Chapter 68 Nerve Injuries
This chapter includes the essentials of treatment of nerve injuries in the digits, palm, and wrist. Although many of the principles discussed here can be applied to injuries in the forearm and arm, more detailed discussions of more proximal nerve injuries can be found in Chapter 62 on peripheral nerve injuries. Nerve entrapments and compression neuropathies also are discussed in detail in Chapter 62. Reconstructive procedures including tendon transfers are discussed in Chapter 34, and an expansion of the discussion of microsurgical technique can be found in Chapter 63.
At times, it is difficult to evaluate the extent of nerve injury in the hand. Factors that interfere with the examination of the nerves in the hand include other injuries that may be life threatening or limb threatening, patient intoxication, anxiety or lack of cooperation of the patient, and injury in a child. These factors and others, including an extensive injury to the hand, may cause nerve injuries to be overlooked during the initial or preliminary examination. If the conditions are not satisfactory for a thorough examination during the initial evaluation, the hand should be reexamined within a reasonable period to determine the extent of nerve and other injuries sustained. An injury to the digital nerves frequently is overlooked; however, if a flexor tendon function deficit is present after a finger laceration, at least one digital nerve probably has been injured as well. A high index of suspicion is necessary in the evaluation of patients with hand injuries. At least four areas of consideration are important when evaluating a patient with an injury to a nerve in the hand: (1) type of injury, (2) sensibility evaluation, (3) motor function, and (4) sudomotor function (sweating).
Nerve injuries seen in a civilian practice commonly are caused by one of several mechanisms, including direct trauma (blow to the limb, fracture, missile wound), laceration, traction or stretching, and entrapment or compression. To help determine the type of treatment and to arrive at tentative prognostic projections, it is helpful to recall the classification of nerve injuries according to Seddon and Sunderland (Table 68-1). Common injuries such as bumping the “funny bone” (ulnar nerve at the elbow) fall easily into the category of neurapraxia (type I injuries), and lacerations are classified as neurotmesis (type V injuries); however, closed injuries with partial nerve deficits are not classified as easily, and the prognosis may not be as well defined. The extent to which the nature of the injuring agent determines primary and secondary repair is discussed in this chapter under their respective headings. Additional discussion of extent of injury may be found in Chapter 62.
From MacKinnon SF, Dellon AL: Surgery of the peripheral nerve, New York, 1988, Thieme.
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).
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.
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.
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.
Three basic tests are recommended for motor function: grip strength, key pinch, and tip pinch strength. The squeeze grip dynamometer should be used, and the results should be recorded at all five positions with three successive determinations. This reflects the overall integrated function of the hand, in addition to areas of extrinsic and intrinsic muscle deficits.
Pinch strength is measured using a pinch dynamometer. Applying the thumb tip to the radial aspect of the middle phalanx of the index finger measures key pinch. Three successive determinations should be made, and the opposite hand should be measured as well. Pinching with the index tip to the ulnar side of the tip of the thumb allows measurement of tip pinch values. Three measurements should be made.
The loss of sweating is an indicator of nerve disruption and loss of sympathetic function. Sweating may return without a return of two-point discrimination; however, usually it returns with the return of two-point discrimination. A statement relative to sweating should be included in the evaluation.
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.
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.
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.
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.
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.
Incisions to expose the nerve and mobilize the nerve proximally and distally should be made in accordance with proven principles of skin incisions in the palm. They should not cross flexion creases at right angles, skin flaps should not be devascularized, and additional neurovascular injury should not be created in extending the skin incisions. The exact extent to which a nerve can be mobilized without creating ischemia is unknown. Generally, within the digits, palm, and wrist, extensive mobilization of the nerve from its surrounding tissues is insufficient to cause harm. Magnification is extremely helpful to permit the most precise and accurate restoration of the anatomy. In the palm and fingers, the magnification achieved by 2.5× to 4.5× magnifying loupes usually is sufficient to allow accurate repair. More proximally, magnification achieved with an operating microscope is more helpful in allowing satisfactory anatomical repair. The operating microscope also may be extremely helpful in repair of the terminal branches of the proper digital nerves distal to the distal flexion crease of the finger. Suture materials reflect the amount of tension to be applied to the nerve repair. Generally, in the forearm, wrist, and hand, 8-0 and 9-0 monofilament nylon sutures are used. Usually in the palm and digits, a repair using a pure perineurial neurorrhaphy (fascicular) (Fig. 68-6) or a combination epiperineurial-perineurial neurorrhaphy (Fig. 68-7) is sufficient for satisfactory anatomical repair.
FIGURE 68-6 Perineurial (fascicular) neurorrhaphy. A, Epineurium has been excised and fascicles exposed. B, Suture passed through corresponding fascicles on either side of cut surface of nerve. C, Neurorrhaphy completed, usually with two 10-0 nylon sutures in each fascicle.
FIGURE 68-7 Epineurial-perineurial neurorrhaphy. A, Epineurium has been excised and retracted. Suture has been placed through epineurium, near large fascicle at periphery of nerve, and then through perineurium of fascicle. B, Suture passed through epineurium of matching fascicle on opposite side of cut surface of nerve, and then out through epineurium. C, Repair completed, after suturing other suitably matched fascicles.
At times, as a result of extensive destruction, a segmental nerve defect is created that cannot be overcome through nerve mobilization, joint flexing, or rerouting of a nerve. A principal indication for nerve grafting in the hand is the bridging of defects after segmental nerve injury if a tension-free neurorrhaphy cannot be accomplished. Less commonly seen indications include nerve grafts to innervate free vascularized muscle grafts and to innervate free neurovascular island flaps.