree of AC
joint ligament damage can vary from a mild strain of one or more of the surrounding ligaments to complete ligament tears and deformity.
What is the AC Joint?
The shoulder joint is formed at the junction of three bones: the collarbone (clavicle), the shoulder blade (scapula), and the arm bone (humerus). The scapula
and clavicle form the socket of the joint, and the humerus has a round head that fits within this socket. The end of the scapula is called the acromion,
and the joint between this part of the scapula and clavicle is called the acromioclavicular joint.
When the acromioclavicular joint is disrupted, it is called a shoulder separation and can form a "step" if displaced. Another name for this injury
is an acromioclavicular joint separation, or AC separation or an AC joint sprain.
The ligaments that hold the joints together are the acromioclavicular, coracoacromial and coracoclavicular (trapezoid and conoid) ligaments.
What Causes an AC Joint Injury?
Direct forces can injure your AC joint when a person collides with a solid object or surface such as a fall from a bicycle or during a football tackle
where the shoulder hits the ground.
You acromioclavicular joint may also be injured indirectly when a person falls on an outstretched arm. The contact force is transmitted up through
the arm, which forces a separation of the acromion and clavicle. The ligaments are overstretched and damaged in the process.
AC Joint Injury Symptoms
Your physiotherapist will suspect an acromioclavicular ligament sprain when you report:
- Pain on the top of the shoulder aggravated by heavy lifting, overhead and across body movements.
- Swelling +/- bruising.
- Loss of shoulder movement.
- Sometimes a hard, visible lump may also be present on the top of the shoulder, indicating displacement of the clavicle (collar bone).
AC joint injury is graded by severity from Grade I (minimal joint disruption) to Grade III (severe injury). If the injury is the more severe, Grade III,
a bump caused by the separated AC joint may be seen or felt at the tip of the shoulder bones. The diagnosis of shoulder separation is often quite apparent
from hearing a story that is typical of this injury, and a simple physical examination.
X-rays should be performed to ensure there is no fracture of these bones. Clavicle fractures from falls are particularly common.
If the diagnosis is unclear, X-rays while holding a weight in your hand may be helpful. When this type of X-ray is performed, the force of the weight will
accentuate any AC joint instability and better show the effects of the separated shoulder.
AC Joint Injury Treatment
Most patients with acromioclavicular joint injury start to feel better within a few days or a week of the injury. However, full ligament healing will take
at least six weeks. During this time it is important to protect your AC joint ligaments from overstretching the immature scar tissue. It can be helpful
to use a sling, taping or a shoulder brace that de-loads your AC joint.
Your physiotherapist's treatment will aim to:
- Reduce pain and inflammation.
- Normalise joint range of motion.
- Strengthen your shoulder.
- Improve your shoulder blade and shoulder alignment.
- Normalise your muscle lengths.
- Improve your upper limb proprioception.
- Improve your technique and function eg lifting, overhead activities.
- Minimise your chance of re-injury as you return to sport or work.
In severe cases, some patients choose to undergo AC joint surgery to pin the AC joint or repair the damaged ligaments surrounding the AC joint.
Post-operative rehabilitation is one of the most important, yet too often neglected, aspects of surgery. The quickest and most successful outcomes
result from the guidance and supervision of an experienced shoulder physiotherapist.
Your rehabilitation following shoulder surgery focuses on restoring full shoulder motion, strength, power and endurance. You will also require proprioception
and functional-based retraining that is individualised towards your specific needs.
Risks of surgery include infection, persistent instability and pain, stiffness, and difficulty returning to your previous level of activity.
Return to Sports with an AC Joint Injury
When returning to your sport, it is important that you undergo a graduated transition to avoid the risk of injury recurrence. This includes the completion
of a full individually designed rehabilitation program aimed at improving strengthening, flexibility and proprioception in your upper limbs.
For more information, please ask the advice of your physiotherapist.
Related Shoulder Injuries
Common AC Joint Injury Treatments
Early Injury Treatment
Avoid the HARM Factors
Soft Tissue Injury? What are the Healing Phases?
What to do after a Muscle Strain or Ligament Sprain?
Acupuncture and Dry Needling
Sub-Acute Soft Tissue Injury Treatment
Scapular Stabilisation Exercises
Rotator Cuff Exercises
Proprioception & Balance Exercises
Agility & Sport-Specific Exercises
Soft Tissue Massage
AC Joint Treatment
Brace or Support
Electrotherapy & Local Modalities
Joint Mobilisation Techniques
Physiotherapy Instrument Mobilisation (PIM)
Scapulohumeral Rhythm Exercises
Supportive Taping & Strapping
FAQs about AC Joint Injuries
Common Physiotherapy Treatment Techniques
What is Pain?
Physiotherapy & Exercise
When Should Diagnostic Tests Be Performed?
Can Kinesiology Taping Reduce Your Swelling and Bruising?
Heat Packs. Why does heat feel so good?
How Much Treatment Will You Need?
Sports Injury? What to do? When?
What are the Common Massage Therapy Techniques?
What are the Early Warning Signs of an Injury?
What Can You Do To Help Arthritis?
What is a TENS Machine?
What is Chronic Pain?
What is Nerve Pain?
What is Sports Physiotherapy?
What is the Shoulder Impingement Zone?
What's the Benefit of Stretching Exercises?
When Can You Return to Sport?
When Should You Use a Shoulder Posture Brace?
Why Kinesiology Tape Helps Reduce Swelling and Bruising Quicker
Helpful Products for AC Joint Injuries