1. Introduction
Supracondylar humerus fracture is one of the most common fractures in children (1). It includes half of all fractures of the elbow and about 30% of all limb fractures in children below 7 years (2-4). According to the fracture pattern and mechanism of the injury, the supracondylar humerus fractures are classified into two types: extension or flexion type (2, 5-7). The standard surgical treatment for displaced supracondylar humeral fracture is reduction followed by percutaneous pin fixation (8). Neurovascular structures are prone to damage because of proximity to fracture location. The neurovascular complication has been reported in 5%-19% of displaced fractures. Neurological complications associated with supracondylar humerus fractures in children, such as Anterior Interosseous Nerve (AIN) syndrome, are well- known (6, 9, 10). The AIN innervates three muscles: the flexor pollicis longus, flexor digitorum profundus of the second digit and the pronator quadratus (11, 12). AIN deficit was discovered as isolated or in combination with other nerve palsies in almost 12.9% of supracondylar humerus fractures (7).
2. Cases Presentation
From November 2014 to November 2016, 33 children with humeral supracondylar fracture were admitted to the orthopedic surgery centers of Imam Hospital in Sari, north of Iran. Four of them had AIN syndrome. The mean age of the patients was 6 years. All patients had extension type fracture. Based on the Gartland grade classification (13), three cases were of grade 3, and 1 case was of grade 2. The average nerve recovery period took up to four weeks. Closed or open reduction and pinning were taken as treatment procedures for these patients (Tables 1 and 2).

3. Discussion
Non-displaced or minimally displaced fractures in children can be treated with a splint at 90° of flexion for 2-3 weeks (8). While the angulation is more clearly visible on lateral radiographs, varus deformities can be measured more effectively on anteroposterior radiographs using Baumann’s angle. In case of an over 10° varus, closed reduction and pinning must be performed. Gartland type II fractures need closed reduction. These fractures may be stabilized at 90° of flexion. However, fixation with pin is required for stabilizing the fracture in more than 90° of elbow flexion (13, 14).
3.1. Reduction maneuver for supracondylar humerus fractures
Wide-wake fluoroscopy-based reduction must be performed. First, for neurovascular release, traction must be performed along the humerus within the range of elbow flexion. Traction must be avoided in elbow extension, as it can entangle blood vessels and nerves. If the proximal segment has penetrated the brachialis muscle, longer traction is required to induce the sensation of release of the fractured segment. The release is achieved by the proximal-to-distal milking of the brachialis muscle. Thus, the reduction maneuver starts by the hyperflexion of elbow, while applying pressure towards the anterior of the olecranon. The control radiograph is taken at this point. If the distal segment is rotated, it can be corrected in two ways. The most prevalent type is the varus rotation of the distal segment. In this case, extra pressure is applied inwardly with simultaneous pronation of the forearm. If the appropriate Baumann’s angle is not achieved, the reduction maneuver is repeated with extra valgus pressure. If the vascular injury is not improved after the initial closed reduction and splinting, the open method must be considered as well, especially in case of open fractures, severe elbow inflammation, and vascular injury (1, 14-16). Gartland type III fractures are susceptible to neurovascular injuries. The preferred treatment for this type of fracture is the open/closed reduction and pinning method, which has fewer complications than reduction and splinting.
3.2. Indication for surgery in supracondylar humerus fractures
Surgical treatment is indicated in supracondylar humerus fractures for the following cases: 1. Closed reduction is not possible; 2. The fracture is unstable after reduction, and reduction cannot be maintained; 3. In case of neural injury during or following reduction; 4. If vascular exploration is required; 5. In open fractures; 6. In all Gartland type II or III fractures which need an over 90° of flexion to maintain reduction; 7. In all Gartland type IV fractures; 8. For polytraumatized patients with another ipsilateral fracture (17).
3.3. Classification of supracondylar humerus fractures
There are various classifications for these fractures: a) Displaced or non-displaced; b) Open or closed; c) Complicated or uncomplicated (with or without neural/vascular involvement; d) Extension type (95%) or flexion type (5%); and e) Gartland classification system which is based on lateral radiographs; it is mostly used for extension-type fractures and can serve as a guide for the treatment method (14, 18).
Patients who suffer from AIN syndrome are typically unable to form an “O” by using the index finger and thumb because of paralysis of the flexor pollicis longus and flexor digitorum profundus (impaired flexion of the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger). For example, the patients will lose the ability to button their shirts or turn on their car keys to start it. On physical examination, the Pinch Grip test shows a positive result for patients who are unable to demonstrate the “OK” sign; instead they clamp the sheet between an extended thumb and index finger (19).
For the surgeon, the most concerning issue in the humeral supracondylar fracture is a vascular state, so there may not be any specific test for flexion of the terminal phalanges of thumb and index. So it can be missed easily. Furthermore, AIN is a motor nerve without a sensory task, so the lack of sensory loss does not exist to help diagnosis. Usually, median nerve and AIN are examined by finger flexion, but children deceive examiner by using the third finger to flex the second finger (18). 
In all our cases, complete nerve palsy recovery was observed within 3 to 5 weeks. In past studies, complete AIN palsy recovery was observed after 4 to 17 weeks. The neurophysiological and electromyographic examination should be performed after 4 months of conservative treatment without any recovery (8).
The clinical findings of AIN syndrome are composed of lack of flexion of the terminal interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. The pinch position can only be accomplished with the terminal phalanges of these fingers hyperextended. Pathological spontaneous activity in the affected muscles can be manifested by the electromyographic examination, positive sharp waves, and fibrillation that show denervation (20-22).
Complete AIN palsy recovery was observed after 4 to 17 weeks. Electromyographic examination should be performed after 4 months of conservative treatment without any recovery (23).
According to the just motor (no sensory) function of AIN and also deceiving children using the third finger to flex the second one, underestimation of AIN syndrome in supracondylar fracture of the humerus can be expected. So, the physician should be more careful about physical examination (OK sign) in supracondylar fracture of humerus besides the vascular state. 
Ethical Considerations
Compliance with ethical guidelines
This study is just a case report for the diagnostic methods and treatments and all procedures are performed according to the standard protocols. 
Funding 
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgements
The authors would like to express their thanks to the Department of Orthopedic Surgery of Imam Khomeini Hospital and Student Research Committee of Mazandaran University of Medical Sciences to support this research.


References