Mixed neuropathy presenting clinically as an anterior interosseous nerve palsy following shoulder arthroscopy: a report of four cases

ARTICLE IN PRESS J Shoulder Elbow Surg (2016) ■■, ■■–■■

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Mixed neuropathy presenting clinically as an anterior interosseous nerve palsy following shoulder arthroscopy: a report of four cases David Pope, MDa, Christopher Wottowa, MDa,b,* a

Division of Orthopaedics and Rehabilitation, Department of Surgery, Southern Illinois University School of Medicine, Springfield, IL, USA b Springfield Clinic, Springfield, IL, USA Background: Anterior interosseous nerve (AIN) palsies can arise spontaneously or be attributed to one of many causes. We present 4 cases, the largest series to date, in which a mixed peripheral neuropathy presented primarily as an AIN palsy following ipsilateral shoulder arthroscopy. In this report, we detail the patient’s presenting symptoms, describe our management of the complication, and provide hypotheses for the mechanism behind the complication. Methods: Four different surgeons performed the initial arthroscopic surgeries, but the senior author in all cases managed follow-up and treatment of the neuropathy. All patients were informed and agreed to have their cases published. Results: All four patients experienced significant recovery, although 2 of 4 required AIN decompression and exploration because of failure to improve with conservative management. Conclusion: Whereas variables such as position, index surgical procedure, and use of regional anesthesia varied among our patients, the one constant was the fluid extravasation from the arthroscopy itself, and for this reason we believe that if there is one singular cause to explain all of these neuropathies, it would be increased pressure in the upper arm and forearm from fluid extravasation in patients with atrisk anatomy. Outside of prevention, recognizing this complication and providing appropriate intervention or referral to a surgeon capable of appropriate intervention are important for any surgeon performing shoulder arthroscopies. Level of evidence: Level IV; Case Series; Treatment Study © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: AIN; median neuropathy; shoulder arthroscopy; complication; pronator syndrome; decompression

Tinel originally identified anterior interosseous nerve (AIN) palsy in 1918 under the title “dissociated paralysis of the median nerve.”29 Parsonage and Turner later described it in associAll four patients provided informed consent to have their cases published. *Reprint requests: Christopher Wottowa, MD, Springfield Clinic, 800 North 1st Street, Springfield, IL 62702, USA. E-mail address: [email protected] (C. Wottowa).

ation with brachial neuritis in 1948,20 and it was labeled a distinct syndrome by Kiloh and Nevin in 1952.12 It is diagnosed in patients presenting with pain in the proximal forearm and paresis of the pronator quadratus, the flexor pollicis longus (FPL), and the radial half of the flexor digitorum profundus (FDP). It can arise spontaneously, it can be associated with trauma, or, as presented in a case series of 3 patients by Sisco and Dumanian,,25 it can occur after shoulder arthroscopy.

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4

SAD, subacromial decompression; DCE, distal clavicle excision; FPL, flexor pollicis longus; FDP, flexor digitorum profundus; FDS, flexor digitorum superficialis; AIN, anterior interosseous nerve. * Total time from patient in room to dressing in place was 94 minutes.

Normal motor function 2 years after AIN decompression AIN decompression 3 months after shoulder arthroscopy (small area of slight constriction near FDS fibers intraoperatively) 0/5 FPL and index FDP, widened 2-point discrimination over volar radial thumb ~70 minutes* General Beach chair

General with interscalene block

Rotator cuff contracture release/ posterior interval slide with cuff repair, SAD, biceps tenotomy, labral débridement SAD 3

Lateral decubitus

167 minutes

0/5 FPL and index FDP, weak FDS

AIN exploration and decompression 8 months postoperatively, no obvious compression noted intraoperatively Conservative treatment with passive stretching 0/5 FPL, index FDP strength, numbness over dorsal aspect of thumb 83 minutes General with regional block SAD, DCE, rotator cuff débridement, biceps tenodesis 2

Beach chair

Passive stretching 0/5 FPL strength, no sensory deficits 90 minutes General SAD, DCE 1

Beach chair

Surgery time Anesthesia Position Surgery Case

Table I

Case 1 is a 49-year-old woman with a several-year history of left shoulder pain. Physical examination and imaging were consistent with impingement syndrome and acromioclavicular joint arthritis. Symptoms continued to progress despite conservative management. Shoulder arthroscopy was performed with the patient in the beach chair position under general anesthesia. No rotator cuff disease was noted, and the subacromial decompression and distal clavicle excision were performed. Roughly 5 days postoperatively, the patient noted inability to flex her left thumb interphalangeal (IP) joint. Examination showed complete paralysis of the left FPL. No other deficits were noted on examination, including normal FDP function in the index finger and normal sensation in the entire hand. EMG findings 6 weeks postoperatively indicated a moderately severe left median nerve injury at the level of the pronator teres involving both the pronator teres and FPL. She also had a mild chronic C7 radiculopathy. She was managed conservatively with passive stretching. She continued to improve until final follow-up at 15 months postoperatively, at which time she had 4/5 strength in her left FPL based on the Medical Research Council muscle strength grading system. Case 2 is a 64-year-old man with right shoulder pain after a fall at work. He also had some wrist pain with associated hand weakness and thumb numbness associated with the fall. Examination and imaging were consistent with a rotator cuff tear. Physical therapy did not relieve his shoulder pain, and he underwent shoulder arthroscopy with both a regional block and general anesthesia. The rotator cuff tear was found to be irreparable and was subsequently débrided. A subacromial decompression, distal clavicle excision, and biceps tenodesis were also performed. Several days after surgery, the patient noted an inability to flex his thumb IP joint and index finger distal IP joint as well as numbness over the dorsal aspect of his thumb. Ex-

Summary of surgical indications/technique, treatment, operative findings, and recovery

Case reports

Postoperative examination

Treatment

Progress

We present a series of 4 cases, summarized in Table I, in which a peripheral neuropathy manifested primarily as an AIN palsy after ipsilateral shoulder arthroscopy. More detailed examination and electromyography (EMG) and nerve conduction velocity (NCV) studies revealed more of a mixed median neuropathy with or without radial nerve sensory involvement in 2 patients, but the AIN palsy was the primary complaint for all patients. Four different surgeons performed the initial arthroscopic surgeries, but the senior author in all cases managed follow-up and treatment of the median neuropathy. All 4 patients experienced significant recovery, although 2 of 4 required AIN decompression and exploration because of failure to improve with conservative management. In this report, we detail the patient’s presenting symptoms, describe our management of the complication, and provide hypotheses for the mechanism behind the complication.

Normal motor function at final follow-up 16 months postoperatively

D. Pope, C. Wottowa

At 15 months postoperatively, 4/5 strength in FPL At 15 months postoperatively, 4/5 FDP strength and 4/5 FPL strength

2

ARTICLE IN PRESS Neuropathy after shoulder arthroscopy amination in the office confirmed complete paralysis of the right FPL and FDP to the index finger. EMG study was ordered and completed 10 weeks postoperatively and showed right median neuropathy in the proximal forearm. Three months after surgery, he had 1/5 strength noted in the thumb FPL and 0/5 strength noted in the index FDP. Conservative management with passive stretching was prescribed. He had some improvement of his dorsal hand numbness but showed no motor improvement 8 months postoperatively. EMG/NCV at this time showed a right radial neuropathy with demyelinating and axonal components as well as a right median neuropathy in the proximal forearm with interval maturation compared with the previous study. He underwent an AIN release 13 months after his initial surgery. Intraoperatively, no areas of nerve constriction were noted, and the nerve appeared healthy. A portion of the pronator teres and flexor digitorum superficialis arch were released. The patient noted rapid improvement in his symptoms postoperatively. At final follow-up 7 months after decompression, he had normal sensation in his entire hand and 4/5 strength to index FDP and FPL. Case 3 is a 59-year-old woman with known left carpal tunnel syndrome and left carpometacarpal joint arthritis who was diagnosed with a rotator cuff tear. She subsequently underwent left shoulder arthroscopy with repair of a massive, chronically contracted rotator cuff tear with contracture release and posterior interval slide, subacromial decompression, biceps tenotomy, and arthroscopic labral débridement. At 2 to 3 weeks postoperatively, she began noticing pain in her forearm and numbness primarily in the radial nerve distribution. Roughly 1 week later, she noted an inability to flex her left index finger or thumb. Complete paralysis of the left FPL and FDP as well as an inability to flex her index proximal IP joint was noted on examination. EMG/NCV at that time showed moderately severe left carpal tunnel syndrome and severe injury to the medial nerve proximal to the level of the pronator teres innervation. At 5 months postoperatively, she still had no active flexion of her thumb IP or index distal IP joints. Repeated EMG/NCV 8 months postoperatively indicated left brachial plexopathy with somewhat diffuse involvement but preferentially involving the AIN branch with chronic reinnervation as far distally as the FPL, an improvement compared with the previous study. At 9 months after surgery, she had 2/5 strength in her FPL and index FDP. At most recent follow-up, which was 16 months after surgery, she had complete recovery of motor function in her FPL and index FDP and normal sensation in her hand. Case 4 is a 51-year-old man diagnosed with right shoulder subacromial impingement. He failed to respond to conservative treatment and elected to undergo a subacromial decompression under general anesthesia in the beach chair position. On his first postoperative visit, the patient reported forearm pain that extended into his wrist, numbness and tingling in his right thumb, and difficulty in using his thumb that began immediately after surgery. On examination, he had no function of his FDP to the index or FPL on

3 the right hand as well as slight widening of the 2-point discrimination on the volar radial aspect of his thumb. EMG ordered at that time showed a chronic C6 radiculopathy and evidence of pronator syndrome. At this point, conservative therapy with passive stretching was determined to be the best course of treatment. Three months later, the patient had developed forearm atrophy and showed no clinical improvement; he subsequently underwent a right AIN decompression and pronator muscle biopsy. Intraoperatively, all the muscles in the flexor pronator mass showed decreased contractility and had a pale appearance grossly. A small area of slight constriction along the fibers of the flexor digitorum superficialis was noted, but it was unclear if this was causing his clinical picture as the whole AIN had an attritional and unhealthy appearance. At 4 months after surgery, his right FDP had nearly normal strength with 3/5 FPL strength. At 9 months after decompression, his FPL strength had improved to 4/5. Although he was not available for examination, the patient reported normal sensation and complete thumb and index finger motor recovery 2 years after AIN decompression.

Discussion We describe 4 patients who presented with an AIN palsy but were later found to have mixed median with or without radial sensory neuropathy after shoulder arthroscopy with variable although uniformly good recovery of motor function with both surgical and nonsurgical management, depending on the presence of spontaneous recovery without surgical management. We do think that the patients represent a similar complication to that presented by Sisco and Dumanian, a neuropathy beginning distal to the elbow after shoulder arthroscopy, and therefore refer to their group of patients and our group of patients similarly in the discussion to follow.25 Multiple causes of median neuropathy and AIN palsy have been discussed in the literature. These include but are not limited to trauma,1,14,28 local compression,17,30 dressings,7 slings,2,16 subacromial injections,22 and elbow arthroscopy.11 Local compression due to constrictive wrapping around the forearm and elbow during surgery must be considered a possible cause of this complication. As discussed previously by Casey and Moed, constrictive dressings are a known cause of AIN palsies.7 During many shoulder arthroscopies, a constrictive dressing is frequently wrapped around the arm from above the elbow to the fingertips. Only 1 of our patients had anything wrapped around the forearm during surgery, so this does not seem to be a likely cause in our group. O’Neill et al and Baldwin et al both reported on shoulder slings causing an AIN palsy.2,16 All of the patients in our series would have been placed in a shoulder sling or shoulder immobilizer postoperatively. This, combined with the excess fluid and swelling in the arm, could have precipitated the AIN palsy. Another possible explanation is surgery-induced neuritis. Brachial neuritis after surgery, or any inflammation-inducing

ARTICLE IN PRESS 4 event (ie, illness), has been described across many surgical specialties.15,18 In their original article in 1948, Parsonage and Turner described 136 cases of brachial neuritis, 5 of which had weakness of the long flexors of the thumb and index finger in addition to shoulder girdle weakness. They also described 1 case with isolated weakness of the left thumb and index finger but ruled out peripheral nerve involvement and considered these cases to be due to an anterior horn cell lesion.20 We believe that the 3 hypotheses presented by Sisco and Dumanian remain valid and discuss them in the following text.25 A well-accepted complication of regional anesthesia is peripheral neuropathy.3,5 Likely causes include direct mechanical trauma, anesthetic toxicity, and compressive hematoma.4 In studies by Bishop et al and Borgeat et al, 11 of 512 and 74 of 520 patients, respectively, reported sensory disturbances after interscalene blocks and shoulder surgery.3,5 Candido et al described 660 patients with interscalene blocks undergoing shoulder and upper arm surgery; 58 neurologic sequelae were reported by 56 patients, but only 2 of those were motor complaints, with the other 56 being sensory.6 One of those 2 patients with motor complaints actually had an AIN palsy and was included in the case series by Sisco and Dumanian.25 On the basis of the current body of literature, sensory neuropathy after nerve blockade is far more common than motor neuropathy, and that, coupled with the fact that 2 of our patients did not have regional anesthesia, makes this an unlikely cause of this complication. Peripheral neuropathy after surgery, likely due to positioning and traction, has been reported in the literature.19 In 1988, Pitman et al reported a nearly 40% rate of abnormal somatosensory evoked potentials in the median and ulnar nerves during shoulder arthroscopy.21 Even though 3 of 4 patients in our study were placed in the beach chair position during surgery, a position designed to prevent traction injuries noted with lateral positioning,26 the AIN is particularly vulnerable to traction in a cadaveric model, and this makes excessive traction during surgery a possible cause of this complication.8 Last, fluid extravasation, with subsequent peripheral neuropathy or compartment syndrome, is a known complication of arthroscopy in both the upper and lower extremities.9,10,21,31 It is possible but unlikely in our opinion that increased fluid around the shoulder could have increased pressure around the median nerve proximally and caused an isolated median neuropathy. It is more likely, in our opinion, that the intrafascicular or extrafascicular pressure in or around the median nerve or AIN in the forearm increased as the fluid tracked distally in patients with nerves at risk for increased compression and subsequent inflammation due to poor nervous blood supply or constrictive baseline anatomy.13 With regard to management, multiple studies reference 3 to 6 months of conservative management before operative intervention.23,27 Schollen et al discussed the importance of determining whether the patient has a compressive neuropathy or an inflammatory neuritis in trying to determine management.24 If the EMG and clinical picture suggest an inflammatory neuritis, surgery has no merit per Wong and

D. Pope, C. Wottowa Dellon.32 If the clinical picture is more that of a compressive neuropathy, decompression should be considered. Our experience would support conservative treatment with passive stretching for a minimum of 3 to 6 months, knowing that 2 of our patients improved significantly with no surgical intervention. After 6 months of no improvement and EMG findings consistent with a compression neuropathy, our experience would indicate that decompression hastens recovery.

Conclusion Whereas variables such as position, index surgical procedure, and use of regional anesthesia varied among our patients, the one constant was the fluid extravasation from the arthroscopy itself, and for this reason we believe that if there is one singular cause to explain all of these median neuropathies, it would be increased pressure in the upper arm and forearm from fluid extravasation in patients with already at-risk anatomy. Outside of prevention, recognizing this complication and providing appropriate followup and, when necessary, surgical intervention or appropriate referral to a surgeon capable of surgical intervention are important for any surgeon performing shoulder arthroscopies. Future research would ideally investigate compartment pressures in the upper arm and forearm during shoulder arthroscopy.

Disclaimer The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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