Overview
Medical language can make even simple shoulder problems sound confusing. This glossary collects the terms you'll see across InjuryAtlas's shoulder pages and explains each one in plain English, so you never have to guess what a word means mid-article.
Terms are listed alphabetically. Each definition is short on purpose. If you want the full picture on any structure, injury, or movement, follow the links throughout the rest of the shoulder module.
A
Abduction: Moving your arm away from the side of your body, like lifting it out to the side. It's the opposite of adduction.
Acromioclavicular (AC) joint: The small joint where your collarbone meets the highest point of your shoulder blade. It's a common site of injury after a fall onto the shoulder.
Acromion: The bony bump on top of your shoulder blade that you can feel at the top of your shoulder. It forms part of the roof over your rotator cuff tendons.
Adduction: Moving your arm in toward or across the front of your body. It's the opposite of abduction.
Adhesive capsulitis: The medical name for frozen shoulder, a condition where the joint capsule tightens and thickens, causing stiffness and pain that limits movement.
Anterior: A direction term meaning toward the front of the body. "Anterior shoulder pain" means pain at the front of the shoulder.
B
Biceps tendon (long head): A tendon that runs from your biceps muscle, up through the front of your shoulder, and attaches inside the joint. It can become irritated on its own or alongside rotator cuff problems.
Bursa: A small, fluid-filled sac that reduces friction between moving structures, like a tendon and a bone. Your shoulder has several bursae; the subacromial bursa is the one most often involved in shoulder pain.
Bursitis: Inflammation of a bursa, usually causing pain, tenderness, and sometimes mild swelling in the affected area.
C
Capsule (joint capsule): A tough, fibrous envelope that surrounds a joint, holding in the fluid that lubricates it and helping keep the joint stable.
Circumduction: A circular movement of the arm that combines flexion, abduction, extension, and adduction in sequence, like drawing a circle with your elbow straight.
Clavicle: The medical name for your collarbone, a long bone that connects your breastbone to your shoulder blade.
Crepitus: A clicking, popping, cracking, or grinding sensation (sometimes audible) felt during joint movement. It's not always a sign of a problem, especially if it's painless.
D
Deltoid: The large, rounded muscle that caps your shoulder and gives it its shape. It's the main muscle responsible for lifting your arm away from your body.
Distal: A direction term meaning farther from the center of the body or the point of attachment. The elbow is distal to the shoulder.
Dynamic stability: The ability of muscles and other soft tissue to keep a joint stable during movement, as opposed to stability that comes purely from bone shape.
E
Extension: Straightening a joint or moving a body part backward, like moving your arm behind your body. It's the opposite of flexion.
External rotation: Rotating your arm outward, away from the midline of your body, with your elbow bent at your side. This motion relies heavily on the infraspinatus and teres minor muscles.
F
Flexion: Bending a joint or moving a body part forward, like raising your arm in front of you. It's the opposite of extension.
Frozen shoulder: The common name for adhesive capsulitis, a condition causing progressive stiffness and pain that can significantly limit shoulder movement for months.
G
Glenohumeral joint: The main shoulder joint, formed where the rounded top of your upper arm bone (humerus) meets the shallow socket on your shoulder blade (glenoid). Often called the "shoulder socket joint" in plain language.
Glenoid (glenoid fossa): The shallow, cup-shaped socket on your shoulder blade that the top of your upper arm bone sits in. It's shallow by design, which is part of why the shoulder is so mobile.
H
Humerus: The medical name for your upper arm bone, running from your shoulder to your elbow. The "head" of the humerus is the rounded top part that sits in the shoulder socket.
I
Impingement: A pinching or compression of soft tissue, usually rotator cuff tendons or the subacromial bursa, between the head of the humerus and the acromion, typically during overhead movement.
Infraspinatus: One of the four rotator cuff muscles, located on the back of your shoulder blade. It's a primary driver of external rotation.
Internal rotation: Rotating your arm inward, toward the midline of your body, with your elbow bent at your side. This motion relies heavily on the subscapularis muscle.
Instability (shoulder instability): A tendency for the shoulder joint to move more than it should, sometimes to the point of partially or fully coming out of the socket.
J
Joint capsule: See "Capsule."
K
Kinetic chain: The connected sequence of body segments (legs, trunk, shoulder, arm) that work together to produce movement, especially in athletic activities like throwing.
L
Labrum: A ring of cartilage attached around the edge of the glenoid (shoulder socket) that deepens the socket and helps hold the joint together. A labral tear can affect shoulder stability.
Lateral: A direction term meaning toward the outside or side of the body, away from the midline.
Ligament: A tough band of tissue that connects bone to bone, providing stability to a joint. The shoulder has several ligaments supporting the glenohumeral, AC, and SC joints.
M
Medial: A direction term meaning toward the midline of the body.
Muscle imbalance: A difference in strength or tightness between opposing muscle groups (for example, the chest versus the upper back) that can pull a joint out of its ideal alignment.
N
Neutral position: A relaxed, balanced posture or joint position that places the least strain on surrounding muscles, tendons, and ligaments.
Numbness: A loss of normal sensation, often described as tingling or a "pins and needles" feeling. In the shoulder or arm, this can sometimes signal nerve involvement and is a symptom worth monitoring.
O
Osteoarthritis: A condition where the smooth cartilage covering the ends of bones in a joint gradually wears down, leading to pain, stiffness, and sometimes bone-on-bone friction over time.
Overuse injury: An injury that develops gradually from repeated stress on a tissue, rather than from a single, sudden event.
P
Posterior: A direction term meaning toward the back of the body. "Posterior shoulder pain" means pain at the back of the shoulder.
Proprioception: Your body's sense of where a joint or limb is in space, without needing to look at it. Good proprioception helps a joint react quickly to unexpected movement and stay stable.
Proximal: A direction term meaning closer to the center of the body or the point of attachment. The shoulder is proximal to the elbow.
R
Range of motion (ROM): How far a joint can move in a given direction. Reduced range of motion often means stiffness or tissue restriction is limiting movement.
Referred pain: Pain felt in one area of the body that actually originates from a different area, such as shoulder pain caused by a problem in the neck.
Retraction (scapular retraction): Pulling the shoulder blades together, toward the spine. This movement is often trained to improve posture and shoulder stability.
Rotator cuff: A group of four muscles and their tendons (supraspinatus, infraspinatus, teres minor, and subscapularis) that surround the shoulder joint, holding the head of the humerus in the socket and controlling rotation.
S
Scapula: The medical name for your shoulder blade, the flat, triangular bone on the back of your upper ribcage.
Scapular dyskinesis: An abnormal pattern of shoulder blade movement, often due to muscle weakness or imbalance, that can change how the whole shoulder moves and contribute to pain.
Scapulothoracic joint: The functional "joint" where your shoulder blade glides against your ribcage. It's not a true joint in the anatomical sense, but its movement is essential for healthy shoulder mechanics.
Sternoclavicular (SC) joint: The joint where your collarbone meets your breastbone (sternum), at the very center of your chest.
Subacromial space: The narrow space beneath the acromion where the rotator cuff tendons and the subacromial bursa pass through. Narrowing of this space is central to impingement-type conditions.
Subacromial bursa: The fluid-filled sac located in the subacromial space, cushioning the rotator cuff tendons as they move beneath the acromion.
Subluxation: A partial dislocation, where the joint surfaces lose some, but not all, of their normal contact.
Subscapularis: One of the four rotator cuff muscles, located on the front surface of the shoulder blade. It's the primary driver of internal rotation.
Supraspinatus: One of the four rotator cuff muscles, running along the top of the shoulder blade. It's commonly involved in impingement and is one of the most frequently torn rotator cuff tendons.
T
Tendinitis (tendonitis): Inflammation of a tendon, usually from overuse, causing pain and tenderness.
Tendinopathy: A broader term for tendon problems that includes both inflammation (tendinitis) and longer-term degeneration of tendon tissue, without necessarily active inflammation.
Tendon: A tough cord of tissue that connects muscle to bone, transmitting the force a muscle generates so it can move a joint.
Teres minor: One of the four rotator cuff muscles, a smaller muscle on the back of the shoulder blade that assists with external rotation.
Trapezius: A large, kite-shaped muscle spanning the upper back and neck, playing a major role in shoulder blade movement and posture.
W
Winging (scapular winging): A visible prominence of the inner edge of the shoulder blade, usually due to weakness or nerve dysfunction affecting the muscles that hold the shoulder blade flat against the ribcage.
References
- Cleveland Clinic. "What Is the Anatomy of the Rotator Cuff?" https://my.clevelandclinic.org/health/body/rotator-cuff
- StatPearls (NCBI Bookshelf). "Anatomy, Rotator Cuff." https://www.ncbi.nlm.nih.gov/books/NBK441844/
- StatPearls (NCBI Bookshelf). "Anatomy, Shoulder and Upper Limb, Glenohumeral Joint." https://www.ncbi.nlm.nih.gov/books/NBK537018/
- StatPearls (NCBI Bookshelf). "Anatomy, Thorax, Scapula." https://www.ncbi.nlm.nih.gov/books/NBK538319/
- StatPearls (NCBI Bookshelf). "Anatomy, Shoulder and Upper Limb, Clavicle." https://www.ncbi.nlm.nih.gov/books/NBK534836/
- StatPearls (NCBI Bookshelf). "Anatomy, Shoulder and Upper Limb, Humerus." https://www.ncbi.nlm.nih.gov/books/NBK537056/
- Physiopedia. "Rotator Cuff." https://www.physio-pedia.com/Rotator_Cuff
- Physiopedia. "Scapular Dyskinesis." https://www.physio-pedia.com/Scapular_Dyskinesis
- Physiopedia. "Subacromial Bursa." https://www.physio-pedia.com/Subacromial_Bursa
- Kenhub. "Rotator cuff muscles: Anatomy, functions, injury." https://www.kenhub.com/en/library/anatomy/the-rotator-cuff
- Mayo Clinic. "Frozen shoulder." https://www.mayoclinic.org/diseases-conditions/frozen-shoulder/symptoms-causes/syc-20372684
- OrthoInfo (AAOS). "Shoulder Anatomy." https://orthoinfo.aaos.org/en/diseases--conditions/shoulder-anatomy/
- OrthoInfo (AAOS). "SLAP Tears." https://www.orthoinfo.org/en/diseases--conditions/slap-tears/