Management of Radial Nerve Palsy Following Fractures of the Humerus

Radial nerve palsy is the most common peripheral nerve injury following a humerus fracture, occurring in 2% to 17% of cases. Radial nerve palsies associated with closed humerus fractures have traditionally been treated with observation, with late exploration restricted to cases without spontaneous nerve recovery at 3 to 6 months. Advocates for early exploration believe that late exploration can result in increased muscular atrophy, motor endplate loss, compromised nerve recovery upon delayed repair, and significant interval loss of patient function and livelihood. In contrast, early exploration can hasten nerve injury characterization and repair, and facilitate early fracture stabilization and rehabilitation.

Key points

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A radial nerve palsy is the most common peripheral nerve injury following a humerus fracture, occurring in up to 2% to 17% of cases.
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Surgical exploration is recommended in cases with open or complex fractures, particularly those associated with penetrating trauma.
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Radial nerve palsies associated with closed fractures of the humerus have traditionally been recommended to be treated with observation, with late exploration restricted to cases without spontaneous nerve recovery at 3 to 6 months.
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Advocates for early exploration believe that late exploration can result in increased muscular atrophy, motor endplate loss, compromised nerve recovery on delayed repair, and significant interval loss of patient function and livelihood.
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Early exploration can hasten nerve injury characterization and repair, as well as facilitate early fracture stabilization and rehabilitation.

Background

In the United States, more than 237,000 humerus fractures occur each year. Humeral shaft fractures represent between 1% and 5% of all fractures. Initial retrospective studies by Mast and colleagues described humeral shaft fractures as being most common among male patients younger than 35 involved in high-energy trauma. However, more recent studies have described a bimodal incidence with women older than 50 years suffering these fractures from low-energy injuries, such as falls from a standing height.

Complicating these fractures are radial nerve injuries, which are the most common peripheral nerve injuries associated with humeral fractures. The incidence of radial nerve injuries with humerus fractures has been documented between 2% and 17%. A prospectively collected database of more than 5700 patients with polytrauma revealed the radial nerve to be the most frequently injured peripheral nerve, seen in 9.5% of humeral fractures. However, this polytrauma population also included open fractures. Controversy still exists in the treatment of humeral shaft fractures with associated radial nerve injuries. Algorithms have been proposed to provide recommendations with regard to management and treatment of these nerve injuries. However, pros and cons are associated with each of these algorithms.

Anatomy

The humeral shaft is defined as the region “between the superior border of the pectoralis major insertion and the area immediately above the supracondylar ridge.”

Prior descriptions historically have placed the radial nerve and profunda brachial artery in the musculospiral groove and lateral intermuscular septum of the humerus. However, the spiral groove is truly the origin of the brachialis muscle. Fibers of the medial head of the triceps and brachialis separate the radial nerve from the humeral cortex. Direct contact with the humerus typically most consistently occurs as the nerve approaches the lateral supracondylar ridge.

Humeral shaft fractures can be described by their anatomic location by dividing the humeral shaft into thirds or fifths. The level of the fracture can provide the initial evidence of a radial nerve injury. Holstein and Lewis described an association of a radial nerve injury with a spiral fracture of the distal third humeral shaft fracture, since referred to as a Holstein-Lewis fracture. However, 1 to 5 cm of muscle separates the humerus and radial nerve at a level just proximal to the distal third of the humerus. Due to the force of injury, the proximal segment moves distally, causing displacement of the intermuscular septum. The radial nerve, which runs through this septum, may subsequently get tethered and injured. The nerve may also get lacerated when the apex of the distal fragment moves radially and proximally. Although this mechanism of radial nerve injury has been widely accepted, many recent studies dispute the constant relationship between the Holstein-Lewis fracture fragment and radial nerve injury. Similarly, a study by Bono and colleagues noted that the radial nerve has a more proximal decussation than previously reported. Their conclusion was that the nerve travels the distal half of the humerus along a superficial course.

In addition, the AO classification can be used to describe fractures and their associated patterns. The AO classification divides diaphyseal humeral shaft fractures into 3 categories depending on the amount of contact between the major fracture fragments. Simple fractures with more than 90% contact between the main fracture fragments are known as AO Type A fractures. AO Type B fractures (wedge fractures) and AO Type C fractures (complex fractures) have little or no contact between major fragments. Subtypes also exist based on direction and fracture extent within the 3 major categories.

According to Tytherleigh-Strong and colleagues, fractures of the middle third of the humeral shaft arise with an incidence of 64.2% and AO Type A fractures have a similar incidence of 63.3%. Researchers differ in their incidence of radial nerve injury with regard to location of the humeral shaft fracture. For instance, Bostman and colleagues noted an equal incidence of radial nerve injuries in fractures of the middle and distal third humeral shaft. However, some have reported that a higher likelihood of neurovascular injuries occurs in middle third of humerus fractures, whereas others have observed an increase in neurovascular injuries in distal third humeral shaft fractures. Fracture pattern associated with radial nerve palsies is also variable; most occur in the presence of a spiral fracture, although transverse and oblique fractures can also result in a radial nerve injury.

Classification/diagnosis

Radial nerve palsies can be classified as either partial or complete. To begin determining the type of palsy, one must perform a complete physical examination. A thorough baseline examination consists of sensory and motor evaluation of the median, ulnar, and radial nerves. Radial nerve sensation can be tested to light touch and pinprick on the dorsal hand at the level of the first web space. Radial nerve motor function can be determined by testing active extension of the wrist and of the fingers (including the thumb) at the metacarpophalangeal joints. In addition, the absence of brachioradialis or extensor carpi radialis longus firing may indicate a proximal injury at the level of the humeral shaft.

After a thorough physical examination, complete motor loss has been noted to occur in 50% to 68% of radial nerve palsies. Primary nerve palsies noted during the initial physical examination usually have occurred at the time of injury. Secondary nerve palsies may arise at any point during the active treatment of the fracture; these can represent up to 20% of all nerve palsies. The Seddon or Sunderland classification system can be used in further defining the type of peripheral nerve injury. The initial definition of a radial nerve injury as primary or secondary may be a prognostic factor in the ultimate recovery of the nerve. One study demonstrated 40% recovery in patients with a primary palsy and 100% recovery in patients with a secondary palsy after treatment of a humeral shaft fracture (closed or open reduction with internal fixation). Other studies with primary radial nerve palsies have demonstrated spontaneous recovery in 85% after closed fractures of the humerus.

Secondary nerve palsies after humeral shaft fractures may occur during closed treatment or after surgical fixation. Shah and Bhatti reviewed 62 patients with radial nerve palsies and humeral shaft fractures, of which 17 patients developed a secondary nerve palsy. Of these 17 patients, 11 of them had true closed management of their fractures consisting of cast/splint treatment, with or without manipulation of their fracture; 4 patients were treated with olecranon pin traction. Eight of these 17 patients had surgical exploration of their nerves, with all of them demonstrating intact nerves; however, 3 patients had nerves impinging on fracture fragments and 1 patient had the radial nerve entrapped in scar. All 17 patients who had secondary nerve palsy demonstrated complete recovery of their radial nerve function. This study demonstrated that closed management of humeral shaft fractures can lead to secondary nerve palsies, all of which recovered.

Surgical management of humeral shaft fractures can also lead to secondary palsies of the radial nerve. The least invasive technique is intramedullary nailing; however, this is not recommended in radial nerve palsies associated with humeral shaft fractures, as potential entrapment of the nerve in the fracture site leaves it vulnerable to further damage. The incidence of radial nerve injury following this technique has been reported to be between 0% and 5%. Other series examining radial nerve palsy following intramedullary nailing has identified that most palsies are temporary and resolve spontaneously. Alternatively, open reduction with compression plating is the most common procedure for humeral shaft fracture fixation. This technique can lead to radial nerve injury in up to 10% of cases. This approach allows for an anatomic reduction with the most predictable rate of fracture union. Routine exploration of the radial nerve is recommended during compression plating of the humerus, particularly in cases with preoperative radial nerve palsies.

Management/treatment

To begin evaluating the status of a radial nerve injury and what type of treatment should be used, an electrodiagnostic study can be helpful. These studies are not useful in the acute setting, but may have a role in the subacute setting in determining the level and extent of nerve injury. It can also be used to determine a baseline nerve function at the 3-week point to guide treatment during the observation period. These baseline electrodiagnostic studies may demonstrate “fibrillation potentials, positive sharp waves, and monophasic action potentials of short duration.” Most patients with spontaneous recovery begin to demonstrate recovery during the first few months; however, an electrodiagnostic study may serve as an adjunct study for those lacking nerve recovery at the 6-week or 12-week point. If a follow-up electrodiagnostic study at the 12-week point shows similar findings as the baseline, then exploration may be indicated. However, if the 12-week follow-up study shows “improved nerve function with larger polyphasic motor unit action potentials of longer duration,” then some degree of spontaneous recovery may be expected. However, the course of this subset of patients is not predictable.

Significant controversy persists with regard to the management of a radial nerve palsy associated with a humeral shaft fracture. Currently, noncontroversial and generally well-accepted indications for early exploration include open fractures, radial nerve palsy after closed reduction, associated vascular injuries, high-velocity gunshot wounds, penetrating injuries, severe soft tissue injuries, or any case with a high suspicion of a direct nerve laceration ( Box 1 ). Ring and colleagues retrospectively reviewed patients with a high-energy humeral shaft fracture with an associated complete radial nerve palsy. All 6 patients with a transected radial nerve had a complex open fracture.

Box 1

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