Peripheral nerve traction injuries may occur after surgical care and can involve any of the upper extremity large peripheral nerves. In this review, injuries after shoulder or elbow surgical intervention are discussed. Understanding the varying mechanisms of injury as well as classification is imperative for preoperative risk stratification as well as management.
Key points
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Perioperative peripheral nerve traction injury is a poorly understood complication, with multiple etiopathologic considerations.
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Presentation may vary along the spectrum of sensory and motor nerve injury.
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Nerve injury can occur along any part of the path traversed, with bias of predisposing factors, like medical comorbidity and female gender.
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Potential nerve and plexus injury surrounding shoulder and elbow surgery are examined.
Introduction
The occurrence of perioperative peripheral nerve traction injuries (PPNTI) during upper and lower extremity orthopedic procedures such as joint replacements is an uncommon and unpleasant complication. PPNTI are regrettable complications of surgery, believed to arise from stretch or compression of vulnerable peripheral nerves secondary to retraction as well as patient limb positioning. PPNTI remains a poorly understood complication, with an incidence that is largely unknown and difficult to establish. Part of the reason for this difficulty is that in a lot of cases the cause of a perioperative nerve injury is unknown. Another reason why it is difficult to establish an incidence for PPNTI is that a definition of a traction injury is not always consistent between investigators. Depending on the investigator, the definition may vary from positioning or retraction, and if compression injury is included, it may be a stretch injury caused by compression or a combination of some of these. Therefore, in most studies, the incidence given for a perioperative nerve injury is all inclusive, and few studies give a PPNTI-specific incidence. Other common mechanisms of surgery-related nerve injuries besides traction include compression, entrapment, direct trauma (eg, crushing or laceration injuries), and indirect trauma (eg, secondary to hematoma formation).
Introduction
The occurrence of perioperative peripheral nerve traction injuries (PPNTI) during upper and lower extremity orthopedic procedures such as joint replacements is an uncommon and unpleasant complication. PPNTI are regrettable complications of surgery, believed to arise from stretch or compression of vulnerable peripheral nerves secondary to retraction as well as patient limb positioning. PPNTI remains a poorly understood complication, with an incidence that is largely unknown and difficult to establish. Part of the reason for this difficulty is that in a lot of cases the cause of a perioperative nerve injury is unknown. Another reason why it is difficult to establish an incidence for PPNTI is that a definition of a traction injury is not always consistent between investigators. Depending on the investigator, the definition may vary from positioning or retraction, and if compression injury is included, it may be a stretch injury caused by compression or a combination of some of these. Therefore, in most studies, the incidence given for a perioperative nerve injury is all inclusive, and few studies give a PPNTI-specific incidence. Other common mechanisms of surgery-related nerve injuries besides traction include compression, entrapment, direct trauma (eg, crushing or laceration injuries), and indirect trauma (eg, secondary to hematoma formation).
Pathophysiology
PPNTI is a type of nerve injury in which inappropriate placement of a noncompliant external object, such as retraction, may create an external pressure on the nerve, producing nerve ischemia and injury. Traction nerve injuries can be acute or chronic. An abrupt external force resulting in the immediate loss of function from the consequential structural changes of the neural tissue causes the acute traction injury. With a chronic traction injury, the nerve is stretched so slowly that considerable deformation of neural tissue occurs before the signs and symptoms appear.
The amount of stretch that a nerve tolerates depends on whether the nerve is freely mobile in supple soft tissue or whether it is bound down by osseous prominences, fascia, or scar. In Lundborg and Rydevik’s study of the sciatic nerve of rabbits, histologic changes were found after lengthening of nerves by 4% to 11%, nerve microcirculation was impaired after 8% stretch and stopped after 15% stretch, and there was conduction failure with 25% lengthening. The rupture of axon fibers precedes the failure of fascicles and may occur with stretch of as little as 4% to 6%. A more recent functional and mechanical evaluation of nerve stretch injury found the minimum threshold for nerve stretch before functional deficit to be between 5% and 10%. The theory is that stretching causes narrowing of both the extraneural and intraneural microvasculature and results in impaired blood flow. Lundborg and Rydevik also studied the temporal effects of ischemia and showed that restoration of blood flow after 2 hours of tourniquet-induced ischemia resulted in complete recovery of nerve function, with no edema in the epineurium or endoneurium. The development of endoneurial edema seems to be the hallmark of irreversible nerve injury.
Four major factors that increase the probability of mechanical disruption are increased load because of compression or stretch, increased rate of loading, increased duration of loading, and uneven application of load to tissues. Clinical experience and the Laplace law (tension is proportional to the pressure and radius of a cylindrical structure) show that large-diameter axons are more susceptible to damage than smaller fibers. Animal models have shown that peripheral nerves are especially sensitive to compression injury. If peripheral nerves are sensitive to compression, then it is possible that some traction injuries may not be secondary to stretch and tension but possibly caused by markedly increased compression from a near osseous or prosthetic prominence while the nerve is stretched. Yet another mechanism is from development of postoperative scar tissue, which puts tension on a nerve, resulting in chronic traction. Reinnervation rates vary depending on the location or severity of the injury and the length to the target tissue (muscle or sensory organ). Reinnervation can occur between 3 and 4 mm/d in nerve injuries when the endoneurial sheath is intact; however, after nerve suture, if reinnervation occurs, the rate decreases to 0.5 to 1 mm/d.
Classification of peripheral nerve injuries
The most widely accepted classifications of nerve injuries are those described by Seddon (neuropraxia, axonotmesis, and neurotmesis) and by Sunderland (grade 1–5 nerve injuries). According to the Seddon classification, nerve injuries can be classified into 3 categories: neuropraxia (mild: focal demyelination after focal injury; axon intact), axonotemesis (moderate: axonal loss; nerve sheath intact), and neurotmesis (severe: axonal loss and disruption of nerve sheath).
Clinical presentation of peripheral nerve traction injuries
Just as any peripheral nerve injury, PPNTI may lead to sensory or motor deficits. Sensory deficit can present as anesthesia, paresthesia, hypoesthesia, hyperesthesia, and pain in the areas supplied by the affected nerves. Motor deficits can include paresis or even paralysis of the affected muscles. Nerve-specific clinical presentations are discussed later.
General predisposing factors to PPNTI
Medical comorbidities that result in microvascular changes, such as hypertension, diabetes mellitus, and smoking, may render these patients to be more susceptible to PPNTI. It is also reported that rheumatoid arthropathy of the knee is a common predisposition for peroneal palsy after total knee arthroplasty. Preexisting peripheral neuropathies also predispose to a PPNTI. Other predisposing factors include anatomic sites of susceptibility (discussed in greater detail later) and anesthesia factors (general and epidural anesthesia are associated with a higher incidence of PPNTI). Perioperative factors such as hypovolemia, dehydration, hypotension, hypoxia, electrolyte disturbances, and hypothermia have also been implicated in the development of PPNTI. At least in studies of total hip arthroplasties, women are more at risk for peripheral nerve injury than men. A possible explanation is that compared with men, women have smaller bodies, with shorter limbs, and therefore shorter nerves as well. Because nerve stretch injury begins at about 4% to 11% elongation from the original length, individuals with shorter nerves need less stretch.
What is important to understand when discussing general and specific predisposing factors is that although there are several preoperative, perioperative, and postoperative factors that have been reported to be significant for the development of PPNTI, no single entity has been consistently shown in all studies to be significant, and some patients without any known risk factor still develop PPNTI.
Peripheral nerve traction injuries of the upper limb
Status After Shoulder Surgery
The nerves in the immediate vicinity of the operative field include the brachial plexus and its branches (axillary, musculocutaneous, suprascapular, subscapular). The incidence of such nerve injuries varies with the procedure, the approach used, and anatomic variation, as well as with the skill and experience of the surgeon. The reported incidence is 1% to 2% in patients undergoing rotator cuff surgery, 1% to 8% in patients undergoing surgery for anterior instability, and 1% to 4% in patients undergoing arthroplasty. However, because injury is usually identified clinically only and because of the difficulty of examining a shoulder postoperatively, true incidence may be even higher.
Brachial plexus injury (C5-T1)
Incidence
The incidence of brachial plexus injury is believed to range from 0.2% to 0.6%. Some studies have looked to intraoperative monitoring of nerves to obtain a better idea of incidence of nerve traction injury and predisposing factors. In a study by Nagda and colleagues of 30 patients in whom the brachial plexus nerves were continuously monitored during shoulder arthroplasty, 17 (56.7%) had 30 nerve alerts (episodes of nerve dysfunction) during surgery. None of these 30 nerve alerts returned to baseline with retractor removal alone. After repositioning of the arm into a neutral position, 23 (76.7%) of the 30 alerts returned to baseline. In those alerts that did not return to baseline, 4 of 7 (57.1%) had positive postoperative electromyography results.
Predisposing factors
Given its superficial nature and its proximity to several mobile bony structures, the brachial plexus is susceptible to injury. Other predisposing factors include running between 2 fixed points (intervertebral foramen and the axillary sheath), and its course through a limited space between the clavicle and first rib, which also make the plexus susceptible to injury. There also seems to be some increased risk of neurologic complications in patients with history of previous open shoulder surgery on the involved extremity. Whether this situation is caused by poor compliance and stretching of scar tissue, resulting in inability of nerves to slide within planes and an increase in local traction, or if it is caused by the need to be placed in more extreme positions for longer periods to obtain an appropriate surgical view, is unknown.
Mechanism of injury
Compression and traction against the clavicle may occur during retraction or in the lateral decubitus position with compression against the thorax and humeral head. Arm abduction and external rotation with posterior shoulder displacement cause considerable stretch on the upper brachial plexus roots. In the intraoperative nerve monitoring study by Nagda and colleagues, the nerve events were triggered during portions of the procedure when the surgical extremity was placed into extreme external rotation, extension, and either abduction or adduction. When the amount of external rotation and extension was decreased, most nerve compromise was reduced or eliminated, lending support to the theory that injury was likely secondary to traction. Nagda and colleagues’ findings are supported by biomechanical data from Kwaan and Rappaport. These investigators used strain gauge testing to delineate that an arm placed in 90° of abduction, external rotation, and slight extension produced traction on the brachial plexus.
Clinical presentation
If the C5-6 nerve roots are affected with involvement of the musculocutaneous, axillary, and suprascapular nerves, the arm is medially rotated, adducted, and pronated, classically described as the waiter’s tip position. If C8-T1 roots are involved, the small muscles of the hand are then involved, resulting in a claw hand and numbness in the ulnar distribution.
Prevention and treatment
Proper positioning and avoiding excessive shoulder abduction, extension, and external rotation should help decrease chance of nerve injury. Some advocate for intraoperative monitoring to avoid nerve injury, and 1 study has shown transcranial electrical motor-evoked potentials to be sensitive indicators of impending injury to the brachial plexus or peripheral nerves during shoulder arthroplasty and also proximal humeral fracture repairs. Should a brachial plexus nerve injury be diagnosed, it is important early on to support the involved upper extremity in order to avoid further traction.
Axillary nerve injury (C5-6)
Axillary nerve injury has been documented during various procedures, including shoulder arthroplasty, the Bristow transfer, and Bankart repair.
Incidence
Varies from 1% to 7% of cases.
Predisposing factors
The axillary nerve is susceptible to injury at the quadrilateral space, near the anteroinferior border of the glenohumeral capsule and the inferior border of the subscapularis muscle. The nerve is particularly susceptible to stretch after it curves around the posterolateral surface of the humerus deep to the deltoid and divides into anterior and posterior branches, where it is tethered posteriorly, as a result of the overlying muscle, making it susceptible to stretch.
Mechanism of injury
The mechanism of in jury is compression against the neck of the humerus and posterior stretch at the tethered zone, described earlier.
Clinical presentation
The presenting complaint is usually arm fatigue with overhead activity or throwing. Examination shows weak lateral abduction and external rotation of the arm. There may be associated paresthesias of the lateral and posterior upper arm.
Prevention and treatment
Preventive measures that should be used during dissection include careful nerve identification and retractor use. In the lateral approach, the axillary nerve can be protected and displaced away from the operative field with adduction and external rotation of the arm. Externally rotating the humerus not only helps expose the area of surgical interest but also helps reduce tension on the axillary nerve. In the posterior approach, it is recommended to stay above the teres minor because of the axillary nerve as well as the posterior circumflex humeral artery, both running in the quadrilateral space below the teres minor. Using an appropriately flat retractor helps minimize traumatic traction.
In arthroscopic shoulder procedures, incorrect trochar direction and portal placement can endanger nerves. Care must be used during dissection or portal placement in this region. For posterior portal placement, the posterolateral corner of the acromion is used as a landmark for the skin incision, aiming approximately 2 cm inferior and 1 cm medial to it. Once the portal is in, the trochar should be directed toward the coracoid. The axillary nerve can be at risk for injury if the portal is made too low. If the portal is made too medial, the suprascapular nerve may be in danger. The anterior portal can be established using an inside-out technique using a Wissenger rod or by puncture of the anterior skin under direct vision from the posterior portal.
If a permanent axillary nerve injury occurs, successful management may include free sural nerve grafting at 3 to 6 months postoperatively, an option that is reported to result in successful recovery of strength to grade 4 of 5. Another option is transferring the nerve innervating the medial head of the triceps to the anterior axillary nerve.
Musculocutaneous nerve injury (C5-7)
Incidence
PPNTI of the musculocutaneous nerve is rare and there are no incidences mentioned in the literature and only 1 case report.
Predisposing factors
Because proximally, the musculocutaneous nerve may bifurcate and has an unpredictable entry point into the coracobrachialis muscle, it is particularly vulnerable to injury in its proximal course, where it lies on the subscapularis muscle. Any surgical procedures involving the anterior aspect of the shoulder therefore risk injuring the musculocutaneous nerve, such as the modified Bristow procedure (for shoulder instability) or shoulder arthroscopy (because of joint distension, excessive traction, and extravasation of fluid).
Mechanism of injury
During the Bristow transfer, the transfer of the conjoined tendon may cause tenting and increased tension on the musculocutaneous nerve branch after successful transfer. During arthroscopic shoulder procedures, the musculocutaneous nerve is at risk if the anterior portal is placed too medial.
Clinical presentation
Weakness of flexion of the elbow and numbness along the lateral border of the forearm are seen if there is involvement of the musculocutaneous nerve.
Prevention and treatment
In the lateral approach of shoulder surgery, the musculocutaneous nerve can be protected by avoiding vigorous retraction of the coracobrachialis, short head of biceps conjoint tendon, and any dissection medial to coracobrachialis.
Given the possibility of anatomic variation, it is recommended that before tendon transfer, the musculocutaneous nerve is identified, and if the anatomic variation is identified, then the tendon transfer should be aborted or a complete neurolysis should be completed before tendon transfer.
Status After Elbow Surgery
Elbow arthroscopy and reconstruction of the ulnar collateral ligament of the elbow have been associated with neurologic injury to the radial, median, and ulnar nerves and their various branches in up to 14% and 31% of cases, respectively.
Radial nerve injury (C5-T1)
Incidence
Radial injury incidence of 4% to 12% is reported for humeral shaft fracture operative treatments, depending on approach used.
Predisposing factors
Arising from the posterior cord, the radial nerve becomes vulnerable at 2 sites: as it tracks along the spiral groove of the humerus, where it is in direct contact with the periosteum (a distance of about 6 cm), and also at the point where it pierces and is tethered by the lateral intermuscular septum.
Mechanism of injury
Common perioperative reasons cited for radial nerve injury include compression against a patient screen or an arm board positioned at an incorrect height, creating a step. Other commonly cited reasons include tourniquets and arterial pressure cuffs. In elbow arthroscopy, the radial nerve is at particular risk during placement of an anterolateral portal, which is most commonly located 5 to 10 mm posterolateral to the radial nerve. A high risk of injury to the radial nerve has also been noted in arthroscopic contracture release.
Clinical presentation
Clinical presentation typically includes wrist drop and numbness along the posterior surface of the lower part of the arm, posterior surface of the forearm, and the lateral 3 and a half digits on the dorsal side, as well as a small area on the dorsum of the hand.
Prevention and treatment
Taking care in proper positioning so that the arm is not compressed against a rigid structure is important in prevention of injury. In arthroscopic procedures, recommendations for preventing nerve injury include 90° of flexion to help displace vital structures in the antecubital fossa away from the portal placement site; careful placement of the anterolateral portal relative to local anatomic landmarks; cautious debridement in the posterior compartment during contracture release.
Median nerve injury (C5-T1)
Incidence
The median nerve is most commonly injured during carpal tunnel release, with an incidence in about 0.1% of cases. It is not known what fraction of those cases of median nerve injury were PPNTI.
Predisposing factors
The nerve is susceptible to compression and stretch at the carpal tunnel. Variant anatomy of the median nerve may increase risk of iatrogenic injury.
Mechanism of injury
When an unpadded pronated arm is left hanging off the table, the median nerve may become compressed and stretched as it traverses the upper arm on the table edge. Hyperextension of the elbow may place the median nerve at risk for injury. Compression or stretch of the nerve may occur during insertion of the endoscopic cannula or with hand positioning.
Clinical presentation
Median nerve injury results in paresthesia along the palmar aspect of the lateral 3 and a half fingers. Motor manifestations include weakness of abduction and opposition of the thumb, weak wrist flexion, and the forearm being kept in supination. The muscles of the thenar eminence become wasted, and the hand appears flattened.
Prevention and treatment
Careful limb positioning and padding, avoiding hyperextension of the elbow, and being mindful of the limb during the operation so as not to lean on it and exacerbate any compression or stretch are all important in preventing PPNTI. If postoperative median nerve palsy is identified, successful management has included exploration or sural nerve grafting, or repair with epineural sutures.
Ulnar nerve injury (C8-T1)
Incidence
The incidence of postoperative ulnar neuropathy has been reported between 0% and 51%, and it is frequently reported to be the most common perioperative nerve injury. As many as 1 in 200 adult surgical patients are affected, and it seems that men are more vulnerable. Two more recent studies have reported incidences of 20% and 16%, respectively. Again, these studies do not go on to stratify type of nerve injury acquired.
Predisposing factors
Ulnar nerve injury seems to be caused by its superficial nature and closeness to the medial condyle. Because the nerve passes through the ulnar groove at the elbow, it is prone to several types of compressive injuries. It is possible that the ulnar nerve and its blood supply may be compromised by internal compression caused by the coronoid tubercle of the ulna. This bony prominence is at least 50% larger in men, consistent with the greater susceptibility to perioperative ulnar nerve damage seen in men. It is also possible that in humeral fracture repair procedures, the type of fracture may be a risk factor for developing PPNTI. A study by Wiggers and colleagues concluded that patients with columnar fractures might be at higher risk for the development of postoperative ulnar neuropathy than patients with capitellum and trochlea fractures. The investigators believed the increased risk to be likely because of more transposition involved in columnar fracture repairs, as well as the additional handling of the ulnar nerve that occurred with reduction of a columnar fracture and application of a medial plate.
Mechanism of injury
Direct pressure on the ulnar groove in the elbow and prolonged forearm flexion are cited as the most common causes of injury. Extreme flexion of the elbow (>90°) tightens the arcuate ligament and shrinks the cubital tunnel, increasing the risk of nerve compression in the tunnel. With sustained elbow flexion, an elongation of 5 to 14 mm of the nerve has been reported. In repairs of supracondylar fractures of the humerus, it is widely accepted that medial pinning can damage the ulnar nerve not only by direct injury during insertion but also with elbow movement after insertion or by constricting the cubital tunnel. It is possible that postoperative scarring may limit the inherent laxity of the ulnar nerve around the elbow, which protects it from traction and compression injury caused by elbow flexion, and can result in chronic traction injury.
Clinical presentations
Ulnar nerve injury is usually characterized by tingling or numbness along the little finger and weakness of fifth digit abduction, adduction, or both. Examination of the hand shows hyperextension of the metacarpophalangeal joints and flexion at the distal and the proximal interphalangeal joints of the ring and the little finger (ulnar claw).
Prevention and treatment
Chances of nerve stretch or traction injury can be reduced with particular care in performing an elbow arthroscopy, especially when there has been previous trauma, surgery, or a congenital anomaly, because tethered or displaced nerves may render them vulnerable to injury. Surgical treatment of ulnar nerve injury may include neurolysis or transposition, or sural nerve intercalary grafting in severe cases.
NOTE: Please see following article entitled, “Perioperative Lower Extremity Peripheral Nerve Traction Injuries.”
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