Shoulder Flashcards
Articular structures
Degrees of Freedom??
Number of Joints??
the proximal joint of the upper limb
most mobile of all the joints in the human body
three degrees of freedom and this permits movement of the upper limb with respect to the three planes in space and the three major axes.
It is make up of Five (5) joints. These five joints fall into two groups.
First group of two joints
- The shoulder or scapulo-humeral joint, which is a true joint anatomically. It is the most important joint of this group.
- The subdeltoid ‘joint’ or ‘the second shoulder joint’. This is not an anatomical but a physiological joint, as it consists of two surfaces sliding with respect to each other. The subdeltoid ‘joint’ is mechanically linked to the shoulder joint because any movement in the latter brings about movement in the former.
Scapulo-humeral joint
These are spherical surfaces, typical of a ball-and-socket joint, which has three axes and three degrees of freedom.
during abduction to 50 o, rotation of the humeral head occurs around a point located somewhere within circle Cl.
- the end of abduction (from 50 o to 90o), the centre of rotation lies within circle C2,
- about 50 o abduction, there is a discontinuity in the movement so that the centre of rotation now lies supe-rior and medial to the humeral head
Scapulo-humeral joint:
The head of the humerus
Facing superiorly, medially and posteriorly it corresponds to 1/3 of a sphere 3 cm in radius.
vertical diameter is 3 to 4 mm greater than its posterior diameter.
Its axis forms with the axis of the shaft an angle of 135° (the neck-shaft angle) and with the frontal plane an angle of 30° (the retrotorsion angle).
It is separated from the rest of the superior epiphysis of the humerus by the anatomical neck which makes an angle of 45° with the horizontal plane.
It bears two tuberosities, which receive the insertions of the periarticular muscles:
- the lesser tuberosity pointing anteriorly
- the greater tuberosity pointing laterally
Scapulo-humeral joint:
The glenoid cavity of the scapula
It lies at the supero-Iateral angle of the scapula and points laterally, anteriorly and slightly superiorly.
It is biconcave vertically and transversely but its concavity is irregular and less marked than the convexity of the humeral head.
Its margin is slightly raised and is grooved anteroposteriorly. The glenoid cavity is much smaller than the head of the humerus.
Scapulo-humeral joint:
The glenoid labrum
This is a ring of Fibro-cartilage attached to the margin of the glenoid cavity and bridging the ante-rosuperior groove.
It widens the cavity only slightly but deepens it appreciably so as to make the articular surfaces more congruent.
Second group of three joints:
- The scapulo-thoracic ‘joint’. This is also a physiological and not an anatomical joint. It is the most important joint of this group, although it cannot function without the other two, which are mechanically linked to it.
- The acromio-clavicular joint is a true joint
- The sterno-clavicular joint, a true joint, located at the sternal end of the clavicle The sternoclavicular joint is the only joint that connects the upper extremity directly with the thorax. The enlarged sternal end of the clavicle and the articular notch of the sternum are separated by an articular disk. The clavicles are connected to each other by the interclavicular ligaments, to the sternum by the anterior and posterior sternoclavicular ligaments, and to the first ribs by the costoclavicular ligaments. The two surfaces are saddle-shaped.
The sternoclavicular joint,
This joint has two axes and two degrees of freedom:
- axis 1 corresponds to the concavity of the clavicular surface and allows movements of the clavicle in the horizontal plane
- axis 2 corresponds to the concavity of the sternocostal surface and allows movements of the clavicle in the vertical plane
The Subdeltoid “joint”
- The lower surface is composed of the humeral head and rotator cuff.
- The upper surface is composed of the inner portion of the deltoid muscle.
- Inside there are the sub-deltoid bursa.
The Scapulo-thoracic ‘joint’
Two ‘spaces’ of this false joint:
The ‘space’ between the scapula and the serratus muscle:
- posteriorly and laterally, by the scapula, covered by the subscapularis muscle.
- anteriorly and medially, by the serratus anterior muscle arising from the medial border of the scapula and inserted into the antero-Iateral border of the thorax.
The ‘space’ between the thoracic wall and the serratus muscle:
- medially and anteriorly, by the thoracic wall (ribs and intercostal muscles).
- posteriorly and laterally, by the serratus anterior.
The scapula in its normal position stretches from the second to the seventh rib. Its supero-medial angle corresponds to the first thoracic vertebra. Its inferior angle corresponds to the seventh or eighth thoracic spine. Medial extremity of the spine of the scapula corresponds to the third thoracic spine. The medial or spinal border of the scapula lies 5 to 6 cm lateral to the thoracic spines.
The Acromioclavicular Joint
a single arthrodial joint involving the medial margin of the acromion and the acromial end of the clavicle.
coracohumeral ligament
crosses from the coracoid process of the scapula
to the greater and lesser tuberosities of the humerus, where it forms a tunnel for the tendon of the long head of the biceps brachii
Capsular ligaments
- The superior, middle, and inferior glenohumeral
- ligaments arise from the glenoid and its labrum, form capsular thickenings, and attach to the humeral neck and lesser tuberosity
- The coracohumeral, superior, and middle glenohumeral ligaments support the dependent (hanging down) arm and limit external rotation in the lower ranges of abduction
The Biceps tendon
- The tendon of the long head of the biceps arises from the supra-glenoid tubercle and the superior margin of the glenoid labrum.
- As it emerges from the joint cavity in the bicipital groove it passes deep to the capsule
- Its two heads are crucial in maintaining the coaptation of the articular surfaces of the shoulder
- The short head, resting on the coracoid process, lifts the humerus relative to the scapula and, along with the other longitudinal muscles (triceps, coracobrachialis and deltoid), prevents its downward dislocation.
- The long head of the biceps presses the humeral head against the glenoid, especially during abduction, since the long head of the biceps is also an abductor.
- Following its rupture there is a 20% drop in the strength of abduction
Muscular structures (general)
The shoulder region muscles are divided into three groups for study:
- Muscles connecting the shoulder girdle with the trunk, the neck and the skull
- Muscles connecting the scapula and the humerus.
- Muscles connecting the trunk and the humerus, having little or no attachment to the scapula
Muscles From Trunk to Shoulder Girdle:
- Serratus anterior
- Trapezius
- Rhomboid Major and Minor
- Pectoralis Minor
- Levator Scapulae
Muscles connecting the scapula and the humerus.
- Deltoid
- Supraspinatus
- Infraspihatus
- Teres Minor
- Subscapualris
- Teres Major
- Pectoralis Major
Muscles connecting the trunk and the humerus, having little or no attachment to the scapula
Latissiumus Dorsi
Serratus anterior
From: the anterolateral aspect of the thorax, from the first to the ninth rib
To: the medial border of the scapula
Function: Abduction and upward rotation of the scapula
Trapezius
From: occipital bone, ligamentum nuchae, and spinous processes from C7- T12
To: the acromial end of the clavicle, the acromion, and the spine of the scapula
Function:
The upper trapezius performs elevation and upward rotation of the scapula, as well as extension, lateral flexion, and contralateral rotation of the neck;
The lower trapezius performs upward rotation, adduction and depression of the scapula; the middle trape-zius performs upward rotation and adduction of the scapula
Rhomboid Major and Minor
From: ligamentum nuchae and spinous processes of the lowest two cervical and the upper four thoracic vertebrae
To: the medial border of scapula
Function: Downward rotation, adduction, and elevation of the scapula
Pectoralis Minor
From: the second to the fifth ribs
To: the coracoid process of the scapula
Function: Depression and ventral tilt of the scapula as well as elevation of ribs 2 to 5
Levator Scapulae
From: the transverse processes of the upper cervical vertebrae
To: the medial border of the scapula
Function: Elevation and downward rotation of the scapula as well as lateral flexion and ipsilateral rotation of the cer-vical spine
Deltoid
From: the acromial end of the clavicle, the acromion process, and the spine of the scapula
To: the deltoid tuberosity
Function: Abduction of the glenohumeral joint. Anterior deltoid performs flexion and horizontal adduction of the glenohumeral joint. Posterior deltoid performs extension and horizontal abduction of the glenohumeral joint
Supraspinatus
From: the supraspinous fossa of the scapula
To: the uppermost facet of the greater tubercle of the humerus
Function: Abduction of the glenohumeral joint.
Infraspihatus
From: the Infraspinous fossa
To: the greater tubercle of the humerus into its middle facet
Function:External rotation and adduction of the glenohumeral joint
Teres Minor
From: the lateral border of the scapula
To: the greater tubercle of the humerus into its lower (posterior) facet
Function: External rotation and adduction of the glenohumeral joint
Subscapualris
From: the costal surface of scapula
To: the Lesser tubercle of the
Function: humerus and shaft below the tubercle. Inward rotation of the glenohumeral joint. Depending on the arm position, the subscapularis can flex, extend, adduct, or abduct the glenohumeral joint
Teres Major
From: the inferior angle of the scapula
To: the crest of the lesser tubercle of the humerus by means of a strong broad tendon
Function: Internal rotation, adduction, and extension of the glenohumeral joint
Pectoralis Major
From: the clavicle (sternal half), sternum, and costal cartilages of the second to seventh ribs, and the apo-neurosis over the abdominal muscles
To: the crest of the greater tuberosity of the humerus, on an area several inches long
Function: Adduction and internal rotation of the glenohumeral joint. Clavicular head performs flexion of the gleno-humeral joint
Latissimus Dorsi:
From: the spinous processes of the thoracic vertebrae from T-6 downward, dorsolumbar fascia, crest of ilium (posterior portion), and the lowest ribs
To: the crest of the lesser tubercle of the humerus, proximal to that of the teres major
Function: Internal rotation, extension and adduction of the glenohumeral joint, scapular depression, elevation of pelvis
Movements of flexion and extension
- Performed in a sagittal plane and around a transverse axis
- Extension: movement of small range, up to 45° 50°
- Flexion: movement of great range, up to 180°
Movements of Adduction:
- Starting from the reference position, adduction is only possible when combined with:
- Extension: this allows a trace of adduction
- Flexion: adduction can reach 30° to 45°
Movements of Abduction:
- Performed in a frontal plane around an antero-posterior axis:
- abduction from 0° to 60°, taking place only at the shoulder joint.
- abduction from 60° to l20°, which requires recruitment of the scapulo-thoracic “joint”.
- abduction from l20° to 180°, involving movement at the shoulder joint and the scapulothoracic “joint” and flexion of the trunk to the opposite side
- After the 90° position, the movement of abduction brings the upper limb once more closer to the sagittal plane of the body.
- The final position of abduction at 180° can also be attained by flexion to 180
- Abduction combined with flexion, i.e. elevation of the arm in the plane of the scapula, at an angle of 30° in front of the frontal plane, is the most common movement
The physiology of abduction:
Role of the deltoid:
- The deltoid, active from the very start of abduction, can by itself complete the full range of abduction.
- It achieves maximal efficiency at about 90° abduction
The physiology of abduction:
The role of the rotator muscles:
o It is evident that the other muscles of the rotator cuff not only play a vital role in the deltoid-supraspinatus
o synergism but also are essential for the efficiency of the deltoid
o Preventing dislocation of the humeral head superiorly and laterally
The physiology of abduction:
The role of the supraspinatus
The supraspinatus is thus a synergism of the other muscles of the cuff of rotators.
o It is a powerful helper of deltoid
First phase of abduction: 0° to 90°
The muscles involved are essentially the deltoid and the supraspinatu
Second phase of abduction: 90° to 150°
o The shoulder is locked and abduction can only proceed with participation of the shoulder girdle
o A ‘swing’ of the scapula with anticlockwise rotation which makes the glenoid cavity face superiorly. The range of this movement is 60°.
o Axial rotation at the sterno-clavicular and acromioclavicular joints, each joint contributing a move-ment of 30°.
o The muscles involved in this second phase are: trapezius and serratus anterior
The third phase of abduction: 150° to 180°
To allow the hand to reach the vertical position once more, movement of the spinal column becomes necessary
Axial rotation of the arm:
- Rotation of the arm about its long axis can occur in any position of the shoulder
- It is a voluntary rotation taking place at joints with three axes and three degrees of freedom
Axial rotation of the arm:
Reference position:
• The position of null rotation, to measure the range of rotatory movements the elbow must be flexed to 90° with the forearm lying within a sagittal plane
Axial rotation of the arm:
Lateral rotation:
Up to 80° and falling short of 90°
Axial rotation of the arm:
Medial rotation
Up to 100°-110°
• The full range is only achieved with the forearm passing behind the trunk and the shoulder slightly extended
Movements of the shoulder girdle
- Reference position
- Forward movement of the shoulder girdle
- Backward movement of the shoulder girdle
- The muscles involved in these movements are:
- Forward movement: pectoralis major, pectoralis minor, serratus anterior
• Backward movement: rhomboids, trapezius, latissimus dorsi
Horizontal flexion and extension:
- These movements occur in the horizontal plane around a vertical axis, since they involve both the shoulder joint and the scapulo-thoracic ‘joint’
- Reference position: the upper limb is abducted 90° in the frontal plane
Horizontal flexion
In action the following muscles: o Deltoid (acromial fibres ) o Supraspinatus o Trapezius (acromial, clavicular o and tubercular fibres) o Serratus anterior
Associated with adduction, has a range of 140°
Horizontal extension
Associated with adduction, has a limited range of 30°-40°
In action the following muscles:
o Deltoid (posterolateral fibres and posteromedial fibres and to a variable numbers of lateral fibres)
o Supraspinatus
o Infraspinatus
o Teres major and teres minor
o Rhomboids
o Trapezius (all fibres including transverse fibres)
o Latissimus dorsi, acting as an antagonist-synergist with the deltoid, which cancels its important ad-ductor function
Throw
Oscillation of the upper limb which aims to give to an object a trajectory in the space.
Wind-up:
The weight is distributed on the side where the movement takes place
Loading:
Shoulder: abducted, extended and externally rotated
Muscles: supraspinatus, middle and posterior deltoid, infraspinatus and teres minor
Center the humeral head on the glenoid
Acceleration: Shoulder: rapid progress from external rotation to internal rotation Muscles: subscapularis, pectoralis major, latissimus dorsi
Deceleration:
Muscles: contraction of the external rotators
“Critical Instant” in the Overhead Throw
• Abduction, exstenction and extrarotation with the elbow above the shoulder plane
