applied anatomy of shoulder joint

APPLIED ANATOMY OF SHOULDER COMPLEX

APPLIED ANATOMY

• Movement of the shoulder is critical to maintain the positioning of the humeral head relative to the glenoid.

• Helps control humeral head movement• Rotator Cuff contraction, they dynamically tighten

the capsule– Helps center the humeral head relative to the glenoid.

• Crucial with ANY over head activity• Scapulohumeral Rhythm

– As humerus elevates to 30’ no movement– 30-90’ scapula abducts & upwardly rotates– 180’ humeral abduction & sternoclavicular jt. moves

Costs of Dynamic Stabilization of the Glenohumeral Joint

When all stabilization factors are intact, the head of the humerus rotates into flexion or abduction around a relatively stable axis with minimal translation. Over time, however, even normal stresses resulting from the complex dynamic stabilization process may lead to degenerative changes or dysfunction at the GH joint. Any disruption in the synergistic action of the dynamic stabilization factors may accelerate degenerative changes in or around the joint.

The supraspinatus muscle is a particularly key structure in dynamic stabilization. The supraspinatus is either passively stretched or actively contracting when the arm is at the side (depending on load); it also participates in humeral elevation throughout the ROM. Mechanical compression and impingement of the stressed supraspinatus tendon can occur when the subacromial space is reduced by osteoligamentous factors, when there is increased superior or anterior translation of the humeral head center with less favorable GH mechanics, when the scapula does not posteriorly tip or upwardly rotate adequately during humeral elevation, or when occupational factors require heavy lifting or sustained overhead arm postures.

Symptomatic and asymptomatic rotator cuff tears are seen in almost all people over the age of 70, with the supraspinatus likely to show lesions before the other tendons of the cuff. Rotator cuff tendinitis or typically produce pain between 60 and 120 of humeral elevation in relation to the trunk. This range constitutes what is known as the painful arc. It is within this ROM that the tendons of the rotator cuff are passing beneath the coracoacromial arch. Beyond 120, the tendons have rotated past the overlying arch structures.

Degenerative changes in the AC joint may result in pain in the same area of the shoulder as pain from supraspinatus or rotator cuff lesions. Pain due to AC degeneration is more typically found when the arm is raised beyond the painful arc or when the arm is adducted across the body, compressing the AC joint surfaces. The long head of the biceps brachii similarly can produce pain in the anterosuperior shoulder.

Because the long head of the biceps tendon

also passes directly beneath the impinging

structures of the coracoacromial arch, it is subject

to some of the same degenerative changes and

the same trauma seen in the tendons of the rotator

cuff. Whether the biceps is actively contributing to

elevation of the arm or to joint stabilization or is

passive, the tendon of the biceps must slide within

the bicipital groove and under the transverse

humeral ligament as the humerus moves around

any of its three rotatory axes.

If the bicipital tendon sheath is worn or inflamed, or if the tendon is hypertrophied (as often seen with rotator cuff tears), the gliding mechanism may be interrupted and pain produced. A tear in the transverse humeral ligament may result in the tendon of the long head popping in and out of the bicipital groove with rotation of the humerus, a potentially wearing and painful microtrauma.

RECOGNITION OF SPECIFIC INJURIES• Fractures:

– Acromioclavicular (common)• Caused by outstretched arm, fall on the tip of shoulder, direct impact• Athletes usually supports the fx’d. side, tilts head and chin to opposite

side• Deformity, pain, swelling

– Scapular (infrequent)• Direct impact, or when force is transmitted through humerus to scapula• Pain with movement

– Humeral • Shaft- (occasionally)

– Direct blow, fall on the arm– Comminuted or transverse with deformity due to muscular pull

• Proximal – dangerous to nerves and blood supply– Direct blow, dislocation, impact received by falling on an

outstretched arm• Head of humerus (Epiphyseal fx)

– Occur in ages 10 or younger– Direct blow or indirect blow– Difficult to recognize

Humeral shaft, Proximal & Epiphyseal

• Sprains– Sternoclavicular (uncommon)

• Initiated by a direct force transmitted through the humerus

– Acromioclavicular• Extremely vulnerable especially in collision sports• Direct impact to the TIP of the shoulder that forces the

acromion process downward, backward, and inward– The clavicle is pushed down against the rib cage

Rockwood’s Classification of AC Sprains

Sternoclavicular & Acromioclavicular Sprains

DISLOCATIONSDislocation is an injury to the joint in which the

ends of the bones are forced from their normal positions. This injury temporarily deforms and immobilizes the joint and may result in sudden and severe pain.The shoulder is more prone to dislocate than any other joint.This due to :• laxity of the capsule• Disproportionate area of articular surfaces

Occurs when the arm is abducted

• Account for 50% of all dislocations– Two Types

• Anterior– Most common– Direct impact to the posterior aspect of shoulder

» Forced abduction, external rotation, and extension that forces the humeral head out (arm tackle)

– Bankart’s Lesion (Labrum tear)– Hill Sachs Lesion (creates a divot in humeral

head)– Slap Lesion (injury to labrum and long head of

biceps)• Posterior

– Account for 1 – 4.3%– Extremely Rare– Forced Adduction and Internal rotation of

shoulder or fall on an extended internally rotated arm

LABRUM TEAR

SLAP stands for "superior labrum, anterior to posterior"-in other words, "the top part of the labrum, from the front to the back."

The labrum is described like a clock face with 12 o'clock being at the top (superior), 3 o'clock at the front (anterior), 6 o'clock at the bottom (inferior) and 9 o'clock at the back (posterior). Clinicians may reverse the 3 o'clock and 9 o'clock for left shoulder describing 3 o'clock at the back.

IMPINGEMENTS

– Involves mechanical compression of Supraspinatus tendon, subacromial bursa, and long head of biceps tendon

– Related to shoulder instability and overhead activities

– Failure of RC muscles to maintain position. Shoulder impingement has primary (structural)

and secondary (posture & movement related)causes.

• Bursitis– Overuse – Chronic Inflammation – Shoulder bursitis and tendonitis

pain will be particularlyacute when the arm is raised about shoulder level

Biceps Brachii Ruptures

– Caused by powerful concentric & eccentric contraction• occurs near the origin of muscle• athlete will hear a “snap”, then feels sudden intense

pain• consequences of loss of strength:

- 30 % decrease in flexion strength - 40 % loss of supination strength

• after the injury there is usually localised pain at the front of the elbow, with bruising and swelling. the biceps muscle may retract up the upper arm crating a prominent bump, known as the 'popeye' sign. this is often visibly different to the other biceps when contracting the muscle.

Biceps Tendon Rupture

FROZEN SHOULDER• Frozen shoulder is an extremely painful condition in

which the shoulder is completely or partially unmovable (stiff). It is one of the most painful conditions of the shoulder (the others being calcific tendonitis  or referred nerve pain from the neck).

• Frozen shoulder often starts out of the blue, but may be triggered by a mild injury to the shoulder. The condition usually goes through three phases, starting with pain, then stiffness and finally A stage of resolution as the pain eases and most of the movement returns. This process may take A long time, sometimes as long as two or more years.

• The lining of the shoulder joint, known as the 'capsule', is normally a very flexible elastic structure. It's looseness and elasticity allows the huge range of motion that the shoulder has. With a frozen shoulder this capsule (and its ligaments) becomes inflamed, swollen, red and contracted. The normal elasticity is lost and pain and stiffness set in.

Baseball Players and their Shoulder Injuries

• Shoulder pain is a common complaint among baseball players, especially pitchers, regardless of age or level of play. Pain experienced during the throwing motion results in an inability to throw with velocity, causing what is commonly referred to as "dead arm" syndrome. The cause of pain is most often injury to either the bones or the soft-tissue structures of the shoulder joint.

Throwing Mechanics• Consists of 5 Phases– Windup or Preparation• 1st movement until ball leaves

glove• Lead leg strides forward• Both shoulders abduct, externally

rotate and horizontally rotate– Cocking• Begins when hands separate• Ends when Maximum external

rotation of humerus has ocurred• Lead foot touches ground

– Acceleration• Lasts from Maximum external rotation until

ball release• Humerus abducts, horizontally abducts, and

internally rotates• Scapula elevates, abducts, and rotates

upward– Deceleration

• From ball release until Maximum shoulder internal rotation

• External rotators of the RC muscles contract eccentrically (lengthening) to decelerate the humerus

• Rhomboids contract eccentrically to decelerate the scapula

– Follow-through• From Maximum shoulder internal rotation

until the end of motion• When athlete is in balanced position

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