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Pronator and AIN Release

57 citationsUpdated Aug 2026

For patients: a plain-language version of this topic is available. See the patient guide.

Overview

Pronator syndrome lacks objective pathophysiology and is supported only by subjective operative findings and relief after surgery [3]. Consequently, there is a paucity of controlled trials demonstrating that operative treatment for pronator syndrome is more effective than other treatments or sham surgery [3]. The term pronator syndrome should be replaced with superficialis-pronator syndrome [12]. Lacertus syndrome and superficialis-pronator syndrome should be clearly presented as distinct targets for surgical release [12].

Surgical decompression of the median nerve or the anterior interosseous nerve (AIN) in the forearm is rarely indicated [9]. A prolonged nonsurgical approach is warranted in most cases of pronator syndrome or anterior interosseous nerve syndrome [9]. Surgical indications for nerve decompression include persistent symptoms for >6 months in patients with pronator syndrome [4]. Surgical indications for nerve decompression include a minimum of 12 months with no signs of motor improvement in those with anterior interosseous nerve syndrome [4].

Release of the flexor-pronator origin improved control and function of the hands in 18 patients with marked flexion deformities of the wrist and fingers and accompanying pronation contractures of the forearm [2]. Pronator teres symptoms disappeared in 93% of cases following a mini-invasive decompression technique [1]. An endoscopically assisted, minimally invasive approach to treat pronator syndrome adequately and safely decompressed all anatomical points of compression and improved DASH scores [10]. Resection of a segment of the persistent median artery is the recommended treatment for pronator syndrome associated with this anomaly [14].

Pronator teres release is more invasive, requires more complicated surgical skills, deeper dissection, and more invasive anesthetic preparation compared to other approaches [8]. A failed supinator to anterior interosseous nerve (Sup-AIN) transfer highlights the importance of patient selection [6]. The use of anterior interosseous nerve (AIN) transfer should improve the outcome for patients with proximal ulnar nerve injuries [17].

Anatomy & Pathophysiology

Vascular & Neural

Anterior Interosseous Nerve (AIN) Syndromes: Fascicular constrictions typify anterior interosseous nerve syndrome, identified in all MRN cases and 88% of ultrasound cases, predominantly in the posterior/posteromedial region proximal to the elbow joint line [27]. Etiologies of Compression: Compression of the anterior interosseous nerve can occur after use of a sling for dislocation of the acromioclavicular joint [20]. Mixed neuropathy presenting clinically as an anterior interosseous nerve palsy following shoulder arthroscopy is hypothesized to be caused by fluid extravasation from arthroscopy causing increased pressure in the upper arm and forearm [30]. Anterior interosseous nerve palsy is a rare complication of open capsular release for elbow stiffness, likely caused by traction or mass effect from packing [18]. Diagnostic Localization: Compression of the median nerve at the elbow in entrapment cases was located by electromyographical findings rather than by abnormalities in conduction [41]. Sonography illustrates the anatomy, biomechanics, and sonographic technique for examining the pronator teres muscle [23]. Elasticity of the pronator teres muscle in youth baseball players with elbow injuries can be evaluated using ultrasound strain elastography [37].

Pronator Teres Function and Pathology: The function of the pronator teres and quadratus cannot be isolated by elbow flexion positioning [43]. Type 4 median nerve entrapment is a severe form of a rare complication of elbow dislocation in children [50]. Pronator teres symptoms disappeared in 93% of cases following mini-invasive decompression [1].

Reconstructive Implications: Transfer of the pronator teres for acquired radial nerve palsy results in loss of pronation function [5]. Combining pronator teres with allogeneic tendon for restoration of forearm supination does not affect pronation function [15]. Transfer of the pronator teres to extensor carpi radialis brevis improves upper limb function through effective correction of forearm pronation and wrist flexion deformities in children with cerebral palsy [46]. Restoration of finger flexion by pronator teres muscle transfer after brachial plexus injury is useful for finger flexion grasp and serves to place the fingers in a more suitable flexed position for lateral pinch [53]. Transfer of the nerve to the brachioradialis muscle to the anterior interosseous nerve is indicated for recovery of flexion of the thumb and fingers in recent lower brachial plexus lesions (C8–T1) without reducing flexor function of the wrist or elbow [49]. Distal anterior interosseous nerve transfer to the deep motor branch of the ulnar nerve for reconstruction of high ulnar nerve injuries does not cause functional deficit in performing tasks in pronation [19]. Release of the flexor-pronator origin improves control and function of the hands in patients with marked flexion deformities of the wrist and fingers and accompanying pronation contractures of the forearm [2].

Classification

Pronator Syndrome: Diagnosis requires a thorough understanding of median nerve anatomy, possible sites of compression, and characteristic clinical findings [11]. The condition lacks objective pathophysiology and is supported only by subjective operative findings and relief after surgery [3]. Compression sites include a high insertion of the pronator teres [16], a supracondylar process [16], and the flexor digitorum superficialis (FDS) arch [22].

FDS Arch Morphology: Two types exist: a distinct fibrous arch and an indistinct fibrous arch with vertical fibers blending into overlying fascia [22]. Only 42% of specimens have a distinct FDS arch, averaging 1.69 cm in length [22]. The majority have an indistinct arch; 77% of those have overlying muscle requiring an average release of 2.6 cm [22].

Anterior Interosseous Nerve (AIN) Anatomy: The AIN arises from the median nerve 5–8 cm distal to the lateral epicondyle [55]. It usually innervates the flexor pollicis longus, the radial half of the flexor digitorum profundus, and the pronator quadratus [55]. The motor branch of the flexor pollicis longus arises approximately 4 cm distal to the AIN origin [55]. The AIN supplies sensory fibers to the radiocarpal, intercarpal, carpometacarpal, and distal radio-ulnar joints [55]. Anatomically, the AIN branches at or distal to the FDS arch in 74% of specimens [22]. Only 8% have an ulnar-sided origin of the AIN off the median nerve [22]. Dissection along the ulnar side of the median nerve decreases the chance of injury to the AIN during decompression [22].

AIN Syndrome: In the majority of cases, this is not a surgically treatable entrapment neuropathy but a multifocal mononeuropathy selectively involving motor fascicles within the main trunk of the median nerve [24]. Injury mechanisms in children with supracondylar humerus fractures likely involve direct contusion of the posterior median nerve by the proximal fragment [13] or stretching of the AIN in Zone 1 due to its fixation in Zone 2 [13].

Other Considerations: Treatment for AIN syndrome begins nonsurgically with rest, splinting, and observation [7]. Most patients improve without surgical intervention [7]. Observation for several months is suggested before decompression [7]. There is a paucity of high-quality literature supporting the appropriate duration of conservative treatment for AIN syndrome [7]. Surgical decompression is recommended for AIN syndrome patients with a space-occupying mass [7] or those who fail a several-month course of nonsurgical treatment [7]. Surgical decompression of the median nerve or AIN in the forearm is rarely indicated, and a prolonged nonsurgical approach is warranted in most cases [9]. Surgical indications for pronator syndrome include persistent symptoms for greater than 6 months [4]. Surgical indications for AIN syndrome include a minimum of 12 months with no signs of motor improvement [4]. Pronator syndrome associated with a persistent median artery is treated by resection of a segment of the persistent median artery [14].

Clinical Presentation

The diagnosis of proximal entrapment of the median nerve requires a high index of suspicion, as clinical examination must be relied upon in the absence of objective tests [34]. Clinical manifestations include aching pain in the anterior forearm, loss of key and tip pinch strength with an inability to make an 'OK' sign, and loss of fine motor skills leading to clumsiness or dropping objects [34]. The severity and completeness of these motor symptoms vary substantially [34]. Less frequently, paresthesias in the median nerve-innervated region of the hand, similar to carpal tunnel syndrome, may be present [34]. Clinicians must have a thorough understanding of median nerve anatomy, possible sites of compression, and characteristic clinical findings to provide a reliable diagnosis [11].

Four distinct situations have been identified for proximal entrapment: Anterior interosseous nerve syndrome, Pronator syndrome, Superficialis tunnel syndrome, and Lacertus tunnel syndrome [34]. The existence of these syndromes as individual entities has been questioned [34]. Differentiating pronator syndrome from carpal tunnel syndrome remains a challenge due to overlapping symptoms and limited reliable information [35]. Electrodiagnostic studies, ultrasound, and MRI are generally unhelpful in diagnosing pronator syndrome concurrent with carpal tunnel syndrome when clinical evaluation is the reference standard [26]. Nerve conduction studies are usually normal and thus unhelpful in proximal entrapment [34]. While ultrasound may identify compression via changes in nerve diameter, it is difficult to use without a mass or haematoma because fibrous bands or scar tissue may be too small to visualize [34].

Clinical suspicion for AIN syndrome should arise in the presence of isolated paralysis of the AIN-supplied muscles [36]. In contrast to pronator syndrome, AIN palsy creates objective weakness and electrophysiological abnormalities [33]. AIN syndrome is uncommon, of unknown etiology and pathophysiology, and in the majority of cases is not a surgically treatable entrapment neuropathy but a multifocal mononeuropathy selectively involving motor fascicles within the main trunk of the median nerve [33, 24]. Median nerve compression can be secondary to a high insertion of the pronator teres [16].

Surgical Indications: * Pronator Syndrome: Decompression is indicated for persistent symptoms for >6 months [4]. * AIN Syndrome: Decompression is recommended for patients with a space-occupying mass or those who fail a several-month course of nonsurgical treatment [7]. For idiopathic cases, treatment recommendations range from surgical exploration after 6 to 12 weeks (if not part of transient idiopathic brachial plexus neuropathy) to observation for at least 18 months [33]. A minimum of 12 months with no signs of motor improvement is an indication for surgery [4]. * Acute/Post-Traumatic: Early diagnosis and prompt release of a constrictive dressing resulted in a rapid, complete return of function in patients with forearm fractures complicated by AIN palsy [38].

Surgical Approach and Anatomy: The surgical approach for pronator or AIN syndrome uses a lazy-S–type incision, beginning with exploration of the median nerve proximal to the antecubital flexion crease [7]. Proximal exploration allows identification of the median nerve proper and exposure of the ligament of Struthers if needed [7]. The extent of proximal exploration can be tailored to the surgeon's specific areas of preoperative concern [7]. After proximal release, the median nerve is dissected free from the lacertus fibrosus, the humeral head of the pronator teres, and the proximal fascial edge of the flexor digitorum superficialis (FDS) arch [7]. Gantzer's accessory flexor pollicis longus (FPL) muscle should be released if present [7].

Anatomical variations influence surgical technique. Nearly all median nerve branches course off its ulnar side at the proximal forearm level, with the exception of the AIN which branches off the radial side [7]. Dissection along the ulnar side of the median nerve can possibly decrease the chance of injury to the AIN during decompression [22]. Only 8% of specimens had an ulnar-sided origin of the AIN off the median nerve [22]. The AIN branched at or distal to the FDS arch in 74% of specimens [22].

Two types of the FDS arch were discovered: a distinct fibrous arch and an indistinct fibrous arch with vertical fibers blending into overlying fascia [22]. Only 42% of specimens had a distinct FDS arch averaging 1.69 cm in length [22]. The majority of specimens had an indistinct arch, and of those, 77% had overlying muscle requiring an average release of 2.6 cm [22]. A longer surgical release is needed with indistinct FDS arches, and overlying muscle during dissection may be indicative of this variant [22]. In AIN syndrome, the AIN should be thoroughly decompressed from any overlying tissue and completely visualized as it travels into the distal forearm [7]. Surgical decompression of the median nerve or AIN in the forearm is rarely indicated; a prolonged nonsurgical approach is warranted in most cases [9].

Outcomes and Complications: Transfer of the pronator teres results in loss of pronation function [5]. Patient selection is critical for supinator to AIN nerve transfer, as failures have been reported [6]. No functional deficit in performing tasks in pronation was reported after distal AIN transfer to the deep motor branch of the ulnar nerve for reconstruction of high ulnar nerve injuries [19].

In a case of endoscopic nerve decompression for AIN syndrome, a 62-year-old patient showed clinical improvement beginning on the first postoperative day [21]. At nearly 2 years postoperatively, thumb and index finger range of movement had completely normalized following endoscopic decompression and tendon transfer [21]. Strength and active forearm pronation improved but were slightly diminished compared with the contralateral side [21]. Neurologically, signs suggestive of persistent denervation of the pronator quadratus muscle remained in a patient nearly 2 years after endoscopic decompression for AIN syndrome [21].

Investigations

Plain radiography: No specific plain radiographic findings are cited for pronator syndrome or anterior interosseous nerve (AIN) syndrome in the provided evidence base.

MRI: Magnetic resonance neurography (MRN) identifies fascicular constrictions as the typifying feature of AIN syndrome, with these lesions identified in all MRN cases [27]. Ultrasound similarly detects these constrictions in 88% of cases, predominantly located in the posterior or posteromedial region proximal to the elbow joint line [27]. Sonography further allows for examination of the pronator teres muscle to illustrate its anatomy, biomechanics, and normal or pathologic appearances [23].

CT: No specific CT findings are cited for pronator syndrome or AIN syndrome in the provided evidence base.

Bone scan: No specific bone scan findings are cited for pronator syndrome or AIN syndrome in the provided evidence base.

Tomosynthesis: No specific tomosynthesis findings are cited for pronator syndrome or AIN syndrome in the provided evidence base.

Aspiration: No aspiration procedures are cited for pronator syndrome or AIN syndrome in the provided evidence base.

Laboratory: No laboratory markers are cited for pronator syndrome or AIN syndrome in the provided evidence base.

Other Considerations: Diagnosis of pronator syndrome lacks objective pathophysiology and is supported only by subjective operative findings and relief after surgery [3]. Electrodiagnostic testing, ultrasound, and MRI are not helpful in making a diagnosis of pronator syndrome concurrent with carpal tunnel syndrome when clinical evaluation is the reference standard [26]. Most cases of AIN compression by normal surrounding tissues likely do not exist or are very rare, with most cases representing neuritis [57]. Consequently, surgical decompression of the median nerve or AIN in the forearm is rarely indicated, and a prolonged nonsurgical approach is warranted in most cases [9]. Conservative treatment for at least 6 months is recommended for AIN syndrome before considering surgery [57]. Most patients with AIN syndrome improve without surgical intervention, suggesting observation for several months before decompression [7]. Injury mechanisms for AIN palsy secondary to supracondylar humerus fractures likely involve direct contusion of the posterior aspect of the median nerve by the proximal fragment and stretching of the AIN in Zone 1 due to its fixation in Zone 2 [13].

Treatment

Non-Operative

Conservative management, including rest, non-steroidal anti-inflammatory drugs (NSAIDs), and corticosteroids, is effective in 50% to 70% of patients with pronator syndrome [42]. Initial treatment for anterior interosseous nerve (AIN) syndrome should be nonsurgical, consisting of rest, splinting, and observation [7]. Most patients with AIN syndrome improve without surgical intervention, supporting a period of observation for several months before considering decompression [7].

Operative

Indications: Surgical indications for nerve decompression include persistent symptoms for greater than 6 months in patients with pronator syndrome [4]. For AIN syndrome, surgery is indicated after a minimum of 12 months with no signs of motor improvement [4]. Surgical decompression is also recommended for patients with AIN syndrome who have a space-occupying mass in the area [7] or who fail a several-month course of nonsurgical treatment [7].

Surgical Approach / Technique: The surgical approach for pronator syndrome (PS) or AIN syndrome typically uses a lazy-S–type incision beginning proximal to the antecubital flexion crease [7]. The surgical approach and extent of proximal exploration can be tailored to the surgeon's specific preoperative concerns [7]. Nearly all median nerve branches course off its ulnar side at this level, with the exception of the AIN, which branches off the radial side [7]. In AIN syndrome, the AIN should be thoroughly decompressed from overlying tissue and completely visualized as it travels into the distal forearm [7].

An enlarged surgical approach begins 5 cm above the elbow fold adjacent to the medial bicipital groove, runs laterally in the elbow fold, and extends 7-8 cm along the forearm axis [44]. In the enlarged approach, the median nerve is identified and released along its whole course from proximal to distal, beyond the emergence of the AIN [44]. All potential entrapment sites are checked and freed as appropriate during the surgical release [44]. Postoperative management following the enlarged approach includes immediate active mobilization without forcing [44].

Endoscopically assisted, minimally invasive approaches adequately and safely decompress all anatomical points of compression for pronator syndrome [10]. Endoscopic decompression for AIN syndrome has been performed with clinical improvement beginning on the first postoperative day [21]. Following endoscopic decompression for AIN syndrome, immobilization of the upper arm for 10 days may be performed [21]. Surgical release in local anesthesia allows for a safe, ambulatory, and cost-efficient procedure with low morbidity for proximal median nerve entrapment [40]. Mini-invasive decompression techniques result in the disappearance of pronator teres symptoms in 93% of cases [1].

Specific Anatomical Releases and Reconstructions: Release of the flexor-pronator origin improves control and function of the hands in patients with marked flexion deformities of the wrist and fingers and accompanying pronation contractures in spastic paralysis [2]. Treatment of pronation contractures in cerebral palsy can involve changing the insertion of the pronator teres [48]. In the pronator teres transfer procedure for cerebral palsy, the tendon is prolonged with a strip of periosteum, detached from the radius, and reinserted into a hole drilled in the anterolateral radial cortex [48]. Restoration of forearm supination can be achieved by combining pronator teres transfer with allogeneic tendon, which provides fine results with low risks and does not affect pronation function [15].

Lacertus syndrome and superficialis-pronator syndrome should be treated as distinct targets for surgical release [12]. The term pronator syndrome should be replaced with superficialis-pronator syndrome to reflect distinct surgical targets [12]. Resection of a segment of a persistent median artery is the recommended treatment for pronator syndrome associated with this anomaly [14].

Supinator to anterior interosseous nerve transfer can restore digital flexion in spinal cord and peripheral nerve injury, though patient selection is critical due to potential failure [6]. Transfer of the anterior interosseous nerve (AIN) can improve outcomes for patients with proximal ulnar nerve injuries [17]. Supercharge end-to-side AIN-to-ulnar motor nerve transfer involves dissecting the AIN entering the pronator quadratus, transecting it at the trifurcation, and coaptating it to the ulnar motor branch [29]. Transfer of the distal AIN can be used for thumb motion reconstruction in radial nerve paralysis [47]. In distal AIN transfer for radial nerve paralysis, the nerve is dissected through a separate incision in the distal volar forearm or via dorsal division of the interosseous membrane, then coapted to the deep branch of the posterior interosseous nerve [47].

Complications and Functional Outcomes: Pronator teres release is more invasive than other procedures, requiring more complicated surgical skills, deeper dissection, and more invasive anesthetic preparation [8]. Transfer of the pronator teres for acquired radial nerve palsy results in the loss of pronation function [5]. AIN palsy is a rare complication of open capsular release for elbow stiffness, likely caused by traction or mass effect from packing [18]. Compression of the AIN can occur after the use of a sling for acromioclavicular joint dislocation [20]. Patients using a sling for acromioclavicular joint dislocation should be encouraged to frequently change forearm rotation position and use the hand to prevent AIN compression [20].

Complications

Nerve palsy: Pronator teres release is more invasive than alternative approaches, requiring more complicated surgical skills, deeper dissection, and more invasive anesthetic preparation [8]. This procedure results in loss of pronation function [5]. Anterior interosseous nerve (AIN) palsy can present as a complication of supracondylar fractures of the humerus in children [28]. Injury mechanisms for AIN palsy secondary to these fractures likely involve direct contusion of the posterior aspect of the median nerve by the proximal fragment and stretching of the AIN in Zone 1 due to its fixation in Zone 2 [13]. AIN palsy can also occur after use of a sling for dislocation of the acromioclavicular joint [20]. Mixed neuropathy presenting clinically as AIN palsy can occur following shoulder arthroscopy, hypothesized to be caused by fluid extravasation from arthroscopy increasing pressure in the upper arm and forearm [30].

Diagnostic uncertainty and failure: Failure of pronator syndrome surgery is attributed to inadequate decompression or misdiagnosis [63]. The diagnosis of pronator syndrome lacks objective pathophysiology and is supported only by subjective operative findings and relief after surgery, with a paucity of controlled trials demonstrating that operative treatment is more effective than other treatments or sham surgery [3].

Recovery

Light activity (weeks): Specific timelines for light activity are not defined in the available evidence. However, patients with symptomatic anomalous pronator teres origins who underwent surgical release returned to full duty [59]. For ulna coronoid process fractures treated via the pronator teres and flexor carpi radialis interval approach, fracture union was achieved in all patients with an average time to radiologic union of 14.2 weeks [32].

Full activity (months): Evidence does not specify a month range for full activity return. In cases of acquired radial nerve palsy treated with pronator teres transfer, the procedure confirmed loss of pronation function [5]. Conversely, restoration of forearm supination using a modified technique combining pronator teres with allogeneic tendon resulted in fine outcomes and low risks without affecting pronation function [15].

Complete recovery / outcome plateau (months): Complete recovery from anterior interosseous nerve (AIN) paralysis following supracondylar fracture of the humerus in children is usual within 3 months [39]. For AIN palsy following elbow surgery, recovery can take a long time, and it remains unclear if surgical exploration would have accelerated recovery [61].

Rehabilitation protocol: Standardized outcome measures, early intervention, and comprehensive rehabilitation are important for optimizing supercharged end-to-side AIN-to-ulnar nerve transfer outcomes [62].

Functional milestones: Patients who underwent AIN-to-ulnar motor nerve (AIN-to-UMN) transfer had significantly better ulnar intrinsic motor recovery when surgery was performed earlier from the onset of motor symptoms [52]. The supercharged end-to-side AIN-to-ulnar motor nerve transfer has broad clinical utility for augmenting partial recovery and preserving motor end plates in second- and third-degree axonotmetic nerve injuries [58]. Release of the flexor-pronator origin for marked flexion deformities of the wrist and fingers with accompanying pronation contractures resulted in improvement in control and function of the hands [2]. The use of AIN transfer for proximal ulnar nerve injuries is expected to improve patient outcomes [17].

Other Considerations: A single failed supinator to anterior interosseous nerve (Sup-AIN) transfer highlights the importance of patient selection for this procedure [6]. Future research is required to determine the proportion of intrinsic recovery attributable to the supercharged end-to-side AIN-to-ulnar nerve transfer [56].

Key Evidence

  • [L4] Pronator teres symptoms disappeared in 93% of cases following the mini-invasive technique. [1] (10.1016/j.jhsa.2012.05.033)
  • [L4] Eighteen patients with marked flexion deformities of the wrist and fingers and accompanying pronation contractures of the forearm have been treated by release of the flexor-pronator origin with improvement in control and function of the hands. [2] (10.2106/00004623-196648050-00002)
  • [L5] The diagnosis of pronator syndrome lacks objective pathophysiology and is supported only by subjective operative findings and relief after surgery, with a paucity of controlled trials demonstrating that operative treatment is more effective than other treatments or sham surgery. [3] (10.1016/j.jhsa.2011.02.014)
  • [Paper] Surgical indications for nerve decompression include persistent symptoms for >6 months in patients with pronator syndrome or for a minimum of 12 months with no signs of motor improvement in those with anterior interosseous nerve syndrome. [4] (10.5435/jaaos-21-05-268)
  • [L4] The clinical arm of the study confirmed our biomechanic findings by showing the loss of pronation function. [5] (10.1016/j.jhsa.2007.01.012)
  • [L4] The one failed Sup-AIN in our series highlights the importance of patient selection. [6] (10.1016/j.jhsa.2024.05.008)
  • [L5] [7] (10.1016/j.jhsa.2009.10.017)
  • [L4] The pronator teres release was more invasive and required more complicated surgical skills, deeper dissection, and more invasive anesthetic preparation. [8] (10.1051/sicotj/2016006)
  • [L5] Surgical decompression of the median nerve or the AIN in the forearm is rarely indicated; a prolonged nonsurgical approach is warranted in most cases. [9] (10.5435/jaaos-d-16-00010)
  • [L4] The endoscopically assisted, minimally invasive approach to treat pronator syndrome adequately and safely decompressed all anatomical points of compression and improved DASH scores. [10] (10.1016/j.jhsa.2012.02.023)
  • [L5] It is essential for clinicians to have a thorough understanding of median nerve anatomy, possible sites of compression, and characteristic clinical findings of pronator syndrome to provide a reliable diagnosis and treat their patients. [11] (10.1016/j.jhsa.2020.07.006)
  • [L5] Lacertus syndrome and superficialis-pronator syndrome should be clearly presented as distinct targets for surgical release, and the term pronator syndrome should be replaced with superficialis-pronator syndrome. [12] (10.1177/17531934211024092)
  • [L4] Injury mechanisms likely involve direct contusion of the posterior aspect of the median nerve by the proximal fragment and stretching of the AIN in Zone 1 due to its fixation in Zone 2. [13] (10.1016/j.otsr.2013.04.002)
  • [Case_report] Resection of a segment of the persistent median artery is the recommended treatment for pronator syndrome associated with this anomaly. [14] (10.2106/00004623-198769020-00026)
  • [L4] This study provides a modified supination function reconstruction with simple operating, fine results, low risks, and no affecting of pronation function. [15] (10.1186/s12891-021-04692-w)
  • [L4] [16] (10.1111/j.1758-5740.2010.00051.x)
  • [L5] The use of this technique for transfer of the AIN should improve the outcome for patients with proximal ulnar nerve injuries. [17] (10.1302/0301-620x.96b6.33656)
  • [L4] Anterior interosseous nerve palsy is a rare complication of open capsular release for elbow stiffness, likely caused by traction or mass effect from packing. [18] (10.1016/j.jhsa.2008.10.019)
  • [L4] No functional deficit in performing tasks in pronation was reported. [19] (10.1055/s-2002-33326)
  • [L4] Patients should be encouraged to change the position of rotation of the forearm frequently and to use the hand while wearing the sling. [20] (10.2106/00004623-199173060-00022)
  • [L4] [21] (10.1016/j.jhsa.2013.07.026)
  • [L5] [22] (10.1007/s11552-014-9639-5)
  • [L5] This pictorial essay illustrates the anatomy, biomechanics, and sonographic technique for examining the pronator teres muscle. [23] (10.1002/jum.14306)
  • [L4] Our data strongly support that AINS in the majority of cases is not a surgically treatable entrapment neuropathy but a multifocal mononeuropathy selectively involving, within the main trunk of the median nerve, the motor fascicles that continue distally to form the anterior interosseous nerve. [24] (10.1212/wnl.0000000000000128)
  • [L4] With clinical evaluation as the reference standard, electrodiagnostic, ultrasound, and MRI are not helpful in making a diagnosis of pronator syndrome concurrent with carpal tunnel syndrome. [26] (10.1016/j.jhsa.2020.06.006)
  • [L4] These constrictions were identified in all MRN cases and 88% of ultrasound cases, predominantly in the posterior/posteromedial region proximal to the elbow joint line. [27] (10.1002/mus.26768)
  • [L4] [28] (10.2106/00004623-196951080-00008)
  • [L3] [29] (10.1097/prs.0000000000002747)
  • [L4] The authors hypothesize that fluid extravasation from arthroscopy causing increased pressure in the upper arm and forearm is the singular cause of these neuropathies. [30] (10.1016/j.jse.2016.04.037)
  • [L4] Fracture union was achieved in each patient with an average time to radiologic union of 14.2 weeks. [32] (10.1016/j.otsr.2020.04.004)
  • [L5] [33] (10.1016/j.jhsa.2010.08.018)
  • [L4] [34] (10.1177/1753193417726214)
  • [L4] The diagnostic process to differentiate pronator syndrome from carpal tunnel syndrome remains a challenge due to overlapping symptoms and limited reliable information in the literature; this review provides a comprehensive clinical comparison to aid in establishing appropriate diagnosis and treatment. [35] (10.3390/diagnostics12102433)
  • [L5] Clinical suspicion should arise in the presence of isolated paralysis of the AIN-supplied muscles. [36] (10.1016/j.ijscr.2016.02.021)
  • [L3] These findings may contribute to an accurate evaluation and prevention of elbow injuries in youth baseball players. [37] (10.1016/j.jse.2018.05.021)
  • [L4] Early diagnosis and prompt release of the offending constrictive dressing resulted in a rapid, complete return of function of the nerve in all of our patients. [38] (10.2106/00004623-199701000-00014)
  • [L4] Complete recovery is usual within 3 months. [39] (10.1016/0020-1383(89)90172-1)
  • [L4] Surgical release in local anesthesia allows for a safe, ambulatory, and cost-efficient procedure with low morbidity. [40] (10.1007/s11552-012-9483-4)
  • [L4] Compression at the elbow was located by electromyographical findings rather than by abnormalities in conduction. [41] (10.1136/jnnp.37.3.340)
  • [L5] Conservative management, including rest, non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids, usually suffice and has been effective in 50 - 70% of patients. [42] (10.1097/phm.0000000000000973)
  • [L4] The findings suggest that the function of the PT and PQ cannot be isolated by elbow flexion positioning. [43] (10.1016/j.jhsa.2025.09.013)
  • [Paper] [44] (10.1016/j.otsr.2021.102825)
  • [L2] The pronator teres to extensor carpi radialis brevis transfer improves upper limb function through effective correction of forearm pronation and wrist flexion deformities. [46] (10.1177/1753193420960330)
  • [L4] [47] (10.1016/j.jhsa.2020.02.011)
  • [L4] [48] (10.2106/00004623-198163040-00016)
  • [Case_report] This technique is indicated for recovery of flexion of the thumb and fingers in recent lower brachial plexus lesions (C8–T1) without reducing flexor function of the wrist or elbow. [49] (10.1016/j.jhsa.2010.11.030)
  • [L4] Type 4 median nerve entrapment is a severe form of a rare complication of elbow dislocation. [50] (10.1007/s00402-003-0565-1)
  • [L4] Patients who underwent an AIN-to-UMN transfer had significantly better ulnar intrinsic motor recovery when they had earlier surgery from the onset of motor symptoms. [52] (10.1177/1558944720928482)
  • [Case_report] Restoring active finger flexion is useful for finger flexion grasp and also serves to place the fingers in a more suitable flexed position for lateral pinch. [53] (10.1007/s11552-013-9502-0)
  • [L4] Future research is required to determine the proportion of intrinsic recovery attributable to this transfer. [56] (10.1097/prs.0000000000001514)
  • [L5] Compression of the anterior interosseous nerve by normal surrounding tissues may not exist or is very rare, with most cases likely representing neuritis; conservative treatment for at least 6 months is recommended before considering surgery. [57] (10.1177/17531934221074903)
  • [L4] The authors believe the procedure has broad clinical utility for augmenting partial recovery and preserving motor end plates in second- and third-degree axonotmetic nerve injuries. [58] (10.1016/j.jhsa.2012.07.022)
  • [Case_report] They note that while the prognosis for AIN palsy is generally good, recovery after elbow surgery can take a long time, and it is unclear if surgical exploration would have accelerated recovery in this case. [61] (10.5397/cise.2022.00899)
  • [L3] The review highlights the importance of standardized outcome measures, early intervention, and comprehensive rehabilitation for optimizing supercharged end-to-side anterior interosseous nerve to ulnar nerve transfer outcomes. [62] (10.1016/j.jhsg.2024.06.003)

See Also

References

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[2] Release of the Flexor-Pronator Origin for Flexion Deformities of the Hand and Wrist in Spastic Paralysis. The Journal of Bone & Joint Surgery. 1966. DOI: 10.2106/00004623-196648050-00002

[3] Pronator Syndrome. The Journal of Hand Surgery. 2011. DOI: 10.1016/j.jhsa.2011.02.014

[4] Pronator Syndrome and Anterior Interosseous Nerve Syndrome. Journal of the American Academy of Orthopaedic Surgeons. 2013. DOI: 10.5435/jaaos-21-05-268

[5] Functional Deficit After Transfer of the Pronator Teres for Acquired Radial Nerve Palsy. The Journal of Hand Surgery. 2007. DOI: 10.1016/j.jhsa.2007.01.012

[6] Supinator to Anterior Interosseous Nerve Transfer to Restore Digital Flexion in Spinal Cord and Peripheral Nerve Injury. The Journal of Hand Surgery. 2024. DOI: 10.1016/j.jhsa.2024.05.008

[7] Unusual Compression Neuropathies of the Forearm, Part II: Median Nerve. The Journal of Hand Surgery. 2009. DOI: 10.1016/j.jhsa.2009.10.017

[8] Role of pronator release in revision carpal tunnel surgery. SICOT-J. 2016. DOI: 10.1051/sicotj/2016006

[9] Ulnar Tunnel Syndrome, Radial Tunnel Syndrome, Anterior Interosseous Nerve Syndrome, and Pronator Syndrome. Journal of the American Academy of Orthopaedic Surgeons. 2017. DOI: 10.5435/jaaos-d-16-00010

[10] Endoscopically Assisted Decompression for Pronator Syndrome. The Journal of Hand Surgery. 2012. DOI: 10.1016/j.jhsa.2012.02.023

[11] Proximal Median Nerve Compression: Pronator Syndrome. The Journal of Hand Surgery. 2020. DOI: 10.1016/j.jhsa.2020.07.006

[12] Median nerve compression: lacertus syndrome versus superficialis-pronator syndrome. Journal of Hand Surgery (European Volume). 2021. DOI: 10.1177/17531934211024092

[13] The anatomical basis for anterior interosseous nerve palsy secondary to supracondylar humerus fractures in children. Orthopaedics & Traumatology: Surgery & Research. 2013. DOI: 10.1016/j.otsr.2013.04.002

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[15] Restoration of forearm supination by combining pronator teres with allogeneic tendon. BMC Musculoskeletal Disorders. 2021. DOI: 10.1186/s12891-021-04692-w

[16] Median Nerve Compression Secondary to a High Insertion of Pronator Teres. Shoulder & Elbow. 2010. DOI: 10.1111/j.1758-5740.2010.00051.x

[17] An anatomical study of transfer of the anterior interosseous nerve for the treatment of proximal ulnar nerve injuries. The Bone & Joint Journal. 2014. DOI: 10.1302/0301-620x.96b6.33656

[18] Anterior Interosseous Nerve Palsy After Open Capsular Release for Elbow Stiffness: Report of 2 Cases. The Journal of Hand Surgery. 2009. DOI: 10.1016/j.jhsa.2008.10.019

[19] Distal Anterior Interosseous Nerve Transfer to the Deep Motor Branch of the Ulnar Nerve for Reconstruction of High Ulnar Nerve Injuries. Journal of Reconstructive Microsurgery. 2002. DOI: 10.1055/s-2002-33326

[20] Compression of the anterior interosseous nerve after use of a sling for dislocation of the acromioclavicular joint. A report of two cases.. The Journal of Bone & Joint Surgery. 1991. DOI: 10.2106/00004623-199173060-00022

[21] Minimally Invasive Endoscopic Decompression for Anterior Interosseous Nerve Syndrome: Technical Notes. The Journal of Hand Surgery. 2013. DOI: 10.1016/j.jhsa.2013.07.026

[22] Median Nerve Compression at the Fibrous Arch of the Flexor Digitorum Superficialis: An Anatomic Study of the Pronator Syndrome. HAND. 2014. DOI: 10.1007/s11552-014-9639-5

[23] Sonography of the Pronator Teres: Normal and Pathologic Appearances. Journal of Ultrasound in Medicine. 2017. DOI: 10.1002/jum.14306

[24] Anterior interosseous nerve syndrome. Neurology. 2014. DOI: 10.1212/wnl.0000000000000128

[26] Clinical, Radiological, and Electrodiagnostic Diagnosis of Pronator Syndrome Concurrent With Carpal Tunnel Syndrome. The Journal of Hand Surgery. 2020. DOI: 10.1016/j.jhsa.2020.06.006

[27] Fascicular constrictions above elbow typify anterior interosseous nerve syndrome. Muscle & Nerve. 2019. DOI: 10.1002/mus.26768

[28] Anterior Interosseous-Nerve Paralysis as a Complication of Supracondylar Fractures of the Humerus in Children. The Journal of Bone & Joint Surgery. 1969. DOI: 10.2106/00004623-196951080-00008

[29] Comparison of Ulnar Intrinsic Function following Supercharge End-to-Side Anterior Interosseous–to–Ulnar Motor Nerve Transfer: A Matched Cohort Study of Proximal Ulnar Nerve Injury Patients. Plastic & Reconstructive Surgery. 2016. DOI: 10.1097/prs.0000000000002747

[30] Mixed neuropathy presenting clinically as an anterior interosseous nerve palsy following shoulder arthroscopy: a report of four cases. Journal of Shoulder and Elbow Surgery. 2016. DOI: 10.1016/j.jse.2016.04.037

[32] The pronator teres and the flexor carpi radialis interval approach for operative fixation of ulna coronoid process fractures. Orthopaedics & Traumatology: Surgery & Research. 2021. DOI: 10.1016/j.otsr.2020.04.004

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[34] The scratch collapse test in the diagnosis of compression of the median nerve in the proximal forearm. Journal of Hand Surgery (European Volume). 2017. DOI: 10.1177/1753193417726214

[35] How to Differentiate Pronator Syndrome from Carpal Tunnel Syndrome: A Comprehensive Clinical Comparison. Diagnostics. 2022. DOI: 10.3390/diagnostics12102433

[36] Anterior interosseous nerve syndrome diagnosis and intraoperative findings: A case report. International Journal of Surgery Case Reports. 2016. DOI: 10.1016/j.ijscr.2016.02.021

[37] Elasticity of the pronator teres muscle in youth baseball players with elbow injuries: evaluation using ultrasound strain elastography. Journal of Shoulder and Elbow Surgery. 2018. DOI: 10.1016/j.jse.2018.05.021

[38] Fractures of the Forearm Complicated by Palsy of the Anterior Interosseous Nerve Caused by a Constrictive Dressing. A Report of Four Cases. The Journal of Bone and Joint Surgery-American Volume*. 1997. DOI: 10.2106/00004623-199701000-00014

[39] Anterior interosseous nerve paralysis: an underdiagnosed complication of supracondylar fracture of the humerus in children. Injury. 1989. DOI: 10.1016/0020-1383(89)90172-1

[40] Clinical Diagnosis and Wide-Awake Surgical Treatment of Proximal Median Nerve Entrapment at the Elbow: A Prospective Study. HAND. 2013. DOI: 10.1007/s11552-012-9483-4

[41] Electrophysiological findings in entrapment of the median nerve at wrist and elbow. Journal of Neurology, Neurosurgery & Psychiatry. 1974. DOI: 10.1136/jnnp.37.3.340

[42] Pronator Syndrome: An Uncommon Median Nerve Entrapment Syndrome. American Journal of Physical Medicine & Rehabilitation. 2019. DOI: 10.1097/phm.0000000000000973

[43] Rethinking Muscle Testing: Dynamic EMG Studies of Elbow Positioning as a Differentiator of Pronator Teres and Quadratus Functions. The Journal of Hand Surgery. 2026. DOI: 10.1016/j.jhsa.2025.09.013

[44] Median nerve entrapment syndrome in the elbow and proximal forearm. Anatomic causes and results for a 55-case surgical series at a mean 7 years’ follow-up. Orthopaedics & Traumatology: Surgery & Research. 2021. DOI: 10.1016/j.otsr.2021.102825

[46] A prospective study on transfer of pronator teres to extensor carpi radialis brevis for forearm and wrist deformity in children with cerebral palsy. Journal of Hand Surgery (European Volume). 2020. DOI: 10.1177/1753193420960330

[47] Transfer of the Distal Anterior Interosseous Nerve for Thumb Motion Reconstruction in Radial Nerve Paralysis. The Journal of Hand Surgery. 2020. DOI: 10.1016/j.jhsa.2020.02.011

[48] Treatment of pronation contractures of the forearm in cerebral palsy by changing the insertion of the pronator radii teres.. The Journal of Bone & Joint Surgery. 1981. DOI: 10.2106/00004623-198163040-00016

[49] Transfer of the Nerve to the Brachioradialis Muscle to the Anterior Interosseous Nerve for Treatment for Lower Brachial Plexus Lesions: Case Report. The Journal of Hand Surgery. 2011. DOI: 10.1016/j.jhsa.2010.11.030

[50] Type 4 median nerve entrapment in a child after elbow dislocation. Archives of Orthopaedic and Trauma Surgery. 2003. DOI: 10.1007/s00402-003-0565-1

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[56] The Supercharge End-to-Side Anterior Interosseous–to–Ulnar Motor Nerve Transfer for Restoring Intrinsic Function. Plastic and Reconstructive Surgery. 2015. DOI: 10.1097/prs.0000000000001514

[57] Compression to the anterior interosseous nerve is very rare: compression by the normal tissues surrounding it may not exist. Journal of Hand Surgery (European Volume). 2022. DOI: 10.1177/17531934221074903

[58] Supercharged End-to-Side Anterior Interosseous to Ulnar Motor Nerve Transfer for Intrinsic Musculature Reinnervation. The Journal of Hand Surgery. 2012. DOI: 10.1016/j.jhsa.2012.07.022

[59] The pronator teres had the anomalous origin from the fibrous band just mentioned. The patient's symptoms were relieved after surgery, and he returned to full duty November 6, 1956.. 1959.

[61] Anterior interosseous nerve palsy in the early postoperative period after open capsular release for elbow stiffness: a case report. Clinics in Shoulder and Elbow. 2023. DOI: 10.5397/cise.2022.00899

[62] Exploring Outcomes and Mediating Factors Following Supercharged End-to-Side Anterior Interosseous Nerve to Ulnar Nerve Transfer: A Scoping Review With Expert Insight. Journal of Hand Surgery Global Online. 2024. DOI: 10.1016/j.jhsg.2024.06.003

[63] The pronator teres syndrome: compressive neuropathy of the median nerve.. The Journal of Bone and Joint Surgery. American Volume. 1981.

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