Validation of a Novel Smartphone Accelerometer-Based Knee Goniometer

Abstract

Loss of full knee extension following anterior cruciate ligament (ACL) surgery has been shown to impair knee function.1,2 However, there can be significant difficulties in accurately and reproducibly measuring a fixed flexion of the knee. Some studies suggest that conventional lower limb goniometry may contain errors of between 5 and 10 degrees even in experienced hands.3-5 Such errors may exceed the magnitude of a given fixed flexion deformity. We sought to find a means to eliminate the difficulties associated with palpating the boney landmarks of the femurby making calculations based entirely on the measured position of the tibia. In the setting of state funded healthcare, even a relatively small capital outlay can be prohibitive-we therefore repurposed commercially available technology.We studied the interobserver and the intraobserver reliabilities of our novel, accelerometer based, knee goniometer technique and compared it with a long-armed conventional goniometer for the assessment of fixed flexion knee deformity. Measurements on radiographs would provide a robust "gold standard" but the use of X-ray for this purpose is not routine and not without risk. We therefore chose the best commonly applied "bed-side" measurement technique. Keywords► fixed flexion ► knee ► goniometer ► accelerometer AbstractLoss of full knee extension following anterior cruciate ligament surgery has been shown to impair knee function. However, there can be significant difficulties in accurately and reproducibly measuring a fixed flexion of the knee. We studied the interobserver and the intraobserver reliabilities of a novel, smartphone accelerometer-based, knee goniometer and compared it with a long-armed conventional goniometer for the assessment of fixed flexion knee deformity. Five healthy male volunteers (age range 30 to 40 years) were studied. Measurements of knee flexion angle were made with a telescopic-armed goniometer (Lafayette Instrument, Lafayette, IN) and compared with measurements using the smartphone (iPhone 3GS, Apple Inc., Cupertino, CA) knee goniometer using a novel trigonometric technique based on tibial inclination. Bland-Altman analysis of validity and reliability including statistical analysis of correlation by Pearson's method was undertaken. The iPhone goniometer had an interobserver correlation (r) of 0.994 compared with 0.952 for the Lafayette. The intraobserver correlation was r ¼ 0.982 for the iPhone (compared with 0.927). The datasets from the two instruments correlate closely (r ¼ 0.947) are proportional and have mean difference of only À0.4 degrees (SD 3.86 degrees). The Lafayette goniometer had an intraobserver reliability AE 9.6 degrees. The interobserver reliability was AE 8.4 degrees. By comparison the iPhone had an interobserver reliability AE 2.7 degrees and an intraobserver reliability AE 4.6 degrees. We found the iPhone goniometer to be a reliable tool for the measurement of subtle knee flexion in the clinic setting.

Goniometer-apps in hand surgery and their applicability in daily clinical practice

“…The four clinical studies support the results of this study with regard to the apps "DrGoniometer", GetMyROM" and "Simple Goniometer". The 'knee goniometer' [15] as well as other programs-not tested in our study-were also confirmed to obtain reliable results in earlier reports [16][17][18]. Interestingly, we did not retrieve clinical studies in hand surgery dealing with the other thirteen apps tested in our study, and so far no Android app was evaluated in a clinical setting.…”

Reliability and Concurrent Validity of the Goniometer-Pro App vs a Universal Goniometer in determining Passive Flexion of Knee

“…In this study, the difference was 5,45º. This value is not available in the work of Ockendon and Gilbert as the authors not compare the results obtained from the measuring instruments with the real flexion value as measured by x-ray [21].…”

“…Indeed, the measurement of the mobile application was slightly more accurate than that obtained from UG, with no statistically significant differences between the measurements made by the students and those of the experienced physicians (ICC > 0,96 in both cases). In a similar study, Jones [20] carry out a comparison between UG and an iPhone app for measuring the passive flexion of the knee in a cohort of 36 subjects, no finding statistically On the basis of a cohort of five subjects, Ockendon and Gilbert [21] compare the validity of a purpose-built mobile application to that of a traditional goniometer for measuring knee range of motion. This results show that the values obtained from both measurement instruments are closely correlated, albeit with slight differences in favor of the mobile app (inter-observer correlation: was 0,994 vs. 0,952 and intraobserver correlation: was 0,982 vs. 0,927); the mean difference between the two is only -0,4º.…”

Accuracy and Precision of an Accelerometer-Based Smartphone App Designed to Monitor and Record Angular Movement over Time

“…The findings in this study coincide with the findings of work previously performed regarding the accuracy and precision of applications using smartphone hardware to monitor Their iPhone goniometer demonstrated superior intra-and inter-rater reliability to the traditional goniometer, reducing inter-rater discrepancy by more than 70%. 25 Smartphone accelerometers have also been shown to be valid and reliable when measuring combined movements. The apps used by Yamada et al 26 and Nishiguchi et al 13 demonstrated ''remarkable consistency'' during gait analysis (e.g., peak frequency and acceleration peak intervals) and correlated significantly (r > 0.82) with more traditional triaxial accelerometers.…”