SHOULDER

p {margin: 0; padding: 0;} .ft00{font-size:18px;font-family:Arial;color:#ff0000;} .ft01{font-size:16px;font-family:ArialMT;color:#000000;} .ft02{font-size:16px;line-height:21px;font-family:ArialMT;color:#000000;} SHOULDER (SCAPULAR BELT) The shoulder girdle is made up of two symmetrical bones, the shoulder blades and theclavicles, and a paired bone, the sternum. These three bony structures are connectedtogether by four joints, the acromioclavicular joints and the sternoclavicular joints. Eachscapula articulates with the humerus via an enarthrosis, the scapulohumeral joint. Thearchitecture of this belt has undergone many changes since the ancient times when ourancestors set out to conquer the mainland. Of each of these stages we keep today indeliblememories, the results of successive adaptations to the antigravity struggle, to brachiation, tothe liberation of the hand... The primitive function of the shoulder girdle in Lower Permian mammalian reptiles wasantigravity. At this time, the scapula, the coracoid(s) and the clavicle still formed a massiveunit on which a large and thick humerus was attached, perfectly adapted to resist thepressure exerted by the weight of the animal on its front limbs. The humeral head of theseanimals was articulated to the scapula along a vertical axis or substantially inclinedbackwards. During the following periods several evolutionary modifications will manifest themselves: ● Firstly, the definitive fixation of the coracoid on the scapula. This structure evolved differently in mammals depending on their mode of locomotion, regressing inquadrupeds, developing and anteriorizing in brachiators (prosimians). ● Secondly, the individualization of the clavicle, a phenomenon linked to a greater mobility of the upper limb. The modern shoulder girdle results from these developments: ● It retains a posterior spine (already in place in the first amphibians and secondary reptiles), separating its posterior face into two fossae. ● Its scapulo-humeral joint allows maximum congruence during the antepulsion of the arm (primary position of the quadrupedalism). ● It has a protruding coracoid process attached to the scapula, but still connected to the latter by a ligament (acromio-coracoid ligament) whose vestigial nature couldexplain its real lack of function in the physiology of the modern shoulder. These particularities of the ape shoulder give the shoulder girdle astonishing mobility, butalso the ability to perform traction exercises (recent development) and pressure exercises(remnant of quadrupedalism). The shoulder joint complex constitutes a particularly mobilejoint with nine degrees of freedom (abduction, adduction, flexion, extension, internal rotation,external rotation, circumduction, elevation, lowering). The participation of each of the threejoints is assessed differently by the authors but classically % of mobility is attributed to thescapulohumeral joint, % to the acromioclavicular and % to the sternoclavicular.