AC Joint Injuries – Acute & Chronic

At a glance

What is an acromioclavicular (AC) joint injury?

An acromioclavicular (AC) joint injury affects the joint at the top of the shoulder, where the collarbone (clavicle) meets the acromion, a part of the shoulder blade. This joint plays an important role in connecting the arm to the body and supporting shoulder movement.

An AC joint injury occurs when the supporting ligaments around this joint are stretched or torn. These ligaments help keep the clavicle aligned with the acromion, and damage to them can disrupt the stability of the joint. The severity of the injury can vary. Mild cases involve a sprain, where the ligaments are overstretched but still intact. More significant injuries involve partial or complete tears, which can lead to separation of the joint and visible deformity at the top of the shoulder.

This type of injury can affect how the shoulder functions. Movement of the arm, particularly lifting, reaching or overhead activities, may become painful or limited. In more severe cases, there may be difficulty using the arm for everyday tasks due to weakness or instability.

What is the acromioclavicular joint and what does it do?

The acromioclavicular joint is a small joint located at the top of the shoulder, formed by the meeting of the clavicle and the acromion. Despite its size, it plays an important role in allowing coordinated movement of the shoulder.

The stability of the AC joint is maintained by two main sets of ligaments. 

• The acromioclavicular ligaments provide horizontal stability, helping keep the joint aligned. 
• The coracoclavicular ligaments, which connect the clavicle to another part of the shoulder blade called the coracoid process, provide vertical stability and prevent the clavicle from moving upwards.

These structures allow the shoulder to move smoothly while maintaining alignment. The AC joint contributes to movements such as lifting the arm, reaching overhead and transferring forces from the arm to the rest of the body. It also helps maintain overall shoulder stability during weight-bearing and functional activities.

What causes an AC joint injury?

AC joint injuries usually occur when a force is applied to the shoulder that exceeds the strength of the supporting ligaments.

• Direct fall onto the shoulder — a fall directly onto the outer part of the shoulder is the most common cause. The impact drives the acromion downward while the clavicle remains in place, placing stress on the ligaments and leading to injury.
• Impact during contact sports — collisions in sports such as football or rugby can result in direct force to the shoulder. These high-impact events can damage the ligaments and cause varying degrees of joint separation.
• Fall onto an outstretched hand — force transmitted through the arm during a fall can travel up to the shoulder and place stress on the AC joint. Although indirect, this mechanism can still lead to ligament injury.
• Road traffic or high-impact trauma — accidents involving greater force, such as road traffic incidents, can result in more severe AC joint injuries, including complete ligament tears and significant displacement of the joint.

What are the symptoms of an AC joint injury?

The symptoms of an acromioclavicular (AC) joint injury vary depending on the severity of ligament damage but commonly affect the top of the shoulder and its movement.

• Pain at the top of the shoulder — discomfort is usually localised over the AC joint and may worsen with pressure or movement of the arm.
• Swelling and tenderness — the area may appear swollen and feel tender to touch, particularly in the early stages after injury.
• Visible deformity — in more severe cases, there may be a noticeable bump or “step-off” at the top of the shoulder, caused by displacement of the clavicle.
• Pain with arm movement — movements such as lifting the arm, reaching across the body or raising the arm overhead can trigger or worsen pain.
• Reduced shoulder strength and range — weakness and stiffness may limit how far the shoulder can move and reduce the ability to perform everyday tasks.

Can you move your arm with an AC joint injury?

The ability to move the arm depends on how severe the injury is. In mild injuries, movement is usually still possible, although it may be uncomfortable or painful, especially with overhead or forceful activities.

In moderate injuries, the range of motion is more limited, and discomfort becomes more noticeable during everyday movements. In severe injuries, movement may be significantly restricted. There may be marked pain, weakness and visible deformity, making it difficult to lift or use the arm normally.

Who is most at risk of AC joint injuries in Singapore?

AC joint injuries are more likely to occur in individuals who are exposed to falls, impact or repetitive strain on the shoulder.

• Athletes — sports such as football, cycling and other contact or high-impact activities increase the risk of falls or direct blows to the shoulder.
• Active individuals with fall risk — those who engage in regular physical activity, especially outdoors or at higher intensity, may be more prone to accidental falls.
• Individuals in physically demanding occupations — jobs that involve manual labour, heavy lifting or working at height can increase the likelihood of shoulder injuries.
• Younger adults — higher activity levels and participation in sports or physically demanding tasks place greater stress on the shoulder, increasing the risk of injury.

How is an AC joint injury diagnosed?

Diagnosis of an acromioclavicular (AC) joint injury begins with a clinical evaluation and may be supported by imaging to confirm the severity and guide treatment.

• Clinical assessment — our doctor takes a detailed history of how the injury occurred, such as a fall or direct impact. The timing of pain, progression of symptoms and any difficulty with movement are considered. This helps identify the likely mechanism and severity of the injury.
• Physical examination — the shoulder is examined for tenderness, swelling and any visible deformity at the AC joint. Range of motion and strength are assessed, especially movements that stress the joint. These findings help determine stability and functional limitation.
• Imaging (if needed) — imaging is used when confirmation or further evaluation of severity is required. It helps assess joint alignment and the extent of ligament damage. This supports accurate diagnosis and treatment planning.
• X-rays — these evaluate the alignment of the AC joint and identify any separation or displacement of the clavicle. In some cases, comparison views may be taken for better assessment.
• MRI — MRI provides a detailed view of ligaments and surrounding soft tissues. It helps assess the extent of ligament injury and detect associated damage. This is useful when symptoms are not fully explained by X-rays.

What are the treatment options for AC joint injuries in Singapore?

Treatment depends on the severity of the injury, with many cases managed conservatively and surgery reserved for more significant injuries.

Conservative (Non-Surgical) Treatment

• Rest and sling support — the arm may be supported in a sling to reduce movement and allow the ligaments to heal. Avoiding activities that place strain on the shoulder is important in the early phase.
• Ice and pain management — applying ice helps reduce swelling and discomfort, particularly in the first few days after injury. Pain relief measures may be used to improve comfort and support recovery.
• Physiotherapy — rehabilitation is introduced in stages. Early exercises focus on gentle movement to prevent stiffness, followed by strengthening and functional training to restore shoulder stability and control.
• Gradual return to activity — activities are reintroduced progressively as pain settles and strength improves, reducing the risk of reinjury.

Surgical Treatment

Surgery may be considered in cases of severe joint separation or when there is ongoing instability that does not improve with conservative care.

• Ligament reconstruction or joint stabilisation — procedures aim to restore the alignment of the clavicle and stabilise the joint by repairing or reconstructing the damaged ligaments.

What is recovery like after an AC joint injury?

Recovery from an acromioclavicular (AC) joint injury takes time and tends to progress in stages. In the early phase, the priority is to protect the joint and allow the injured ligaments to settle, which usually means limiting movement and avoiding activities that trigger pain. As discomfort and swelling begin to ease, gentle movement is introduced to prevent stiffness while still keeping the joint protected.

Physiotherapy becomes more important as recovery progresses. Exercises are introduced gradually, starting with simple movements and moving towards strengthening and functional use of the shoulder. This helps rebuild stability and coordination, allowing the shoulder to handle everyday tasks more comfortably.

It is important not to rush this process. Returning to activity too soon or pushing through pain can delay healing and increase the chance of reinjury. A steady, guided approach to rehabilitation gives the best chance of regaining strength and maintaining long-term shoulder function.

What can happen if an AC joint injury is left untreated?

If an acromioclavicular (AC) joint injury is not managed appropriately, the joint may not heal in a stable or aligned position, which can lead to ongoing problems. Persistent shoulder pain may develop, especially during movement or when placing weight on the arm. Damage to the supporting ligaments can also result in chronic instability, affecting control and coordination of the shoulder during everyday activities.

Over time, reduced strength and limited range of motion may interfere with tasks such as lifting, reaching or carrying objects. In the longer term, abnormal joint mechanics can place additional stress on the joint, increasing the risk of wear and tear and leading to degenerative changes that affect overall shoulder function.

How can AC joint injuries be prevented?

Preventing AC joint injuries involves reducing the risk of excessive strain and improving shoulder resilience.

• Strengthening shoulder muscles — regular strengthening of the shoulder and surrounding muscles helps support joint stability and absorb stress during activity.
• Proper technique in sports — using correct form during physical activity reduces unnecessary strain on the shoulder joint.
• Protective gear in contact sports — appropriate padding or protective equipment can help minimise the impact of direct blows to the shoulder.
• Fall prevention strategies — improving balance, awareness and safety during physical activity can reduce the likelihood of falls that may lead to injury.

Summary

An acromioclavicular (AC) joint injury affects the small joint at the top of the shoulder, where the collarbone meets the shoulder blade. It is most often caused by a fall onto the shoulder or a direct impact, and can range from a mild ligament strain to a complete tear with joint separation. These injuries typically present with pain at the top of the shoulder, swelling, reduced strength and difficulty with movements such as lifting the arm or reaching overhead.

The majority of AC joint injuries can be managed without surgery through a combination of rest, short-term support, and a structured physiotherapy programme aimed at restoring movement, strength and stability. In more severe cases, particularly where there is significant displacement or persistent instability, surgical treatment may be required to realign and stabilise the joint. Recovery is gradual and depends on both the severity of the injury and adherence to rehabilitation, with careful progression helping to prevent reinjury and long-term complications.

If you are experiencing shoulder pain, swelling or difficulty using your arm, schedule a consultation with Cove Orthopaedics for a detailed assessment and a personalised treatment plan.