of the Shoulder in Sports
The shoulder complex is very important in most athletic competition.
Shoulder movement is described as combined motions of the glenohumeral and
the scapula thoracic joint.
The joints of the shoulder complex function as a series of links, all
cooperating to maximize the range of motion available to the upper limb. A
weakened, painful or unstable link anywhere along the chain ultimately
decreases the effectiveness of the entire complex.
There are four joints within the shoulder complex. They are as follows:
The sternoclavicular joint is enclosed by a capsule and reinforced by
anterior and posterior sternoclavicular ligaments. There is a connecting
ligament between the medial end of the right and left clavicles called the
interclavicular ligament. The tissues that stabilize the sternoclavicular
joint include these three ligaments in addition a costoclavicular ligament
as well as the sternocleidomastoid, sternothyroid and sternohyoid muscles.
The acromioclavicular joint is susceptible to dislocation when landing on
the tip of the shoulder abruptly against the ground tearing the supporting
The acromioclavicular joint is the articulation between the lateral end of
the clavicle and the acromium of the scapula. The acromioclavicular joint
is surrounded by a capsule that is reinforced by superior and inferior
ligaments. These ligaments are further reinforced by the attachments of
the deltoid and trapezius muscles. The tissues that stabilize the acromioclavicular joint are the superior inferior capsular ligaments as
well as the coracoclavicular ligament. The articular disc is held in
place by the overlying deltoid and upper trapezial muscles.
The scapulothoracic joint is not a true anatomical joint but an
interfacing of two bones. The point of contact between the anterior
surface of the scapula and posterior lateral surface of the thorax is the
area of the scapulothoracic joint.
The glenohumeral joint is the articulation formed between the head of the
humerus and the concavity of the glenoid fossa. The glenohumeral joint is
surrounded by a fibrous capsule, which isolates the internal joint from
the surrounding tissue. The rotator cuff muscle (subscapularis,
supraspinatus, infraspinatus and teres minor) and the capsular ligaments
run into the fibrous capsule providing stabilization of this joint. The
long head of the biceps also contributes to stabilizing the glenohumeral
joint as well as the glenoid labrum. The glenohumeral joint capsules
receive additional reinforcement from the coracohumeral ligament.
EMG work by Dr. Basmajian revealed that vertically running muscles,
such as the biceps, triceps and middle deltoids, are not
actively involved in providing stability to the glenohumeral joint even
when significant downward traction is applied to the arm. The
supraspinatus and, to a lesser extent, the posterior deltoid provide the
secondary source of static stability.
Additionally, the normally negative intraarticular pressure within the glenohumeral joint offers a secondary source of static stability.
Experimental release of the pressure by piercing the capsule with a needle
shows to cause inferior subluxation of the humeral head, when this vacuum
pressure is disrupted.
Eight separate bursa sacs are located in the shoulder providing a buffer
to reduce frictional forces between tendons, capsule, bone, muscle,
ligaments or two muscles acting on each other.
Chronic impingement syndrome of the shoulder is common to athletes and
laborers who repeatedly abduct the shoulders over 90 degrees. Many factors
predispose the shoulder impingement syndrome. One factor is the inability
of muscles, especially the rotator cuff or the serratus anterior, to
optimally coordinate the glenohumeral joint in abduction. Additional
factors include the posture, degeneration of the rotator cuff
muscles, instability of the glenohumeral joint, and adhesions within the
joint capsule. Finally, physical
barriers such as osteophytes or bone spurs around the acromioclavicular
joint, can lead to impingement syndromes.
A study showed that individuals with chronic impingement syndrome have a
reduced upward movement of the scapula with reduced muscle activity from the serratus anterior during abduction. Slight weakness of the serratus
anterior can disrupt the normal dynamics of the shoulder. Without the
normal range of upward rotation, the acromium is more likely to interfere
with the abducting humeral head. Similarly, should the serratus
anterior be shortened, the latissimuss dorsi is usually also shortened not
allowing for elevation of the acronioclavicular joint and resulting
The supraspinatus muscle is usually the most utilized muscle of the entire
shoulder complex. In addition to assisting the deltoid during abduction,
the muscle provides dynamic and static stability to the glenohumeral
joint. The supraspinatus muscle can generate the force 20 times greater
than the load. Unfortunately, with overuse, these loads increase the rate
of tendon tears, making them more susceptible to injury.
Should you have any further questions
regarding this article, please direct your questions or comments to "Ask
the Doctor" section.
Copyright © 2004 - 2012Taras V.
Kochno, M.D. All Rights Reserved
Board Certified in
Physical Medicine and Rehabilitation