Gunshot and Other Missile Wounds to the Peripheral Nerves

Missile injuries to the brachial plexus and peripheral nerves may be produced by both low- and high-velocity missiles. Low-velocity missile (less than 700 m/s) injuries are caused by hand guns, revolvers, and shell fragments (for which the velocity is generally around 300 m/s), although some authors exclude the last of these three. In such cases, nerve elements are damaged by small shock waves, by temporary cavitation, and sometimes by direct impact. Thus, the lesions are largely neurapraxia, and spontaneous recovery can take place, even in patients with severe neurologic deficits at presentation, unless the nerve is transected by direct impact. ¹^, ²^, ³^, ⁴^, ⁵^, ⁶ These lesions are characteristic of older military series ⁷^, ⁸ and civilian practice. ⁴ On the other hand, high-velocity missile (with velocities over 700 m/s, averaging 1,000 m/s) injuries, produced by modern rifles or machine guns, cause more extensive damage. The destructive effects of these projectiles depend on the amount of energy that is released, which in turn is determined by the mass, velocity, and angle of incidence of the bullet. Nerve elements are rarely injured by direct impact; rather, these injuries are most often attributable to shock waves and cavitation that cause them to be compressed and stretched. ⁹^, ¹⁰ These extensive injuries also involve soft tissues, blood vessels, and bones. Nerve structures, all or only in part, may be damaged outside the projectile path, at the longer nerve segment or at multiple levels. ¹^, ⁹ Furthermore, different degrees of injury usually coexist, and spontaneous recovery may or may not occur. In recent wars, the effects of blast explosions from improvised explosive devices are often devastating to the whole extremity, including the nerves. ¹¹

The first large series of brachial plexus injuries were reported by Brooks in 1954 ⁷ and Nulsen and Slade in 1956. ⁸ Thereafter, no large series were published for about 30 years, until the reports made by Kline and Judice in 1983 ⁵ and Kline in 1989, ⁴ who analyzed injuries in civilian practices. Generally, gunshot wounds to the brachial plexus are infrequent in civilian practice, such that there have been only few large series published over the past two decades. ²^, ³^, ¹² However, in recent military conflicts, these injuries constituted 2.6 to 14% of all peripheral nerve injuries. ¹³^, ¹⁴

The largest surgical series on peripheral nerve missile injuries have been based on war practice. In 1924, Delageniere ¹⁵ published his experiences from World War I among 375 surgically treated penetrating injuries (mostly gunshot injuries to the peripheral nerves). Pollock and Davis ¹⁶ reviewed their cumulative experiences with 397 cases from the same war. ¹⁶ After World War II, Seddon reported on the British experience with 699 missile nerve injuries, 8.6% of which were treated with nerve grafts, ¹⁷ while Woodhal and Beebe reported on American experiences with 3,656 nerve injuries, but only 30 grafting procedures. ¹⁸ Thereafter, there were no large series on this subject until the Vietnam War. At that time, Omer published a series of 917 injuries involving the upper extremity peripheral nerves, 753 (66.6%) of which were gunshot wounds, including 269 surgically treated nerves. ¹⁹ Similar experiences, with 135 nerve injuries operated on during the Vietnam War, were reported by Brown. ²⁰ Somewhat later, Samardzic et al reported a series of 90 missile injuries involving upper arm peripheral nerves operated upon during the war which took place within the former country of Yugoslavia. ²¹ Kline and Hudson also published their series of 64 surgically treated gunshot injuries from civilian practice. ²²

Few reports have detailed the incidence and results of the surgical management of sciatic nerve injuries. ²²^, ²³^, ²⁴^, ²⁵^, ²⁶ Published opinions based on World War II experiences generally were very pessimistic and led to the conclusion that nerve reconstruction should not be recommended, given that foot drop could be managed via tendon transfers, arthrodesis, or orthotic support. ⁵ Similarly, Seddon reported his experiences and concluded that there was no need to repair severe nerve lesions with lost substance. ²⁵ However, a number of recent papers ²³^, ²⁶ have challenged this traditional approach, particularly one paper that described a series of 324 patients with sciatic nerve lesions, including surgically managed gunshot wounds that affected 43 tibial and 42 peroneal divisions. ²²

As stated previously, the largest series of missile injuries to the peripheral nerves were drawn from war practice. ¹⁵^, ¹⁶^, ¹⁷^, ¹⁸^, ¹⁹^, ²⁰ However, these series are difficult to evaluate and compare, because they include heterogeneous patient populations, especially regarding the characteristics of the nerve lesions, timing of surgery, and surgical techniques used. It should be remembered that magnification, delicate instruments, and less reactive suture materials only became available for use during the Vietnam War. ¹⁹ Techniques such as interfascicular nerve and modified cable grafting also were not used at that time.

Gunshot wounds to the brachial plexus are technically difficult to explore and treat, since the anatomy is complex, including great vessels that are close to the nerve elements, such that intraoperative vascular injury is a genuine risk during surgery. However, recently, there have been considerable advances in this respect, owing to improved preoperative evaluations, intraoperative monitoring, and nerve repair techniques.

12.2 Clinical Characteristics

12.2.1 Brachial Plexus

Older reports used to emphasize partial neurologic deficits in large numbers of patients, with the potential for spontaneous recovery, especially in the upper trunk and posterior cord, but not with injuries affecting the lower elements. ⁷^, ⁸ In the first published series that Brooks reviewed, only 31.8% of 170 patients with open injuries were operated upon. ⁷ Nulsen and Slade reported a larger number of operated-upon patients, 76% of their selected case group. ⁸ Kline reported similar clinical characteristics in his series. ⁴ Complete or nearly complete functional loss in the distribution of all nerve elements at the injured level was present in only 19 patients (21%). Kline operated on 63.8% of his patients and stated that complete injury to one element could recover spontaneously, but often did not. Meanwhile, incomplete functional loss in the distribution of one element usually recovered spontaneously; but this did not guarantee that other elements would experience the same recovery.

In recent years, it has been appreciated that many missile injuries to the brachial plexus do not recover spontaneously; many, in fact, cause persistent pain and severe disability, even though lesions-in-continuity are common. ¹^, ¹¹^, ²⁷ Most of these lesions are associated with complete functional loss. ³^, ⁶ Kim et al documented complete loss of function in 69% of the nerve elements, which was clearly contradictory to older reports. ³ Moreover, Samardzic et al registered complete functional loss in the distribution of all brachial elements in 62.9% of patients, with spontaneous recovery noted only in 16.6%. ⁹ A significant number of patients with upper trunk and posterior cord injuries who present with only partial neurologic deficits will recover spontaneously, but not those with injury to the lower elements. ¹⁰ Patients exhibiting signs of spontaneous recovery over the first 4 weeks are likely to have a good or excellent outcome. ²⁷ It should be emphasized that lesions-in-continuity, with functionally and electromyographically complete loss persisting for 3 months after injury, displayed nerve impulse transmission in 23% of the elements, which meant that neurolysis was indicated as the surgical method of choice. ²⁸ Lesions affecting multiple levels of the brachial plexus are common, and will never recover spontaneously. ¹

12.2.2 Peripheral Nerves

Spontaneous recovery may also occur in a significant number of peripheral nerve missile injuries, though this recovery can be delayed for up to 11 months. ²⁹ Interestingly, the noted rates of spontaneous recovery were similar in the retrospective studies for World War I, World War II, and Vietnam War missile injuries, ranging from 67 to 69% of cases.

12.3 Characteristics of Nerve Lesions

12.3.1 Brachial Plexus

In previously published series, ⁴^, ⁵^, ⁷^, ⁸ a large majority of brachial plexus lesions preserved some nerve continuity. Brooks identified division of some neural elements in 29.6% of his patients who underwent surgical repair. ⁷ Meanwhile, Kline noted that 46.6% of the nerve elements had complete functional loss without any continuity. ⁴ Lesions-in-continuity were detected in 221 elements, among which 75% exhibited complete functional loss. Among nerve elements with incomplete loss, only seven required nerve repair. Conversely, studies on intraoperative nerve action potentials confirmed signs of early regeneration in 48 of these elements (28.9%), and only neurolysis or a split repair had to be performed. Samardzic et al reported that 23.9% of the nerve elements lacked any continuity and, consequently, were associated with complete functional loss. ⁹ Among the remaining nerve elements, 15.3% were preserved but compressed by an external scar, and 60.8% had lesions-in-continuity (fibrosis, a neuroma-in-continuity, or partial loss of continuity). Recent series have confirmed the predominance of nerve lesions-in-continuity. ³^, ⁶^, ¹⁴^, ²⁷^, ²⁸

Gunshot wounds to this region may also injure the neighboring vessels (e.g., axillary and subclavian arteries and veins), bones (e.g., clavicle, scapula, humerus, ribs), and viscera (e.g., lung, pharynx, esophagus). ⁶ Generally, there is a high incidence of associated injuries. The most frequent injuries are vascular, which are apparent in over 30% of patients. These vascular injuries are of two types. ²⁷ The first results in major vascular interruption, while the second is manifested as a pseudoaneurysm, which is often difficult to diagnose and treat. ¹² Bone fractures increase the risk of nerve damage since the shattered bone fragments become secondary projectiles and travel in almost all directions, causing extraneous damage to surrounding tissues. ¹^, ⁶

12.3.2 Peripheral Nerves

The radial nerve was the most commonly injured peripheral nerve in World Wars I and II. ¹⁶^, ¹⁷^, ¹⁸ Injuries were otherwise equally distributed among the rest of the upper extremity nerves. ¹⁹^, ²⁰^, ²¹ It should be noted that, in 26% of all patients, and in 32% of those with injuries to upper extremity nerves, there were multiple injuries that involved two or even three nerves. ²¹ Proximal injuries predominate in all of the published series. Preserved nerve continuity was noted in roughly one-third of surgically treated cases from the Vietnam War ¹⁹^, ²⁹ and in the majority of cases drawn from civilian practice. ²² In the series reported by Samardzic et al, ²¹