Fig. 1.1 Peripheral nerve: morphology. (a) The normal peripheral nerve is composed of neural tissue and connective tissue components. The nerve fibers may be myelinated or unmyelinated. (b) A population of myelinated and unmyelinated nerve fibers are seen. The basement membrane of the Schwann cell is a double basement membrane (arrow) that can only be identified by electron microscopy. A, axon; C, endoneurial collagen; M, myelin; NR, node of Ranvier; SCN, Schwann cell nucleus; ua, unmyelinated axon (uranyl acetate, 4750x).

Fig. 1.2 Peripheral nerve axon: anatomical organization. Axons are either myelinated or unmyelinated and are shown here as the small (yellow) fibers to the right. Myelinated axons are associated with a single Schwann cell, whereas unmyelinated axons are small, and multiple axons can be associated with one Schwann cell. Individual axons are immediately surrounded by thin collagen fibers forming an endoneurium and are further sorted into fascicles defined by a discrete connective tissue sheath known as the perineurium (green). Between these fascicles is the internal epineurium (dark yellow). A thicker connective tissue sheath, the external epineurium, encompasses all the fascicles that group together to form a single nerve. Nerves accommodate shortening and lengthening during flexion and extension of an extremity by being bounded by the epineurium and delimited by areolar connective tissue, the mesoneurium, interspersed with a protective fatty tissue cocoon.

(Used with permission from Mackinnon SE, Dellon AL, eds. Surgery of the Peripheral Nerve. New York, NY: Thieme; 1988:21.)

Fig. 1.3 Internal topographical anatomy of the ulnar nerve. The ulnar nerve has a distinct fascicular pattern as it courses distally from the forearm into the hand. The motor component of the ulnar nerve is found between the sensory component and the dorsal cutaneous fascicles. Distal to the dorsal cutaneous nerve branch point, the motor component is identified on the medial aspect of the ulnar nerve. This motor component branches from the ulnar nerve on its medial/ulnar aspect to become the deep motor branch, then dives deep to the leading edge of the hypothenar muscles to course around the hook of the hamate and innervate the intrinsic muscles. The sensory component of the ulnar nerve is a larger fascicular group than the motor component and innervates the ulnar aspect of the ring finger, the small finger, and the fourth web space.

Fig. 1.4 Internal topographical anatomy of the median nerve. Proximal forearm: The median nerve is composed of several motor and sensory fascicles. In the proximal forearm, the pronator teres fascicle is on the most anterior aspect, followed medially by the flexor carpi radialis (FCR) and palmaris longus (PL) fascicles. Further medially, the flexor digitorum superficialis (FDS) fascicular group is identified. This fascicular group usually includes two fascicles that correspond to two branch points to the FDS. The anterior interosseous fascicle is on the posterior aspect of the ulnar nerve and continues distally to become lateral/radial before its branch point. This fascicle includes a small sensory articular component to the wrist joint. It is important to acknowledge a thenar motor component within the sensory component. Distal forearm: The anterior interosseous nerve includes three fascicles: flexor pollicis longus (FPL), flexor digitorum profundus (FDP), and pronator quadratus (PQ)/articular. The FPL and FDP fascicles are large compared to the PQ fascicle and have an anterior orientation. The median nerve includes a recurrent thenar fascicle that is found posterior and lateral. As the median nerve courses distally, the sensory fascicles are revealed to have three major groups: first web space and radial aspect of thumb, second web space, and third web space. These groups have a lateral, middle, and medial orientation, respectively. The palmar cutaneous nerve branches from the anterior and lateral aspect of the median nerve. Hand: The recurrent thenar nerve branches from the...