mHealth Research Digest by Anupam Kumar

Hallux valgus (HV) is an orthopedic deformity of the foot necessitating a complex series of detailed evaluations for management.

Measurement of angles between bones on radiographic images is used to determine severity of the deformity, monitor progression, and indicate the best course for surgical correction.

Such measurements were previously conducted manually in an error-prone procedure involving a hardcopy radiograph, pencil and protractor; however, in recent years this has largely given way to computerized measurements with greater reliability and validity.

The iPhone and other smartphones are equipped with a micro-electro-mechanical accelerometer that can measure acceleration and inclination accurately. Through a freely available application, this technology has been applied in the clinical setting to the measurement of HV angles on radiographic images; this technique is increasingly popular among podiatric surgeons.

However, there is currently a dearth of investigation into the accuracy and reliability of this practice despite its acceptance among surgeons. In a study recently published in Skeletal Radiology, Ege et al. compared HV angle measurements conducted on the iPhone with those determined by computer software, which is currently accepted as the most accurate method.

HV angles on radiographic images of 32 patients were first measured using the Pi-View Star software on a digital workstation with these values being set as the reference standard. Two attending orthopedic surgeons, blinded to the computerized measurements, utilized the iPhone running the Hallux Angles application to measure the angles on images displayed on a parallel-positioned computer monitor.

Both observers reviewed all images on two occasions separated by three weeks; the images were shuffled in between measurements to prevent possible recall of previous recordings. The Hallux Angles software employs the iPhone camera to allow the user to choose the desired angle and adjust the position of the device for the measurements. Also, the coronal tilt between positions is used by the app to calculate the angle.

The authors found the measurements taken by the iPhone comparable to those recorded with computer software assistance. It was noted that there was no statistical difference. Also, no statistical difference was found between the iPhone measurements and the computer-assisted measurements (reference standard).

In addition, they stated that “interobserver variability between iPhone measurements and computer-assisted measurements was less than 2° for HVA and DMAA and less than 1° for IMA with high correlation coefficients ranging from 0.912 to 0.998.”

Additionally, intra-observer reliability was also tested, and displayed a high degree of agreement between readings recorded by the same observer. Based on this data, Ege et al. conclude that “Hallux Angles software is a reliable and valid measurement tool for radiographic evaluation of hallux valgus.”They also noted that the software was prone to parallax errors when the iPhone was not held directly parallel to the computer screen; while this could theoretically lead to variations, a statistically significant impact of this effect was not found by the authors.

Decision-making regarding the myriad surgical options to correct hallux valgus is a complex procedure involving radiographic assessment of standardized angles that define severity. When performed manually, these measurements show a great deal of variability between-and are highly error-prone. Computerized assessment is the current standard, utilizing a software program to calculate the angles.

However, these tools are not available at all facilities, while smartphones are largely ubiquitous among medical personnel.

The authors note that subjectively, “iPhone measurements were faster and more practical than computerized measurements,” and can be “used for measurement of hallux valgus angles in clinical practice and even for research purposes. It is an accurate and reproducible method.”

As smartphones continue to be equipped with accelerometers and other such tools for measuring unique data, these devices will continue to expand in clinical utility and functionality.


  • Tolga Ege
  • Ozkan Kose
  • Kenan Koca
  • Bahtiyar Demiralp
  • Mustafa Basbozkurt


  • Department of Orthopaedics and Traumatology
  • Gulhane Military Medical Academy,
 Ankara, Turkey.

Original abstract: