biomechanics Bio= life; Mechanics= physical actions We might think of biomechanics as the “physics of human movement” : Biomechanics is the science of movement of a living body, including how muscles, bones, tendons and ligaments work together to produce movement.

Structure of shoulder Most complex joint in human body Include 5 different articulations 1) Glenohumeral joint 2) Strenoclavicular joint 3) Acromioclavicular joint 4) Coracoclavicular joint 5) Scapulothoracic joint

1.Sternoclavicular joint Proximal end of clavical articulate the clavicular notch of manubrium of sternum and with the cartilage of 1 st rib Fibro cartilagenious disc improve the fit of articulating bone and act as shock absorber. Characteristics Modified ball and socket joint Major axis of rotation for the movement of clavical and scapula

Characteristics of sternoclavicular joint Movement in frontal and transverse plane and farward and backward saggital plane rotation Rotation occur during shrugging of shoulders, Elevation of arms above head Close pack position of SC joint occur with max. shoulder elevation

Sternoclavicular joint

acromioclavicular joint Articulation of acromion process of scapula with distil end of clavicle is known as acromioclavicular joint Characteristics 1) Irregular joint 2) Allow limited motion in three plane 3) Rotation occur at AC joint during arm elevation

Characteristics of AC joint Close pack position of AC joint occur when arm is abducted at 90 degree

Acromioclavicular joint

Coracoclavicular joint This joint is a syndyesmosis ( joint surface is bound by ligament) Coracoid process of scapula and inferior surface of clavicle bound together by coracoclavicular ligament This joint permits little movement

Coracoclavicular ligament

Glenohumeral joint Ball and socket joint, head of humerus articulate with glenoid fossa of scapula. Most freely moving joint in human body Hemispherical head of humerus has three to four time the amount of surface area as the shallow glenoid cavity Glenoid fossa is also less curved as compare to head of humerus,

Movement in glenohumeral joint Flexion Extension Abduction Adduction Horizontal adduction, abduction Medial rotation and lateral rotation circumduction

Characteristics of glenohumeral joint Glenoid fossa composed of part of joint capsule, tendon of long head of biceps, and glenohumeral ligament located on the periphery of glenoid fossa deepen fossa and add stability to glenohumeral joint Ligaments : Superior, middle and inferior glenohumeral ligaments on anterior side of jointglenohumeral ligaments Coracohumeral ligament on superior side of joint. Coracohumeral ligament Transverse humeral ligament

Ligaments of glenohumeral joint

Rotator cuff muscles and Jt. stability Tendon of four muscles also join the joint capsule. these are rotator cuff. The rotator cuff muscles are the group of muscles in the upper arm and shoulder area that support the or stabilize the shoulder area. The four muscles that make up the rotator cuff are the supraspinatus, infraspinatus, subscapularis, and the teres minor muscles. Reffered to as SITS

Factors contributing to stability Supraspinatus, infraspinatus teres minor participate in lateral rotation Subscapularis causes medial rotation Rotator cuff surround the shoulder from posterior, superior and anterior side Contraction of theses muscles pulls the head of humerus toward glenoid fossa contributing to joint sability.

Factors contributing to stability Negative pressure within capsule of joint also helps to stabilize the joint Joint is most stable in closed-pack position Abducted and laterally rotated

Rotator cuff

Scapulothoracic joint Region between anterior scapula and thoracic wall is referred to scapulothoracic joint, as scapula can move in both saggital and frontal plane. Functions of muscles attaching to scapula 1) Either stabilize shoulder region 2) Or facilitate movement of upper extremity through appropriate positioning of glenohumeral joint ex. Rhomboids during overhead through