## Embryology informs pattern ![[Pasted image 20250212071535.png]] → During upper extremity development, muscles (and attached nerves) migrates distally in pre- and post-axial compartments centered around the bone. Thus: - the C5-7 sticks with the preaxial compartment while C8-T1 follows the postaxial compartment - following the bone, the anterior compartment moves joints in flexor fashion, while the posterior compartment moves joints in an extensor movement ## Plexus schematic ![[Pasted image 20250212073208.png]] → Divisions occur under the clavicle with the subsequent cords named relative to the axillary artery - In general, muscle innervations are segmental and sequential wrt to C5-T1 as you move more distally > 3 questions to think through plexus injury: > 1. What named nerves would be affected by this injury, either completely or partially? > 2. What dermatome or cutaneous nerve pattern is lost? > 3. What muscle groups would be affected? Flexors? Extensors? Both? > 4. Generally speaking, what losses of movement might one anticipate in an individual with this injury? Which muscles, unaffected by the injury, would be able to compensate for the losses? > **Hilton's Law**: Joint proprioception comes from named nerves that innervate muscle crossing and producing motion across the joint <div class="sketchfab-embed-wrapper"> <iframe title="Brachial Plexus" frameborder="0" allowfullscreen mozallowfullscreen="true" webkitallowfullscreen="true" allow="autoplay; fullscreen; xr-spatial-tracking" xr-spatial-tracking execution-while-out-of-viewport execution-while-not-rendered web-share width="640" height="480" src="https://sketchfab.com/models/932dbecba80541ce9168cef085fc15fa/embed?autostart=1&camera=0&ui_infos=0"> </iframe> </div> ## Upper Extremity Dermatomes - Cutaneous innervation branches off from main named nerve, with a (loose) dermatomal pattern that follows embryologic development. - Because the cutaneous nerve come from 2+ spinal roots and because of inter digitization between zone, dermatomal zoning are often loose ![[Pasted image 20250212142106.png | 600]] ![[Pasted image 20250213114812.png]] → Evidenced based dermatome map ^[Lee M w. l., McPhee R w., Stringer M d. An evidence-based approach to human dermatomes. _Clinical Anatomy_. 2008;21(5):363-373. doi:[10.1002/ca.20636](https://doi.org/10.1002/ca.20636)] ![[Pasted image 20250212141804.png | 900]] ## Vacuolization ![[Pasted image 20250212080656.png]] ![[Pasted image 20250212151725.png | 300]] 1. Cephalic v. 2. Basilic v. 3. Median cubital v. 4. Dorsal venous arch ##### Other references ![[Pasted image 20250212074640.png]]