BONES FORMING THE SHOULDER JOINT

1) Humerus Proximal Tip:

Caput consists of large-small tubercles and neck-spinal groove. ANATOMIC NECK/COLLUM ANATOMICUM, which is parallel to the humeral head and connects the humeral head to the tubercles, and SURGICAL NECK/COLLUM CHIRURGICUM, which is just below the tubercles.
Retroversion angle: It is the angle between the imaginary axis drawn from the humeral head and the imaginary axis drawn from the epicondyles and is approximately 30 degrees. When the shoulder is externally rotated, it prevents the humerus from coming out of the glenoid cavity, that is, it provides the stability of the humerus.
Angle of inclination: It is the angle between the imaginary axis drawn from the humeral head and the humeral shaft and is approximately 135-145 degrees.

2) Scapula:

It contains important structures such as spina scapula, acromion, glenoid fossa and coracoid process. It is between the 2nd and 7th ribs.
Glenoid inclination: Two lines are drawn from the lateral of the coracoid process and between the upper and lower processes of the glenoid, and the angle between is 4 degrees. If the angle is negative, it indicates that it returns to the glenoid inferior, and if it is positive, it indicates that it returns to the superior. Its clinical importance is that if the glenoid turns superior, it narrows the subacromial space accordingly. The incidence of ROTATOR Cuff MUSCLE REAR may be increased.

3) Clavicle:

It is a curved bone in the shape of the letter S and can be palpated on the skin. It has convex and concave faces. It has protraction, retraction, elevation and depression movements.

4) Sternum:

It consists of manubrium, corpus and xiphoid process. It is the middle point of the rib cage. It articulates with the clavicle and costae.

JOINTS THAT FORM THE SHOULDER COMPLEX AND RELATED LIGAMENTS+MUSCLES

1) GLENOHUMERAL JOINT:

It is the synovial joint between the humeral head and the glenoid fossa of the acromion.
*It is the joint with the widest range of motion in the shoulder complex.
*While this joint increases its range of motion, it makes it vulnerable to trauma.
* It is the most dislocated joint.
* Injuries are most commonly caused by falling on the abducted arm.
* Stabilization of the joint is important. This is provided by ligamentous structures and muscles.

》Ligamentous Structures That Provide Glenohumeral Joint Stability:

*Glenohumeral Labrum: Attaches to the edges of the glenoid fossa. Increases the depth of the joint surface by 50%.
*Coracohumeral Ligament: It connects the humeral head to the coracoid process of the scapula. It provides tension and stability when the arms are at the side. It is the strongest ligament that supports the glenohumeral ligament.
*Superior Glenohumeral Ligament: It is in the anterior of the shoulder. It follows the long head of the biceps muscle. It limits the external rotation and adduction of the humerus. It provides stability in the inferior direction in abduction up to 50 degrees.
*Middle Glenohumeral Ligament: It continues under the subscapularis muscle. It is the anterior stabilizer and limits the external rotation in movements up to 90 degrees.
*Inferior Glenohumeral Ligament: It attaches to the labrum. It is the main stabilizer in the neutral position and limits the elevation.

》The Muscles That Provide Glenohumeral Joint Stability

The glenohumeral joint is controlled by 12 muscles.

1) Superficial Group:

*M.Deltoideus: It starts from the clavicle, acromion and spina scapula and ends by attaching to the tuberositas deltoidea. Its primary function is abduction up to 90 degrees. It is innervated by the nerve axillaris (C5-6).

*M.Pectoralis Major: It has clavicular and sternal parts. The clavicular part is important for the shoulder complex. The inner side of the clavicle starts from the sternum and 1-6th ribs and ends by attaching to the crista tuberculi majoris. It is innervated by the lateral and medial pectoral nerves. rotation is its primary task. It adducts the arm and helps with inspiration.

*M.Corocobrachialis: It starts from the coracoid process and ends by attaching to the humerus shaft. It is innervated by the N. Musculokutaneus (C5-6). It makes the arm flexion and adduction.

*M.Biceps Brachii: Short head; long head from proc.coracoideus; starts from tub.supraglenoidale. They end by attaching to tuberositas radii with common tendon. Innervated by N. Musculocutaneus(C5-6). Flexion and supination of forearm, arm. The long head is important for stability in the shoulder complex.

2)Deep Group:

*Rotator Cuff Muscles:
》M. Supraspinatus: It starts from the fossa supraspinata and ends by attaching to the tuberculum majus humeri. It is innervated by the N. Suprascapularis (C5-6). Besides providing the stabilization of the shoulder joint, it initiates the first 15-degree abduction of the arm.

》M. Infraspinatus: It starts from the fossa infraspinata and ends at the tuberculum majus humeri. It is innervated by the N. Suprascapularis (C5-6). External rotation of the arm is the primary mover task.

》M. Teres Minor: It starts from the upper 2/3 of the lateral edge of the scapula and ends at the tuberculum majus humeri. It is innervated by the N. Axillaris (C5-6). It makes the arm externally rotated.

》M. Subscapularis: It starts from the fossa subscapularis and ends at the tuberculum minus humeri. It is innervated by the N. Subscapulares (C5-6). It is the primary mover muscle that makes the arm internally rotate.

3) Peripheral Group:

*M.Pectoralis Major: In the tongueeripheric group, its sternal part is important in stabilizing the shoulder complex.

*M. Latissimus Dorsi: The proc.spinosus of the last 6 thoracic and chymbal vertebrae, crista iliaca, attaches to the 8th-12th ribs and ends in the crista tuberculi minor. It is innervated by N. Thoracodorsalis. It makes the arm adduction and internal rotation (primary mover function).

2) STERNOCLAVICULAR Joint

It is the synovial type joint between the clavicle and the manbrium.
* Ligaments and capsule structure provide joint stabilization. THERE IS NO MUSCLE DIRECTLY AFFECTING THIS JOINT.

It is the only joint where the shoulder connects the body with the bone.

》Ligaments Involved in Sternoclavicular Joint Stability:

*Articular Disc: Located in the joint cavity and absorbs shock.
*Interclavicular Ligament: It joins the medial ends of the two clavicles, thus creating a traction force between the clavicles.
*Costaclavicular Ligament: It is located between the medial edge of the clavicle and the first rib. While providing stabilization in these two structures, it limits the superior shift and elevation of the clavicle.
*Sternoclavicular Ligament: The anterior part wraps the clavicle and sternum anteriorly and limits the clavicle to go anteriorly.

3)ACROMIOCLAVICULAR JOINT:

It is the synovial type joint between the distal end of the clavicle and the acromion of the scapula.
*The humeral is located on the top of the head and limits the mobility of the humerus in overhead activities.
*Transfers the upper extremity forces to the clavicle and then to the trunk.

Most injuries occur as a result of a blow from the lateral arm while the shoulder is adduction.

》Ligaments that provide the stability of the acromioclavicular joint:

*Acromioclavicular Ligament: It has 4 sections. These are anterior, posterior, superior and inferior. The strongest of them are superior and posterior parts. It provides horizontal stability of the joint. It works synergistically with the coracoclavicular ligament. In addition, deltoid and trapezoidal muscle fibers support the superior part, thus increasing joint stabilization.
*Corococlavicular Ligament: Trapezoidal ligament part provides stability against posterior forces, conoid ligament part prevents anterior-superior displacement and rotational forces. It provides vertical stability and works synergistically with acromioclavicular ligament.
*Coracoacromial Ligament: It contributes to the provision of vertical stability. As the supraspinatus and deltoid muscles abduct, it limits the movement of the humeral head in the glenoid fossa.

4) SCAPULATORASIC JOINT:

* It does not form a joint in the real sense, therefore it is physiological.
*If the movements of this joint are not coordinated, the Glenohumeral ligaments will be overloaded.
* Stabilization provides muscles.

》Muscles Involved in Scapulothoracic Joint Stabilization:

*Scapulasic muscles: They provide smooth scapular movement.
*Scapulohumeral muscles: Dynamic stabilizers of the glenohumeral joint.
1)M.Trapeze:Occiput,lig.nuchae etc. It starts from the C7-T12 vertebra proc.spinosus and ends by attaching to the clavicula, acromion and spina scapula. It is innervated by N.Accessorius(cranial 11). It makes the scapula adduct and elevate.
2)M.Pectoralis Minor: It starts from 2-5 ribs and ends by attaching to proc.coracoideus. It is innervated by the lateral and medial pectoral nerves. It makes the scapula protraction and depression movement.
3)M.Levator Scapula: It starts from the proc.transversus of the first 4 neck vertebrae and inserts into the upper corner of the medial edge of the scapula. It is innervated by the N. Dorsalis Scapula. It makes the neck lateral flexion while elevating the scapula.
4)M.Rhomboid:Major and minor muscles.It starts from Lig.Nuchae and C7-T5 proc.spinosus and ends by attaching to the inner lateral edge of the scapula and is innervated by N.Dorsalis Scapula.Scapular adduction is the primary mover task.
5) M. Serratus Anterior: It starts from the 2-9 ribs. It ends at the inner lateral edge of the scapula. It is innervated by N. Thoracisus Longus. Upward rotation of the scapula is the primary mover’s duty. It plays a role in shoulder abduction above 90 degrees. If this muscle is weak, the WING SCAPULA develops.

SCAPULOHUMERAL RHYTHM

The joint movement of the scapulohumeral joint and the glenohumeral joint is called the scapulohumeral rhythm. In activities above 30 degrees, 2 degrees of glenohumeral joint movement is required for every 1 degree of scapulohumeral joint movement.
While 180 degrees of total shoulder flexion is 120 degrees of glenohumeral movement, 60 degrees is scapular movement. Glenohumeral and scapular movements work synchronized after 60 degrees and up to 150 degrees.