The Shoulder: Bony Anatomy, Part 1

The shoulder is made up of three bones and two joints.  This blog will break down the anatomy of the scapula.  Part two will cover the clavicle and humerus.  

FIRST… 

A fossa is a scooped out hollow or depression in the bone.

Process just means bony projection.

A tubercle is a small rounded projection on a bone.

THE SCAPULA

Lateral Border - the outer border of the scapula, away from the midline

Medial Border - the inner border of the scapula, closest to the spine

Inferior Angle - the very bottom tip of the shoulder blade 

Superior Angle - this is not the entire top of the scapula but rather just the tip top of the medial border

Spine of the scapula - bony ridge that separates the supraspinous fossa from the infraspinous fossa. The lateral end flattens out to become the...

Acromion - flat, lateral aspect of the spine of the scapula.  

Supraspinous Fossa - supraspinous means above (supra- superior- above) the spine (spinous) of the scapula. It’s smaller than the infraspinous fossa but it’s pretty deep. The supraspinatus muscle originates here. 

Infraspinous Fossa - large scooped out hollow beneath the spine of the scapula where the infraspinatus originates.

Subscapular Fossa - this is on the anterior (front) surface of the shoulder blade. The subscapularis originates here.

Coracoid Process - beak shaped bony prominence on the anterior surface of the scapula, serves as the attachment site for several muscles.  

Infraglenoid Tubercle - bony projection just below the glenoid fossa. The long head of triceps brachii starts here. 

Glenoid Fossa - more commonly known as the shoulder socket, the glenoid fossa is the shallow hollowed out space in the bone where the head of the humerus sits

Kinesiology Lingo: Movements of the Body

When we talk about a direction the body is moving, we are always looking at it from anatomical neutral regardless of which position we are in.  For example, the hairy side of my forearm is always the back of my forearm whether my palms are facing forward or behind me (and the smooth side is always the front).  To be in anatomical neutral means you are standing upright with the arms hanging by your sides, palms open and forward facing.  Whether you are on your front, back, side, upside down or right side up, the front is always the front and the back is always the back when it comes to describing these movements.  

FLEXION
Flexion starts with an F.  Let this remind you of ‘forward’ or ‘front’.  Also think about when you flex your biceps brachii, you bend the elbow and curl it in.  Most joints are flexed when you’re in child’s pose, or when you are born in the fetal position.   If your spine is flexed, it’s rounded.  If your fingers are flexed, they’re curled in toward your palms, if your neck is flexed your chin is tucked to your chest, if your wrist is flexed your fingers are coming toward what we call the inner wrist but anatomically speaking it’s actually the front of the wrist. If the knee is flexed it’s bending, if the hip is flexed the knee is coming up toward the chest, etc.  Just remember:  flexion = forward.  This action occurs at many joints and always brings the bones that make up a joint closer together, or closes the joint.  

EXTENSION
Extension is the opposite of flexion, which means it lessens the angle between the two bones or opens the joint.  In wheel pose (a full backbend), the hips, spine and wrist are extended.  When you’re in crescent lunge pose, your back leg is extended (hip extension via the glutes). When you lift your knee to your chest and then kick the leg straight out in front of you, that’s extension of the knee (but flexion of the hip).  Think about it:  the knee joint is open but the hip joint is closed.  When you lift into cobra pose, that’s extension of the spine.  

MEDIAL ROTATION
This can also be called internal rotation.  These directions and terms are all in relation to the midline of the body so medial rotation means coming in toward the midline.  The median is always in the middle of the road.  Medial means toward the middle. This occurs at the shoulder and hip joints, and because there is a small amount of medial and lateral rotation available at the knee the tibia can be medially or laterally rotated as well.  For the most part though, consider both medial and lateral rotation as movements of the shoulder and the hip.  In warrior two, your back leg (the straight one) is medially rotating.  When doing cow’s face arms (I still don’t get why they call it that), the bottom arm is medially rotating.  In other words, if you have an itch on the middle of your back and you reach around to scratch it, your shoulder is medially rotating.  Or if you go to unhook your bra, your shoulder is medially rotating.  

LATERAL ROTATION
This is also sometimes called external rotation, or rotating away from the midline.  When you’re standing with your arms by your side in tadasana and you turn your palms forward, your shoulders are laterally rotating.  The top arm during cow’s face pose is laterally rotating.  Pigeon pose laterally rotates the hip.  The front leg in warrior two is laterally rotated.  

ROTATION
A rotation can be either medial or lateral but when we are talking about rotation on its own, we are referring specifically to the spine.  Rotation occurs only along the axial skeleton which means the head and vertebral column.  When you look over your shoulder, that’s rotation of the head and the neck.  When you’re standing with your feet planted and you turn and reach for something to your right, that’s rotation of the trunk.  Any twisting pose in yoga requires rotation.  

UPWARD ROTATION
This action occurs only at the scapula and it refers to the movement of the acromion.  It is possible to upwardly rotate the scapula without elevating the whole thing.  The inferior angle of the scapula swings outward when upward rotation occurs.

DOWNWARD ROTATION
Also only occurring at the scapula, this is the opposite of upward rotation.

ELEVATION
The ribs elevate on the inhale.  When you lift your shoulders to your ears, you are elevating the scapula. When you close your mouth, you are elevating the mandible (jaw bone).

DEPRESSION
Exact opposite of elevation.  If it can be elevated, it can be depressed.

LATERAL FLEXION
Lateral flexion only occurs along the axial skeleton as well, so this action is available at the neck and spine.  If you drop your right ear to your right shoulder, that is lateral flexion of the neck.  If you’re bending to one side or the other, that is lateral flexion of the spine. 

ABDUCTION
Abduct means to take away and in this case abduction means to take away from the midline.  This action is available at the hip and shoulder, both ball and socket joints.  If you’re standing in neutral and take an arm or a leg out to the side, that is abduction of the shoulder or the hip.  The deltoid produces this action for the shoulder and the gluteus medius, which is sometimes called the deltoid of the hip, does it for the hip.  You can also use the term abduction in place of protraction for the scapula, as protracting the scapula means you’re moving it away from the midline.

ADDUCTION
Adduction is exactly the opposite of abduction and therefore it means to add something back to the midline. It’s available at the hip and the shoulder, and you can call it adduction of the scapula as well but I prefer to say retraction. 

RETRACTION
To retract is to pull back.  You can retract your mandible (jaw) by contracting the temporalis muscle.  You can retract the shoulder blades by engaging the rhomboids major and minor.

PROTRACTION
You guessed it... protraction is the opposite of retraction.  To protract the mandible would be to stick the bottom jaw out.  

CIRCUMDUCTION
Circumduction happens at the hip and shoulder and involves a combination of adduction, abduction, flexion and extension all at once.  Making hip or shoulder circles is circumduction. 

SUPINATION
To be in the supine position means to be on the back.  When you’re lying in savasana, you are lying supine.  If your palms are up when you’re in savasana, your forearms are supinated.  If you’re going to hold a bowl of soup, you need to supinate in order to do that (little word tricks like that have always helped me remember things better).  Some people say the feet are either supinated or pronated, but a better term for that would be inversion/eversion (more on those in just a moment).  Supination occurs at the forearms (thanks to the radius) and is also used to describe the position of the whole body (on the back is supine, on the belly is prone, which leads me to our next topic)…

PRONATION
Put your forearms and elbows on a table, keep everything else still and turn your palm down.  That is pronation of the forearm, again, thanks to the radius.  When the forearms and elbow are on the table you’ll notice that the ulna (pinky side) stays put while the radius (thumb side) spins to create the pronation and supination of the forearm.  If you’re in dolphin pose (without clasped hands) or setting up for a forearm stand, the forearms are pronated.  

These last four actions all occur at the ankle joint, or talocrural if we’re speaking anatomically.  While we do have the ability to roll the ankle around, take note the next time you do that that you aren’t making a full circle like the hip does during circumduction.  The distal (far) end of the tibia (shin bone) articulates with the talus, which is one of the 7 tarsal bones to create the following four actions:

INVERSION
If you’re standing in tasadasa, and you roll toward the outer edge of your foot to lift the inner balls of the feet, this is called inversion.  The soles of the feet are moving IN toward the midline, this is called INversion of the ankle.

EVERSION
If you’re standing in tasadana and shift your weight inward to the balls of your feet to try to lift the pinky side of the foot, this is eversion.  E for external, you’re opening the sole of the foot to the outside.

DORSIFLEXION
This is more commonly called flexing your foot, or pulling your toes back toward your shin bone.  It may be a little confusing but the top part of the foot is called the dorsal surface and dorsal means back.  The top of your foot is actually the back of your foot.  Think about it: when you’re in child’s pose (or being born), you’re all curled up.  All of the surfaces that are closed in and protected are on the front side of the body.  If we could look at a 3D image of you in child’s pose (wouldn’t that be cool?), all of the surfaces pointing outward are the back side of the body, and that includes the tops of your feet.

PLANTAR FLEXION
Stepping on the gas pedal, balancing on the balls of your feet and pointing your toes like a good ballerina are all examples of plantar flexion.  The plantar surface of your foot is the bottom of your foot. 

The Lats + Teres Major

In part two of my fascial layers blog, I wrote about aponeuroses being thick sheets of connective tissue that serve as attachment sites for some muscles.  One of those muscles that has a point of origin on the thoracolumbar aponeurosis is the very large, thin and superficial back and arm muscle known as the latissimus dorsi, or the lats.  This muscle is particularly interesting for a few reasons.  One, while most of its fibers are found covering the majority of the lower and middle back, it’s actually an arm mover.  The lats connect the pelvis to the upper arm bone to create medial rotation, adduction and extension at the glenohumeral joint, which is the ball and socket joint more commonly known as the shoulder joint.  The actions of the latissimus dorsi are easy to remember if you can remember that it’s the handcuff muscle.  If you were being arrested and handcuffed (and I hope you never are), your arms would be medially rotated, a little bit extended and also adducting across the midline behind you.  

The main actions of the lats are medial rotation, adduction and extension of the shoulder.  If you stand or sit upright with your arms relaxed heavily by your sides and turn the palm back behind you or spin your thumbs back behind you, that’s medial rotation of the shoulder.  If you reach both arms back behind you, that’s extension of the shoulder and if you then clasp your hands, bringing the arms together behind the back, that’s adduction.  (Side note: ABduction is when you take away from the midline. To abduct is to take away so it you take the arm or leg out to the side away from the body, that is abduction of the shoulder or hip.  ADduction is the opposite, it’s adding to the midline.  When the arms are out to the side and you bring them back down, that’s called adduction because you’re adding the arms back to the midline).  In addition to being able to move the arm, the lats also assist in lateral flexion of the trunk and can help extend the spine as well as tilt the pelvis anteriorly and laterally.  

HOW DOES A BACK MUSCLE MOVE THE ARM?

The lats have points of origin on the posterior iliac crest (top of the back of your hip bones), the thoracolumbar aponeurosis, the last few ribs (varies in cadavers), the spinous processes of last six thoracic vertebrae and in some people they cross the inferior angle of the scapula as well.  That is a huge origin and a lot of words.  All you really need to know is that it’s a large and superficial back muscle that originates on the pelvis, ribs, spine, fascia and sometimes the scapula so it can affect all of those things.  

The second interesting thing about the latissimus dorsi is that from its origin, it thickens around the armpit and wraps underneath to insert on the front of the upper arm bone in the space between the greater and lesser tubercles of the humerus called the intertubercular groove.  The lats form the posterior wall of the axilla, which is the fancy word for armpit.  You can feel for these more lateral fibers by taking your right hand to find the back flap of your left armpit and gently pressing your elbow in to your side to engage the fibers.  

A third interesting thing is that the lats have a helper, a smaller muscle that does exactly the same thing to help get the job done.  This muscle is called teres major, not to be confused with teres minor which is just above it and rotates the shoulder in the opposite direction.  Teres major originates on the inferior angle of the scapula (as the lats sometimes do too) and the lower third of the lateral border of the scapula.  Just like the lats, teres major wraps under the armpit to also insert on the front of the arm just distal to the intertubercular groove at the crest of the greater tubercle.  It doesn’t affect the trunk or the pelvis because it doesn’t cross them, but it does medially rotate, extend and adduct the shoulder.  Both the latissimus dorsi and the teres major are handcuff muscles.  

WHEN ARE THE LATS + TERES MAJOR CONTRACTING?

When you grab onto a pull up bar and pull yourself up, the lats and teres major are contracting (or shortening) which means the origin is working to bring the insertion toward it to complete one, some or all of the actions.  When the hands are clasped behind the back, the lats and teres major are also contracting as the shoulder is medially rotates, extended and adducted.  People with really developed lats may have a hard time clasping their hands behind their backs because of high motor tone and lots of dense muscle fibers.  

WHEN ARE THE LATS + TERES MAJOR LENGTHENING? 

Child’s pose with the arms stretched out in front is a nice stretch for the lats and teres major.  You can walk the arms and upper body off to one side to deepen the stretch on the other and vice versa.  Any time you are reaching the arms overhead, the lats are stretching.