Shoulder Range of Motion
The shoulder joint has the greatest range of motion of any other joint in the body. Due to the uniqueness of the joint design, a healthy individual should be able to freely move their shoulder in eleven planes — flexion, extension, neutral and horizontal abduction, neutral and horizontal adduction, neutral and horizontal internal rotation, neutral and horizontal external rotation, and circumduction.
Movement at the shoulder joint, however, is much more complicated than simple movement in the one joint. To see just how involved shoulder movement is first requires a look at the anatomy of the shoulder complex of bones and joints.
Anatomy of the Shoulder
The bony architecture of the shoulder consists of the shoulder blade and acromion in a single unit, the clavicle, and the humerus. The head of the humerus sits in a hollowed indentation in the edge of the shoulder blade called the glenoid fossa. The humerus is held in place by tiny, loosely fitted ligaments attached to the edge of the fossa. Because the glenoid is considerably shallower than a true ball-and-socket joint, a small cup made of cartilage gives the joint a slightly larger socket, called the labrum (not shown).
The most fascinating thing about the shoulder is that the entire complex has no direct, stable, connection to the axial skeleton. Rather, most of the bones just float on muscles and fascia covering and attaching to the spine, ribcage and humerus. The single attachment point is at the acromioclavicular joint (ACJ), where a small ligament connects the acromion to the outer end of the collarbone, known as the clavicle.
Because of this lack of axial strength, stability of the shoulder joint and shoulder range of motion relies on the muscles of the rotator cuff and shoulder girdle, ligaments, fascia, and the joint capsule.
However, the extraordinary range of motion in arcs of movement require that the very structures which give the joint stability also give it flexibility as well. The distinction works out to be a fine line. Too lax and the joint becomes hypermobile. Too tight and it becomes hypomobile. Both dysfunctional amounts of tension result in range of motion problems.
Altogether, eighteen muscles control the movement and stability of the shoulder, with the primary stabilizers being the four rotator cuff muscles, supraspinatus, infraspinatus, teres minor, and subscapularis. All of these muscles are subject to dysfunction of different kinds: inhibition, facilitation, tearing, weakness, atrophy, hypertonicity, repetitive motion trauma, and inflammation.
As mentioned earlier, shoulder movement is possible because the shoulder complex itself is so mobile. Not only does movement occur at the glenohumeral joint, where the head of the humerus sits in the glenoid fossa. The shoulder blade itself is mobile and, through muscles with various attachments on the humerus, spine, clavicle, and ribs, is able to rotate upwards and downwards, lifted up and down, and can slide around the ribcage forward and backward.
The clavicle is also mobile, but nowhere near as much as the shoulder blade. The two attachment points of the collarbone are at the acromion (acromioclavicular joint) at the outer end, and the breastbone (sternoclavicular joint) at the inner end. Both attach at the joint by ligament, the names of which are the same as the joint (acromioclavicular ligament and sternoclavicular ligament).
Both ends of the clavicle are slightly mobile to accommodate movement at the shoulder joint.
Mechanics of Shoulder Range of Motion
About half of the shoulder joint movement takes place at the glenohumeral joint without involving the other bones of the complex. All of this movement happens with the humerus below approximately 80 degrees of abduction. However, once the arm is raised above 80 degrees, the other bones of the complex must give way a little. In the picture above, “Scapular motion”, you can see how the shoulder blade moves in relation to arm motion.
The humerus fits easily in the glenoid fossa up til about 80 degrees of abduction. At that point, the head of the humerus comes in contact with the bottom of the acromion. To raise the arm further, the head of the humerus must glide downward, still in contact with the acromion, and the shoulder blade must rotate upwards as if the arm was a lever, prying it up. At the same time, the inner end of the clavicle drops down against the sternum and the acromion rises up against the outer end of the clavicle.
Complex motion also takes place in horizontal adduction. As the humerus is horizontally adducted across the front of the body, the shoulder blade slides out toward the side of the ribcage (protracts) and the inner end of the clavicle glides backwards (posteriorly) into the body. The reverse takes place in horizontal abduction.
Limiting Shoulder Range of Motion
A properly trained doctor or therapist will be able to assess movement of the shoulder and determine whether the range limitation is caused by bone-on-bone, is muscle-related, if there are ligament problems at work, or something more problematic is involved, such as arthritis or shoulder joint adhesions.
If the shoulder blade does not rotate upwards or downwards properly, and if the head of the humerus cannot slide downwards upon contacting the acromion, the arm cannot be raised above that height unless the entire torso is sidebent away from the elevated arm. Sometimes, the scapula will begin to rotate before it should. This is also a dysfunctional mechanism because the scapula will reach its upward rotational limit before the humerus will. In other words, you won’t be able to raise your arm as high as it should be able to go. The limitation is not normally painful; you simply won’t be able to move the arm any further.
All of the muscles used to move the shoulder have the ability to limit its range of motion, too. If a muscle is habitually shorthened, range of motion will have limitations, often painful. Ligaments and tendons, too, can be problematic.
Scarring from injury or surgery in or on the joint capsule can result in limited range of motion. As previously mentioned, scar tissue may tear because of the nature of the repair. Microtearing can be painful and sharp, and will usually kick-in the inflammatory response to start repair.
Other range of motion pages: