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the segments of

THE ARM

The upper extremity must be viewed as an integrated whole, especially when the hand is on the floor and we have a closed kinetic chain (in a kinetic chain when the centre joint moves in this case the elbow the surrounding joints also move) The changes in hand position not only affect the shoulder joint, but also impact the movement of the scapula and therefore the entire shoulder girdle.

 

the SHOULDER

 

The shoulder is a strong and flexible complex that connects the arm to the torso, and it is considered one of the most mobile parts of body. It is responsible for:

 

  • Moving and rotating the upper arm

  • Weight-bearing

 

3 bones come together to create the shoulder girdle.

THE SCAPULA (shoulder blade). The scapula is a large, flat, and somewhat triangular bone that sits between the humerus (upper arm bone) and collarbone. It is responsible for stabilising the upper arm bone, which sits in a shallow socket on the outer edge of the shoulder blade. The acromion and coracoid are bony processes on the scapula. Together they extends laterally over the shoulder joint serving to stabilise the shoulder joint. 

 

THE CLAVICLE (collarbone). The collarbone is a long and thin bone located between the shoulder and top of the ribcage. The collarbones help support and keep the arms in place when away from the body.

THE HUMERUS (upper arm). The top of the humerus is rounded and fits into the shallow socket of the scapula, called the glenoid cavity, creating the shoulder’s ball-and-socket joint. This ball-and-socket construction allows for the arm’s large range of motion. 

 

The shoulder is technically made up of 4 joints.

 

  • The ball and socket, glenohumeral joint is considered the main joint in the shoulder and is where the rounded top, or head, of the humerus (arm bone) nestles into the shallow, rounded socket of the scapula (shoulder blade) The medical term for the shoulder socket is glenoid cavity. The shoulder labrum, a slippery, tough ring of cartilage rims the socket. It expands the depth of the cavity, allows for increased, smooth motion while helping keep the head of the humerus in place.  

 

  • The only place a bone from the shoulder girdle attaches to the centre component of the body (axis) is where the clavicle attaches to the sternum on one end, the sternoclavicualr joint. It connects the upper arm to the rest of the body. A small cartilaginous disc between them helps mitigate the forces that naturally run through it.

  • The other end of the clavicle attaches onto the scapula at the acromion process and bound together by ligaments - the acromioclavicular joint (AC joint) There is not much movement here. 

 

  • The 4th, not everyone considers this area a joint because the bones are not attached by ligaments. The scapulothoracic joint is located where the scapula glides against the rib cage at the back of the body. 

 

The shoulder joint flexes, extends, abducts, adducts and rotates both internally and externally. When the humerus reaches its end range of motion at the shoulder joint, it triggers movements of the scapula. i.e reaching the arm over head, the humerus moves at the shoulder joint until the head of the humerus bumps into the shelf-like acromion process sitting above it. The muscles that move the scapula kick in to get the arms the rest of the way over head. This bumping is normal and isn’t painful unless something else is going on. 

 

 

FOREARM &

ELBOW

The joint where the end of the radius meets the  end of the ulna, allows the forearm to twist, turning your palms up (supination) or down (pronation).

To get from supination to pronation the radius rotates around the ulna. When fully pronated the radius actually lies diagonally across the ulna which has remained pretty still. The amount we can pronate is determined by compression of these 2 bones.

 

It is pronation that we use to weight bear through our hands in poses like Down Dog (Adho Mukha Svanasana) and Cobra (Bhujangasana).  If you cannot pronate 180° the shoulders will have to compensate. 

 

WRIST / HAND

The entire upper extremity is designed to allow us to put our hand in almost any position we want it. The upper limb has sacrificed locomotor function and stability for mobility, dexterity and precision. 

 

There are 3 distinct arches, longitudinal, oblique and transverse, that are formed by the bones, ligaments and tendons that are of vital importance when gripping, grasping and manipulating objects. 

 

The bones in and around the wrist consist of the 

 

  • Radius - The radius is the bone that makes the most contact with the carpal bones. The radiocarpal joint is the main joint of the wrist. It is known as a condyloid joint. A condyloid joint allows combined motions in multiple planes, including backward and forward bending motions, side-to-side motions, and circular motions.

  • Ulna - The end of the ulna is covered by a triangular shaped articular disc—a piece of fibrous cartilage that cushions the wrist bones, it does not directly form a joint with the carpals. It connects with the radius - the radioulnar joint, allowing for rotation of the forearm. The ulna stays in a stable position while the radius rotates around it. 

  • 8 Carpal bones - are located between the radius and ulna, and the metacarpals. They are firmly bound and provide stability and a little bit of movement. The underside (the palm side) of the carpals is arch like, creating a channel through which tendons, nerves and ligaments pass from the forearm through to the hand – this is the carpal tunnel. The carpals also link to the metacarpal bones of the hand (carpometacarpal joints). Because of the complex range of movements the wrist and hand can perform, the joint has a crosshatching web of ligaments connecting all these bones so that there can be mobility without losing stability. 

  • Hand Bones - The 5 metacarpals (the heads of the metacarpals, commonly known as knuckles) and 14 phalange bones (Each finger has 3 phalanges the thumb has 2) are linked by ligaments and surrounded by muscles, nerves, vessels, fascia and skin. The tips of the fingers are loaded with sensory receptors and have the ability to sense subtle changes in texture and shape.

 

 

In asana practice, the hand provides one of the most important foundational anchors, included in all the arm balances, many backbends, even leveraged hip openers, twists, and forward bends. The wrist transfers forces from the arm to the hand. Given considerable mobility by the wrist, this precious tool is also one of the most vulnerable parts of the human body and the wrist one of the most commonly injured in yoga practice.

 

When the hand is placed on the floor, in supported postures, we want to recruit more than just the tiny carpals. The metacarpals and phalanges need to become part of the support structure. We want to emphasise a balanced pressure into both sides of the hand, or even an added emphasis on grounding through the thumb side of the hand. These actions help distribute the weight as well as keep the pressure off of the soft tissues on the outside of the wrist.

HASTA BANDHA

 

When the hands go to the floor, particularly in arm balancing, we can create a routing action similar to the one we create with our feet. Hasta bandha (hand lock), Assists energy up through the soft centre of your palms to bring strength and stability to your arms and upper body. The action will help protect the wrists in yoga poses - 

 

Root down through the pads and mounds of the thumb and fingers, and energetically draw/suction upwards through the centre of the palms, creating a lift upwards through the hands, wrists and lower arms.

 

MOVEMENTS OF THE WRIST/HAND

 

  • Flexion draws the hand towards the inner foream, which tends to elongate the fingers. 

  • Extension draws the hand towards the outer forearm, the fingers tend to tighten as in the tendency for the fingers and knuckles to rise from the floor in Yoga. Having tight hand and wrist flexors/ could make it difficult to extend (technically hyperextend) your wrist as needed in a pose like chaturanga. This lack of flexibility is a potential cause of generalised wrist and/or hand pain in yoga. Reducing the wrist angle may be needed to create less compression allowing their elbow to move behind the wrist rather than having to stay at 90° over  them. 

  • Abduction & Adduction (towards and away from the midline /side to side movements)

 

Joints stay healthy by being kept mobile. During most of our day our wrists are only in a slight angle of extension or flexion – perhaps pushing a door open is the most extreme angle we’ll get into. Then yoga comes along and we ask our wrists to bend at 90 degrees and support some, or all, of our body weight. This is good! It stops us losing that range of motion but it’s also where we are vulnerable to injury.

 

In the elbow, the key ligaments are the medial collateral ligament and the lateral collateral ligament. The medial collateral is on the inside edge of the elbow, and the lateral collateral is on the outside edge. Together these two ligaments connect the humerus to the ulna and keep it tightly in place as it slides through the groove at the end of the humerus. These ligaments add to the stability of the elbow. They can be torn when there is an injury or dislocation to the elbow. If they do not heal correctly the elbow can be too loose, or unstable. There is also an annular ligament that wraps around the radial head and holds it tight against the ulna. 

 

CARRYING ANGLE

Your carrying angle is formed between the axis of a radially deviated forearm and the axis of the humerus. It helps the arms to swing without hitting the hips while walking. ‘Normally' it is 5-15o away from the body but this also varies. Those with a large carrying angle may demonstrate a bowed-inward appearance while doing straight arm supported postures.

HUMERAL TORSION

Another skeletal variation that occurs is humeral torsion. This dictates where the ‘eye of the elbow’ ‘looks’. Where it looks, doesn’t matter.

 

The elbow, where the humerus and radius articulate is essentially a hinge joint which allows the arm to flex (bend), extend (straighten) and in some people ‘hyperextend’. Some extend their elbow past 180°, some people cannot get their elbows to extend open to 180°.

 

  • Flexion

  • Extension

  • Hyperextension

  • Hypoextension

 

This is not ‘clinical elbow hyperextension’ but it is hyperextension by the yogic definition which is generally used to describe the situation where a limb is extended past the perfectly straight 180° line. The term elbow hyperextension is also used medically to describe a situation where a joint has been taken past its normal range of motion, resulting in injury. These are two very different uses of the term hyperextension. 

 

What stops the elbow from extending further? “full extension is limited by tension in the (elbow’s joint) capsule and muscles anterior to the joint … and the entry of the tip of the olecranon into the olecranon fossa.” - Grey’s Anatomy Another text explains more succinctly, “Elbow extension ROM is limited by contact of the olecranon process of the ulna with the olecranon fossa of the humerus.”

When we lock out the elbows what we are doing essentially is allowing our bones to compress.

 

Here we see the lower portion of the upper arm bone, the humerus. (1) Below it we see the upper end of the main lower arm bone, the ulna. (2) and the radius (3) Notice how they are supposed to fit together.

 

At the bottom of the of humerus is a notch, called the olecranon fossa (4). At the top of the ulna is a protrusion of bone called the olecranon (5), which just happens to fit into the fossa of the humerus. A perfect match – most of the time. Shown together with the elbow in extension you can see that the hook of the ulna nestles snugly into the opening of the humerus.

 

 
 

As our bones differ, this place will be different on each individual.

 

Place your hand on your opposite shoulder and pull it down so it can’t move, you will find you can only lift your arm to the side about parallel to the floor. The same happens as you lift it forward. 

 

To find a bit more space and increase the amount of flexion or abduction that you get in the joint before it hits the acromion, externally rotate your humerus before abducting or flexing. If you internally rotate you usually loose a bit of space.

Movements of the scavicle (clavicle & scapula) Remember when the scapula moves the humerus comes along with it. 

 

  • elevation & depression

  • protraction and retraction 

  • upward and downward rotation 

BRACHIAL PLEXUS 

The brachial plexus is the network of nerves that sends signals from your spinal cord to your shoulder, arm and hand. A brachial plexus injury occurs when these nerves are stretched, compressed, or in the most serious cases, ripped apart or torn away from the spinal cord.

INJURIES 

 

The most common shoulder injuries involve the muscles, ligaments, cartilage, and tendons, rather than the bones. It is easy and common to overwork and overload the connective tissues that are trying so hard to keep everything intact. In some forms of yoga we are seeing the over-stretching of ligaments which then increase the instability of the shoulder. In other systems of yoga we are witnessing repetitive motion injuries (too many Chaturanga Dandasanas) as well as traumatic injuries, for example, jumping back to Plank with straight arms. Common shoulder injuries include rotator cuff tears, shoulder impingement, and dislocation. Tendonitis (inflammation of the muscle attachment to bone), bursitis (inflammation of the fluid-filled sacs that protect joints against friction) and overtime, arthritis (inflammation in the joint)

 

 

Architectural Stability versus Muscular Stability

Being able to stack the bones right on top of each other has benefits. Architecturally, when the bones are aligned, the stresses of the weight in the posture are taken by the full column of the bones, not by the joints nor by the muscles. In this case the muscles are used simply to keep the bones aligned, not to support the weight of the body. Bones are great at supporting weight. 

 

Muscular stability is harder to maintain: When we are not architecturally aligned, the bones are not doing this job, and more of the stress of the body’s weight falls onto the muscles and/or the joint and its ligaments. It’s then work, but that may be quite desirable. When we are stacked, we can stay much longer in a pose than if we have to rely on muscles or ligaments to maintain it. Wether we can stack or not will ultimately be dependant on our bones. 

Locking the Elbow ‘Locking out’ is not necessarily hyperextension: it can happen even when your normal range of motion is exactly 180° It simply means that you are using your bones to support the stress of the position rather than employing only the muscles. This is an important distinction, as we will see, because most people who cannot hyperextend will still tend to lock the elbows when in a posture that puts a lot of strain on the arms - i.e Plank Pose Remember some students wont be able to lock out if they don’t have that range available at the elbow. Turbo-Dog is hardwork. Those who are limited can never get to the architecturally stable point; and arms will always want to collapse inward. For them to stay in Down Dog or Side Plank will be very challenging because their muscles will have to be active all the time. They have no choice in the yoga asanas and their practice will be all about building strength, and dealing with frustration. Those that are on the other end have a choice: they can choose to straighten their elbow to 180° and build strength, or they can go to thier full length, lock out, and enjoy her full range of motion and stressing her joints. Neither person is doing his or her yoga wrong: they are just dealing with the reality of their bodies. 

 

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