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SPORTS INJURIES REFRESHER SHOULDER JOINT THE
BY DR SIMON KAY, GP INTRODUCTION
The shoulder is the most flexible joint of the body, providing us with a wide range of motion of the upper limb as well as generating power movements like throwing, lifting and carrying. Unfortunately this mobility comes at the expense of instability and high injury potential. This article briefly reviews the anatomy and movements of the shoulder before going into a more detailed look at the diagnosis of injuries to the various soft tissue structures making up the shoulder girdle. We outline some simple assessment techniques with accompanying online video footage, showing how each structure can be assessed and differentially diagnosed.
ANATOMY OVERVIEW The shoulder, or specifically the gleno-humeral (GH) joint, is one of five joints that make up the shoulder girdle. These joints are as follows: 1) gleno-humeral joint 2) acromioclavicular (AC) joint 3) coracoclavicular joint 4) scapulothoracic joint 5) sternoclavicular joint The neutral position of the shoulder is with the arm at the side of the chest, neither externally nor internally rotated. Note that this isn’t the anatomical position (in which the shoulder is positioned in full external rotation).
SHOULDER MOVEMENTS Movement of the shoulder occurs in six ‘basic’ directions: flexion and extension (sagittal plane), abduction/adduction (coronal plane), and internal and external rotation (around axis of the humerus). The seventh movement is a ‘multiple’ movement called circumduction, which is a combination of all six ‘basic’ movements. Rotation occurs primarily at the GH joint, the other
movements involve multiple joints in the shoulder depending on the degree of angulation from the vertical. For example during abduction:
n from neutral to 25-30 degrees, the majority of the movement is at the GH joint n from 30-90 degrees the movement is 2:1 ratio of GH movement to scapula-thoracic movement
SHOULDER JOINT
ASSESSMENT AND DIAGNOSIS
n after 90 degrees of abduction the clavicle comes into play with the AC joint and sterno-manubrial movement to achieve 180 degrees of abduction n from 150 degrees onwards and greater than 180 degrees, abduction/flexion is achieved with some thoracic rotation at T1-3.
Observation from behind the patient demonstrates some of the changes in joint movements well.
MUSCLE MOVEMENTS Different muscle groups are involved in movement of the shoulder. Movement can roughly be divided into two gross areas:
1. Rotator cuff (RC) – the contractor/stabilising muscles of supraspinatus (SS), infraspinatus (IS), teres minor, and subscapularis (SSc)) (see Video 1) 2. Primary movers (PM) – pectoralis major, latissimus dorsi, deltoid, teres major,
pectoralis minor, biceps and triceps.
These muscles act mostly in a concentric/eccentric fashion, to move the humerus.
The RC muscles lie close to the joint and surround it like an incomplete sleeve. Their job is to hold the humerus head against the glenoid fossa thus maintaining stability during shoulder movements. The rotator cuff muscles are covered by the prime movers and act in a slow twitch contraction/ isometric fashion, pulling the head of the humerus into the glenoid fossa, allowing the PM muscles to move the head of the humerus. The RC muscles shorten as the tendon is pulled medially under the acromium of the scapula. Rotation is effected by the rotator cuff with infraspinatus being responsible for external rotation and the subscapularis muscle responsible for internal rotation, in a concentric/ eccentric fashion (see Video 1).
online
Video 1: Animation showing the movement of the GH joint and the action of the rotator cuff muscles (credit to YouTube user sanjuananestesia)
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