Shoulders 101: Your Guide to Basic Shoulder Anatomy

September 29, 2019

Shoulders 101: Your Guide to Basic Shoulder Anatomy

Love shooting hoops or lifting 20-pound weights at the gym? You gotta thank your shoulders for that.

Your shoulders are one of the most complex and mobile parts of your body. They help you stretch, rotate, and support your arms, as well as allow you to do an array of activities like basketball and weight-lifting. 

To learn more about the structures that make up your shoulders, let's take a quick anatomy lesson and learn about the basics of the most mobile joint in your body. 

 

Shoulder Bone Structures

Your shoulders are made up of 3 main bones: the scapula, clavicle, and the humerus. They serve as the basic structure and support for the joints and ligaments that make up your shoulders as a whole. These bones are necessary not only for stability but also for the protection of the rest of your shoulder structures. 

anatomy of the shoulder bone structures with labels for the scapula, clavicle, and humerus

 

Let's take a closer look at these bone structures. 

The scapula, or commonly known as the shoulder blade, is prominently seen from your back. The scapula is the blade-like structure found a few inches away from your spine. This bone supports most of the shoulder motion. 

The clavicle or collarbone connects your arm to your chest. The clavicle looks like a pair of bicycle handles along the collar area a few inches down the neck. 

The humerus, or the arm bone, is the long bone that runs from the shoulder to the elbow.

 

 

Shoulder Joints

Now that we have discussed the bone structures, the frame wherein all the other parts rest, let's proceed to the structures that connect them – the joints. The primary function of the joints is to allow movement between the bones. Let's dive deeper into each one.

The shoulder complex has four main joints: the glenohumeral, sternoclavicular, scapulothoracic, and acromioclavicular joints. 


anatomy of the joints in the shoulders with labels

 

The glenohumeral joint,commonly referred to as the shoulder joint, is a ball and socket joint that allows a wide range of movement. It is also considered as the most mobile joint of the body. Because it supports the long humerus bone and relatively smaller glenoid cavity, the glenohumeral joint is quite unstable. 

The sternoclavicular joint is a type of saddle joint which connects the inner part of the collarbone to the breastbone. It allows movements such as elevation and depression (shrugging motion), and protraction and retraction (back and forth motion.)

The scapulothoracic joint connects the scapula and the rib cage. It allows motion such as elevation and depression and supports the arms when you perform push-ups and pull-ups. 

The acromioclavicular joint connects the outer part of the clavicle to the projection at the top of the shoulder blade called the acromion process. The acromion process is located at the edge of the scapula, which makes up the highest point of the shoulder. 

While the joints allow movement in the shoulders, the grinding in between bones and joints is painful without the bursae. Bursae are sacs of synovial fluid that reduce friction between bones and protect them from grinding against each other. Essentially, the bursae allow mobility within the joints.


There are three types of bursae within the shoulder area: 

anatomy of the different bursae found in the shoulders with label

The subacromial bursa is found below the acromion process and is responsible for the free movement of the rotator cuff tendons, which we’ll discuss later on. 

The subscapular bursa is located along one of the rotator cuff muscles, subscapularis, and prevents wear and tear on the tendon during the movement at the glenohumeral joint.

The subcoracoid bursa is located below the coracoid process (the small hook-like structure at theedge of the scapula) and facilitates internal and external rotation of the shoulders.
 

Shoulder Ligaments

With the bones and joints in place, let's proceed to the structures that are integral to stabilizing the shoulder bones – the ligaments. Your ligaments are soft tissue structures that connect bones. Think of them as strong ropes that help connect bones and provide stability to joints. 

Four ligaments are essential to the shoulder complex: the glenohumeral, coracoacromial, coracohumeral, and coracoclavicular ligaments. 

anatomy of the shoulder ligaments

Glenohumeral Ligaments

The glenohumeral ligaments are the primary source of stability for the shoulders. They prevent the shoulders from dislocating by helping secure it in place. 

Coracoacromial Ligaments

The coracoacromial ligament connects the shoulder blade to the acromion and the coracoid process. It is responsible for maintaining the alignment of the clavicle. Calcification, or the accumulation of calcium salts, of the coracoacromial ligament, causes impingement syndrome.

Coracohumeral ligaments

The coracohumeral ligament strengthens the upper part of the shoulder joint capsule. 

Coracoclavicular Ligaments

The coracoclavicular ligament connects the clavicle to the scapula's coracoid process. It keeps the acromioclavicular joint stable. 

 

Shoulder Muscles

Your shoulders' muscles are responsible for movement and maintaining posture. Three main muscles make up the shoulders: Deltoid, Biceps, and the Rotator Cuff.

anatomy of the shoulder muscles

Deltoid

When people refer to the shoulders, they would most likely refer to their deltoids. The deltoid is also known as the common shoulder muscle and is composed of three segments: the anterior, lateral, and posterior fibers.

The deltoid muscles allow you to rotate your arm inwards, reach forward and backward.

The anterior deltoid is located at - as the name suggests - the front portion of your shoulder, and is attached to the collarbone. The primary function of the anterior deltoid is for flexing the arm at the shoulder joint, rotating the shoulder inward, or raising your arms sideways.

The lateral or acromial deltoid is responsible for necessary shoulder abduction. Shoulder abduction is any motion of the shoulder joint that involves lifting your arm away from the body.

The posterior deltoid's purpose is to extend the shoulder, like when you bring your arms behind you.

Biceps

The biceps is a bi-articular, double-headed muscle on the front part of the upper arm. It is responsible for the motion of two different joints: the shoulder and the elbow. The short head begins at the coracoid process, and the long head starts at the shoulder joint. Both of these heads meet at the elbow.

Rotator Cuff

Your rotator cuff is a group of muscles and tendons that surround the shoulder joint. It keeps the head of the upper arm bone securely attached to the shoulder socket. The rotator cuff is responsible for most arm movements, from raising to the rotation of the arm. It is the most commonly injured part of the shoulder, which usually manifests as a dull ache.

different muscles that make up the shoulder's rotator cuff with labels

Your rotator cuff is a group of muscles composed of the following: 

The supraspinatus muscle holds the humerus in place and is the muscle responsible for lifting your arm and giving it the support to keep it elevated.

The infraspinatus muscle assists in the rotation and extension of the shoulders.

The tres minor muscle assists shoulder abduction.

The subscapularis is the muscle responsible for holding the arms straight out and keeping it elevated. It also supports the upper arm with the shoulder blade.

Aside from the deltoids, biceps, and rotator cuff, three muscles also help stabilize the scapula. These are the rhomboid, trapezius, and the serratus anterior muscles.

different muscles supporting the shoulders

The rhomboid muscle is located in the upper back and helps to connect the shoulder blades to the ribs and the spine. The rhomboid muscles are responsible for maintaining good posture. 

The trapezius muscleis composed of 3 muscle segments: the upper, middle, and lower trapezius. It is commonly called as "traps," and is responsible for motions like shrugging and pulling the shoulders back. 

The serratus anterior muscle lies deep beneath the scapula and the pecs or pectoral muscles. This muscle is responsible for the forward rotation of the arm. 

 

Why learning about your shoulders is important

Learning about the anatomy of your shoulders is key to preventing shoulder injuries.  By learning how each part works, you can better understand how to take care of your shoulders.

Injuries can happen either through accidents or by wear and tear. Having an active lifestyle makes you susceptible to these injuries, but don’t fret - there are a few preventive measures you can take:

  1. Maintain a good posture. Your shoulders (and your body) will thank you for it! Maintaining a good posture keeps your bones and muscles in alignment, which will get rid of all the unnecessary strain from your shoulders. Sitting in abnormal positions benefits no one.
  2. Warm-up properly. Stretching and warming up before doing any form of strenuous activity prevents muscle strain in your shoulders. Warming up increases muscle temperature, which makes your shoulders become more productive by contracting forcefully and relaxing quicker. Once your shoulder muscles are warm, they are less prone to overstretching, so don’t go straight to working out without a few stretches. 
  3. Eat a healthy diet. Eating certain foods can trigger inflammation in your joints and muscles! Different foods can trigger different people, but generally speaking, you must avoid the following: added sugars, processed meat, vegetable and seed oils, and alcohol (well, too much that is.)
  4. Avoid overuse.Recovery days are just as important as workout days. Exercising, while it feels good, causes your muscles to break down. Don’t think that grinding it out will make you progress faster - the opposite is actually true. You must allow ample time for your muscles to recover to build proper strength in order to get better results. 
  5. Provide proper care. Injuries may be preventable, but they are not inevitable. The moment an injury occurs, provide proper first-aid care to your shoulders by using a hot or cold compress to the affected area. Hot compress works for muscle stiffness, while cold compress works best for inflammation and swelling. Caring to your injuries as soon as you can prevents more serious conditions from occurring.

 

Final Thoughts

Learning about how your shoulders work is the first step to properly taking care of them. By learning what makes up your shoulders and what allows it to fulfill its functions, you can accurately address any conditions that may arise in the future.

For more tips, you can visit our blog and learn more about other injuries and taking care of your body. 


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