Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Shoulder and Upper Arm

Shoulder motion

Shoulder motion is guided by the integrated motion of several joints such as the sternoclavicular, acromioclavicular, scapulothoracic, and glenohumeral joints.
– The glenohumeral joint is the main shoulder joint, comprising the head (ball) of the humerus and the glenoid (socket) of the scapula (shoulder blade). The surrounding capsule is loosely applied and allows a
wide range of movements. The articular surface of the socket is enhanced by the glenoid labrum, which is an extension of the joint that increases its stability.
– The sternoclavicular joint is the joint between the clavicle (collar bone) and the sternum (breast bone).The joint is surrounded by the joint capsule and strong ligaments.
– The acromioclavicular joint is the joint between the clavicle and the scapula. The clavicle is a rather flattened and elongated S-shaped bone and is connected by strong ligaments to the scapula.
– The scapulothoracic joint is a pseudojoint (it acts like a joint) where the scapula moves against the rib cage.

The total range of motion of the shoulder is extensive because the shoulder joint itself has a shallow socket and a loose capsule. The arm is allowed to move from 0° to 180° of elevation and for approximately 150° of internal and external rotation. Anterior and posterior rotation in the horizontal plane is about 170°. Twenty-six muscles are required to control the various joints for optimal shoulder function.

Shoulder stability

The shoulder is a lax joint with great mobility; it is mainly the muscles and tendons of the rotator cuff that are responsible for stability.

Static stability

The shoulder does have some static stability from capsular ligaments, the articular components, negative intra-articular pressure, and the glenoid labrum.
The capsular ligamentous complex consists of the superior, middle, and anterior and posterior inferior glenohumeral ligaments, as well as the coracohumeral ligaments.

1. The superior glenohumeral ligament is present in approximately 90% of shoulders. It originates on the glenoid (shoulder socket) anterior to the tendon of the long head of the biceps and courses inferior and
lateral to insert on to the lesser tuberosity, which is located on the lateral aspect of the humerus. This ligament resists inferior translation of the humeral head with the humerus at the side of the body.

2. The middle glenohumeral ligament is present in 70% of shoulders and courses from the labrum to insert medially to the lesser tuberosity under the subscapularis tendon. This ligament protects against
instability by acting as a secondary restraint to anterior translation.

3. The inferior glenohumeral ligament is present in 90% of shoulders, and consists of an anterior and a posterior band. The origin is on the inferior half of the glenoid labrum and the insertion is on the humerus. This ligament provides most of the stability, especially when the shoulder is abducted (moved out from the body) and externally rotated.

4. The coracohumeral ligament originates from the coracoid process, blends into the capsule and attaches onto the humerus. This ligament is put in tension in external rotation and resists inferior subluxation to the joint.

The effects of articular geometry are limited. The concavity of the glenoid, however, when combined with a compressive force, does provide significant stability of the humeral head.

The negative intra-articular pressure at rest is −4 mmHg (−0.5 kPa). A 52% increase in the humeral head translation (anterior-posterior motion) after incision of the capsule has been documented.

The stability of the glenohumeral joint is enhanced by the glenoid labmm, which is a fibrous structure that forms a ring around the periphery of the glenoid and provides an anchor point on the glenoid for
the capsular ligaments. The labrum attaches to the glenoid articular surface. It contributes to glenohumeral stability by increasing the depth of the glenoid socket. Loss of the glenoid labrum decreases
the depth of the socket by 50% in either direction. The labrum also contributes to stability by increasing the surface area of the glenoid and acting as a loadbearing structure for the humeral head. The labrum is consistently attached tightly to the glenoid articular cartilage below the equator, and, therefore, detachment in this area is more likely to represent instability.

The rotator interval is the triangular region between the anterior border of the supraspinatus tendon and the upper border of the subscapularis tendon. An injury to the capsular structures in the rotator interval area of shoulder may result in instability.

Dynamic stability

Dynamic stability is provided by the muscles around the shoulders. The rotator cuff is the key to dynamic glenohumeral stability. The supraspinatus muscle tendon plays a major stabilizing role, as exemplified by the throwing movement; peak supraspinatus activity occurs during late cocking when the arm is already abducted and is most susceptible to subluxation. The supraspinatus contributes to stability by drawing the humeral head toward the glenoid.

The infraspinatus and teres minor muscles are activated after the supraspinatus and they externally rotate
the humerus in addition to stabilizing the shoulder by joint compression. The peak activity is shown to be in late cocking and follow-through phases of the throwing motion.
The subscapularis muscle is active during the late cocking phase of throwing to protect the anterior shoulder structures. Thereafter, it functions as an internal rotator during acceleration and follow-through.
The long head of the biceps tendon is activated during shoulder flexion and abduction. It acts as a humeral head depressor. The pectoralis major and latissimus dorsi muscles are internal rotators of the glenohumeral joint. The trapezius muscles act as an important scapular stabilizer and also decelerate scapular protraction during follow-through.

The deltoid muscle functions in three sections. The middle deltoid participates in all arm activities. The anterior deltoid acts in flexion and is assisted by the pectoralis major and biceps. The posterior deltoid provides extension of the arm.

Investigation of shoulder and upper arm injuries

History

Thorough history-taking is the key to correct diagnosis. This involves asking the correct questions—and more importantly—giving the athlete adequate time to answer. The physician must listen carefully to the answers and also watch the patient during the interview to obtain clues through body language. The primary questions should focus on the following areas.

What happened? This is particularly important in acute traumatic injuries. If the athlete can recreate the mechanism of injury, a general biomechanical analysis can indicate which tissues were abnormally stressed. The more detail that the athlete can recall, the better the cause and mechanism of the injury can be recreated to point to the injured structure.
Where does it hurt? The best way to approach this is to have the injured athlete place one finger on the most painful area. Sometimes this can be difficult because the pain may be deep and/or diffuse.
What is the nature of the pain? Burning pain that radiates down the extremity can indicate nerve pain. Throbbing pain can indicate pain of vascular origin. Pain of brief duration that disappears quickly can indicate possible mechanical problems from tissues rubbing or locking together. Dull, aching pain is more likely to be caused by chronic overuse problems.
What makes it better or worse? Activities that can change the course of the pain can give clues to the diagnosis. For example, stress fractures will become worse with prolonged activity, and injuries that respond well to anti-inflammatory medications are probably due to inflammatory processes.
Has the athlete been injured before? Often injuries are recurrences of previous problems, or can be related to changes in training habits from previous injury.
What treatments have been used, and did they help? Perhaps the treatment has exacerbated the injury rather than relieved it.
What other health problems are present, and what medications are used? Many musculoskeletal problems are due to disease and not injury. Many times these diseases will have other associated problems that the patient believes are unrelated to the musculoskeletal injury. Finally, all medicines have sideeffects, which can sometimes affect the musculoskeletal system.

Physical examination
Both shoulders should be exposed for comparison. Lost range of motion, muscle hypotrophy, bone deformity, and shoulder asymmetry should be looked for. A prominent scapular spine suggests rotator cuff
hypotrophy, which may indicate a rotator cuff tear or a suprascapular nerve lesion. Deltoid hypotrophy can be noted in association with axillary nerve lesions or fracture.

Range-of-motion testing

Range of motion should be examined in both the upright and the supine positions. The examination includes assessment of total range and rhythm of motion, as well as pain at the limits of motion. To determine total active elevation, the arm is observed from the side, and the angle between the arm and the chest is measured. Evaluation of external and internal rotation is important. Abduction (moving the arm from the body) can give useful information relating to impingement and strength. Pain between 80° and 120° of abduction is a reliable indicator of tendinitis due to impingement. This is called the ‘painful arc’.

Strength testing

The strength of forward flexion, abduction, adduction, and external and internal rotation should be documented. The strength is decreased in abduction and external rotation when there is rotator cuff disease. Specific testing of the supraspinatus is performed by abducting the athlete’s arm to 90°, then forward flexing 20°, and maximal rotation of the arm internally into the thumb-down position. Muscle strength in this position is a test of the supraspinatus and a small portion of the central deltoid. This is an important test, since rotator cuff tears usually involve the supraspinatus.
The muscles providing external rotation are the infraspinatus and teres minor. External rotation (strength) is assessed with the arms at the side in a neutral position; resistance is applied and compared with the
opposite side. Internal strength is a test of subscapular strength.

Stability testing

The apprehension test, relocation test and drawer stability test are essential procedures, described under the injury concerned.

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