When evaluating the injured hand for sensibility, in addition to an awareness of the classic sensory distribution of the median, radial, and ulnar nerves (Fig. 68-1), it is helpful to recall the autonomous sensory distributions of the median, radial, and ulnar nerves in the volar pulp of the index finger, the volar pulp of the little finger, and the thumb-index web space. If the injury is a laceration, and the nerve has been transected, the examination usually is more definitive than in closed injuries or in lacerations in which the depth may not be fully known. Even if a wound is to be explored to determine the extent of the nerve injury, it is helpful to document the clinical deficit before surgical exploration. Careful evaluation, especially in the presence of a closed injury, defines the initial deficit, allowing for assessment of progress if observation of the injury is elected rather than exploration of the nerve. Closed partial rupture of a common digital nerve in the palm requiring MRI and surgical exploration for diagnosis was described. The customary methods used to evaluate damaged sensory nerves include the use of a sharp pin to assess pain, a cotton-tipped applicator or a finger eraser to assess light touch, and the tips of a paper clip or commercially prepared tool to assess two-point discrimination. Normal two-point discrimination usually is 6 mm or less. If the nerve is transected, a patient would not feel light touch, would not appreciate the pin as a sharp stimulus, and would be unable to discriminate between one and two points. Patients with closed injuries or partial injuries to nerves may show spotty appreciation of light touch and pain and have markedly widened two-point discrimination (Fig. 68-2).

FIGURE 68-1 Distribution of major nerves innervating hand for sensory function.

FIGURE 68-2 Two-point discrimination of hand sensibility, palmar surface. Dorsal surface averages 7 mm distally to 12 mm proximally.

Motor Function

Although the function in the hand served by the underlying median nerve includes the proximally innervated pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum sublimis, index and middle flexor digitorum profundus, flexor pollicis longus, and pronator quadratus, the usual median-innervated muscles of concern in the hand include the lumbricals to the index and long fingers, the opponens pollicis, the abductor pollicis brevis, and the superficial portion of the flexor pollicis brevis. The single median nerve–mediated motor function that usually is checked is apposition of the tip of the thumb to the pulp of the ring or little finger with palpation of active contraction of the abductor pollicis brevis muscle belly to supplement the visual inspection. Anatomical variations that cause cross-innervation of the muscles usually innervated by the median nerve should be kept in mind.

The muscles proximally innervated by the ulnar nerve include the flexor carpi ulnaris and flexor digitorum profundus tendons to the ring and little fingers. In the hand, the ulnar-innervated muscles of interest include the flexor pollicis brevis, adductor pollicis, abductor digiti minimi, flexor digiti minimi, opponens digiti minimi, and all the interosseous muscles. When testing for motor function of the ulnar nerve in the hand, the usual motions mediated by the ulnar intrinsic muscles include active abduction of the middle finger from the ulnar to the radial side with the palm resting on a flat surface. This motion should be observed carefully to exclude the functions of the long flexor tendons, which tend to converge the digits and confuse accurate interpretation of the function of the volar interosseous muscles, and the long extensor tendons, which tend to diverge the fingers and confuse accurate interpretation of the dorsal interosseous muscles. Additionally, thumb adduction usually is tested by having the patient maintain a piece of paper tightly in the thumb-index web, squeezing the paper between the thumb interphalangeal joint and the base of the index finger proximal phalanx. If the adductor is weak or paralyzed, the patient is unable to hold the piece of paper against resistance. The function of the abductor digiti minimi also may be tested by having the patient abduct the little finger against resistance and by palpating the muscle belly of the abductor digiti minimi (Fig. 68-3). Although clawing of the little and ring fingers may not be seen at the time of an acute injury, it is present sometimes, and careful observation of the hand should reveal this finding. The first dorsal interosseous muscle may receive an anomalous innervation from the median nerve in about 10% of hands. The posterior interosseous or superficial branches of the radial nerve also may supply the first dorsal and the second and third dorsal interosseous muscles in some hands.

FIGURE 68-3 Testing of function of abductor digiti minimi. Patient abducts little finger against resistance while muscle belly is palpated.

Proximal muscles innervated by the radial nerve include the triceps, brachioradialis, supinator, and anconeus. The radially innervated muscles having influence on the hand include the extensor carpi radialis longus and brevis, the extensor carpi ulnaris, the extensor digitorum communis, the extensor indicis proprius, the extensor digiti minimi, the abductor pollicis longus, the extensor pollicis longus, and the extensor pollicis brevis. The motions that can be examined and that are mediated by the radial nerve in the hand and wrist include wrist dorsiflexion and radial and ulnar deviation and thumb abduction and extension. Metacarpophalangeal extension, mediated by the radial nerve, should be evaluated carefully so that the examiner is not confused by extension of the proximal and distal interphalangeal joints of the fingers, controlled by the intrinsic muscles.

Sudomotor Function

Usually a denervated area shows no sweating within about 30 minutes after a nerve injury. It is helpful to compare the normal and suspected injured areas by palpation with a dry fingertip.

Postoperative Assessment

In evaluating the progress of peripheral nerve injury and repair sensibility testing, motor testing, subjective evaluation, and sudomotor function are important.

Sensibility Evaluation

The basic minimum tests recommended for sensibility evaluation are stationary two-point discrimination and moving two-point discrimination.

Two-Point and Moving Two-Point Discrimination Testing

Technique 68-1

The hand should be warm, and the instrument should be at room temperature.

Rest the hand on a flat surface, palm up.

Apply a blunt, two-pointed caliper or paper clip distally over the distal pulp in the longitudinal axis on the radial or ulnar side (Fig. 68-4). The pressure applied should be just slightly less than blanching pressure. Test each area three times. Start at a width of 10 mm, and gradually decrease the distance.

Perform the moving two-point discrimination test in a similar fashion. Apply the caliper in an axial direction, and move it from proximal to distal along the digital pad. Two of three correct answers are considered proof of perception with either test.

FIGURE 68-4 Two-point discrimination testing. SEE TECHNIQUE 68-1.

Nerve Regeneration

After a nerve injury, the response in the proximal elements of the peripheral nerve includes an increased rate of metabolic activity and proliferation from the nerve cell bodies distally, resulting in the sprouting of axonal processes at the injury site within the first 1 to 3 weeks. The response distally consists of the elements of wallerian degeneration, including disruption of the myelin sheath and phagocytosis, and preparation of the distal segment to receive the regenerating elements of the proximal axons. A more detailed discussion of this response is presented in Chapter 62.

Usually, after repair of a sensory nerve (digital, pure sensory, mixed motor and sensory), the area of anesthesia decreases in size as regeneration progresses and the quality of sensation changes. In 2 to 3 months, the entire area supplied by the nerve may become paresthetic. It then becomes hyperesthetic to light touch or cold. Firm pressure usually is less painful. With time and the use of various physical and occupational therapy techniques, the hyperesthesia resolves. Patients usually have less objectionable sensation after the period of hyperesthesia.

With progression of regeneration, the quality of sensation improves significantly within the first 1.5 to 2 years with additional gradual improvement thereafter. Fully normal sensation with appreciation of functional two-point discrimination rarely is expected in adults. Although the functional result after digital nerve regeneration usually is better than that seen for injuries to nerves more proximally and to mixed motor and sensory nerves (e.g., the ulnar nerve), age seems to have an influence on the final functional result after peripheral nerve repair. A fully functional hand with minimal loss of power can be expected in children after epineurial repair. Studies suggest that patients younger than age 20 can be expected to have a better prognosis for return of functional two-point discrimination than can older patients. Patients younger than age 40 have been shown to have better sensibility recovery than patients older than age 40. Although exceptions may be encountered, it is rare for patients older than age 50 to regain more than protective sensation.

In considering the repair of multiple digital nerves in an injured hand, the location of the injured nerves should be considered. Although it is general practice to repair all digital nerves, the most important areas of sensory innervation of the digits include the ulnar side of the thumb, the radial side of the index and middle fingers, and the ulnar side of the little finger. These areas are important for pinch and for ulnar border contact of the hand. These nerves should be given priority if there are limiting factors, such as prolonged operative time in a patient with multiple injuries, multiple soft tissue problems on the various fingers, or segmental nerve loss.

Primary and Delayed Primary Nerve Repair

Timing of Repair

The controversy regarding the timing of nerve repairs in general is unresolved. The terms applied to the timing of the nerve repair include primary repair (immediately after injury, or within 6 to 12 hours), delayed primary repair (usually within the first 2 to 2.5 weeks), and secondary repair (after 2.5 to 3 weeks). Advocates of primary repair are supported by experimental work, which suggests that the results may be better after primary repair. Authors advocating a delay in repair are supported by the clinical observations after nerve injuries that occurred during wars. Generally, however, the longer the delay in repair, the poorer the return of motor function that can be expected. The reinnervation of denervated muscle may occur 12 months later; however, after that period, irreversible changes occur in the muscle cells and there is little hope of recovery of motor function after reinnervation. The return of sensation has been observed when nerve repair has been performed 2 years after injury. Satisfactory return of function can occur after nerve repair performed within 3 months of injury. Delay in nerve repair assumes the following: (1) muscle atrophy occurs, (2) contraction in the endoneural tubules of the distal segment progresses, (3) retraction of the nerve ends may occur, (4) joint contractures may develop, (5) a second operation is involved, and (6) intraneural alignment of fascicles may be more difficult. Additional factors to consider in the timing of peripheral nerve repairs include the condition of the patient and the state of preparedness of the surgeon and the institution, including the availability of instruments and personnel to allow a satisfactory primary repair.

Regardless of the timing of repair, tension should be avoided at the site of nerve repair. Nerve grafts accomplished without tension heal and function better than nerve repairs performed with tension, despite the need for regeneration to occur across two suture lines with a nerve graft.

Indications

In general, a nerve repair can be done immediately after injury or within the first 2 to 2.5 weeks in the presence of a clean, sharp injury. A delay of 2 to 2.5 weeks can be caused by a variety of factors, including the condition of the patient and the availability of appropriate personnel, including a surgeon to treat the wound. We repair injured nerves, if the wound is clean and sharp, either on the day of injury or in the first 5 to 7 days.

Secondary Nerve Repair

Indications

Several conditions should influence the surgeon to delay the repair of injured peripheral nerves, including (1) the existence of extensive soft tissue injury and loss with extensive trauma to the nerve, (2) the presence of extensive wound contamination, (3) the presence of multiple limb injuries requiring aggressive and expeditious management in preference to the nerve injury, (4) the existence of extensive crush injury, (5) the presence of an extensive traction injury, and (6) a nerve injury that has been treated by another surgeon, in which the extent and nature of the nerve repair are unknown to the second treating surgeon.

If multiple tissue injuries have occurred, especially in the presence of soft tissue loss, the nerve repair is secondary and is indicated only after good skin coverage has been obtained. After satisfactory and complete healing of all wounds and the establishment of satisfactory nutrition to the skin and other tissues of the hand, common and proper digital nerves usually can be sutured as a secondary procedure 3 weeks or more after injury. Although most reports suggest that the results after secondary repair are similar to, if not better than, the results after primary repair, the best results seem to occur if repairs are done within the first 3 months of injury. The reports of patients treated after World War II suggest that useful sensation can occur after repairs 2 years after injury. This is not the normal expectation, however. Return of motor function after excessive delay is even more unpredictable.

With a severe soft tissue injury, skin coverage is a priority. The extent of intraneural injury is unknown. It is best to wait 3 to 6 weeks to allow clear demarcation of intraneural scar to have a better chance at more precise nerve apposition at the time of repair.

An extensively contaminated wound may require a delay in nerve repair because infection may supervene and delay not only definitive treatment of the nerve but also wound closure itself. Although initial débridement may remove significant wound contamination and allow delayed primary repair, if wound contamination and necrotic material persist, additional débridements of necessity interpose a delay until definitive nerve repair later.

Multiple limb injuries may create priorities of wound cleansing, bone stabilization, vascular repair, and soft tissue coverage. Segmental injury to nerves also might dictate secondary repair. Crush and traction injuries cause intraneural damage that cannot be assessed accurately at the time of primary wound evaluation. When the nerve has sustained extensive intraneural or extensive segmental intraneural injury or loss because of crush or traction, it is best to wait 3 to 6 weeks to allow clear demarcation between scar and normal nerve to become established. If the extent of intraneural injury is unclear, or if extensive segmental loss of nerve requires grafting, primary repair should not be done and secondary repair or nerve reconstruction by graft should be considered.

A special situation occurs when the patient’s initial and primary care have been accomplished by another surgeon. Frequently, one does not know the extent of the initial injury and has no awareness of the nature of the repair. At times, it may be necessary to consider exploration of the nerve, possibly considering secondary repair. Exploration of the nerve may reveal that secondary repair is unnecessary. The exploration of a nerve injury in such a situation may help ensure that a skillful nerve repair has been done, which is one important determinant of outcome.

Suturing of Nerves

For additional discussion of surgical techniques, see Chapter 62 on peripheral nerve injuries and Chapter 63 on microsurgery. Generally, the principles that apply to the suture of other peripheral nerves also apply to suturing of the peripheral nerves of the hand. Important considerations include (1) mixed versus pure motor or sensory nerves, (2) internal arrangement of the nerves, (3) incisions to be used, (4) amount of mobilization and limb positioning required for tension-free apposition, (5) suture materials to be used, (6) nature of the suture arrangement, (7) magnification, and (8) postoperative management.

Careful technique is crucial to provide the best restoration and repair of the anatomy. The internal arrangement of the nerve in the palm and digits usually is oligofascicular as described by Millesi (Fig. 68-5). In the median and ulnar nerves at the wrist, an intraneural polyfascicular or group arrangement is found. The outlook is better after repair of common digital and proper digital nerves because of their internal arrangement, their pure sensory function, and the short distance from the injury to the end organ.