AC Joint Injuries

An AC joint injury occurs when the ligaments that connect the collarbone to the shoulder blade are stretched or torn due to trauma.

AC joint injuries are classified by severity, ranging from mild sprains to complete ligament tears:

1. Grade I – A mild sprain where the ligaments are stretched but not torn.
2. Grade II – A partial tear of the AC ligaments, causing noticeable pain and some instability.
3. Grade III – A complete tear of the AC and coracoclavicular (CC) ligaments, often resulting in a visible deformity where the clavicle appears elevated.
4. Grade IV-VI – Severe injuries with significant clavicle displacement, requiring surgical repair for return to high-level athletic performance.

Dr. Stephanie Boden, a fellowship-trained orthopedic surgeon at the University of Louisville, specializes in sports medicine and shoulder surgery, utilizing minimally invasive arthroscopic techniques and advanced open reconstruction to treat AC joint injuries effectively.

Athletes who engage in the following sports are at an increased risk of AC joint injuries due to falls, collisions, or repetitive shoulder strain:

• Football and Rugby – Tackling, blocking, and direct blows to the shoulder make AC joint injuries a frequent occurrence.
• Hockey – Players are at risk due to body checks, falls on the ice, and contact with the boards.
• Wrestling and Mixed Martial Arts (MMA) – Direct impact and throws can cause significant force on the shoulder joint.
• Cycling and Mountain Biking – Falls over handlebars and crashes put cyclists at risk of landing on the shoulder.
• Skiing and Snowboarding – High-speed falls, especially on icy or uneven terrain, can lead to AC joint trauma.
• Baseball and Softball – Overhead throwing places stress on the AC joint, increasing susceptibility to both acute and chronic injuries.
• Weightlifting and CrossFit – Heavy lifting, especially exercises like bench press, clean and jerk, and overhead presses, can strain the AC joint.
• Gymnastics – Athletes frequently put stress on their shoulders with high-impact landings and complex movements.

The most common ways athletes sustain an AC joint injury include:

• Direct impact to the shoulder – A hit from an opponent, a hard fall, or a collision with the ground.
• Falling on an outstretched arm – Trying to break a fall with an extended arm can transmit force to the AC joint.
• Repetitive stress and overuse – Athletes in throwing sports or weightlifting may develop AC joint irritation or degeneration over time.

Athletes with an AC joint injury may experience:

• Sharp pain at the top of the shoulder that worsens with movement.
• Swelling and bruising over the joint.
• A visible bump or deformity in moderate to severe cases.
• Limited range of motion, especially when reaching overhead or across the body.
• Shoulder weakness or instability, making it difficult to lift weights or perform athletic movements.

Athletes who have sustained an AC joint injury are at a higher risk of re-injury, especially if they return to sports too quickly or do not complete proper rehabilitation. Factors that increase the risk of another AC joint injury include:

• Returning to contact sports before full recovery – Incomplete healing makes the joint more vulnerable.
• Insufficient shoulder strengthening – Weak muscles around the shoulder fail to protect the AC joint from impact.
• Poor biomechanics – Incorrect throwing, lifting, or tackling techniques increase strain on the joint.
• Lack of protective equipment – In football, rugby, and hockey, shoulder padding can help absorb impact forces.
• Repetitive stress – Overuse from weightlifting or overhead sports can lead to chronic irritation or degeneration of the AC joint.