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The scapula, commonly known as the shoulder blade, is a bone in the upper back that sits above the rib cage. The scapula can move in six directions, and each movement is produced by specific muscles. The scapula's movement can be described by rotations in relation to the thorax, and it follows the contour of the ribs by rotating internally and externally at the AC joint. The internal rotation of the scapula has been linked to the prominence of the vertebral border of the scapula, which may be indicative of pathology or poor neuromuscular control. The scapular dyskinesis condition is characterised by increased internal rotation and anterior tilting of the scapula, which can be treated with manual therapy and stretching.
| Characteristics | Values |
|---|---|
| Motion | The scapula moves in six directions, including internal rotation. |
| Role | The scapula, or shoulder blade, creates the shoulder joint where it meets the head of the humerus (upper arm bone). |
| Function | The scapula's upward rotation prevents impingement between the humerus and acromion. |
| Clinical Term | Internal rotation of the scapula is also known as scapular "winging". |
| Clinical Examination | LSST (lateral scapular slide test) evaluates scapular symmetry with varying loads on supporting musculature. |
| Rehabilitation | Tightness of the pectoralis minor and posterior glenohumeral capsule is common in patients with scapular dyskinesis, which can be treated with manual therapy and stretching. |
| Dysfunction | Scapulohumeral rhythm dysfunction can be caused by shortening of muscles like pectoralis minor, latissimus dorsi, and levator scapulae. |
| Anatomy | The scapula moves around a dorso-ventral axis, resulting in a rotation in the frontal plane. |
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What You'll Learn
- The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back
- The scapula moves in six directions, including internal and external rotation
- The scapulothoracic joint allows for scapular elevation, depression, and protraction/retraction
- Scapular dyskinesis is characterised by a lack of upward rotation and increased internal rotation
- The LSST evaluates scapular symmetry and can identify abnormal patterns
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back
Internal rotation of the scapula occurs when the glenoid cavity turns towards the body's longitudinal axis. This movement is considered a “secondary” scapular motion, as it is typically difficult to observe. However, excessive internal rotation may be noticeable as scapular "winging," and it can indicate pathology or poor neuromuscular control of the ST muscles.
The scapula plays a crucial role in shoulder injuries, with many abnormal biomechanics and overuse injuries traced to alterations in its function. For example, subacromial impingement can occur if there is limited relative movement between the humerus and the scapula due to their difference in size. Additionally, scapular dyskinesis, characterised by a lack of upward rotation, posterior tilting, and increased internal or medial rotation, is often treated through rehabilitation programs that aim to restore the balance of musculature and normal scapular position and motion.
Understanding the normal biomechanics of the scapula and the muscles that control it is essential for comprehending pathomechanics and treating injuries or dysfunctions effectively. Therapies should be individualised, addressing specific contributory impairments and incorporating stretching and mobilisation exercises to lengthen muscles or connective tissue.
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The scapula moves in six directions, including internal and external rotation
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the shoulder joint. The scapula moves in six directions: protraction, retraction, elevation, depression, upward rotation, and downward rotation. These movements are produced by specific primary muscles.
Protraction is accomplished by the actions of the serratus anterior, pectoralis major, and pectoralis minor muscles. Retraction is achieved by the trapezius, rhomboids, and latissimus dorsi muscles. The elevation is the result of contraction by the trapezius, levator scapulae, and rhomboid muscles. Depression is caused by gravity and the actions of the latissimus dorsi, serratus anterior, pectoralis major and minor, and the trapezius muscles. Upward rotation is facilitated by the trapezius and serratus anterior muscles, while downward rotation is caused by gravity and the latissimus dorsi, levator scapulae, rhomboids, and the pectoralis major and minor muscles.
The scapula also internally and externally rotates. The internal rotation turns the glenoid cavity more towards the back, while the external rotation brings the glenoid cavity more into the frontal plane. The scapula's deep position and overlying muscles make it challenging to assess and track its movement. Quantitative measurement of scapular positioning can be achieved through the lateral scapular slide test (LSST), which evaluates scapular symmetry under varying loads.
The intrinsic muscles of the scapula include the rotator cuff muscles (infraspinatus, teres minor, subscapularis, and supraspinatus), which attach to the scapular surface and assist with internal and external rotation of the glenohumeral joint. The extrinsic muscles include the triceps, biceps, and deltoid. The third group of muscles, including the levator scapulae, trapezius, rhomboids, and serratus anterior, are responsible for rotational movements and stabilization of the scapula.
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The scapulothoracic joint allows for scapular elevation, depression, and protraction/retraction
The scapulothoracic joint enables the scapula, or shoulder blade, to move against the chest wall. This movement is important for the proper positioning of the shoulder joint in space. The scapula moves by gliding against the chest wall in three degrees of freedom: elevation, depression, and protraction/retraction.
Elevation and depression occur when the scapula moves upward or downward along the rib cage from its resting position. These movements occur as a composite of rotations at the SC (sternoclavicular) and AC (acromioclavicular) joints. For example, the motion of shrugging the shoulders involves scapular elevation, which occurs as the scapula follows the path of the elevating clavicle about the SC joint. This requires subtle adjustments in anterior/posterior tipping and internal/external rotation at the AC joint. Downward rotation of the scapula occurs as the arm is returned to the side from a raised position.
Protraction and retraction are translatory motions of the scapula away from or toward the vertebral column, respectively. However, in reality, full scapular protraction results in the glenoid fossa facing anteriorly, with the full scapula in contact with the rib cage. The scapula follows the contour of the ribs by rotating internally and externally at the AC joint, in combination with clavicular protraction and retraction at the SC joint.
The movements of the scapula at the scapulothoracic joint are stabilized by the muscles that attach to it and by the ligaments of the AC joint. The ultimate functions of scapular motion are to orient the glenoid fossa for optimal contact with the maneuvering arm, to add range to elevation of the arm, and to provide a stable base for the controlled motions between the humeral head and glenoid fossa.
The muscles that control scapular movement include the pectoralis minor, levator scapulae, serratus anterior, trapezius, and rhomboids. For example, the levator scapulae muscle can neutralize rotation, producing the elevation of the scapula. Depression and internal rotation are passive movements that occur with the relaxation of the trapezius and levator scapulae, allowing the scapula to drop by the force of gravity. Pectoralis minor and the lowermost fibers of the serratus anterior muscle can actively depress the scapula, while the levator scapulae, rhomboids, and pectoralis minor are active internal rotators. Protraction happens with the pull of the serratus anterior and pectoralis minor muscles, while retraction is produced by the horizontal and ascending parts of the trapezius muscle and the rhomboid minor and major muscles.
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Scapular dyskinesis is characterised by a lack of upward rotation and increased internal rotation
Scapular dyskinesis is a physical impairment characterised by altered scapula position and motion. The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It creates the shoulder joint where it meets the head of the humerus, the bone of the upper arm. The scapula can move in six directions, each produced by specific primary muscles.
Scapular dyskinesis is characterised by a lack of upward rotation, a lack of posterior tilting, and increased internal or medial rotation of the scapula. This can be caused by a lack of opposing pull by the serratus and trapezius muscles, allowing the deltoid to pull the scapula down. It can also be caused by tightness or adaptive shortening of the pectoralis minor and posterior glenohumeral capsule, which can inhibit the activation of opposing muscle groups.
The scapula should protract, medially rotate, and posteriorly tilt significantly. Some upward rotation will also occur due to the combination of posterior tilt during the protracted scapula position. The scapula moves around a dorso-ventral axis, resulting in a rotation in the frontal plane. In this movement, the glenoid cavity is turned cranially (upward rotation) or caudally (downward rotation). In the sagittal plane, around a latero-lateral axis, the scapula rotates posteriorly (posterior tilting) or anteriorly (anterior tilting). External and internal rotation occurs around a cephalo-caudal (longitudinal) axis.
Abnormal patterns of movement in scapular dyskinesis can be observed by determining the position of the scapula with the patient's arms resting by their side. Dynamic scapula motion testing (DSMT) can also be used to understand the mechanics of scapular dyskinesis by lowering and raising the arm to 120 degrees with or without holding weights.
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The LSST evaluates scapular symmetry and can identify abnormal patterns
The scapula, or shoulder blade, is the bone that sits above the rib cage in the upper back. It creates the shoulder joint where it meets the head of the humerus, the bone of the upper arm. The scapula can move in six directions, and each movement is produced by specific primary muscles.
The Lateral Scapular Slide Test (LSST) is a clinical examination tool used to evaluate scapular asymmetry and identify abnormal patterns. It is a quantitative measurement of scapular positioning that assesses the scapular stabilizer muscles in three arm positions with varying loads on the supporting musculature. The LSST evaluates scapular symmetry by measuring the distance between the inferior angle of the scapula and the closest spinous process in each position, allowing for the calculation of an average value. A difference of 1.5 cm or greater in any position is generally considered a threshold for an abnormal pattern, which may be indicative of shoulder dysfunction.
The LSST is a relatively simple, inexpensive, and non-time-intensive procedure. However, its reliability has been questioned, with some researchers finding it to be too variable and, therefore, unreliable. Nevertheless, it has been found to be useful in assessing scapular positioning and symmetry, particularly when compared to clinical observation.
Scapular dyskinesis, characterised by a lack of upward rotation, posterior tilting, and increased internal or medial rotation of the scapula, can be addressed through rehabilitation programs that restore the balance of musculature and normal flexibility of the muscles surrounding the scapula. Manual therapy, stretching, and strengthening exercises may be employed to correct scapular impairments and improve scapulohumeral rhythm, which refers to the coordinated movement pattern of arm elevation involving the scapula and humerus.
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Frequently asked questions
The scapula, commonly referred to as the shoulder blade, is the bone that sits above the rib cage in the upper back.
Internal rotation of the scapula refers to the movement of the scapula on the thorax, resulting in a rotation in the frontal plane. This movement can be observed as the scapula follows the contour of the ribs.
The muscles involved in internal rotation of the scapula include the pectoralis minor, latissimus dorsi, and levator scapulae. Tightness or shortening of these muscles can lead to increased internal rotation.
The lateral scapular slide test (LSST) is a method used to quantitatively measure scapular positioning and symmetry. It involves assessing the scapula's position in three different arm positions while varying loads are applied.
