Muscle of the back
• Muscle are arranged in 2 layers:
1. Superficial layer: trapezius and latissimus dorsi
2. Deep layer: levator scapulae, rhomboidus minor and
major
1. Trapezius
Origin:
1. The upper fibers arises from medial third of superior
nuchal line & external occipital protuberance
2. The middle fibers arises from nuchal ligament & spinous
process of C7
3. The lower fibers arises from spinous processes of all
thoracic vertebrae and supraspinous ligament
Insertion:
1. The upper fibers pass downwards and forwards to be
inserted to the posterior border of the lateral third of the
clavicle
2. The middle fibers pass transversly to the
medial border of acromion and upper lip of the
crest of spine of scapula
3. The lower fibers are inserted into rough
tubercle on the crest of the spine of scapula
Nerve supply: spinal part of accessory nerve
Actions:
• Upper fibers elevates the scapula
• middle fibers retracts scapula;
• Lower fibers together with the lower five
digitations of serratus anterior rotate the scapula
laterally as in raising the arm above the head
Latissimus dorsi
• Origin:
1. Tips of spinous processes of the lower 6 thoracic
vertebrae and supraspinous ligament
2. thoracolumbar fascia,
3. Outer lip of iliac crest,
4. lower 3 or 4 ribs
• Insertion: Floor of intertubercular groove of
humerus
• Nerve supply: Thoracodorsal nerve (C6, C7, C8)
• Action: Extends, adducts, and medially rotates the
arm as in swimming and raises body toward arms
during climbing
Levator scapulae
• Origin: from posterior tubercles of transverse
processes of C1 to C4 vertebrae
• Insertion: into the posterior aspect of the
medial border of scapula from the superior
angle to the root of spine
• Nerve supply: from dorsal scapular nerve (C5)
• Action: Elevates scapula and rotates it
medially so the glenoid cavity looks downwards
Rhomboidus minor
Origin: ligamentum nuchae and spinous processes of C7 and T1
Insertion: posterior aspect of the medial margin of the scapula
opposite its spine
Nerve supply: Dorsal scapular nerve (C4, C5)
Action: Retract scapula and rotates it medially to depress the
glenoid cavity
Rhomboidus major
Origin: spinous processes of T2 to T4 vertebrae and
supraspinous ligament
Insertion: posterior aspect of the medial border of scapula from
level of spine to inferior angle
Nerve supply: Dorsal scapular nerve (C4, C5)
Action: the same as rhomboidus minor
Shoulder region
1. Deltoid muscle
Origin:
•Anterior borders of lateral third of clavicle;
•Lateral border of acromion
•Lower lip of the crest of the spine of scapula
Insertion: Deltoid tuberosity of humerus
Nerve supply: Axillary nerve (C5, C6)
Action: 1. Anterior fibers: flexes and medially
rotates the arm
2. Middle fibers: abducts the arm from 15 to 90
degrees
3. Posterior fibers: extends and laterally rotates
the arm
• Subacromial bursa: it is a large bursal
sac that lies between the acromion and
deltoid muscle superiorly and muscles on
the upper surface of the capsule of
shoulder joint inferiorly.
• Coracoacromial arch: it is formed by the
coracoid process, acromion, and coracoacromial ligament. It is separated from the
shoulder joint by subacromial bursa and
tendons of supraspinatus, infraspinatus
and subscapularis. It overhangs and
protects the shoulder joint
2. Supraspinatus
Origin: from the medial two-thirds of the
supraspinous fossa
Insertion: fibres converge into a tendon which
crosses above the shoulder joint and is
attached to the highest facet of the greater
tuberosity of the humerus.
Nerve supply: suprascapular nerve, C5 and 6.
Action: 1. initiates abduction of the arm from 0
to 15 degrees
2. it helps to stabilize the head of the humerus in the
glenoid fossa during shoulder movements as one
of the rotator cuff muscles.
3. Infraspinatus
Origin: from the medial two-thirds of the fossa
Insertion: Its fibres converge to a tendon which
passes behind the shoulder joint to be attached to
the middle facet on greater tuberosity of humerus.
Nerve supply: suprascapular nerve, C5 and 6.
Action:
1. lateral rotator of the arm.
2. it helps to stabilize the head of the humerus in the
glenoid fossa during shoulder movements as one of
the rotator cuff muscles.
N.B. rotator cuff muscles are: supraspinatus,
infraspinatus, subscapularis and teres minor
4. Teres minor
Origin: from the upper two-thirds of a flattened strip on
posterior surface of scapula adjoining its lateral border,
Insertion: to the lowest facet of the greater tuberosity of
the humerus.
Nerve supply: Axillary nerve (C5, C6)
Action: Laterally rotate the arm
5. Teres major
Origin: from the lower third of a strip on the posterior
surface of the scapula adjoining its lateral border
Insertion: to the medial lip of the intertubercular sulcus
of the humerus.
Nerve supply: Lower subscapular nerve (C5, C6)
Action: Adducts and medially rotates the arm
6. Subscapularis
• Origin: from medial two thirds of the subscapular fossa
of the scapula
• Insertion: into the lesser tubercle of humerus
• Nerve supply: Upper and lower subscapular nerves
(C5, C6)
• Action: Medially rotates and adduct arm and helps hold
humeral head in glenoid cavity
• Subscapular bursa:
1. it is prolongation of the synovial membrane of shoulder
joint through a gap in the upper anterior part of capsule.
2. It extends between subscapularis muscle and the medial
part of the capsule, front of the neck of scapula and root
of coracoid process.
3. facilitates movement of subscapularis over these parts.
Intermuscular Spaces
I- Quadrangular space:
1. Boundaries: as follows:
• Above: the subscapularis and capsule of
the shoulder joint,
• Below: the teres major muscle,
• Medially: the long head of the triceps and
• Laterally: the surgical neck of the
humerus.
2. Contents: The axillary nerve and the
posterior circumflex humeral vessels pass
backward through this space.
II- The upper triangular space:
1. Boundaries: as follows:
• above by subscapularis anteriorly,
teres minor posteriorly,
• below by teres major, and
• laterally by the long head of triceps.
2. Contents: The circumflex scapular
artery
III- The lower triangular space:
1. Boundaries:
• above by subscapularis anteriorly and
teres major posteriorly
• medially by the long head of triceps
• laterally by the humerus.
2. Contents: The radial nerve and the
profunda brachii vessels
The suprascapular nerve:
• Beginning: from the upper trunk of the brachial
plexus (C5 and 6) in the posterior triangle in the
neck.
• Course: It runs downward and laterally and
passes beneath the suprascapular ligament,
which bridges the suprascapular notch, to reach
the supraspinous fossa.
• Distribution: It supplies the supraspinatus and
infraspinatus muscles and the shoulder joint.
Axillary Nerve
• Beginning: The axillary nerve arises from the posterior
cord of the brachial plexus (C5 and 6) in the axilla.
• Course: It passes backward and enters the
quadrangular space with the posterior circumflex
humeral artery. it comes into close relationship with the
surgical neck of the humerus. It terminates by dividing
into anterior and posterior branches
• Branches
1. An articular branch to the shoulder joint
2. An anterior terminal branch supplies the deltoid and
the skin that covers its lower part.
3. A posterior terminal branch, which gives off a branch
to the teres minor muscle and a few branches to the
deltoid, then emerges from the posterior border of the
deltoid as the upper lateral cutaneous nerve of the arm
Diagram of circumflex arteries and axillary nerve
1. Axillary artery
2. Anterior
circumflex
humeral artery
3. Posterior
circumflex
humeral artery
4. Axillary nerve
5. Articular branch
6. T.S. of humerus
7. Branch to teres
minor
8. Cutaneous
branches
Anastomosis around the scapula
• Three arteries share in the anastomosis:
1. Deep branch of transverse cervical artery: arises from
thyrocervical trunk from the first part of subclavian artery.
It descends along the medial border of scapula and gives
branches to both surfaces of scapula
2. Suprascapular artery: arises from the thyrocervical trunk
that originates from the first part of subclavian artery. It
passes over suprascapular ligament giving branches to
supraspinatus, then it descends through the spinoglenoid
notch to end by ramifying in infraspinatus
3. Subscapular artery arises from the 3rd part of axillary
artery. It descends along the lower border of subscapularis
giving branches as the circumflex scapular artery which
anastomosis with the branches of the previous arteries
• This anastomosis is important as if a ligature is applied to
the artery between the 1st part of subclavian and 3rd part of
axillary, collaterals of anastomosis open and establish
sufficient arterial supply for the upper limb.