The Anatomy of the Scapula

The scapula stabilizes the arm and neck

In This Article

The scapula, better known as the shoulder blade, is a triangular bone which serves as a joining force between the clavicle and the humerus. This bone is located posteriorly (on the back half of the body). The scapula plays an important role in stabilizing the other bones involved in the rhythm of shoulder motion. Many muscles are located in the area of the shoulder girdle, including rotator cuff muscles, nerve networks such as the brachial plexus, and upper arm muscles.

The nerve supply to the scapula is often impaired in neurological conditions such as cerebrovascular accidents or strokes and other brain hemorrhages. This can cause significant dysfunction in the rhythm of movement in the impaired shoulder and arm. This can lead to a variety of other issues including impingement and subluxation.

Anatomy

With the location of the scapula being posterior, meaning on the back of the body, there are some muscles from several groups which play a role in its movement. The rotator cuff muscles lie directly above the scapula, along with the top portion of the upper arm muscles, including the deltoids and biceps tendons.

Two important arteries, the axillary artery and the subclavian artery, run anterior to the scapula and posterior to the clavicle. Additionally, due to the location of the scapula on the axilla, there are many lymph nodes and lymph networks in this area which assist with fluid drainage and balance within the body.

A rare abnormality affecting the development of the scapula is Sprengel’s deformity. This congenital defect results in excessive elevation of the scapula. This can range in severity, with only slight elevation at rest up to nearly 5 centimeters of elevation.

Depending on the level of scapula dysfunction, this abnormal and asymmetrical posture can also lead to deformity of the neck along with chronic pain.

This condition may be associated with other musculoskeletal defects in the body.

Function

The scapula is responsible for several motions which are integral to daily movement and smooth upper extremity motion. Protraction and retraction of the scapula assist with movement of the pectoral girdle and chest muscles both forward and back, respectively. Elevation and depression of the scapula assist with the movement of the entire shoulder capsule up and down, seen in motions such as shrugging of the shoulders.

Upward rotation and downward rotation of the scapula assist with stabilization of the shoulder capsule during excessive arm motion. Upward rotation of the scapula occurs when the arm moves both up and outward simultaneously. This seemingly simple motion requires significant shoulder stabilization due to the intricacies of the humerus and scapula. Similar stability is required for downward rotation of the scapula when the arm moves both down and inward simultaneously.

The complexity of the rhythm between the scapula and the humerus is called the scapulohumeral rhythm, which is a large focus of treatment in many therapy sessions for shoulder dysfunction. As mentioned, this is often a crucial impairment in those affected by neurological events such as a stroke due to a blockage of nerve and blood supply to this area.

An additional mechanism the scapula plays a large role in is the scapulothoracic rhythm, which is the interaction of the scapula with the thoracic vertebra. Similar to the scapulohumeral rhythm, this relationship is vital to the stability of the shoulder joint as a whole.

Associated Conditions

Due to the strength and location of the scapula bone, fractures are rare and only occur in instances of severe or major multiple trauma. Ligaments are vital to aid in the maintenance of scapula stability. Injury to the ligaments surrounding the scapula can occur and result in a range of symptoms depending on the severity. This can cause mild pain and loss of range of motion in simple cases or symptoms mimicking that of nerve damage, where there is no motion in the scapula due to loss of ligament function.

Shoulder Impingement Syndrome

Shoulder impingement syndrome is partially caused by impaired scapular movements. This serves to place undue pressure on the nerves and blood supply running through the scapular muscles. When excessive pressure is placed on nerves over an extended period of time, this can lead to a permanent loss of nerve function. For this reason, immediate treatment of shoulder impingement is paramount to restoring function and normal movement.

Subluxation

Subluxation is a condition which can occur in any joint in the body. Subluxation of the shoulder joint occurs from extreme forms of ligament laxity. This can be difficult to reverse and, again, early intervention is important to minimize the complications which can result from this condition. Splints and braces are very helpful in promoting proper posture and preventing further injury. Rest will help lessen the pressure placed on the joint, along with decreasing overall swelling and pain.

Rehabilitation

Rehabilitation of injury to a shoulder ligament injury and shoulder impingement syndrome would include rest and splinting to ensure proper positioning. Proper positioning is important to give the ligament(s) the opportunity to return to their natural and taut form, if possible. Positioning is also beneficial to minimize the frequency of the nerve pinching and causing acute, persistent pain.

Splints, braces, or slings can be provided by medical professionals or through treatment by a physical or occupational therapist as part of a treatment course.

Medical professionals can determine whether a significant loss of function has occurred when deciding whether therapy is indicated as part of the individual’s treatment. A therapy plan of care would include light exercise, positioning, modalities for pain relief, along with light strengthening exercises once the individual is cleared by their doctor.

Subluxation typically occurs as a result of a neurological incident, such as a brain hemorrhage or a stroke. This causes loss of nerve function to the large nerve network, called the brachial plexus, which lies over the shoulder joint. This means partial or complete loss of motor and sensory function in the impaired arm.

In such instances, due to the likelihood of simultaneous cognitive impairment, a treatment method called neuromuscular re-education is a large component of physical and occupational therapy treatments. This type of treatment guides an individual to complete basic strengthening activities (and eventually functional activities such as dressing, toileting, bathing, and more) using outlined methods in order to assist with reshaping the brain and building motor programs.

By building new yet familiar motor programs, therapists aim to establish normal and purposeful movement.

Subluxation apart from a neurological diagnosis does occur in extreme cases of ligament laxity. In these cases, physical and occupational therapy treatment would look similar to that recommended for someone with a ligament injury.

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Article Sources

  • Sprengel deformity. Genetic and Rare Diseases Information Center.  Published February 1, 2018.

  • Cowan PT, Varacallo M. Anatomy, Back, Scapula. In StatPearls. Treasure Island, FL: StatPearls Publishing; 2019.

  • Ellen MI, Gilhool JJ, Rogers DP. Scapular instability. The scapulothoracic joint. Phys Med Rehabil Clin N Am. 2000;11(4),755-770.