Continuing Education: Shoulder Stability
Anatomy & Kinesiology:
The GHJ consists of the articulation of three bones: the scapula, clavicle and humerus. The
scapula has three protrusions: the coracoid, acromion and glenoid 1. These protrusions as
well as the scapula itself serve as attachment sites for the ligaments and muscles that move
and stabilise the GHJ 1. The ligaments of the GHJ, the superior, inferior and mid
glenohumeral ligaments stabilise the GHJ while the coracoacromial, and acromioclavicuar
ligaments attach to the acromion, coracoid and/or clavicle and provide stability to the scapula
2
.
1. Sternoclavicular Joint
Synovial joint that articulates with 1st rib and sternal notch.
• Elevation (4–60°)
• Depression (5–15°)
• Protraction/retraction (15°) from resting position
• Rotation (30–50° posteriorly about horizontal axis)
2. Acromioclavicular Joint
Formed by articulation of acromion process of scapula with acriomial end of clavicle
• Upward/downward rotation
• Medial (winging)/
lateral rotation)
• Anterior/posterior tilting (tipping)
3. Scapulothoracic Joint
Functional, not “true” joint, where the scapula articulates with convex rib cage.
Motions of Scapula
• Elevation/depression
• Abduction/adduction
• Medial/lateral rotation
• Upward/downward rotation
4. Glenohumeral Joint
Synovial joint where the head of humerus articulates with glenoid fossa of scapula
• Flexion/extension
• Abduction/adduction
• Internal rotation/external rotation
• Horizontal flexion/horizontal extension
There are three sets of muscles influencing stability and movement of the GHJ, the
periscapula muscles, rotator cuff, and other muscles that move the GHJ. The periscapula
muscles (rhomboids, trapezius, levator scapula, pectoralis minor, and serratus anterior)
control the positioning of the scapula 3,4. The rotator cuff (supraspinatus, infraspinatus,
subscapularis and teres minor) in combination with the long head of biceps brachii (LHBB),
surround the humeral head and provide stability and some movement at the GHJ 1. Through
their origin on the scapula they are also influenced by the function of the periscapula muscles
4
. As individual muscles, the rotator cuff assists in various movements of the GHJ 5.
Supraspinatus assists in abduction, infraspinatus and teres minor perform external rotation,
and subscapularis performs internal rotation. LHBB originate on the GHJ and insert on the
radius, assisting flexion of the GHJ 5. Other muscles contributing to strength and movement
of the joint are deltoids, pectoralis major, latissimus dorsi, triceps brachii, biceps brachii,
coracobracialis, and teres major 1,6-8.
Movement
Glenohumeral
Prime movers
Anterior deltoid
Coracobrachialis
Latissimus dorsi
Teres major
Extension
Infraspinatus
Posterior deltoid
Deltoid (mid)
Abduction
Supraspinatus
Pectoralis major
Adduction
Latissimus dorsi
Infraspinatus
External rotation
Teres minor
Subscapularis
Pectoralis major
Internal rotation
Latissimus dorsi
Teres major
Infraspinatus
Horizontal
Teres Minor
Extension
Posterior Deltoid
Coracobrachialis
Pectoralis major
Horizontal
Biceps – short head
Flexion
Anterior Deltoid
Flexion
Secondary movers
Pectoralis major
(clavicular head)
Teres minor
Triceps
Anterior/posterior deltoid
Serratus anterior
Teres major
Posterior deltoid
Anterior deltoid
Scapular
Rhomboid major/minor
Trapezius
Protraction
Serratus anterior
Trapezius (upper and
lower)
Upward rotation
Serratus anterior (upper
and lower)
Downward
Rhomboids (major/minor)
rotation
Pectoralis minor
Trapezius
Levator scapulae
Elevation
Rhomboids
Latissimus dorsi
Depression
Pectoralis minor
Retraction
Pectoralis minor
Latissimus dorsi
Scapulohumeral rhythm:
•
First
–
–
•
–
–
•
–
–
degrees of shoulder elevation involves a "setting phase":
The movement is largely glenohumeral.
Scapulothoracic movement is small and inconsistent.
degrees of shoulder elevation:
The glenohumeral and scapulothoracic joints move simultaneously.
Ratio
:
of glenohumeral to scapulothoracic movement.
degrees of shoulder elevation:
The glenohumeral and scapulothoracic joints move simultaneously.
Ratio
:
of glenohumeral to scapulothoracic movement.
You can observe scapulohumeral rhythm by palpating the scapula's position as a person
elevates the shoulder.
Helpful scapular landmarks for palpation are the base of the spine and the inferior angle.
Scapulohumeral rhythm serves at least two purposes:
1.
The muscles do not shorten as much as they would without the scapula's
upward rotation, and so can sustain their force production through a larger portion
of the range of motion.
2.
Because of the difference in size between the glenoid fossa and the humeral
head, subacromial impingement can occur unless relative movement between the
humerus and scapula is limited. Simultaneous movement of the humerus and
scapula during shoulder elevation limits relative (arthrokinematic) movement
between the two bones.
Important Force Couples:
Rotator Cuff - Deltoid
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›
›
›
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Traps – Serratus Ant
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Integrated RC – Deltoid and Scapular Force Couples
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References:
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6.
7.
8.
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stability: Biomechanical properties of passive and active stabilizers. Clinical
Orthopaedics and Related Research 330, 13 - 30 (1996).
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26, 325-37 (1998).
Paine, R. M. & Voight, M. The role of the scapula. J Orthop Sports Phys Ther 18,
386-91 (1993).
Sinnatamby, C. S. Last's Anatomy: Regional and Applied (Churchill Livingstone,
1999).
Krabak, B. J., Sugar, R. & McFarland, E. G. Practical nonoperative management of
rotator cuff injuries. Clin J Sport Med 13, 102-5 (2003).
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disease (impingement syndrome stages II and III): A treatment regimen and its
rationale. Physiotherapy Theory and Practice 14, 93 - 105 (1998).
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