BIOMECHANICS & KINESIOLOGY OF GLENOHUMERAL JOINT.pptx

This is a ball and socket type synovial joint with 3° of freedom.
The GH Joint has sacrificed congruency to serve mobility needs of hands.
The articulation is made up of the large head of the humerus and small glenoid fossa.
The glenoid fossa at scapula serves as the proximal articular surface for this joint.
The fossa may be tilted slightly upward or downward when the arm is at the side, although commonly show a slight upward tilt.
The distal articular surface that is larger than that of proximal segment forming 1/3rd to one half of sphere.
Generally, the head faces medially, superiorly and posteriorly with respect to the shaft of humerus

1. BIOMECHANICS OF GLENOHUMERAL JOINT DR. NIDHI SHUKLA

2. CONTENTS Introduction Anatomical contents of the joint Angles in GH joint Glenoid Labrum GH joint capsule GH joint Ligaments Rotator cuff muscles Bursae Coracoacromial arch Muscles at the Shoulder joint

3. INTRODUCTION This is a ball and socket type synovial joint with 3° of freedom. The GH Joint has sacrificed congruency to serve mobility needs of hands. The articulation is made up of the large head of the humerus and small glenoid fossa. The glenoid fossa at scapula serves as the proximal articular surface for this joint. The fossa may be tilted slightly upward or downward when the arm is at the side, although commonly show a slight upward tilt. The distal articular surface that is larger than that of proximal segment forming 1/3 rd to one half of sphere. Generally, the head faces medially, superiorly and posteriorly with respect to the shaft of humerus.

4. ANATOMICAL ASPECT OF JOINT The glenohumeral joint is the most freely moving joint in the human body, enabling flexion, extension, hyperextension, abduction, adduction, horizontal abduction and adduction, and medial and lateral rotation of the humerus. The almost hemispherical head of the humerus has three to four times the amount of surface area as the shallow glenoid fossa of the scapula with which it articulates. The glenoid fossa is also less curved than the surface of the humeral head, enabling the humerus to move linearly across the surface of the glenoid fossa in addition to its extensive rotational capability.

5. ANGLES IN GH JOINT ANGLE OF INCLINATION- The axis through the humeral head of shaft and longitudinal axis of shaft of the humerus may form an angle of 130°-150° in the frontal plane. This is known as Angle Of Inclination. ANGLE OF TORSION- This is an angle formed between the axis through the humeral head on the axis through the humeral condyles. This angle is about 30° posteriorly. The normal posterior portion of the humeral head with respect to the humeral condyles may be termed posterior torsion or retro-torsion of humerus.

6. Figure A. The normal angle of inclination (the angle between the humeral head and the shaft) varies between 130 and 150. B. The humeral head is normally angled posteriorly approximately 30 (angle of torsion) with regard to an axis through the humeral condyles. ANGLES IN GH JOINT

7. GLENOID LABRUM The glenoid fossa is encircled by the glenoid labrum, a lip composed of part of the joint capsule, the tendon of the long head of the biceps brachii, and the glenohumeral ligament. The total available articular surface of the glenoid fossa is enhanced by an accessory structure known as glenoid labrum . This is attached to the periphery of the glenoid fossa enhancing the depth or curvature of fossa. Superiorly, the labrum is attached loosely. Inferior portion is firmly attached and immobile.

8. GH JOINT CAPSULE The entire GH joint in resting position is surrounded by a large, loose capsule that is taut superiorly and slack anteriorly and inferiorly. The capsular surface area is twice that of the humeral head and when slack allows more than 1 inch of distraction of head from glenoid fossa in loose pack position. When humerus is abducted and laterally rotated on glenoid, the capsule twists on itself and tightens, making abduction and lateral rotation the closed pack position for the GH joint. Several ligaments merge with the glenohumeral joint capsule, including the superior, middle, and inferior glenohumeral ligaments on the anterior side of the joint and the coracohumeral ligament on the superior side. The tendons of four muscles also join the joint capsule. These are known as the rotator cuff muscles because they contribute to rotation of the humerus and because their tendons form a collagenous cuff around the glenohumeral joint.

9. GH JOINT LIGAMENTS The capsule is reinforced by three glenohumeral ligaments (Superior, Middle, Inferior ) and a coracohumeral ligament. However, a thin area of capsule between the superior and middle GH ligament known as “Foramen of Weibrecht” is a point of weakness in the capsule in spite of anterior reinforcement by Subscapularis tendon. It is common site of extrusion of humeral head with anterior dislocation of the joint. The Coracoacromial ligament originates from the coracoid process as two bands. The first band insert into the edge of the supraspinatus and onto the greater tubercle where it joins the superior GH ligament. The other band inserts into the subscapularis of the lesser tubercle. The two band forms a tunnel through which the tendon of biceps passes

10. ROTATOR CUFF MUSCLES The tendons of four muscles also join the joint capsule. These are known as the rotator cuff muscles because they contribute to rotation of the humerus and because their tendons form a collagenous cuff around the glenohumeral joint. These include supraspinatus, infraspinatus, teres minor, and subscapularis, and are also sometimes referred to as the SITS muscles after the first letter of the muscles’ names. Supraspinatus, infraspinatus, and teres minor participate in lateral rotation, and subscapularis contributes to medial rotation. The muscles of the lateral rotator group exchange muscle bundles with one another, which increases their ability to quickly develop tension and functional power. The rotator cuff surrounds the shoulder on the posterior, superior, and anterior sides. Tension in the rotator cuff muscles pulls the head of the humerus toward the glenoid fossa, contributing significantly to the joint’s minimal stability. The rotator cuff muscles and the biceps develop tension to provide shoulder stability prior to motion of the humerus. Negative pressure within the capsule of the glenohumeral joint also helps to stabilize the joint. The joint is most stable in its close-packed position, when the humerus is abducted and laterally rotated.

11. BURSAE AT GH JOINT Out of several bursae the most important are the subacromial or subdeltoid bursae. These bursae separates the supraspinatus tendon and head of humerus from the acromion, coracoid process, coracoacromial ligament and deltoid muscle. The bursae may be separate or continuous with each other. Collectively the two are known as sub acromial bursa the permits a smooth gliding of supraspinatus tendon and head of humerus under the deltoid muscle and acromion process. The inferior wall of bursa is continuous with the superior portion of the supraspinatus tendon sheath. Sub acromial bursitis is most commonly secondary to the inflammation or degeneration of the supraspinatus tendon.

12. The subscapularis and sub-coracoid bursae are responsible for managing friction of the superficial fibers of the subscapularis muscle against the neck of the scapula, the head of the humerus, and the coracoid process. In 28% of studied cases, these two bursae physically merge into a single wide bursa. Given that the subscapularis undergoes significant changes in orientation during movements of the arm at the glenohumeral joint, especially where the upper portion of the muscle coils around the coracoid process, the role of these bursae is important. The subacromial bursa lies in the subacromial space, between the acromion process of the scapula and the coracoacromial ligament (above) and the glenohumeral joint (below). This bursa cushions the rotator cuff muscles, particularly the supraspinatus, from the overlying bony acromion. The subacromial bursa may become irritated when repeatedly compressed during overhead arm action

13. CORACO-ACROMIAL ARCH The coracoacromial or (supra-humeral arch) is formed by the coracoid process, the acromion process and the coracoacromial ligament that spans the 2 bony projections. The arch forms an osteo-ligamentous vault that covers the humeral head and forms the space within which the subacromial bursa, the supraspinatus tendon and a portion of the tendon of long head of the biceps lie. It also protects the structure we need from direct trauma from above. This also prevents the head of humerus from dislocating superiorly, when an upward translatory force applied on the humerus would cause the head of humerus to hit the coracoacromial arch. The impact of the humeral head into the arch simultaneously can cause painful impingement when this space is narrowed and the likelihood of supraspinatus tendon and sub acromial bursa increases.

14. MUSCLES AT THE GH JOINT Many muscles cross the glenohumeral joint. Because of their attachment sites and lines of pull, some muscles contribute to more than one action of the humerus. A further complication is that the action produced by the development of tension in a muscle may change with the orientation of the humerus because of the shoulder’s large range of motion. With the basic instability of the structure of the glenohumeral joint, a significant portion of the joint’s stability is derived from tension in the muscles and tendons crossing the joint. However, when one of these muscles develops tension, tension development in an antagonist may be required to prevent dislocation of the joint.