A. Bone mark of scapula
The scapula is a triangular flat bone, located at the back of the thorax, and together with the clavicle, it forms the scapular band. There are three edges (upper edge, lateral edge, medial edge), triangle (upper angle, lower angle, lateral angle) and two sides (front, back). The scapula is slightly concave in front and slides over the projecting posterior ribs.
In the resting position, the scapula is between the 2nd and 7th ribs. The scapular gon is approximately flat against the 3rd and 4th thoracic vertebrae. The superior and inferior angles are located at the superior and inferior ends of the medial margin, flat against the 2nd and 7th ribs, respectively.
II. Types of scapular girdle movement
The scapular girdle is used to describe the movement of the scapula and clavicle. The sternoclavicular and acromioclavicular joints produce motion in the scapular girdle. There are six types of movement of the scapular girdle: lifting, descending, forward extension, retraction, upward rotation and downward rotation. There are five muscles that attach to the scapula and clavicle and provide movement of the scapular girdle.
Supination/descension and anterior extension/retroversion are linear movements.
Upward and downward rotation are angular movements.
In addition to the above, another type of scapular motion is scapular tilt. This motion usually occurs with hyperextension of the shoulder joint.
Third, scapular girdle muscle group
There are five main muscles that accomplish the movement of the scapula. They are the trapezius, scapularis, rhomboid, serratus anterior and pectoralis minor muscles.
1.The trapezius muscle
The trapezius is a larger superficial muscle that looks rhomboid-shaped on the left and right sides. According to the function, it is divided into three parts: upper trapezius, middle trapezius and lower trapezius. The reason for this division is that they move the muscle in three different directions of stretch (upper, inner and lower) respectively.
1. Superior oblique muscle
Starting point: from the occipital bone and the collateral ligament of the cervical spine
Stopping point: ends at the outer 1/3 of the clavicle and the acromion
Main activity: Scapular lift and upward rotation
Nerves: spinal accessory nerve (cerebral nerve D.), sensory part of C3 and C4
2.Middle trapezius muscle
Origin: from C7-T3
End point: ends at the scapular gland
Main activity: Retraction of the scapula
Nerves: spinal accessory nerve (cerebral nerve D.), sensory part of C3 and C4
3.Lower trapezius muscle
Origin: from the middle part of the spinous process and the lower part of the thoracic spine
Stopping point: at the base of the scapular gland
Main activity: descent and upward rotation of the scapula
Nerves: spinal accessory nerve (cerebral nerve D.), sensory part of C3 and C4
Of the three components of the trapezius muscle, the middle trapezius is the primary source of power, while the superior and inferior trapezius play only a secondary role. The superior and inferior trapezius muscles antagonize each other in supination and descent, whereas they are the active muscles during upward rotation movements. During upward rotation, the combined action of these muscles creates a steering disc in the scapula.
For example, the picture above shows the scapula on the right. Tie a band at the bottom of the steering wheel to represent the lower corner of the scapula. Place your right hand at the 2 o’clock position to represent the superior trapezius. And place your left hand at the 10 o’clock position to represent the lower trapezius. Turn the steering wheel to the left and you can see the band move up to the right. In this example, the upper trapezius (right hand) moves inward and upward, and the lower trapezius (left hand) moves inward and downward. The combined force makes the lower angle move outward and upward (upward rotation).
2.Scapularis lift muscle
Starting point: from the transverse process of the 1st-4th cervical vertebrae
Stopping point: ends at the upper angle of the scapula
Main activity: upward and downward rotation of the scapula
Nerves: 3rd and 4th cervical nerves and dorsal scapular nerve (C5)
3.Rhomboid muscle
Origin: from C7-T5
Stopping point: ends at the medial border and inferior angle of the scapula
Main activity: posterior retraction, supination and inferior rotation of the scapula
Nerve: dorsal scapular nerve (C5)
4.Anterior serratus
Origin: from the lateral side of the first 8 ribs
Stopping point: ends at the medial edge of the scapula and in front
Main activity: forward extension and upward rotation of the scapula
Nerve: long thoracic nerve (C5, C6, C7)
5.Pectoralis minor muscle
Origin: from the front of the 3rd-5th ribs
Stopping point: ends at the rostral process of the scapula
Main activity: descent, retraction, downward rotation and tilt of the scapula
Nerve: medial thoracic nerve (C8, T1)
Fourth, summarize the main motor muscles of the scapular belt and their roles
1.Retraction: upper trapezius muscle, rhomboid muscle
2.Anterior extension: anterior serratus, pectoralis minor
3.Superior elevation: upper trapezius, scapularis elevator, rhomboid muscle
4.Descent: lower trapezius, pectoralis minor
5.Upward rotation: upper trapezius, lower trapezius and serratus anterior (lower fibers)
6.Downward rotation: rhomboid, scapularis raphe, pectoralis minor
7.Scapular tilt: pectoralis minor