The reliability of a smartphone goniometer application compared with a traditional goniometer for measuring first metatarsophalangeal joint dorsiflexion

BACKGROUND Adequate sagittal plane motion of the first metatarsalphalangeal joint (1st MTPJ) is important during normal gait and goniometric measurement is commonly used as a diagnostic and outcome assessment tool. We aimed to determine the intra and inter-rater reliability together with the concurrent validity of a universal plastic goniometer (UG) and a smartphone applicationlication (Dr G) for the measurement of dorsiflexion at the 1st MTPJ. METHODS Measurement of joint position and passive range of motion of the 1st MTPJ dorsiflexion was compared using a UG and DrG goniometer. A double-blind repeated measures design was utilized, with intraclass correlation coefficient (ICC) used to determine levels of reliability. RESULTS For joint position good intra-rater reliability (ICC >0.861) and good inter-rater reliability (ICC >0.823) was noted. However, the Dr G application consistently measured lower angles (mean 27.8° (SD 8.37)) than the UG (mean 32° (SD 11.7)) and these associations were significant (r = 0.399, p < 0.001). For passive range of motion, the mean total range of dorsiflexion motion (from maximum plantarflexed position to maximum dorsiflexed position) was 82.8° (SD 12.2) for the UG and 82.9° (SD 11.3) for the Dr G application. Both instruments demonstrated high levels of intra-rater reliability (ICC >0.809). Inter-rater reliability was moderate to good for the UG (ICC 0.693 (95 % CI 0.580 to 0.788)) and good for the Dr G application (ICC 0.708 (95 % CI 0.597 to 0.799)). CONCLUSIONS Moderate to high intra and inter-rater reliability of joint position and passive 1st MTPJ motion can be achieved with traditional and smartphone-based goniometric measurement. The Dr G application may provide a slightly higher reliability, but devices should not be used inter-changeably as significant variation in measurement between devices may occur.