Kinesiology of the Upper Extremity

Instructor’s Manual Chapter 8

UNIT 1: SHOULDER UNIT: THE SHOULDER COMPLEX

STRUCTURE OF THE BONES OF THE SHOULDER COMPLEX

 Consists of the clavicle, scapula, and humerus and is affected by the sternum and thorax

Clavicle

 Functions as strut  Several important landmarks  Articular surfaces differ from one another, but both are covered by fibrocartilage.

Scapula

 Provides site for muscle attachment  Several important landmarks  Orientation of glenoid fossa depends on frame of reference and posture  Plane of scapula is 30–45° from frontal plane  Rotation of the scapula about an AP axis is upward (lateral) or downward (medial).  At rest, the scapula typically tilts anteriorly approximately 10° about a medial–lateral axis.

Proximal Humerus

 Head of humerus projects medially, superiorly, and posteriorly and is approximately half a sphere  Several important landmarks

Sternum and Thorax

 Sternum provides attachment to axioskeleton, and the shape of the thorax helps define the motion of scapula.  Several palpable landmarks of shoulder\

STRUCTURE OF THE JOINTS AND SUPPORTING STRUCTURES OF THE SHOULDER COMPLEX

 Shoulder complex consists of sternoclavicular, acromioclavicular, scapulothoracic, and glenohumeral joints; all but the scapulothoracic are synovial

Sternoclavicular Joint

 Triaxial

 Articular surfaces provide little stability.  Supporting structures: relatively weak capsule, anterior and posterior SC ligaments, interclavicular ligament, costoclavicular ligament, and intra-articular disk.  Joint is well supported, so dislocation is less common than fracture  Motion: elevation and depression, protraction and retraction, and posterior ( upward) and anterior ( downward) rotation

Acromioclavicular Joint

 Gliding joint  Supporting structures: capsule, superior and inferior AC ligaments, and the coracoclavicular ligament, particularly the trapezoid portion that prevents medial displacement of the scapula.  Gliding motion that is sometimes described as rotation about three axes  Allows variable movement of the clavicle and scapula

Scapulothoracic Joint

 Lacks traditional components of a joint  Allows elevation and depression, abduction and adduction, upward and downward rotation, anterior and posterior scapular tilt, and internal and external rotation.

Glenohumeral Joint

 Ball-and-socket, triaxial joint  Congruent articular surfaces of unequal size allow considerable mobility but little stability.

SUPPORTING STRUCTURES OF THE GLENOHUMERAL JOINT

 Include the labrum, capsule, three glenohumeral ligaments, coracohumeral ligament, and surrounding muscles  Labrum deepens the glenoid fossa and is highly variable.  Capsuloligamentous complex consists of the capsule and reinforcing ligaments.  Capsule is lax, especially inferiorly.  Glenohumeral ligaments prevent excessive lateral rotation and excessive anterior translation of the humeral head, especially when pulled taut by lateral rotation of the shoulder.  Inferior glenohumeral ligament provides most of the resistance to translation when the shoulder is abducted beyond midrange.  Posterior capsule limits excessive posterior translation.  Protection against inferior dislocation comes from the coracohumeral and perhaps the superior or inferior glenohumeral ligaments.  Intra-articular joint pressure also stabilizes the glenohumeral joint.  Muscles provide additional stability.

MOTIONS OF THE GLENOHUMERAL JOINT

 Undergoes flexion/extension, abduction/adduction, and medial/lateral rotation  Abduction occurs with lateral rotation and flexion also occurs with simultaneous rotation. The direction of this rotation is unclear, but these rotations are necessary to help preserve the subcromial space.  Translation accompanies glenohumeral rotations. These translations are not consistent with the concave–convex rule: slight superior glide followed by no or less inferior glide in flexion or abduction; anterior translation with medial rotation and abduction; and posterior translation with extension and lateral rotation.  Glenohumeral ROM: 100–120° of flexion and abduction, 70–90° of medial and lateral rotation  Other joints of the shoulder complex can substitute for glenohumeral joint motion.

TOTAL SHOULDER MOVEMENT

Shoulder motion is measured as the displacement of the arm with respect to the trunk and therefore is also known as arm– trunk motion. Motion comes from all four joints of the shoulder complex.

Movement of the Scapula and Humerus during Arm–Trunk Elevation

 Scapulohumeral rhythm indicates the proportion of glenohumeral and scapulothoracic joint motion in shoulder motion.  In active shoulder flexion or abduction, the glenohumeral joint contributes most of the motion.  Scapulothoracic joint rotates upwardly and externally and tilts posteriorly during flexion and abduction.  Scapulothoracic and glenohumeral joints move simultaneously throughout the motion.  Humerus and scapula move in a coordinated and systematic rhythm.  Exact ratio of scapulothoracic and glenohumeral joint motion may vary with plane of movement and location within the ROM.  Likely significant variability among individuals

Sternoclavicular and Acromioclavicular Motion during Arm-Trunk Elevation

 Sternoclavicular joint elevates approximately 40° with full flexion or abduction.  Sternoclavicular joint undergoes upward rotation flexion and abduction.  Acromioclavicular joint undergoes motion to allow the clavicle and scapula to move independently.

Impairments in Individual Joints and Their Effects on Shoulder Motion

 Impairments in mobility can affect any of the four joints of the shoulder complex.

LOSS OF GLENOHUMERAL OR SCALPULOTHORACIC JOINT MOTION

 Absence of glenohumeral motion results in 50–65% loss in overall shoulder flexion and abduction and the loss of all normal shoulder rotation ROM.  Absence of scapulothoracic motion results in up to one third of shoulder flexion and abduction ROM. Active shoulder flexion and abduction ROM may be reduced by 90° as the result of active insufficiency of the glenohumeral muscles.

LOSS OF STERNOCLAVICULAR OR ACROMIOCLAVICULAR JOINT MOTION

 Loss of sternoclavicular or acromioclavicular joint motion affects the ability of the scapulothoracic joint to move, resulting in losses up to (but usually less than) 60 of shoulder flexion or abduction.

SHOULDER RANGE OF MOTION

 Differences exist among reported ROMs  Lateral rotation ROM appears greater than medial rotation ROM.

SUMMARY