Final answer:
AC joint injuries can be graded into different categories - grade 1, grade 2, and grade 3 - depending on the severity of the injury. The coracoclavicular ligaments provide important support for the acromioclavicular joint. The deltoid and trapezius muscles are also affected in an AC joint injury.
Step-by-step explanation:
AC joint injuries, also known as acromioclavicular joint injuries, can be graded into different categories depending on the severity of the injury. The grades range from mild to severe and are based on the extent of damage to the ligaments and joint itself.
In a grade 1 AC joint injury, there is a mild sprain or stretching of the acromioclavicular ligaments. The joint remains stable and there is no displacement.
In a grade 2 AC joint injury, there is a partial tear of the acromioclavicular ligaments. This can result in some displacement of the joint and a visible bump on the shoulder.
In a grade 3 AC joint injury, there is a complete tear of the acromioclavicular ligaments, as well as possible damage to the coracoclavicular ligaments. The joint is significantly displaced and there is a noticeable bump on the shoulder.
The coracoclavicular ligaments provide important support for the acromioclavicular joint. When these ligaments are ruptured, the shoulder becomes unstable and the scapula separates from the clavicle, pulling the shoulder downward.
In addition to the ligament damage, the deltoid and trapezius muscles are also affected in an AC joint injury. These muscles help to stabilize the shoulder and are often weakened or strained as a result of the injury.