Back To Search Results

Anterior Interosseous Syndrome

Editor: Matthew A. Varacallo Updated: 7/7/2025 1:37:40 AM

Introduction

The anterior interosseous nerve serves as the terminal motor branch of the median nerve. Originating approximately 5 to 8 cm distal to the lateral epicondyle, this nerve emerges in the proximal forearm between the 2 heads of the pronator teres muscle and courses deep along the interosseous membrane. As a purely motor nerve, the anterior interosseous nerve innervates, in proximal-to-distal order, the flexor pollicis longus (FPL) of the thumb, the flexor digitorum profundus (FDP) of the index and middle fingers, and the pronator quadratus of the forearm (see Images. Anterior Interosseous Nerve and Forearm Innervations).[1][2]

Anterior interosseous nerve syndrome refers to an isolated palsy affecting these 3 muscles, without any associated sensory loss. The condition typically presents with forearm pain and a distinctive weakness in the pincer movement of the index finger and thumb. The underlying pathophysiology remains uncertain and continues to prompt debate. Many cases appear secondary to transient inflammatory neuritis, though nerve compression and trauma represent established causes. Current theories often cite either an idiopathic immune-mediated neuritis or an intrinsic compressive lesion within the forearm.[3]

Multiple hypotheses have emerged regarding the etiology of the condition. Despite ongoing discussion among upper extremity surgeons, the prevailing view classifies the syndrome as a form of neuritis.[4] Clinicians should note that direct external trauma to the anterior interosseous nerve, which can produce similar muscle weakness, does not qualify as true anterior interosseous nerve syndrome due to its distinct pathophysiological mechanism.[3]

Parsonage and Turner first identified the syndrome in 1948, followed by Leslie Gordon Kiloh and Samuel Nevin in 1952, who characterized it as an isolated lesion of the anterior interosseous nerve. Historically, the condition was known as Kiloh-Nevin syndrome. Various treatment approaches have demonstrated reasonable outcomes. Most cases resolve spontaneously, and conservative management, including symptomatic treatment over a period of 3 to 6 months, remains the preferred initial strategy.[3] Both medical and surgical interventions have been explored, with variable timing and results.[5]

Etiology

Register For Free And Read The Full Article
Get the answers you need instantly with the StatPearls Clinical Decision Support tool. StatPearls spent the last decade developing the largest and most updated Point-of Care resource ever developed. Earn CME/CE by searching and reading articles.
  • Dropdown arrow Search engine and full access to all medical articles
  • Dropdown arrow 10 free questions in your specialty
  • Dropdown arrow Free CME/CE Activities
  • Dropdown arrow Free daily question in your email
  • Dropdown arrow Save favorite articles to your dashboard
  • Dropdown arrow Emails offering discounts

Learn more about a Subscription to StatPearls Point-of-Care

Etiology

Several causes of anterior interosseous nerve syndrome have been well documented. Injuries to the anterior interosseous nerve resulting from direct external trauma do not meet the diagnostic criteria for anterior interosseous nerve syndrome.[6] Documented external traumatic causes include forearm and elbow fractures, penetrating injuries such as stab wounds, cast fixation, venipuncture, and complications arising from open reduction and internal fixation of fractures. Only spontaneous cases presenting with weakness of the muscles innervated by the anterior interosseous nerve qualify as true anterior interosseous nerve syndrome.

Many physicians, particularly surgeons, consider anterior interosseous nerve syndrome a form of compressive neuropathy. However, several clinical features set this condition apart from other compressive neuropathies. In contrast to the more gradual onset seen in typical compression syndromes, paralysis in anterior interosseous nerve syndrome often develops suddenly and resolves spontaneously. Recurrence remains uncommon, unlike the higher recurrence rates observed in other compressive neuropathies.

Electrodiagnostic studies in many patients with anterior interosseous nerve syndrome reveal a more widespread median motor involvement extending beyond the muscles specifically innervated by the anterior interosseous nerve.[7] The most frequently identified cause involves an idiopathic immune-mediated neuritis. An intrinsic compressive lesion in the forearm, including conditions such as compartment syndrome and localized compression neuropathy, represents the second most common etiology.[8][7]

The most common site of intrinsic anterior interosseous nerve entrapment or 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 has been implicated)
  • Lacertus fibrous

A careful analysis of the anterior interosseous nerve anatomy in the forearm will indicate that compression of the anterior interosseous nerve cannot explain most of the anterior interosseous nerve syndromes. The anterior interosseous nerve branches from the median nerve 5 to 8 cm distal to the lateral epicondyle beneath the pronator teres. The nerve passes between the FDP and FPL muscles. There should be sensory involvement if the compression occurs proximal to the anterior interosseous nerve. Compression distal to the anterior interosseous nerve branch point should have only selective FDP or FPL denervation. Observing all 3 muscle involvements is difficult secondary to compressive etiology.

Anterior interosseous nerve syndrome should be clinically differentiated from stenosing tenosynovitis or pathologies limited to local pathology affecting the flexor tendons alone (ie, flexor tendon adhesions or partial versus complete flexor tendon rupture). The nerve is typically 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.[9]

An FPL tendon rupture is also a possibility among patients with 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.[10] Rheumatoid disease and gouty arthritis may be predisposing factors in anterior interosseous nerve entrapment.

Epidemiology

Anterior interosseous nerve syndrome is rare when compared with other entrapment neuropathies, comprising <1% of all upper extremity palsies. No difference between the incidence of the anterior interosseous nerve in men and women or between dominant and nondominant upper extremities has been demonstrated.

Pathophysiology

The exact pathophysiology can occur secondary to primary entrapment, direct trauma, or in more ambiguous or vague clinical presentations. The condition also manifests following viral 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 or exposure.[11][12]

History and Physical

Clinical Features

True anterior interosseous nerve syndrome generally presents with motor deficits alone, without accompanying sensory changes. Most patients report a sudden or acute onset of poorly localized pain in the forearm and cubital fossa, often as the primary complaint. Symptoms, eg, numbness, tingling, or other sensory deficits, remain absent. Patients frequently describe difficulty bringing the distal phalanges of the thumb and index finger together.

On physical examination, the pinch grip test or "OK" sign typically yields a positive result; instead of forming a proper circle with the thumb and index finger, the patient presses the sheet between an extended thumb and index finger (see Image. Pinch Grip Test). Additional complaints may include difficulty forming a fist or fastening buttons. Sensation remains intact on examination.[13][14]

Evaluation

Alongside a thorough history and detailed neurological examination, electrodiagnostic studies play a critical role in evaluating anterior interosseous nerve syndrome of spontaneous origin. Sensory nerve conduction studies of the median nerve should yield normal results, given the absence of sensory innervation to the anterior interosseous nerve. Electromyography typically reveals abnormalities in the flexor pollicis longus, the radial portion of the flexor digitorum profundus, and the pronator quadratus, aiding in the distinction between neurologic amyotrophy and compression neuropathy.[15] Magnetic resonance imaging (MRI) also offers significant value in assessing patients with suspected anterior interosseous nerve syndrome.[16]

Treatment / Management

Nonsurgical Management

The consensus on the preferred management of anterior interosseous nerve syndrome includes conservative interventions, eg, a period of rest, observation, and splinting of the elbow at 90 degrees of flexion (or the position of most comfort for the patient). Most patients experience improvement and even recovery within 6 to 12 weeks of activity modification.[17] Other conservative modalities to consider include NSAIDs and physical therapy, including reduced pain and massage techniques if tolerated. 

Surgical Modalities

Surgical treatment consists of exploration, neurolysis, and decompression after several months of failed nonoperative modalities. The literature reports 75% or more significant positive outcomes following surgery, with higher rates reported in patients with an identifiable, apparent 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 3 months of failed conservative treatment.[18][19](B3)

During median nerve surgical decompression, meticulous dissection is necessary to establish the exact sites of compression and is critical in identifying and releasing compressing edges or fibrous bands. Because many anterior interosseous nerve syndrome cases are caused by inflammatory neuritis rather than compressive neuropathy, other surgical options may be considered to improve hand function, including tendon transfers and reconstructive surgeries.

Differential Diagnosis

Anterior interosseous nerve entrapment or compression injury presents a challenging clinical diagnosis due to its predominantly motor function and frequent misidentification as a ligamentous finger injury. The differential diagnosis includes stenosing tenosynovitis, flexor tendon adherence or adhesion, flexor tendon rupture, and brachial neuritis. Brachial plexus neuritis may present with a similar clinical picture.[9][10]

Selective fascicular involvement of the median nerve trunk above the elbow has emerged as a recently recognized cause of anterior interosseous nerve syndrome, displaying the characteristic clinical and electromyographic features. Diagnosis of this variant relies on advanced MRI techniques and an increasing number of supporting case reports.[16]

Pertinent Studies and Ongoing Trials

Anterior interosseous nerve studies are usually retrospective. No randomized controlled trials have been performed since the condition is relatively rare. Patients who have undergone surgery typically have good postoperative records; many 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.[10]

Prognosis

The prognosis is usually good, and most cases don't require surgical treatment. If conservative therapy fails beyond 3 months, surgery might be offered in select cases.[20]

Complications

Complications of anterior interosseous syndrome primarily involve persistent motor deficits that affect fine motor function, particularly impairing the ability to perform tasks requiring thumb and index finger coordination, eg, writing, buttoning clothing, or gripping objects. Delayed or incorrect diagnosis may lead to prolonged dysfunction, as the condition is often mistaken for tendon injuries or other neuropathies. In cases where spontaneous recovery does not occur, chronic weakness and muscle atrophy may develop, especially if the underlying cause is unrecognized or untreated. Surgical complications, although uncommon, may include nerve damage, scarring, or failure to relieve symptoms if the entrapment site is not accurately identified. Misdiagnosis of traumatic injuries as true anterior interosseous syndrome can also result in ineffective treatment plans. Additionally, patients with autoimmune conditions, eg, rheumatoid arthritis or gout, may face higher risks for tendon rupture or inflammatory recurrence, further complicating the clinical picture. Incomplete recovery, especially in cases with diffuse median nerve involvement or immune-mediated neuritis, may lead to long-term functional limitations, making early identification and appropriate management essential to minimizing adverse outcomes.

Deterrence and Patient Education

Anterior interosseus nerve syndrome is very rare when compared with other more common entrapment neuropathies of the upper extremities, eg, carpal tunnel syndrome and ulnar neuropathy. Furthermore, usually no obvious trauma is noted in the clinical history, and the patients and clinicians may miss the diagnosis, resulting in a missed opportunity to understand the illness, its management, and prognosis. A high index of suspicion by the clinician, combined with education of the patient regarding the diagnosis, its underlying cause, and the necessary tests, will ultimately improve the outcome and patient satisfaction.

Enhancing Healthcare Team Outcomes

Effective management of anterior interosseous syndrome demands a coordinated, interprofessional approach that leverages the distinct expertise of multiple healthcare professionals. Primary care physicians often serve as the first point of contact, responsible for recognizing the hallmark motor deficits and initiating timely referrals. Advanced practitioners, including nurse practitioners and physician assistants, contribute by conducting thorough clinical assessments, ordering diagnostic studies, and supporting continuity of care. Electrophysiologists perform electrodiagnostic evaluations such as nerve conduction studies and electromyography, providing essential data to differentiate anterior interosseous syndrome from other neuromuscular or tendon-related conditions. Orthopedic surgeons play a critical role in guiding the treatment course, particularly in cases requiring surgical intervention, and must assess for compressive lesions or structural anomalies identified through imaging or clinical progression. Pharmacists enhance medication safety and optimize pharmacologic management, particularly with analgesics or anti-inflammatory agents, ensuring appropriate dosing and monitoring for interactions. Nurses contribute by educating patients, monitoring symptoms, administering medications, and facilitating communication among clinicians.

Physical therapists also play an essential role in post-diagnosis recovery, employing targeted rehabilitation strategies that support the restoration of functional hand use and minimize compensatory movement patterns. They collaborate closely with both surgical and nonsurgical teams to adapt therapy based on clinical status and treatment response. Interprofessional communication remains vital throughout the diagnostic and treatment process, with each team member responsible for maintaining accurate documentation and promptly sharing relevant clinical updates. By coordinating efforts and engaging in shared decision-making, the healthcare team fosters patient-centered care, enhances safety, and improves functional outcomes. A collaborative model not only ensures appropriate diagnosis and tailored treatment but also promotes patient education, adherence to therapy, and long-term recovery, ultimately elevating the quality and efficiency of care delivered to individuals affected by anterior interosseous nerve syndrome.

Media


(Click Image to Enlarge)
<p>Pinch Grip Test

Pinch Grip Test. On physical examination, the pinch grip test or "OK" sign typically yields a positive result; instead of forming a proper circle with the thumb and index finger, the patient presses the sheet between an extended thumb and index finger.

Contributed by M Raj, DO


(Click Image to Enlarge)
<p>Anterior Interosseous Nerve. The Image shows the anterior interosseous nerve and surrounding nerves.</p>

Anterior Interosseous Nerve. The Image shows the anterior interosseous nerve and surrounding nerves.

Contributed by S Bhimji, MD


(Click Image to Enlarge)
<p>Forearm Innervations

Forearm Innervations. As a purely motor nerve, the anterior interosseous nerve innervates, in proximal-to-distal order, the flexor pollicis longus (FPL) of the thumb, the flexor digitorum profundus (FDP) of the index and middle fingers, and the pronator quadratus of the forearm.

Contributed by S Bhimji, MD

References


[1]

Krishnan KR, Sneag DB, Feinberg JH, Wolfe SW. Anterior Interosseous Nerve Syndrome Reconsidered: A Critical Analysis Review. JBJS reviews. 2020 Sep:8(9):e2000011. doi: 10.2106/JBJS.RVW.20.00011. Epub     [PubMed PMID: 32890049]


[2]

Aljawder A, Faqi MK, Mohamed A, Alkhalifa F. Anterior interosseous nerve syndrome diagnosis and intraoperative findings: A case report. International journal of surgery case reports. 2016:21():44-7. doi: 10.1016/j.ijscr.2016.02.021. Epub 2016 Feb 20     [PubMed PMID: 26921536]

Level 2 (mid-level) evidence

[3]

Li N, Russo K, Rando L, Gulotta-Parrish L, Sherman W, Kaye AD. Anterior Interosseous Nerve Syndrome. Orthopedic reviews. 2022:14(4):38678. doi: 10.52965/001c.38678. Epub 2022 Oct 7     [PubMed PMID: 36225171]


[4]

Tyszkiewicz T, Atroshi I. Bilateral anterior interosseous nerve syndrome with 6-year interval. SAGE open medical case reports. 2018:6():2050313X18777416. doi: 10.1177/2050313X18777416. Epub 2018 May 17     [PubMed PMID: 29796273]

Level 3 (low-level) evidence

[5]

Rodner CM, Tinsley BA, O'Malley MP. Pronator syndrome and anterior interosseous nerve syndrome. The Journal of the American Academy of Orthopaedic Surgeons. 2013 May:21(5):268-75. doi: 10.5435/JAAOS-21-05-268. Epub     [PubMed PMID: 23637145]


[6]

Komaru Y, Inokuchi R. Anterior interosseous nerve syndrome. QJM : monthly journal of the Association of Physicians. 2017 Apr 1:110(4):243. doi: 10.1093/qjmed/hcw227. Epub     [PubMed PMID: 28073933]


[7]

Na KT, Jang DH, Lee YM, Park IJ, Lee HW, Lee SU. Anterior Interosseous Nerve Syndrome: Is it a Compressive Neuropathy? Indian journal of orthopaedics. 2020 Sep:54(Suppl 1):193-198. doi: 10.1007/s43465-020-00099-2. Epub 2020 Apr 6     [PubMed PMID: 32952930]


[8]

Xing SG, Tang JB. Entrapment neuropathy of the wrist, forearm, and elbow. Clinics in plastic surgery. 2014 Jul:41(3):561-88. doi: 10.1016/j.cps.2014.03.007. Epub     [PubMed PMID: 24996472]


[9]

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:46(1):19-24. doi: 10.3109/2000656X.2011.634558. Epub     [PubMed PMID: 22455572]

Level 2 (mid-level) evidence

[10]

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:47(6):519-23. doi: 10.3109/2000656X.2013.791624. Epub 2013 Apr 30     [PubMed PMID: 23627594]

Level 3 (low-level) evidence

[11]

Ikumi A, Yoshii Y, Nagashima K, Takeuchi Y, Tatsumura M, Mammoto T, Hirano A, Yamazaki M. Anterior interosseous nerve syndrome following infection with COVID-19: a case report. Journal of medical case reports. 2023 Jun 11:17(1):253. doi: 10.1186/s13256-023-03952-8. Epub 2023 Jun 11     [PubMed PMID: 37301873]

Level 3 (low-level) evidence

[12]

Ishizuka K, Shikino K, Ikusaka M. Anterior interosseous nerve palsy caused by Parsonage-Turner syndrome. Cleveland Clinic journal of medicine. 2021 Mar 1:88(3):155-156. doi: 10.3949/ccjm.88a.20019. Epub 2021 Mar 1     [PubMed PMID: 33648967]


[13]

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:67(1):63-71     [PubMed PMID: 18335416]


[14]

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:69(3):519-24     [PubMed PMID: 21755133]

Level 3 (low-level) evidence

[15]

Pham M, Bäumer P, Meinck HM, Schiefer J, Weiler M, Bendszus M, Kele H. Anterior interosseous nerve syndrome: fascicular motor lesions of median nerve trunk. Neurology. 2014 Feb 18:82(7):598-606. doi: 10.1212/WNL.0000000000000128. Epub 2014 Jan 10     [PubMed PMID: 24415574]


[16]

Park JE, Sneag DB, Choi YS, Oh SH, Choi S. Fascicular Involvement of the Median Nerve Trunk in the Upper Arm: Manifestation as Anterior Interosseous Nerve Syndrome With Unique Imaging Features. Korean journal of radiology. 2024 May:25(5):449-458. doi: 10.3348/kjr.2023.1218. Epub     [PubMed PMID: 38685735]


[17]

Boeckstyns M. My current views on the anterior interosseous nerve syndrome. The Journal of hand surgery, European volume. 2022 May:47(5):542-543. doi: 10.1177/17531934221076268. Epub 2022 Feb 6     [PubMed PMID: 35128983]


[18]

Strohl AB, Zelouf DS. Ulnar Tunnel Syndrome, Radial Tunnel Syndrome, Anterior Interosseous Nerve Syndrome, and Pronator Syndrome. Instructional course lectures. 2017 Feb 15:66():153-162     [PubMed PMID: 28594495]


[19]

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:89(2):392-5     [PubMed PMID: 17272456]

Level 3 (low-level) evidence

[20]

McLeod GJ, Peters BR, Quaife T, Clark TA, Giuffre JL. Anterior Interosseous-to-Ulnar Motor Nerve Transfers: A Single Center's Experience in Restoring Intrinsic Hand Function. Hand (New York, N.Y.). 2022 Jul:17(4):609-614. doi: 10.1177/1558944720928482. Epub 2020 Jul 22     [PubMed PMID: 32696669]