TIBIAL NERVE ANATOMY

The tibial nerve is the larger of the two major divisions of the sciatic nerve. It is derived from L5, S1 and S2 roots. It leaves the popliteal fossa between the heads of the gastrocnemius and supplies all muscles in the posterior compartment of the legs, i.e. gastrocnemius, soleus, plantaris, popliteus, flexor digitorum longus, flexor hallucis longus and tibialis posterior.

At the ankle the tibial nerve runs posterior to the medial malleolus under the flexor retinaculum (tarsal tunnel) to enter the foot. While coming out of (or within) tarsal tunnel, the nerve divides into four branches.

Two of these, the medial and lateral calcaneal nerves are purely sensory and supply sensation to the heel.

The other two branches, the medial and lateral plantar nerves innervate the intrinsic muscles of the foot and provide sensation to the medial and lateral sole respectively. Notably, medial plantar nerve supplies abductor hallucis brevis and lateral plantar nerve supplies abductor digiti quinti pedis.

Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition


2. Cimino WR. Tarsal tunnel syndrome: review of the literature. Foot Ankle 1990, 11:47.


3. Kimura J. Electrodiagnosis in disease of nerve and muscle: Principles and Practice, New York: Oxford V. Press, 3rd edition

COMMON PERONEAL NERVE ANATOMY

Sciatic nerve originates form the L4 thru’ S2 roots. It leaves pelvis by passing thru’ the greater sciatic foramen and enters thigh. In the upper popliteal fossa, it divides into common peroneal and tibial nerves. Within the sciatic nerve, the fibers that eventually form the common peroneal and tibial division run separately from each other.

In the upper thigh, tibial division provides innervation to all hamstring muscles except short head of biceps femoris which is supplied by the peroneal division. Thus, short head of biceps femoris is the only peroneal innervated muscle above knee joint.

Soon after separating from tibial division, the common peroneal gives off the lateral cutaneous nerve of the calf, which innervates the skin over the upper third of the lateral aspect of the leg (not highlighted in figure). Then the peroneal nerve winds around the fibular neck and divides into its terminal braches, the superficial and deep peroneal nerves.







Superficial peroneal nerve
The superficial peroneal nerve is predominantly sensory; it innervates the skin of the lower two thirds of the lateral aspect of the leg and the dorsum of the foot and sends motor branches to the peroneus longus and brevis.














Deep peroneal nerve
The deep peroneal nerve is predominantly motor; it innervates tibialis anterior, extensor hallucis, extensor digitorum longus & brevis (all ankle and toe extensors) and peroneus tertius. It sensory branches supply the skin of the web space b/w the first and second toe.


Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition
   
2. Preston DC. Distal Median Neuropathies. In: Entrapment and other focal neuropathies; Neurologic Clinics: WB Saunders company, August 1999
   
3. Katriji MB, Wilbourn AJ. Common peroneal neuropathy: a clinical and electrophysiologic study of 116 lesions. Neurology 1988;38:1723.

RADIAL NERVE ANATOMY

The radial nerve is the largest branch of the brachial plexus. The radial nerve is derived primarily from the C5, C6, C7, C8 and T1.
The radial nerve enters the arm from axilla along the medial side of the humerus to reach the spiral groove. From the axilla to the spiral groove, the radial nerve gives off motor branches to triceps and anconeus. It also receives the posterior cutaneous nerve of the arm, the posterior cutaneous nerve of the forearm and the lower lateral cutaneous nerve of the arm in this region.
At the spiral groove, the radial nerve is in contact with the humerus as the nerve travels laterally, and then it pierces the lateral intermuscular septum. Here, it is bordered medially by the brachialis (Br) muscle, and laterally (from proximal to distal) by the brachioradialis (BR), the extensor carpi radialis longus (ECRL), and the extensor carpi radialis brevis (ECRB). All these muscles receive motor supply from radial nerve. The radial nerve then crosses the elbow joint anterior to the lateral epicondyle of the humerus. At the elbow the radial nerve divides into a motor nerve, the posterior interosseus nerve; and a sensory nerve, the superficial radial nerve.

Posterior Interosseus Nerve
The posterior interosseus nerve enters and innervates the supinator (Sup) muscle. The nerve then gives motor branches to - extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and extensor indicis proprius (EIP).

Superficial Radial Nerve (SRN)
At the elbow, the superficial radial nerve stays superficial to the supinator and proceeds anterolaterally, deep to the BR muscle. Approximately at the junction of the proximal two thirds and the distal one third of the forearm (approx 8 cm from tip of radial styloid), the SRN becomes superficial and crosses over to the posterior aspect of the distal radial forearm, passing superficial to the tendons of the anatomical snuffbox (APL, EPL, and EPB) and traversing the wrist over the extensor retinaculum. It supplies cutaneous sensation to the dorsal surface of the lateral hand, as shown in the figure.

Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition
2. Preston DC. Distal Median Neuropathies. In: Entrapment and other focal neuropathies; Neurologic Clinics: WB Saunders company, August 1999
3. http://www.wheelessonline.com/ortho/the_superficial_branch_of_the_radial_nerve_an_anatomic_study_with_surgical_implications
   

ULNAR NERVE ANATOMY

The ulnar nerve derives from C8 and T1 nerve roots. It runs on the medial aspect of upper arm, and gives off no branches in the upper arm. It passes posterior to the medial epicondyle of the humerus to enter the cubital tunnel. Near elbow, ulnar nerve gives motor branches to flexor carpi and medial portion of flexor digitorum profundus.

In forearm, it gives rise to a palmar cutaneous branch which arises near the middle of the forearm and supplies the skin on the medial part of the palm, and the dorsal cutaneous branch which arises in the distal half of the forearm and supplies cutaneous sensation on the dorsal, ulnar surface of the hand and digits 4 and 5.

At the wrist, the nerve enters Guyon's canal and divides into a superficial sensory and deep motor branch. The superficial branch supplies sensation to the palmar surface of the ring and the little fingers. The deep motor branch supplies abductor digit minimi flexor digit minimi muscles, opponens digiti minimi, third and fourth lumbricals, the palmar and dorsal interossei, the flexor pollicis brevis and adductor pollicis brevis and first dorsal interosseous. In essence, ulnar nerve supplies all small muscles of hands except abductor pollicis brevis, flexor pollicis brevis, opponens pollicis and 1st and 2nd lumbricals (which are supplied by median nerve).

Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition
2. Preston DC. Distal Median Neuropathies. In: Entrapment and other focal neuropathies; Neurologic Clinics: WB Saunders company, August 1999
3. http://depts.washington.edu/anesth/regional/ulnarnerve.html

MEDIAN NERVE ANATOMY

Median nerve arises from C5-T1 roots. In upper arm, it does not give any branches. Once in the forearm, the nerve passes between the two heads of the pronator teres (PT) muscle, and innervates them. The nerve then innervates flexor digitorum superficialis (FDS) and flexor carpi radialis (FCR).


The median nerve’s largest branch, the anterior interosseous nerve originates approximately 5 cm distal to the radial epicondyle, travels between the flexor pollicis longus (FPL) and flexor digitorum profundus (FDP) mus­cles, and finally reaches pronator quadratus, supplying all the three muscles.


Just before reaching the carpal tunnel, the palmar cutaneous branch (a sensory nerve) leaves the trunk of the median nerve and enters the palm above the flexor retinaculum, outside the carpal tunnel. Palmar cutaneous branch supplies sensation over the thenar eminence. The majority of the median nerve enters the hand via the carpal tunnel. In the palm, the median nerve terminates into motor and sensory divisions. The motor division supplies first and the second lumbricals, opponens pollicis, abductor pollicis brevis, and superficial head of the flexor pollicis brevis.


The sensory fibers of the median nerve that pass through the carpal tunnel supply sensation to the index and the middle fingers in addition to the medial thumb and lateral half of the ring finger.


Reference:

1. Richard S Snell, Clinical Anatomy: Lippincott Williams & Wilkins, 7th edition
2. Preston DC. Distal Median Neuropathies. In: Entrapment and other focal neuropathies; Neurologic Clinics: WB Saunders company, August 1999