Introduction. Rarely does a single muscle act in isolation at the shoulder complex.

Transcription

1 Shoulder complex 1

2 Introduction Our study of the upper limb begins with the shoulder complex, a set of four articulations involving the sternum, clavicle, ribs, scapula, and humerus. Rarely does a single muscle act in isolation at the shoulder complex. Muscles work in teams to produce a highly coordinated action that is expressed over multiple joints. The very cooperative nature of shoulder muscles increases the versatility, control, and range of active movements.

3 Four joints within the shoulder complex Sternoclavicular joint Acromioclavicular joint Scapulothoracic joint Glenohumeral joint

4 Sternum The sternum consists of the manubrium, body, and xiphoid process.

5 Clavicle When looking from above, the shaft of the clavicle is curved with its anterior surface being generally convex medially and concave laterally.

6 Superior view of both shoulders in the anatomic position A. The orientation of the clavicle deviated about 20 posterior to the frontal plane. B. The orientation of the scapula deviated about 35 anterior to the frontal plane. C. Retroversion of the humeral head about 30 posterior to the mediallateral axis at the elbow.

7 Scapula The triangular-shaped scapula has three angles: inferior, superior, and lateral.

8 Scapula Anterior view of the right scapula showing an approximate 5 upward tilt of the glenoid fossa relative to the medial border of the scapula.

9 (A)The right hummerus showing a 135 angle of inclination between the shaft and head of the humerus in the frontal plane. (B)The retroversion of the humeral head relative to the distal humerus.

10 Arthrology The most proximal articulation within the shoulder complex is the sternoclavicular joint. The clavicle, through its attachment to the sternum, functions as a mechanical strut, or prop, holding the scapula at a relatively constant distance from the trunk. Located at the lateral end of the clavicle is the acromioclavicular joint. This joint, and associated ligaments, firmly attaches the scapula to the clavicle. Motions of the right scapula against the posterior-lateral surface of the thorax, forming the scapulothoracic joint.

11 Arthrology Movements at the scapulothoracic joint are mechanically linked to the movements at both the sternoclavicular and acromioclavicular joints. The position of the scapula on the thorax provides a base of operation for the glenohumeral joint, the most distal and mobile link of the complex. The term shoulder movement describes the combined motions at both the glenohumeral and the scapulothoracic joints. 11

12 Primary movements at the scapulothoracic joint Elevation The scapula slides superiorly on the thorax, such as in the shrugging of the shoulders. Depression From an elevated position, the scapula slides inferiorly on the thorax. 12

13 Primary movements at the scapulothoracic joint Protraction The medial border of the scapula slides anterior-laterally on the thorax away from the midline. Retraction The medial border of the scapula slides posterior-medially on the thorax toward the midline, such as occurs during the pinching of the shoulder blades together. 13

14 Primary movements at the scapulothoracic joint Upward Rotation The inferior angle of the scapula rotates in a superior-lateral direction such that the glenoid fossa faces upward. This rotation occurs as a natural component of the arm reaching upward. Downward Rotation The inferior angle of the scapula rotates in an inferior-medial direction such that the glenoid fossa faces downward. This motion occurs as a natural component of the lowering of the arm to the side from the elevated position. 14

15 Sternoclavicular joint The sternoclavicular(sc) joint is a complex articulation, involving the medial end of the clavicle, the clavicular facet on the sternum, and the superior border of the cartilage of the first rib. The SC joint functions as the basiar joint of the entire upper extremity, linking the appendicular skeleton with the axial skeleton. The joint therefore must be firmly attached while simultaneously allowing considerable range of movement.

16 Sternoclavicular joint Complex saddle shaped articular surface

17 Periarticular connective tissue The SC joint is enclosed by a capsule reinforced by anterior and posterior sternoclavicular ligaments. The interclavicular ligament spans the jugular notch, connecting the medial end of the right and left clavicles. 17

18 Periarticular connective tissue The costoclavicular ligament is a strong structure extending from the cartilage of the first rib to the costal tuberosity on the inferior surface of the clavicle. The articular disc at the SC joint separates the joint into distinct medial and lateral joint cavities. The disc not only strengthens the articulation but functions as a shock absorber by increasing the surface area of joint contact. 18

19 kinematics The osteokinematics of the clavicle involve a rotation in all 3 of freedom. The primary purpose of these movements is to place the scapula in an optimal position to accept the head of the humerus.

20 kinematics Elevation and depression of the clavicle occur approximmately parallel to the frontal plane, around a near anterior-posterior axis of rotation. Maximums of approximately 45 degrees of elevation and 10 degrees of depression.

21 Arthrokinematics Elavation and depression 21

22 kinematics Protraction and retraction of the clavicle occur nearly parallel to the horizontal plane around a vertical axis of rotation.

23 Arthrokinematics Protraction and retraction 23

24 Axial(longitudinal)rotation of the clavicle The 3 rd degree of freedom at the SC joint is a rotation of the clavicle around the bone s longitudinal axis. During shoulder abduction or flexion, a point on the superior aspect of the clavicle rotates posteriorly 20 to 35 degrees. The arthrokinematics of clavicular rotation involve a spin of the head of the clavicle about the lateral surface of the articular disc.

25 Acromioclavicular Joint The acromioclavicular(ac) joint is the articulation between the lateral end of the clavicle and the acromion of the scapula. A. an anterior view showing the sloping nature. B. a posterior view of the joint opened up from behind, showing the clavicular facet on the acromion and the disc.

26 Periarticular connective tissue The AC joint is surrounded by a capsule that is direectly reinforced by superior and inferior ligaments. The coracoclavicular ligament provides an important extrinsic source of stability to the AC joint. The articular surfaces at the AC joint are lined with a layer of fibrocartilage and often separated by a complete or incomplete articular disc. 26

27 kinematics Upward rotation of the scapula at the AC joint occurs as the scapula swing upwardly and outwardly in relation to the lateral edge of the clavicle. Downward rotation at the AC joint returns the scapula back to its anatomic position, a motion mechanically associated with shoulder adduction or extension.

28 Acromioclavicular joint dislocation The resulting medially directed ground force may displace the acromion medially and under the sloped articular facet of the wellstabilized clavicle.

29 Scapulothoracic joint In the anatomic position, the scapula is typically positioned between the second and the seventh rib, with the medial border located about 6 cm lateral to the spine. Although highly variable, the average resting posture of the scapula is about 10 degrees of anterior tilt, 5 to 10 degrees of upward rotation, and about 35 degrees of internal rotation-a position consistent with the previously described plane of the scapula.

30 kinematics Scapular elevation at the scapulothoracic joint occurs as a composite of SC and AC joint rotations. 30

31 kinematics Protraction of the scapula occurs through a summation of horizontal plane rotations at both the SC and AC joints.

32 kinematics Upward rotation of the scapulothoracic joint is an integral part of raising the arm over the head. Downward rotation of the scapula occurs as the arm is returned to the side from a raised position