Understanding the Shoulder Structure ー Learning Anatomy Through My Left Arm Rehabilitation ー August 2, 2026 (Reiwa 8)
## Introduction
After experiencing difficulty moving my left arm due to a proximal humerus fracture, I started studying anatomy again.
Simply memorizing names of bones and muscles is not enough. When I understand how bones, joints, and muscles work together, I can better understand the purpose of my rehabilitation.
The shoulder is not moved by the arm alone. The clavicle, scapula, humerus, and surrounding muscles all work together.
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# Three Important Bones of the Shoulder
## 1. Clavicle
The clavicle is the thin bone that runs across the upper chest near the neckline.
It connects:
- The sternum on the inner side
→ Sternoclavicular joint
- The acromion of the scapula on the outer side
→ Acromioclavicular joint
The clavicle works like a support bar that helps hold the arm away from the body.
---
## 2. Scapula
The scapula is the triangular bone located on each side of the upper back.
The bony point felt at the top of the shoulder is called the acromion.
The scapula has a shallow hollow called the glenoid cavity.
The round head of the humerus fits into this cavity and forms the shoulder joint.
The scapula is not directly connected to the ribs by a joint. It is held in position by several muscles, allowing it to move during arm movements.
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## 3. Humerus
The humerus is the bone extending from the shoulder to the elbow.
The upper end of the humerus has a round part called the humeral head.
It connects with the glenoid cavity of the scapula to form the shoulder joint.
The shoulder joint is a ball-and-socket joint, allowing movement in many directions:
- Forward and backward
- Sideways
- Rotation
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# Why the Shoulder Has Such a Wide Range of Motion
The glenoid cavity of the scapula is shallow and small, while the humeral head is large and rounded.
This structure allows the shoulder to have the greatest range of motion in the human body.
However, because it prioritizes movement over stability, the shoulder is also a joint that can easily become dislocated.
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# Muscles That Move the Arm
## Deltoid Muscle
The deltoid creates the rounded shape of the shoulder.
It connects the clavicle and scapula to the humerus.
Different parts have different functions:
- Front part
→ Raises the arm forward
- Middle part
→ Raises the arm sideways
- Back part
→ Moves the arm backward
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## Teres Major Muscle
The teres major runs from the lower part of the scapula to the humerus.
It helps:
- Pull the arm backward
- Bring the arm closer to the body
- Rotate the arm inward
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## Latissimus Dorsi
This large back muscle helps:
- Pull the arm backward
- Bring the arm toward the body
- Rotate the arm inward
It is also an important muscle for swimming movements.
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## Pectoralis Major
This large chest muscle helps:
- Move the arm forward
- Bring the arm toward the body
It is used when pushing or hugging.
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## Trapezius
The trapezius does not attach to the humerus.
Instead, it moves the scapula and supports arm movements.
It helps with:
- Raising the shoulders
- Moving the scapula
- Assisting arm elevation
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# Connection to Rehabilitation
Raising the arm is not done by the humerus alone.
The:
- Humerus
- Scapula
- Clavicle
must move together.
Therefore, shoulder rehabilitation is not only about increasing muscle strength. It is also about restoring smooth coordination between bones and muscles.
After a proximal humerus fracture, feelings such as heaviness, limited movement, and difficulty with external rotation can occur because this complex system is still recovering.
Learning about my own body is also a part of my rehabilitation.
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# What I Learned Today
The shoulder is not simply the connection point of the arm.
It is a precise system in which bones, joints, and muscles cooperate.
Anatomy becomes easier to understand when it is connected to our own movements and experiences.
#ShoulderAnatomy
#Clavicle
#Scapula
#Humerus
#ShoulderJoint
#DeltoidMuscle
#MuscleFunction
#HumanBody
#LearningAnatomy
#RehabilitationJourney
#FractureRecovery
#ShoulderRehabilitation
#UnderstandingMyBody
#LifelongLearning
#ChallengeForTheFuture
