Anatomic Level of Nerve Injury
Upper extremity PNI most frequently occurred at the upper arm level (44%). Sixty-two percent of the 58 radial nerve injuries occurred in the arm, 6.9% were at the elbow level, 19% in the forearm, and 12% in the wrist. Median nerve injuries most commonly were at the forearm level (10 of 25, or 40%), 36% were in the arm, 8% were in the elbow, 12% in the wrist, and 4% were in the palm. Ulnar nerve injuries occurred with equal frequency (13 of the 38 injured ulnar nerves) at the forearm and elbow levels, 21% were in the arm, and the remaining 11% in the wrist.
Of the 28 sciatic nerve injuries, 61% of the injuries were at the pelvic level, the remainder were in the upper leg. Only one tibial nerve injury occurred at the ankle level, the remaining seven injuries were in the lower leg. Of the 39 peroneal nerve injuries, 56% of the injuries were at the level of the lower leg, 33% were at the knee level, and 10% were at the ankle level. Femoral nerve injuries occurred with equal frequency at the pelvic and upper leg levels (n = 2 at each level).
Grade of Nerve Injury and Functional Outcome
The frequency distribution of grade of nerve injury, using a modification of the Sunderland grading system (as outlined in the Patients and Methods section) is presented in Figure 5. Note, grade of nerve injury information could not be ascertained in four of the 200 injured nerves. There were no significant differences in the frequency of injury grade in the overall, nor in the individual nerve injury population (chi squared = 15.3, p = 0.08).
Functional outcome could be determined with good accuracy for 125 of the 200 injured nerves. Of these, 40% returned to normal function, 16% had good function, 10% had average recovery, 22% had poor recovery, and 12% had no function in the injured nerve territory. Final functional outcome was assessed from 5 to 1,786 days after injury (mean, 300 days; median, 133 days).
There was no relationship found between grade of nerve injury and cause of injury. However, severity of nerve injury was found to strongly correlate with functional outcome (rho = -0.744, p < 0.001). Of the cases in which both nerve injury grade and outcome were both known (n = 125), 97% of grade 1 nerve injuries attained a normal functional outcome and 3% had good function; grade 2 nerve injuries had mostly good to normal outcome; grade 3 and 4 had more variable outcome; and 83% of grade 5 nerve injuries had no or poor functional recovery. No grade 5 injury attained a normal functional outcome.
Sixty percent of patients in the study had an associated head injury, and in 7.4% of patients, the head injury was severe enough to result in a coma. Thoracic spine injuries occurred in 9.3%, lumbar spine injuries in 9.9%, fractured rib(s) in 39%, internal thoracic injuries in 34%, vascular injuries in 34%, and 9% of patient with peripheral nerve injuries suffered tendon injuries. Injuries occurring in musculoskeletal structures anatomically adjacent to injured nerve are listed in Table 2. Humeral fractures accompanied 72% of radial nerve injuries, whereas radius/ulna injuries occurred with 45% of median and ulnar nerve injuries. Pelvic fractures occurred with 79% of sciatic nerve injuries, and an injury to the tibia/fibula was present in 56% of peroneal nerve injuries.
In the population of trauma patients with humeral fractures (444 cases), the incidence of upper extremity nerve injuries was as follows: radial nerve, 9.5%; median nerve, 1.4%; and ulnar nerve, 3.8%. Within the population of patients with radius/ulna fractures (703 cases), 1.3% median nerve and 2.4% ulnar nerve injuries were diagnosed. Femur fractures (818 cases) were accompanied by sciatic nerve injuries in 1.1% of cases. Within the population of patients with pelvic fractures (1,283 cases), the incidence of sciatic nerve injuries was 1.7% and 0.16% for femoral nerve injuries. Tibia and fibula fractures (996 cases) were accompanied by peroneal nerve injuries 2.2% of the time and tibial nerve injuries 0.50% of the time. Hip dislocations (168 cases) occurred with sciatic nerve injuries in 7.1% of cases.
The overall incidence of PNI was 2.8% from our population of patients with multiple injuries over the past 11 years. There have been only rare publications on PNI that provide some comparison to the inferences of the present study. [14,15] For example, a large series on neurotrauma in 21,973 patients from New South Wales treated in 1977 reported a similar PNI incidence of 2%.  The dominance of male sex (83% of patients were male) and age distribution is consistent with the existing literature on trauma. [11,15-18]
The annual incidence of PNI in the present study started to increase in the beginning of the decade with a steep rise in 1993 and 1994. The initial increase may have reflected more thorough data collection from the use of standardized trauma assessment forms, introduced in 1989 at SHSC. [9,10] There is no obvious explanation for the marked rise in 1993 and 1994; however, there was an increase in total trauma admissions at SHSC during 1993 and 1994 and 1994 and 1995 (approximately 20%). This increase may be one contributing factor, although PNI incidence decreased in subsequent years, despite overall trauma admissions staying more or less constant.
The majority of the patient (52%) treated by the SHSC trauma center had been involved in MVCs, a Figure thatis in agreement with other trauma center studies.  Although MVCs were responsible for 46% of the PNI, only 2.5% of patients treated for injuries after an MVC were found to have sustained a PNI. Industrial accidents, gunshot wounds, motorcycle and recreational motor vehicle crashes, and stab wounds represented much higher risk activities. Many of these injuries resulted from a sharp mechanism of damage to the nerve. Upper extremity PNI, analyzed by McAllister et al.,  reported a sharp object most frequently producing the lesion, either by domestic or industrial accidents. However, this report was based on a patient population referred to a hand surgery unit, with most cases seen after diagnosis of injury. In a report of neurovascular trauma of upper limb, penetrating injuries dominated.  The cause of PNI from developing countries is also predominantly a penetrating injury; 98% of 74 patients over a 5-year retrospective study reported from Pakistan had penetrating injury, with 83.8% injured by gunshot wounds, whereas less than 1% had been injured in an MVC. 
The literature is consistent in reporting the higher incidence of PNI in the upper compared with the lower extremity.  Additionally, in the upper extremity, the majority of PNI occur at the level of the upper arm. [6,20] This area is where the radial nerve was most commonly injured in our study. The exceptions reported in the literature of ulnar nerve injury predominating at elbow  and the median nerve injury occurring most often at the wrist  may reflect the populations studied. Stone and Keenan investigated patients with brain injuries, and included the pressure neuropathy of the ulnar nerve, which is often associated with head injuries.  McAllister et al. studied patients with sharp injuries to the upper extremities predominantly at wrist, at a referral center for hand surgery.  It is interesting here to observe that lower extremity peripheral nerves are much more commonly affected in childhood trauma and almost all had an underlying bony injury. 
PNI are frequently associated with traumatic brain injury. The incidence depends on the population studied. In our patients, from a Level 1 trauma center, 60% of patients with PNI also had some form of head injury. Moreover, the incidence of PNI in our overall trauma population (2.8%) was almost identical to the incidence of PNI in the patients who sustained a head injury. Our data also did not reveal a higher incidence in the patients with the more severe head injuries. However, a prolonged depressed level of consciousness and inability to perform a full peripheral neurologic assessment may have resulted in some cases of PNI being missed. In studies of patients admitted with severe traumatic brain injury to rehabilitation units, the reported frequency of peripheral nerve dysfunction varies from 7%,  10%,  11%,  to a high of 34%. 
Evaluation of the type of PNI with associated head injuries revealed that many could be explained on the basis of initial trauma, for example, humeral fracture with radial nerve injury, posterior acetabular displacement with sciatic nerve injury, and pelvic fracture with femoral nerve injury.  Some of the delayed neuropathies were attributed to poor bed positioning and pressure, especially ulnar and peroneal. [4,6,22] Both initial trauma and a delayed posttraumatic mechanism contribute to peripheral neuropathy. Garland and Bailey  reported an 11% incidence of initially missed musculoskeletal injury and a similar incidence of delayed diagnosis of peripheral neuropathy in their retrospective study of 91 head injured adults. In their report, the majority of the PNI had associated local skeletal injury, or resulted from pressure by hematomas and bed positioning.
In the present study, 78% of PNI were diagnosed within 4 days. Delay in diagnosis of PNI are often attributed to the severity of associated head injuries, because the dysfunction is not brought to the attention of the physician by the patient with a head injury or all the neurologic deficits are assumed to be due to central nervous system injuries.  However, in a recent study, no statistical association between the severity of head injury and the delay in diagnosis of brachial plexus injury was identified.  For the more distal PNI, an ischemic or badly injured limb may also make clinical assessment difficult. In the present study, upper extremity nerve injuries tended to be diagnosed much earlier than lower extremity ones. This finding may have occurred because of the bedridden nature of the patient with multiple injuries, with the lower limb neurologic deficit not clearly manifested until the patient was mobilized and ambulated. Alternatively, the onset of PNI may truly have occurred in a delayed fashion, secondary to the underlying leg musculoskeletal injury (compression from hematoma, compartment syndrome) or from a complication of the injuries management (traction or surgery). The delay in diagnosis of femoral nerve injuries is well recognized,  often being attributed to the need for emergency management of an adjacent life-threatening (vascular) injury, with the initial femoral nerve injury being overlooked. Moreover, the femoral palsy often does not declare itself until the patient attempts to ambulate.
The skeletal injuries were found to have a very close relationship to the PNI in our study, which is well supported in the literature. [25,26] Fractures and other musculoskeletal injuries are common and may damage the adjacent nerves either by direct trauma or stretch with hemorrhage in the nerve.  Adduction injury of the knee and dislocation of proximal tibial fibular shaft very often injures the peroneal nerve, as is the radial nerve injured frequently in cases of humeral fractures. In children, 52% of type III supracondylar humerus fractures injured the median nerve when displaced posterolaterally, whereas radial nerve involvement was 28% (always with posteromedial displacement).  Similarly, axillary nerve injury has a very close association with shoulder dislocation and blunt injury to the shoulder. [29,30] Due to the associated movement at the shoulder, cases of scapular fracture also injure the axillary nerve along with the brachial plexus.  Our observations regarding brachial plexus injury and shoulder trauma in the SHSC trauma population was reported earlier.  Femoral nerve injury is known to occur secondary to an iliopsoas hematoma from high energy sports and also with pelvic fractures. [24,31] The sciatic nerve injury is very often associated with dislocated hip and is, unlike the femoral neuropathy, diagnosed early.  It is important to recognize the PNI with musculoskeletal trauma at the earliest possible point, because approximately 50% of neuropathies are potentially preventable and early diagnosis yields optimal results with surgical or nonsurgical treatment.
Similar to the close association between the injuries to the subclavian artery and brachial plexus, close proximity of median and ulnar nerves to the brachial artery makes them more vulnerable to concomitant injury. As many as 50% of the brachial artery injuries had associated PNI, often with an underlying skeletal fracture. [19,33] It is crucial to recognize the PNI, because the long-term disabilities are caused by nerve injury, whereas vascular repair itself is often successful in revascularizing the limb.  At exploration for vascular repair, the nerve injury may not be recognized unless looked for. In penetrating injuries, acute repair of the divided nerve produces the best long-term results, which approach close to 50% good outcomes.  On the other hand, bluntly injured nerves and transected, but heavily contused, nerves should not be repaired primarily. 
The Abbreviated Injury Scale score and peripheral nerve function recovery had a statistically significant relationship, and the Abbreviated Injury Scale was the most valid prognostic classification in assessment of war inflicted PNI.  Most of our patients (71%) had an ISS between 10 and 29. There was no relationship found between the grade of nerve injury and the cause of PNI. The outcome, however, strongly correlated with the severity of the nerve injury. Both ISS and Abbreviated Injury Scale at higher scores reflect the overall injury severity and the nerve injuries are also likely to be severe (e.g., crush, laceration). The majority of these are vehicular crashes. Permanent disability (2 years after injury) has strong association with increasing ISS scores.  In a group of 49,500 patients analyzed by van der Sluis et al.,  97% of residual disabilities caused by neuropathy and myositis ossificans were direct consequences of the original injuries, whereas 3% were complications during hospitalization. In their study, many thoracic and abdominal injuries were accompanied by injuries that caused disabilities in other body parts. Disablement (Glasgow Outcome Scale (GOS) scores 3 and 4) was especially related to injuries of the nervous system (spinal cord injuries and peripheral neuropathies), in the majority of patients with thoracoabdominal trauma, indicating the vulnerability of the nervous system. [17,36] However, even moderately disabled patients (GOS 4) continued to show recovery until the end of first year of follow-up and up to two thirds of patients with multiple injuries eventually returned to work. [16,37] The recovery pattern of PNI in our series also shows a similar trend. These observations support a thorough initial examination and evaluation of a patient with multiple injuries for early diagnosis and management of PNI.
The authors thank Cyndy Rogers for assistance with data collection and Dr. Michael Schwartz for critical review of the manuscript.
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