M01.09.002 Superficial Muscles

The muscles of the back are categorized into three groups based on their location and function:

Groups of Back Muscles

1. Superficial Muscles: Involved in movements of the shoulder and upper limb.
2. Intermediate Muscles: Associated with movements of the thoracic cage (e.g., respiration).
3. Deep Muscles: Control movements of the vertebral column and are intrinsic to the back.

Developmental Classification

• Intrinsic Muscles: Develop embryologically in the back (deep group).
• Extrinsic Muscles: Do not develop in the back (superficial and intermediate groups).

Superficial Back Muscles

These muscles lie just beneath the skin and superficial fascia. They connect the vertebral column to the shoulder girdle and upper limb, facilitating shoulder and arm movements.

Superficial Back Muscle Group

• Trapezius
• Latissimus Dorsi
• Levator Scapulae
• Rhomboids (Major and Minor)

Anatomy of Superficial Back Muscles

| Latissimus Dorsi| Origin: Spinous processes (T6-T12), thoracolumbar fascia, iliac crest, inferior ribs.
| Inserts: Intertubercular sulcus of humerus. | Thoracodorsal nerve. | Extends, adducts, and medially rotates the upper limb. |
| Levator Scapulae| Origin: Transverse processes (C1-C4).
| Inserts: Medial border of scapula. | Dorsal scapular nerve. | Elevates scapula. |
| Rhomboid Major | Origin: Spinous processes (T2-T5).
| Inserts: Medial scapular border (below scapular spine). | Dorsal scapular nerve. | Retracts and rotates scapula. |
| Rhomboid Minor | Origin: Spinous processes (C7-T1).
| Inserts: Medial scapular border (at spine level). | Dorsal scapular nerve. | Retracts and rotates scapula. |

Detailed Muscle Descriptions

1. Trapezius

• Shape: Broad, flat, triangular. Forms a trapezoid shape when combined with its counterpart.
• Clinical Relevance:
  • Accessory Nerve Damage: Often caused by medical procedures like cervical lymph node biopsy or jugular vein cannulation.
  • Testing: Ask the patient to shrug their shoulders to assess function.
  • Symptoms of Damage: Muscle wasting, partial paralysis of the sternocleidomastoid, asymmetrical neckline.

2. Latissimus Dorsi

• Shape: Large and covers the lower back.
• Clinical Function: Important in actions like pulling and swimming due to its extension and medial rotation of the arm.

3. Levator Scapulae

• Shape: Strap-like, descending from the neck to the scapula.
• Function: Elevates the scapula, playing a role in shrugging movements.

4. Rhomboids

• Major and Minor: Work synergistically to retract and stabilize the scapula.

Points to Remember

1. Classification: Superficial back muscles are extrinsic and aid in upper limb movement.
2. Clinical Testing: Accessory nerve testing for trapezius function.
3. Key Innervation: Dorsal scapular nerve (rhomboids, levator scapulae) and thoracodorsal nerve (latissimus dorsi).