Clinical Anatomy of the Dermatomes and Innervation of the Joints


Motion

Nerve

Cord

Division

Trunk

Root

Arm abduction

Suprascapulara
  
Upper

C5, C6

Arm abduction

Axillary

Posterior

Posterior

Upper

C5, C6

Elbow flexion

Musculocutaneousb

Lateral

Posterior

Upper

C5, C6

Anterior

Extension (dorsiflexion) of the elbow, wrist, hand, and fingers

Radial

Posterior

Posterior

Upper

C5, C6

Posterior

Middle

C7

Latissimus dorsi twitch (shoulder shrug)

Thoracodorsal

Posterior

Posterior

Middle

C7

Forearm pronation and wrist flexion

Median (lateral head)

Lateral

Anterior

Upper

C5, C6

Medial

Anterior and posterior

Middle

C7

Anterior

Lower

C8, T1

Thumb flexion and opposition (flexion middle and ring finger)

Median

Medial

Anterior

Lower

C8, T1

Thumb flexion and opposition

Anterior interosseous

Medial

Anterior

Lower

C8, T1

Fifth finger flexion and opposition, ulnar deviation of the wrist

Ulnar

Medial

Anterior

Lower

C8, T1


aThe suprascapular nerve may not be blocked during supraclavicular block if the needle is placed at the level of the divisions rather than the trunks. Also, infraclavicular block will not target the suprascapular nerve since this nerve leaves the plexus at the trunks

bThe targets of brachial plexus block using the axillary approach are the terminal nerves of the upper extremity and branches at the cord level of the plexus. The musculocutaneous nerve may not be blocked if the injection fails to spread to the proximal location where it branches





14.1.3 Osteotomes


Osteotomes refer to specific regions of the bones throughout the extremities that are innerved by the terminal nerves (rather than by spinal segments as with dermatomes). The innervation of bones can be significantly different from that of the muscles and skin. A good knowledge of joint innervation is important for orthopedic surgery as well as other surgical specialties and neurology.



14.2 Innervation of the Upper Extremity



14.2.1 Dermatomes and Cutaneous Distribution of the Peripheral Nerves (Figs. 14.1, 14.2, 14.3, and 14.4)




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Fig. 14.1
Dermatomes; anterior view


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Fig. 14.2
Dermatomes; posterior view


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Fig. 14.3
Cutaneous distribution of the peripheral nerves of the upper extremity; anterior view


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Fig. 14.4
Cutaneous distribution of the peripheral nerves of the upper extremity; posterior view



Segmental Cutaneous Innervation of the Upper Extremity



  • C3 and 4: upper shoulder region (supraclavicular nerves)


  • C5: deltoid and lateral aspect of the arm


  • C6: lateral arm, forearm, and thumb


  • C7: the hand and middle three fingers


  • C8: fifth finger and medial side of both the hand and lower forearm


  • T1: medial side of the lower arm and upper forearm


  • T2: medial side of the upper arm (intercostobrachial nerve)


14.2.2 Myotomes


For clinical practice, it is important to understand that there is a specific distribution of innervation to skeletal muscles that is derived from the terminal nerves (Figs. 14.5 and 14.6). Table 14.1 summarizes the origin of each terminal nerve and its objective movement upon electrical stimulation.

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Fig. 14.5
Distribution of muscular innervations by the terminal nerves of the upper extremity; anterior view


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Fig. 14.6
Distribution of muscular innervations by the terminal nerves of the upper extremity; posterior view


Segmental Motor Responses Associated with Nerve Stimulation



  • C5: lateral rotation and abduction of the arm at the shoulder joint


  • C6: pronation and supination of the forearm


  • C5 and 6: elbow flexion


  • C6-8: medial rotation and adduction of the arm at the shoulder


  • C6 and 7: elbow extension


  • C6 and 7: wrist flexion and extension (long flexor and extensor muscles of the wrist)


  • C7 and 8: digit flexion and extension (long flexors and extensors of the fingers), opposition of the thumb


  • T1: intrinsic movements of the hand


Muscular Distribution of the Spinal Segments



  • C5: rhomboids, supraspinatus, infraspinatus, anterior portion of deltoid, long head of biceps


  • C6: teres major and minor, middle and posterior deltoid, short head of biceps, coracobrachialis, brachialis, brachioradialis, extensor carpi radialis longus and brevis, supinator, pronator teres


  • C7: triceps, anconeus, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus and brevis, extensor indicis, flexor carpi radialis


  • C8: flexor digitorum superficialis and profundus, flexor carpi ulnaris, flexor pollicis longus, pronator quadratus, abductor and flexor pollicis brevis, opponens pollicis


  • T1: flexor digitorum superficialis, abductor digiti minimi, adductor pollicis, flexor digiti minimi brevis, opponens digiti minimi, palmar and dorsal interossei, lumbricals


14.2.3 Osteotomes


Terminal nerves, rather than spinal cord segments, distribute sensory innervation to specific regions of bones throughout the extremities. These terminal nerves also send articular branches to specific joints in the extremity. These regions of the bones, each supplied by a specific branch of a terminal nerve, are termed osteotomes; those for the upper extremity are summarized in Figs. 14.7 and 14.8.

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Fig. 14.7
Osteomes of the upper extremity; anterior view


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Fig. 14.8
Osteomes of the upper extremity; posterior view


14.2.4 Innervation of the Major Joints of the Upper Extremity


In general, the nerve supplying a joint also supplies the muscles which move the joint and the skin covering the articular attachments of those muscles (Hilton’s law).

Table 14.2 outlines the innervation of the joints of the upper extremity joint innervation and associated motor responses associated with nerve stimulation during nerve block procedures.


Table 14.2
Innervation of the joints of the upper extremity joint innervation and motor responses associated with nerve stimulation






























































Joint
Nerve
Root
Motion

Shoulder

 Anterior and posterior
Suprascapular
C5, C6
Arm abduction

Axillary
C5, C6
Arm abduction

Elbow

 Anterior
Musculocutaneous
C5, C6
Elbow flexion

Radial
C5–C7
Extension of the elbow, wrist, and fingers

Median
C5–T1
Thumb flexion and forearm pronation

 Posterior
Radial
C5–C7
Extension of the elbow, wrist, and fingers

Ulnar
C8, T1
Fifth finger flexion and opposition

Wrist
Radial (superficial)
C5–C7
Extension of the elbow, wrist, and fingers

Median
C5–T1
Thumb flexion and forearm pronation

Ulnar
C8, T1
Fifth finger flexion and opposition


14.2.4.1 Innervation of the Shoulder


The nerve supply to shoulder joint nerve supply is derived from the axillary, suprascapular, and lateral pectoral nerves, from branches arising from the posterior cord of the brachial plexus, possibly the radial nerve. Sympathetic innervation is derived directly from the stellate and perhaps from other lower cervical and/or upper thoracic sympathetic ganglia (Table 14.2). Recommended block(s) is/are shown in Fig. 14.9.

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Fig. 14.9
Innervation of the major joints




  • Axillary nerve (articular branch): after leaving the posterior cord of the brachial plexus and descending laterally across the subscapularis muscle, the articular branch of the axillary nerve innervates mainly the inferior aspect of the joint capsule



    • A portion of the articular branch innervates the bicipital sulcus and forms anastomoses with fiber bundles from the posterior cord.


    • The branch leaves the plexus in proximity to where the axillary nerve forms and courses obliquely across the subscapularis muscle to reach the bicipital sulcus and inferior and superior aspects of the anterior surface of the joint capsule.


    • Terminal twigs course superiorly from the inferior aspect of the capsule to reach the anterior and posterior surfaces of the capsule.



      • Nerve fibers largely penetrate the fibrous layer of the capsule, while there is some penetration into the synovial layer and adjacent portions of the humerus.


      • Fibers which reach the posterior capsule join the lower articular branch of the suprascapular nerve; those coursing toward the anterior capsular surface jointly innervate this area with the branch from the posterior cord of the plexus.


  • Lateral pectoral nerve: articular branches arise mainly from the lateral pectoral nerve.

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Sep 22, 2016 | Posted by in ANESTHESIA | Comments Off on Clinical Anatomy of the Dermatomes and Innervation of the Joints

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