Sep 3

Effective Rehabilitation of the Burned Shoulder: Understanding the Scapula

Vita Yu-Hsien TU, Occupational Therapist and Project Manager

Sunshine Social Welfare Foundation

The scapula, despite being just one of the 206 bones in the human body, plays a unique and vital role in shoulder movement. For burn rehabilitation therapists, understanding the scapula's structure and function is crucial for developing effective intervention strategies for patients with burned shoulders. This article delves into the significance of the scapula and its importance in the rehabilitation of the burned shoulder.

Structure of the scapula

The scapula is a flat, triangular bone featuring multiple protrusions and depressions, including the acromion, coracoid process, and scapular spine. Key joints related to the scapula include the glenohumeral joint, acromioclavicular joint, and scapulothoracic joint.

Over 15 muscles attach directly or indirectly to the scapula, contributing to the movement and stability of the shoulder and upper limbs.

These complex muscle attachments and joint structures enable the scapula to move in five directions:

Elevation and depression
Anterior and posterior tilt
Upward and downward rotation
Retraction and protraction
External and internal rotation

The scapula and the scapulohumeral rhythm

The scapula must maintain a coordinated movement rhythm with the humerus, known as the scapulohumeral rhythm, for optimal shoulder function. If the muscles associated with the scapula are weak or are too tight and cannot contract normally, scapular movement in any direction will be affected, which in turn will disrupt the scapulohumeral rhythm, thereby affecting the performance of shoulder joint movement.

Within the scapulohumeral rhythm, the contribution ratio from the scapula and humerus is generally defined as 1:2. This means that during 180-degree shoulder abduction, the scapula contributes 60 degrees and the humerus contributes 120 degrees. However, this is a commonly used ratio, and individual differences exist based on age, plane of action, dominant hand, or range of abduction, which will affect the contribution ratio of the humerus and scapula.

Clinically, this 180-degree movement will be further broken down into different levels of ROM, because the muscle dynamics of 0 to 30 degrees and 30 to 180 degrees are different. In the abduction stage of 0 to 30 degrees, the scapula has almost no movement. The movement of 30 to 180 degrees requires serratus anterior, upper trapezius and lower trapezius to bring out the scapula in upward rotation, and serratus anterior and lower trapezius bring out the scapula in external rotation and posterior tilt. In addition to the agonist muscles mentioned above, each action also requires antagonist muscles to coordinate together for smooth movement.

Impact of burns on the scapula and scapulohumeral rhythm

When the relevant muscles are weak or tight and cannot contract normally, it will cause abnormal scapula movement and lead to abnormal scapulohumeral rhythm, which is manifested in abnormal shoulder joint movement.

Three main factors contribute to post-burn abnormal scapulohumeral rhythm:

Prolonged Immobilization: Often occurs when patients are bedridden during hospitalization.
Compensatory Movements: Using muscles not intended for specific movements, leading to muscle imbalance.
Scar Contracture: Causes changes in soft tissue elasticity and muscle strength.

These factors disrupt normal scapular movement and scapulohumeral rhythm, complicating shoulder joint rehabilitation.

Challenges in Diagnosing Scapular Problems for the Rehabilitation of the Burned Shoulder

Although the scapula is very important in the kinematics of the upper limb, it is easily overlooked. Because the scapula is hidden in the thoracic area and covered by a large amount of muscles, it is not as easy to detect as other bones. Scapula problems usually cause widespread pain in the shoulder or upper back, making it difficult to identify a cause, making diagnosis more difficult. More apparent joints such as glenohumeral joint and elbow joint are more likely to draw attention. However, the scapula is very important for shoulder joint movement. Only through good scapulohumeral rhythm can smooth shoulder joint movement is possible, allowing the upper limbs to function to their full potential.

Conclusion

Effective rehabilitation of the burned shoulder requires a deep understanding of the scapula's role in shoulder movement. By recognizing the impact of burns on the scapula and addressing factors that disrupt scapulohumeral rhythm, burn rehabilitation therapists can develop targeted intervention strategies that enhance patient recovery and improve functional outcomes.

To learn more about shoulder joint movement abnormalities after burns and scapulohumeral rhythm, check out our series of courses on burned shoulder issues.