Biology
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Acromioclavicular Joint (AC joint)
Function:
The AC joint is a gliding joint within the shoulder. This joint is specific to primates and humans, allowing for the ability to raise the arm above the head. This joint functions as a pivot point, acting like a strut to help with movement of the scapula resulting in a greater degree of arm rotation. Also, the AV joint allows for the transmission of force from the upper arm to the rest of the skeleton. (6)
Bones:
The AC joint is a joint that is formed between the clavicle and the scapula. The acromion, a section of the scapula, is the binding site for the clavicle. These two bones fit together, but are not stable on their own. Thus other structures are needed to provide stability.
Cartilage:
Articular cartilage between the clavicle and the acromion in the AC joint helps minimize friction as the bones pivot around each other.
http://www.orthogastonia.com/patient_ed/html_pages/shoulder/shoulder_ac_separation.html
Muscles:
Two sets of muscles are important for the stabilization of this joint. The first set is the group of muscle fibers known as the trapezius muscle. The upper trapezius muscle fibers connects the lower base of the skull to the clavicle. The middle and lower trapezius muscle fibers connect vertebrae in the spine to the scapula. The second muscle is a group of muscle fibers known as the deltoid. The anterior deltoid connects the clavicle to the humerus, while the posterior and lateral deltoid fibers connect the scapula to the humerus. These two muscles help stabilize the clavicle and the scapula, holding the proper joint formation (7)(8).
Ligaments:
Three ligaments also help stabilize the AC joint: the acromioclavicular ligament and the two coracoclavicular ligaments. The acromioclavicular ligament is the ligament that directly connects the acromion to the clavicle and covers the joint. This ligament is labeled the AC joint capsule in the picture above. The two coraco-clavicular ligaments also provide stablity by connecting the coracoid process, a part of the scapula, to the s clavicle, once again directly connecting the scapula and the clavicle in the proper orientation (9).
Created by: Blair Smith, Connie Lee, Daniel Solomon, Matthew Whitson and Stephanie Chang
Date last modified: 5/2/2004