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Shoulder is the meeting place of three bones viz. clavicle, scapula and humerus.  The junction of these three bones and the chest bone (sternum) form three joints:

Glenohumeral joint:  It is the shallow ball-and-socket style joint created by the humerus and scapula.  This joint allows the arm to rotate circularly and to move up and out of the body.  Glenohumeral joint is surrounded by soft tissue and strengthened by fibrous ligaments.

Acromioclavicular joint (AC joint):  This joint is the highest point of the shoulder.  It is because of this joint that we are able to raise the arm above the head.  The joint is formed at the meeting of the scapula and clavicle.

Sternoclavicular joint:  This joint is located at the centre of the chest where the clavicle meets the sternum.  It allows the clavicle to move.

Each shoulder joint is surrounded by:

• cartilage, to pad the meetings of the bones
• ligaments, to connect the bones
• muscles
• tendons, to attach the muscles to the bones

The collection of muscles and tendons around the shoulder is called rotator cuff.  It stabilizes the shoulder and holds the head of the humerus in the glenoid, a shallow cavity in the scapula.  The muscles of the rotator cuff include the supraspinatus, infraspinatus, teres minor and subscapularis.

Clavicle (Collar bone):

Shoulder is the most mobile joint in the human body.  However, due to its extreme flexibility, shoulder joint is susceptible to dislocation.  One of the bones that meet at the shoulder is clavicle, which is also referred to as collarbone.  The clavicle is long, thin, curved and located at the base of the neck.  The main function of the clavicle is to hold the arm free, supported, away from the main body.  Strong ligaments hold the clavicle in place at either end.  Clavicle gives attachment to muscles of the shoulder girdle and neck.  Clavicle can be palpated along its length.

Clavicle has three main functions:

• Attaches the upper limb to the trunk
• Protects the underlying neurovascular structures supplying the upper limb
• Transmits force from the upper limb to the axial skeleton

Fractures of the collarbone are a common occurrence.  A clavicle fracture is easy to detect as the clavicle lies directly under the skin, making any deformity immediately palpable.  Symptoms of a fractured clavicle include tenderness, swelling and an inability to move the arm.  It is a standard practice to apply sling to stabilize the fracture, allowing it to heal.  However, if the fracture is severe and complex, surgery may be recommended to pin the collar bone back together.

Scapula (shoulder blade):

The scapula, or shoulder blade, is a large triangular-shaped bone that lies in the upper back.  The bone is surrounded and supported by a complex system of muscles that work together to help you move your arm.  If these muscles get weak or imbalanced, it can change the position of the scapula both at rest and in motion.  If there is an alternation in the position of the scapula, it may be difficult for you to move your arm, especially while performing overhead activities.  You may feel an overall weakness in your shoulder.  Moreover, if the normal ball-and-socket alignment of your shoulder joint is not maintained, alteration can also cause an injury.

If there is a scapular disorder, it may result in deviation or alteration in the normal resting position of the scapula or normal motion of the scapula.  The medical term used for alteration in scapula is dyskinesis.  In most cases, scapular alteration can be seen by looking at the patient from behind.  The alteration gets more evident as the patient moves the arm away from the body.  This is commonly referred to as “winged” scapula.

Causes of scapular dyskinesis include:

• Weakness, imbalance, tightness or detachment of the muscles that control the scapula
• Injuries to the nerves that supply the muscles
• Injuries to the bones that support the scapula or injuries within the shoulder joint

Treatment for scapular problems usually involves physical therapy, primarily aimed to strengthen the shoulder muscles and restore proper position and posture of the shoulder blade.

Humerus (Upper arm bone):

Humerus is the longest and the largest bone of the upper arm.  It is located between the elbow joint and the shoulder.  At the elbow, it connects primarily to the ulna. At the shoulder, the humerus connects to the frame of the body via the glenoid fossa of the scapula, so it can participate in the movements of the shoulder.  The humerus is the foundation to which many muscles insert, such as the deltoid, the pectoralis major and others.  Humerus consists of a proximal end, a shaft and a distal end, all of which contain important anatomical landmarks.

The proximal end of the humerus consists of a head, an anatomical neck and the greater and lesser tubercles.  The rounded humeral head fits into the glenoid fossa (cavity) of the scapula. This shallow depression on the lateral side of the scapula allows the shoulder joint to be very mobile and reduces its stability.  Muscles from the shoulder girdle help stabilize the joint and control the front-to-back, side-to-side and rotational movements of the humerus.

Humerus fracture refers to any break in the humeral bone.  The pain from the humeral fracture can extend to either your shoulder or elbow, depending on where the fracture is and recovery may take several weeks.  There are three types of humeral fractures depending on the location of the break:

Proximal:  A proximal humerus fracture is a break in the upper part of your humerus near your shoulder.

Mid-shaft:  A mid-shaft humerus fracture is a break in the middle of your humerus.

Distal:  Distal humerus fractures occur near your elbow. This is usually part of a more complex elbow injury and sometimes involves loose bone fragments.

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