The shoulder is where three bones meet – the humerus of the forearm, the clavicle (collarbone) and the scapula (shoulder blade). Pain in one of these bones does not always lead to shoulder pain as we know it. A fracture in the scapula for example can cause what is described as upper back pain, depending on which part of the scapula is the most affected. Therefore it is important to consider the possible causes of scapula pain separately from shoulder pain although there is a large degree of overlap.
What is the scapula?
Scapula Function and Joints
The scapula, or shoulder blade, is a flat triangular-shaped bone that lies at the upper back. It plays an important part in strengthening and stabilizing the shoulder joint which in turn assists with the power of the upper limbs. The glenoid cavity on the scapula is where the humerus (forearm bone) articulates with the scapula and it is known as the glenohumeral joint. The acromion of the scapular articulates with the clavicle (collarbone) at what it termed the acromioclavicular joint.
Several muscles attach to the scapula and these muscles also protect it. These 17 muscles include the:
- Pectoralis Minor
- Serratus Anterior
- Triceps Brachii (long head)
- Biceps Brachii (short head and long head)
- Rhomboid Major
- Rhomboid Minor
- Levator Scapulae
- Teres Minor
- Teres Major
- Latissimus Dorsi
The scapula is capable of the following movements:
- Protraction (abduction)
- Retraction (adduction)
- Upward (lateral) rotation
- Downward (medial) rotation
- Anterior tipping
- Posterior tipping
However, if one of the muscles that attach to the scapula are torn, injured or diseased then some of these movements may then be compromised.
Causes of Shoulder Blade Pain
Most of the time we do not give the scapula much thought as it is tucked out of easy view although it does protrude with certain movements of the upper limbs (arms). It is only when there is an abnormal protrusion (known as winging) or pain that the scapula becomes a cause for concern. The scapula, like any bone in body, can become injured or diseased in many ways to result in pain. Sometimes it is the muscles, tendons, joints or other tissue associated with the scapula is the source of the pain.
Soft tissue refers to any of the structures apart from the bone. This includes the muscles, tendons and joints discussed below as well as the skin and underlying tissue (subcutaneous tissue) as well as the connective tissue and ligaments. Most of the time soft tissue injuries arise from blunt force trauma, including injuries from contact sports, assault and falls. It may lead to contusions and can be very painful although deeper tissue like muscles, tendons and joints are unaffected. Penetrating injuries are more likely to affect deeper tissues.
Patients confined to a bed or wheelchair may also experience pressure-related injuries like bed sores from lying on their back for long periods of time. The slight protrusion of the back due to the scapula may increase the pressure on the skin just over the scapula. Therefore pressure sores may be more likely to occur here. Another condition that needs to be considered with pain of the skin over the scapula is herpes zoster (shingles). Since it affects dermatomes, the pain and other symptoms may extend from the center of the back to the center of the chest.
Injury to the shoulder blade commonly occurs with trauma but scapula fractures are overall uncommon. In fact scapula fractures account for less than 1% of all fractures in humans. Fractures of the scapula are usually due to high impact injuries with most of the force directed at the scapula. This may occur with falling on the back from a height or in motor vehicle accidents. Often there are accompanying fractures of the ribs and neighboring bones. Cancer of the scapula can occur as a primary malignancy. The scapula is one of the common sites for osteosarcoma or chondrosarcoma. It is also possible for the scapula to be affected by secondary (metastatic) spread of a cancer.
Spasm of the muscles that attach to the scapula is very common. It is one of the main reasons for upper back, shoulder, upper arm and even neck pain. The spasm arises for a host of reasons but muscle strain is the main trigger. Strenuous physical activity, trauma to the muscle, poor posture and prolonged use of the hands can cause it. A spasm may not always be as obvious as a painful muscle cramp and can persist for days or even weeks.
Winged scapula is a condition where the scapula abnormally protrudes from the back. It is caused by paralysis of certain scapula muscles. The more commonly affected muscle that leads to a winged scapula is the serratus anterior muscle. It occurs with injury or disease to the long thoracic nerve that controls this muscle. Paralysis of the rhomboids and trapezius muscles can also cause winged scapula. Inflammation of the muscle (myositis), a torn muscle and benign or malignant tumors of the muscles may also be responsible for scapula pain.
The tendons attach muscles to bones. Inflammation of the muscles (tendonitis) is a common condition. It usually occurs when the muscle is stretched or strained beyond the limits of its physical conditioning. Sometimes the tendons can tear and if it can be either a partial or complete tendon tear. A complete tear can affect movement that the attached muscle is responsible for. The long head tendon of the biceps which attaches to the scapula is one of the common tendons to be torn and is often caused by injury or overuse.
The joints of the scapula can be affected in a similar way to joints elsewhere in the body. Joint inflammation (arthritis) can occur for a number of reasons, including injury (trauma), infection, wear and tear or as an autoimmune condition. The shoulder joints can also become dislocated. It is a consequence of the articulating ends of the bones shifting out of place so that it does not fit in a normal alignment within the joint. Shoulder dislocations may be partial or complete. A frozen shoulder (adhesive capsulitis) is another relatively common and very painful shoulder joint condition.
Apart from the conditions discussed above, a host of other conditions may also cause pain that is felt in or around the scapula. However, not all the causes of scapula pain involves the scapula or structures that attach to it or lie next to it.
- Angina pectoris or a heart attack
- Lung infections and other respiratory conditions
- Gallstones and other gallbladder or bile duct conditions
- Compression of the spinal nerves (cervical or thoracic)