Reliability of a Measurement Method for Upper Limb Raised Standing Spinal Alignment Using a Smartphone Inclinometer Application

Purpose: To evaluate the reliability and validity of spinal alignment measurements in the raised arm standing posture using a smartphone app.

Background: An inclinometer is a reliable tool for measuring spinal alignment. Measurement of static standing posture spinal curvature angles using smartphone inclinometer applications has been investigated in the lumbar spine but has not been reported for the thoracic spine. However, the sacral vertebrae were used as the reference point for the measurement of the lumbar spine, and the method of palpation of the sacral vertebrae was unclear. No measurement methods, including inclinometers, have been found for upper limb elevation.

Methods: Thoracic kyphosis and lumbar lordosis angles were measured in 18 healthy young adults (mean age: 21.0 ± 3.5). Measurements were taken in the raised standing posture. The points of measurement included angle α at the thoracic spine (T)1/2, angle β at the T12/lumbar spine (L)1, and angle γ at the L4/L5 spinous processes. The thoracic kyphosis angle was calculated as the sum of α and β, while the lumbar lordosis angle was the sum of β and γ. Two raters measured these angles twice using the same smartphones. Inter-rater reliability was assessed using intraclass correlation coefficients (ICC 2.1), and measurement precision was determined by calculating MDC95 from the ICC values. Validity was also carried out on 12 healthy young adults (age: 20.8 ± 4.0 years). The measurement points were the same as described above, and two types of measurements were taken with a smartphone and an inclinometer; the results of the two types of measurements were used to determine the relationship using Pearson's correlation coefficient.

Results: During upper limb raising, the smartphone's ICC (95% confidence interval) was 0.92 (0.81-0.97) for thoracic kyphosis and 0.90 (0.74-0.96) for lumbar lordosis. The MDC95 values indicated acceptable precision, with 7.00° for thoracic kyphosis and 9.95° for lumbar lordosis. All correlation coefficients between inclinometers and smartphones were above 0.9 for both the thoracic and lumbar spines.

Conclusions: Measuring spinal alignment angles using a smartphone inclinometer app in the raised standing posture demonstrates good reliability for inter-rater comparisons. It was also good with regard to validity.