The shoulder is a complex region of the body as it is comprised of several different joints: glenohumeral, sternoclavicular (SC), acromioclavicular (AC), and scapulothoracic. In this post I will primarily be discussing the AC joint anatomy, joint mobility, and how to address movement restrictions in this region.
The AC joint is primarily responsible for subtle adjustments of the scapula relative to the clavicle. The scapula upwardly rotates at the AC joint during shoulder flexion and abduction. It downwardly rotates during extension and adduction. With the horizontal plane, the AC joint permits some internal and external rotation. Additionally, the AC joint has slight anterior/posterior titling in the sagittal plane. It is important to remember that the majority of the AC joint kinematics are pretty minimal. Not much motion occurs here at all, but it is still important.
Assessment and Treatment
The AC joint is often responsible for the end-range elevation mobility in the shoulder. While this joint should always be assessed, it should definitely be considered when elevation mobility is restricted. Should there be an actual injury to the AC joint, it typically will present as pain over the joint and possible visual deformity. There are also several tests for AC joint injury, a couple (Active Compression Test and Horizontal Adduction Test) of which are shown below:
However, the AC joint is important to assess in non-AC joint shoulder pain as well. Consider the regional interdependence concept on a smaller scale: restriction in the AC joint or SC joint may lead to excessive motion and pain in the GH joint. Due to the planar alignment of the joint surfaces, it is recommended that a gliding assessment is used to simply determine if the area is moving or not. We will recommend using the directions of anterior-posterior and posterior-anterior when assessing to identify joint mobility stiffness. If restricted, you can use the same technique to mobilize it or some of the other ones shown in the video below:
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To help improve or retain mobility in the AC joint, I recommend some general mobility exercises or possibly some upper trap/serratus anterior strengthening to facilitate end-range elevation.
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-Dr. Chris Fox, PT, DPT, OCS
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