ANTERIOR interosseous neuropathy is an uncommon perioperative neuropathy. Although two large series from the American Society of Anesthesiologists Closed Claims Project have categorized anesthetic-related perioperative neuropathies, neither has included cases involving the anterior interosseous nerve. 1,2However, perioperative anterior interosseous neuropathy has been described in isolated case reports. 3,4
The anterior interosseous nerve lies primarily in the proximal forearm (fig. 1). Symptoms of neuropathy involving this nerve include weakness or paralysis in the thumb and index finger. Anterior interosseous neuropathy does not present with any sensory disturbance because the nerve does not contain cutaneous sensory fibers. Signs of neuropathy found through physical examination include weakened flexion of the interphalangeal joint of the thumb and distal interphalangeal joint of the index or middle finger, and weakened pronation with the elbow in a flexed position. The clinical situation causes a characteristic square pinch rather than an “O” when the thumb and index finger are opposed (fig. 2). 5
Fig. 1. Anatomic drawing of the deep structures of the right forearm with superficial tissue, the median cubital vein, the flexor pollicis longus, and the brachioradialis muscles removed. The anterior interosseous nerve separates from the median nerve in the proximal forearm. It innervates the flexor pollicis longus, the flexor digitorum profundus, and the pronator quadratus muscles.
Fig. 1. Anatomic drawing of the deep structures of the right forearm with superficial tissue, the median cubital vein, the flexor pollicis longus, and the brachioradialis muscles removed. The anterior interosseous nerve separates from the median nerve in the proximal forearm. It innervates the flexor pollicis longus, the flexor digitorum profundus, and the pronator quadratus muscles.
Fig. 2. Characteristic square pinch in the right hand due to a lesion of the anterior interosseous nerve. The left hand demonstrates a normal pinch. Used with permission. 5
Fig. 2. Characteristic square pinch in the right hand due to a lesion of the anterior interosseous nerve. The left hand demonstrates a normal pinch. Used with permission. 5
In this report, we present four patients with anterior interosseous neuropathy that developed in the perioperative period whom we have evaluated over a 3-yr period at the Mayo Clinic (Rochester, MN) and elsewhere. The purpose of this report is to alert anesthesiologists of the potential for anterior interosseous neuropathy in the perioperative period.
Case Reports
The four cases described illustrate anterior interosseous neuropathy occurring in the perioperative period. The case reports have varied etiologies as the causes of neuropathy.
Case 1
A 43-yr-old healthy male anesthesiologist who was donating blood before undergoing surgery experienced a block of his anterior interosseous nerve function after the injection of 1 ml lidocaine, 1%, into his right antecubital fossa. The local anesthetic was injected to produce anesthesia for insertion of a 12-gauge needle for blood collection. He noticed an inability to flex the distal interphalangeal joint of his right index finger while squeezing a sponge ball approximately 2 min after injection. Further inspection showed that he also was unable to flex the interphalangeal joint of his right thumb. There was no sensory loss. The nerve dysfunction lasted approximately 75 min.
Case 2
A 42-yr-old healthy man underwent a 90-min appendectomy performed with him in the supine position while receiving a general anesthetic. Multiple attempts to cannulate veins on the right hand and mid-forearm and the antecubital fossa were unsuccessful. The intravenous cannula was eventually placed in the left forearm, and the procedure continued uneventfully. Both arms were tucked at the side and reportedly padded. Two hours after discontinuation of the anesthetic, the patient noted an inability to hold a pencil in his right hand. Examination of his right upper limb showed that he was unable to oppose his thumb and index finger or to flex the distal phalanx of both these digits. He had no sensory disturbance. A neurologist confirmed these findings 24 h later. The weakness resolved over the next 6 days and was no longer detectable by postoperative day 7.
Case 3
A 63-yr-old woman with hypertension and asthma underwent a 30-min cervical dilation and curettage performed with her in a lithotomy position while receiving general anesthesia. One milliliter lidocaine, 1%, was injected subcutaneously in the right antecubital fossa for an unsuccessful attempt at intravenous cannula placement. A cannula subsequently was placed in the left upper limb. Both limbs were positioned on padded arm boards, with her elbows extended and her arms abducted approximately 45°. Twenty minutes after discontinuation of the anesthetic, the patient noted a weak grasp of her right hand. Examination showed that she had severe weakness during opposition of her right thumb and index finger. She also was noted to be unable to flex the distal phalanx of both of these digits, but no sensory loss or paresthesia could be detected. A 3 × 5–cm hematoma was noted in the right antecubital fossa surrounding the failed catheter placement site. The weakness of opposition resolved over the next 45 min, and she had no residual weakness the next day.
Case 4
A 26-yr-old healthy man underwent a 2-h arthroscopic repair of his left anterior cruciate ligament while he was in a supine position and receiving general anesthesia. He was a competitive weightlifter, and it was noted that he was unable to extend his elbows completely during the preanesthetic evaluation. After successful placement of an intravenous cannula into the dorsum of his left hand, he was anesthetized, and his arms were padded and tucked at his sides. Six hours after discontinuation of the anesthetic, he found that he was unable to hold a pencil easily in his right hand. Examination showed that he had weakness of opposition of his right thumb and index finger and was unable to flex the distal phalanx of both of these digits fully. There was no sensory loss. A neurologist confirmed these findings 1 day later. An electromyogram 4 weeks after the initial procedure showed denervation of the flexor pollicis longus and flexor digitorum profundus. The patient had slow resolution of the neuropathy, with complete recovery of strength of opposition in 4 months.
Discussion
These four patients all experienced anterior interosseous neuropathy in the extended perioperative period. Perioperative neuropathies have been directly associated with various events, such as needle stick, hematomas, and positioning. 6In addition, perioperative neuropathies of the upper extremities also have been described as part of idiopathic brachial neuritis (or Parsonage-Turner syndrome). 7This condition, thought to be immune mediated, usually presents with pain in the shoulder region followed by diffuse neurologic findings; occasionally, it may affect only one nerve, including the anterior interosseous nerve. The etiologic factors in these four cases are speculative. Our following remarks represent our reflections on possible mechanisms of anterior interosseous neuropathy based on these cases.
Case 1
Local anesthetic infiltration of the subcutaneous tissue in the antecubital fossa may lead to transient block of the anterior interosseous nerve. This patient experienced a block of his anterior interosseous nerve function after injection of 1 ml lidocaine, 1%, into the antecubital fossa.
Case 2
Direct penetrating trauma to a nerve may cause neuropathy. The median nerve fibers supplying the anterior interosseous nerve may be vulnerable to trauma during placement of intravenous cannula, 8needle sticks, cutdowns, 9or arterial blood collections performed in the antecubital fossa (fig. 3). This patient had a neuropathy after multiple needle sticks of the right forearm. In an awake patient, direct injury typically would produce immediate pain in the distribution of the nerve. However, it is not clear whether any needle stick directly injured the nerve in this patient.
Fig. 3. Anatomic drawing of right forearm with the median cubital vein removed shows how a steep trajectory during intravenous cannulation in the proximal forearm could directly traumatize the anterior interosseous nerve. The anterior interosseous nerve fascicles of the median nerve also could be injured in the antecubital fossa by a needle stick. In addition, edema or hematoma could cause nerve compression in the forearm if compartment expansion is limited by fibrous sheaths or bands.
Fig. 3. Anatomic drawing of right forearm with the median cubital vein removed shows how a steep trajectory during intravenous cannulation in the proximal forearm could directly traumatize the anterior interosseous nerve. The anterior interosseous nerve fascicles of the median nerve also could be injured in the antecubital fossa by a needle stick. In addition, edema or hematoma could cause nerve compression in the forearm if compartment expansion is limited by fibrous sheaths or bands.
Case 3
Compression of the anterior interosseous nerve or the anterior interosseous nerve fibers within the median nerve by hematoma or compartmentalized edema can occur during or up to several days after surgery. For example, infiltration of an intravenous fluid has been reported with a case of anterior interosseous neuropathy. 5In our patient, a hematoma seemed to develop at the sight of an unsuccessful intravenous cannulation. We speculate this hematoma may have transiently compressed the anterior interosseous nerve.
Case 4
Stretch of most nerves, especially to lengths greater than 10% of their normal resting lengths, can cause neuropraxia. 6We speculate that extension of the elbows beyond the normally tolerated limits of motion may stretch the anterior interosseous nerve sufficiently to cause transient dysfunction. We recommend that anesthesia providers assess elbow range of motion before anesthetizing patients, extending the elbows, and wrapping their forearms on arm boards.
In summary, anterior interosseous neuropathy is a rarely reported perioperative event. The symptoms are unique because the anterior interosseous nerve is a pure motor nerve with no cutaneous distribution sensory fibers. The symptoms of anterior interosseous neuropathy in several of these patients resolved early in the perioperative period; however, there may be patients with prolonged disability. The etiology of anterior interosseous neuropathy in many cases is unclear, but our cases suggest potential preventable causes to consider.
