Preliminary study on a smartphone‐based measurement of knee hyperextension

-An examination of inter‐rater reliability among 　physiotherapy students-

Abstract

【Introduction】Goniometer measurements for range of motion are commonly used to determine the presence of knee hyperextension; however, these measurements may differ depending on the participant's limb position and examiner's manipulation. In these manners, we devised an original measurement method using a smartphone that measures the knee joint extension angle independent of the measurement limb position and manipulation. The purpose of this study was to examine the inter‐rater reliability of a smartphone‐based measurement.

【Methods】The knee extension angles of 54 extremities in 27 women (mean age: 21.4 years) were measured by two physiotherapy students, once using a goniometer and once with a smartphone. The smartphone is already installed with free applications called level, inclinometer, and angle meter. The angles measured by each student were compared to calculate the intraclass correlation coefficient (2.1) for each method, and the presence of hyperextended knee was assessed to calculate the kappa coefficient.

【Results】The intraclass correlation coefficient (2.1) for the knee extension angle was 0.22 for the goniometer and 0.89 for the smartphone measures. The kappa coefficient for the diagnosis of hyperextended knee was -0.03 for the goniometer and 0.63 for the smartphone method.

【Conclusion】Measurements using smartphone was classified as “good" in the determination of the intraclass correlations. This suggests that smartphone‐based measurement more accurately reflects the knee extension angle. Moreover, the kappa coefficient for the diagnosis of hyperextended knee for the smartphone method was also classified as “possible," which suggests its potential for assessment.