Upper limb
Deltoid, spinal part (posterior fibers)
Musculus deltoideus (pars spinalis)
- Origin
- Scapular spine
- Insertion
- Deltoid tuberosity of the humerus
- Function
- Extension (retroflexion) and external rotation of the shoulder
- Innervation
- Axillary nerve (C5–C6)
- Movement & chain
- Retroflexes and externally rotates the arm; works together with latissimus dorsi, teres major and infraspinatus in this movement.
- Palpation
- Felt at the back of the shoulder during resisted retroflexion, distinguished from the acromial part by raising the arm backward rather than purely sideways.
- Clinical
- Injury to the axillary nerve (in shoulder dislocation or a fracture of the surgical neck of the humerus) causes loss of strength in all three parts and a numb area over the lateral shoulder.
- Segmental innervation
- Axillary nerve, C5–C6.
- In clinical practice
- Ergonomic patient repositioning (log-roll technique in spinal trauma) and pressure offloading; maintain neutral spinal alignment in bedridden patients.
- Region in the model
- Upper limb