An overview of the shoulder and its functions
The shoulder is a complex and versatile joint essential for various daily activities, providing both stability and mobility to the upper limb. It is composed of three bones—the clavicle (collarbone), scapula (shoulder blade), and humerus (upper arm bone)—which form four distinct joints: the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic joints. Together, these structures enable a wide range of motion, such as lifting, reaching, pushing, and pulling, making the shoulder one of the most mobile joints in the body (Miniato et al., 2019; Epperson & Varacallo, 2019).
This intricate structure relies on a network of muscles, tendons, and ligaments for stability and functionality. The rotator cuff, a group of four muscles, plays a vital role in stabilizing the shoulder joint and facilitating rotation. Meanwhile, the clavicle acts as a support strut, stabilizing shoulder movements (American Academy of Orthopaedic Surgeons, 2010). Any injury or dysfunction in these components can significantly impair shoulder performance and lead to discomfort or limited mobility.
The shoulder is prone to several injuries and conditions due to its frequent use and structural complexity:
- Rotator cuff tears: These injuries involve one or more muscles of the rotator cuff and can result from acute trauma or degenerative wear over time (Mayo Clinic, 2023).
- Shoulder impingement syndrome: This occurs when the soft tissues of the shoulder become compressed between bones, leading to pain and restricted movement (Wong & Kiel, 2023).
- Frozen shoulder: Also called adhesive capsulitis, this condition causes stiffness and pain due to inflammation of the shoulder joint capsule (Johns Hopkins Medicine, n.d.).
- Shoulder instability: Conditions like dislocation or subluxation occur when the joint's supporting structures fail to maintain alignment.
- Radicular pain and cervical radiculopathy: Often caused by nerve root compression, these conditions result in pain, numbness, or weakness radiating down the arm (Mayo Clinic, 2023).
Understanding the shoulder's anatomy and common pathologies is essential for accurate assessment and intervention, particularly when performing clinical tests like the Shoulder Depression Test.