Anterior Interosseous Syndrome


Article Author:
Hossein Akhondi


Article Editor:
Matthew Varacallo


Editors In Chief:
Amie Kim
Todd May
Matthew Varacallo


Managing Editors:
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Frank Smeeks
Kristina Soman-Faulkner
Benjamin Eovaldi
Radia Jamil
Sobhan Daneshfar
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Steve Bhimji
John Shell
Matthew Varacallo
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Hajira Basit
Phillip Hynes
Kavin Sugumar


Updated:
6/4/2019 7:44:38 PM

Introduction

The anterior interosseous nerve (AIN) is the terminal motor branch of the median nerve.  It branches from the median nerve in the proximal forearm between the two heads of the pronator teres muscle to run deep along the interosseous membrane. From proximal to distal, it innervates the flexor pollicus longus (FPL), the index and long fingers of the flexor digitorum profundus (FDP), and the pronator quadratus (PQ).[1] AIN syndrome is an isolated palsy of these three muscles. It manifests mostly as pain in the forearm accompanied frequently by a characteristic weakness of the index and thumb finger pincer movement. Many cases of AIN syndrome arise secondary to a transient neuritis, although nerve compression and trauma are known etiologies as well. Different explanations have been proposed as the etiology of the disease. Controversy still exists among upper extremity surgeons about it; nevertheless, the condition is considered a neuritis in most cases.[2]

Parsonage and Turner first described the syndrome in 1948. Leslie Gordon Kiloh and Samuel Nevin defined it as an isolated lesion of the anterior interosseous nerve in 1952. Its old name was Kiloh-Nevin syndrome. Different methods of treatment with reasonable outcomes have been reported. Both surgical and medical interventions have been addressed with different timing and variable results.[3]

Etiology

Several causes of anterior interosseous nerve syndrome have been documented. Etiologies can be grouped as either spontaneous or traumatic.[4] Among the traumatic causes are forearm fractures such as supracondylar fractures, penetrating injuries and stab wounds, cast fixation, venipuncture, and complication of open reduction and internal fixation of fractures. Among the most common of the spontaneous causative factors are brachial plexus neuritis, compartment syndrome, and compression neuropathy.[5]

The most common site of AIN entrapment/compression is the tendinous edge of the deep head of the pronator teres muscle.  Other potential sites include:

  • The proximal edge of the flexor digitorum superficialis (FDS) arch (the FDS arcade)
  • Gantzer's muscle (accessory head of the FPL muscle)
  • FDS or FDP accessory muscles
  • Arterial thrombosis (radial or ulnar artery have been implicated)
  • Lacertus fibrous

AIN syndrome should be clinically differentiating from stenosing tenosynovitis or pathologies limited to local pathology affecting the flexor tendons alone (i.e., flexor tendon adhesions or partial versus complete flexor tendon rupture). The nerve is even normally compressed by the fibrous bands that often originate from the deep head of the brachialis fascia and the pronator teres, and this pressure can increase with minor variations.[6]

Differential diagnosis of the condition consists of a non-compressive neuropathy like brachial neuritis, which might mimic anterior interosseous nerve neuropathy. An FPL tendon rupture is also a possibility among patients who have rheumatoid arthritis. To exclude the differential diagnosis, the wrist must be flexed passively and extended to confirm that the individual has an intact tenodesis effect.[7] Rheumatoid disease and gouty arthritis may be predisposing factors in anterior interosseous nerve entrapment.

Epidemiology

This disease is rare, comprising only 1% of all upper extremity palsies

Pathophysiology

The exact pathophysiology can occur secondary to primary entrapment, direct trauma, or in more ambiguous or vague clinical presentations, the condition manifests following vial neuritis.  Very similar syndromes can be caused by more proximal lesions, such as brachial plexus neuritis.  In the latter, clinicians should have a heightened diagnostic suspicion in patients presenting with motor loss following prodromal symptoms consisting of intense shoulder pain or recent viral illness/exposure.

History and Physical

True AIN syndrome presentation will present with motor deficits only.  No sensory changes should be appreciated.  Most patients experience poorly localized pain in the forearm and cubital fossa. This pain is usually the primary complaint. There are no sensations of numbness, tingling, or sensory deficits. The patient will complain of having difficulty bringing the distal phalanx of the thumb and index finger together. On a physical exam, the pinch grip test would turn positive; rather than making the "OK" sign, the patient will clap the sheet between the index finger and an extended thumb. The patient may also complain of having difficulty forming a fist or the inability to button their shirts. Sensation should be spared on the exam.[8][9]

Evaluation

Electrodiagnostic studies are instrumental for anterior interosseous nerve syndrome of spontaneous etiology.  Sensory nerve conduction studies of the median nerve should be normal as there is no sensory innervation to the anterior interosseous nerve. Electromyography will show findings in the flexor pollicus longus, the radial portion of the flexor digitorum profundus, and the pronator quadratus. These will be helpful in differentiating neurologic amyotrophy from compression neuropathy.[10] Magnetic resonance imaging is also useful in the evaluation of these patients.

Treatment / Management

Nonoperative modalities

The general consensus for managing AIN syndrome includes a period of rest, observation, and splinting of the elbow near 90 degrees of flexion (or position of most comfort for the patient).  The majority of patients will experience improvement between 6 and 12 weeks of activity modification.  

Other modalities to consider include NSAIDs and physical therapy modalities (including pain modalities and massage techniques if tolerated) 

Surgical decompression

Surgical treatment consists of exploration, neurolysis, and decompression after several months of failed nonoperative modalities.  The literature reports 75% or greater positive outcomes following surgery, with higher rates reported in patients with an identifiable, clear space-occupying mass. 

Unless a clear cause is identified, surgical intervention is typically offered only in select cases, and the option is discussed following at least three months of failed conservative treatment.[11][12]

During median nerve surgical decompression, meticulous dissection is necessary to establish exact sites of compression. It is critical in the identification and release of compressing edges or fibrous bands.

Differential Diagnosis

Anterior interosseous nerve entrapment or compression injury remains a challenging clinical diagnosis. It is difficult because it is mainly a motor nerve and the syndrome is often mistaken for a ligamentous finger injury. Differential diagnosis includes stenosing tenosynovitis, flexor tendon adherence or adhesion, flexor tendon rupture, and brachial neuritis. Brachial plexus neuritis can cause very similar syndromes.[6][7]

Pertinent Studies and Ongoing Trials

Anterior interosseous nerve studies are usually retrospective. No randomized controlled trials have been performed, partially since the condition is relatively rare. Patients who have undergone surgery have good post operation records; many patients will resolve with conservative treatment. Therefore, the natural history of the disease seems to be benign. Those retrospective studies have shown the surgical and nonsurgical methods to be equivocal.[7]

Prognosis

The prognosis is usually good, and most cases don't require surgical treatment. If conservative therapy fails beyond three months, surgery might be offered in select cases.

Complications

Complications include those of the disease process that caused the syndrome or those of the surgery intended to treat it.

Enhancing Healthcare Team Outcomes

Even though anterior interosseous nerve syndrome is very rare, clinical suspicion ought to arise in the presence of the radial flexor digitorum profundus and weak flexor pollicis longus muscles. The utilization of electrodiagnostic studies, coupled with MRI, is poised to assist in the diagnosis of anterior interosseous syndrome and help to specify the possible etiology.

Anterior interosseous nerve syndrome's optimal treatment has not yet been established. It is recommended that surgical interventions be offered only to those patients who do not demonstrate any clinical improvement during the first few months or to those with confirmed cases of compression neuropathy. Meticulous dissection is necessary during median nerve surgical decompression to establish sites of compression. It is critical in the identification and release of any other compressing edges or fibrous bands.[13]

An interdisciplinary approach to treatment is ideal. This approach includes primary care providers who encounter the disease first and electrophysiologists who run the nerve and muscle studies. It also includes orthopedic surgeons who follow the course of treatment, pharmacists who provide the medication needed, and physical therapists who perform the rehabilitation. Other healthcare team personnel such as the nursing staff should also assist in the coordinated care of the patient.


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Anterior Interosseous Syndrome - Questions

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A 28-year-old male sustains a forearm fracture during a skiing accident. His cast is formed too tightly, and he develops anterior interosseous nerve syndrome. Which of the following will be expected in this patient?



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The anterior interosseous syndrome is due to which of the following?



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A 47-year-old female is being investigated in your clinic for left forearm symptoms that have bothered her while she is washing dishes and do gardening over the past several months. Her vital signs are normal and general neurologic exam is intact. Examination of the forearm reveals forearm pain, hand weakness, and inability to make an "OK" sign. There is no sensory loss. What is the most likely diagnosis?

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A 25-year-old male with a recent right forearm fracture presents with complaints of the inability to make a fist since his cast was removed 2 weeks ago. The patient denies any pain or sensory loss. On physical exam, the patient is unable to perform the "OK sign" on the right. What is the diagnostic test of choice?

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A 42-year-old male presents with a 3-month history of pain in his right forearm. It is worse at night and frequently wakes him up. He is right-handed and reports that he is unable to button or unbutton his shirt daily. He denies numbness or tingling in his right forearm or hand. He has type 2 diabetes mellitus. His current medications are metformin and sitagliptin. He has been working as a carpenter for 8 years, and he went on a camping trip 4 months ago. His temperature is 37.5C, pulse 81 beats/min, and blood pressure 128/80 mmHg. Examination shows he cannot make an "OK" or "O" sign with his right hand. Laboratory studies show a hemoglobin of 14.2 grams/dL, WBC 8,700/mm3, hemoglobin A1C 5.3%, and erythrocyte sedimentation rate 12 mm/hr. What is the most likely diagnosis?



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A 51-year-old female presents with a 4-week history of pain in her right forearm and weakness in her right first and second finger. The pain is worse at night and is sometimes relieved by shaking her wrist. In the past week, she has noticed a worsening of her symptoms. She has rheumatoid arthritis and type 2 diabetes mellitus. Her medications include insulin, methotrexate, and naproxen. Her vital signs are within normal limits. Examination shows a swan neck deformity of the fingers on both hands and multiple subcutaneous nodules over the olecranon process bilaterally. There is weakness of the right thumb and index finger when she is asked to make an "OK" sign. The remainder of the examination shows no abnormalities. Which of the following is the most appropriate next step in management?



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A 53-year-old female with a history of left forearm fracture 6 months ago presents with a 3-month history of intermittent, severe left arm and forearm pain. She first noticed her symptoms 1 week after she removed her cast. X-rays at that point showed completely healed bone. There is no family history of serious illness. She appears healthy. Her vital signs are within normal limits. The brachioradialis reflex is 2+ on the left and 2+ on the right. The radial pulse is palpable bilaterally. The remainder of the examination shows no abnormalities. Which of the following is most likely to confirm the diagnosis?



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A 17-year-old woman comes to the emergency department because of left forearm pain and swelling for 5 hours. She fell on her left arm while playing basketball. She ignored it initially as she thought it was just a bruise, but the pain and swelling worsened throughout the day. The analgesic spray she used did not provide adequate relief. There is no family history of serious illness. Her only medication is an oral contraceptive pill. Her immunizations are up to date. She appears anxious. Her temperature is 37.1 C (99 F), pulse is 88/min, and blood pressure is 118/72 mmHg. Examination shows a swollen and tender left forearm. The thumb and index finger can’t make okay or O sign. X-rays show left forearm fractures. Which of the following muscle group is most likely been affected by this forearm fracture?



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Anterior interosseous nerve syndrome (AINS) presents with forearm pain with no sensory deficit. What are the two main etiologies of AINS?



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What is the most affected nerve root in anterior interosseous nerve (AIN) syndrome?



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A 33-year-old woman presents reporting three months of mild discomfort in the right proximal forearm and deterioration in her handwriting. She denied paresthesias, and median nerve compression tests were negative at the wrist. Sensory and motor examination of the ulnar nerve are normal. Strength testing revealed weakness of the flexor pollicis longus and flexor digitorum profundus of the index finger with an inability to make an “okay” sign. What syndrome is she demonstrating?



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Anterior Interosseous Syndrome - References

References

Anterior interosseous nerve syndrome diagnosis and intraoperative findings: A case report., Aljawder A,Faqi MK,Mohamed A,Alkhalifa F,, International journal of surgery case reports, 2016     [PubMed]
[Common and not so common nerve entrapment syndromes: diagnostics, clinical aspects and therapy]., Schulte-Mattler WJ,Grimm T,, Der Nervenarzt, 2015 Feb     [PubMed]
Anterior interosseous nerve syndrome: fascicular motor lesions of median nerve trunk., Pham M,Bäumer P,Meinck HM,Schiefer J,Weiler M,Bendszus M,Kele H,, Neurology, 2014 Feb 18     [PubMed]
Pronator syndrome and anterior interosseous nerve syndrome., Rodner CM,Tinsley BA,O'Malley MP,, The Journal of the American Academy of Orthopaedic Surgeons, 2013 May     [PubMed]
Tyszkiewicz T,Atroshi I, Bilateral anterior interosseous nerve syndrome with 6-year interval. SAGE open medical case reports. 2018     [PubMed]
Komaru Y,Inokuchi R, Anterior interosseous nerve syndrome. QJM : monthly journal of the Association of Physicians. 2017 Apr 1     [PubMed]
Xing SG,Tang JB, Entrapment neuropathy of the wrist, forearm, and elbow. Clinics in plastic surgery. 2014 Jul     [PubMed]
Ochi K,Horiuchi Y,Tazaki K,Takayama S,Matsumura T, Fascicular constrictions in patients with spontaneous palsy of the anterior interosseous nerve and the posterior interosseous nerve. Journal of plastic surgery and hand surgery. 2012 Feb     [PubMed]
Park IJ,Roh YT,Jeong C,Kim HM, Spontaneous anterior interosseous nerve syndrome: clinical analysis of eleven surgical cases. Journal of plastic surgery and hand surgery. 2013 Dec     [PubMed]
El Domiaty MA,Zoair MM,Sheta AA, The prevalence of accessory heads of the flexor pollicis longus and the flexor digitorum profundus muscles in Egyptians and their relations to median and anterior interosseous nerves. Folia morphologica. 2008 Feb     [PubMed]
Flores LP, Distal anterior interosseous nerve transfer to the deep ulnar nerve and end-to-side suture of the superficial ulnar nerve to the third common palmar digital nerve for treatment of high ulnar nerve injuries: experience in five cases. Arquivos de neuro-psiquiatria. 2011 Jun     [PubMed]
Strohl AB,Zelouf DS, Ulnar Tunnel Syndrome, Radial Tunnel Syndrome, Anterior Interosseous Nerve Syndrome, and Pronator Syndrome. Instructional course lectures. 2017 Feb 15     [PubMed]
Sisco M,Dumanian GA, Anterior interosseous nerve syndrome following shoulder arthroscopy. A report of three cases. The Journal of bone and joint surgery. American volume. 2007 Feb     [PubMed]

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