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The Secret Keeper of the Shoulder: What Makes the Acromioclavicular Joint So Unique?
The acromioclavicular joint, also known as the acromioclavicular joint, is a key tissue located in the shoulder. This joint connects the acromion of the scapula and the clavicle, supporting the movement and flexibility of the upper limb. It is not only a flat sliding joint, but also provides strong structural stability to the shoulder, allowing us to swing our arms freely.
The acromioclavicular joint plays an integral role in adjusting and moving the shoulder, especially in sports and daily activities.
Structure and stability
The acromioclavicular joint is stabilized and protected by multiple ligaments:
- Acromioclavicular ligament: connects the clavicle to the acromion and provides core stability.
- Superior acromioclavicular ligament: Covering the upper part of the joint, this ligament is composed of parallel fibers that provide additional support.
- Inferior acromioclavicular ligament: relatively thin, covering the lower part of the joint and helping to protect it.
- Coracoacromial ligament: extends from the coracoid process to the acromion, forming a protective "vault" to protect the humeral head.
- Coracoclavicular ligament: It includes coracoclavicular ligament and coracoclavicular ligament, which further strengthens the connection between the clavicle and scapula.
The existence of these ligaments ensures the flexibility and stability of the acromioclavicular joint during movement, allowing it to withstand various challenges in daily life.
Motion functions
The function of the acromioclavicular joint is crucial, especially in over-the-shoulder movements. This joint serves as a pivot point, and although it is technically a sliding synovial joint, it effectively assists the movement of the scapula, thus promoting overall arm rotation.
Clinical significance
Injury issues
The most common injury to the acromioclavicular joint is a dislocation, often referred to as AC separation or shoulder separation. This is different from a "shoulder dislocation," which is when the humeral head separates from the shoulder joint. Dislocation of the acromioclavicular joint is common in many contact sports, such as ice hockey, rugby, and horseback riding. The most common mechanism of injury is a sudden fall onto the shoulder or an outstretched hand.
Depending on the degree of dislocation of the acromioclavicular joint, it is classified into grades I to VI, depending on the separation between the joints.
Specifically:
- Grade I: slight displacement, AC ligament stretching or partial tear, normal separation less than 4 mm.
- Grade II: Partial dislocation, complete tear of the AC ligament, partial damage to the CC ligament, and AC gap exceeding 5 mm.
- Grade III: The AC and CC ligaments are completely torn, with clinical manifestations of obvious swelling and pain.
- Grades IV to VI: Usually involve more complex dislocations and almost always require surgical treatment.
Osteoarthritis
Osteoarthritis of the acromioclavicular joint is not uncommon. It may result from previous trauma or as a chronic degenerative disease, often associated with subacromial impingement.
As age increases, the acromioclavicular joint is more susceptible to damage, and how to effectively prevent and treat it has become an urgent issue for people to solve.
Conclusion
The unique structure and function of the acromioclavicular joint not only make our daily lives more flexible, but also play an important protective role during intense exercise. However, when joints are injured or diseased, how should we properly care for and recover them?
