Prognostic Factors Several factors influence the final outcome following nerve repair, most of them independent of the surgeon. These factors can be subdivided as follows: Patient age. Characteristics of the nerve, including: Topography of the motor neurons. Nerve microanatomy. Main muscle effectors. Characteristics of the nerve injury, including: Mechanism. Level. Length of the nerve defect. Associated injuries. Surgery. Postoperative rehabilitation. It has been generally accepted that a patient’s age is the most important predictor of outcome following nerve repair, with significantly better results generally observed in children and teenagers. The prognosis for functional recovery is the best in children younger than 10 years, with good to excellent results in more than 90% of cases. This compares with 75% in patients between 10 and 20 years old, with results in older children and adolescents still better than those attained in adults. On the other hand, there is no significant difference in the outcomes obtained between different age groups among adults. No critical age at which outcomes tend to decline has been established, though other factors may play a more significant role in the elderly. Possible explanations for the enhanced results that children typically experience are: (1) the earlier initiation of regeneration; (2) an increased rate of neural regeneration; (3) greater stability of the neuromuscular junction after denervation; (4) shorter extremities; and (5) increased adaptability and ability for other nonaffected muscles to substitute or modify their motor function to compensate for muscles that have been paralyzed. 1 It is obvious that repair outcomes vary between different nerves, even within the heterogeneous series that have been reported. Generally, repair of a pure motor or sensory nerve is technically simpler, and its results are better than for combined motor–sensory nerves because of the diminished likelihood of axonal mixing. Discrepancies in repair outcomes between nerves in the upper and lower extremities have also long been described, as well as greater recovery in the tibial nerve versus the peroneal nerve, and better outcomes with radial nerve versus median and peroneal nerve repairs. Most investigators have been unable to detect any meaningful difference in recovery potential between the median and ulnar nerves, though opposing claims also exist in favor of either one or the other. The reasons for differences in motor recovery potential include the topography of motor neurons in the spinal cord, characteristics pertaining to the nerve’s microanatomy, and the nature of the main muscle effectors. 2 Examining the topography of motor neurons within the anterior horns of the spinal cord, peroneal nerve neurons are found to be numerous and scattered, while radial nerve neurons are concentrated over a small area within the cross-section of the anterior horn. The topography of the neurons for other nerves is between these two extremes. Considering the characteristics of nerve microanatomy, the following may contribute to different nerve recovery potentials: A great proportion of intraneural connective tissue (e.g., within the peroneal nerve) makes it difficult for regenerating axons to grow into empty endoneurial tubes. A greater proportion of sensory fibers (e.g., within the median, ulnar, and tibial nerves) is a risk factor for poor recovery, because of the potential for cross motor–sensory reinnervation. An oligofascicular pattern within the nerve and sparse connections between the bundles increase the probability of good recovery (such are characteristics of the radial, musculocutaneous, and axillary nerve, but not of the tibial and peroneal nerves). Inadequate vascularization in some regions (e.g., the peroneal nerve as it passes by the fibular neck). With respect to main muscle effector characteristics, repair outcomes tend to be better in the following cases: If the main effectors receive their input relatively proximal within the limb (e.g., the main effectors for the musculocutaneous, axillary, radial, tibial, and femoral nerves). If functionally useful reinnervation of the main effectors requires relatively few nerve fibers (e.g., the tibial and radial nerves), as opposed to the lion’s share of the regenerating axons (e.g., the ulnar nerve). If complete return of muscle strength is not necessary for good functional recovery (e.g., contraction of finger extensors with only 20% of maximal strength results in minimal functional disability after radial nerve repair). If it is not necessary to restore precise or coordinated muscle contractions; such contractions only need to be restored by median, ulnar, and peroneal nerve repairs. If any major disability can be precluded or alleviated by muscles supplied by an uninjured nerve; only injuries to the peroneal, ulnar, and radial nerve lack such potential. Reviewing these factors, it is clear that risk factors portending poorer motor recovery are especially numerous for the peroneal nerve, which is likely why the peroneal nerve must be considered, among the major nerves, probably the worst candidate for graft repair. The peroneal nerve also has less connective tissue and is less vascularized than the tibial nerve, which is also protected by fatty tissue in the popliteal fossa. Contrary to the peroneal nerve, only one to three risk factors exist for nerves with the best recovery potential (e.g., the radial, musculocutaneous, femoral, and axillary nerve), while four to six risk factors are present among nerves with moderate motor recovery potential (e.g., the median, ulnar, and tibial nerve). Final repair outcomes are influenced considerably by the mechanism of injury and the severity of trauma. In particular, nerve injuries resulting from projectiles/missiles and from traction have a poorer prognosis than other types of injury, because they involve longer segments of nerve. Numerous authors have also recognized the influence of the repair level on the outcome ( ▶ Table 11.1). Poor prognosis after high-level repairs can be attributed to variations in nerve mapping, especially in cases of nerve tissue loss, and to the irreversible degeneration of sensorimotor effectors. Muscle atrophy starts within 3 weeks of denervation, with almost complete replacement of the muscle with fibrous tissue over the next 2 years. If the calculated reinnervation period for the main muscle effectors is longer than that, nerve repair cannot be accompanied by motor recovery, because of irreversible muscle fibrosis (e.g., useful reinnervation of hand muscles cannot be expected after ulnar nerve repair in the axilla). Conversely, after high radial nerve repairs, regenerating axons grow into distal effectors early enough to prevent irreversible muscle fibrosis (for thumb extensors, within 16–18 months). Such limitations do not apply to sensory recovery, which can be anticipated even after delayed and high-level nerve repairs ( ▶ Table 11.1 and ▶ Table 11.2). Nerve High Medium Low Median Above midarm Above the lower margin of the pronator teres muscle Below the pronator teres muscle Ulnar Above midarm Above the middle third of the forearm Middle and lower third of the forearm Radial Above midarm Above the nerve bifurcation Posterior interosseous nerve Musculocutaneous Above the biceps-brachialis muscle space Below the biceps-brachialis muscle space – Nerve High Medium Low Peroneal Above midthigh Above the final division Peroneus profundus Tibial Above midthigh Above the soleus muscle arc Below the soleus muscle arc Femoral Above Poupart’s ligament Below Poupart’s ligament – The length of nerve defect—which is determined by both the extent of the initial trauma and the passage of time (due to stump distraction)—impacts outcomes more than the length of the graft. In principle, shorter grafts do better than longer ones. Several authors have claimed that nerve grafts longer than 5 to 10 cm considerably limit the probability of a good outcome, even though experimental data indicate that certain other factors (e.g., the concomitant damage of effectors) also may be responsible for the poor results typically observed with long nerve grafts. 3 Combined nerve injuries, particularly simultaneous lesions affecting the ulnar and median nerve, are frequent, especially after projectile-caused wounds. Although opposing claims also exist, most authors consider that such injuries almost always result in a nonfunctional hand, warranting additional corrective measures. Comorbid injuries in the repair region (e.g., bone fractures, injuries to main arteries, and soft-tissue defects) influence repair outcomes through ischemia, perineural scarring, and defects involving the effectors. Useful motor recovery is more frequent among patients with less local damage. One of the most significant determinants of repair outcomes is the duration of time between the initial trauma and surgery. Progressive closing of distal endoneural tubes, resulting in increasingly disproportionate sizes in the proximal and distal nerve stumps, is the consequence of a prolonged preoperative interval. Delaying surgery beyond the aforementioned critical denervation period of 24 months is particularly problematic, particularly for proximal repairs. According to some published data, operations may be postponed safely for 4 to 6 months, but further delay may endanger motor recovery. If the preoperative interval is longer than 24 months, the outcome is likely to be poor, though good results have been sporadically reported for surgeries performed 3 or more years after injury. The choice of surgical procedure is directly influenced by the characteristics of the nerve injury and the timing of nerve repair. Unquestionably, the best results are obtained with neurolysis of lesions-in-continuity. In nerve transections, the chances for useful functional recovery are best following direct nerve suture. It should be emphasized that there is no significant difference in the results obtained with direct epineural or fascicular repair versus nerve grafting with nerve defects up to 5 cm in length. Certainly, other favorable circumstances are necessary in these situations. Consistent rehabilitation is also necessary for good recovery after nerve repair, particularly after repairs in the upper extremity. Soon after surgery, the patient should be encouraged to use his/her injured extremity as much as possible to prevent contractures and achieve maximal functional recovery. As stated at the outset, grading systems are needed not only for individual muscle and sensory functions, but also for the evaluation of entire nerve or plexus elements. Most nerves and plexus elements innervate one or more proximal muscles, a group of distal muscles, and also some distal sensory field, the functional importance of which may vary. 4 The British Medical Research Council (MRC) system for grading loss or the return of motor function after nerve injury and repair was originally based on grading systems developed to evaluate paralysis associated with poliomyelitis ( ▶ Table 11.3 and ▶ Table 11.4). To expand the scale, grade 4 subdivisions were introduced, as follows: (4–) slight movement without resistance; (4) moderate movement against resistance; and (4+) strong movement against resistance. Paternostro-Sluga et al introduced further modifications to this scale, including range of movement (ROM) to indicate subgrades 5: Grade 2–3: active movement against gravity over less than 50% of the feasible ROM. Grade 3: the same as 2–3, with feasible ROM over more than 50%. Grade 3–4: active movement against resistance over less than 50% of the feasible ROM. Grade 4: the same as 3–4, with feasible ROM over more than 50%. Grade 4–5: active movement against strong resistance over the feasible ROM, but distinctly weaker than the contralateral side. Grade 5: normal power. Score Motor outcome 0 Total paralysis 1 Muscle fibrillation 2 Visible muscle contraction 3 Movement against gravity 4 Movement against gravity and some resistance 5 Normal muscle function Motor recovery M0 No contractions M1 Visible or palpable contractions in the proximal muscles M2 Voluntary contractions of proximal muscles and trace or no contractions of distal muscles M3 Some voluntary contractions of distal muscles M4 Contractions of distal muscles against resistance M5 Full and separate contractions of all distal muscles A similar grading system was introduced by the Louisiana State University Medical Center (LSUMC), wherein movement with gravity eliminated was excluded ( ▶ Table 11.4 and ▶ Table 11.5). Useful motor function was considered to be grade 3 with the MRC scale, versus grade 2 with the LSUMC rating system. Individual muscle grade Grade Evaluation Description 0 Absent No contraction 1 Poor Trace contraction 2 Fair Movement against gravity only 3 Moderate Movement against gravity and some resistance 4 Good Movement against moderate resistance 5 Excellent Movement against maximal resistance
11.1.1 Patient Age
11.1.2 Characteristics of the Nerve
11.1.3 Characteristics of the Nerve Injury
11.1.4 Surgery
11.1.5 Postoperative Rehabilitation
11.2 General Grading Systems
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