Glenohumeral Joint

Function:

The glenohumeral joint is a ball-and-socket joint that allows for the arm to move in a circular rotation as well as movement of the arm towards and away from the body. The motion that the glenohumeral joint provides is flexion, extension, abduction and adduction. For images of these movements, see http://www.exrx.net/Articulations/Shoulder.html#anchor105322 (1).

Bones:

The glenohumeral joint is a ball-and socket joint that is formed between two bones, the humerus and the scapula. The humerus head, acting as the ball, fits into the end of the scapula known as the glenoid, the socket. In this specific joint, the humerus head, however, does not fit perfectly within the glenoid because the humerus head is much larger than the surface area of the glenoid socket. This size discrepancy creates a situation where the two bones do not snugly fit together without the help of other physical structures. Thus this joint is dependent upon other structures for stability (2).

Cartilage:

The most important piece of cartilage is the labrum, otherwise descibed as the articular cartilage. The labrum is a piece of cartilage that lies directly between the the humerus head and the glenoid. This piece of cartilage provides a smooth surface that allows for the humerus head to rotate with minimal friction, thus cushioning both the humerus and the scapula. Also, the labrum is shaped like a ring, with the outer part of the labrum being much thicker than the center of the ring. This specific shape allows for the labrum to fit against the humerus head and the glenoid, physically matching up the larger humerus head with the small surface of the glenoid. Thus the labrum is also very important for the stabilization of the joint (3).

http://www.athleticadvisor.com/Injuries/UE/Shoulder/shoulder.htm

Muscles:

Rotator Cuff

The main muscles that are used in conjunction with the glenohumeral joint are the group of muscles known as the rotator cuff. The rotator cuff is made up of four muscles, the supraspinatus, subscapularis, infraspinatus, and teres minor. All four of these muscles connect the scapula to the humerus. One main purpose of the rotator cuff muscles is to pull the humerus into the scapula such that the two bones are fitted tightly against one another. Thus rotator cuff muscles are important for stabilizing the glenohumeral joint. Strengthening of the rotator cuff helps prevent further instability and repeat damage after the shoulder has dislocated. The other important role of the rotator cuff is to help with movement of the arm, particularly the rotation of the arm. The supraspinatus helps with abduction of the arm, and is particularly susceptible to injury during flexion and abduction of the arm (4).

http://www.medicalmultimediagroup.com/pated/shoulder_problems/cufftearold.html

Ligaments:

In addition to the labrum and the rotator cuff muscles, other structures exist that help with the stabilization and movement of the joint. There are four ligaments that help with the glenohumeral joint. These ligaments are the coracohumeral ligament (between the coracoid process and the humerus) and the three glenohumeral ligaments (between the glenoid and the humerus) (5).

from: http://biomed.brown.edu/Courses/BI108/BI108_2004_Groups/Group01/bioghj.htm

 

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Joint Structures:

• Coracohumeral ligament
  • elongates with and limits external rotation.
  • Anterior band elongates with and limits GH EXTENSION
  • Posterior band elongates with and limits GH FLEXION
  • image of coracohumeral ligament (Palmer & Blakely, 1986)

• Glenohumeral ligament
  • Once the glenohumeral joint joint is externally rotated, this ligament elongates with and limits abduction.
  • sagittal plane image of glenohumeral joint capsule (Culham & Peat, 1993) showing bands of glenohumeral ligament: SGHL – SUPERIOR GLENOHUMERAL LIGAMENT
    MGHL – MIDDLE GLENOHUMERAL LIGAMENT
    IGHL – INFERIOR GLENOHUMERAL LIGAMENT
• Transverse humeral ligament
  

  depicted in blue in figure to right crosses the bicipital groove and contains the tendon of the long head of the biceps brachii within the groove (Hertling & Kessler, 1996, Fig. 9-7, pp.169-170)

• Subacromial region
  • a region that lies superior to the humeral head
    and inferior to the acromion process and the coracoacromial ligament
  • location of subacromial/subdeltoid bursae and supraspinatus tendon
  • image of subacromial region in frontal plane

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Arthrokinematics of the glenohumeral joint
during glenohumeral abduction:

• Convex humeral head rolls upward and glides downward on scapula’s concave glenoid fossa.
• Humerus’ greater tubercle will impinge on the coracoacromial ligament or the acromion process unless the humerus externally rotates.
• Forces that guide the arthrokinematics:
  1. glenohumeral ligament
  2. rotator cuff muscles

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Close-packed positions of the GH joint:

1. horizontal abduction and external rotation (Hertling & Kessler, 1996)
2. flexion and internal rotation (Culham & Peat, 1993)

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References

Culham, E. & Peat, M. (1993). Functional anatomy of the shoulder complex. Journal of Orthopedic and Sports Physical Therapy, 18, 342-350.Hertling, D., & Kessler, R. M. (1996). Management of common musculoskeletal disorders: Physical therapy principles and methods. (3rd ed.). Philadelphia: J.B. Lippincott.

Palmer, M. L. & Blakely, R. L. (1986). Documentation of medial rotation accompanying shoulder flexion. A case report. Physical Therapy, 66, 55-58.

from:  http://moon.ouhsc.edu/dthompso/namics/gh.htm#struct

Shoulder Articulations

Glenohumeral
Flexion Bending the joint resulting in a decrease of angle; moving the upper arm upward to the front. Deltoid (anterior) Deltoid (lateral) Pectoralis major (clavicular head) Coracobrachialis Biceps brachii (short head)
Extension Straightening the joint resulting in an increase of angle; moving the upper arm down to the rear. Latissimus dorsi Deltoid (posterior) Pectoralis major (sternal head) Teres major Triceps brachii (long head)
Adduction Medial movement toward the midline of the body; moving the upper arm down to the side toward the body. Latissimus dorsi Pectoralis major (sternal head) Pectoralis major (clavicular head) Teres major Coracobrachialis Triceps brachii (long head)
Abduction Lateral movement away from the midline of the body; moving the upper arm up to the side away from the body. Deltoid (lateral) Deltoid (anterior) Supraspinatus Pectoralis major (clavicular head)
Transverse Adduction Medial movement toward the midline of the body in a horizontal plane; moving the upper arm toward and across the chest with the back of the arm facing down. Pectoralis major (sternal head) Pectoralis major (clavicular head) Coracobrachialis
Transverse Flexion Medial movement toward the midline of the body in a horizontal plane; moving the upper arm toward and across the chest with the elbows facing out to the sides. Pectoralis major (sternal head) Pectoralis major (clavicular head) Deltoid (anterior) Coracobrachialis Biceps brachii (short head)
Transverse Abduction Lateral movement away from the midline of the body in a horizontal plane; moving the upper arm away from the chest with the elbows facing down. Deltoid (posterior) Deltoid (lateral) Infraspinatus Teres minor
Transverse Extension Lateral movement away from the midline of the body in a horizontal plane; moving the upper arm away from the chest with the elbows out to the sides. Deltoid (posterior) Latissimus dorsi Infraspinatus Teres minor
Medial Rotation (Internal Rotation) Rotary movement around the longitudinal axis of the bone toward the center of the body; turning the upper arm inward. See shoulder internal rotation inflexibility. Pectoralis major (sternal head) Pectoralis major (clavicular head) Latissimus dorsi Deltoid (anterior) Subscapularis Teres major
Lateral Rotation (External Rotation) Rotary movement around the longitudinal axis of the bone away from the center of the body; turning the upper arm outward. See shoulder external rotation inflexibility. Teres minor Infraspinatus Deltoid (posterior)

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