The shoulders and arms belong to the upper extremity or upper limb region, which starts from the shoulder joints and ends at the hands(1).
Both the shoulders and arms are vital for upper limb mobility. These body parts are used for performing everyday activities, such as lifting an object and pushing a door open.
Shoulder joints have the most extensive range of movement among all other joints in the human body(2).
While advantageous for daily living and sports, the shoulders’ wide flexibility may lead to problems, like instability and greater injury risk.
Three types of bones make up the shoulder joint(3):
The shoulder joint, or the glenohumeral joint, is where the entire upper limb is connected to the trunk(4).
The glenohumeral joint is often described as a ball-and-socket joint(5). The description is based on how the humerus bone fits into the scapula’s glenoid cavity (6).
However, the glenohumeral joint may be described more accurately as a ball-and-saucer joint(7). Unlike the hip and upper leg, another ball-and-socket joint in the body, the glenoid has a shallower curve, akin to a saucer.
The shallow curve permits a wide range of movement, though the joint and its movements may be compromised or less stable(8).
Cartilage and soft tissues surround and support the shoulder joint, ensuring that the shallow socket can hold all the components together.
Inside the shoulder socket or glenoid sits a soft fibrous ring of cartilage called the labrum(9). This cartilage ring surrounds the end of the humerus bone and makes a deeper socket for the bone to fit(10).
The labrum deepens the socket by almost 50%, making a stronger fit for the arm bone(11). The deeper socket helps stabilize the joint without restricting arm movement(12).
A thin membrane called the synovium also lines the shoulder joint. The synovial fluid produced by the synovium serves as a lubricant and additional cushion for the joint(13).
Two groups of muscles reinforce the shoulder joint and keep the humerus centered in the glenoid or shoulder socket(14):
The deltoid and trapezius muscles give the shoulder its shape or contour(15).
The deltoid muscle is also known as the strongest shoulder muscle. It provides the power needed for lifting the upper limb and heavy weights(16).
The deep layer muscles are also known as rotator cuff muscles(17).
These muscles cover the end of the humerus, ensure it stays in place, and enable rotational movement of the arm(18).
The humerus is the only bone of the arm. It serves as an anchor or pillar for all the soft tissue structures or muscles of the arm.
The upper end of the arm bone connects to the scapula or shoulder blade. Meanwhile, the lower end (also known as distal humerus) attaches to the elbow joint(20).
The five muscles of the arm are divided into two compartments(21):
The anterior compartment muscles are flexor muscles, meaning their primary function is flexion or bending of the arm(22).
Meanwhile, the posterior compartment muscles are extensor muscles that function primarily to extend or straighten the arm(23).
The triceps brachii is attached to the scapula and acts as a weak extensor of the arm from the shoulder joint. However, this muscle serves as the main extensor of the forearm from the elbow joint(24).
Shoulder problems may be divided into four major categories: tendon inflammation or tears, instability, arthritis, and fractures or broken bones.
Shoulder dislocations, which fall under the instability category, are common in the US(25).
A study showed that the incidence rate of shoulder dislocations presented at emergency departments in the US is estimated at 23.9 per 100,000 people(26). The findings further note that 71.8% of the dislocations occurred among males.
Moreover, the shoulders had the second-highest injury incidence rate (16.8%) among other upper limb injuries(27). Injuries to the upper arm had the lowest incidence rate (3.7%).
Researchers also noted that fractures are the most common injury to the upper limbs(28).
Radiology and diagnostic imaging tecniques allow doctors to correctly diagnose shoulder and arm problems and keep track of the healing progress.
Some diagnostic imaging modalities used to examine the shoulders and arms are X-ray exams, magnetic resonance (MR) imaging, and computed tomography (CT) scans.
Johns Hopkins Medicine defines arthrography as an imaging method to assess joints, such as the shoulder, knee, and hip(1). This procedure may be performed if standard X-rays do not offer the necessary information about the joint’s anatomy and function. Arthrography may be indirect, in which contrast material is injected into the blood, or direct […]
This webpage presents the anatomical structures found on MR arthrography of the shoulder. T1 FATSAT Coronal view T1-FATSAT Axial view T1 Sagittal view T1 FATSAT Coronal view MR arthrography of the shoulder: coronal view, T1 FATSAT. Image 1. 1, Deltoid muscle. 2, Coracoid process. 3, Clavicle. 4, Trapezius muscle. MR arthrography of the shoulder:
Shoulder MR Arthrography Anatomy Read More
This webpage presents the anatomical structures found on shoulder X-ray. Shoulder X-ray, AP projection Shoulder X-ray: lateral view Experts agree that imaging assessment of shoulder disorders must begin with radiographs. Radiologists have developed several radiographic examinations to best show the areas affected by specific clinical disorders(1). Grashey View This projection is a true anterior-posterior
Atlas of Shoulder MRI Anatomy Radiologists primarily perform shoulder imaging to assess injuries within the shoulder joint. Experts analyze the different imaging techniques to identify better diseases associated with the shoulder, including AC joint osteoarthritis and RC tendinosis(1).This webpage presents the anatomical structures found on shoulder MRI. T1 Axial view T2-FATSAT Axial view T1
Atlas of Shoulder MRI Anatomy Read More
